< draft-ietf-alto-reqs-05.txt		draft-ietf-alto-reqs-06.txt >
	Network Working Group S. Kiesel, Ed.		Network Working Group S. Kiesel, Ed.
	Internet-Draft University of Stuttgart		Internet-Draft University of Stuttgart
	Intended status: Informational S. Previdi		Intended status: Informational S. Previdi
	Expires: December 16, 2010 Cisco Systems, Inc.		Expires: April 28, 2011 Cisco Systems, Inc.
	M. Stiemerling		M. Stiemerling
	NEC Europe Ltd.		NEC Europe Ltd.
	R. Woundy		R. Woundy
	Comcast Corporation		Comcast Corporation
	Y R. Yang		Y R. Yang
	Yale University		Yale University
	June 14, 2010		October 25, 2010
	Application-Layer Traffic Optimization (ALTO) Requirements		Application-Layer Traffic Optimization (ALTO) Requirements
	draft-ietf-alto-reqs-05.txt		draft-ietf-alto-reqs-06.txt
	Abstract		Abstract
	Many Internet applications are used to access resources, such as		Many Internet applications are used to access resources, such as
	pieces of information or server processes, which are available in		pieces of information or server processes, which are available in
	several equivalent replicas on different hosts. This includes, but		several equivalent replicas on different hosts. This includes, but
	is not limited to, peer-to-peer file sharing applications. The goal		is not limited to, peer-to-peer file sharing applications. The goal
	of Application-Layer Traffic Optimization (ALTO) is to provide		of Application-Layer Traffic Optimization (ALTO) is to provide
	guidance to applications, which have to select one or several hosts		guidance to applications, which have to select one or several hosts
	from a set of candidates, that are able to provide a desired		from a set of candidates, that are able to provide a desired
	skipping to change at page 2, line 13 ¶		skipping to change at page 2, line 13 ¶
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	The list of current Internet-Drafts can be accessed at		The list of current Internet-Drafts can be accessed at
	http://www.ietf.org/ietf/1id-abstracts.txt.		http://www.ietf.org/ietf/1id-abstracts.txt.
	The list of Internet-Draft Shadow Directories can be accessed at		The list of Internet-Draft Shadow Directories can be accessed at
	http://www.ietf.org/shadow.html.		http://www.ietf.org/shadow.html.
	This Internet-Draft will expire on December 16, 2010.		This Internet-Draft will expire on April 28, 2011.
	Copyright Notice		Copyright Notice
	Copyright (c) 2010 IETF Trust and the persons identified as the		Copyright (c) 2010 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 3, line 21 ¶		skipping to change at page 3, line 21 ¶
	2.3. Architectural Framework for ALTO . . . . . . . . . . . . . 6		2.3. Architectural Framework for ALTO . . . . . . . . . . . . . 6
	2.4. Sample Use Cases . . . . . . . . . . . . . . . . . . . . . 6		2.4. Sample Use Cases . . . . . . . . . . . . . . . . . . . . . 6
	3. ALTO Requirements . . . . . . . . . . . . . . . . . . . . . . 9		3. ALTO Requirements . . . . . . . . . . . . . . . . . . . . . . 9
	3.1. ALTO Client Protocol . . . . . . . . . . . . . . . . . . . 9		3.1. ALTO Client Protocol . . . . . . . . . . . . . . . . . . . 9
	3.1.1. General Requirements . . . . . . . . . . . . . . . . . 9		3.1.1. General Requirements . . . . . . . . . . . . . . . . . 9
	3.1.2. Host Group Descriptor Support . . . . . . . . . . . . 9		3.1.2. Host Group Descriptor Support . . . . . . . . . . . . 9
	3.1.3. Rating Criteria Support . . . . . . . . . . . . . . . 10		3.1.3. Rating Criteria Support . . . . . . . . . . . . . . . 10
	3.1.4. Placement of Entities and Timing of Transactions . . . 11		3.1.4. Placement of Entities and Timing of Transactions . . . 11
	3.1.5. Protocol Extensibility . . . . . . . . . . . . . . . . 13		3.1.5. Protocol Extensibility . . . . . . . . . . . . . . . . 13
	3.1.6. Error Handling and Overload Protection . . . . . . . . 13		3.1.6. Error Handling and Overload Protection . . . . . . . . 13
	3.2. ALTO Server Discovery . . . . . . . . . . . . . . . . . . 13		3.2. ALTO Server Discovery . . . . . . . . . . . . . . . . . . 14
	3.3. Security and Privacy . . . . . . . . . . . . . . . . . . . 15		3.3. Security and Privacy . . . . . . . . . . . . . . . . . . . 15
	4. Host Group Descriptors . . . . . . . . . . . . . . . . . . . . 16		4. Host Group Descriptors . . . . . . . . . . . . . . . . . . . . 16
	5. Rating Criteria . . . . . . . . . . . . . . . . . . . . . . . 17		5. Rating Criteria . . . . . . . . . . . . . . . . . . . . . . . 17
	5.1. Distance-related Rating Criteria . . . . . . . . . . . . . 17		5.1. Distance-related Rating Criteria . . . . . . . . . . . . . 17
	5.2. Charging-related Rating Criteria . . . . . . . . . . . . . 17		5.2. Charging-related Rating Criteria . . . . . . . . . . . . . 17
	5.3. Performance-related Rating Criteria . . . . . . . . . . . 18		5.3. Performance-related Rating Criteria . . . . . . . . . . . 18
	5.4. Inappropriate Rating Criteria . . . . . . . . . . . . . . 19		5.4. Inappropriate Rating Criteria . . . . . . . . . . . . . . 19
	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 21		7. Security Considerations . . . . . . . . . . . . . . . . . . . 21
	7.1. High-level security considerations . . . . . . . . . . . . 21		7.1. High-level security considerations . . . . . . . . . . . . 21
	skipping to change at page 9, line 11 ¶		skipping to change at page 9, line 11 ¶
	Figure 2: Overview of protocol interaction between ALTO elements,		Figure 2: Overview of protocol interaction between ALTO elements,
	scenario with resource directory		scenario with resource directory
	3. ALTO Requirements		3. ALTO Requirements
	3.1. ALTO Client Protocol		3.1. ALTO Client Protocol
	3.1.1. General Requirements		3.1.1. General Requirements
	REQ. ARv05-1: The ALTO service is provided by one or more ALTO		REQ. ARv06-1: The ALTO service is provided by one or more ALTO
	servers. ALTO servers MUST implement the ALTO client protocol, for		servers. ALTO servers MUST implement the ALTO client protocol, for
	receiving ALTO queries from ALTO clients and for sending the		receiving ALTO queries from ALTO clients and for sending the
	corresponding ALTO replies.		corresponding ALTO replies.
	REQ. ARv05-2: ALTO clients MUST implement the ALTO client protocol,		REQ. ARv06-2: ALTO clients MUST implement the ALTO client protocol,
	for sending ALTO queries to ALTO servers and for receiving the		for sending ALTO queries to ALTO servers and for receiving the
	corresponding ALTO replies.		corresponding ALTO replies.
	REQ. ARv05-3: The format of the ALTO query message MUST allow the		REQ. ARv06-3: The format of the ALTO query message MUST allow the
	ALTO client to solicit guidance for selecting appropriate resource		ALTO client to solicit guidance for selecting appropriate resource
	providers.		providers.
	REQ. ARv05-4: The format of the ALTO reply message MUST allow the		REQ. ARv06-4: The format of the ALTO reply message MUST allow the
	ALTO server to express its guidance for selecting appropriate		ALTO server to express its guidance for selecting appropriate
	resource providers.		resource providers.
	REQ. ARv05-5: The detailed specification of a protocol is out of the		REQ. ARv06-5: The detailed specification of a protocol is out of the
	scope of this document. However, any protocol specification that		scope of this document. However, any protocol specification that
	claims to implement the ALTO client protocol MUST be compliant to the		claims to implement the ALTO client protocol MUST be compliant to the
	requirements itemized in this document.		requirements itemized in this document.
	3.1.2. Host Group Descriptor Support		3.1.2. Host Group Descriptor Support
	The ALTO guidance is based on the evaluation of several resource		The ALTO guidance is based on the evaluation of several resource
	providers or groups of resource providers, which are characterized by		providers or groups of resource providers, which are characterized by
	means of host group descriptors, considering one or several rating		means of host group descriptors, considering one or several rating
	criteria.		criteria.
	REQ. ARv05-6: The ALTO client protocol MUST support the usage of		REQ. ARv06-6: The ALTO client protocol MUST support the usage of
	several different host group descriptor types.		several different host group descriptor types.
	REQ. ARv05-7: The ALTO client protocol specification MUST define a		REQ. ARv06-7: The ALTO client protocol specification MUST define a
	basic set of host group descriptor types, which MUST be supported by		basic set of host group descriptor types, which MUST be supported by
	all implementations of the ALTO client protocol.		all implementations of the ALTO client protocol.
	REQ. ARv05-8: The ALTO client protocol MUST support the host group		REQ. ARv06-8: The ALTO client protocol MUST support the host group
	descriptor types "IPv4 address prefix" and "IPv6 address prefix."		descriptor types "IPv4 address prefix" and "IPv6 address prefix."
	They can be used to specify the IP address of one host, or an IP		They can be used to specify the IP address of one host, or an IP
	address range (in CIDR notation), which contains all hosts in		address range (in CIDR notation), which contains all hosts in
	question. It is also possible to specify a broader address range		question. It is also possible to specify a broader address range
	(i.e., a shorter prefix length) than the intended group of hosts		(i.e., a shorter prefix length) than the intended group of hosts
	actually uses, in order to conceal their exact identity.		actually uses, in order to conceal their exact identity.
	REQ. ARv05-9: The ALTO client protocol specification MUST define an		REQ. ARv06-9: The ALTO client protocol specification MUST define an
	appropriate procedure for adding new host group descriptor types,		appropriate procedure for adding new host group descriptor types,
	e.g., by establishing an IANA registry.		e.g., by establishing an IANA registry.
	See Section 4 for a discussion of possible other host group		See Section 4 for a discussion of possible other host group
	descriptor types.		descriptor types.
	REQ. ARv05-10: ALTO clients and ALTO servers MUST clearly identify		REQ. ARv06-10: ALTO clients and ALTO servers MUST clearly identify
	the type of each host group descriptor sent in ALTO queries or		the type of each host group descriptor sent in ALTO queries or
	replies.		replies.
	REQ. ARv05-11: For host group descriptor types other than "IPv4		REQ. ARv06-11: For host group descriptor types other than "IPv4
	address prefix" and "IPv6 address prefix", the host group descriptor		address prefix" and "IPv6 address prefix", the host group descriptor
	type identification MUST be supplemented by a reference to a		type identification MUST be supplemented by a reference to a
	facility, which can be used to translate host group descriptors of		facility, which can be used to translate host group descriptors of
	that type to IPv4/IPv6 address prefixes, e.g., by means of a mapping		that type to IPv4/IPv6 address prefixes, e.g., by means of a mapping
	table or an algorithm.		table or an algorithm.
	REQ. ARv05-12: Protocol functions for mapping other host group		REQ. ARv06-12: Protocol functions for mapping other host group
	descriptor types to IPv4/IPv6 address prefixes SHOULD be designed and		descriptor types to IPv4/IPv6 address prefixes SHOULD be designed and
	specified as part of the ALTO client protocol, and the corresponding		specified as part of the ALTO client protocol, and the corresponding
	address mapping information SHOULD be made available by the same		address mapping information SHOULD be made available by the same
	entity that wants to use these host group descriptors within the ALTO		entity that wants to use these host group descriptors within the ALTO
	client protocol. However, an ALTO server or an ALTO client MAY also		client protocol. However, an ALTO server or an ALTO client MAY also
	send a reference to an external mapping facility, e.g., a translation		send a reference to an external mapping facility, e.g., a translation
	table to be downloaded as file via HTTP.		table to be downloaded as file via HTTP.
	REQ. ARv05-13: The ALTO client protocol specification MUST define		REQ. ARv06-13: The ALTO client protocol specification MUST define
	mechanisms, which can be used by the ALTO client and the ALTO server		mechanisms, which can be used by the ALTO client and the ALTO server
	to indicate that a host group descriptor used by the other party is		to indicate that a host group descriptor used by the other party is
	of an unsupported type, or that the indicated mapping mechanism could		of an unsupported type, or that the indicated mapping mechanism could
	not be used.		not be used.
	3.1.3. Rating Criteria Support		3.1.3. Rating Criteria Support
	REQ. ARv05-14: The ALTO client protocol MUST support the usage of		REQ. ARv06-14: The ALTO client protocol MUST support the usage of
	several different rating criteria types.		several different rating criteria types.
	REQ. ARv05-15: The ALTO client protocol specification MUST define a		REQ. ARv06-15: The ALTO client protocol specification MUST define a
	basic set of rating criteria types, which MUST be supported by all		basic set of rating criteria types, which MUST be supported by all
	implementations of the ALTO client protocol.		implementations of the ALTO client protocol.
	REQ. ARv05-16: The ALTO client protocol specification MUST support		REQ. ARv06-16: The ALTO client protocol specification MUST support
	the rating criteria type "relative operator's preference." This is a		the rating criteria type "relative operator's preference." This is a
	relative measure, i.e., it is not associated with any unit of		relative measure, i.e., it is not associated with any unit of
	measurement. A higher rating according to this criterion indicates		measurement. A higher rating according to this criterion indicates
	that the application should prefer the respective candidate resource		that the application should prefer the respective candidate resource
	provider over others with lower ratings (if no other reasons speak		provider over others with lower ratings (if no other reasons speak
	against it, such as transmission attempts suggesting that the path is		against it, such as transmission attempts suggesting that the path is
	currently congested). The operator of the ALTO server does not have		currently congested). The operator of the ALTO server does not have
	to disclose how and based on which data the ratings are actually		to disclose how and based on which data the ratings are actually
	computed. Examples could be: cost for peering or transit traffic,		computed. Examples could be: cost for peering or transit traffic,
	traffic engineering inside the network, and other policies.		traffic engineering inside the network, and other policies.
	REQ. ARv05-17: The ALTO client protocol specification MUST define an		REQ. ARv06-17: The ALTO client protocol specification MUST define an
	appropriate procedure for adding new rating criteria types, e.g., by		appropriate procedure for adding new rating criteria types, e.g., by
	establishing an IANA registry.		establishing an IANA registry.
	See Section 5 for a discussion of possible other rating criteria.		See Section 5 for a discussion of possible other rating criteria.
	REQ. ARv05-18:The ALTO query message SHOULD allow the ALTO client to		REQ. ARv06-18:The ALTO query message SHOULD allow the ALTO client to
	express which rating criteria should be considered, as well as their		express which rating criteria should be considered, as well as their
	relative relevance for the specific application that will eventually		relative relevance for the specific application that will eventually
	make use of the guidance.		make use of the guidance.
	REQ. ARv05-19:The ALTO reply message SHOULD allow the ALTO server to		REQ. ARv06-19:The ALTO reply message SHOULD allow the ALTO server to
	express which rating criteria have been considered when generating		express which rating criteria have been considered when generating
	the reply.		the reply.
	REQ. ARv05-20: The ALTO client protocol specification MUST define		REQ. ARv06-20: The ALTO client protocol specification MUST define
	mechanisms, which can be used by the ALTO client and the ALTO server		mechanisms, which can be used by the ALTO client and the ALTO server
	to indicate that a rating criteria used by the other party is of an		to indicate that a rating criteria used by the other party is of an
	unsupported type.		unsupported type.
	3.1.4. Placement of Entities and Timing of Transactions		3.1.4. Placement of Entities and Timing of Transactions
	With respect to the placement of ALTO clients, several modes of		With respect to the placement of ALTO clients, several modes of
	operation exist:		operation exist:
	o One mode of ALTO operation is that ALTO clients may be embedded		o One mode of ALTO operation is that ALTO clients may be embedded
	directly in the resource consumer (e.g., peer of a DHT-based P2P		directly in the resource consumer (e.g., peer of a DHT-based P2P
	application), which wants to access a resource.		application), which wants to access a resource.
	o Another mode of operation is to perform ALTO queries indirectly,		o Another mode of operation is to perform ALTO queries indirectly,
	via resource directories (e.g., tracker of a P2P application),		via resource directories (e.g., tracker of a P2P application),
	which may issue ALTO queries to solicit preference on potential		which may issue ALTO queries to solicit preference on potential
	resource providers, considering the respective resource consumer.		resource providers, considering the respective resource consumer.
	REQ. ARv05-21: The ALTO client protocol MUST support the mode of		REQ. ARv06-21: The ALTO client protocol MUST support the mode of
	operation, in which the ALTO client is directly embedded in the		operation, in which the ALTO client is directly embedded in the
	resource consumer.		resource consumer.
	REQ. ARv05-22: The ALTO client protocol MUST support the mode of		REQ. ARv06-22: The ALTO client protocol MUST support the mode of
	operation, in which the ALTO client is embedded in the resource		operation, in which the ALTO client is embedded in the resource
	directory.		directory.
	REQ. ARv05-23: The ALTO client protocol MUST be designed in a way		REQ. ARv06-23: The ALTO client protocol MUST be designed in a way
	that the ALTO service can be provided by an entity which is not the		that the ALTO service can be provided by an entity which is not the
	operator of the IP access network.		operator of the IP access network.
	REQ. ARv05-24: The ALTO client protocol MUST be designed in a way		REQ. ARv06-24: The ALTO client protocol MUST be designed in a way
	that different instances of the ALTO service operated by different		that different instances of the ALTO service operated by different
	providers can coexist.		providers can coexist.
	With respect to the timing of ALTO queries, several modes of		With respect to the timing of ALTO queries, several modes of
	operation exist:		operation exist:
	o In target-aware query mode, an ALTO client performs the ALTO query		o In target-aware query mode, an ALTO client performs the ALTO query
	when the desired resource and a set of candidate resource		when the desired resource and a set of candidate resource
	providers are already known, i. e., after DHT lookups, queries to		providers are already known, i. e., after DHT lookups, queries to
	the resource directory, etc.		the resource directory, etc.
	o In target-independent query mode, ALTO queries are performed in		o In target-independent query mode, ALTO queries are performed in
	advance or periodically, in order to receive comprehensive,		advance or periodically, in order to receive comprehensive,
	"target-independent" guidance, which will be cached locally and		"target-independent" guidance, which will be cached locally and
	evaluated later, when a resource is to be accessed.		evaluated later, when a resource is to be accessed.
	REQ. ARv05-25: The ALTO client protocol MUST support at least one of		REQ. ARv06-25: The ALTO client protocol MUST support at least one of
	these two modes, either the target-aware or the target-independent		these two modes, either the target-aware or the target-independent
	query mode.		query mode.
	REQ. ARv05-26: The ALTO client protocol SHOULD support both the		REQ. ARv06-26: The ALTO client protocol SHOULD support both the
	target-aware and the target-independent query mode.		target-aware and the target-independent query mode.
	REQ. ARv05-27: The ALTO client protocol SHOULD support lifetime		REQ. ARv06-27: The ALTO client protocol SHOULD support lifetime
	attributes, to enable caching of recommendations at ALTO clients.		attributes, to enable caching of recommendations at ALTO clients.
	REQ. ARv05-28: The ALTO client protocol SHOULD specify an aging		REQ. ARv06-28: The ALTO client protocol SHOULD specify an aging
	mechanism, which allows to give newer recommendations precedence over		mechanism, which allows to give newer recommendations precedence over
	older ones.		older ones.
	REQ. ARv05-29: The ALTO client protocol SHOULD allow the ALTO server		REQ. ARv06-30: The ALTO client protocol SHOULD allow the ALTO server
	to specify a "target audience" in an ALTO reply. This is a set of		to add information about appropriate modes of re-use to its ALTO
	resource consumers (expressed, e.g., as a list of host group		replies. Re-use may include redistributing an ALTO reply to other
	descriptors). The guidance provided in the respective ALTO reply can		parties, as well as using the same ALTO information in a resource
	be used and possibly re-used during the specified lifetime by or for		directory to improve the replies to different resource consumers,
	the resource consumers in the "target audience". Re-using may		within the specified lifetime of the ALTO reply. The ALTO server
	include redistributing the ALTO reply to other parties in the		SHOULD be able to express that
	specified set, as well as using the same ALTO information in a
	resource directory to improve the replies to different resource
	consumers.
	REQ. ARv05-30: The ALTO client protocol MUST support scenarios with		o no re-use should occur
			o re-use is appropriate for a specific "target audience", i.e., a
			set of resource consumers explicitly defined by a list of host
			group descriptors. The ALTO server MAY specify a "target
			audience" in the ALTO reply, which is only a subset of the known
			actual "target audience", e.g., if required by operator policies
			o re-use is appropriate for any resource consumer that would send
			(or cause a third party sending on behalf of it) the same ALTO
			query (i.e., with the same query parameters, except for the
			resource consumer ID, if applicable) to this ALTO server
			o re-use is appropriate for any resource consumer that would send
			(or cause a third party sending on behalf of it) the same ALTO
			query (i.e., with the same query parameters, except for the
			resource consumer ID, if applicable) to any ALTO server
			REQ. ARv06-31: The ALTO client protocol MUST support scenarios with
	the ALTO client located in the private address realm behind a network		the ALTO client located in the private address realm behind a network
	address translator (NAT). There are different types of NAT, see		address translator (NAT). There are different types of NAT, see
	[RFC4787] and [RFC5382].		[RFC4787] and [RFC5382].
	3.1.5. Protocol Extensibility		3.1.5. Protocol Extensibility
	REQ. ARv05-31: The ALTO client protocol MUST include support for		REQ. ARv06-32: The ALTO client protocol MUST include support for
	adding protocol extensions in a non-disruptive, backward-compatible		adding protocol extensions in a non-disruptive, backward-compatible
	way.		way.
	REQ. ARv05-32: The ALTO client protocol MUST include protocol		REQ. ARv06-33: The ALTO client protocol MUST include protocol
	versioning support, in order to clearly distinguish between		versioning support, in order to clearly distinguish between
	incompatible versions of the protocol.		incompatible versions of the protocol.
	3.1.6. Error Handling and Overload Protection		3.1.6. Error Handling and Overload Protection
	REQ. ARv05-33: Any application designed to use ALTO MUST also work		REQ. ARv06-34: Any application designed to use ALTO MUST also work
	if no ALTO servers can be found or if no responses to ALTO queries		if no ALTO servers can be found or if no responses to ALTO queries
	are received, e.g., due to connectivity problems or overload		are received, e.g., due to connectivity problems or overload
	situation.		situation.
	REQ. ARv05-34: The ALTO client protocol MUST use TCP based		REQ. ARv06-35: The ALTO client protocol MUST use TCP based
	transport.		transport.
	REQ. ARv05-35: An ALTO server, which is operating close to its		REQ. ARv06-36: An ALTO server, which is operating close to its
	capacity limit, MUST be able to inform clients about its impending		capacity limit, MUST be able to inform clients about its impending
	overload situation, and require them to throttle their query rate.		overload situation, and require them to throttle their query rate.
	REQ. ARv05-36: An ALTO server, which is operating close to its		REQ. ARv06-37: An ALTO server, which is operating close to its
	capacity limit, MUST be able to inform clients about its impending		capacity limit, MUST be able to inform clients about its impending
	overload situation, and redirect them to another ALTO server.		overload situation, and redirect them to another ALTO server.
	REQ. ARv05-37: An ALTO server, which is operating close to its		REQ. ARv06-38: An ALTO server, which is operating close to its
	capacity limit, MUST be able to inform clients about its impending		capacity limit, MUST be able to inform clients about its impending
	overload situation, and terminate the conversation with the ALTO		overload situation, and terminate the conversation with the ALTO
	client.		client.
	REQ. ARv05-38: An ALTO server, which is operating close to its		REQ. ARv06-39: An ALTO server, which is operating close to its
	capacity limit, MUST be able to inform clients about its impending		capacity limit, MUST be able to inform clients about its impending
	overload situation, and reject new conversation attempts.		overload situation, and reject new conversation attempts.
	3.2. ALTO Server Discovery		3.2. ALTO Server Discovery
	The ALTO client protocol is supported by one or several ALTO server		The ALTO client protocol is supported by one or several ALTO server
	discovery mechanisms, which will be used by ALTO clients in order to		discovery mechanisms, which will be used by ALTO clients in order to
	find out where to send ALTO requests.		find out where to send ALTO requests.
	REQ. ARv05-39: ALTO clients which are embedded in the resource		REQ. ARv06-40: ALTO clients which are embedded in the resource
	consumer MUST be able to use the ALTO server discovery mechanism, in		consumer MUST be able to use the ALTO server discovery mechanism, in
	order to find one or several ALTO servers that can provide ALTO		order to find one or several ALTO servers that can provide ALTO
	guidance suitable for the resource consumer. This mode of operation		guidance suitable for the resource consumer. This mode of operation
	is called "resource consumer initiated ALTO server discovery".		is called "resource consumer initiated ALTO server discovery".
	REQ. ARv05-40: ALTO clients which are embedded in a resource		REQ. ARv06-41: ALTO clients which are embedded in a resource
	directory and perform third-party ALTO queries on behalf of a remote		directory and perform third-party ALTO queries on behalf of a remote
	resource consumer MUST be able to use the ALTO server discovery		resource consumer MUST be able to use the ALTO server discovery
	mechanism, in order to find one or several ALTO servers that can		mechanism, in order to find one or several ALTO servers that can
	provide ALTO guidance suitable for the respective resource consumer.		provide ALTO guidance suitable for the respective resource consumer.
	This mode of operation is called "third-party ALTO server discovery".		This mode of operation is called "third-party ALTO server discovery".
	A classification and evaluation of architectural options for third-
	party ALTO server discovery can be found in [I-D.kiesel-alto-3pdisc].
	REQ. ARv05-41: ALTO clients MUST be able to perform resource		REQ. ARv06-42: ALTO clients MUST be able to perform resource
	consumer initiated ALTO server discovery, even if they are located		consumer initiated ALTO server discovery, even if they are located
	behind a network address translator (NAT).		behind a network address translator (NAT).
	REQ. ARv05-42: ALTO clients MUST be able to perform third-party ALTO		REQ. ARv06-43: ALTO clients MUST be able to perform third-party ALTO
	server discovery, even if they are located behind a network address		server discovery, even if they are located behind a network address
	translator (NAT).		translator (NAT).
	REQ. ARv05-43: ALTO clients MUST be able to perform third-party ALTO		REQ. ARv06-44: ALTO clients MUST be able to perform third-party ALTO
	server discovery, even if the resource consumer, on behalf of which		server discovery, even if the resource consumer, on behalf of which
	the ALTO query will be sent, is located behind a network address		the ALTO query will be sent, is located behind a network address
	translator (NAT).		translator (NAT).
	REQ. ARv05-44: The ALTO server discovery mechanism may be specified		REQ. ARv06-45: The ALTO server discovery mechanism may be specified
	and provided using an existing protocol or mechanism, such as DNS,		and provided using an existing protocol or mechanism, such as DNS,
	DHCP, or PPP based automatic configuration, etc. These candidate		DHCP, or PPP based automatic configuration, etc. These candidate
	"base protocols" differ with respect to their availability in various		"base protocols" differ with respect to their availability in various
	access network architectures and their suitability for third-party		access network architectures and their suitability for third-party
	queries. When evaluating different options this should be taken into		queries. When evaluating different options this should be taken into
	account, in order to limit the total number of ALTO server discovery		account, in order to limit the total number of ALTO server discovery
	mechanisms that have to be specified for supporting a reasonably wide		mechanisms that have to be specified for supporting a reasonably wide
	range of deployment scenarios.		range of deployment scenarios.
	REQ. ARv05-45: The ALTO server discovery mechanism SHOULD be able to		REQ. ARv06-46: The ALTO server discovery mechanism SHOULD be able to
	return the respective contact information for several ALTO servers.		return the respective contact information for several ALTO servers.
	REQ. ARv05-46: The ALTO server discovery mechanism SHOULD be able to		REQ. ARv06-47: The ALTO server discovery mechanism SHOULD be able to
	indicate preferences for each returned ALTO server contact		indicate preferences for each returned ALTO server contact
	information.		information.
	3.3. Security and Privacy		3.3. Security and Privacy
	REQ. ARv05-47: The ALTO client protocol MUST support mechanisms for		REQ. ARv06-48: The ALTO client protocol MUST support mechanisms for
	the authentication of ALTO servers.		the authentication of ALTO servers.
	REQ. ARv05-48: The ALTO client protocol MUST support mechanisms for		REQ. ARv06-49: The ALTO client protocol MUST support mechanisms for
	the authentication of ALTO clients.		the authentication of ALTO clients.
	REQ. ARv05-49: The ALTO client protocol MUST support different		REQ. ARv06-50: The ALTO client protocol MUST support different
	levels of detail in queries and responses, in order for the operator		levels of detail in queries and responses, in order for the operator
	of an ALTO service to be able to control how much information (e.g.,		of an ALTO service to be able to control how much information (e.g.,
	about the network topology) is disclosed.		about the network topology) is disclosed.
	REQ. ARv05-50: The operator of an ALTO server MUST NOT assume that		REQ. ARv06-51: The operator of an ALTO server MUST NOT assume that
	an ALTO client will implement mechanisms or comply with rules that		an ALTO client will implement mechanisms or comply with rules that
	limit the ALTO client's ability to redistribute information retrieved		limit the ALTO client's ability to redistribute information retrieved
	from the ALTO server to third parties.		from the ALTO server to third parties.
	REQ. ARv05-51: The ALTO client protocol MUST support different		REQ. ARv06-52: The ALTO client protocol MUST support different
	levels of detail in queries and responses, in order to protect the		levels of detail in queries and responses, in order to protect the
	privacy of users, to ensure that the operators of ALTO servers and		privacy of users, to ensure that the operators of ALTO servers and
	other users of the same application cannot derive sensitive		other users of the same application cannot derive sensitive
	information.		information.
	REQ. ARv05-52: The ALTO client protocol SHOULD be defined in a way,		REQ. ARv06-53: The ALTO client protocol SHOULD be defined in a way,
	that the operator of one ALTO server cannot easily deduce the		that the operator of one ALTO server cannot easily deduce the
	resource identifier (e.g., file name in P2P file sharing) which the		resource identifier (e.g., file name in P2P file sharing) which the
	resource consumer seeking ALTO guidance wants to access.		resource consumer seeking ALTO guidance wants to access.
	REQ. ARv05-53: The ALTO client protocol MUST include appropriate		REQ. ARv06-54: The ALTO client protocol MUST include appropriate
	mechanisms to protect the ALTO service against DoS attacks.		mechanisms to protect the ALTO service against DoS attacks.
	4. Host Group Descriptors		4. Host Group Descriptors
	Host group descriptors are used in the ALTO client protocol to		Host group descriptors are used in the ALTO client protocol to
	describe the location of a host in the network topology. The ALTO		describe the location of a host in the network topology. The ALTO
	client protocol specification defines a basic set of host group		client protocol specification defines a basic set of host group
	descriptor types, which have to be supported by all implementations,		descriptor types, which have to be supported by all implementations,
	and an extension procedure for adding new descriptor types (see		and an extension procedure for adding new descriptor types (see
	Section 3.1.2). The following list gives an overview on further host		Section 3.1.2). The following list gives an overview on further host
	skipping to change at page 24, line 18 ¶		skipping to change at page 24, line 18 ¶
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119, March 1997.		Requirement Levels", BCP 14, RFC 2119, March 1997.
	8.2. Informative References		8.2. Informative References
	[ALTO-charter]		[ALTO-charter]
	Marocco, E. and V. Gurbani, "Application-Layer Traffic		Marocco, E. and V. Gurbani, "Application-Layer Traffic
	Optimization (ALTO) Working Group Charter", February 2009.		Optimization (ALTO) Working Group Charter", February 2009.
	[I-D.kiesel-alto-3pdisc]
	Kiesel, S. and M. Tomsu, "Third-party ALTO server
	discovery", draft-kiesel-alto-3pdisc-00 (work in
	progress), August 2009.
	[RFC4787] Audet, F. and C. Jennings, "Network Address Translation		[RFC4787] Audet, F. and C. Jennings, "Network Address Translation
	(NAT) Behavioral Requirements for Unicast UDP", BCP 127,		(NAT) Behavioral Requirements for Unicast UDP", BCP 127,
	RFC 4787, January 2007.		RFC 4787, January 2007.
	[RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P.		[RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P.
	Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142,		Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142,
	RFC 5382, October 2008.		RFC 5382, October 2008.
	[RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic		[RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic
	Optimization (ALTO) Problem Statement", RFC 5693,		Optimization (ALTO) Problem Statement", RFC 5693,
End of changes. 60 change blocks.
	74 lines changed or deleted		81 lines changed or added
This html diff was produced by rfcdiff 1.48. The latest version is available from http://tools.ietf.org/tools/rfcdiff/