< draft-ietf-dime-app-design-guide-13.txt		draft-ietf-dime-app-design-guide-14.txt >
	Diameter Maintanence and Extensions V. Fajardo		Diameter Maintenance and Extensions L. Morand, Ed.
	(DIME)		(DIME) Orange Labs
	Internet-Draft H. Tschofenig		Internet-Draft V. Fajardo
	Intended status: Informational Nokia Siemens Networks		Intended status: Informational
	Expires: July 14, 2012 L. Morand, Ed.		Expires: October 3, 2012 H. Tschofenig
	Orange Labs		Nokia Siemens Networks
	January 11, 2012		April 1, 2012
	Diameter Applications Design Guidelines		Diameter Applications Design Guidelines
	draft-ietf-dime-app-design-guide-13		draft-ietf-dime-app-design-guide-14
	Abstract		Abstract
	The Diameter Base protocol provides facilities for protocol		The Diameter Base protocol provides facilities for protocol
	extensibility enabling to define new Diameter applications or modify		extensibility enabling to define new Diameter applications or modify
	existing applications. This document is a companion document to the		existing applications. This document is a companion document to the
	Diameter Base protocol that further explains and clarifies the rules		Diameter Base protocol that further explains and clarifies the rules
	to extend the Diameter Base protocol. It is meant as a guidelines		to extend the Diameter Base protocol. It is meant as a guidelines
	document and therefore it does not add, remove or change existing		document and therefore it does not add, remove or change existing
	rules.		rules.
	skipping to change at page 2, line 26 ¶		skipping to change at page 2, line 26 ¶
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.		Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	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."
	This Internet-Draft will expire on July 14, 2012.		This Internet-Draft will expire on October 3, 2012.
	Copyright Notice		Copyright Notice
	Copyright (c) 2012 IETF Trust and the persons identified as the		Copyright (c) 2012 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 10 ¶		skipping to change at page 3, line 10 ¶
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
	3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 6		3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
	4. Adding a new command . . . . . . . . . . . . . . . . . . . . . 8		4. Reusing existing Diameter applications . . . . . . . . . . . . 8
	5. Deleting a Command . . . . . . . . . . . . . . . . . . . . . . 9		4.1. Adding a new command . . . . . . . . . . . . . . . . . . . 8
	6. Reusing Existing Commands . . . . . . . . . . . . . . . . . . 10		4.2. Deleting a command . . . . . . . . . . . . . . . . . . . . 9
	6.1. Adding AVPs to a Command . . . . . . . . . . . . . . . . . 10		4.3. Reusing existing commands . . . . . . . . . . . . . . . . 9
	6.2. Deleting AVPs from a Command . . . . . . . . . . . . . . . 11		4.3.1. Adding AVPs to a command . . . . . . . . . . . . . . . 10
	7. Reusing Existing AVPs . . . . . . . . . . . . . . . . . . . . 13		4.3.2. Deleting AVPs from a Command . . . . . . . . . . . . . 11
	8. Rules for new Applications . . . . . . . . . . . . . . . . . . 14		4.4. Reusing existing AVPs . . . . . . . . . . . . . . . . . . 12
	8.1. Use of Application-Id in a Message . . . . . . . . . . . . 14		4.4.1. Setting of the AVP flags . . . . . . . . . . . . . . . 12
	8.2. Application Specific Session State Machine . . . . . . . . 15		4.4.2. Reuse of AVP of type Enumerated . . . . . . . . . . . 12
	9. End-to-End Applications Capabilities Exchange . . . . . . . . 16		5. Rules for new Applications . . . . . . . . . . . . . . . . . . 13
	10. Diameter Accounting Support . . . . . . . . . . . . . . . . . 17		5.1. Use of Application-Id in a Message . . . . . . . . . . . . 13
	11. Generic Diameter Extensions . . . . . . . . . . . . . . . . . 19		5.2. Application Specific Session State Machine . . . . . . . . 14
	12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21		6. End-to-End Applications Capabilities Exchange . . . . . . . . 15
	13. Security Considerations . . . . . . . . . . . . . . . . . . . 22		7. Diameter Accounting Support . . . . . . . . . . . . . . . . . 16
	14. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 23		8. Generic Diameter Extensions . . . . . . . . . . . . . . . . . 18
	15. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24		9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
	16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25		10. Security Considerations . . . . . . . . . . . . . . . . . . . 21
	16.1. Normative References . . . . . . . . . . . . . . . . . . . 25		11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 22
	16.2. Informative References . . . . . . . . . . . . . . . . . . 26		12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27		13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
			13.1. Normative References . . . . . . . . . . . . . . . . . . . 24
			13.2. Informative References . . . . . . . . . . . . . . . . . . 24
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
	1. Introduction		1. Introduction
	The Diameter Base protocol provides facilities to extend the Diameter		The Diameter Base protocol provides facilities to extend the Diameter
	Base protocol (see Section 1.3 of [I-D.ietf-dime-rfc3588bis]). In		Base protocol (see Section 1.3 of [I-D.ietf-dime-rfc3588bis]) for
	the context of this document, extending Diameter means one of the		supporting new functionalities. In the context of this document,
	following:		extending Diameter means one of the following:
	1. A new functionality is being added to an existing Diameter		1. Addition of a new functionality to an existing Diameter
	application without defining a new application.		application without defining a new application.
	2. A new Diameter application is being defined by extending an		2. Addition of a new functionality to an existing Diameter
	existing application.		application that requires the definition of a new application.
	3. A completely new application is being defined that has nothing in		3. The definition of a new Diameter application to provide a set of
	common with existing applications.		functionalities not supporting by existing applications.
	4. A new generic functionality is being defined that can be reused		4. The definition of a new generic functionality that can be reused
	across different applications.		across different applications.
	All of these choices are design decisions that can done by any		All of these choices are design decisions that can done by any
	combination of reusing existing or defining new commands, AVPs or AVP		combination of reusing existing or defining new commands, AVPs or AVP
	values. Protocol designers do, however, not have total freedom when		values. Protocol designers do, however, not have total freedom when
	making their design. A number of rules defined in		making their design. A number of rules defined in
	[I-D.ietf-dime-rfc3588bis] place constraints on when an extension		[I-D.ietf-dime-rfc3588bis] place constraints on when an extension
	demands a new Diameter Application to be defined or a new Command		demands a new Diameter application to be defined or a new command
	Code to be registered. The objective of this document is the		code to be registered. The objective of this document is the
	following:		following:
	o Clarify updated Diameter extensibility rules in the Diameter Base		o Clarify updated Diameter extensibility rules in the Diameter Base
	Protocol.		Protocol.
	o Clarify usage of certain Diameter functionalitiessi which are not		o Clarify usage of certain Diameter functionalities that are not
	explicitly described in the Diameter Base specification.		explicitly described in the Diameter Base specification.
	o Discuss design choices and provide guidelines when defining		o Discuss design choices and provide guidelines when defining
	applications.		applications.
	o Present tradeoffs of design choices.		o Present tradeoffs of design choices.
	2. Terminology		2. Terminology
	This document reuses the terminology used in		This document reuses the terminology used in
	[I-D.ietf-dime-rfc3588bis].		[I-D.ietf-dime-rfc3588bis].
	3. Overview		3. Overview
	As it is currently interpreted and practiced, the Diameter Base		As designed, the Diameter Base protocol can be seen as a two-layer
	protocol is a two-layer protocol. The lower layer is mainly		protocol. The lower layer is mainly responsible for managing
	responsible for managing connections between neighboring peers and		connections between neighboring peers and for message routing. The
	for message routing. The upper layer is where the Diameter		upper layer is where the Diameter applications reside. This model is
	applications reside. This model is in line with a Diameter node		in line with a Diameter node having an application layer and a peer-
	having an application layer and a peer-to-peer delivery layer. The		to-peer delivery layer. The Diameter Base protocol document
	Diameter Base protocol document completely defines the architecture		completely defines the architecture and behavior of the message
	and behavior of the message delivery layer and then provides the		delivery layer and then provides the framework for designing Diameter
	framework for designing Diameter applications on the application		applications on the application layer. This framework includes
	layer. This framework includes definitions of application sessions		definitions of application sessions and accounting support (see
	and accounting support (see Section 8 and 9 of		Section 8 and 9 of [I-D.ietf-dime-rfc3588bis]). The remainder of
	[I-D.ietf-dime-rfc3588bis]). The remainder of this document also		this document also treats a Diameter node as a single instance of a
	treats a Diameter node as a single instance of a Diameter message		Diameter message delivery layer and one or more Diameter applications
	delivery layer and one or more Diameter applications using it.		using it.
	Extending Diameter can mean the reuse of commands, AVPs and AVP		The Diameter protocol is designed to be extensible and the principles
	values in any combination for the purpose of inheriting the features		are descibed in the section 1.3 of [I-D.ietf-dime-rfc3588bis].
	of an existing Diameter application. This section discusses the		Extending Diameter can mean the definition of a new Diameter
	rules on how such reuse can be done.		application and/or the reuse of commands, AVPs and AVP values in any
			combination for the purpose of inheriting the features of an existing
			Diameter application. The reuse recommendation is meaningful as most
			of the requirements defined for a new application are likely already
			fulfilled by an existing application.
	When reusing existing applications, the requirements of the new		However, when reusing existing applications, there is a greater
	applications are typically not completely unique and hence a lot can		likelihood of ambiguity on how much of the existing application can
	be re-used from existing specifications. Therefore, there is a		be enhanced without being distorted too much and therefore requiring
	greater likelihood of ambiguity on how much of the existing		the definition of a new application.
	application can be reused and what would be the implications for both
	the new and existing application. To broadly categorize, the rules
	for reusing existing applications can fall into two categories, as
	listed below.
	Minor Extension: This, for example, is the case when optional AVPs		The impacts of extending existing applications can be categorized as
	are being defined. In general, this includes everything that is		follow:
	not covered by the next category. The standardization effort will
	be fairly small.
	Major Extension: Such an extension requires the definition of a new		Minor Extension: Enhancing the functional scope of an existing
	Diameter application. The rules outlined in Section 1.2 of		application by the addition of optional features to support. Such
	[I-D.ietf-dime-rfc3588bis] indicate when an extension requires a a		enhancement has no backward compatibility issue with the existing
	new Command Code to be registered and when new Diameter		application. A typical example would be the definition of a new
	applications have to be defined. Typically, these types of		optional AVP to use in an existing command. In general, this
	extensions require a longer and more careful effort depending on		includes everything that is not covered by the next category. The
	the degree of re-use. Therefore, the amount of time and effort to		standardization effort will be fairly small.
	complete the specification should also be considered by the
	designer.
	The subsequent sections provide discussions about the specific		Major Extension: Enhancing the functional scope of an existing
	Diameter Base protocol rules.		application in such a way that this implies backward compatible
			change to the existing application and then requires the
			definition of a new Diameter application. A typical example would
			be the creation of a new command for providing functionality not
			supported by existing applications. For such extension, a
			significant specification effort is required and a carefull
			approach is recommended.
	4. Adding a new command		The rules outlined in the section 1.3 of [I-D.ietf-dime-rfc3588bis]
			indicate when an extension requires a new command code to be
			registered and when new Diameter applications have to be defined.
			The subsequent sections further explain and clarify the rules to
			extend the Diameter Base protocol. It is meant as a guidelines
			document and therefore it does not add, remove or change existing
			rules.
	Adding a new command is considered a major extension and requires a		4. Reusing existing Diameter applications
	new Diameter application to be defined. Adding a new command to an
			When selecting the Diameter Base protocol to support new
			functionalities, protocol designers are advised to try to re-use as
			much as possible existing Diameter applications to simplify
			standardization, implementation and avoid potential interoperability
			issues. However, existing application needs to be adapted to support
			new requirements and these modifications can be at the command level
			and/or at the AVP level. The following sections describe the
			possible modifications that can be performed on existing applications
			and their related impacts.
			4.1. Adding a new command
			Adding a new command is considered as a major extension and requires
			a new Diameter application to be defined. Adding a new command to an
	application means either defining a completely new command or		application means either defining a completely new command or
	importing an existing command from another application whereby the		importing the command's CCF syntax specification from another
	new application inherits some or all of the functionality of the		application whereby the new application inherits some or all of the
	application where the command came from. In the former case, the		functionality of the application where the command came from. In the
	decision to create an new application is straightforward since this		former case, the decision to create an new application is
	is typically a result of adding a new functionality that does not		straightforward since this is typically a result of adding a new
	exist yet. For the latter, the decision will depend on whether		functionality that does not exist yet. For the latter, the decision
	importing the command in a new application is more suitable than		to create a new application will depend on whether importing the
	simply using the existing application as it is in conjunction with		command in a new application is more suitable than simply using the
	any other application. Therefore, a case by case study of each		existing application as it is in conjunction with any other
	application requirement should be applied.		application. Therefore, a case by case study of each application
			requirement should be applied.
	In general, it is difficult to come to a hard guideline, and so a		An illustrative example is the command pair defined in Diameter EAP
	case by case study of each application requirement should be applied.		application [RFC4072] that can be re-used conjointly with any other
	Before adding or importing a command, application designers should		application (e.g. the Diameter NASREQ application [RFC4005]) as soon
	consider the following:		as standard EAP-based authentication procedures need to be supported
			by the implementation. It may therefore not be required to import
			the command pair in the new defined application.
	o Can the new functionality be fulfilled by creating a new		However, in general, it is difficult to come to a hard guideline, and
	application independent from the existing applications? In this		so a case by case study of each application requirement should be
	case, both old and new application can work independent of, but		applied. Before adding or importing a command, application designers
	cooperating with each other.		should consider the following:
	o Can the existing application be reused without major extensions		o Can the new functionality be fulfilled by creating a new command
	that requires the definition of a new application, e.g. new		independent from any existing command? In this case, the
	funtionality introduced by the creation of new optional AVPs.		resulting new application and the existing application can work
			independent of, but cooperating with each other.
			o Can the existing command be reused without major extensions and
			therefore without the need for the definition of a new
			application, e.g. new funtionality introduced by the creation of
			new optional AVPs.
	o Care should be taken to avoid a liberal method of importing		o Care should be taken to avoid a liberal method of importing
	existing commands that results in a monolithic and hard to manage		existing command's CCF syntax specification. This would result in
	application which supports many different functionalities.		a monolithic and hard to manage applications supporting too many
			different functionalities and can cause interoperability issues
			between the different applications. .
	5. Deleting a Command		4.2. Deleting a command
	Although this process is not typical, removing a command to an		Although this process is not typical, removing a command to an
	application requires a new Diameter application to be defined. It is		application requires a new Diameter application to be defined. this
	unusual to delete an existing command from an application for the		is due to the fact that the reception of the deleted command would
	sake of deleting it or the functionality it represents. This		systematically result in a protocol error
			(DIAMETER_COMMAND_UNSUPPORTED).
			It is unusual to delete an existing command from an application for
			the sake of deleting it or the functionality it represents. This
	normally indicates of a flawed design. An exception might be if the		normally indicates of a flawed design. An exception might be if the
	intent of the deletion is to create a newer version of the same		intent of the deletion is to create a newer version of the same
	application which is somehow simpler than the previous version.		application which is somehow simpler than the previous version.
	6. Reusing Existing Commands		4.3. Reusing existing commands
	This section discusses rules in adding and/or deleting AVPs from an		This section discusses rules in adding and/or deleting AVPs from an
	existing command of an existing application. The cases described in		existing command of an existing application. The cases described in
	this section may not necessarily result in the creation of new		this section may not necessarily result in the creation of new
	applications.		applications.
	6.1. Adding AVPs to a Command		It is worth to note that the strong recommendation to re-use existing
			commands in the [RFC3588] was to prevent rapid scarcity of code
			values available for vendor-specific commands.
			[I-D.ietf-dime-rfc3588bis] relaxes the policy with respect to the
			allocation of command codes for vendor-specific uses and enlarges the
			range of available code values for vendor-specific applications.
			Therefore, if it is still recommended to re-use as much as possible
			existing commands, protocol designers can consider more easily the
			definition of a new command when it is a solution more suitable than
			twisting existings command use and applications.
			4.3.1. Adding AVPs to a command
	Based on the rules in [I-D.ietf-dime-rfc3588bis], AVPs that are added		Based on the rules in [I-D.ietf-dime-rfc3588bis], AVPs that are added
	to an existing command can be categorized into:		to an existing command can be categorized into:
	o Mandatory to understand AVPs. As defined in		o Mandatory (to understand) AVPs. As defined in
	[I-D.ietf-dime-rfc3588bis], these are AVPs with the M-bit flag		[I-D.ietf-dime-rfc3588bis], these are AVPs with the M-bit flag
	set, which means that a Diameter node receiving are required to		set, which means that a Diameter node receiving are required to
	understand not only their values but their semantics. Failure to		understand not only their values but their semantics. Failure to
	do so will cause an message handling error. This is regardless of		do so will cause an message handling error. This is regardless of
	whether these AVPs are required or optional as specified by the		whether these AVPs are required or optional as specified by the
	commands ABNF.		command's CCF syntax specification.
	o Optional AVPs. [TBD]		o Optional (to understand) AVPs. As defined in
			[I-D.ietf-dime-rfc3588bis], these are AVPs with the M-bit flag
			cleared, which mean that a Diameter node receiving these AVP can
			simply ignore them if not supported in the process of the received
			command.
	The rules are strict in the case where the AVPs to be added are		The rules are strict in the case where the AVPs to be added are
	mandatory. A mandatory AVP cannot be added to or deleted from an		mandatory to understand i.e. with the M-bit set. A mandatory AVP
	existing command with defining a new Diameter application.		cannot be added to an existing command without defining a new
	[I-D.ietf-dime-rfc3588bis] states that doing so would require the		Diameter application, as stated in [I-D.ietf-dime-rfc3588bis]. This
	definition of a new application. This falls into the "Major		falls into the "Major Extensions" category. Despite the clarity of
	Extensions" category. Despite the clarity of the rule, ambiguity		the rule, ambiguity still arises when evaluating whether a new AVP
	still arises when trying to decide whether a new AVP being added		being added should be mandatory to begin with. Here is a list of few
	should be mandatory to begin with. The follow are a few common		common questions that application designers should wonder when trying
	questions that application designers should contemplate when trying
	to decide:		to decide:
	o Is it required for the receiving side to be able to process and		o Would it be required for the receiving side to be able to process
	understand the AVP and its content (rather than just writing it's		and understand the AVP and its content?
	content into to a file)?
	o Do the AVPs change the state machine of the application ?		o Would the new AVPs change the state machine of the application?
	o Would the presence of the new AVPs (or the newly specified value		o Would the presence of the new AVP lead to a different number of
	contained in an existing AVP) lead to a different number of
	roundtrips, effectively changing the state machine of the		roundtrips, effectively changing the state machine of the
	application?		application?
	o Would the AVP be used to differentiate between old and new		o Would the new AVP be used to differentiate between old and new
	versions of the same application whereby the two versions are not		versions of the same application whereby the two versions are not
	backward compatible?		backward compatible?
	o Will it have duality in meaning, i.e., be used to carry		o Would the new AVP have duality in meaning i.e. be used to carry
	application related information as well as be used to indicate		application related information as well as be used to indicate
	that the message is for a new application?		that the message is for a new application?
	When one of the above questions can be answered with 'yes' then the		When one of the above questions can be answered in the affirmative
	M-bit has to be set. If application designers are contemplating on		then the M-bit has to be set for the new AVP.
	the use of optional AVPs instead, then the following are some of the
	pitfalls that should be avoided:		If application designers are instead contemplating on the use of
			optional AVPs i.e. with the M-bit cleared, then the following are
			some of the pitfalls that should be avoided:
	o Use of optional AVPs with intersecting meaning. One AVP has		o Use of optional AVPs with intersecting meaning. One AVP has
	partially the same usage and meaning as another AVP. The presence		partially the same usage and meaning as another AVP. The presence
	of both can lead to confusion.		of both can lead to confusion.
	o An optional AVPs with dual purpose, i.e. to carry applications		o An optional AVPs with dual purpose, i.e. to carry applications
	data as well as to indicate support for one or more features.		data as well as to indicate support for one or more features.
	This has a tendency to introduce interpretation issues.		This has a tendency to introduce interpretation issues.
	o Adding one or more optional AVPs and indicating (usually within		o Adding one or more optional AVPs and indicating (usually within
	descriptive text for the command) that at least one of them has to		descriptive text for the command) that at least one of them has to
	be present in the command. This essentially circumventing the		be present in the command. This essentially circumventing the
	ABNF and is equivalent to adding a mandatory AVPs to the command.		ABNF and is equivalent to adding a mandatory AVPs to the command.
	These practices generally result in interoperability issues and		These practices generally result in interoperability issues and
	should be avoided as much as possible.		should be avoided as much as possible.
	6.2. Deleting AVPs from a Command		4.3.2. Deleting AVPs from a Command
	When deleting an AVP from a Command the following cases need to be		When deleting an AVP from a command, the following cases need to be
	differentiated:		differentiated:
	o An AVP that is indicated as {} in the ABNF in the Command (with or		o Deleting an AVP that is indicated as { AVP } in the command's CCF
	without the M-bit set). In this case the new Command Code and		syntax specification, whatever the setting of the M-bit set. This
	subsequently a new Diameter application has to be specified.		means the definition of a new command. In this case, a new
			command code and subsequently a new Diameter application have to
			be specified.
	o An AVP that is indicated as [] in the ABNF in the Command (with		o Deleting an AVP with M-bit set that is indicated as [ AVP ] in the
	the M-bit set). No new Command Code has to be specified but the		command's CCF syntax specification. No new command code has to be
	definition of a new Diameter application is required.		specified but the definition of a new Diameter application is
			required.
	o An AVP that is indicated as [] in the ABNF in the Command (without		o Deleting an AVP with the M-bit cleared that is indicated as [ AVP
	the M-bit set). In this case the AVP can be deleted without		] in the command's CCF syntax specification. In this case, the
	consequences.		AVP can be deleted without consequences.
	If possible application designers should attempt the reuse the		If possible application designers should attempt the reuse the
	Command ABNF without modification and simply ignore (but not delete)		command's CCF syntax specification without modification and simply
	any optional AVP that will not be used. This is to maintain		ignore (but not delete) any optional AVP that will not be used. This
	compatibility with existing applications that will not know about the		is to maintain compatibility with existing applications that will not
	new functionality as well as maintain the integrity of existing		know about the new functionality as well as maintain the integrity of
	dictionaries.		existing dictionaries.
	7. Reusing Existing AVPs		4.4. Reusing existing AVPs
	This section discusses rules in adding, deleting or modifying the		This section discusses rules in reusing existing AVP when reusing an
	specified values of an AVP.		existing command or defining a new command in a new application.
			4.4.1. Setting of the AVP flags
	When reusing AVPs in a new application, the AVP flag setting, such as		When reusing AVPs in a new application, the AVP flag setting, such as
	the mandatory flag ('M'-bit), has to be re-evaluated for a new		the mandatory flag ('M'-bit), has to be re-evaluated for a new
	Diameter application and, if necessary, even for every Command within		Diameter application and, if necessary, even for every command within
	the application. In general, for AVPs defined outside of the base		the application. In general, for AVPs defined outside of the base
	protocol, its mandatory characteristics are tied to its role within		protocol, its mandatory characteristics are tied to its role within
	an application and Command.		an application and command.
	8. Rules for new Applications		All other AVP flags shall remain unchanged
	The general theme of Diameter extensibility is to reuse commands,		4.4.2. Reuse of AVP of type Enumerated
	AVPs and AVP values as much as possible. However, some of the
	extensibility rules described in the previous section also apply to		When modifying the set of values supported by an AVP of type
	scenarios where a designer is trying to define a completely new		Enumerated, this means defining a new AVP. Modifying the set of
			Enumerated values includes adding a value or deprecating the use of a
			value defined initially for the AVP. Defining a new AVP will avoid
			interoperability issues.
			5. Rules for new Applications
			The general recommendation for Diameter extensibility is to reuse
			commands, AVPs and AVP values as much as possible. However, some of
			the extensibility rules described in the previous section also apply
			to scenarios where a designer is trying to define a completely new
	Diameter application.		Diameter application.
	This section discusses the case where new applications have		This section discusses the case where new applications have
	requirements that cannot be filled by existing applications and would		requirements that cannot be filled by existing applications and would
	require definition of completely new commands, AVPs and/or AVP		require definition of completely new commands, AVPs and/or AVP
	values. Typically, there is little ambiguity about the decision to		values. Typically, there is little ambiguity about the decision to
	create these types of applications. Some examples are the interfaces		create these types of applications. Some examples are the interfaces
	defined for the IP Multimedia Subsystem of 3GPP, i.e. Cx/Dx		defined for the IP Multimedia Subsystem of 3GPP, i.e. Cx/Dx
	([TS29.228] and [TS29.229]), Sh ([TS29.328] and [TS29.329]) etc.		([TS29.228] and [TS29.229]), Sh ([TS29.328] and [TS29.329]) etc.
	Application designers should also follow the theme of Diameter		Application designers should also follow the theme of Diameter
	extensibility which in this case means to import existing AVPs and		extensibility which in this case means to import existing AVPs and
	AVP values for any newly defined commands. In certain cases where		AVP values for any newly defined commands. In certain cases where
	accounting will be used, the models described in Section 10 should		accounting will be used, the models described in Section 7 should
	also be considered. Though some decisions may be clear, designers		also be considered. Though some decisions may be clear, designers
	should also consider certain aspects of defining a new application.		should also consider certain aspects of defining a new application.
	Some of these aspects are described in following sections.		Some of these aspects are described in following sections.
	8.1. Use of Application-Id in a Message		5.1. Use of Application-Id in a Message
	When designing new applications, designers should specify that the		When designing new applications, designers should specify that the
	application ID carried in all session level messages must be the		application ID carried in all session level messages must be the
	application ID of the application using those messages. This		application ID of the application using those messages. This
	includes the session level messages defined in base protocol, i.e.,		includes the session level messages defined in base protocol, i.e.,
	RAR/RAA, STR/STA, ASR/ASA and possibly ACR/ACA in the coupled		RAR/RAA, STR/STA, ASR/ASA and possibly ACR/ACA in the coupled
	accounting model, see Section 10. Existing specifications may not		accounting model, see Section 7. Existing specifications may not
	adhere to this rule for historical or other reasons. However, this		adhere to this rule for historical or other reasons. However, this
	scheme should be followed to avoid possible routing problems for		scheme should be followed to avoid possible routing problems for
	these messages.		these messages.
	In general, when a new application has been allocated with a new		In general, when a new application has been allocated with a new
	application id and it also reuses existing commands with or without		application id and it also reuses existing commands with or without
	modifications (Sec 4.1), it must use the newly allocated application		modifications (Sec 4.1), it must use the newly allocated application
	id in the header and in all relevant application id AVPs (Auth-		id in the header and in all relevant application id AVPs (Auth-
	Application-Id or Acct-Application-Id) present in the commands		Application-Id or Acct-Application-Id) present in the commands
	message body.		message body.
	Additionally, application designs using		Additionally, application designs using
	Vendor-Specific-Application-Id AVP should not use the Vendor-Id AVP		Vendor-Specific-Application-Id AVP should not use the Vendor-Id AVP
	to further dissect or differentiate the vendor-specification		to further dissect or differentiate the vendor-specification
	application id. Diameter routing is not based on the Vendor-Id. As		application id. Diameter routing is not based on the Vendor-Id. As
	such, the Vendor-ID should not be used as an additional input for		such, the Vendor-ID should not be used as an additional input for
	routing or delivery of messages. In general, the Vendor-Id AVP is an		routing or delivery of messages. In general, the Vendor-Id AVP is an
	informational AVP only and kept for backward compatibility reasons.		informational AVP only and kept for backward compatibility reasons.
	8.2. Application Specific Session State Machine		5.2. Application Specific Session State Machine
	Section 8 of [I-D.ietf-dime-rfc3588bis] provides session state		Section 8 of [I-D.ietf-dime-rfc3588bis] provides session state
	machines for authentication, authorization and accounting (AAA)		machines for authentication, authorization and accounting (AAA)
	services. When a new application is being defined that cannot		services. When a new application is being defined that cannot
	clearly be categorized into any of these services it is recommended		clearly be categorized into any of these services it is recommended
	that the application itself define its own session state machine.		that the application itself define its own session state machine.
	The existing session state machines defined by		The existing session state machines defined by
	[I-D.ietf-dime-rfc3588bis] is not intended for general use beyond AAA		[I-D.ietf-dime-rfc3588bis] is not intended for general use beyond AAA
	services, therefore any behavior not covered by that category would		services, therefore any behavior not covered by that category would
	not fit well. Support for server initiated request is a clear		not fit well. Support for server initiated request is a clear
	example where an application specific session state machine would be		example where an application specific session state machine would be
	needed, for example, the Rw interface for ITU-T push model.		needed, for example, the Rw interface for ITU-T push model (
			cf.[Q.3303.3]).
	9. End-to-End Applications Capabilities Exchange		6. End-to-End Applications Capabilities Exchange
	It is also possible that applications can use optional AVPs to		It is also possible that applications can use optional AVPs to
	exchange application specific capabilities and features. These AVPs		exchange application specific capabilities and features. These AVPs
	are exchanged on an end-to-end basis. Examples of this can be found		are exchanged on an end-to-end basis. Examples of this can be found
	in [I-D.ietf-dime-mip6-integrated] and		in [I-D.ietf-dime-mip6-integrated] and
	[I-D.ietf-dime-qos-attributes].		[I-D.ietf-dime-qos-attributes].
	The end-to-end capabilities AVPs can aid in the following cases:		The end-to-end capabilities AVPs can aid in the following cases:
	o Formalizing the way new functionality is added to existing		o Formalizing the way new functionality is added to existing
	skipping to change at page 17, line 5 ¶		skipping to change at page 15, line 28 ¶
	o Applications that do not understand these AVP can discard it upon		o Applications that do not understand these AVP can discard it upon
	receipt. In such case, senders of the AVP can also safely assume		receipt. In such case, senders of the AVP can also safely assume
	the receiving end-point does not support any functionality carried		the receiving end-point does not support any functionality carried
	by the AVP if it is not present in subsequent responses.		by the AVP if it is not present in subsequent responses.
	o Useful in cases where deployment choices are offered and the		o Useful in cases where deployment choices are offered and the
	generic design can be made available for a number of applications.		generic design can be made available for a number of applications.
	Note that this list is not meant to be comprehensive.		Note that this list is not meant to be comprehensive.
	10. Diameter Accounting Support		When used in a new application, protocol designers should clearly
			specify this end-to-end capabilities exchange and the corresponding
			behaviour of the Diameter nodes supporting the application.
			7. Diameter Accounting Support
	Accounting can be treated as an auxiliary application which is used		Accounting can be treated as an auxiliary application which is used
	in support of other applications. In most cases, accounting support		in support of other applications. In most cases, accounting support
	is required when defining new applications. This document provides		is required when defining new applications. This document provides
	two(2) possible models for using accounting:		two(2) possible models for using accounting:
	Split Accounting Model		Split Accounting Model
	In this model, the accounting messages will use the Diameter base		In this model, the accounting messages will use the Diameter base
	accounting application ID (value of 3). The design implication		accounting application ID (value of 3). The design implication
	skipping to change at page 19, line 5 ¶		skipping to change at page 18, line 5 ¶
	In all cases above, there will generally be no direct Diameter		In all cases above, there will generally be no direct Diameter
	access to the accounting server.		access to the accounting server.
	These models provide a basis for using accounting messages.		These models provide a basis for using accounting messages.
	Application designers may obviously deviate from these models		Application designers may obviously deviate from these models
	provided that the factors being addressed here have also been taken		provided that the factors being addressed here have also been taken
	into account. Though it is not recommended, examples of other		into account. Though it is not recommended, examples of other
	methods might be defining a new set of commands to carry application		methods might be defining a new set of commands to carry application
	specific accounting records.		specific accounting records.
	11. Generic Diameter Extensions		8. Generic Diameter Extensions
	Generic Diameter extensions are AVPs, commands or applications that		Generic Diameter extensions are AVPs, commands or applications that
	are designed to support other Diameter applications. They are		are designed to support other Diameter applications. They are
	auxiliary applications meant to improve or enhance the Diameter		auxiliary applications meant to improve or enhance the Diameter
	protocol itself or Diameter applications/functionality. Some		protocol itself or Diameter applications/functionality. Some
	examples include the extensions to support auditing and redundancy		examples include the extensions to support auditing and redundancy
	(see [I-D.calhoun-diameter-res-mgmt]), improvements in duplicate		(see [I-D.calhoun-diameter-res-mgmt]), improvements in duplicate
	detection scheme (see [I-D.asveren-dime-dupcons]), and piggybacking		detection scheme (see [I-D.asveren-dime-dupcons]), and piggybacking
	of QoS attributes (see [I-D.ietf-dime-qos-attributes]).		of QoS attributes (see [I-D.ietf-dime-qos-attributes]).
	skipping to change at page 21, line 5 ¶		skipping to change at page 20, line 5 ¶
	should be sufficient to specify such a use case and perhaps provide		should be sufficient to specify such a use case and perhaps provide
	specific examples of applications using them.		specific examples of applications using them.
	In most cases, these optional AVPs piggybacked by applications would		In most cases, these optional AVPs piggybacked by applications would
	be defined as a Grouped AVP and it would encapsulate all the		be defined as a Grouped AVP and it would encapsulate all the
	functionality of the generic extension. In practice, it is not		functionality of the generic extension. In practice, it is not
	uncommon that the Grouped AVP will encapsulate an existing AVP that		uncommon that the Grouped AVP will encapsulate an existing AVP that
	has previously been defined as mandatory ('M'-bit set) e.g., 3GPP IMS		has previously been defined as mandatory ('M'-bit set) e.g., 3GPP IMS
	Cx / Dx interfaces ([TS29.228] and [TS29.229]).		Cx / Dx interfaces ([TS29.228] and [TS29.229]).
	12. IANA Considerations		9. IANA Considerations
	This document does not require actions by IANA.		This document does not require actions by IANA.
	13. Security Considerations		10. Security Considerations
	This document does provides guidelines and considerations for		This document does provides guidelines and considerations for
	extending Diameter and Diameter applications. It does not define nor		extending Diameter and Diameter applications. It does not define nor
	address security related protocols or schemes.		address security related protocols or schemes.
	14. Contributors		11. Contributors
	The content of this document was influenced by a design team created		The content of this document was influenced by a design team created
	to revisit the Diameter extensibility rules. The team consisting of		to revisit the Diameter extensibility rules. The team consisting of
	the members listed below was formed in February 2008 and finished its		the members listed below was formed in February 2008 and finished its
	work in June 2008.		work in June 2008.
	o Avi Lior		o Avi Lior
	o Glen Zorn		o Glen Zorn
	skipping to change at page 24, line 5 ¶		skipping to change at page 23, line 5 ¶
	o Glenn McGregor		o Glenn McGregor
	o Hannes Tschofenig		o Hannes Tschofenig
	o Dave Frascone		o Dave Frascone
	We would like to thank Tolga Asveren, Glenn McGregor, and John		We would like to thank Tolga Asveren, Glenn McGregor, and John
	Loughney for their contributions as co-authors to earlier versions of		Loughney for their contributions as co-authors to earlier versions of
	this document.		this document.
	15. Acknowledgments		12. Acknowledgments
	We greatly appreciate the insight provided by Diameter implementers		We greatly appreciate the insight provided by Diameter implementers
	who have highlighted the issues and concerns being addressed by this		who have highlighted the issues and concerns being addressed by this
	document.		document.
	16. References		13. References
	16.1. Normative References		13.1. Normative References
	[I-D.ietf-dime-diameter-qos]		[I-D.ietf-dime-rfc3588bis]
	Sun, D., McCann, P., Tschofenig, H., ZOU), T., Doria, A.,		Fajardo, V., Arkko, J., Loughney, J., and G. Zorn,
	and G. Zorn, "Diameter Quality of Service Application",		"Diameter Base Protocol", draft-ietf-dime-rfc3588bis-31
	draft-ietf-dime-diameter-qos-15 (work in progress),		(work in progress), March 2012.
	March 2010.
			[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
			Requirement Levels", BCP 14, RFC 2119, March 1997.
			[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
			Arkko, "Diameter Base Protocol", RFC 3588, September 2003.
			13.2. Informative References
			[I-D.asveren-dime-dupcons]
			Asveren, T., "Diameter Duplicate Detection Cons.",
			draft-asveren-dime-dupcons-00 (work in progress),
			August 2006.
			[I-D.calhoun-diameter-res-mgmt]
			Calhoun, P., "Diameter Resource Management Extensions",
			draft-calhoun-diameter-res-mgmt-08.txt (work in progress),
			March 2001.
	[I-D.ietf-dime-mip6-integrated]		[I-D.ietf-dime-mip6-integrated]
	Korhonen, J., Bournelle, J., Tschofenig, H., Perkins, C.,		Korhonen, J., Bournelle, J., Tschofenig, H., Perkins, C.,
	and K. Chowdhury, "Diameter Mobile IPv6: Support for		and K. Chowdhury, "Diameter Mobile IPv6: Support for
	Network Access Server to Diameter Server Interaction",		Network Access Server to Diameter Server Interaction",
	draft-ietf-dime-mip6-integrated-12 (work in progress),		draft-ietf-dime-mip6-integrated-12 (work in progress),
	January 2009.		January 2009.
	[I-D.ietf-dime-mip6-split]
	Korhonen, J., Tschofenig, H., Bournelle, J., Giaretta, G.,
	and M. Nakhjiri, "Diameter Mobile IPv6: Support for Home
	Agent to Diameter Server Interaction",
	draft-ietf-dime-mip6-split-17 (work in progress),
	April 2009.
	[I-D.ietf-dime-qos-attributes]		[I-D.ietf-dime-qos-attributes]
	Korhonen, J., Tschofenig, H., Arumaithurai, M., Jones, M.,		Korhonen, J., Tschofenig, H., Arumaithurai, M., Jones, M.,
	and A. Lior, "Traffic Classification and Quality of		and A. Lior, "Traffic Classification and Quality of
	Service Attributes for Diameter",		Service Attributes for Diameter",
	draft-ietf-dime-qos-attributes-15 (work in progress),		draft-ietf-dime-qos-attributes-15 (work in progress),
	December 2009.		December 2009.
	[I-D.ietf-dime-rfc3588bis]		[Q.3303.3]
	Fajardo, V., Arkko, J., Loughney, J., and G. Zorn,		3rd Generation Partnership Project, "ITU-T Recommendation
	"Diameter Base Protocol", draft-ietf-dime-rfc3588bis-29		Q.3303.3, "Resource control protocol no. 3 (rcp3):
	(work in progress), August 2011.		Protocol at the Rw interface between the Policy Decision
			Physical Entity (PD-PE) and the Policy Enforcement
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		Physical Entity (PE-PE): Diameter"", 2008.
	Requirement Levels", BCP 14, RFC 2119, March 1997.
	[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.		[RFC4005] Calhoun, P., Zorn, G., Spence, D., and D. Mitton,
	Arkko, "Diameter Base Protocol", RFC 3588, September 2003.		"Diameter Network Access Server Application", August 2005,
			<http://www.rfc-editor.org/rfc/rfc4005.txt>.
	[RFC4006] Hakala, H., Mattila, L., Koskinen, J-P., Stura, M., and J.		[RFC4072] Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible
	Loughney, "Diameter Credit-Control Application", RFC 4006,		Authentication Protocol (EAP) Application", August 2005,
	August 2005.		<http://www.rfc-editor.org/rfc/rfc4072.txt>.
	[TS29.228]		[TS29.228]
	3rd Generation Partnership Project, "3GPP TS 29.228;		3rd Generation Partnership Project, "3GPP TS 29.228;
	Technical Specification Group Core Network and Terminals;		Technical Specification Group Core Network and Terminals;
	IP Multimedia (IM) Subsystem Cx and Dx Interfaces;		IP Multimedia (IM) Subsystem Cx and Dx Interfaces;
	Signalling flows and message contents",		Signalling flows and message contents",
	<http://www.3gpp.org/ftp/Specs/html-info/29272.htm>.		<http://www.3gpp.org/ftp/Specs/html-info/29272.htm>.
	[TS29.229]		[TS29.229]
	3rd Generation Partnership Project, "3GPP TS 29.229;		3rd Generation Partnership Project, "3GPP TS 29.229;
	skipping to change at page 26, line 30 ¶		skipping to change at page 26, line 5 ¶
	flows and message content",		flows and message content",
	<http://www.3gpp.org/ftp/Specs/html-info/29328.htm>.		<http://www.3gpp.org/ftp/Specs/html-info/29328.htm>.
	[TS29.329]		[TS29.329]
	3rd Generation Partnership Project, "3GPP TS 29.329;		3rd Generation Partnership Project, "3GPP TS 29.329;
	Technical Specification Group Core Network and Terminals;		Technical Specification Group Core Network and Terminals;
	Sh Interface based on the Diameter protocol; Protocol		Sh Interface based on the Diameter protocol; Protocol
	details",		details",
	<http://www.3gpp.org/ftp/Specs/html-info/29329.htm>.		<http://www.3gpp.org/ftp/Specs/html-info/29329.htm>.
	16.2. Informative References		Authors' Addresses
	[I-D.asveren-dime-dupcons]
	Asveren, T., "Diameter Duplicate Detection Cons.",
	draft-asveren-dime-dupcons-00 (work in progress),
	August 2006.
	[I-D.calhoun-diameter-res-mgmt]		Lionel Morand (editor)
	Calhoun, P., "Diameter Resource Management Extensions",		Orange Labs
	draft-calhoun-diameter-res-mgmt-08.txt (work in progress),
	March 2001.
	Authors' Addresses		Phone: +33 1 4529 6257
			Email: lionel.morand@orange.com
	Victor Fajardo		Victor Fajardo
	Email: vf0213@gmail.com		Email: vf0213@gmail.com
	Hannes Tschofenig		Hannes Tschofenig
	Nokia Siemens Networks		Nokia Siemens Networks
	Linnoitustie 6		Linnoitustie 6
	Espoo 02600		Espoo 02600
	Finland		Finland
	Phone: +358 (50) 4871445		Phone: +358 (50) 4871445
	Email: Hannes.Tschofenig@gmx.net		Email: Hannes.Tschofenig@gmx.net
	URI: http://www.tschofenig.priv.at		URI: http://www.tschofenig.priv.at
	Lionel Morand (editor)
	Orange Labs
	Phone: +33 1 4529 6257
	Email: lionel.morand@orange-ftgroup.com
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