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It is based on thecurrent ones, xml2rfc will fillset of transport features in RFC 8303.</t> </abstract> </front> <middle> <section anchor="sec-intro" numbered="true" toc="default"> <name>Introduction</name> <t>Currently, thecurrent day for you. If only the current year is specified, xml2rfc will fill in the current day and month for you. If the year is not the current one, it is necessary to specify at least a month (xml2rfc assumes day="1" if not specified for the purpose of calculating the expiry date). With drafts it is normally sufficient to specify just the year. --> <!-- Meta-data Declarations --> <area>Transport</area> <workgroup>TAPS</workgroup> <!-- WG name at the upperleft corner of the doc, IETF is fine for individual submissions. If this element is not present, the default is "Network Working Group", which is used by the RFC Editor as a nod to the history of the IETF. --> <keyword>taps, transport services</keyword> <!-- Keywords will be incorporated into HTML output files in a meta tag but they have no effect on text or nroff output. If you submit your draft to the RFC Editor, the keywords will be used for the search engine. --> <abstract> <t>This draft recommends a minimal set of Transport Services offered by end systems, and gives guidance on choosing among the available mechanisms and protocols. It is based on the set of transport features in RFC 8303.</t> </abstract> </front> <middle> <!-- <section title="Definitions" anchor='sec-def'> <t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in <xref target="RFC2119">RFC 2119</xref>.</t> <t><list style="hanging" hangIndent="6"> <t hangText="Wha'ever:"> <vspace /> Wha'ever is short for Whatever.</t> </list></t> </section> --> <section anchor="sec-intro" title="Introduction"> <t>Currently, the set of transport services that most applications useset of Transport Services that most applications use is based on TCP and UDP (and protocols that are layered on top of them); this limits the ability for the network stack to make use of features of other transport protocols. For example, if a protocol supports out-of-order message delivery but applications always assume that the network provides an orderedbytestream,byte stream, then the network stack can not immediately deliver a message that arrivesout-of-order:out of order; doing so would break a fundamental assumption of the application. The net result is unnecessary head-of-line blocking delay.</t> <t>By exposing thetransport servicesTransport Services of multiple transport protocols, a transport system can make it possible for applications to use these services without being statically bound to a specific transport protocol. The first step towards the design of such a system was taken by <xreftarget="RFC8095"></xref>,target="RFC8095" format="default"/>, which surveys a large number of transports, and <xreftarget="RFC8303"></xref>target="RFC8303" format="default"/> as well as <xreftarget="RFC8304"/>,target="RFC8304" format="default"/>, which identify the specific transport features that are exposed to applications by the protocols TCP,MPTCP, UDP(-Lite)Multipath TCP (MPTCP), UDP(-Lite), andSCTPStream Control Transmission Protocol (SCTP), as well as theLEDBATLow Extra Delay Background Transport (LEDBAT) congestion control mechanism. LEDBAT was included as the only congestion control mechanism in this list because the "low extra delay background transport" service that it offers is significantly different from the typical service provided by other congestion control mechanisms. This memo is based on these documents and follows the same terminology (also listed below). Because the considered transport protocols conjointly cover a wide range of transport features, there is reason to hope that the resulting set (and the reasoning that led to it) will also apply to many aspects of other transport protocols that may be in usetoday,today or may be designed in the future. </t> <t>By decoupling applications from transport protocols, a transport system provides a different abstraction level than the Berkeley sockets interface <xreftarget="POSIX"/>.target="POSIX" format="default"/>. As with high- vs. low-level programming languages, a higher abstraction level allows more freedom for automation below the interface, yet it takes some control away from the application programmer. This is the design trade-off that a transport system developer is facing, and this document provides guidance on the design of this abstraction level. Some transport features are currently rarely offered by APIs, yet they must be offered or they can never be used. Other transport features are offered by the APIs of the protocols covered here, but not exposing them in an API would allow for more freedom to automate protocol usage in a transport system. The minimal set presented here is an effort to find a middle ground that can be recommended for transport systems to implement, on the basis of the transport features discussed in <xreftarget="RFC8303"/>.</t>target="RFC8303" format="default"/>.</t> <t>Applications use a wide variety of APIs today. While this document was created to ensure the API developed in the Transport Services (TAPS) Working Group(<xref<xref target="I-D.ietf-taps-interface"/>)format="default"/> includes the most important transport features, the minimal set presented here must be reflected in *all* network APIs in order for the underlying functionality to become usable everywhere. For example, it does not help an application that talks to a librarywhichthat offers its own communication interface if the underlying Berkeley Sockets API is extended to offer "unordered message delivery", but the library only exposes an orderedbytestream.byte stream. Both the Berkeley Sockets API and the library would have to expose the "unordered message delivery" transport feature (alternatively, there may be ways for certain types of libraries to use this transport feature without exposing it, based on knowledge about theapplications --applications, but this is not the general case). Similarly, transport protocols such asSCTPthe Stream Control Transmission Protocol (SCTP) offer multi-streaming, which cannot be utilized, e.g., to prioritize messages between streams, unless applications communicate the priorities and the group of connections upon which these priorities should be applied. In most situations, in the interest of being as flexible and efficient as possible, the best choice will be for a library to expose at least all of the transport features that are recommended as a "minimal set" here.<!-- MICHAEL: The point of the example below was to mention something that's already valid today - but now I don't think this is necessary or improves the text quality.--> <!--As an example considering only TCP and UDP, a middleware or library that only offers TCP's reliable bytestream cannot make use of UDP (unless it implements extra functionality on top of UDP) - doing so could break a fundamental assumption that applications make about the data they send and receive.--></t> <t> This "minimal set" can be implemented "one-sided" over TCP. This means that a sender-side transport system can talk to a standard TCP receiver, and a receiver-side transport system can talk to a standard TCP sender. If certain limitations are put in place, the "minimal set" can also be implemented "one-sided" over UDP. While the possibility of such "one-sided" implementation may help deployment, it comes at the cost of limiting the set to services that can also be provided by TCP (or, with further limitations, UDP). Thus, the minimal set of transport features here is applicable for many, but not all,applications:applications; some application protocols have requirements that are not met by this "minimal set". </t> <t> Note that, throughout this document, protocols are meant to be used natively. For example, when transport features ofUDP,TCP, or "implementation over"UDPTCP is discussed, this refers to native usage of TCP rather than TCP being encapsulated in some other transport protocol such as UDP. </t> </section> <sectiontitle="Terminology"> <!-- <t>The following terms are used throughout this document, and in subsequent documents produced by TAPS that describe the composition and decomposition of transport services.</t> --> <t><list style="hanging"> <t hangText='Transport Feature:'> anumbered="true" toc="default"> <name>Terminology</name> <dl newline="false" > <dt>Transport Feature:</dt> <dd> A specific end-to-end feature that the transport layer provides to an application. Examples include confidentiality, reliable delivery, ordered delivery, message-versus-stream orientation,etc.</t> <t hangText='Transport Service:'> aetc.</dd> <dt>Transport Service:</dt> <dd> A set of Transport Features, without an association to any given framing protocol,whichthat provides a complete service to anapplication.</t> <t hangText='Transport Protocol:'> anapplication.</dd> <dt>Transport Protocol:</dt> <dd> An implementation that provides one or more differenttransport servicesTransport Services using a specific framing and header format on thewire.</t> <t hangText='Application:'> anwire.</dd> <dt>Application:</dt> <dd> An entity that uses atransport layertransport-layer interface for end-to-end delivery of data across the network (this may also be anupper layerupper-layer protocol or tunnelencapsulation).</t> <t hangText='Application-specific knowledge:'> knowledgeencapsulation).</dd> <dt>Application-specific knowledge:</dt> <dd> Knowledge that only applicationshave.</t> <t hangText='End system:'> anhave.</dd> <dt>End system:</dt> <dd> An entity that communicates with one or more other end systems using a transport protocol. An end system provides atransport layertransport-layer interface to applications.</t> <t hangText='Connection:'> shared</dd> <dt>Connection:</dt> <dd> Shared state of two or more end systems that persists across messages that are transmitted between these endsystems.</t> <t hangText='Connection Group:'> asystems.</dd> <dt>Connection Group:</dt> <dd> A set of connectionswhichthat share the same configuration (configuring one of them causes all other connections in the same group to be configured in the same way). We call connections that belong to a connection group "grouped", while "ungrouped" connections are not a part of a connectiongroup.</t> <t hangText='Socket:'> thegroup.</dd> <dt>Socket:</dt> <dd> The combination of a destination IP address and a destination portnumber.</t> </list></t>number.</dd> </dl> <t>Moreover, throughout the document, the protocol name "UDP(-Lite)" is used when discussing transport features that are equivalent for UDP and UDP-Lite; similarly, the protocol name "TCP" refers to both TCP and MPTCP. </t> </section> <section anchor="deriving"title="Deriving the minimal set"> <t><!-- MICHAEL: Gorry suggested this is unnecessary to state. --> <!--Because QoS is out of scope of TAPS, this document assumes a "best effort" service model <xref target="RFC5290"></xref>, <xref target="RFC7305"></xref>. Applications using a TAPS system can therefore not make any assumptions about e.g.numbered="true" toc="default"> <name>Deriving thetime it will take to send a message. -->Minimal Set</name> <t> We assume that applications have no specific requirements that need knowledge about the network,e.g.e.g., regarding the choice of network interface or the end-to-end path. Even with these assumptions, there are certain requirements that are strictly kept by transport protocols today, and these must also be kept by a transport system. Some of these requirements relate to transport features that we call "Functional". </t> <t>Functional transport features provide functionality that cannot be used without the application knowing about them, or else they violate assumptions that might cause the application to fail. For example, ordered message delivery is a functional transport feature: it cannot be configured without the application knowing about it because the application's assumption could be that messages always arrive in order. Failure includes any change of the application behavior that is not performance oriented,e.g.e.g., security. </t> <t>"Change DSCP" and "Disable Nagle algorithm" are examples of transport features that we call"Optimizing":"Optimizing"; if a transport system autonomously decides to enable or disable them, an application will not fail, but a transport system may be able to communicate more efficiently if the application is in control of this optimizing transport feature. These transport features require application-specific knowledge (e.g., about delay/bandwidth requirements or the length of future data blocks that are to be transmitted). </t> <t> The transport features of IETF transport protocols that do not require application-specific knowledge and could therefore be utilized by a transport system on its own without involving the application are called "Automatable". </t> <t>We approach the construction of a minimal set of transport features in the following way:<list style="numbers"> <t>Categorization</t> <ol type="1"> <li>Categorization (<xreftarget="super"/>): thetarget="super" format="default"/>): The superset of transport features from <xreftarget="RFC8303"></xref>target="RFC8303" format="default"/> is presented, and transport features are categorized as Functional,OptimizingOptimizing, or Automatable for laterreduction.</t> <t>Reductionreduction.</li> <li>Reduction (<xreftarget="Reduction"/>): atarget="Reduction" format="default"/>): A shorter list of transport features is derived from the categorization in the first step. This removes all transport features that do not require application-specific knowledge or would result in semantically incorrect behavior if they were implemented over TCP orUDP.</t> <t>DiscussionUDP.</li> <li>Discussion (<xreftarget="Discussion"/>): thetarget="Discussion" format="default"/>): The resulting list shows a number of peculiarities that are discussed, to provide a basis for constructing the minimalset.</t> <t>Constructionset.</li> <li>Construction (<xreftarget="minset"/>):target="minset" format="default"/>): Based on the reduced set and the discussion of the transport features therein, a minimal set isconstructed.</t> </list></t>constructed.</li> </ol> <t>Following <xreftarget="RFC8303"></xref>target="RFC8303" format="default"/> and retaining its terminology, we divide the transport features into two main groups as follows:<list style="numbers"> <t>CONNECTION related transport features <vspace /> - ESTABLISHMENT<vspace /> - AVAILABILITY<vspace /> - MAINTENANCE<vspace /> - TERMINATION<vspace /> </t> <t>DATA Transfer related transport features <vspace /> - Sending Data<vspace /> - Receiving Data<vspace /> - Errors<vspace /> </t> </list></t> <ol type="1"> <li> <t>CONNECTION-related transport features</t> <ul spacing="compact"> <li>ESTABLISHMENT</li> <li>AVAILABILITY</li> <li>MAINTENANCE</li> <li>TERMINATION</li> </ul> </li> <li> <t>DATA-Transfer-related transport features</t> <ul spacing="compact"> <li>Sending Data</li> <li>Receiving Data</li> <li>Errors</li> </ul> </li> </ol> </section> <section anchor="Reduction"title="Thenumbered="true" toc="default"> <name>The Reduced Set of TransportFeatures">Features</name> <t>By hiding automatable transport features from the application, a transport system can gain opportunities to automate the usage of network-related functionality. This can facilitate using the transport system for the application programmer and it allows for optimizations that may not be possible for an application. For instance, system-wide configurations regarding the usage of multiple interfaces can better be exploited if the choice of the interface is not entirely up to the application. Therefore, since they are not strictly necessary to expose in a transport system, we do not include automatable transport features in the reduced set of transport features. This leaves us with only the transport features that are either optimizing or functional. </t> <t>A transport system should be able to communicate via TCP or UDP if alternative transport protocols are found not to work. For many transport features, this ispossible --possible, often by simply not doing anything when a specific request is made. For some transport features, however, it was identified that direct usage of neither TCP nor UDP ispossible:possible; in these cases, even not doing anything would incur semantically incorrect behavior. Whenever an application would make use of one of these transport features, this would eliminate the possibility to use TCP or UDP. Thus, we only keep the functional and optimizing transport features for which an implementation over either TCP or UDP is possible in our reduced set. </t> <t>The following list contains the transport features from <xreftarget="super"/>,target="super" format="default"/>, reduced using these rules. The "minimal set" derived in this document is meant to be implementable "one-sided" overTCP,TCP and, with limitations, UDP. In the list, we therefore precede a transport feature with "T:" if an implementation over TCP is possible, "U:" if an implementation over UDP is possible, and "T,U:" if an implementation over either TCP or UDP is possible. </t> <section anchor="conn-reduced"title="CONNECTION Relatednumbered="true" toc="default"> <name>CONNECTION-Related TransportFeatures"> <t>ESTABLISHMENT:<vspace /> <list style="symbols"> <t>T,U: Connect</t> <t>T,U:Features</name> <t>ESTABLISHMENT: </t> <ul spacing="compact"> <li>T,U: Connect</li> <li>T,U: Specify number of attempts and/or timeout for the first establishmentmessage</t> <t>T,U:message</li> <li>T,U: DisableMPTCP</t> <t>T:MPTCP</li> <li>T: Configureauthentication</t> <t>T:authentication</li> <li>T: Hand over a message to reliably transfer (possibly multiple times) before connectionestablishment</t> <t>T:establishment</li> <li>T: Hand over a message to reliably transfer during connectionestablishment</t> </list></t> <t>AVAILABILITY:<vspace /> <list style="symbols"> <t>T,U: Listen</t> <t>T,U:establishment</li> </ul> <t>AVAILABILITY: </t> <ul spacing="compact"> <li>T,U: Listen</li> <li>T,U: DisableMPTCP</t> <t>T:MPTCP</li> <li>T: Configureauthentication</t> </list></t> <t>MAINTENANCE:<vspace /> <list style="symbols"> <t>T:authentication</li> </ul> <t>MAINTENANCE: </t> <ul spacing="compact"> <li>T: Change timeout for aborting connection (using retransmit limit or timevalue)</t> <t>T:value)</li> <li>T: Suggest timeout to thepeer</t> <t>T,U:peer</li> <li>T,U: Disable Naglealgorithm</t> <t>T,U:algorithm</li> <li>T,U: Notification of Excessive Retransmissions (early warning below abortionthreshold)</t> <t>T,U:threshold)</li> <li>T,U: Specify DSCPfield</t> <t>T,U:field</li> <li>T,U: Notification of ICMP error messagearrival</t> <t>T:arrival</li> <li>T: Change authenticationparameters</t> <t>T:parameters</li> <li>T: Obtain authenticationinformation</t> <t>T,U:information</li> <li>T,U: Set Cookie lifevalue</t> <t>T,U:value</li> <li>T,U: Choose a scheduler to operate between streams of anassociation</t> <t>T,U:association</li> <li>T,U: Configure priority or weight for ascheduler</t> <t>T,U:scheduler</li> <li>T,U: Disable checksum whensending</t> <t>T,U:sending</li> <li>T,U: Disable checksum requirement whenreceiving</t> <t>T,U:receiving</li> <li>T,U: Specify checksum coverage used by thesender</t> <t>T,U:sender</li> <li>T,U: Specify minimum checksum coverage required byreceiver</t> <t>T,U:receiver</li> <li>T,U: Specify DFfield</t> <t>T,U:field</li> <li>T,U: Get max. transport-message size that may be sent using a non-fragmented IP packet from the configuredinterface</t> <t>T,U:interface</li> <li>T,U: Get max. transport-message size that may be received from the configuredinterface</t> <t>T,U:interface</li> <li>T,U: Obtain ECNfield</t> <t>T,U:field</li> <li>T,U: Enable and configure a "Low Extra Delay BackgroundTransfer"</t> </list></t> <t>TERMINATION:<vspace /> <list style="symbols"> <t>T:Transfer"</li> </ul> <t>TERMINATION: </t> <ul spacing="compact"> <li>T: Close after reliably delivering all remaining data, causing an event informing the application on the otherside</t> <t>T:side</li> <li>T: Abort without delivering remaining data, causing an event informing the application on the otherside</t> <t>T,U:side</li> <li>T,U: Abort without delivering remaining data, not causing an event informing the application on the otherside</t> <t>T,U:side</li> <li>T,U: Timeout event when data could not be delivered for toolong</t> </list></t>long</li> </ul> </section> <section anchor="data-reduced"title="DATA Transfer Relatednumbered="true" toc="default"> <name>DATA-Transfer-Related TransportFeatures">Features</name> <section anchor="data-sending-reduced"title="Sending Data"> <t><list style="symbols"> <t>T:numbered="true" toc="default"> <name>Sending Data</name> <ul spacing="compact"> <li>T: Reliably transfer data, with congestioncontrol</t> <t>T:control</li> <li>T: Reliably transfer a message, with congestioncontrol</t> <t>T,U:control</li> <li>T,U: Unreliably transfer amessage</t> <t>T:message</li> <li>T: Configurable MessageReliability</t> <t>T:Reliability</li> <li>T: Ordered message delivery (potentially slower thanunordered)</t> <t>T,U:unordered)</li> <li>T,U: Unordered message delivery (potentially faster thanordered)</t> <t>T,U:ordered)</li> <li>T,U: Request not to bundlemessages</t> <t>T:messages</li> <li>T: Specifying a key id to be used to authenticate amessage</t> <t>T,U:message</li> <li>T,U: Request not to delay the acknowledgement (SACK) of amessage</t> </list></t>message</li> </ul> </section> <section anchor="data-receiving-reduced"title="Receiving Data"> <t> <list style="symbols"> <t>T,U:numbered="true" toc="default"> <name>Receiving Data</name> <ul spacing="compact"> <li>T,U: Receive data (with no messagedelimiting)</t> <t>U:delimiting)</li> <li>U: Receive amessage</t> <t>T,U:message</li> <li>T,U: Information about partial messagearrival</t> </list> </t>arrival</li> </ul> </section> <section anchor="data-errors-reduced"title="Errors">numbered="true" toc="default"> <name>Errors</name> <t>This section describes sending failures that are associated with a specific call to in the "Sending Data" category (<xreftarget="data-sending-pass3"/>).</t> <t> <list style="symbols"> <t>T,U:target="data-sending-pass3" format="default"/>).</t> <ul spacing="compact"> <li>T,U: Notification of sendfailures</t> <t>T,U:failures</li> <li>T,U: Notification that the stack has no more user data tosend</t> <t>T,U:send</li> <li>T,U: Notification to a receiver that a partial message delivery has beenaborted</t> </list> </t>aborted</li> </ul> </section> </section> </section> <section anchor="Discussion"title="Discussion">numbered="true" toc="default"> <name>Discussion</name> <t>The reduced set in the previous section exhibits a number of peculiarities, which we will discuss in the following. This section focuses on TCP because, with the exception of one particular transport feature ("Receive amessage" --message"; we will discuss this in <xreftarget="sendmsg"/>),target="sendmsg" format="default"/>), the list shows that UDP is strictly a subset of TCP. We can first try to understand how to build a transport system that can run over TCP, and then narrow down the result further to allow that the system can always run over either TCP or UDP (which effectively means removing everything related to reliability, ordering,authenticationauthentication, and closing/aborting with a notification to the peer). </t> <t>Note that, because the functional transport features of UDPare --are, with the exception of "Receive amessage" --message", a subset of TCP, TCP can be used as a replacement for UDP whenever an application does not need message delimiting (e.g., because the application-layer protocol already does it). This has been recognized by many applications that already do this in practice, by trying to communicate with UDP atfirst,first and falling back to TCP in case of a connection failure. </t> <section anchor="sendmsg"title="Sendingnumbered="true" toc="default"> <name>Sending Messages, ReceivingBytes">Bytes</name> <t>For implementing a transport system over TCP, there are several transport features related to sending, but only a single transport feature related to receiving: "Receive data (with no message delimiting)" (and, strangely, "information about partial message arrival"). Notably, the transport feature "Receive a message" is also the only non-automatable transport feature of UDP(-Lite) for which no implementation over TCP is possible.</t><!-- FROM MICHAEL: this is true, but not helping the explanation. It is also represents the only way that UDP(-Lite) applications can receive data today.</t> --><t>To support these TCP receiver semantics, we define an "Application-FramedBytestream" (AFra-Bytestream). AFra-BytestreamsByte Stream" (AFra Byte Stream). AFra Byte Streams allow senders to operate on messages while minimizing changes to the TCP socket API. In particular, nothing changes on the receiverside -side; data can be accepted via a normal TCP socket. </t> <t>In anAFra-Bytestream,AFra Byte Stream, the sending application can optionally inform the transport about message boundaries and required properties per message (configurable order and reliability, or embedding a request not to delay the acknowledgement of a message). Whenever the sending application specifies per-message properties that relax the notion of reliable in-order delivery of bytes, it must assume that the receiving application is 1) able to determine message boundaries, provided that messages are always kept intact, and 2) able to accept these relaxed per-message properties. Any signaling of such information to the peer is up to an application-layer protocol and considered out of scope of this document. </t><!--<t>Forthe transportexample, if an application requests tooperate on messages, it onlytransfer fixed-size messages of 100 bytes with partial reliability, this needsbe informed about them as they are handed over by a sending application; on the receiver side, giving an application a message only differs from giving it a bytestream in that a message-oriented receiver-side transport informs the application about message boundaries. When the application knows about these boundaries on its own, this information is unnecessary.</t> --> <t>For example, if an application requests to transfer fixed-size messages of 100 bytes with partial reliability, this needs the receiving application tothe receiving application to be prepared to accept data in chunks of 100 bytes.If, then,Then, if some of these 100-byte messages are missing (e.g., if SCTP with Configurable Reliability is used), this is the expected application behavior. With TCP, no messages would be missing, but this is also correct for the application, and the possible retransmission delay is acceptable within the best-effort service model (see <xreftarget="RFC7305"/>, Section 3.5).target="RFC7305" sectionFormat="of" section="3.5"/>). Still, the receiving application would separate the byte stream into 100-byte chunks. </t> <t>Note that this usage of messages does not require all messages to be equal in size. Many application protocols use some form of Type-Length-Value (TLV) encoding,e.g.e.g., by defining a header including length fields; another alternative is the use of byte stuffing methods such asCOBSConsistent Overhead Byte Stuffing (COBS) <xreftarget="COBS"/>.target="COBS" format="default"/>. If an application needs message numbers,e.g.e.g., to restore the correct sequence of messages, these must also be encoded by the application itself, as SCTP's transport features that are related to the sequence numberrelated transport features of SCTPare not provided by the "minimum set" (in the interest of enabling usage of TCP). </t> </section> <section anchor="nostream"title="Streamnumbered="true" toc="default"> <name>Stream SchedulersWithout Streams">without Streams</name> <t>We have already stated that multi-streaming does not require application-specific knowledge. Potential benefits or disadvantages of, e.g., using two streams of an SCTP association versus using two separate SCTP associations or TCP connections are related to knowledge about the network and the particular transport protocol in use, not the application. However, the transport features "Choose a scheduler to operate between streams of an association" and "Configure priority or weight for a scheduler" operate on streams. Here, streams identify communication channels between which a scheduler operates, and they can be assigned a priority. Moreover, the transport features in the MAINTENANCE category all operate onassocationsassociations in case of SCTP,i.e.i.e., they apply to all streams in thatassocation.association. </t> <t>With only these semantics necessary to represent, the interface to a transport system becomes easier if we assume that connections may be not only a transport protocol's connection or association, but could also be a stream of an existing SCTP association, for example. We only need to allow for a way to define a possible grouping of connections. Then, all MAINTENANCE transport features can be said to operate on connection groups, not connections, and a scheduler operates on the connections within a group. </t> <t>To be compatible with multiple transport protocols and uniformly allow access to both transport connections and streams of a multi-streaming protocol, the semantics of opening and closing need to be the most restrictive subset of all of the underlying options. For example, TCP's support of half-closed connections can be seen as a feature on top of the more restrictive "ABORT"; this feature cannot be supported because not all protocols used by a transport system (including streams of an association) support half-closed connections. </t> </section> <section anchor="earlydata"title="Earlynumbered="true" toc="default"> <name>Early DataTransmission">Transmission</name> <t>There are two transport features related to transferring a message early: "Hand over a message to reliably transfer (possibly multiple times) before connection establishment", which relates to TCP Fast Open <xreftarget="RFC7413"/>,target="RFC7413" format="default"/>, and "Hand over a message to reliably transfer during connection establishment", which relates to SCTP's ability to transfer data together with the COOKIE-Echo chunk. Also without TCP Fast Open, TCP can transfer data during the handshake, together with the SYNpacket --packet; however, the receiver of this data may not hand it over to the application until the handshake has completed. Also, different from TCP Fast Open, this data is not delimited as a message by TCP (thus, not visible as a``message'')."message"). This functionality is commonly available in TCP and supported in several implementations, even though the TCP specification does not explain how to provide it to applications. </t> <t>A transport system could differentiate between the cases of transmitting data "before" (possibly multiple times) or "during" the handshake. Alternatively, it could also assume that data that are handed over early will be transmitted as early as possible, and "before" the handshake would only be used for messages that are explicitly marked as "idempotent" (i.e., it would be acceptable to transfer them multiple times). </t> <t>The amount of data that can successfully be transmitted before or during the handshake depends on various factors: the transport protocol, the use of header options, the choice of IPv4 andIPv6IPv6, and the Path MTU. A transport system should therefore allow a sending application to query the maximum amount of data it can possibly transmit before (or, if exposed, during) connection establishment. </t> </section> <section anchor="rundry"title="Sendernumbered="true" toc="default"> <name>Sender RunningDry">Dry</name> <t>The transport feature "Notification that the stack has no more user data to send" relates to SCTP's "SENDER DRY" notification. Such notifications can, in principle, be used to avoid having an unnecessarily large send buffer, yet ensure that the transport sender always has data available when it has an opportunity to transmit it. This has been found to be very beneficial for some applications <xreftarget="WWDC2015"/>.target="WWDC2015" format="default"/>. However, "SENDER DRY" truly means that the entire send buffer (including both unsent and unacknowledged data) hasemptied --emptied, i.e., when it notifies the sender, it is already toolate,late; the transport protocol already missed an opportunity to send data. Some modern TCP implementations now include the unspecified "TCP_NOTSENT_LOWAT" socket option that was proposed in <xreftarget="WWDC2015"/>,target="WWDC2015" format="default"/>, which limits the amount of unsent data that TCP can keep in the socket buffer; this allowsto specifyspecifying at which buffer filling level the socket becomes writable, rather than waiting for the buffer to run empty. </t> <t>SCTP allowsto configureconfiguring the sender-side buffertoo:too; the automatable Transport Feature "Configure send buffer size" provides this functionality, but only for the complete buffer, which includes both unsent and unacknowledged data. SCTP does not allow to control these two sizes separately. It therefore makes sense for a transport system to allow for uniform access to "TCP_NOTSENT_LOWAT" as well as the "SENDER DRY" notification. </t> </section> <section anchor="profile"title="Capacity Profile">numbered="true" toc="default"> <name>Capacity Profile</name> <t>The transport features:<list style="symbols"> <t>Disable</t> <ul spacing="compact"> <li>Disable Naglealgorithm</t> <t>Enablealgorithm</li> <li>Enable and configure a "Low Extra Delay BackgroundTransfer"</t> <t>SpecifyTransfer"</li> <li>Specify DSCPfield</t> </list> allfield</li> </ul> <t> All relate to a QoS-like application need such as "low latency" or "scavenger". In the interest of flexibility of a transport system, they could therefore be offered in a uniform, more abstract way, where a transport systemcould e.g.could, e.g., decide by itself how to use combinations of LEDBAT-like congestion control and certain DSCP values, and an application would only specify a general "capacity profile" (a description of how it wants to use the available capacity). A need for "lowest possible latency at the expense of overhead" could then translate into automatically disabling the Nagle algorithm. </t> <t>In some cases, the Nagle algorithm is best controlled directly by the application because it is not only related to a general profile but also to knowledge about the size of future messages. For fine-grain control over Nagle-like functionality, the "Request not to bundle messages" is available. </t> </section> <section anchor="security"title="Security">numbered="true" toc="default"> <name>Security</name> <t>Both TCP and SCTP offer authentication. TCP authenticates complete segments. SCTP allowsto configureconfiguring which of SCTP's chunk types must always beauthenticated --authenticated; if this is exposed as such, it creates an undesirable dependency on the transport protocol. For compatibility with TCP, a transport system should only allow to configure complete transport layer packets, including headers, IP pseudo-header (if any) and payload. </t> <t>Security is discussed in a separate document <xreftarget="I-D.ietf-taps-transport-security"/>.target="RFC8922" format="default"/>. The minimal set presented in the present document excludes allsecurity relatedsecurity-related transport features from <xreftarget="super"/>:target="super" format="default"/>: "Configure authentication", "Change authentication parameters", "Obtain authenticationinformation"information", and "Set Cookie lifevalue"value", as well as "Specifying a key id to be used to authenticate a message". It also excludes security transport features not listed in <xreftarget="super"/>,target="super" format="default"/>, including content privacy to in-path devices. </t> </section> <section anchor="packetsize"title="Packet Size">numbered="true" toc="default"> <name>Packet Size</name> <t>UDP(-Lite) has a transport feature called "Specify DF field". This yields an error message in the case of sending a message that exceeds the Path MTU, which is necessary for a UDP-based application to be able to implement Path MTU Discovery (a function that UDP-based applications must do by themselves). The "Get max. transport-message size that may be sent using a non-fragmented IP packet from the configured interface" transport feature yields an upper limit for the Path MTU (minus headers) and can therefore help to implement Path MTU Discovery more efficiently.</t><!-- <t>This also relates to the fact that the choice of path is automatable: if a TAPS system can switch a path at any time, unknown to an application, yet the application intends to do Path MTU Discovery, this could yield a very inefficient behavior. Thus, a TAPS system should probably inform the application about path changes when the application requests to disallow fragmentation with the "Specify DF field" feature. </t> --></section> </section> <section anchor="minset"title="Thenumbered="true" toc="default"> <name>The Minimal Set of TransportFeatures">Features</name> <t> Based on the categorization, reduction, and discussion in <xreftarget="deriving"/>,target="deriving" format="default"/>, this section describes a minimal set of transport features that end systems should offer. Any configuration based on the described minimum set of transport feature can always be realized over TCP but also gives the transport system flexibility to choose another transport if implemented. In the text of this section, "not UDP" is used to indicate elements of the system that cannot be implemented over UDP. Conversely, all elements of the system that are not marked with "not UDP" can also be implemented over UDP.<!-- To implement a transport system that can also work over UDP, these marked transport features should be excluded.--> <!--We categorize them as before, but instead of connections they operate on NEAT flows. Since the "Errors" category only contains errors related to sending a particular message and there is only one transport feature left in this category, this category was removed and the only transport feature in it was moved to the "Sending data" category. --></t> <t> The arguments laid out in <xref target="Discussion"/>format="default"/> ("discussion") were used to make the final representation of the minimal set as short,simplesimple, and general as possible. There may be situations where these arguments do notapply --apply, e.g., implementers may have specific reasons to expose multi-streaming as a visible functionality to applications, or the restrictiveopen / closeopen/close semantics may be problematic under some circumstances. In such cases, the representation in <xref target="Reduction"/>format="default"/> ("reduction") should be considered. </t> <t> As in <xreftarget="deriving"/>,target="deriving" format="default"/>, <xreftarget="Reduction"/>target="Reduction" format="default"/>, and <xreftarget="RFC8303"></xref>,target="RFC8303" format="default"/>, we categorize the minimal set of transport features as 1) CONNECTION related (ESTABLISHMENT, AVAILABILITY, MAINTENANCE, TERMINATION) and 2) DATA Transfer related (Sending Data, Receiving Data, Errors). Here, the focus is on connections that the transport system offers as an abstraction to the application, as opposed to connections of transport protocols that the transport system uses.<!--We categorize them as before, but instead of connections they operate on NEAT flows. Since the "Errors" category only contains errors related to sending a particular message and there is only one transport feature left in this category, this category was removed and the only transport feature in it was moved to the "Sending data" category. --></t> <section anchor="minset-init"title="ESTABLISHMENT, AVAILABILITYnumbered="true" toc="default"> <name>ESTABLISHMENT, AVAILABILITY, andTERMINATION">TERMINATION</name> <t>A connection must first be "created" to allow for some initial configuration to be carried out before the transport system can actively or passively establish communication with a remote end system. As a configuration of the newly created connection, an application can choose to disallow usage of MPTCP. Furthermore, all configuration parameters in <xreftarget="minset-groupconfig"/>target="minset-groupconfig" format="default"/> can be used initially, although some of them may only take effect when a connection has been established with a chosen transport protocol. Configuring a connection early helps a transport system make the right decisions. For example, grouping information can influence whether or not the transport systemto implementimplements a connection as a stream of a multi-streaming protocol's existingassociation or not.association. </t> <t> For ungrouped connections, early configuration is necessary because it allows the transport system to know which protocols it should try to use. In particular, a transport system that only makes a one-time choice for a particular protocol must know early about strict requirements that must be kept, or it can end up in a deadlock situation (e.g., having chosen UDP and later be asked to support reliable transfer). As an example description of how to correctly handle these cases, we provide the following decision tree (this is derived from <xreftarget="conn-reduced"/>target="conn-reduced" format="default"/> excluding authentication, as explained in <xreftarget="Security"/>): <figure align="left"> <!--<preamble>Preamble</preamble>--> <artwork align="left"> <![CDATA[ -target="Security" format="default"/>): </t> <artwork> +----------------------------------------------------------+ | Will it ever be necessary to offer any of the following? | | * Reliably transfer data | | * Notify the peer of closing/aborting | | * Preserve data orderingYes: SCTP or TCP| +----------------------------------------------------------+ | | |Yes |No | (SCTP or TCP) | (All protocols | can beused. -used.) | can be used.) V V +--------------------------------------+ +-----------------------------+ | Is any of the following useful to | | Is any of the following | | the application? | | useful to the application? | | * Choosing a scheduler to operate | | * Specify checksum coverage | | between connections in a group, | | used by the sender | | with the possibility to configure | | * Specify minimum checksum | | a priority or weight perconnectionconnection| | coverage required by the | | * Configurable message reliability | | receiver | | * Unordered message delivery | +-----------------------------+ | * Request not to delay the | | | | acknowledgement (SACK) of amessage Yes:message| |Yes |No +--------------------------------------+ | | | | | | |Yes |No | | V | V V SCTP is | UDP-Lite is UDP is preferred. | preferred.No: -preferred. V +------------------------------------------------------+ | Is any of the following useful to the application? | | * Hand over a message to reliably transfer (possibly | | multiple times) before connection establishment | | * Suggest timeout to the peer | | * Notification of Excessive Retransmissions (early | | warning below abortion threshold) | | * Notification of ICMP error message arrivalYes:| +------------------------------------------------------+ | | |Yes |No V V TCP is preferred.No:SCTP and TCP are equally preferable.No: all protocols can be used. - Is any of the following useful to the application? * Specify checksum coverage used by the sender * Specify minimum checksum coverage required by receiver Yes: UDP-Lite is preferred. No: UDP is preferred. ]]></artwork><!--<postamble>Figure 1: RTO restart example</postamble>--> </figure> </t><t>Note that this decision tree is not optimal for all cases. For example, if an application wants to use "Specify checksum coverage used by the sender", which is only offered by UDP-Lite, and "Configure priority or weight for a scheduler", which is only offered by SCTP, the above decision tree will always choose UDP-Lite, making it impossible to use SCTP's schedulers with priorities between grouped connections. Also, several other factors may influence the decisions for or against aprotocol -- e.g.protocol, e.g., penetration rates, the ability to work through NATs, etc. We caution implementers to be aware of the full set of trade-offs, for which we recommend consulting the list in <xreftarget="conn-reduced"/>target="conn-reduced" format="default"/> when deciding how to initialize a connection. </t> <t>To summarize, the following parameters serve as input for the transport system to help it choose and configure a suitable protocol:</t><t> <list style="symbols"> <t>Reliability: a<dl> <dt>Reliability: </dt> <dd>a boolean that should be set to true when any of the following will be useful to the application: reliably transfer data; notify the peer of closing/aborting; or preserve dataordering.</t> <t>Checksumordering. </dd> <dt>Checksum coverage:a</dt> <dd>a boolean to specify whether it will be useful to the application to specify checksum coverage when sending orreceiving.</t> <t>Configurereceiving. </dd> <dt>Configure message priority:a</dt> <dd>a boolean that should be set to true when any of the following per-message configuration or prioritization mechanisms will be useful to the application: choosing a scheduler to operate between grouped connections, with the possibility to configure a priority or weight per connection; configurable message reliability; unordered message delivery; or requesting not to delay the acknowledgement (SACK) of amessage.</t> <t>Earlymessage. </dd> <dt>Early message timeout notifications:a</dt> <dd>a boolean that should be set to true when any of the following will be useful to the application: hand over a message to reliably transfer (possibly multiple times) before connection establishment; suggest timeout to the peer; notification of excessive retransmissions (early warning below abortion threshold); or notification of ICMP error messagearrival.</t> </list> </t>arrival. </dd> </dl> <t>Once a connection is created, it can be queried for the maximum amount of data that an application can possibly expect to have reliably transmitted before or during transport connection establishment (with zero being a possible answer) (see <xreftarget="minset-maintenance-grouped"/>).target="minset-maintenance-grouped" format="default"/>). An application can also give the connection a message for reliable transmission before or during connection establishment (not UDP); the transport system will then try to transmit it as early as possible. An application can facilitate sending a message particularly early by marking it as "idempotent" (see <xreftarget="minset-datatrans-sending"/>);target="minset-datatrans-sending" format="default"/>); in this case, the receiving application must be prepared to potentially receive multiple copies of the message (because idempotent messages are reliably transferred, asking for idempotence is not necessary for systems that support UDP). </t> <t> After creation, a transport system can actively establish communication with a peer, or it can passively listen for incoming connection requests. Note that active establishment may or may not trigger a notification on the listening side. It is possible that the first notification on the listening side is the arrival of the first data that the active side sends (a receiver-side transport system could handle this by continuing to block a "Listen" call, immediatelyfollowedfollowed, for example, by issuing"Receive", for example;"Receive"; callback-based implementations could simply skip the equivalent of "Listen"). This also means that the active opening side is assumed to be the first side sending data. </t> <t>A transport system can actively close a connection,i.e.i.e., terminate it after reliably delivering all remaining data to the peer (if reliable data delivery was requested earlier (not UDP)), in which case the peer is notified that the connection is closed. Alternatively, a connection can be aborted without delivering outstanding data to the peer. In case reliable or partially reliable data delivery was requested earlier (not UDP), the peer is notified that the connection is aborted. A timeout can be configured to abort a connection when data could not be delivered for too long (not UDP); however, timeout-based abortion does not notify the peer application that the connection has been aborted. Because half-closed connections are not supported, when a host implementing a transport system receives a notification that the peer is closing or aborting the connection (not UDP), its peer may not be able to read outstanding data. This means that unacknowledged data residing in a transport system's send buffer may have to be dropped from that buffer upon arrival of a "close" or "abort" notification from the peer. </t> </section> <section anchor="minset-groupconfig"title="MAINTENANCE">numbered="true" toc="default"> <name>MAINTENANCE</name> <t>A transport system must offer means to group connections, but it cannot guarantee truly grouping them using the transport protocols that it uses (e.g., it cannot be guaranteed that connections become multiplexed as streams on a single SCTP association when SCTP may not be available). The transport system must therefore ensure that group- versus non-group-configurations are handled correctly in some way (e.g., by applying the configuration to all grouped connections even when they are not multiplexed, or informing the application about grouping success or failure). </t> <t>As a general rule, any configuration described below should be carried out as early as possible to aid the transport system's decision making. </t> <section anchor="minset-maintenance-grouped"title="Connection groups">numbered="true" toc="default"> <name>Connection Groups</name> <t>The following transport features and notifications (some directly from <xreftarget="Reduction"/>,target="Reduction" format="default"/>; some new or changed, based on the discussion in <xreftarget="Discussion"/>)target="Discussion" format="default"/>) automatically apply to all grouped connections: </t><t>(not UDP) Configure<t>Configure atimeout: thistimeout (not UDP)<br/>This can be done with the following parameters:</t><t><list style="symbols"> <t>A<ul> <li>A timeout value for aborting connections, inseconds</t> <t>Aseconds.</li> <li>A timeout value to be suggested to the peer (if possible), inseconds</t> <t>Theseconds.</li> <li>The number of retransmissions after which the application should benotifednotified of "ExcessiveRetransmissions"</t> </list> </t>Retransmissions".</li> </ul> <t>Configureurgency: thisurgency<br/>This can be done with the following parameters:</t><t><list style="symbols"> <t>A<ul> <li>A number to identify the type of scheduler that should be used to operate between connections in the group (no guarantees given). Schedulers are defined in <xreftarget="RFC8260"/>.</t> <t>Atarget="RFC8260" format="default"/>.</li> <li>A "capacity profile" number to identify how an application wants to use its available capacity. Choices can be "lowest possible latency at the expense of overhead" (which would disable any Nagle-like algorithm), "scavenger", or values that help determine the DSCP value for aconnection (e.g. similar to table 1 in <xref target="I-D.ietf-tsvwg-rtcweb-qos"/>).</t> <t>Aconnection.</li> <li>A buffer limit (in bytes); when the sender has less than the provided limit of bytes in the buffer, the application may be notified. Notifications are not guaranteed, and it is optional for a transport system to support buffer limit values greater than 0. Note that this limit and its notification should operate across the buffers of the whole transport system,i.e.i.e., also any potential buffers that the transport system itself may use on top of the transport's sendbuffer.</t> </list> </t>buffer.</li> </ul> <t>Following <xreftarget="packetsize"/>,target="packetsize" format="default"/>, these properties can be queried:</t><t><list style="symbols"> <t>The<ul> <li>The maximum message size that may be sent without fragmentation via the configured interface. This is optional for a transport system tooffer,offer and may return an error ("not available"). It can aid applications implementing Path MTUDiscovery.</t> <t>TheDiscovery.</li> <li>The maximum transport message size that can be sent, in bytes. Irrespective of fragmentation, there is a size limit for the messages that can be handed over to SCTP or UDP(-Lite); because the service provided by a transport system is independent of the transport protocol, it must allow an application to query thisvalue --value: the maximum size of a message in anApplication-Framed-BytestreamApplication-Framed Byte Stream (see <xreftarget="sendmsg"/>).target="sendmsg" format="default"/>). This may also return an error when data is not delimited ("notavailable").</t> <t>Theavailable").</li> <li>The maximum transport message size that can be received from the configured interface, in bytes (or "notavailable").</t> <t>Theavailable").</li> <li>The maximum amount of data that can possibly be sent before or during connection establishment, inbytes.</t> </list> <vspace blankLines="1"/> </t>bytes.</li> </ul> <t>In addition to the already mentionedclosing / abortingclosing/aborting notifications and possible send errors, the following notifications can occur:</t><t><list style="symbols"> <t>Excessive<dl> <dt>Excessive Retransmissions:the</dt> <dd>The configured (or a default) number of retransmissions has been reached, yielding this early warning below an abortionthreshold.</t> <t>ICMPthreshold. </dd> <dt>ICMP Arrival (parameter: ICMP message):an</dt> <dd>An ICMP packet carrying the conveyed ICMP message hasarrived.</t> <t>ECNarrived. </dd> <dt>ECN Arrival (parameter: ECN value):a</dt> <dd>A packet carrying the conveyedECNExplicit Congestion Notification (ECN) value has arrived. This can be useful for applications implementing congestioncontrol.</t> <t>Timeoutcontrol. </dd> <dt>Timeout (parameter: s seconds):data</dt> <dd>Data could not be delivered for sseconds.</t> <t>Drain: theseconds. </dd> <dt>Drain: </dt> <dd>The send buffer has either drained below the configured buffer limit or it has become completely empty. This is a generic notification that tries to enable uniform access to "TCP_NOTSENT_LOWAT" as well as the "SENDER DRY" notification (as discussed in <xreftarget="rundry"/> --target="rundry"/>; SCTP's "SENDER DRY" is a special case where the threshold (for unsent data) is 0 and there is also no more unacknowledged data in the sendbuffer).</t> </list> </t>buffer). </dd> </dl> </section> <section anchor="minset-maintenance-individual"title="Individual connections">numbered="true" toc="default"> <name>Individual Connections</name> <t>Configure priority or weight for a scheduler, as described in <xreftarget="RFC8260"/>.</t>target="RFC8260" format="default"/>.</t> <t>Configure checksum usage:thisThis can be done with the following parameters, but there is no guarantee that any checksum limitations will indeed be enforced (the default behavior is "full coverage, checksum enabled"):</t><t><list style="symbols"> <t>A<ul> <li>a boolean toenable / disableenable/disable usage of a checksum whensending</t> <t>Thesending</li> <li>the desired coverage (in bytes) of the checksum used whensending</t> <t>Asending</li> <li>a boolean toenable / disableenable/disable requiring a checksum whenreceiving</t> <t>Thereceiving</li> <li>the required minimum coverage (in bytes) of the checksum whenreceiving</t> </list> </t>receiving</li> </ul> </section> </section> <section anchor="minset-datatrans"title="DATA Transfer">numbered="true" toc="default"> <name>DATA Transfer</name> <section anchor="minset-datatrans-sending"title="Sending Data">numbered="true" toc="default"> <name>Sending Data</name> <t>When sending a message, no guarantees are given about the preservation of message boundaries to the peer; if message boundaries are needed, the receiving application at the peer must know about them beforehand (or the transport system cannot use TCP). Note that an application should already be able to hand over data before the transport system establishes a connection with a chosen transport protocol. Regarding the message that is being handed over, the following parameters can be used:</t><t><list style="symbols"> <t>Reliability: this<dl> <dt>Reliability: </dt> <dd>This parameter is used to convey a choice of: fully reliable with congestion control (not UDP), unreliable without congestion control, unreliable with congestion control (not UDP), and partially reliable with congestion control (see <xreftarget="RFC3758"/>target="RFC3758" format="default"/> and <xreftarget="RFC7496"/>target="RFC7496" format="default"/> for details on how to specify partial reliability) (not UDP). The latter two choices are optional for a transport system to offer and may result in full reliability. Note that applications sending unreliable data without congestion control should themselves perform congestion control in accordance with <xreftarget="RFC8085"/>.</t> <t>(not UDP) Ordered: thistarget="RFC8085" format="default"/>. </dd> <dt>Ordered (not UDP): </dt> <dd>This booleanparameterlets an application choose between ordered message delivery (true) and possibly unordered, potentially faster message delivery(false).</t> <t>Bundle: a(false). </dd> <dt>Bundle: </dt> <dd>This booleanthatexpresses a preference for allowing to bundle messages (true) or not (false). No guarantees aregiven.</t> <t>DelAck: a boolean that,given. </dd> <dt>DelAck: </dt> <dd>This boolean, if false, lets an application request that the peerwouldnot delay the acknowledgement for thismessage.</t> <t>Fragment: amessage. </dd> <dt>Fragment: </dt> <dd>This booleanthatexpresses a preference for allowing to fragment messages (true) or not (false), at the IP level. No guarantees aregiven.</t> <t>(not UDP) Idempotent: agiven. </dd> <dt>Idempotent (not UDP): </dt> <dd>This booleanthatexpresses whether a message is idempotent (true) or not (false). Idempotent messages may arrive multiple times at the receiver (but they will arrive at least once). When data isidempotentidempotent, it can be used by the receiver immediately on a connection establishment attempt. Thus, if data is handed over before the transport system establishes a connection with a chosen transport protocol, stating that a message is idempotent facilitates transmitting it to the peer application particularly early.</t> </list> </t></dd> </dl> <t>An application can be notified of a failure to send a specific message. There is no guarantee of such notifications,i.e.i.e., send failures can also silently occur.</t> </section> <section anchor="minset-datatrans-receiving"title="Receiving Data">numbered="true" toc="default"> <name>Receiving Data</name> <t>A receiving application obtains an "Application-FramedBytestream" (AFra-Bytestream);Byte Stream" (AFra Byte Stream); this concept is further described in <xreftarget="sendmsg"/>).target="sendmsg" format="default"/>. In line with TCP's receiver semantics, anAFra-BytestreamAFra Byte Stream is just a stream of bytes to the receiver. If message boundaries were specified by the sender, a receiver-side transport system implementing only the minimum set oftransport servicesTransport Services defined here will still not inform the receiving application about them (this limitation is only needed for transport systems that are implemented to directly use TCP).</t> <t>Different from TCP's semantics, if the sending application has allowed that messages are not fully reliably transferred, or delivered out of order, then suchre-orderingreordering or unreliability may be reflected per message in the arriving data. Messages will always stayintact - i.e.intact, i.e., if an incomplete message is contained at the end of the arriving data block, this message is guaranteed to continue in the next arriving data block.</t> </section> </section> </section><!-- </section> --> <section anchor="Acknowledgements" title="Acknowledgements"> <t>The authors would like to thank all the participants of the TAPS Working Group and the NEAT and MAMI research projects for valuable input to this document. We especially thank Michael Tuexen for help with connection connection establishment/teardown, Gorry Fairhurst for his suggestions regarding fragmentation and packet sizes, and Spencer Dawkins for his extremely detailed and constructive review. This work has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 644334 (NEAT). <!-- The views expressed are solely those of the author(s).--> </t> </section> <!-- Possibly a 'Contributors' section ... --> <section anchor="IANA" title="IANA Considerations"> <t>This memo includes no request to IANA.</t><section anchor="IANA" numbered="true" toc="default"> <name>IANA Considerations</name> <t>This document has no IANA actions. </t> </section> <section anchor="Security"title="Security Considerations">numbered="true" toc="default"> <name>Security Considerations</name> <t>Authentication, confidentiality protection, and integrity protection are identified as transport features by <xreftarget="RFC8095"/>.target="RFC8095" format="default"/>. Often, these features are provided by a protocol or layer on top of the transport protocol; none of the full-featured standards-track transport protocols in <xreftarget="RFC8303"/>,target="RFC8303" format="default"/>, which this document is based upon,providesprovide all of these transport features on its own. Therefore, they are not considered in this document, with the exception of native authentication capabilities of TCP and SCTP for which the security considerations in <xreftarget="RFC5925"/>target="RFC5925" format="default"/> and <xreftarget="RFC4895"/>target="RFC4895" format="default"/> apply. The minimum requirements for a secure transport system are discussed in a separate document(Section 5 on Security Features and Transport Dependencies of<xreftarget="I-D.ietf-taps-transport-security"/>).</t>target="RFC8922" format="default"/>. </t> </section> </middle><!-- *****BACK MATTER ***** --><back><!-- References split into informative and normative --> <!-- There are 2 ways to insert reference entries from the citation libraries: 1. define an ENTITY at the top, and use "ampersand character"RFC2629; here (as shown) 2. simply use a PI "less than character"?rfc include="reference.RFC.2119.xml"?> here (for I-Ds: include="reference.I-D.narten-iana-considerations-rfc2434bis.xml") Both are cited textually in the same manner: by using xref elements. If you use the PI option, xml2rfc will, by default, try to find included files in the same directory as the including file. You can also define the XML_LIBRARY environment variable with a value containing a set of directories to search. These can be either in the local filing system or remote ones accessed by http (http://domain/dir/... ).--> <references title="Normative References"> &RFC8095; &RFC8303; &I-D.ietf-taps-transport-security; </references> <references title="Informative References"> <!--&RFC2119;--> &RFC8085; &RFC3758; &RFC4895; &RFC4987; &RFC5925; &RFC6897; &RFC7305; &RFC7413; &RFC7496; &RFC8260; &RFC8304; &I-D.ietf-tsvwg-rtcweb-qos; &I-D.ietf-taps-interface; <!-- unnecessary<displayreference target="I-D.ietf-taps-interface" to="TAPS-INTERFACE"/> <references> <name>References</name> <references> <name>Normative References</name> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8095.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8303.xml"/> <referenceanchor="RFC793bis" target="">anchor="RFC8922" target="https://www.rfc-editor.org/info/rfc8922"> <front><title>Transmission Control Protocol Specification</title><title>A Survey of the Interaction between Security Protocols and Transport Services</title> <authorfullname="Wesley Eddy" initials="W." surname="Eddy"></author> <date month="July" year="2017"initials='T' surname='Enghardt' fullname='Theresa Enghardt'> <organization /></front> <seriesInfo name="Internet-draft" value="draft-ietf-tcpm-rfc793bis-06"</author> <author initials='T' surname='Pauly' fullname='Tommy Pauly'> <organization /></reference> --> <reference anchor="LBE-draft" target=""> <front> <title>A Lower Effort Per-Hop Behavior (LE PHB)</title></author> <author initials='C' surname='Perkins' fullname='Colin Perkins'> <organization /> </author> <author initials='K' surname='Rose' fullname='Kyle Rose'> <organization /> </author> <authorfullname="Roland Bless" initials="R." surname="Bless"></author>initials='C' surname='Wood' fullname='Christopher Wood'> <organization /> </author> <datemonth="February" year="2018"month="October" year='2020' /> </front> <seriesInfoname="Internet-draft" value="draft-tsvwg-le-phb-03" />name="RFC" value="8922"/> <seriesInfo name="DOI" value="10.17487/RFC8922"/> </reference> </references> <references> <name>Informative References</name> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8085.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3758.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4895.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4987.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5925.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6897.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7305.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7413.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7496.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8260.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8304.xml"/> <xi:include href="https://datatracker.ietf.org/doc/bibxml3/reference.I-D.ietf-taps-interface.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8622.xml"/> <reference anchor="COBS"> <front> <title>ConsistentOverhead Byte Stuffing</title>overhead byte stuffing</title> <author fullname="Stuart Cheshire" initials="S" surname="Cheshire"> <organization>StanfordUniversity</organization></author>University</organization> </author> <author fullname="Mary Baker" initials="M"surname="Baker" >surname="Baker"> <organization>StanfordUniversity</organization></author>University</organization> </author> <date month="April"year="1999" />year="1999"/> </front> <seriesInfoname="IEEE/ACMname="DOI" value="10.1109/90.769765"/> <refcontent>IEEE/ACM Transactions onNetworking" value="Vol.Networking, Volume 7,No. 2"/>Issue 2 </refcontent> </reference> <reference anchor="WWDC2015" target="https://developer.apple.com/videos/wwdc/2015/?id=719"> <front> <title>Your App and Next Generation Networks</title> <author fullname="Prabhakar Lakhera" initials="P."surname="Lakhera"></author>surname="Lakhera"/> <author fullname="Stuart Cheshire" initials="S."surname="Cheshire"></author>surname="Cheshire"/> <date month="June"year="2015" />year="2015"/> </front><seriesInfo name="Apple<refcontent>Apple Worldwide DevelopersConference" value="2015, SanConference 2015</refcontent> <refcontent>San Francisco,USA" />USA</refcontent> </reference> <reference anchor="POSIX"target="http://www.opengroup.org/onlinepubs/9699919799/functions/contents.html">target="https://www.opengroup.org/onlinepubs/9699919799/functions/contents.html"> <front> <title>IEEE Standard for Information Technology--Portable Operating System Interface (POSIX(R)) Base Specifications, Issue 7</title><author fullname="IEEE"></author><author><organization>The Open Group</organization></author> <date month="January"year="2018" />year="2018"/> </front> <seriesInfo name="IEEE Std"value= "1003.1-2017 (Revisionvalue="1003.1-2017"/> <refcontent>(Revision of IEEE Std1003.1-2008)" />1003.1-2008)</refcontent> </reference> <referenceanchor="SCTP-stream-1">anchor="SCTP-STREAM-1"> <front> <title>Transparent Flow Mapping for NEAT</title> <author fullname="Felix Weinrank" initials="F"surname="Weinrank"></author>surname="Weinrank"/> <author fullname="Michael Tuexen" initials="M"surname="Tuexen" ></author>surname="Tuexen"/> <date month="June"year="2017" />year="2017"/> </front><seriesInfo name="IFIP NETWORKING Workshop<refcontent>IFIP Networking 2017</refcontent> <refcontent>Workshop on Future of InternetTransport" value ="(FIT 2017)"/>Transport (FIT 2017)</refcontent> </reference> <referenceanchor="SCTP-stream-2">anchor="SCTP-STREAM-2"> <front> <title>Beneficial Transparent Deployment ofSCTP</title>SCTP: The Missing Pieces</title> <author fullname="Michael Welzl" initials="M"surname="Welzl"></author>surname="Welzl"/> <author fullname="Florian Niederbacher" initials="F"surname="Niederbacher" ></author>surname="Niederbacher"/> <author fullname="Stein Gjessing" initials="S"surname="Gjessing" ></author>surname="Gjessing"/> <date month="December"year="2011" />year="2011"/> </front> <seriesInfoname="IEEE GlobeCom" value="2011"/>name="DOI" value="10.1109/GLOCOM.2011.6133554"/> <refcontent>IEEE GlobeCom 2011</refcontent> </reference> </references><!-- Change Log v00 2006-03-15 EBD Initial version --></references> <section anchor="super"title="Thenumbered="true" toc="default"> <name>The Superset of TransportFeatures">Features</name> <t> In this description, transport features are presented following the nomenclature "CATEGORY.[SUBCATEGORY].FEATURENAME.PROTOCOL", equivalent to "pass 2" in <xref target="RFC8303"/>. <!-- this was moved to terminology because it applies throughout: The PROTOCOL name "UDP(-Lite)" is used when transport features are equivalent for UDP and UDP-Lite; the PROTOCOL name "TCP" refers to both TCP and MPTCP. -->format="default"/>. We also sketch how functional or optimizing transport features can be implemented by a transport system. The "minimal set" derived in this document is meant to be implementable "one-sided" overTCP,TCP and, with limitations, UDP. Hence, for all transport features that are categorized as "functional" or "optimizing", and for which no matching TCP and/or UDP primitive exists in "pass 2" of <xref target="RFC8303"/>,format="default"/>, a brief discussion on how to implement them over TCP and/or UDP is included. </t> <t>We designate some transport features as "automatable" on the basis of a broader decision that affects multiple transport features:<list style="symbols"> <t>Most</t> <ul> <li>Most transport features that are related to multi-streaming were designated as "automatable". This was done because the decision on whether or not to use multi-streamingor notdoes not depend on application-specific knowledge. This means that a connection that is exhibited to an application could be implemented by using a single stream of an SCTP association instead of mapping it to a complete SCTP association or TCP connection. This could be achieved by using more than one stream when an SCTP association is first established (CONNECT.SCTP parameter "outbound stream count"), maintaining an internal stream number, and using this stream number when sending data (SEND.SCTP parameter "stream number"). Closing or aborting a connection could then simply free the stream number for future use. This is discussed further in <xreftarget="nostream"/>. </t> <t>Withtarget="nostream" format="default"/>. </li> <li>With the exception of "Disable MPTCP", all transport features that are related to using multiple paths or the choice of the network interface were designated as "automatable". For example, "Listen" could always listen on all available interfaces and "Connect" could use the default interface for the destination IP address.</t> </list> </t></li> </ul> <t> Finally, in three cases, transport features are aggregated and/or slightly changed from <xref target="RFC8303"/>format="default"/> in the description below. These transport features are marked as "CHANGED FROMRFC8303".RFC 8303". These do not add any new functionality but just represent a simple refactoring step that helps to streamline the derivation process (e.g., by removing a choice of a parameter for the sake of applications that may not care about this choice). The corresponding transport features are automatable, and they are listed immediately below the "CHANGED FROMRFC8303"RFC 8303" transport feature. </t> <section anchor="conn-super"title="CONNECTION Relatednumbered="true" toc="default"> <name>CONNECTION-Related TransportFeatures"> <t>ESTABLISHMENT:<vspace /> <list style="symbols">Features</name> <t>ESTABLISHMENT: </t> <ul> <li> <t>Connect<vspace /></t> <t> Protocols: TCP, SCTP, UDP(-Lite)<vspace /></t> <t> Functional because the notion of a connection is often reflected in applications as an expectation to be able to communicate after a "Connect" succeeded, with a communication sequence relating to this transport feature that is defined by the applicationprotocol.<vspace />protocol.</t> <t> Implementation: via CONNECT.TCP, CONNECT.SCTP orCONNECT.UDP(-Lite).<vspace /> <vspace blankLines='1'/> </t>CONNECT.UDP(-Lite).</t> <t/> </li> <li> <t>Specify which IP Options must always beused<vspace />used</t> <t> Protocols: TCP,UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Automatable because IP Options relate to knowledge about the network, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>Request multiplestreams<vspace />streams</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because using multi-streaming does not require application-specific knowledge (example implementations of using multi-streaming without involving the application are described in <xreftarget="SCTP-stream-1"/>target="SCTP-STREAM-1" format="default"/> and <xreftarget="SCTP-stream-2"/>).<vspace />target="SCTP-STREAM-2" format="default"/>).</t> <t> Implementation: see <xreftarget="nostream"/>. <vspace blankLines='1'/>target="nostream" format="default"/>. </t> <t/> </li> <li> <t>Limit the number of inboundstreams<vspace />streams</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because using multi-streaming does not require application-specificknowledge.<vspace />knowledge.</t> <t> Implementation: see <xreftarget="nostream"/>. <vspace blankLines='1'/>target="nostream" format="default"/>. </t> <t/> </li> <li> <t>Specify number of attempts and/or timeout for the first establishmentmessage<vspace />message</t> <t> Protocols: TCP,SCTP<vspace />SCTP</t> <t> Functional because this is closely related to potentially assumed reliable data delivery for data that is sent before or during connectionestablishment.<vspace />establishment.</t> <t> Implementation:Usingusing a parameter of CONNECT.TCP andCONNECT.SCTP.<vspace />CONNECT.SCTP.</t> <t> Implementation over UDP:Dodo nothing (this is irrelevant in the case of UDP because there, reliable data delivery is not assumed).<vspace blankLines='1'/></t> <t/> </li> <li> <t>Obtain multiplesockets<vspace />sockets</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because the non-parallel usage of multiple paths to communicate between the same end hosts relates to knowledge about the network, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>DisableMPTCP<vspace />MPTCP</t> <t> Protocols:MPTCP<vspace />MPTCP</t> <t> Optimizing because the parallel usage of multiple paths to communicate between the same end hosts can improve performance. Whether or not to use this feature depends on knowledge about the network as well as application-specific knowledge (seeSection 3.1 of<xreftarget="RFC6897"/>).<vspace />target="RFC6897" sectionFormat="of" section="3.1"/>).</t> <t> Implementation: via a boolean parameter inCONNECT.MPTCP.<vspace />CONNECT.MPTCP.</t> <t> Implementation over TCP:Do nothing.<vspace />do nothing.</t> <t> Implementation over UDP:Dodo nothing.<vspace blankLines='1'/></t> <t/> </li> <li> <t>Configureauthentication<vspace />authentication</t> <t> Protocols: TCP,SCTP<vspace />SCTP</t> <t> Functional because this has a direct influence onsecurity.<vspace />security.</t> <t> Implementation: via parameters in CONNECT.TCP and CONNECT.SCTP. With TCP, this allowsto configureconfiguring Master Key Tuples (MKTs) to authenticate complete segments (including the TCP IPv4 pseudoheader, TCP header, and TCP data). With SCTP, this allowsto specifyspecifying which chunk types must always be authenticated. Authenticating only certain chunk types creates a reduced level of security that is not supported by TCP; to be compatible, this should therefore only allow to authenticate all chunk types. Key material must be provided in a way that is compatible with both <xreftarget="RFC4895"/>target="RFC4895" format="default"/> and <xreftarget="RFC5925"/>.<vspace />target="RFC5925" format="default"/>.</t> <t> Implementation over UDP:Notnot possible (UDP does not offer this functionality).<vspace blankLines='1'/></t> <t/> </li> <li> <t>Indicate (and/or obtain upon completion) an Adaptation Layer via an adaptation codepoint<vspace />point</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Functional because it allowsto sendsending extra data for the sake of identifying an adaptation layer, which by itself isapplication-specific.<vspace />application specific.</t> <t> Implementation: via a parameter inCONNECT.SCTP.<vspace />CONNECT.SCTP.</t> <t> Implementation over TCP: notpossiblepossible. (TCP does not offer thisfunctionality).<vspace />functionality.)</t> <t> Implementation over UDP: notpossiblepossible. (UDP does not offer thisfunctionality).<vspace /> <vspace blankLines='1'/> </t>functionality.)</t> <t/> </li> <li> <t>Request to negotiate interleaving of usermessages<vspace />messages</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because it requires using multiple streams, but requesting multiple streams in the CONNECTION.ESTABLISHMENT category isautomatable.<vspace />automatable.</t> <t> Implementation: controlled via a parameter in CONNECT.SCTP. One possible implementation is to always try to enableinterleaving.<vspace /> <vspace blankLines='1'/> </t>interleaving.</t> <t/> </li> <li> <t>Hand over a message to reliably transfer (possibly multiple times) before connectionestablishment<vspace />establishment</t> <t> Protocols:TCP<vspace />TCP</t> <t> Functional because this is closely tied to properties of the data that an application sends or expects toreceive.<vspace />receive.</t> <t> Implementation: via a parameter inCONNECT.TCP.<vspace />CONNECT.TCP.</t> <t> Implementation over UDP: notpossiblepossible. (UDP does not providereliability). <vspace blankLines='1'/>reliability.) </t> <t/> </li> <li> <t>Hand over a message to reliably transfer during connectionestablishment<vspace />establishment</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Functional because this can only work if the message is limited in size, making it closely tied to properties of the data that an application sends or expects toreceive.<vspace />receive.</t> <t> Implementation: via a parameter inCONNECT.SCTP.<vspace />CONNECT.SCTP.</t> <t> Implementation over TCP:not possible (TCP does not allow identification oftransmit the messageboundaries because it provides a byte stream service)<vspace /> <!-- The text below is wrong because TCP is not message-based! Implementation over TCP: this is also possiblewithTCP, but not addressed in <xref target="RFC8303"/> becausethespecification that it is based upon does not clearly specify how to implement it usingSYN packet, sacrificing theTCP's ``user commands''. This will be addressed in an update <xref target="RFC793bis"/>.<vspace /> -->ability to identify message boundaries. </t> <t> Implementation over UDP: notpossiblepossible. (UDP isunreliable). <vspace blankLines='1'/>unreliable.) </t> <t/> </li> <li> <t>Enable UDP encapsulation with a specified remote UDP portnumber<vspace />number</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because UDP encapsulation relates to knowledge about the network, not theapplication.<vspace /> <vspace blankLines='1'/>application.</t> <t/> </li> </ul> <t>AVAILABILITY: </t></list></t> <t>AVAILABILITY:<vspace /> <list style="symbols"> <t>Listen<vspace /><ul > <li> <t>Listen</t> <t> Protocols: TCP, SCTP,UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Functional because the notion of accepting connection requests is often reflected in applications as an expectation to be able to communicate after a "Listen" succeeded, with a communication sequence relating to this transport feature that is defined by the applicationprotocol.<vspace />protocol.</t> <t> CHANGED FROMRFC8303.RFC 8303. This differs from the 3 automatable transport features below in that it leaves the choice of interfaces for listeningopen.<vspace />open.</t> <t> Implementation: by listening on all interfaces via LISTEN.TCP (not providing a local IP address) or LISTEN.SCTP (providing SCTP port number / address pairs for all local IP addresses). LISTEN.UDP(-Lite) supports bothmethods.<vspace blankLines='1'/> </t>methods.</t> <t/> </li> <li> <t>Listen, 1 specified localinterface<vspace />interface</t> <t> Protocols: TCP, SCTP,UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Automatable because decisions about local interfaces relate to knowledge about the network and the Operating System, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>Listen, N specified localinterfaces<vspace />interfaces</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because decisions about local interfaces relate to knowledge about the network and the Operating System, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>Listen, all localinterfaces<vspace />interfaces</t> <t> Protocols: TCP, SCTP,UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Automatable because decisions about local interfaces relate to knowledge about the network and the Operating System, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>Specify which IP Options must always beused<vspace />used</t> <t> Protocols: TCP,UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Automatable because IP Options relate to knowledge about the network, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>DisableMPTCP<vspace />MPTCP</t> <t> Protocols:MPTCP<vspace />MPTCP</t> <t> Optimizing because the parallel usage of multiple paths to communicate between the same end hosts can improve performance. Whether or not to use this feature depends on knowledge about the network as well as application-specific knowledge (seeSection 3.1 of<xreftarget="RFC6897"/>).<vspace />target="RFC6897" sectionFormat="of" section="3.1"/>).</t> <t> Implementation: via a boolean parameter inLISTEN.MPTCP.<vspace />LISTEN.MPTCP.</t> <t> Implementation over TCP:Do nothing.<vspace />do nothing.</t> <t> Implementation over UDP:Dodo nothing.<vspace blankLines='1'/></t> <t/> </li> <li> <t>Configureauthentication<vspace />authentication</t> <t> Protocols: TCP,SCTP<vspace />SCTP</t> <t> Functional because this has a direct influence onsecurity.<vspace />security.</t> <t> Implementation: via parameters in LISTEN.TCP andLISTEN.SCTP.<vspace />LISTEN.SCTP.</t> <t> Implementation over TCP:Withwith TCP, this allowsto configureconfiguring Master Key Tuples (MKTs) to authenticate complete segments (including the TCP IPv4 pseudoheader, TCP header, and TCP data). With SCTP, this allowsto specifyspecifying which chunk types must always be authenticated. Authenticating only certain chunk types creates a reduced level of security that is not supported by TCP; to be compatible, this should therefore only allow to authenticate all chunk types. Key material must be provided in a way that is compatible with both <xreftarget="RFC4895"/>target="RFC4895" format="default"/> and <xreftarget="RFC5925"/>.<vspace />target="RFC5925" format="default"/>.</t> <t> Implementation over UDP: notpossiblepossible. (UDP does not offerauthentication). <vspace blankLines='1'/>authentication.) </t> <t/> </li> <li> <t>Obtain requested number ofstreams<vspace />streams</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because using multi-streaming does not require application-specificknowledge.<vspace />knowledge.</t> <t> Implementation: see <xreftarget="nostream"/>. <vspace blankLines='1'/>target="nostream" format="default"/>. </t> <t/> </li> <li> <t>Limit the number of inboundstreams<vspace />streams</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because using multi-streaming does not require application-specificknowledge.<vspace />knowledge.</t> <t> Implementation: see <xreftarget="nostream"/>. <vspace blankLines='1'/>target="nostream" format="default"/>. </t> <t/> </li> <li> <t>Indicate (and/or obtain upon completion) an Adaptation Layer via an adaptation codepoint<vspace />point</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Functional because it allowsto sendsending extra data for the sake of identifying an adaptation layer, which by itself isapplication-specific.<vspace />application specific.</t> <t> Implementation: via a parameter inLISTEN.SCTP.<vspace />LISTEN.SCTP.</t> <t> Implementation over TCP: notpossiblepossible. (TCP does not offer thisfunctionality).<vspace />functionality.)</t> <t> Implementation over UDP: notpossiblepossible. (UDP does not offer thisfunctionality). <vspace blankLines='1'/>functionality.) </t> <t/> </li> <li> <t>Request to negotiate interleaving of usermessages<vspace />messages</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because it requires using multiple streams, but requesting multiple streams in the CONNECTION.ESTABLISHMENT category isautomatable.<vspace />automatable.</t> <t> Implementation: via a parameter inLISTEN.SCTP.<vspace /> <vspace blankLines='1'/>LISTEN.SCTP.</t> <t/> </li> </ul> <t>MAINTENANCE: </t></list></t> <t>MAINTENANCE:<vspace /> <list style="symbols"><ul > <li> <t>Change timeout for aborting connection (using retransmit limit or timevalue)<vspace />value)</t> <t> Protocols: TCP,SCTP<vspace />SCTP</t> <t> Functional because this is closely related to potentially assumed reliable datadelivery.<vspace />delivery.</t> <t> Implementation: via CHANGE_TIMEOUT.TCP orCHANGE_TIMEOUT.SCTP.<vspace />CHANGE_TIMEOUT.SCTP.</t> <t> Implementation over UDP: notpossiblepossible. (UDP is unreliable and there is no connectiontimeout).<vspace /> <vspace blankLines='1'/> </t>timeout.)</t> <t/> </li> <li> <t>Suggest timeout to thepeer<vspace />peer</t> <t> Protocols:TCP<vspace />TCP</t> <t> Functional because this is closely related to potentially assumed reliable datadelivery.<vspace />delivery.</t> <t> Implementation: viaCHANGE_TIMEOUT.TCP.<vspace />CHANGE_TIMEOUT.TCP.</t> <t> Implementation over UDP: notpossiblepossible. (UDP is unreliable and there is no connectiontimeout).<vspace /> <vspace blankLines='1'/> </t>timeout.)</t> <t/> </li> <li> <t>Disable Naglealgorithm<vspace />algorithm</t> <t> Protocols: TCP,SCTP<vspace />SCTP</t> <t> Optimizing because this decision depends on knowledge about the size of future data blocks and the delay betweenthem.<vspace />them.</t> <t> Implementation: via DISABLE_NAGLE.TCP andDISABLE_NAGLE.SCTP.<vspace />DISABLE_NAGLE.SCTP.</t> <t> Implementation over UDP: do nothing (UDP does not implement the Naglealgorithm).<vspace /> <vspace blankLines='1'/> </t>algorithm).</t> <t/> </li> <li> <t>Request an immediate heartbeat, returningsuccess/failure<vspace />success/failure</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because this informs about network-specificknowledge.<vspace /> <vspace blankLines='1'/> </t>knowledge.</t> <t/> </li> <li> <t>Notification of Excessive Retransmissions (early warning below abortionthreshold)<vspace />threshold)</t> <t> Protocols:TCP<vspace />TCP</t> <t> Optimizing because it is an early warning to the application, informing it of an impending functionalevent.<vspace />event.</t> <t> Implementation: viaERROR.TCP.<vspace />ERROR.TCP.</t> <t> Implementation over UDP: do nothing (there is no abortionthreshold).<vspace /> <vspace blankLines='1'/> </t>threshold).</t> <t/> </li> <li> <t>Addpath<vspace />path</t> <t> Protocols: MPTCP,SCTP<vspace />SCTP</t> <t> MPTCP Parameters: source-IP; source-Port; destination-IP;destination-Port<vspace />destination-Port</t> <t> SCTP Parameters: local IPaddress<vspace />address</t> <t> Automatable because the choice of paths to communicate between the same end hosts relates to knowledge about the network, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>Removepath<vspace />path</t> <t> Protocols: MPTCP,SCTP<vspace />SCTP</t> <t> MPTCP Parameters: source-IP; source-Port; destination-IP;destination-Port<vspace />destination-Port</t> <t> SCTP Parameters: local IPaddress<vspace />address</t> <t> Automatable because the choice of paths to communicate between the same end host relates to knowledge about the network, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>Set primarypath<vspace />path</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because the choice of paths to communicate between the same end hosts relates to knowledge about the network, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>Suggest primary path to thepeer<vspace />peer</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because the choice of paths to communicate between the same end hosts relates to knowledge about the network, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>Configure PathSwitchover<vspace />Switchover</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because the choice of paths to communicate between the same end hosts relates to knowledge about the network, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>Obtain status (query ornotification)<vspace />notification)</t> <t> Protocols: SCTP,MPTCP<vspace />MPTCP</t> <t> SCTP parameters: association connection state; destination transport address list; destination transport address reachability states; current local and peer receiver window size; current local congestion window sizes; number of unacknowledged DATA chunks; number of DATA chunks pending receipt; primary path; most recent SRTT on primary path; RTO on primary path; SRTT and RTO on other destination addresses; MTU per path; interleaving supportedyes/no<vspace />yes/no</t> <t> MPTCP parameters: subflow-list (identified by source-IP; source-Port; destination-IP;destination-Port)<vspace />destination-Port)</t> <t> Automatable because these parameters relate to knowledge about the network, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>Specify DSCPfield<vspace />field</t> <t> Protocols: TCP, SCTP,UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Optimizing because choosing a suitable DSCP value requires application-specificknowledge.<vspace />knowledge.</t> <t> Implementation: via SET_DSCP.TCP / SET_DSCP.SCTP /SET_DSCP.UDP(-Lite)<vspace /> <vspace blankLines='1'/> </t>SET_DSCP.UDP(-Lite).</t> <t/> </li> <li> <t>Notification of ICMP error messagearrival<vspace />arrival</t> <t> Protocols: TCP,UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Optimizing because these messages can inform about success or failure of functional transport features (e.g., host unreachable relates to"Connect")<vspace />"Connect").</t> <t> Implementation: via ERROR.TCP orERROR.UDP(-Lite).<vspace /> <vspace blankLines='1'/> </t>ERROR.UDP(-Lite.)</t> <t/> </li> <li> <t>Obtain information about interleavingsupport<vspace />support</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because it requires using multiple streams, but requesting multiple streams in the CONNECTION.ESTABLISHMENT category isautomatable.<vspace />automatable.</t> <t> Implementation: viaSTATUS.SCTP.<vspace /> <vspace blankLines='1'/> </t>STATUS.SCTP.</t> <t/> </li> <li> <t>Change authenticationparameters<vspace />parameters</t> <t> Protocols: TCP,SCTP<vspace />SCTP</t> <t> Functional because this has a direct influence onsecurity.<vspace />security.</t> <t> Implementation: via SET_AUTH.TCP andSET_AUTH.SCTP.<vspace />SET_AUTH.SCTP.</t> <t> Implementation over TCP:Withwith SCTP, this allowsto adjustadjusting key_id, key, and hmac_id. With TCP, this allowsto changechanging the preferred outgoing MKT (current_key) and the preferred incoming MKT (rnext_key), respectively, for a segment that is sent on the connection. Key material must be provided in a way that is compatible with both <xreftarget="RFC4895"/>target="RFC4895" format="default"/> and <xreftarget="RFC5925"/>.<vspace />target="RFC5925" format="default"/>.</t> <t> Implementation over UDP: notpossiblepossible. (UDP does not offerauthentication).<vspace /> <vspace blankLines='1'/> </t>authentication.)</t> <t/> </li> <li> <t>Obtain authenticationinformation<vspace />information</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Functional because authentication decisions may have been made by the peer, and this has an influence on the necessary application-level measures to provide a certain level ofsecurity.<vspace />security.</t> <t> Implementation: viaGET_AUTH.SCTP.<vspace />GET_AUTH.SCTP.</t> <t> Implementation over TCP:Withwith SCTP, this allowsto obtainobtaining key_id and a chunk list. With TCP, this allowsto obtainobtaining current_key and rnext_key from a previously received segment. Key material must be provided in a way that is compatible with both <xreftarget="RFC4895"/>target="RFC4895" format="default"/> and <xreftarget="RFC5925"/>.<vspace />target="RFC5925" format="default"/>.</t> <t> Implementation over UDP: notpossiblepossible. (UDP does not offerauthentication).<vspace /> <vspace blankLines='1'/> </t>authentication.)</t> <t/> </li> <li> <t>ResetStream<vspace />Stream</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because using multi-streaming does not require application-specificknowledge.<vspace />knowledge.</t> <t> Implementation: see <xreftarget="nostream"/>. <vspace blankLines='1'/>target="nostream" format="default"/>. </t> <t/> </li> <li> <t>Notification of StreamReset<vspace />Reset</t> <t> Protocols:STCP<vspace />STCP</t> <t> Automatable because using multi-streaming does not require application-specificknowledge.<vspace />knowledge.</t> <t> Implementation: see <xreftarget="nostream"/>. <vspace blankLines='1'/>target="nostream" format="default"/>. </t> <t/> </li> <li> <t>ResetAssociation<vspace />Association</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because deciding to reset an association does not require application-specificknowledge.<vspace />knowledge.</t> <t> Implementation: viaRESET_ASSOC.SCTP.<vspace /> <vspace blankLines='1'/> </t>RESET_ASSOC.SCTP.</t> <t/> </li> <li> <t>Notification of AssociationReset<vspace />Reset</t> <t> Protocols:STCP<vspace />STCP</t> <t> Automatable because this notification does not relate to application-specificknowledge.<vspace /> <vspace blankLines='1'/> </t>knowledge.</t> <t/> </li> <li> <t>AddStreams<vspace />Streams</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because using multi-streaming does not require application-specificknowledge.<vspace />knowledge.</t> <t> Implementation: see <xreftarget="nostream"/>. <vspace blankLines='1'/>target="nostream" format="default"/>. </t> <t/> </li> <li> <t>Notification of AddedStream<vspace />Stream</t> <t> Protocols:STCP<vspace />STCP</t> <t> Automatable because using multi-streaming does not require application-specificknowledge.<vspace />knowledge.</t> <t> Implementation: see <xreftarget="nostream"/>. <vspace blankLines='1'/>target="nostream" format="default"/>. </t> <t/> </li> <li> <t>Choose a scheduler to operate between streams of anassociation<vspace />association</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Optimizing because the scheduling decision requires application-specific knowledge. However, if a transport system would not use this, or wrongly configure it on its own, this would only affect the performance of data transfers; the outcome would still be correct within the "best effort" servicemodel.<vspace />model.</t> <t> Implementation: usingSET_STREAM_SCHEDULER.SCTP.<vspace />SET_STREAM_SCHEDULER.SCTP.</t> <t> Implementation over TCP: do nothing (streams are not available in TCP, but no guarantee is given that this transport feature has anyeffect).<vspace />effect).</t> <t> Implementation over UDP: do nothing (streams are not available in UDP, but no guarantee is given that this transport feature has anyeffect).<vspace /> <vspace blankLines='1'/> </t>effect).</t> <t/> </li> <li> <t>Configure priority or weight for ascheduler<vspace />scheduler</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Optimizing because the priority or weight requires application-specific knowledge. However, if a transport system would not use this, or wrongly configure it on its own, this would only affect the performance of data transfers; the outcome would still be correct within the "best effort" servicemodel.<vspace />model.</t> <t> Implementation: usingCONFIGURE_STREAM_SCHEDULER.SCTP.<vspace />CONFIGURE_STREAM_SCHEDULER.SCTP.</t> <t> Implementation over TCP: do nothing (streams are not available in TCP, but no guarantee is given that this transport feature has anyeffect).<vspace />effect).</t> <t> Implementation over UDP: do nothing (streams are not available in UDP, but no guarantee is given that this transport feature has anyeffect).<vspace /> <vspace blankLines='1'/> </t>effect).</t> <t/> </li> <li> <t>Configure send buffersize<vspace />size</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because this decision relates to knowledge about the network and the Operating System, not the application (see also the discussion in <xreftarget="rundry"/>).<vspace /> <vspace blankLines='1'/> </t>target="rundry" format="default"/>).</t> <t/> </li> <li> <t>Configure receive buffer (and rwnd)size<vspace />size</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because this decision relates to knowledge about the network and the Operating System, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>Configure messagefragmentation<vspace />fragmentation</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because this relates to knowledge about the network and the Operating System, not the application. Note that this SCTP feature does not control IP-level fragmentation, but decides on fragmentation of messages by SCTP, in the endsystem.<vspace />system.</t> <t> Implementation: done by always enabling it with CONFIG_FRAGMENTATION.SCTP and auto-setting the fragmentation size based on network or Operating Systemconditions.<vspace /> <vspace blankLines='1'/> </t>conditions.</t> <t/> </li> <li> <t>ConfigurePMTUD<vspace />PMTUD</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because Path MTU Discovery relates to knowledge about the network, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>Configure delayed SACKtimer<vspace />timer</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because the receiver-side decision to delay sending SACKs relates to knowledge about the network, not the application (it can be relevant for a sending application to request not to delay the SACK of a message, but this is a different transportfeature).<vspace /> <vspace blankLines='1'/> </t>feature).</t> <t/> </li> <li> <t>Set Cookie lifevalue<vspace />value</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Functional because it relates to security (possibly weakened by keeping a cookie very long) versus the time between connection establishment attempts. Knowledge about both issues can beapplication-specific.<vspace />application specific.</t> <t> Implementation over TCP: the closest specified TCP functionality is the cookie in TCP Fast Open; for this, <xreftarget="RFC7413"/>target="RFC7413" format="default"/> states that the server "can expire the cookie at any time to enhancesecurity"security", andsection 4.1.2<xref target="RFC7413" sectionFormat="of" section="4.1.2"/> describes an example implementation where updating the key on the server side causes the cookie to expire. Alternatively, for implementations that do not support TCP Fast Open, this transport feature could also affect the validity of SYN cookies (seeSection 3.6 of<xreftarget="RFC4987"/>). <vspace />target="RFC4987" section="3.6" sectionFormat="of"/>). </t> <t> Implementation over UDP: notpossiblepossible. (UDP does not offer thisfunctionality).<vspace /> <vspace blankLines='1'/> </t>functionality.)</t> <t/> </li> <li> <t>Set maximumburst<vspace />burst</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because it relates to knowledge about the network, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>Configure size where messages are broken up for partialdelivery<vspace />delivery</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Functional because this is closely tied to properties of the data that an application sends or expects toreceive.<vspace />receive.</t> <t> Implementation over TCP: notpossiblepossible. (TCP does not offer identification of messageboundaries).<vspace />boundaries.)</t> <t> Implementation over UDP: notpossiblepossible. (UDP does not fragmentmessages).<vspace /> <vspace blankLines='1'/> </t>messages.)</t> <t/> </li> <li> <t>Disable checksum whensending<vspace />sending</t> <t> Protocols:UDP<vspace />UDP</t> <t> Functional because application-specific knowledge is necessary to decide whether it can be acceptable to lose data integrity with respect to randomcorruption.<vspace />corruption.</t> <t> Implementation: viaSET_CHECKSUM_ENABLED.UDP.<vspace />SET_CHECKSUM_ENABLED.UDP.</t> <t> Implementation over TCP: do nothing (TCP does not offer to disable the checksum, but transmitting data with an intact checksum will not yield a semantically wrong result).<vspace blankLines='1'/></t> <t/> </li> <li> <t>Disable checksum requirement whenreceiving<vspace />receiving</t> <t> Protocols:UDP<vspace />UDP</t> <t> Functional because application-specific knowledge is necessary to decide whether it can be acceptable to lose data integrity with respect to randomcorruption.<vspace />corruption.</t> <t> Implementation: viaSET_CHECKSUM_REQUIRED.UDP.<vspace />SET_CHECKSUM_REQUIRED.UDP.</t> <t> Implementation over TCP: do nothing (TCP does not offer to disable the checksum, but transmitting data with an intact checksum will not yield a semantically wrong result).<vspace blankLines='1'/></t> <t/> </li> <li> <t>Specify checksum coverage used by thesender<vspace />sender</t> <t> Protocols:UDP-Lite<vspace />UDP-Lite</t> <t> Functional because application-specific knowledge is necessary to decide for which parts of the data it can be acceptable to lose data integrity with respect to randomcorruption.<vspace />corruption.</t> <t> Implementation: viaSET_CHECKSUM_COVERAGE.UDP-Lite.<vspace />SET_CHECKSUM_COVERAGE.UDP-Lite.</t> <t> Implementation over TCP: do nothing (TCP does not offer to limit the checksum length, but transmitting data with an intact checksum will not yield a semantically wrongresult).<vspace />result).</t> <t> Implementation over UDP: if checksum coverage is set to cover payload data, do nothing. Else, either do nothing (transmitting data with an intact checksum will not yield a semantically wrong result), or use the transport feature "Disable checksum when sending".<vspace blankLines='1'/></t> <t/> </li> <li> <t>Specify minimum checksum coverage required byreceiver<vspace />receiver</t> <t> Protocols:UDP-Lite<vspace />UDP-Lite</t> <t> Functional because application-specific knowledge is necessary to decide for which parts of the data it can be acceptable to lose data integrity with respect to randomcorruption.<vspace />corruption.</t> <t> Implementation: viaSET_MIN_CHECKSUM_COVERAGE.UDP-Lite.<vspace />SET_MIN_CHECKSUM_COVERAGE.UDP-Lite.</t> <t> Implementation over TCP: do nothing (TCP does not offer to limit the checksum length, but transmitting data with an intact checksum will not yield a semantically wrongresult).<vspace />result).</t> <t> Implementation over UDP: if checksum coverage is set to cover payload data, do nothing. Else, either do nothing (transmitting data with an intact checksum will not yield a semantically wrong result), or use the transport feature "Disable checksum requirement when receiving".<vspace blankLines='1'/></t> <t/> </li> <li> <t>Specify DF field<vspace /></t> <t> Protocols:UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Optimizing because the DF field can be used to carry out Path MTU Discovery, which can lead an application to choose message sizes that can be transmitted moreefficiently.<vspace />efficiently.</t> <t> Implementation: via MAINTENANCE.SET_DF.UDP(-Lite) andSEND_FAILURE.UDP(-Lite).<vspace />SEND_FAILURE.UDP(-Lite).</t> <t> Implementation over TCP: do nothing (with TCP, the sending application is not in control of transport message sizes, making this functionality irrelevant).<vspace blankLines='1'/></t> <t/> </li> <li> <t>Get max. transport-message size that may be sent using a non-fragmented IP packet from the configuredinterface<vspace />interface</t> <t> Protocols:UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Optimizing because this can lead an application to choose message sizes that can be transmitted moreefficiently.<vspace />efficiently.</t> <t> Implementation over TCP: do nothing (this information is not available withTCP).<vspace /> <vspace blankLines='1'/> </t>TCP).</t> <t/> </li> <li> <t>Get max. transport-message size that may be received from the configuredinterface<vspace />interface</t> <t> Protocols:UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Optimizing because this can, for example, influence an application's memorymanagement.<vspace />management.</t> <t> Implementation over TCP: do nothing (this information is not available withTCP).<vspace /> <vspace blankLines='1'/> </t>TCP).</t> <t/> </li> <li> <t>Specify TTL/Hop countfield<vspace />field</t> <t> Protocols:UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Automatable because a transport system can use a large enough system default to avoid communication failures. Allowing an application to configure it differently can produce notifications of ICMP error message arrivals that yield informationwhichthat only relates to knowledge about the network, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>Obtain TTL/Hop countfield<vspace />field</t> <t> Protocols:UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Automatable because the TTL/Hop count field relates to knowledge about the network, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>Specify ECNfield<vspace />field</t> <t> Protocols:UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Automatable because the ECN field relates to knowledge about the network, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>Obtain ECNfield<vspace />field</t> <t> Protocols:UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Optimizing because this information can be used by an application to better carry out congestion control (this is relevant when choosing a data transmissiontransport serviceTransport Service that does not already do congestioncontrol).<vspace />control).</t> <t> Implementation over TCP: do nothing (this information is not available withTCP).<vspace /> <vspace blankLines='1'/> </t>TCP).</t> <t/> </li> <li> <t>Specify IPOptions<vspace />Options</t> <t> Protocols:UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Automatable because IP Options relate to knowledge about the network, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>Obtain IPOptions<vspace />Options</t> <t> Protocols:UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Automatable because IP Options relate to knowledge about the network, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>Enable and configure a "Low Extra Delay BackgroundTransfer"<vspace />Transfer"</t> <t> Protocols:Aa protocol implementing the LEDBAT congestion controlmechanism<vspace />mechanism</t> <t> Optimizing because whether this feature is appropriate or not depends on application-specific knowledge. However, wrongly using this will only affect the speed of data transfers (albeit including other transfers that may compete with the transport system's transfer in the network), so it is still correct within the "best effort" servicemodel.<vspace />model.</t> <t> Implementation: via CONFIGURE.LEDBAT and/or SET_DSCP.TCP / SET_DSCP.SCTP / SET_DSCP.UDP(-Lite) <xreftarget="LBE-draft"/>.<vspace />target="RFC8622" format="default"/>.</t> <t> Implementation over TCP: do nothing (TCP does not support LEDBAT congestion control, but not implementing this functionality will not yield a semantically wrongbehavior).<vspace />behavior).</t> <t> Implementation over UDP: do nothing (UDP does not offer congestioncontrol).<vspace /> <vspace blankLines='1'/>control).</t> <t/> </li> </ul> <t>TERMINATION: </t></list></t> <t>TERMINATION:<vspace /> <list style="symbols"><ul > <li> <t>Close after reliably delivering all remaining data, causing an event informing the application on the otherside<vspace />side</t> <t> Protocols: TCP,SCTP<vspace />SCTP</t> <t> Functional because the notion of a connection is often reflected in applications as an expectation to have all outstanding data delivered and no longer be able to communicate after a "Close" succeeded, with a communication sequence relating to this transport feature that is defined by the applicationprotocol.<vspace />protocol.</t> <t> Implementation: via CLOSE.TCP andCLOSE.SCTP.<vspace />CLOSE.SCTP.</t> <t> Implementation over UDP: notpossiblepossible. (UDP is unreliable and hence does not know when all remaining data is delivered; it does also not offer to cause an event related to closing at thepeer).<vspace /> <vspace blankLines='1'/> </t>peer.)</t> <t/> </li> <li> <t>Abort without delivering remaining data, causing an event informing the application on the otherside<vspace />side</t> <t> Protocols: TCP,SCTP<vspace />SCTP</t> <t> Functional because the notion of a connection is often reflected in applications as an expectation to potentially not have all outstanding data delivered and no longer be able to communicate after an "Abort" succeeded. On both sides of a connection, an application protocol may define a communication sequence relating to this transportfeature.<vspace />feature.</t> <t> Implementation: via ABORT.TCP andABORT.SCTP.<vspace />ABORT.SCTP.</t> <t> Implementation over UDP: notpossiblepossible. (UDP does not offer to cause an event related to aborting at thepeer).<vspace /> <vspace blankLines='1'/> </t>peer.)</t> <t/> </li> <li> <t>Abort without delivering remaining data, not causing an event informing the application on the otherside<vspace />side</t> <t> Protocols:UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Functional because the notion of a connection is often reflected in applications as an expectation to potentially not have all outstanding data delivered and no longer be able to communicate after an "Abort" succeeded. On both sides of a connection, an application protocol may define a communication sequence relating to this transportfeature.<vspace />feature.</t> <t> Implementation: viaABORT.UDP(-Lite).<vspace />ABORT.UDP(-Lite).</t> <t> Implementation over TCP: stop using the connection, wait for atimeout.<vspace /> <vspace blankLines='1'/> </t>timeout.</t> <t/> </li> <li> <t>Timeout event when data could not be delivered for toolong<vspace />long</t> <t> Protocols: TCP,SCTP<vspace />SCTP</t> <t> Functional because this notifies that potentially assumed reliable data delivery is no longerprovided.<vspace />provided.</t> <t> Implementation: via TIMEOUT.TCP andTIMEOUT.SCTP.<vspace />TIMEOUT.SCTP.</t> <t> Implementation over UDP: do nothing (this event will not occur withUDP).<vspace /> <vspace blankLines='1'/> </t> </list></t>UDP).</t> <t/> </li> </ul> </section> <section anchor="data-pass3"title="DATA Transfer Relatednumbered="true" toc="default"> <name>DATA-Transfer-Related TransportFeatures">Features</name> <section anchor="data-sending-pass3"title="Sending Data"> <t><list style="symbols">numbered="true" toc="default"> <name>Sending Data</name> <ul > <li> <t>Reliably transfer data, with congestioncontrol<vspace />control</t> <t> Protocols: TCP,SCTP<vspace />SCTP</t> <t> Functional because this is closely tied to properties of the data that an application sends or expects toreceive.<vspace />receive.</t> <t> Implementation: via SEND.TCP andSEND.SCTP.<vspace />SEND.SCTP.</t> <t> Implementation over UDP: notpossiblepossible. (UDP isunreliable).<vspace /> <vspace blankLines='1'/> </t>unreliable.)</t> <t/> </li> <li> <t>Reliably transfer a message, with congestioncontrol<vspace />control</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Functional because this is closely tied to properties of the data that an application sends or expects toreceive.<vspace />receive.</t> <t> Implementation: viaSEND.SCTP.<vspace />SEND.SCTP.</t> <t> Implementation over TCP: via SEND.TCP. With SEND.TCP, message boundaries will not be identifiable by the receiver, because TCP provides abyte stream service.<vspace />byte-stream service.</t> <t> Implementation over UDP: notpossiblepossible. (UDP isunreliable).<vspace /> <vspace blankLines='1'/> </t>unreliable.)</t> <t/> </li> <li> <t>Unreliably transfer amessage<vspace />message</t> <t> Protocols: SCTP,UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Optimizing because only applications know about the time criticality of their communication, and reliablytransferingtransferring a message is never incorrect for the receiver of a potentially unreliable data transfer, it is justslower.<vspace />slower.</t> <t> CHANGED FROMRFC8303.RFC 8303. This differs from the 2 automatable transport features below in that it leaves the choice of congestion controlopen.<vspace />open.</t> <t> Implementation: via SEND.SCTP orSEND.UDP(-Lite).<vspace />SEND.UDP(-Lite).</t> <t> Implementation over TCP: use SEND.TCP. With SEND.TCP, messages will be sent reliably, and message boundaries will not be identifiable by thereceiver.<vspace /> <vspace blankLines='1'/> </t>receiver.</t> <t/> </li> <li> <t>Unreliably transfer a message, with congestioncontrol<vspace />control</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because congestion control relates to knowledge about the network, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>Unreliably transfer a message, without congestioncontrol<vspace />control</t> <t> Protocols:UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Automatable because congestion control relates to knowledge about the network, not theapplication.<vspace /> <vspace blankLines='1'/> </t>application.</t> <t/> </li> <li> <t>Configurable MessageReliability<vspace />Reliability</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Optimizing because only applications know about the time criticality of their communication, and reliablytransferingtransferring a message is never incorrect for the receiver of a potentially unreliable data transfer, it is justslower.<vspace />slower.</t> <t> Implementation: viaSEND.SCTP.<vspace />SEND.SCTP.</t> <t> Implementation over TCP:Bydone by using SEND.TCP and ignoring thisconfiguration: basedconfiguration. Based on the assumption of the best-effort service model, unnecessarily delivering data does not violate application expectations. Moreover, it is not possible to associate the requested reliability to a "message" in TCPanyway.<vspace />anyway.</t> <t> Implementation over UDP: notpossiblepossible. (UDP isunreliable).<vspace /> <vspace blankLines='1'/> </t>unreliable.)</t> <t/> </li> <li> <t>Choice ofstream<vspace />stream</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because it requires using multiple streams, but requesting multiple streams in the CONNECTION.ESTABLISHMENT category is automatable. </t> <t> Implementation: see <xreftarget="nostream"/>. <vspace blankLines='1'/>target="nostream" format="default"/>. </t> <t/> </li> <li> <t>Choice of path (destinationaddress)<vspace />address)</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because it requires using multiple sockets, but obtaining multiple sockets in the CONNECTION.ESTABLISHMENT category isautomatable.<vspace /> <vspace blankLines='1'/> </t>automatable.</t> <t/> </li> <li> <t>Ordered message delivery (potentially slower thanunordered)<vspace />unordered)</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Functional because this is closely tied to properties of the data that an application sends or expects toreceive.<vspace />receive.</t> <t> Implementation: viaSEND.SCTP.<vspace />SEND.SCTP.</t> <t> Implementation over TCP:Bydone by using SEND.TCP. With SEND.TCP, messages will not be identifiable by thereceiver.<vspace />receiver.</t> <t> Implementation over UDP: notpossiblepossible. (UDP does not offer any guarantees regardingordering).<vspace /> <vspace blankLines='1'/> </t>ordering.)</t> <t/> </li> <li> <t>Unordered message delivery (potentially faster thanordered)<vspace />ordered)</t> <t> Protocols: SCTP,UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Functional because this is closely tied to properties of the data that an application sends or expects toreceive.<vspace />receive.</t> <t> Implementation: viaSEND.SCTP.<vspace />SEND.SCTP.</t> <t> Implementation over TCP:Bydone by using SEND.TCP and always sending dataordered: basedordered. Based on the assumption of the best-effort service model, ordered delivery may just be slower and does not violate application expectations. Moreover, it is not possible to associate the requested delivery order to a "message" in TCPanyway.<vspace /> <vspace blankLines='1'/> </t>anyway.</t> <t/> </li> <li> <t>Request not to bundlemessages<vspace />messages</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Optimizing because this decision depends on knowledge about the size of future data blocks and the delay betweenthem.<vspace />them.</t> <t> Implementation: viaSEND.SCTP.<vspace />SEND.SCTP.</t> <t> Implementation over TCP:Bydone by using SEND.TCP and DISABLE_NAGLE.TCP to disable the Nagle algorithm when the request is made and enable it again when the request is no longer made. Note that this is not fully equivalent because it relates to the time of issuing the request rather than a specificmessage.<vspace />message.</t> <t> Implementation over UDP: do nothing (UDP never bundlesmessages).<vspace /> <vspace blankLines='1'/> </t>messages).</t> <t/> </li> <li> <t>Specifying a "payload protocol-id" (handed over as such by thereceiver)<vspace />receiver)</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Functional because it allowsto sendsending extra application data with every message, for the sake of identification of data, which by itself isapplication-specific.<vspace />application specific.</t> <t> Implementation:SEND.SCTP.<vspace />SEND.SCTP.</t> <t> Implementation over TCP: notpossible (thispossible. (This functionality is not available inTCP).<vspace />TCP.)</t> <t> Implementation over UDP: notpossible (thispossible. (This functionality is not available inUDP).<vspace /> <vspace blankLines='1'/> </t>UDP.)</t> <t/> </li> <li> <t>Specifying a key id to be used to authenticate amessage<vspace />message</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Functional because this has a direct influence onsecurity.<vspace />security.</t> <t> Implementation: via a parameter inSEND.SCTP.<vspace />SEND.SCTP.</t> <t> Implementation over TCP:Thisthis could be emulated by using SET_AUTH.TCP before and after the message is sent. Note that this is not fully equivalent because it relates to the time of issuing the request rather than a specificmessage.<vspace />message.</t> <t> Implementation over UDP: notpossiblepossible. (UDP does not offerauthentication).<vspace /> <vspace blankLines='1'/> </t>authentication.)</t> <t/> </li> <li> <t>Request not to delay the acknowledgement (SACK) of amessage<vspace />message</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Optimizing because only an application knows for which message it wants to quickly be informed aboutsuccess / failuresuccess/failure of itsdelivery.<vspace />delivery.</t> <t> Implementation over TCP: do nothing (TCP does not offer this functionality, but ignoring this request from the application will not yield a semantically wrongbehavior).<vspace />behavior).</t> <t> Implementation over UDP: do nothing (UDP does not offer this functionality, but ignoring this request from the application will not yield a semantically wrongbehavior).<vspace /> <vspace blankLines='1'/> </t> </list></t>behavior).</t> <t/> </li> </ul> </section> <section anchor="data-receiving-pass3"title="Receiving Data"> <t> <list style="symbols">numbered="true" toc="default"> <name>Receiving Data</name> <ul > <li> <t>Receive data (with no messagedelimiting)<vspace />delimiting)</t> <t> Protocols:TCP<vspace />TCP</t> <t> Functional because a transport system must be able to send and receivedata.<vspace />data.</t> <t> Implementation: viaRECEIVE.TCP.<vspace />RECEIVE.TCP.</t> <t> Implementation over UDP: do nothing (UDP only works on messages; these can be handed over, the application can still ignore the messageboundaries).<vspace /> <vspace blankLines='1'/> </t>boundaries).</t> <t/> </li> <li> <t>Receive amessage<vspace />message</t> <t> Protocols: SCTP,UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Functional because this is closely tied to properties of the data that an application sends or expects toreceive.<vspace />receive.</t> <t> Implementation: via RECEIVE.SCTP andRECEIVE.UDP(-Lite).<vspace />RECEIVE.UDP(-Lite).</t> <t> Implementation over TCP: notpossiblepossible. (TCP does not support identification of messageboundaries).<vspace /> <vspace blankLines='1'/> </t>boundaries.)</t> <t/> </li> <li> <t>Choice of stream to receivefrom<vspace />from</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because it requires using multiple streams, but requesting multiple streams in the CONNECTION.ESTABLISHMENT category isautomatable.<vspace />automatable.</t> <t> Implementation: see <xreftarget="nostream"/>. <vspace blankLines='1'/>target="nostream" format="default"/>. </t> <t/> </li> <li> <t>Information about partial messagearrival<vspace />arrival</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Functional because this is closely tied to properties of the data that an application sends or expects toreceive.<vspace />receive.</t> <t> Implementation: viaRECEIVE.SCTP.<vspace />RECEIVE.SCTP.</t> <t> Implementation over TCP: do nothing (this information is not available withTCP).<vspace />TCP).</t> <t> Implementation over UDP: do nothing (this information is not available withUDP).<vspace /> <vspace blankLines='1'/> </t> </list> </t>UDP).</t> <t/> </li> </ul> </section> <section anchor="data-errors-pass3"title="Errors">numbered="true" toc="default"> <name>Errors</name> <t>This section describes sending failures that are associated with a specific call to in the "Sending Data" category (<xreftarget="data-sending-pass3"/>).</t> <t> <list style="symbols">target="data-sending-pass3" format="default"/>).</t> <ul > <li> <t>Notification of sendfailures<vspace />failures</t> <t> Protocols: SCTP,UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Functional because this notifies that potentially assumed reliable data delivery is no longerprovided.<vspace />provided.</t> <t> CHANGED FROMRFC8303.RFC 8303. This differs from the 2 automatable transport features below in that it does notdistinugishdistinguish between unsent and unacknowledgedmessages.<vspace />messages.</t> <t> Implementation: via SENDFAILURE-EVENT.SCTP andSEND_FAILURE.UDP(-Lite).<vspace />SEND_FAILURE.UDP(-Lite).</t> <t> Implementation over TCP: do nothing (this notification is not available and will therefore not occur withTCP).<vspace /> <vspace blankLines='1'/> </t>TCP).</t> <t/> </li> <li> <t>Notification of an unsent (part of a)message<vspace />message</t> <t> Protocols: SCTP,UDP(-Lite)<vspace />UDP(-Lite)</t> <t> Automatable because the distinction between unsent and unacknowledged does not relate to application-specific knowledge.<vspace /> <vspace blankLines='1'/></t> <t/> </li> <li> <t>Notification of an unacknowledged (part of a)message<vspace />message</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Automatable because the distinction between unsent and unacknowledged does not relate to application-specific knowledge.<vspace /> <vspace blankLines='1'/></t> <t/> </li> <li> <t>Notification that the stack has no more user data tosend<vspace />send</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Optimizing because reacting to this notification requires the application to be involved, and ensuring that the stack does not run dry of data (for too long) can improveperformance.<vspace />performance.</t> <t> Implementation over TCP: do nothing (see the discussion in <xreftarget="rundry"/>).<vspace />target="rundry" format="default"/>).</t> <t> Implementation over UDP: do nothing (this notification is not available and will therefore not occur withUDP).<vspace /> <vspace blankLines='1'/> </t>UDP).</t> <t/> </li> <li> <t>Notification to a receiver that a partial message delivery has beenaborted<vspace />aborted</t> <t> Protocols:SCTP<vspace />SCTP</t> <t> Functional because this is closely tied to properties of the data that an application sends or expects toreceive.<vspace />receive.</t> <t> Implementation over TCP: do nothing (this notification is not available and will therefore not occur withTCP).<vspace />TCP).</t> <t> Implementation over UDP: do nothing (this notification is not available and will therefore not occur withUDP).<vspace /> <vspace blankLines='1'/> </t> </list> </t>UDP).</t> <t/> </li> </ul> </section> </section> </section> <sectiontitle="Revision information"> <t> XXX RFC-Ed please remove this section prior to publication.</t> <t>-02: implementation suggestions added, discussion section added, terminology extended, DELETED category removed, various other fixes; list of Transport Features adjusted to -01 version of <xref target="RFC8303"/> except that MPTCP is not included.</t> <t>-03: updated to be consistent with -02 version of <xref target="RFC8303"/>.</t> <t>-04: updated to be consistent with -03 version of <xref target="RFC8303"/>. Reorganized document, rewrote intro and conclusion, and made a first stab at creating a real "minimal set".</t> <t>-05: updated to be consistent with -05 version of <xref target="RFC8303"/> (minor changes). Fixed a mistake regarding Cookie Life value. Exclusion of security related transport features (to be covered in a separate document). Reorganized the document (now begins with the minset, derivation is in the appendix). First stab at an abstract API for the minset.</t> <t>draft-ietf-taps-minset-00: updated to be consistent with -08 version of <xref target="RFC8303"/> ("obtain message delivery number" was removed, as this has also been removed in <xref target="RFC8303"/> because it was a mistake in RFC4960. This ledanchor="Acknowledgements" numbered="false" toc="default"> <name>Acknowledgements</name> <t>The authors would like to thank all theremovalparticipants oftwo more transport features that were only designated as functional because they affected "obtain message delivery number"). Fall-back to UDP incorporated (this was requested at IETF-99); this also affectedthetransport feature "Choice between unordered (potentially faster) or ordered delivery of messages" because this is a boolean which is always true for one fall-back protocol,TAPS Working Group andalways false fortheother one. This was therefore now divided into two features, one for ordered, one for unordered delivery. The word "reliably" was added to the transport features "Hand over a message to reliably transfer (possibly multiple times) before connection establishment"NEAT and"Hand over a message to reliably transfer during connection establishment"MAMI research projects for valuable input tomake it clearer whythisis not supported by UDP. Clarified that the "minset abstract interface" is not proposing a specific APIdocument. We especially thank <contact fullname="Michael Tüxen"/> forall TAPS systems to implement, but it is just a way to describe the minimum set. Author order changed. </t> <t>WG -01: "fall-back to" (TCP or UDP) replaced (mostly with "implementation over"). References to post-sockets removed (these were statments that assumed that post-sockets requires two-sided implementation). Replaced "flow" with "TAPS Connection" and "frame" with "message" to avoid introducing new terminology. Made sections 3 and 4 in linehelp withthe categorization that is already used in the appendix and <xref target="RFC8303"/>, and changed style of section 4 to be even shorter and less interface-like. Updated reference draft-ietf-tsvwg-sctp-ndata to RFC8260. </t> <t>WG -02: rephrased "the TAPS system"connection establishment/teardown, <contact fullname="Gorry Fairhurst"/> for his suggestions regarding fragmentation and"TAPS connection" etc. to more generally talk about transport after the intro (mostly replacing "TAPS system" with "transport system" and "TAPS connection" with "connection". Merged sections 3packet sizes, and4 to form a new section 3. </t> <t>WG -03: updated sentence referencing <xref target="I-D.ietf-taps-transport-security"/> to say that "the minimum security requirements<contact fullname="Spencer Dawkins"/> fora taps system are discussed in a separate security document", wrote "example" in the paragraph introducing the decision tree. Removed reference draft-grinnemo-taps-he-03 and the sentence that referred to it. </t> <t>WG -04: addressed comments from Theresa Enghardthis extremely detailed andTommy Pauly. As part of that, removed "TAPS" as a term everywhere (abstract, intro, ..). </t> <t>WG -05: addressed comments from Spencer Dawkins. </t> <t>WG -06: Fixed nits. </t> <t>WG -07: Addressed Genart comments from Robert Sparks. </t> <t>WG -08: Addressed one more Genart comment from Robert Sparks. </t> <t>WG -09: Addressed comments from Mirja Kuehlewind, Alvaro Retana, Ben Campbell, Benjamin Kaduk and Eric Rescorla. </t> <t>WG -10: Addressed commentsconstructive review. This work has received funding fromBenjamin Kadukthe European Union's Horizon 2020 research andEric Rescorla. </t> <t>WG -11: Addressed comments from Alissa Cooper.innovation program under grant agreement No. 644334 (NEAT). </t> </section> </back> </rfc>