6lo Lijo
Internet Engineering Task Force (IETF) L. Thomas
Internet-Draft
Request for Comments: 9034 C-DAC
Intended status:
Category: Standards Track S. Anamalamudi
Expires: January 9, 2020
ISSN: 2070-1721 SRM University-AP
S.V.R.Anand
Malati
S.V.R. Anand
M. Hegde
Indian Institute of Science
C. Perkins
Futurewei
July 8, 2019
Lupin Lodge
June 2021
Packet Delivery Deadline time Time in 6LoWPAN the Routing Header
draft-ietf-6lo-deadline-time-05 for IPv6 over Low-
Power Wireless Personal Area Networks (6LoWPANs)
Abstract
This document specifies a new type for the 6LoWPAN routing header
containing the deadline time for data packets, designed for use over
constrained networks. The deadline time enables forwarding and
scheduling decisions for time critical IoT machine to machine time-critical machine-to-machine (M2M)
applications running on Internet-enabled devices that operate within
time-synchronized networks that
agree on the meaning of the time representations used networks. This document also specifies a
representation for the deadline time values. values in such networks.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of six months this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 9, 2020.
https://www.rfc-editor.org/info/rfc9034.
Copyright Notice
Copyright (c) 2019 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. 6LoRHE Generic Format . . . . . . . . . . . . . . . . . . . . 3
4. Deadline-6LoRHE . . . . . . . . . . . . . . . . . . . . . . . 4
5. Deadline-6LoRHE Format . . . . . . . . . . . . . . . . . . . 6
6. Deadline-6LoRHE in Three Network Scenarios . . . . . . . . . 8
6.1. Scenario 1: Endpoints in the same Same DODAG (N1) . . . . . . 9
6.2. Scenario 2: Endpoints in Networks with Dissimilar L2
Technologies. . . . . . . . . . . . . . . . . . . . . . . 10
Technologies
6.3. Scenario 3: Packet transmission Transmission across different Different DODAGs (N1
to N2). . . . . . . . . . . . . . . . . . . . . . . . 11 N2)
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8. Synchronization Aspects . . . . . . . . . . . . . . . . . . . 13
9. Security Considerations . . . . . . . . . . . . . . . . . . . 14
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
11.1.
10.1. Normative References . . . . . . . . . . . . . . . . . . 15
11.2.
10.2. Informative References . . . . . . . . . . . . . . . . . 17
Appendix A. Changes from revision 04 to revision 05 . . . . . . 18
Appendix B. Changes from revision 03 to revision 04 . . . . . . 18
Appendix C. Changes from revision 02 to revision 03 . . . . . . 19
Appendix D. Changes from revision 01 to revision 02 . . . . . . 19
Appendix E. Changes between earlier versions . . . . . . . . . . 20 Modular Arithmetic Considerations
Acknowledgments
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction
Low Power
Low-Power and Lossy Networks (LLNs) are likely to be deployed for
real time
real-time industrial applications requiring end-to-end delay
guarantees [I-D.ietf-detnet-use-cases]. [RFC8578]. A Deterministic Network
("detnet") ("DetNet") typically
requires some data packets to reach their receivers within strict
time bounds. Intermediate nodes use the deadline information to make
appropriate packet forwarding and scheduling decisions to meet the
time bounds.
This document specifies a new type for the Elective 6LoWPAN Routing
Header (6LoRHE), Deadline-6LoRHE, so that the deadline time (i.e.,
the time of latest acceptable delivery) of data packets can be
included within the
6LoWPAN routing header. 6LoRHE. [RFC8138] specifies the 6LoWPAN Routing
Header (6LoRH), compression schemes for RPL (Routing Protocol for
Low-Power and Lossy Networks) source routing (source routing)
operation [RFC6554], header
compression of RPL Packet Information packet information [RFC6553], and IP-in-IP
encapsulation. This document also specifies the handling of the
deadline time when packets traverse between time-
synchronized time-synchronized networks
operating in different timezones time zones or distinct reference clocks. Time synchronization
Time-synchronization techniques are outside the scope of this
document. There are a number of standards available for this
purpose, including IEEE 1588 [ieee-1588], [IEEE.1588.2008], IEEE 802.1AS
[dot1AS-2011],
[IEEE.802.1AS.2011], IEEE 802.15.4-2015 TSCH [dot15-tsch], Time-Slotted Channel Hopping
(TSCH) [IEEE.802.15.4], and more.
The Deadline-6LoRHE can be used in any time synchronized 6Lo time-synchronized 6LoWPAN
network. A 6TiSCH (IPv6 over the TSCH mode of IEEE 802.15.4) network
is used to describe the implementation of the Deadline-6LoRHE, but
this does not preclude its use in scenarios other than 6TiSCH. For
instance, there is a growing interest in using 6lo 6LoWPAN over a BLE
Bluetooth Low Energy (BLE) mesh network [I-D.ietf-6lo-blemesh] [6LO-BLEMESH] in industrial
IoT [dotBLEMesh]. (Internet of Things) [IEEE-BLE-MESH]. BLE mesh time
synchronization is being explored by the Bluetooth community. There
are also cases under consideration in Wi-SUN [Wi-SUN_PHY], [dotWi-SUN]. [PHY-SPEC] [Wi-SUN].
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174]. [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document uses the terminology defined in [RFC6550] and
[I-D.ietf-6tisch-terminology].
[RFC9030].
3. 6LoRHE Generic Format
Note: this section is not normative and is included for convenience.
The generic header format of the 6LoRHE is specified in
[I-D.ietf-roll-routing-dispatch]. [RFC8138].
Figure 1 illustrates the 6LoRHE generic format.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+
|1|0|1| Length | Type | Options |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+
<--- length --->
Figure 1: 6LoRHE format
o Format
Length: Length of the 6LoRHE expressed in bytes, excluding the first
2 bytes. This enables a node to skip a 6LoRHE if the Type is not recognized/supported.
o
recognized or supported.
Type (variable length): Type of the 6LoRHE (see Section 7) 7).
4. Deadline-6LoRHE
The Deadline-6LoRHE (see Figure 3) is an elective 6LoRH (i.e., a 6LoRHE [RFC8138]) [RFC8138] that
provides the Deadline Time (DT) for an IPv6 datagram in a compressed
form. Along with the deadline, DT, the header can include the packet Origination Time
Delta (OTD), (OTD) packet, which contains the time at
which when the packet is was
enqueued for transmission (expressed as a value to be subtracted from
DT); this enables a close estimate of the total delay incurred by a
packet. The OTD field is initialized by the sender based on the
current time at the outgoing network interface through which the
packet is forwarded. Since the OTD is a delta, the length of the OTD
field (i.e., OTL) will require fewer bits than the length of the DT
field (i.e., DTL).
The deadline DT field contains the value of the deadline time for the packet
-- in other words, the time by which the application expects the
packet to be delivered to the Receiver. receiver.
packet_deadline_time = packet_origination_time + max_delay
In order to support delay-sensitive delay-sensitive, deterministic applications, all
nodes within the network should process the Deadline-6LoRHE. The
packet deadline time (DT) DT
and origination time (OTD) OTD packets are represented in time units determined by a scaling
parameter in the routing
header. Routing Header. The Network ASN (Absolute Slot
Number) can be used as a time unit in a time slotted time-slotted synchronized
network (for instance instance, a 6TiSCH network, where global time is
maintained in the units of slot lengths of a certain resolution).
The delay experienced by packets in the network is a useful metric
for network diagnostics and performance monitoring. Whenever a
packet crosses into a network using a different reference clock, the
Destination Time
DT field is updated to represent the same Destination
Time, deadline time, but
expressed using the reference clock of the interface into the new
network. Then the origination time is the same as the current time
when the packet is transmitted into the new network, minus the delay
already experienced by the packet, say 'current_dly'. In this way,
within the newly entered network, the packet will appear to have
originated 'current_dly' time units earlier with respect to the
reference clock of the new network.
new_network_origin_time = time_now_in_new_network - current_dly
The following example illustrates these calculations when a packet
travels between three networks, each in a different time zone. zone (TZ).
'x' can be 1, 2 2, or 3. Suppose that the deadline time as measured in
timezone 1
TZ1 is 1050 1050, and the origination time is 50. Suppose that the
difference between TZ2 and TZ1 is 900, and the difference between TZ3 TZ2
and TZ3 is 3600. In the figure, OT is the origination time as
measured in the current timezone, time zone, and is equal to DT - OTD, that is,
DT - 1000. Figure 2 uses the following abbreviations:
TxA :
TxA: Time of arrival of packet in the network 'x'
TxD :
TxD: Departure time of packet from the network 'x'
dlyx :
dlyx: Delay experienced by the packet in the previous network(s)
TZx :
TZx: The time zone of network 'x'
TZ1 TZ2 TZ3
T1A=50| | |
|---- dly1=50 | |
| \ | |
| \ | |
| \ T1D=100 |T2A=1000 |
| -------->|----- dly2=450 |
| | \ |
| | \ |
| | \ T2D=1400 | T3A=5000
| | ------------------->|---------->
| | |
v v v
dly0 = 0 dly1 = T1D-OT1 dly2 = T2D-OT2
= 100-50 = 1400 - 950
= 50 = 450
OT1 = T1A-dly0 OT2 = T2A-dly1 OT3 = T3A-dly2
= 50 = 1000-50 = 5000 - 450
= 950 = 4550
Figure 2: Destination Deadline Time Update example Example
There are multiple ways that a packet can be delayed, including
queuing delay, MAC Media Access Control (MAC) layer contention delay,
serialization delay, and propagation delays. delay. Sometimes there are
processing delays as well. For the purpose of determining whether or
not the deadline has already passed, these various delays are not
distinguished.
5. Deadline-6LoRHE Format
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0|1| Length | 6LoRH Type |D| TU| DTL | OTL | BinaryPt |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DT (variable length) | OTD(variable length)(optional)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Deadline-6LoRHE format
o Format
Length (5 bits): Length represents the total length of the
Deadline-6LoRHE type Deadline-
6LoRHE Type measured in octets.
o
6LoRH Type: TBD (see 7 (See Section 7)
o 7.)
D flag (1 bit): The 'D' flag, set by the Sender, sender, qualifies the
action to be taken when a 6LR 6LoWPAN Router (6LR) detects that the
deadline time has elapsed.
If 'D' bit is 1, then the 6LR MUST drop the packet if the deadline
time is elapsed.
If 'D' bit is 0, the packet MAY be forwarded on an exception
basis, if the forwarding node is NOT in a situation of constrained
resource, and if there are reasons to suspect that downstream
nodes might find it useful (delay measurements, interpolations,
etc.).
o
TU (2 bits) : bits): Indicates the time units for DT and OTD fields. The
encodings for the DT and OTD fields use the same time units and
precision.
*
00 : Time represented in seconds and fractional seconds
*
01 : Reserved
*
10 : Network ASN
*
11 : Reserved
o
DTL (4 bits): Length of the DT field as an unsigned 4-bit integer,
encoding the length of the field in hex digits, minus one.
o
OTL (3 bits) : bits): Length of the OTD field as an unsigned 3-bit integer,
encoding the length of the field in hex digits. If OTL == 0, the
OTD field is not present. The value of OTL MUST NOT exceed the
value of DTL plus one.
*
For example, DTL = 0b0000 means the deadline time DT field in the 6LoRHE is 1
hex digit (4 bits) long. OTL = 0b111 means the
origination time OTD field is 7 hex
digits (28 bits) long.
o Binary Pt
BinaryPt (6 bits) : bits): If zero, the number of bits of the integer part
the DT is equal to the number of bits of the fractional part of
the DT. if If nonzero, the Binary Pt BinaryPt is a (2's complement) signed
integer determining the position of the binary point within the
value for the DT. This allows BinaryPt to be within the range
[-32,31].
* If BinaryPt value is positive, then the number of bits for the
integer part of the DT is increased by the value of BinaryPt,
and the number of bits for the fractional part of the DT is
correspondingly reduced. This increases the range of DT.
* If BinaryPt value is negative, then the number of bits for the
integer part of the DT is decreased by the value of BinaryPt,
and the number of bits for the fractional part of the DT is
correspondingly increased. This increases the precision of the
fractional seconds part of DT.
o
DT Value (8..64-bit) : (4..64 bits): An unsigned integer of DTL+1 hex digits
giving the Deadline Time value
o DT value.
OTD Value (8..64-bit) : An (4..28 bits): If present, an unsigned integer of OTL hex
digits giving the Origination Time origination time as a negative offset from the
DT value value.
Whenever a sender initiates the IP datagram, it includes the
Deadline-6LoRHE along with other 6LoRH information. For information
about the time synchronization time-synchronization requirements between sender and
receiver
receiver, see Section 8.
For the chosen time unit, a compressed time representation is
available as follows. First, the application on the originating node
has to determine
determines how many time bits are needed to represent the difference
between the time at which the packet is launched and the deadline
time, including the representation of fractional time units. That
number of bits (say, N_bits) determines DTL (the length of the
Deadline Time (DT)) as follows:
DTL = (N_bits mod ((N_bits - 1) / 4)
The number of bits determined by DTL allows the counting of any
number of fractional time units in the range of interest determined
by DT and the origination time OT. Denote this number of fractional time units to be
Epoch_Range(DTL) (i.e., Epoch_Range is a function of DTL). DTL):
Epoch_Range(DTL) = (2^(4*(DTL+1)) 2^(4*(DTL+1))
Each point of time between OT and DT is represented by a time unit
and a fractional time unit; in this section, this combined
representation is called a rational time unit (RTU). 1 RTU measures
the smallest fractional time that can be represented between two
points of time in the epoch (i.e., within the range of interest).
DT - OT cannot exceed 2^(4*(DTL+1)) == 16^(DTL+1). A low value of
DTL leads to a small Epoch_Range; if DTL = 0, there will only be 16
RTUs within the Epoch_Range (DTL) (i.e., Epoch_Range(DTL) = 16^1 (for 16^1) for any time unit TU).
TU. The values that can be represented in the current epoch are in
the range [0, (Epoch_Range(DTL) - 1)]. To minimize the required DTL,
wraparound is allowed but works naturally with the arithmetic modulo
Epoch_Range.
By default, DTL determines t_0 in the chosen RTUs as follows:
t_0 = [current_time - (current_time mod Epoch_Range (DTL))].
Naturally, t_0 occurs at time 0 (or time 0.0000...) in the current
epoch. The last possible origination time representable in the
current epoch (counted in RTUs) is t_last = (t0 + (2^(4*(DTL+1))-1)).
In the RTUs chosen, the current epoch resides at the underlying time
interval [t_0, t_last]. If DT - OT is greater than t_last - OT, then
Assuming wraparound within the Epoch_Range occurs naturally. In all cases, does not occur, OT is represented by the value
(OT mod Epoch_Range) Epoch_Range), and DT is represented by the value (DT mod
Epoch_Range). All arithmetic is to be performed modulo
(Epoch_Range(DTL)), yielding only positive values for DT - OT.
Example: Consider a 6TiSCH network with time-slot length
In order to allow fine-grained control over the setting of 10ms.
Let the time units be ASNs (TU == (binary)0b10). Let
deadline time, the current
ASN when fields for DT and OTD use fractional seconds.
This is done by specifying a binary point, which allocates some of
the bits for fractional times. Thus, all such fractions are
restricted to be negative powers of 2. Each point of time between OT
and DT is then represented by a time unit (either seconds or ASNs)
and a fractional time unit.
Let OT_abs, DT_abs, and CT_abs denote the true (absolute) values (on
the synchronized timelines) for OT, DT, and current time. Let N be
the number of bits to be used to represent the integer parts of
OT_abs, DT_abs, and CT_abs:
N = {4*(DTL+1)/2} + BinaryPt
The originating node has to pick a segment size (2^N) so that DT_abs
- OT_abs < 2^N, and so that intermediate network nodes can detect
whether or not CT_abs > DT_abs.
Given a value for N, the value for DT is represented in the deadline-
time format by DT = (DT_abs mod 2^N). DT is typically represented as
a positive value (even though negative modular values make sense).
Also, let OT = OT_abs mod 2^N and CT = CT_abs mod 2^N, where both OT
and CT are also considered as non-negative values.
When the packet is launched by the originating node, CT_abs == OT_abs
and CT == OT. Given a particular value for N, then in order for
downstream nodes to detect whether or not the deadline has expired
(i.e., whether DT_abs > CT_abs), the following is required:
Assumption 1: DT_abs - OT_abs < 2^N.
Otherwise the ambiguity inherent in the modulus arithmetic yielding
OT and DT will cause failure: one cannot measure time differences
greater than 2^N using numbers in a time segment of length less than
2^N.
Under Assumption 1, downstream nodes must effectively check whether
or not their current time is later than the DT -- but the value of
the DT has to be inferred from the value of DT in the 6LoRHE, which
is a number less than 2^N. This inference cannot be expected to
reliably succeed unless Assumption 1 is valid, which means that the
originating node has to be careful to pick proper values for DTL and
for BinaryPt.
Since OT is not necessarily provided in the 6loRHE, there may be a
danger of ambiguity. Surely, when DT = CT, the deadline time is
expiring and the packet should be dropped. However, what if an
intermediate node measures that CT = DT+1? Was the packet launched a
short time before arrival at the intermediate node, or has the
current time wrapped around so that CT_abs - OT_abs > 2^N?
In order to solve this problem, a safety margin has to be provided,
in addition to requiring that DT_abs - OT_abs < 2^N. The value of
this safety margin is proportional to 2^N and is determined by a new
parameter, called the "SAFETY_FACTOR". Then, for safety the
originating node MUST further ensure that (DT_abs - OT_abs) <
2^N*(1-SAFETY_FACTOR).
Each intermediate node that receives the packet with the Deadline-
6LoRHE must determine whether ((CT - DT) mod 2^N) >
SAFETY_FACTOR*2^N. If this test condition is not satisfied, the
deadline time has expired. See Appendix A for more explanation about
the test condition. All nodes that receive a packet with a Deadline-
6LoRHE included MUST use the same value for the SAFETY_FACTOR. The
SAFETY_FACTOR is to be chosen so that a packet with the Deadline-
6LoRHE included will be tested against the current time at least once
during every subinterval of length SAFETY_FACTOR*2^N. In this way,
it can be guaranteed that the packet will be tested often enough to
make sure it can be dropped whenever CT_abs > DT_abs. The value of
SAFETY_FACTOR is specified in this document to be 20%.
Example: Consider a 6TiSCH network with time-slot length of 10 ms.
Let the time units be ASNs (TU == (binary)0b10). Let the current
ASN when the packet is originated be 54400, and the maximum
allowable delay (max_delay) for the packet delivery be 1 second
from the packet origination, then:
deadline_time = packet_origination_time + max_delay
= 0xD480 + 0x64 (Network ASNs)
= 0xD4E4 (Network ASNs)
Then, the Deadline-6LoRHE encoding with nonzero OTL is:
DTL = 3, OTL = 2, TU = 0b10, BinaryPt = 8, DT = 0xD4E4,
OTD = 0x64
6. Deadline-6LoRHE in Three Network Scenarios
In this section, the Deadline-6LoRHE operation is described for 3 three
network scenarios. Figure 4 depicts a constrained time-synchronized
LLN that has two subnets subnets, N1 and N2, connected through LBRs
[I-D.ietf-6lo-backbone-router] 6LoWPAN Border
Routers (6LBRs) [RFC8929] with different reference clock times times, T1
and T2.
+-------------------+
| Time Synchronized Time-Synchronized |
| Network |
+---------+---------+
|
|
|
+--------------+--------------+
| |
+-----+ +-----+
| | Backbone | | Backbone
o | | router | | router
+-----+ +-----+
o o o
o o o o o o o o o
o LLN o o LLN o o
o o o o o o o o o
6LoWPAN Network (subnet N1) 6LoWPAN Network (subnet N2)
Figure 4: Intra-network Timezone Intra-Network Time Zone Scenario
6.1. Scenario 1: Endpoints in the same Same DODAG (N1)
In scenario Scenario 1, shown in Figure 5, the Sender 'S' has an IP datagram
to be routed to a Receiver 'R' within the same DODAG. Destination-Oriented
Directed Acyclic Graph (DODAG). For the route segment from Sender the
sender to the 6LBR, the Sender sender includes a Deadline-6LoRHE by encoding
the deadline time contained in the packet. Subsequently, each 6LR
will perform hop-by-hop routing to forward the packet towards the
6LBR. Once the 6LBR receives the IP datagram, it sends the packet
downstream towards 'R'.
In the case of a network running in RPL non-storing mode, the 6LBR
generates
a an IPv6-in-IPv6 encapsulated packet when sending the packet
downwards to the Receiver [I-D.ietf-roll-useofrplinfo]. receiver [RFC9008]. The 6LBR copies the
Deadline-6LoRHE Deadline-
6LoRHE from the Sender originated sender-originated IP header to the outer IP header.
The Deadline-6LoRHE contained in the inner IP header is removed.
+-------+
^ | 6LBR | |
| | | |
| +-------+ |
Upward | / /| \ | Downward
routing | (F) / | \ | routing
| / \ (C) | (D) |
| / \ | | / |\ |
| (A) (B) : (E) : R |
| /|\ | \ / \ |
| S : : : : : : v
Figure 5: End points Endpoints within same the Same DODAG (subnet (Subnet N1)
At the tunnel endpoint of the encapsulation, the Deadline-6LoRHE is
copied back from the outer header to inner header, and the inner IP
packet is delivered to 'R'.
6.2. Scenario 2: Endpoints in Networks with Dissimilar L2 Technologies. Technologies
In scenario Scenario 2, shown in Figure 6, the Sender 'S' (belonging to DODAG
1) has an IP datagram to be routed to a Receiver 'R' over a time-
synchronized IPv6 network. For the route segment from 'S' to 6LBR,
'S' includes a Deadline-6LoRHE. Subsequently, each 6LR will perform
hop-by-hop routing to forward the packet towards the 6LBR. Once the
Deadline Time
deadline time information reaches the border router, 6LBR, the packet will be
encoded according to the mechanism prescribed in the other time-
synchronized network depicted as "Time Synchronized "Time-Synchronized Network" in the
figure
Figure 6. The specific data encapsulation mechanisms followed in the
new network are beyond the scope of this document.
+----------------+
| Time Time- |
| Synchronized |------R
| Network |
+----------------+
|
|
----------+-----------
^ |
| +---+---+
| | 6LBR |
Upward | | |
routing | +------++
| (F)/ /| \
| / \ / | \
| / \ (C) | (D)
| (A) (B) | | / |\
| /|\ |\ : (E) : :
| S : : : : / \
: :
Figure 6: Packet transmission Transmission in Dissimilar L2 Technologies or
Internet
For instance, the IP datagram could be routed to another time
synchronized time-
synchronized, deterministic network using the mechanism specified in
the In-band OAM [I-D.ietf-ippm-ioam-data],
In-situ Operations, Administration, and Maintenance (IOAM)
[IOAM-DATA], and then the deadline time would be updated according to
the measurement of the current time in the new network.
6.3. Scenario 3: Packet transmission Transmission across different Different DODAGs (N1 to
N2). N2)
Consider the scenario depicted in Figure 7, in which the Sender 'S'
(belonging to DODAG 1) has an IP datagram to be sent to Receiver 'R'
belonging to another DODAG (DODAG 2). The operation of this scenario
can be decomposed into a combination of case Scenarios 1 and case 2 scenarios. 2. For the
route segment from 'S' to 6LBR1, 'S' includes the Deadline-
6LoRHE. Deadline-6LoRHE.
Subsequently, each 6LR will perform hop-by-hop operation operations to forward
the packet towards the 6LBR1. Once the IP datagram reaches 6LBR1 of
DODAG1, it 6LBR1 applies the same rule as described in Case Scenario 2 while
routing the packet to 6LBR2 over a (likely) time synchronized time-synchronized wired
backhaul. The wired side of 6LBR2 can be mapped to the receiver of
Case
Scenario 2. Once the packet reaches 6LBR2, it updates the Deadline-
6LoRHE by adding or subtracting the difference of time of DODAG2 and
sends the packet downstream towards 'R'.
Time Synchronized
Time-Synchronized Network
-+---------------------------+-
| |
DODAG1 +---+---+ +---+---+ DODAG2
| 6LBR1 | | 6LBR2 |
| | | |
+-------+ +-------+
(F)/ /| \ (F)/ /| \
/ \ / | \ / \ / | \
/ \ (C) | (D) / \ (C) | (D)
(A) (B) | | / |\ (A) (B) | | |\
/|\ |\ : (E) : : /|\ |\ : (E) : :
S : : : : / \ : : : : : / \
: : : R
Network N1, time zone T1 Network N2, time zone T2
Figure 7: Packet transmission Transmission in different DODAGs(N1 Different DODAGs (N1 to N2)
Consider an example of a 6TiSCH network in which S in DODAG1
generates the packet at ASN 20000 to R in DODAG2. Let the maximum
allowable delay be 1 second. The time-slot length in DODAG1 and
DODAG2 is assumed to be 10ms. 10 ms. Once the deadline time is encoded in
Deadline-6LoRHE, the packet is forwarded to 6LBR 6LBR1 of DODAG1. Suppose
the packet reaches 6LBR 6LBR1 of DODAG1 at ASN 20030.
current_time = ASN at LBR 6LBR * slot_length_value
remaining_time = deadline_time - current_time
= ((packet_origination_time + max_delay) - current time)
= (20000 + 100) - 20030
= 30 (in Network ASNs)
= 30 * 10^3 milliseconds. milliseconds
Once the Deadline Time deadline time information reaches the border router, 6LBR2, the packet will be
encoded according to the mechanism prescribed in the other time-synchronized time-
synchronized network.
7. IANA Considerations
This document defines a new Elective 6LoWPAN Routing Header Type, and
IANA is requested to assign a has assigned the value (TBD) 7 from the 6LoWPAN Dispatch
Page1 Page 1 number
space for this purpose.
Elective 6LoRH Type
+=======+=================+===========+
| Value
+----------------------+--------+ | Deadline-6LoRHE Description | TBD Reference |
+=======+=================+===========+
| 7 |
+----------------------+--------+
Figure 8: Deadline-6LoRHE type | RFC 9034 |
+-------+-----------------+-----------+
Table 1: Entry in the "Elective
6LoWPAN Routing Header Type"
Registry
8. Synchronization Aspects
The document supports time representation of the deadline and
origination times carried in the packets traversing through networks of
different time zones having different time synchronization time-synchronization
mechanisms. For instance, in a 6TiSCH network where the time is
maintained as ASN time slots, the time synchronization is achieved
through beaconing among the nodes as described in [RFC7554]. There
could be 6lo networks that employ NTP where the nodes are
synchronized with an external reference clock from an NTP server.
The specification of the time synchronization time-synchronization method that need needs to be
followed by a network is beyond the scope of the document.
The number of hex digits chosen to represent DT, and the portion of
that field allocated to represent the integer number of seconds,
determines the meaning of t_0, i.e., the meaning of DT == 0 in the
chosen representation. If DTL == 0, then there are only 4 bits that
can be used to count the time units, so that DT == 0 can never be
more than 16 time units (or fractional time units) in the past. This
then requires that the time synchronization between sender and
receiver has to be tighter than 16 units. If the binary point were
moved so that all the bits were used for fractional time units (e.g.,
fractional seconds or fractional ASNs), the time synchronization time-synchronization
requirement would be correspondingly tighter.
A 4-bit field for DT allows up to 16 hex digits, which is 64 bits.
That is enough to represent the NTP [RFC5905] 64-bit timestamp
format, format
[RFC5905], which is more than enough for the purposes of establishing
deadline times. Unless the binary point is moved, this is enough to
represent time since year 1900.
For example, suppose that DTL = 0b0000 and the DT bits are split
evenly; then we can count up to 3.75 seconds by quarter-seconds.
If DTL = 3 and the DT bits are again split evenly, then we can count
up to 256 seconds (in steps of 1/256 of a second).
In all cases, t_0 is defined as specified in Section 5 5.
t_0 = [current_time - (current_time mod (2^(4*(DTL+1))))]
regardless of the choice of TU.
For TU = 0b00, the time units are seconds. With DTL == 15, and
Binary Pt
BinaryPt == 0, the epoch is (by default) January 1, 1900 1900, at 00:00
UTC. The resolution is then (2 ^ (- 32)) 2^-32 seconds, which is the maximum
possible. This time format wraps around every 2^32 seconds, which is
roughly 136 years.
For TU = 0b10, the time units are ASNs. The start time is relative,
and updated by a mechanism that is out of scope for this document.
With 10 ms slots, DTL = 15, and Binary Pt BinaryPt == 0, it would take over a
year for the ASN to wrap around. Typically, the number of hex digits
allocated for TU = 0b10 would be less than 15.
9. Security Considerations
The security considerations of [RFC4944], [RFC4944] (Section 13), [RFC6282]
(Section 6), and [RFC6553] (Section 5) apply. Using a compressed
format as opposed to the full in-line inline format is logically equivalent
and does not create an opening for a new threat when compared to
[RFC6550], [RFC6553] [RFC6553], and [RFC6554].
The protocol elements specified in this document are designed to work
in controlled operational environments (e.g., industrial process
control and automation). In order to avoid misuse of the deadline
information that could potentially result in a Denial of Service
(DoS) attack, proper functioning of this deadline time mechanism
requires the provisioning and management of network resources for
supporting traffic flows with deadlines, performance monitoring, and
admission control policy enforcement. The network provisioning can
be done either centrally or in a distributed fashion. For example,
tracks in a 6tisch 6TiSCH network could be established by a centralized PCE, Path
Computation Element (PCE), as described in the 6tisch 6TiSCH architecture
[I-D.ietf-6tisch-architecture].
[RFC9030].
The Security Considerations security considerations of Detnet DetNet architecture
[I-D.ietf-detnet-architecture] [RFC8655]
(Section 5) mostly apply to this document as well, as follows. To
secure the request and control of resources allocated for tracks,
authentication and authorization can be used for each
device, device and
network controller devices. In the case of distributed control
protocols, security is expected to be provided by the
security properties of the protocols in use.
When deadline bearing flows are identified on a per-flow basis, which
may provide attackers with additional information about the data
flows, when compared to networks that do not include per-flow
identification. The security implications of disclosing that
additional information deserve consideration when implementing this
deadline specification.
Because of the requirement of precise time synchronization, the
accuracy, availability, and integrity of time synchronization is of
critical importance. Extensive discussion of this topic can be found
in [RFC7384].
10. Acknowledgements
The authors thank Pascal Thubert for suggesting the idea and
encouraging the work. Thanks to Shwetha Bhandari's suggestions which
were instrumental in extending the timing information to
heterogeneous networks. The authors acknowledge the 6TiSCH WG
members for their inputs on the mailing list. Special thanks to
Jerry Daniel, Dan Frost (Routing Directorate) Charlie Kaufman
(Security Directorate) Seema Kumar, Tal Mizrahi Avinash Mohan, Shalu
Rajendran, Anita Varghese, and Dale Worley (Gen-ART review) for their
support and valuable feedback.
11. References
11.1. Normative References
[I-D.ietf-6tisch-terminology]
Palattella, M., Thubert, P., Watteyne, T., and Q. Wang,
"Terms Used in IPv6 over by the TSCH mode security
properties of IEEE 802.15.4e",
draft-ietf-6tisch-terminology-10 (work in progress), March
2018.
[I-D.ietf-detnet-architecture]
Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", draft-ietf-
detnet-architecture-13 (work the protocols in progress), May 2019.
[I-D.ietf-roll-routing-dispatch]
Thubert, P., Bormann, C., Toutain, L., use.
The identification of deadline-bearing flows on a per-flow basis may
provide attackers with additional information about the data flows
compared to networks that do not include per-flow identification.
The security implications of disclosing that additional information
deserve consideration when implementing this deadline specification.
Because of the requirement of precise time synchronization, the
accuracy, availability, and R. Cragie,
"6LoWPAN Routing Header", draft-ietf-roll-routing-
dispatch-05 (work integrity of time synchronization is of
critical importance. Extensive discussion of this topic can be found
in progress), October 2016. [RFC7384].
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
<https://www.rfc-editor.org/info/rfc4944>.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<https://www.rfc-editor.org/info/rfc5905>.
[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<https://www.rfc-editor.org/info/rfc6282>.
[RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks", RFC 6550,
DOI 10.17487/RFC6550, March 2012,
<https://www.rfc-editor.org/info/rfc6550>.
[RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low-
Power and Lossy Networks (RPL) Option for Carrying RPL
Information in Data-Plane Datagrams", RFC 6553,
DOI 10.17487/RFC6553, March 2012,
<https://www.rfc-editor.org/info/rfc6553>.
[RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6
Routing Header for Source Routes with the Routing Protocol
for Low-Power and Lossy Networks (RPL)", RFC 6554,
DOI 10.17487/RFC6554, March 2012,
<https://www.rfc-editor.org/info/rfc6554>.
[RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in
Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384,
October 2014, <https://www.rfc-editor.org/info/rfc7384>.
[RFC7554] Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using
IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the
Internet of Things (IoT): Problem Statement", RFC 7554,
DOI 10.17487/RFC7554, May 2015,
<https://www.rfc-editor.org/info/rfc7554>.
[RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie,
"IPv6 over Low-Power Wireless Personal Area Network
(6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138,
April 2017, <https://www.rfc-editor.org/info/rfc8138>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
11.2. Informative References
[dot15-tsch]
"IEEE 802 Wireless", "IEEE Standard
[RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", RFC 8655,
DOI 10.17487/RFC8655, October 2019,
<https://www.rfc-editor.org/info/rfc8655>.
[RFC9030] Thubert, P., Ed., "An Architecture for Low-Rate Wireless
Networks, Part 15.4, IPv6 over the Time-
Slotted Channel Hopping Mode of IEEE Std 802.15.4-2015", April 2016.
[dot1AS-2011]
"IEEE Standards", "IEEE Standard for Local and
Metropolitan Area Networks - Timing 802.15.4 (6TiSCH)",
RFC 9030, DOI 10.17487/RFC9030, May 2021,
<https://www.rfc-editor.org/info/rfc9030>.
10.2. Informative References
[6LO-BLEMESH]
Gomez, C., Darroudi, S. M., Savolainen, T., and Synchronization
for Time-Sensitive Applications M. Spoerk,
"IPv6 Mesh over BLUETOOTH(R) Low Energy using IPSP", Work
in Bridged Local Area
Networks", March 2011.
[dotBLEMesh] Progress, Internet-Draft, draft-ietf-6lo-blemesh-10, 22
April 2021,
<https://tools.ietf.org/html/draft-ietf-6lo-blemesh-10>.
[IEEE-BLE-MESH]
Leonardi, L., Pattim, Patti, G., and L. Lo Bello, "Multi-Hop
Real-Time Real-
Time Communications Over Bluetooth Low Energy Industrial
Wireless Mesh Networks", IEEE Access Access, Vol 6, pp.
26505-26519, DOI 10.1109/ACCESS.2018.2834479, May 2018.
[dotWi-SUN]
Harada, H., Mizutani, K., Fujiwara, J., Mochizuki, K.,
Obata, K., and R. Okumura, 2018,
<https://doi.org/10.1109/ACCESS.2018.2834479>.
[IEEE.1588.2008]
IEEE, "IEEE 802.15.4g Based Wi-SUN
Communication Systems", IEICE Transactions on
Communications volume E100.B, Jan 2017.
[I-D.ietf-6lo-backbone-router]
Thubert, P., Perkins, C., and E. Levy-Abegnoli, "IPv6
Backbone Router", draft-ietf-6lo-backbone-router-11 (work
in progress), February 2019.
[I-D.ietf-6lo-blemesh]
Gomez, C., Darroudi, S., Savolainen, T., Standard for a Precision Clock Synchronization
Protocol for Networked Measurement and M. Spoerk,
"IPv6 Mesh over BLUETOOTH(R) Low Energy using IPSP",
draft-ietf-6lo-blemesh-05 (work in progress), March 2019.
[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture Control Systems",
DOI 10.1109/IEEESTD.2008.4579760, July 2008,
<https://doi.org/10.1109/IEEESTD.2008.4579760>.
[IEEE.802.15.4]
IEEE, "IEEE Standard for IPv6 over the TSCH mode
of Low-Rate Wireless Networks", IEEE 802.15.4", draft-ietf-6tisch-architecture-24 (work
Standard 802.15.4-2015, DOI 10.1109/IEEESTD.2016.7460875,
April 2016,
<https://ieeexplore.ieee.org/document/7460875>.
[IEEE.802.1AS.2011]
IEEE, "IEEE Standard for Local and Metropolitan Area
Networks - Timing and Synchronization for Time-Sensitive
Applications in progress), July 2019.
[I-D.ietf-detnet-use-cases]
Grossman, E., "Deterministic Networking Use Cases", draft-
ietf-detnet-use-cases-20 (work in progress), December
2018.
[I-D.ietf-ippm-ioam-data] Bridged Local Area Networks", IEEE Std
802.1AS-2011, DOI 10.1109/IEEESTD.2011.5741898, March
2011, <https://doi.org/10.1109/IEEESTD.2011.5741898>.
[IOAM-DATA]
Brockners, F., Ed., Bhandari, S., Pignataro, C., Gredler, H.,
Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov,
P., Chang, R., daniel.bernier@bell.ca, d., Ed., and J. Lemon, T. Mizrahi,
Ed., "Data Fields for In-situ OAM", draft-ietf-ippm-ioam-
data-06 (work Work in progress), July 2019.
[I-D.ietf-roll-useofrplinfo] Progress,
Internet-Draft, draft-ietf-ippm-ioam-data-12, 21 February
2021, <https://tools.ietf.org/html/draft-ietf-ippm-ioam-
data-12>.
[PHY-SPEC] Wi-SUN Alliance, "Wi-SUN PHY Specification V1.0", March
2016, <http://wi-sun.org>.
[RFC8578] Grossman, E., Ed., "Deterministic Networking Use Cases",
RFC 8578, DOI 10.17487/RFC8578, May 2019,
<https://www.rfc-editor.org/info/rfc8578>.
[RFC8929] Thubert, P., Ed., Perkins, C.E., and E. Levy-Abegnoli,
"IPv6 Backbone Router", RFC 8929, DOI 10.17487/RFC8929,
November 2020, <https://www.rfc-editor.org/info/rfc8929>.
[RFC9008] Robles, I., M.I., Richardson, M., and P. Thubert, "Using RPL RPI
Option Type, Routing Header for Source Routes Routes, and IPv6-in-
IPv6 encapsulation IPv6-
in-IPv6 Encapsulation in the RPL Data Plane", draft-ietf-
roll-useofrplinfo-31 (work in progress), July 2019.
[ieee-1588]
"IEEE Standards", "IEEE Std 1588-2008 Standard for a
Precision Clock Synchronization Protocol for Networked
Measurement RFC 9008,
DOI 10.17487/RFC9008, April 2021,
<https://www.rfc-editor.org/info/rfc9008>.
[Wi-SUN] Harada, H., Mizutani, K., Fujiwara, J., Mochizuki, K.,
Obata, K., and Control Systems", July 2008.
[Wi-SUN_PHY] R. Okumura, "IEEE 802.15.4g Based Wi-SUN Alliance, "Wi-SUN PHY Specification V1.0", March
2016.
Communication Systems", IEICE Transactions on
Communications, Volume E100.B, Issue 7, pp. 1032-1043,
DOI 10.1587/transcom.2016SCI0002, January 2017,
<https://doi.org/10.1587/transcom.2016SCI0002>.
Appendix A. Changes Modular Arithmetic Considerations
Graphically, one might visualize the timeline as follows:
OT_abs CT_abs DT_abs
-------|-------------|-------------|------------------>
Figure 8: Absolute Timeline Representation
In Figure 8, the value of CT_abs is envisioned as traveling to the
right as time progresses, getting farther away from revision 04 OT_abs and
getting closer to revision 05
This section lists DT_abs. The timeline is considered to be
subdivided into time subintervals [i,j] starting and ending at
absolute times equal to k*(2^N), for integer values of k. Let I_k =
k*(2^N) and I_(k+1) = (k+1)*2^N. Intervals starting at I_k and
I_(k+1) may occur at various placements in the above timeline. Even
though OT_abs is _always_ less than DT_abs, it could be that DT < OT
because of the way that DT and OT are represented within the range
[0, 2^N) and similarly for CT_abs and CT compared to OT and DT.
Representing the above situation in time segments of length 2^N (and
values OT, CT, DT) results in several cases where the deadline time
has not elapsed:
1) OT < CT < DT (e.g., I_k < OT_abs < CT_abs < DT_abs < I_(k+1) )
2) DT < OT < CT (e.g., I_k < OT_abs < CT_abs < I_(k+1) < DT_abs )
3) CT < DT < OT (e.g., I_k < OT_abs < I_(k+1) < CT_abs < DT_abs )
In the following cases, the changes between draft-ietf-6lo-deadline-time
revisions ...-04.txt deadline time has elapsed and ...-05.txt.
o Included additional relevant material the packet
should be dropped.
4) DT < CT < OT
5) OT < DT < CT
6) CT < OT < DT
Again in Security Considerations
regarding expected deployment scenarios Figure 8, consider CT_abs as time moving away from OT_abs
and towards DT_abs. For times CT_abs before the effect of
disclosing additional information during the travel expiration of a packet.
o Reworked the specification
deadline time, we also have CT_abs - OT_abs == CT - OT mod 2^N and
similarly for using DT_abs - CT_abs.
As time ranges shorter than the
maximum allowed by proceeds, DT_abs - CT_abs gets smaller. When the choice of TU, so that fewer bits are needed deadline
time expires, DT_abs - CT_abs begins to represent DT grow negative. A proper
selection for SAFETY_FACTOR allows it to go _slightly negative_ but
for an intermediate point to _detect_ that it has gone negative.
Note that in modular arithmetic, "slightly negative" means _exactly_
the same as "almost as large as the modulus (i.e., 2^N)". Now
consider the test condition ((CT - DT) mod 2^N) > SAFETY_FACTOR*2^N.
(DT_abs - OT_abs) < 2^N*(1-SAFETY_FACTOR) satisfies the test
condition when CT_abs == OT_abs (i.e., when the packet is launched).
In modular arithmetic, 2^N*(1-SAFETY_FACTOR) == 2^N -
2^N*SAFETY_FACTOR == -2^N*(SAFETY_FACTOR). Then DT_abs - OT_abs <
-2^N*(1-SAFETY_FACTOR). Inverting the inequality, OT_abs - DT_abs >
2^N*(1-SAFETY_FACTOR), and OT.
o Revised thus at launch CT_abs - DT_abs >
2^N*(1-SAFETY_FACTOR).
As CT_abs grows larger, CT_abs - DT_abs gets LARGER in (non-negative)
modular arithmetic until the figures time at which CT_ABS == DT_ABS, and
suddenly CT_ABS - DT_abs becomes zero. Also suddenly, the test
condition is no longer fulfilled.
As CT_abs grows still larger, CT_abs > DT_abs, and examples we need to use new parameters
o Reordered detect
this condition as soon as possible. Requiring the field definitions SAFETY_FACTOR
enables this detection until CT_abs exceeds DT_abs by an amount equal
to SAFETY_FACTOR*2^N.
A note about "inverting the inequality". Observe that a < b implies
that -a > -b on the real number line. Also, (a - b) == -(b - a).
These facts hold also for modular arithmetic.
During the Deadline-6LoRHE.
o Responded times prior to numerous reviewer comments the expiration of the deadline, for Safe =
2^N*SAFETY_FACTOR we have:
(DT_abs - 2^N) < OT_abs < CT_abs < DT_abs < DT_abs+Safe
Naturally, DT_abs - 2^N == DT_abs mod 2^N == DT.
Again considering Figure 8, it is easy to improve terminology see that {CT_abs - (DT_abs
- 2^N)} gets larger and
editorial consistency.
Appendix B. Changes from revision 03 to revision 04
This section lists larger until the changes between draft-ietf-6lo-deadline-time
revisions ...-03.txt and ...-04.txt.
o Replaced OT (Origination Time) field by OTD (Origination Time
Delta), allowing a more compressed representation time at which CT_abs =
DT_abs, which is the first time at which CT - DT == 0 mod 2^N. As
CT_abs increases past the deadline time, 0 < CT_abs - DT_abs < Safe.
In this range, any intermediate node can detect that needs less
processing during transitions between networks.
o Changed representation the deadline has
expired. As CT_abs increases past DT_abs+Safe, it is no longer
possible for DTL, OTL, DT, OTD. Eliminated EXP an intermediate node to determine with certainty whether
or not the deadline time has expired. These statements also apply
when reduced to modular arithmetic in
favor the modulus 2^N.
In particular, the test condition no longer allows detection of BinaryPt.
o Revised
deadline expiration when the figures and examples to use new parameters
o Added new section on Synchronization Aspects current time becomes later than
(DT_abs+Safe). In order to supply pertinent
information about how nodes agree on maintain correctness even for packets
that are forwarded after expiration (i.e., the meaning of t=0.
o Responded 'D' flag), N has to numerous reviewer comments to improve editorial
consistency and improve terminology.
Appendix C. Changes from revision 02 be
chosen to revision 03
This section lists the changes between draft-ietf-6lo-deadline-time
revisions ...-02.txt and ...-03.txt.
o Added non-normative 6LoRHE description, citing RFC 8138.
o Specified be so large that the Origination Time (OT) is the time test condition will not fail -- i.e.,
that packet
is enqueued for transmission.
o Mentioned more sources in all scenarios of interest, the packet delay.
o Clarified reasons that packet MAY will be forwarded if 'D' bit is 0.
o Clarified that DT, OT, DTL and OTL are unsigned integers.
o Updated bibliographic citations, including BLEmesh and Wi-SUN.
Appendix D. Changes from revision 01 dropped before
the current time becomes equal to revision 02
This section lists DT_abs+2^N*SAFETY_FACTOR.
Acknowledgments
The authors thank Pascal Thubert for suggesting the changes between draft-ietf-6lo-deadline-time
revisions ...-01.txt idea and ...-02.txt.
o Replaced 6LoRHE description by reference
encouraging the work. Thanks to RFC 8138.
o Added figure Shwetha Bhandari's suggestions,
which were instrumental in extending the timing information to illustrate change
heterogeneous networks. The authors acknowledge the 6TiSCH WG
members for their inputs on the mailing list. Special thanks to Origination Time when a
packet crosses timezone boundaries.
o Clarified that use of 6tisch networks is descriptive, not
normative.
o Clarified that In-Band OAM is used as an example
Jerry Daniel, Dan Frost (Routing Directorate), Charlie Kaufman
(Security Directorate), Seema Kumar, Tal Mizrahi, Avinash Mohan,
Shalu Rajendran, Anita Varghese, and is not
normative.
o Updated bibliographic citations.
o Alphabetized contributor names.
Appendix E. Changes between earlier versions
This section lists the changes between draft-ietf-6lo-deadline-time
revisions ...-00.txt Dale Worley (General Area Review
Team (Gen-ART) review) for their support and ...-01.txt.
o Changed "SHOULD drop" to "MUST drop" a packet if the deadline is
passed (see Section 5).
o Added explanatory text about how packet delays might arise. (see
Section 4).
o Mentioned availability of time-synchronization protocols (see
Section 1).
o Updated bibliographic citations.
o Alphabetized contributor names.
o Added this section. valuable feedback.
Authors' Addresses
Lijo Thomas
C-DAC
Centre for Development of Advanced Computing (C-DAC),
Vellayambalam
Trivandrum 695033
India
Email: lijo@cdac.in
Satish Anamalamudi
SRM University-AP
Amaravati Campus
Amaravati, Andhra Pradesh 522 502
India
Email: satishnaidu80@gmail.com
S.V.R
S.V.R. Anand
Indian Institute of Science
Bangalore 560012
India
Email: anand@ece.iisc.ernet.in anandsvr@iisc.ac.in
Malati Hegde
Indian Institute of Science
Bangalore 560012
India
Email: malati@ece.iisc.ernet.in malati@iisc.ac.in
Charles E. Perkins
Futurewei
2330 Central Expressway
Santa Clara 95050
Unites
Lupin Lodge
20600 Aldercroft Heights Rd.
Los Gatos, CA 95033
United States of America
Email: charliep@computer.org