rfc8895v2.txt		rfc8895.txt
	Internet Engineering Task Force (IETF) W. Roome		Internet Engineering Task Force (IETF) W. Roome
	Request for Comments: 8895 Nokia Bell Labs		Request for Comments: 8895 Nokia Bell Labs
	Category: Standards Track Y. Yang		Category: Standards Track Y. Yang
	ISSN: 2070-1721 Yale University		ISSN: 2070-1721 Yale University
	September 2020		October 2020
	Application-Layer Traffic Optimization (ALTO) Incremental Updates Using		Application-Layer Traffic Optimization (ALTO) Incremental Updates Using
	Server-Sent Events (SSE)		Server-Sent Events (SSE)
	Abstract		Abstract
	The Application-Layer Traffic Optimization (ALTO) (RFC 7285) protocol		The Application-Layer Traffic Optimization (ALTO) (RFC 7285) protocol
	provides network-related information, called network information		provides network-related information, called network information
	resources, to client applications so that clients can make informed		resources, to client applications so that clients can make informed
	decisions in utilizing network resources. This document presents a		decisions in utilizing network resources. This document presents a
	skipping to change at line 1404 ¶		skipping to change at line 1404 ¶
	stream server using its control update message(s), due to the modular		stream server using its control update message(s), due to the modular
	design.		design.
	8. Examples		8. Examples
	8.1. Example: IRD Announcing Update Stream Services		8.1. Example: IRD Announcing Update Stream Services
	Below is an example IRD announcing three update stream services. The		Below is an example IRD announcing three update stream services. The
	first, which is named "update-my-costs", provides updates for the		first, which is named "update-my-costs", provides updates for the
	network map, the "routingcost" and "hopcount" cost maps, and a		network map, the "routingcost" and "hopcount" cost maps, and a
	filtered cost map resource. The second, which is named "update-my-		Filtered Cost Map resource. The second, which is named "update-my-
	prop", provides updates to the endpoint properties service. The		prop", provides updates to the endpoint properties service. The
	third, which is named "update-my-pv", provides updates to a		third, which is named "update-my-pv", provides updates to a
	nonstandard ALTO service returning a multipart response.		nonstandard ALTO service returning a multipart response.
	Note that in the "update-my-costs" update stream shown in the example		Note that in the "update-my-costs" update stream shown in the example
	IRD, the update stream server uses JSON patch for network map, and it		IRD, the update stream server uses JSON patch for network map, and it
	uses JSON merge patch to update the other resources. Also, the		uses JSON merge patch to update the other resources. Also, the
	update stream will only provide full replacements for "my-simple-		update stream will only provide full replacements for "my-simple-
	filtered-cost-map".		filtered-cost-map".
	Also, note that this IRD defines two filtered cost map resources.		Also, note that this IRD defines two Filtered Cost Map resources.
	They use the same cost types, but "my-filtered-cost-map" accepts cost		They use the same cost types, but "my-filtered-cost-map" accepts cost
	constraint tests, while "my-simple-filtered-cost-map" does not. To		constraint tests, while "my-simple-filtered-cost-map" does not. To
	avoid the issues discussed in Section 9.3, the update stream provides		avoid the issues discussed in Section 9.3, the update stream provides
	updates for the second but not the first.		updates for the second but not the first.
	This IRD also announces a nonstandard ALTO service, which is named		This IRD also announces a nonstandard ALTO service, which is named
	"my-pv". This service accepts an extended endpoint cost request as		"my-pv". This service accepts an extended endpoint cost request as
	an input and returns a multipart response, including an endpoint cost		an input and returns a multipart response, including an endpoint cost
	resource and a property map resource. This document does not rely on		resource and a property map resource. This document does not rely on
	any other design details of this new service. In this document, the		any other design details of this new service. In this document, the
	skipping to change at line 2122 ¶		skipping to change at line 2122 ¶
	version tag of the last version of any tagged resources and give		version tag of the last version of any tagged resources and give
	those version tags when requesting the new update stream. In this		those version tags when requesting the new update stream. In this
	case, if a version is still current, the update stream server will		case, if a version is still current, the update stream server will
	not resend that resource.		not resend that resource.
	Although not as efficient as possible, this recovery method is simple		Although not as efficient as possible, this recovery method is simple
	and reliable.		and reliable.
	9.3. Considerations for Updates to Filtered Cost Maps		9.3. Considerations for Updates to Filtered Cost Maps
	If an update stream provides updates to a filtered cost map that		If an update stream provides updates to a Filtered Cost Map that
	allows constraint tests, then an ALTO client MAY request updates to a		allows constraint tests, then an ALTO client MAY request updates to a
	Filtered cost map request with a constraint test. In this case, when		Filtered Cost Map request with a constraint test. In this case, when
	a cost changes, the update stream server MUST send an update if the		a cost changes, the update stream server MUST send an update if the
	new value satisfies the test. If the new value does not, whether the		new value satisfies the test. If the new value does not, whether the
	update stream server sends an update depends on whether the previous		update stream server sends an update depends on whether the previous
	value satisfied the test. If it did not, the update stream server		value satisfied the test. If it did not, the update stream server
	SHOULD NOT send an update to the ALTO client. But if the previous		SHOULD NOT send an update to the ALTO client. But if the previous
	value did, then the update stream server MUST send an update with a		value did, then the update stream server MUST send an update with a
	"null" value to inform the ALTO client that this cost no longer		"null" value to inform the ALTO client that this cost no longer
	satisfies the criteria.		satisfies the criteria.
	An update stream server can avoid having to handle such a complicated		An update stream server can avoid having to handle such a complicated
	behavior by offering update streams only for filtered cost maps that		behavior by offering update streams only for Filtered Cost Maps that
	do not allow constraint tests.		do not allow constraint tests.
	9.4. Considerations for Updates to Ordinal Mode Costs		9.4. Considerations for Updates to Ordinal Mode Costs
	For an ordinal mode cost map, a change to a single cost point may		For an ordinal mode cost map, a change to a single cost point may
	require updating many other costs. As an extreme example, suppose		require updating many other costs. As an extreme example, suppose
	the lowest cost changes to the highest cost. For a numerical mode		the lowest cost changes to the highest cost. For a numerical mode
	cost map, only that one cost changes. But for an ordinal mode cost		cost map, only that one cost changes. But for an ordinal mode cost
	map, every cost might change. While this document allows an update		map, every cost might change. While this document allows an update
	stream server to offer incremental updates for ordinal mode cost		stream server to offer incremental updates for ordinal mode cost
	skipping to change at line 2289 ¶		skipping to change at line 2289 ¶
	future ALTO resource can contain multiple objects, then either each		future ALTO resource can contain multiple objects, then either each
	individual object also has a resource-id or an extension to this		individual object also has a resource-id or an extension to this
	design is made.		design is made.
	At the low-level encoding level, new line in SSE has its own		At the low-level encoding level, new line in SSE has its own
	semantics. Hence, this design requires that resource encoding does		semantics. Hence, this design requires that resource encoding does
	not include new lines that can be confused with SSE encoding. In		not include new lines that can be confused with SSE encoding. In
	particular, the data update message MUST NOT include "event: " or		particular, the data update message MUST NOT include "event: " or
	"data: " at a new line as part of data message.		"data: " at a new line as part of data message.
	If an update stream provides updates to a filtered cost map that		If an update stream provides updates to a Filtered Cost Map that
	allows constraint tests, the requirements for such services are		allows constraint tests, the requirements for such services are
	stated in Section 9.3.		stated in Section 9.3.
	12. IANA Considerations		12. IANA Considerations
	This document defines two new media types: "application/alto-		This document defines two new media types: "application/alto-
	updatestreamparams+json", as described in Section 6.5, and		updatestreamparams+json", as described in Section 6.5, and
	"application/alto-updatestreamcontrol+json", as described in		"application/alto-updatestreamcontrol+json", as described in
	Section 5.3. All other media types used in this document have		Section 5.3. All other media types used in this document have
	already been registered, either for ALTO, JSON merge patch, or JSON		already been registered, either for ALTO, JSON merge patch, or JSON
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