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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == The document seems to use 'NOT RECOMMENDED' as an RFC 2119 keyword, but does not include the phrase in its RFC 2119 key words list. == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'SHOULD not' in this paragraph: As a general recommendation, commands SHOULD not be defined from scratch. It is instead RECOMMENDED to re-use an existing command offering similar functionality and use it as a starting point. Code re-use lead to a smaller implementation effort as well as reduce the need for testing. == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'SHOULD not' in this paragraph: Additionally, application designers using Vendor-Specific-Application-Id AVP SHOULD not use the Vendor-Id AVP to further dissect or differentiate the vendor-specification Application Id. == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'SHOULD not' in this paragraph: Diameter routing is not based on the Vendor-Id. As such, the Vendor-Id SHOULD not be used as an additional input for routing or delivery of messages. The Vendor-Id AVP is an informational AVP only and kept for backward compatibility reasons. -- The document seems to contain a disclaimer for pre-RFC5378 work, and may have content which was first submitted before 10 November 2008. The disclaimer is necessary when there are original authors that you have been unable to contact, or if some do not wish to grant the BCP78 rights to the IETF Trust. If you are able to get all authors (current and original) to grant those rights, you can and should remove the disclaimer; otherwise, the disclaimer is needed and you can ignore this comment. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (April 15, 2014) is 3654 days in the past. Is this intentional? Checking references for intended status: Best Current Practice ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'AVP' is mentioned on line 404, but not defined == Missing Reference: 'RFC4005bis' is mentioned on line 713, but not defined ** Obsolete undefined reference: RFC 4005 (Obsoleted by RFC 7155) -- Obsolete informational reference (is this intentional?): RFC 2409 (Obsoleted by RFC 4306) -- Obsolete informational reference (is this intentional?): RFC 3588 (Obsoleted by RFC 6733) -- Obsolete informational reference (is this intentional?): RFC 4005 (Obsoleted by RFC 7155) -- Obsolete informational reference (is this intentional?): RFC 5226 (Obsoleted by RFC 8126) -- Obsolete informational reference (is this intentional?): RFC 5996 (Obsoleted by RFC 7296) Summary: 1 error (**), 0 flaws (~~), 7 warnings (==), 7 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Diameter Maintenance and Extensions (DIME) L. Morand, Ed. 3 Internet-Draft Orange Labs 4 Intended status: Best Current Practice V. Fajardo 5 Expires: October 17, 2014 Independent 6 H. Tschofenig 7 Nokia Siemens Networks 8 April 15, 2014 10 Diameter Applications Design Guidelines 11 draft-ietf-dime-app-design-guide-22 13 Abstract 15 The Diameter base protocol provides facilities for protocol 16 extensibility enabling to define new Diameter applications or modify 17 existing applications. This document is a companion document to the 18 Diameter Base protocol that further explains and clarifies the rules 19 to extend Diameter. It is meant as a guidelines document and 20 therefore as informative in nature. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on October 17, 2014. 39 Copyright Notice 41 Copyright (c) 2014 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 This document may contain material from IETF Documents or IETF 55 Contributions published or made publicly available before November 56 10, 2008. The person(s) controlling the copyright in some of this 57 material may not have granted the IETF Trust the right to allow 58 modifications of such material outside the IETF Standards Process. 59 Without obtaining an adequate license from the person(s) controlling 60 the copyright in such materials, this document may not be modified 61 outside the IETF Standards Process, and derivative works of it may 62 not be created outside the IETF Standards Process, except to format 63 it for publication as an RFC or to translate it into languages other 64 than English. 66 Table of Contents 68 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 69 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 70 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4 71 4. Reusing Existing Diameter Applications . . . . . . . . . . . 5 72 4.1. Adding a New Command . . . . . . . . . . . . . . . . . . 5 73 4.2. Deleting an Existing Command . . . . . . . . . . . . . . 6 74 4.3. Reusing Existing Commands . . . . . . . . . . . . . . . . 7 75 4.3.1. Adding AVPs to a Command . . . . . . . . . . . . . . 7 76 4.3.2. Deleting AVPs from a Command . . . . . . . . . . . . 9 77 4.4. Reusing Existing AVPs . . . . . . . . . . . . . . . . . . 9 78 4.4.1. Setting of the AVP Flags . . . . . . . . . . . . . . 10 79 4.4.2. Reuse of AVP of Type Enumerated . . . . . . . . . . . 10 80 5. Defining New Diameter Applications . . . . . . . . . . . . . 10 81 5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 10 82 5.2. Defining New Commands . . . . . . . . . . . . . . . . . . 10 83 5.3. Use of Application-Id in a Message . . . . . . . . . . . 11 84 5.4. Application-Specific Session State Machines . . . . . . . 12 85 5.5. Session-Id AVP and Session Management . . . . . . . . . . 12 86 5.6. Use of Enumerated Type AVPs . . . . . . . . . . . . . . . 13 87 5.7. Application-Specific Message Routing . . . . . . . . . . 15 88 5.8. Translation Agents . . . . . . . . . . . . . . . . . . . 15 89 5.9. End-to-End Application Capabilities Exchange . . . . . . 16 90 5.10. Diameter Accounting Support . . . . . . . . . . . . . . . 17 91 5.11. Diameter Security Mechanisms . . . . . . . . . . . . . . 18 92 6. Defining Generic Diameter Extensions . . . . . . . . . . . . 19 93 7. Guidelines for Registrations of Diameter Values . . . . . . . 20 94 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 95 9. Security Considerations . . . . . . . . . . . . . . . . . . . 22 96 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 22 97 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23 98 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 23 99 12.1. Normative References . . . . . . . . . . . . . . . . . . 23 100 12.2. Informative References . . . . . . . . . . . . . . . . . 23 101 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25 103 1. Introduction 105 The Diameter base protocol provides facilities to extend Diameter 106 (see Section 1.3 of [RFC6733]) to support new functionality. In the 107 context of this document, extending Diameter means one of the 108 following: 110 1. Addition of new functionality to an existing Diameter application 111 without defining a new application. 113 2. Addition of new functionality to an existing Diameter application 114 that requires the definition of a new application. 116 3. The definition of an entirely new Diameter application to offer 117 functionality not supported by existing applications. 119 4. The definition of a new generic functionality that can be reused 120 across different applications. 122 All of these choices are design decisions that can be done by any 123 combination of reusing existing or defining new commands, AVPs or AVP 124 values. However, application designers do not have complete freedom 125 when making their design. A number of rules have been defined in 126 [RFC6733] that place constraints on when an extension requires the 127 allocation of a new Diameter application identifier or a new command 128 code value. The objective of this document is the following: 130 o Clarify the Diameter extensibility rules as defined in the 131 Diameter base protocol. 133 o Discuss design choices and provide guidelines when defining new 134 applications. 136 o Present trade-off choices. 138 2. Terminology 140 This document reuses the terminology defined in [RFC6733]. 141 Additionally, the following terms and acronyms are used in this 142 application: 144 Application Extension of the Diameter base protocol [RFC6733] via 145 the addition of new commands or AVPs. Each application is 146 uniquely identified by an IANA-allocated application identifier 147 value. 149 Command Diameter request or answer carrying AVPs between Diameter 150 endpoints. Each command is uniquely identified by a IANA- 151 allocated command code value and is described by a Command Code 152 Format (CCF) for an application. 154 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 155 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 156 document are to be interpreted as described in [RFC2119]. 158 3. Overview 160 As designed, the Diameter base protocol [RFC6733] can be seen as a 161 two-layer protocol. The lower layer is mainly responsible for 162 managing connections between neighboring peers and for message 163 routing. The upper layer is where the Diameter applications reside. 164 This model is in line with a Diameter node having an application 165 layer and a peer-to-peer delivery layer. The Diameter base protocol 166 document defines the architecture and behavior of the message 167 delivery layer and then provides the framework for designing Diameter 168 applications on the application layer. This framework includes 169 definitions of application sessions and accounting support (see 170 Section 8 and Section 9 of [RFC6733]). Accordingly, a Diameter node 171 is seen in this document as a single instance of a Diameter message 172 delivery layer and one or more Diameter applications using it. 174 The Diameter base protocol is designed to be extensible and the 175 principles are described in the Section 1.3 of [RFC6733]. As a 176 summary, Diameter can be extended by: 178 1. Defining new AVP values 180 2. Creating new AVPs 182 3. Creating new commands 184 4. Creating new applications 186 As a main guiding principle, application designers SHOULD follow the 187 following recommendation: "try to re-use as much as possible!". It 188 will reduce the time to finalize specification writing, and it will 189 lead to a smaller implementation effort as well as reduce the need 190 for testing. In general, it is clever to avoid duplicate effort when 191 possible. 193 However, re-use is not appropriate when the existing functionality 194 does not fit the new requirement and/or the re-use leads to 195 ambiguity. 197 The impact on extending existing applications can be categorized into 198 two groups: 200 Minor Extension: Enhancing the functional scope of an existing 201 application by the addition of optional features to support. Such 202 enhancement has no backward compatibility issue with the existing 203 application. 205 A typical example would be the definition of a new optional AVP 206 for use in an existing command. Diameter implementations 207 supporting the existing application but not the new AVP will 208 simply ignore it, without consequences for the Diameter message 209 handling, as described in [RFC6733]. The standardization effort 210 will be fairly small. 212 Major Extension: Enhancing an application that requires the 213 definition of a new Diameter application. Such enhancement causes 214 backward compatibility issue with existing implementations 215 supporting the application. 217 Typical examples would be the creation of a new command for 218 providing functionality not supported by existing applications or 219 the definition of a new AVP to be carried in an existing command 220 with the M-bit set in the AVP flags (see Section 4.1 of [RFC6733] 221 for definition of the "M-bit"). For such extension, a significant 222 specification effort is required and a careful approach is 223 recommended. 225 4. Reusing Existing Diameter Applications 227 An existing application may need to be enhanced to fulfill new 228 requirements and these modifications can be at the command level and/ 229 or at the AVP level. The following sections describe the possible 230 modifications that can be performed on existing applications and 231 their related impact. 233 4.1. Adding a New Command 235 Adding a new command to an existing application is considered as a 236 major extension and requires a new Diameter application to be 237 defined. Adding a new command means either defining a completely new 238 command or importing the command's Command Code Format (CCF) syntax 239 from another application whereby the new application inherits some or 240 all of the functionality of the application where the command came 241 from. In the former case, the decision to create a new application 242 is straightforward since this is typically a result of adding a new 243 functionality that does not exist yet. For the latter, the decision 244 to create a new application will depend on whether importing the 245 command in a new application is more suitable than simply using the 246 existing application as it is in conjunction with any other 247 application. Therefore, a case by case study of each application 248 requirement SHOULD be applied. 250 An example considers the Diameter EAP application [RFC4072] and the 251 Diameter Network Access Server application [RFC7155]. When network 252 access authentication using EAP is required, the Diameter EAP 253 commands (Diameter-EAP-Request/Diameter-EAP-Answer) are used; 254 otherwise the Diameter Network Access Server application will be 255 used. When the Diameter EAP application is used, the accounting 256 exchanges defined in the Diameter Network Access Server may be used. 258 However, in general, it is difficult to come to a hard guideline, and 259 so a case-by-case study of each application requirement should be 260 applied. Before adding or importing a command, application designers 261 should consider the following: 263 o Can the new functionality be fulfilled by creating a new command 264 independent from any existing command? In this case, the 265 resulting new application and the existing application can work 266 independent of, but cooperating with each other. 268 o Can the existing command be reused without major extensions and 269 therefore without the need for the definition of a new 270 application, e.g. new functionality introduced by the creation of 271 new optional AVPs. 273 Note: Importing commands too liberally could result in a monolithic 274 and hard to manage application supporting too many different 275 features. 277 4.2. Deleting an Existing Command 279 Although this process is not typical, removing a command from an 280 application requires a new Diameter application to be defined and 281 then it is considered as a major extension. This is due to the fact 282 that the reception of the deleted command would systematically result 283 in a protocol error (i.e., DIAMETER_COMMAND_UNSUPPORTED). 285 It is unusual to delete an existing command from an application for 286 the sake of deleting it or the functionality it represents. This 287 normally indicates of a flawed design. An exception might be if the 288 intent of the deletion is to create a newer variance of the same 289 application that is somehow simpler than the application initially 290 specified. 292 4.3. Reusing Existing Commands 294 This section discusses rules in adding and/or deleting AVPs from an 295 existing command of an existing application. The cases described in 296 this section may not necessarily result in the creation of new 297 applications. 299 From a historical point of view, it is worth to note that there was a 300 strong recommendation to re-use existing commands in the [RFC3588] to 301 prevent rapid depletion of code values available for vendor-specific 302 commands. However, [RFC6733] has relaxed the allocation policy and 303 enlarged the range of available code values for vendor-specific 304 applications. Although reuse of existing commands is still 305 RECOMMENDED, protocol designers MAY consider defining a new command 306 when it provides a solution more suitable than the twisting of an 307 existing command's use and applications. 309 4.3.1. Adding AVPs to a Command 311 Based on the rules in [RFC6733], AVPs that are added to an existing 312 command can be categorized into: 314 o Mandatory (to understand) AVPs. As defined in [RFC6733], these 315 are AVPs with the M-bit flag set in this command, which means that 316 a Diameter node receiving them is required to understand not only 317 their values but also their semantics. Failure to do so will 318 cause an message handling error. 320 o Optional (to understand) AVPs. As defined in [RFC6733], these are 321 AVPs with the M-bit flag cleared in this command. A Diameter node 322 receiving these AVPs can simply ignore them if it does not support 323 them. 324 It is important to note that the definition given above are 325 independent of whether these AVPs are required or optional in the 326 command as specified by the command's Command Code Format (CCF) 327 syntax [RFC6733]. 329 NOTE: As stated in RFC6733, the M-bit setting for a given AVP is 330 relevant to an application and each command within that 331 application that includes the AVP. 333 The rules are strict in the case where the AVPs to be added in an 334 exiting command are mandatory to understand, i.e., they have the 335 M-bit set. A mandatory AVP MUST NOT be added to an existing command 336 without defining a new Diameter application, as stated in [RFC6733]. 337 This falls into the "Major Extensions" category. Despite the clarity 338 of the rule, ambiguity still arises when evaluating whether a new AVP 339 being added should be mandatory to begin with. Application designers 340 SHOULD consider the following questions when deciding about the M-bit 341 for a new AVP: 343 o Would it be required for the receiving side to be able to process 344 and understand the AVP and its content? 346 o Would the new AVPs change the state machine of the application? 348 o Would the presence of the new AVP lead to a different number of 349 round-trips, effectively changing the state machine of the 350 application? 352 o Would the new AVP be used to differentiate between old and new 353 variances of the same application whereby the two variances are 354 not backward compatible? 356 o Would the new AVP have duality in meaning, i.e., be used to carry 357 application-related information as well as to indicate that the 358 message is for a new application? 360 If the answer to at least one of the questions is "yes" then the 361 M-bit MUST be set for the new AVP. This list of questions is non- 362 exhaustive and other criteria MAY be taken into account in the 363 decision process. 365 If application designers are instead contemplating the use of 366 optional AVPs, i.e., with the M-bit cleared, then the following are 367 some of the pitfalls that SHOULD be avoided: 369 o Use of optional AVPs with intersecting meaning. One AVP has 370 partially the same usage and meaning as another AVP. The presence 371 of both can lead to confusion. 373 o An optional AVPs with dual purpose, i.e., to carry application 374 data as well as to indicate support for one or more features. 375 This has a tendency to introduce interpretation issues. 377 o Adding one or more optional AVPs and indicating (usually within 378 descriptive text for the command) that at least one of them has to 379 be present in the command. This essentially circumventing the 380 ABNF and is equivalent to adding a mandatory AVP to the command. 382 These practices generally result in interoperability issues and 383 SHOULD be avoided. 385 4.3.2. Deleting AVPs from a Command 387 Application designers may want to reuse an existing command but some 388 of the AVP present in the command's CCF syntax specification may be 389 irrelevant for the functionality foreseen to be supported by this 390 command. It may be then tempting to delete those AVPs from the 391 command. 393 The impacts of deleting an AVP from a command depends on its command 394 code format specification and M-bit setting: 396 o Deleting an AVP that is indicated as a required AVP (noted as 397 {AVP}) in the command's CCF syntax specification (regardless of 398 the M-bit setting). 400 In this case, a new command code and subsequently a new Diameter 401 application MUST be specified. 403 o Deleting an AVP, which has the M-bit set, and is indicated as 404 optional AVP (noted as [AVP]) in the command CCF) in the command's 405 CCF syntax specification. 407 No new command code has to be specified but the definition of a 408 new Diameter application is REQUIRED. 410 o Deleting an AVP, which has the M-bit cleared, and is indicated as 411 [ AVP ] in the command's CCF syntax specification. 413 In this case, the AVP can be deleted without consequences. 415 Application designers SHOULD attempt the reuse the command's CCF 416 syntax specification without modification and simply ignore (but not 417 delete) any optional AVP that will not be used. This is to maintain 418 compatibility with existing applications that will not know about the 419 new functionality as well as maintain the integrity of existing 420 dictionaries. 422 4.4. Reusing Existing AVPs 424 This section discusses rules in reusing existing AVP when reusing an 425 existing command or defining a new command in a new application. 427 4.4.1. Setting of the AVP Flags 429 When reusing AVPs in a new application, the AVP flag setting, such as 430 the mandatory flag ('M'-bit), has to be re-evaluated for a new 431 Diameter application and, if necessary, even for every command within 432 the application. In general, for AVPs defined outside of the 433 Diameter base protocol, the characteristics of an AVP are tied to its 434 role within an application and the commands. 436 All other AVP flags MUST remain unchanged. 438 4.4.2. Reuse of AVP of Type Enumerated 440 When reusing an AVP of type Enumerated in a command for a new 441 application, it is RECOMMENDED to avoid modifying the set of valid 442 values defined for this AVP. Modifying the set of Enumerated values 443 includes adding a value or deprecating the use of a value defined 444 initially for the AVP. Modifying the set of values will impact the 445 application defining this AVP and all the applications using this AVP 446 with potential interoperability issues. When the full range of 447 values defined for this Enumerated AVP is not suitable for the new 448 application, it is RECOMMENDED to define a new AVP to avoid backwards 449 compatibility issues with existing implementations. 451 5. Defining New Diameter Applications 453 5.1. Introduction 455 This section discusses the case where new applications have 456 requirements that cannot be fulfilled by existing applications and 457 would require definition of completely new commands, AVPs and/or AVP 458 values. Typically, there is little ambiguity about the decision to 459 create these types of applications. Some examples are the interfaces 460 defined for the IP Multimedia Subsystem of 3GPP, e.g., Cx/Dx 461 ([TS29.228] and [TS29.229]), Sh ([TS29.328] and [TS29.329]) etc. 463 Application designers SHOULD try to import existing AVPs and AVP 464 values for any newly defined commands. In certain cases where 465 accounting will be used, the models described in Section 5.10 SHOULD 466 also be considered. 468 Additional considerations are described in the following sections. 470 5.2. Defining New Commands 472 As a general recommendation, commands SHOULD not be defined from 473 scratch. It is instead RECOMMENDED to re-use an existing command 474 offering similar functionality and use it as a starting point. Code 475 re-use lead to a smaller implementation effort as well as reduce the 476 need for testing. 478 Moreover, the new command's CCF syntax specification SHOULD be 479 carefully defined when considering applicability and extensibility of 480 the application. If most of the AVPs contained in the command are 481 indicated as fixed or required, it might be difficult to reuse the 482 same command and therefore the same application in a slightly changed 483 environment. Defining a command with most of the AVPs indicated as 484 optional MUST NOT be seen as a sub-optimal design introducing too 485 much flexibility in the protocol. The protocol designers SHOULD only 486 clearly state the condition of presence of these AVPs and properly 487 define the corresponding behaviour of the Diameter nodes when these 488 AVPs are absent from the command. 490 NOTE: As a hint for protocol designers, it is not sufficient to just 491 look at the command's CCF syntax specification. It is also 492 necessary to carefully read through the accompanying text in the 493 specification. 495 In the same way, the CCF syntax specification SHOULD be defined such 496 that it will be possible to add any arbitrary optional AVPs with the 497 M-bit cleared (including vendor-specific AVPs) without modifying the 498 application. For this purpose, "* [AVP]" SHOULD be added in the 499 command's CCF, which allows the addition of any arbitrary AVP as 500 described in [RFC6733]. 502 5.3. Use of Application-Id in a Message 504 When designing new applications, application designers SHOULD specify 505 that the Application Id carried in all session-level messages is the 506 Application Id of the application using those messages. This 507 includes the session-level messages defined in Diameter base 508 protocol, i.e., RAR/RAA, STR/STA, ASR/ASA and possibly ACR/ACA in the 509 coupled accounting model, see Section 5.10. Some existing 510 specifications do not adhere to this rule for historical reasons. 511 However, this guidance SHOULD be followed by new applications to 512 avoid routing problems. 514 When a new application has been allocated with a new Application Id 515 and it also reuses existing commands with or without modifications, 516 the commands SHOULD use the newly allocated Application Id in the 517 header and in all relevant Application Id AVPs (Auth-Application-Id 518 or Acct-Application-Id) present in the commands message body. 520 Additionally, application designers using Vendor-Specific- 521 Application-Id AVP SHOULD not use the Vendor-Id AVP to further 522 dissect or differentiate the vendor-specification Application Id. 524 Diameter routing is not based on the Vendor-Id. As such, the Vendor- 525 Id SHOULD not be used as an additional input for routing or delivery 526 of messages. The Vendor-Id AVP is an informational AVP only and kept 527 for backward compatibility reasons. 529 5.4. Application-Specific Session State Machines 531 Section 8 of [RFC6733] provides session state machines for 532 authentication, authorization and accounting (AAA) services and these 533 session state machines are not intended to cover behavior outside of 534 AAA. If a new application cannot clearly be categorized into any of 535 these AAA services, it is RECOMMENDED that the application defines 536 its own session state machine. Support for server-initiated request 537 is a clear example where an application-specific session state 538 machine would be needed, for example, the Rw interface for ITU-T push 539 model (cf.[Q.3303.3]). 541 5.5. Session-Id AVP and Session Management 543 Diameter applications are usually designed with the aim of managing 544 user sessions (e.g., Diameter network access session (NASREQ) 545 application [RFC4005]) or specific service access session (e.g., 546 Diameter SIP application [RFC4740]). In the Diameter base protocol, 547 session state is referenced using the Session-Id AVP. All Diameter 548 messages that use the same Session-Id will be bound to the same 549 session. Diameter-based session management also implies that both 550 Diameter client and server (and potentially proxy agents along the 551 path) maintain session state information. 553 However, some applications may not need to rely on the Session-Id to 554 identify and manage sessions because other information can be used 555 instead to correlate Diameter messages. Indeed, the User-Name AVP or 556 any other specific AVP can be present in every Diameter message and 557 used therefore for message correlation. Some applications might not 558 require the notion of Diameter session concept at all. For such 559 applications, the Auth-Session-State AVP is usually set to 560 NO_STATE_MAINTAINED in all Diameter messages and these applications 561 are therefore designed as a set of stand-alone transactions. Even if 562 an explicit access session termination is required, application- 563 specific commands are defined and used instead of the Session- 564 Termination-Request/Answer (STR/STA) or Abort-Session-Request/Answer 565 (ASR/ASA) defined in the Diameter base protocol [RFC6733]. In such a 566 case, the Session-Id is not significant. 568 Based on these considerations, protocol designers SHOULD carefully 569 appraise whether the application currently defined relies on its own 570 session management concept or whether the Session-Id defined in the 571 Diameter base protocol would be used for correlation of messages 572 related to the same session. If not, the protocol designers MAY 573 decide to define application commands without the Session-Id AVP. If 574 any session management concept is supported by the application, the 575 application documentation MUST clearly specify how the session is 576 handled between client and server (as possibly Diameter agents in the 577 path). 579 5.6. Use of Enumerated Type AVPs 581 The type Enumerated was initially defined to provide a list of valid 582 values for an AVP with their respective interpretation described in 583 the specification. For instance, AVPs of type Enumerated can be used 584 to provide further information on the reason for the termination of a 585 session or a specific action to perform upon the reception of the 586 request. 588 As described in the section 4.4.2 above, defining an AVP of type 589 Enumerated presents some limitations in term of extensibility and 590 reusability. Indeed, the finite set of valid values defined at the 591 definition of the AVP of type Enumerated cannot be modified in 592 practice without causing backward compatibility issues with existing 593 implementations. As a consequence, AVPs of Type Enumerated MUST NOT 594 be extended by adding new values to support new capabilities. 595 Diameter protocol designers SHOULD carefully consider before defining 596 an Enumerated AVP whether the set of values will remain unchanged or 597 new values may be required in a near future. If such extension is 598 foreseen or cannot be avoided, it is RECOMMENED to rather define AVPs 599 of type Unsigned32 or Unsigned64 in which the data field would 600 contain an address space representing "values" that would have the 601 same use of Enumerated values. 603 For illustration, an AVP describing possible access networks would be 604 defined as follow: 606 Access-Network-Type AVP (XXX) is of type Unsigned32 and contains an 607 32-bit address space representing types of access networks. This 608 application defines the following classes of access networks, all 609 identified by the thousands digit in the decimal notation: 611 o 1xxx (Mobile Access Networks) 613 o 2xxx (Fixed Access Network) 615 o 3xxx (Wireless Access Networks) 617 Values that fall within the Mobile Access Networks category are used 618 to inform a peer that a request has been sent for a user attached to 619 a mobile access networks. The following values are defined in this 620 application: 622 1001: 3GPP-GERAN 624 TBD. 626 1002: 3GPP-UTRAN-FDD 628 TBD. 630 Unlike Enumerated AVP, any new value can be added in the address 631 space defined by this Unsigned32 AVP without modifying the definition 632 of the AVP. There is therefore no risk of backward compatibility 633 issue, especially when intermediate nodes may be present between 634 Diameter endpoints. 636 In the same line, AVPs of type Enumerated are too often used as a 637 simple Boolean flag, indicating for instance a specific permission or 638 capability, and therefore only two values are defined, e.g., TRUE/ 639 FALSE, AUTORIZED/UNAUTHORIZED or SUPPORTED/UNSUPPORTED. This is a 640 sub-optimal design since it limits the extensibility of the 641 application: any new capability/permission would have to be supported 642 by a new AVP or new Enumerated value of the already defined AVP, with 643 the backward compatibility issues described above. Instead of using 644 an Enumerated AVP for a Boolean flag, protocol designers SHOULD use 645 AVPs of type Unsigned32 or Unsigned64 AVP in which the data field 646 would be defined as bit mask whose bit settings are described in the 647 relevant Diameter application specification. Such AVPs can be reused 648 and extended without major impact on the Diameter application. The 649 bit mask SHOULD leave room for future additions. Examples of AVPs 650 that use bit masks are the Session-Binding AVP defined in [RFC6733] 651 and the MIP6-Feature-Vector AVP defined in [RFC5447]. 653 5.7. Application-Specific Message Routing 655 As described in [RFC6733], a Diameter request that needs to be sent 656 to a home server serving a specific realm, but not to a specific 657 server (such as the first request of a series of round trips), will 658 contain a Destination-Realm AVP and no Destination-Host AVP. 660 For such a request, the message routing usually relies only on the 661 Destination-Realm AVP and the Application Id present in the request 662 message header. However, some applications may need to rely on the 663 User-Name AVP or any other application-specific AVP present in the 664 request to determine the final destination of a request, e.g., to 665 find the target AAA server hosting the authorization information for 666 a given user when multiple AAA servers are addressable in the realm. 668 In such a context, basic routing mechanisms described in [RFC6733] 669 are not fully suitable, and additional application-level routing 670 mechanisms MUST be described in the application documentation to 671 provide such specific AVP-based routing. Such functionality will be 672 basically hosted by an application-specific proxy agent that will be 673 responsible for routing decisions based on the received specific 674 AVPs. 676 Examples of such application-specific routing functions can be found 677 in the Cx/Dx applications ([TS29.228] and [TS29.229]) of the 3GPP IP 678 Multimedia Subsystem, in which the proxy agent (Subscriber Location 679 Function aka SLF) uses specific application-level identities found in 680 the request to determine the final destination of the message. 682 Whatever the criteria used to establish the routing path of the 683 request, the routing of the answer MUST follow the reverse path of 684 the request, as described in [RFC6733], with the answer being sent to 685 the source of the received request, using transaction states and hop- 686 by-hop identifier matching. In particular, this ensures that the 687 Diameter Relay or Proxy agents in the request routing path will be 688 able to release the transaction state upon receipt of the 689 corresponding answer, avoiding unnecessary failover. Application 690 designers SHOULD NOT modify the answer-routing principles described 691 in [RFC6733] when defining a new application. 693 5.8. Translation Agents 695 As defined in [RFC6733], a translation agent is a device that 696 provides interworking between Diameter and another AAA protocol, such 697 as RADIUS . 699 In the case of RADIUS, it was initially thought that defining the 700 translation function would be straightforward by adopting few basic 701 principles, e.g., by the use of a shared range of code values for 702 RADIUS attributes and Diameter AVPs. Guidelines for implementing a 703 RADIUS-Diameter translation agent were put into the Diameter NASREQ 704 Application ([RFC4005]). 706 However, it was acknowledged that such translation mechanism was not 707 so obvious and deeper protocol analysis was required to ensure 708 efficient interworking between RADIUS and Diameter. Moreover, the 709 interworking requirements depend on the functionalities provided by 710 the Diameter application under specification, and a case-by-case 711 analysis is required. As a consequence, all the material related to 712 RADIUS-to-Diameter translation is removed from the new version of the 713 Diameter NASREQ application specification [RFC4005bis], (see 714 [RFC7155]) which deprecates the RFC4005 ([RFC4005]). 716 Therefore, protocol designers SHOULD NOT assume the availability of a 717 "standard" Diameter-to-RADIUS gateways agent when planning to 718 interoperate with the RADIUS infrastructure. They SHOULD specify the 719 required translation mechanism along with the Diameter application, 720 if needed. This recommendation applies for any kind of translation. 722 5.9. End-to-End Application Capabilities Exchange 724 New Diameter applications can rely on optional AVPs to exchange 725 application-specific capabilities and features. These AVPs can be 726 exchanged on an end-to-end basis at the application layer. Examples 727 of this can be found with the MIP6-Feature-Vector AVP in [RFC5447] 728 and the QoS-Capability AVP in [RFC5777]. 730 The end-to-end capabilities AVPs formalize the addition of new 731 optional functionality to existing applications by announcing support 732 for it. Applications that do not understand these AVPs can discard 733 them upon receipt. Receivers of these AVPs can discover the 734 additional functionality supported by the end-point originating the 735 request and behave accordingly when processing the request. Senders 736 of these AVPs can safely assume the receiving end-point does not 737 support any functionality carried by the AVP if it is not present in 738 corresponding response. This is useful in cases where deployment 739 choices are offered, and the generic design can be made available for 740 a number of applications. 742 When used in a new application, protocol designers SHOULD clearly 743 specify this end-to-end capabilities exchange and the corresponding 744 behaviour of the Diameter nodes supporting the application. 746 It is also important to note that this end-to-end capabilities 747 exchange relying on the use of optional AVPs is not meant as a 748 generic mechanism to support extensibility of Diameter applications 749 with arbitrary functionality. When the added features drastically 750 change the Diameter application or when Diameter agents must be 751 upgraded to support the new features, a new application SHOULD be 752 defined. 754 5.10. Diameter Accounting Support 756 Accounting can be treated as an auxiliary application that is used in 757 support of other applications. In most cases, accounting support is 758 required when defining new applications. This document provides two 759 possible models for using accounting: 761 Split Accounting Model: 763 In this model, the accounting messages will use the Diameter base 764 accounting Application Id (value of 3). The design implication 765 for this is that the accounting is treated as an independent 766 application, especially for Diameter routing. This means that 767 accounting commands emanating from an application may be routed 768 separately from the rest of the other application messages. This 769 may also imply that the messages end up in a central accounting 770 server. A split accounting model is a good design choice when: 772 * The application itself does not define its own accounting 773 commands. 775 * The overall system architecture permits the use of centralized 776 accounting for one or more Diameter applications. 778 Centralizing accounting may have advantages but there are also 779 drawbacks. The model assumes that the accounting server can 780 differentiate received accounting messages. Since the received 781 accounting messages can be for any application and/or service, the 782 accounting server MUST have a method to match accounting messages 783 with applications and/or services being accounted for. This may 784 mean defining new AVPs, checking the presence, absence or contents 785 of existing AVPs, or checking the contents of the accounting 786 record itself. One of these means could be to insert into the 787 request sent to the accounting server an Auth-Application-Id AVP 788 containing the identifier of the application for which the 789 accounting request is sent. But in general, there is no clean and 790 generic scheme for sorting these messages. Therefore, the use of 791 this model is NOT RECOMMENDED when all received accounting 792 messages cannot be clearly identified and sorted. For most cases, 793 the use of Coupled Accounting Model is RECOMMENDED. 795 Coupled Accounting Model: 797 In this model, the accounting messages will use the Application Id 798 of the application using the accounting service. The design 799 implication for this is that the accounting messages are tightly 800 coupled with the application itself; meaning that accounting 801 messages will be routed like the other application messages. It 802 would then be the responsibility of the application server 803 (application entity receiving the ACR message) to send the 804 accounting records carried by the accounting messages to the 805 proper accounting server. The application server is also 806 responsible for formulating a proper response (ACA). A coupled 807 accounting model is a good design choice when: 809 * The system architecture or deployment does not provide an 810 accounting server that supports Diameter. Consequently, the 811 application server MUST be provisioned to use a different 812 protocol to access the accounting server, e.g., via LDAP, SOAP 813 etc. This case includes the support of older accounting 814 systems that are not Diameter aware. 816 * The system architecture or deployment requires that the 817 accounting service for the specific application should be 818 handled by the application itself. 820 In all cases above, there will generally be no direct Diameter 821 access to the accounting server. 823 These models provide a basis for using accounting messages. 824 Application designers may obviously deviate from these models 825 provided that the factors being addressed here have also been taken 826 into account. An application MAY define a new set of commands to 827 carry application-specific accounting records but it is NOT 828 RECOMMENDED to do so. 830 5.11. Diameter Security Mechanisms 832 As specified in [RFC6733], the Diameter message exchange SHOULD be 833 secured between neighboring Diameter peers using TLS/TCP or DTLS/ 834 SCTP. However, IPsec MAY also be deployed to secure communication 835 between Diameter peers. When IPsec is used instead of TLS or DTLS, 836 the following recommendations apply. 838 IPsec ESP [RFC4301] in transport mode with non-null encryption and 839 authentication algorithms MUST be used to provide per-packet 840 authentication, integrity protection and confidentiality, and support 841 the replay protection mechanisms of IPsec. IKEv2 [RFC5996] SHOULD be 842 used for performing mutual authentication and for establishing and 843 maintaining security associations (SAs). 845 IKEv1 [RFC2409] was used with RFC 3588 [RFC3588] and for easier 846 migration from IKEv1 based implementations both RSA digital 847 signatures and pre-shared keys SHOULD be supported in IKEv2. 848 However, if IKEv1 is used, implementers SHOULD follow the guidelines 849 given in Section 13.1 of RFC 3588 [RFC3588]. 851 6. Defining Generic Diameter Extensions 853 Generic Diameter extensions are AVPs, commands or applications that 854 are designed to support other Diameter applications. They are 855 auxiliary applications meant to improve or enhance the Diameter 856 protocol itself or Diameter applications/functionality. Some 857 examples include the extensions to support realm-based redirection of 858 Diameter requests (see [RFC7075]), convey a specific set of priority 859 parameters influencing the distribution of resources (see [RFC6735]), 860 and the support for QoS AVPs (see [RFC5777]). 862 Since generic extensions may cover many aspects of Diameter and 863 Diameter applications, it is not possible to enumerate all scenarios. 864 However, some of the most common considerations are as follows: 866 Backward Compatibility: 868 When defining generic extensions designed to be supported by 869 existing Diameter applications, protocol designers MUST consider 870 the potential impacts of the introduction of the new extension on 871 the behavior of node that would not be yet upgraded to support/ 872 understand this new extension. Designers MUST also ensure that 873 new extensions do not break expected message delivery layer 874 behavior. 876 Forward Compatibility: 878 Protocol designers MUST ensure that their design will not 879 introduce undue restrictions for future applications. 881 Trade-off in Signaling: 883 Designers may have to choose between the use of optional AVPs 884 piggybacked onto existing commands versus defining new commands 885 and applications. Optional AVPs are simpler to implement and may 886 not need changes to existing applications. However, this ties the 887 sending of extension data to the application's transmission of a 888 message. This has consequences if the application and the 889 extensions have different timing requirements. The use of 890 commands and applications solves this issue, but the trade-off is 891 the additional complexity of defining and deploying a new 892 application. It is left up to the designer to find a good balance 893 among these trade-offs based on the requirements of the extension. 895 In practice, generic extensions often use optional AVPs because they 896 are simple and non-intrusive to the application that would carry 897 them. Peers that do not support the generic extensions need not 898 understand nor recognize these optional AVPs. However, it is 899 RECOMMENDED that the authors of the extension specify the context or 900 usage of the optional AVPs. As an example, in the case that the AVP 901 can be used only by a specific set of applications then the 902 specification MUST enumerate these applications and the scenarios 903 when the optional AVPs will be used. In the case where the optional 904 AVPs can be carried by any application, it SHOULD be sufficient to 905 specify such a use case and perhaps provide specific examples of 906 applications using them. 908 In most cases, these optional AVPs piggybacked by applications would 909 be defined as a Grouped AVP and it would encapsulate all the 910 functionality of the generic extension. In practice, it is not 911 uncommon that the Grouped AVP will encapsulate an existing AVP that 912 has previously been defined as mandatory ('M'-bit set) e.g., 3GPP IMS 913 Cx/Dx interfaces ([TS29.228] and [TS29.229]). 915 7. Guidelines for Registrations of Diameter Values 917 As summarized in the Section 3 of this document and further described 918 in the Section 1.3 of [RFC6733], there are four main ways to extend 919 Diameter. The process for defining new functionality slightly varies 920 based on the different extensions. This section provides protocol 921 designers with some guidance regarding the definition of values for 922 possible Diameter extensions and the necessary interaction with IANA 923 to register the new functionality. 925 a. Defining new AVP values 927 The specifications defining AVPs and AVP values MUST provide 928 guidance for defining new values and the corresponding policy for 929 adding these values. For example, the RFC 5777 [RFC5777] defines 930 the Treatment-Action AVP which contains a list of valid values 931 corresponding to pre-defined actions (drop, shape, mark, permit). 932 This set of values can be extended following the Specification 933 Required policy defined in [RFC5226]. As a second example, the 934 Diameter base specification [RFC6733] defines the Result-Code AVP 935 that contains a 32-bit address space used to identity possible 936 errors. According to the Section 11.3.2 of [RFC6733], new values 937 can be assigned by IANA via an IETF Review process [RFC5226]. 939 b. Creating new AVPs 941 Two different types of AVP Codes namespaces can be used to create 942 a new AVPs: 944 * IETF AVP Codes namespace; 946 * Vendor-specific AVP Codes namespace. 948 In the latter case, a vendor needs to be first assigned by IANA 949 with a private enterprise number, which can be used within the 950 Vendor-Id field of the vendor-specific AVP. This enterprise 951 number delimits a private namespace in which the vendor is 952 responsible for vendor-specific AVP code value assignment. The 953 absence of a Vendor-Id or a Vendor-Id value of zero (0) in the AVP 954 header identifies standard AVPs from the IETF AVP Codes namespace 955 managed by IANA. The allocation of code values from the IANA- 956 managed namespace is conditioned by an Expert Review of the 957 specification defining the AVPs or an IETF review if a block of 958 AVPs needs to be assigned. Moreover, the remaining bits of the 959 AVP Flags field of the AVP header are also assigned via Standard 960 Action if the creation of new AVP Flags is desired. 962 c. Creating new commands 964 Unlike the AVP Code namespace, the Command Code namespace is flat 965 but the range of values is subdivided into three chunks with 966 distinct IANA registration policies: 968 * A range of standard Command Code values that are allocated via 969 IETF review; 971 * A range of vendor-specific Command Code values that are 972 allocated on a First-Come/First-Served basis; 974 * A range of values reserved only for experimental and testing 975 purposes. 977 As for AVP Flags, the remaining bits of the Command Flags field of 978 the Diameter header are also assigned via a Standards Action to 979 create new Command Flags if required. 981 d. Creating new applications 983 Similarly to the Command Code namespace, the Application-Id 984 namespace is flat but divided into two distinct ranges: 986 * A range of values reserved for standard Application-Ids 987 allocated after Expert Review of the specification defining the 988 standard application; 990 * A range for values for vendor specific applications, allocated 991 by IANA on a First-Come/First-Serve basis. 993 The IANA AAA parameters page can be found at http://www.iana.org/ 994 assignments/aaa-parameters/aaa-parameters.xml and the enterprise 995 number IANA page is available at http://www.iana.org/assignments/ 996 enterprise-numbers. More details on the policies followed by IANA 997 for namespace management (e.g. First-Come/First-Served, Expert 998 Review, IETF Review, etc.) can be found in [RFC5226]. 1000 NOTE: 1001 When the same functionality/extension is used by more than one 1002 vendor, it is RECOMMENDED to define a standard extension. 1003 Moreover, a vendor-specific extension SHOULD be registered to 1004 avoid interoperability issues in the same network. With this aim, 1005 the registration policy of vendor-specific extension has been 1006 simplified with the publication of [RFC6733] and the namespace 1007 reserved for vendor-specific extensions is large enough to avoid 1008 exhaustion. 1010 8. IANA Considerations 1012 This document does not require actions by IANA. 1014 9. Security Considerations 1016 This document provides guidelines and considerations for extending 1017 Diameter and Diameter applications. Although such an extension may 1018 be related to a security functionality, the document does not 1019 explicitly give guidance on enhancing Diameter with respect to 1020 security. 1022 10. Contributors 1024 The content of this document was influenced by a design team created 1025 to revisit the Diameter extensibility rules. The team was formed in 1026 February 2008 and finished its work in June 2008. Except the 1027 authors, the design team members were: 1029 o Avi Lior 1031 o Glen Zorn 1033 o Jari Arkko 1034 o Jouni Korhonen 1036 o Mark Jones 1038 o Tolga Asveren 1040 o Glenn McGregor 1042 o Dave Frascone 1044 We would like to thank Tolga Asveren, Glenn McGregor, and John 1045 Loughney for their contributions as co-authors to earlier versions of 1046 this document. 1048 11. Acknowledgments 1050 We greatly appreciate the insight provided by Diameter implementers 1051 who have highlighted the issues and concerns being addressed by this 1052 document. The authors would also like to thank Jean Mahoney, Ben 1053 Campbell, Sebastien Decugis and Benoit Claise for their invaluable 1054 detailed reviews and comments on this document. 1056 12. References 1058 12.1. Normative References 1060 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1061 Requirement Levels", BCP 14, RFC 2119, March 1997. 1063 [RFC6733] Fajardo, V., Arkko, J., Loughney, J., and G. Zorn, 1064 "Diameter Base Protocol", RFC 6733, October 2012. 1066 12.2. Informative References 1068 [Q.3303.3] 1069 3rd Generation Partnership Project, "ITU-T Recommendation 1070 Q.3303.3, "Resource control protocol no. 3 (rcp3): 1071 Protocol at the Rw interface between the Policy Decision 1072 Physical Entity (PD-PE) and the Policy Enforcement 1073 Physical Entity (PE-PE): Diameter"", 2008. 1075 [RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange 1076 (IKE)", RFC 2409, November 1998. 1078 [RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. 1079 Arkko, "Diameter Base Protocol", RFC 3588, September 2003. 1081 [RFC4005] Calhoun, P., Zorn, G., Spence, D., and D. Mitton, 1082 "Diameter Network Access Server Application", RFC 4005, 1083 August 2005. 1085 [RFC4072] Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible 1086 Authentication Protocol (EAP) Application", RFC 4072, 1087 August 2005. 1089 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 1090 Internet Protocol", RFC 4301, December 2005. 1092 [RFC4740] Garcia-Martin, M., Belinchon, M., Pallares-Lopez, M., 1093 Canales-Valenzuela, C., and K. Tammi, "Diameter Session 1094 Initiation Protocol (SIP) Application", RFC 4740, November 1095 2006. 1097 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1098 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 1099 May 2008. 1101 [RFC5447] Korhonen, J., Bournelle, J., Tschofenig, H., Perkins, C., 1102 and K. Chowdhury, "Diameter Mobile IPv6: Support for 1103 Network Access Server to Diameter Server Interaction", RFC 1104 5447, February 2009. 1106 [RFC5777] Korhonen, J., Tschofenig, H., Arumaithurai, M., Jones, M., 1107 and A. Lior, "Traffic Classification and Quality of 1108 Service (QoS) Attributes for Diameter", RFC 5777, February 1109 2010. 1111 [RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, 1112 "Internet Key Exchange Protocol Version 2 (IKEv2)", RFC 1113 5996, September 2010. 1115 [RFC6733] Fajardo, V., Arkko, J., Loughney, J., and G. Zorn, 1116 "Diameter Base Protocol", RFC 6733, October 2012. 1118 [RFC6735] Carlberg, K. and T. Taylor, "Diameter Priority Attribute- 1119 Value Pairs", RFC 6735, October 2012. 1121 [RFC7075] Tsou, T., Hao, R., and T. Taylor, "Realm-Based Redirection 1122 In Diameter", RFC 7075, November 2013. 1124 [RFC7155] Zorn, G., "Diameter Network Access Server Application", 1125 RFC 7155, April 2014. 1127 [TS29.228] 1128 3rd Generation Partnership Project, "3GPP TS 29.228; 1129 Technical Specification Group Core Network and Terminals; 1130 IP Multimedia (IM) Subsystem Cx and Dx Interfaces; 1131 Signalling flows and message contents", 1132 . 1134 [TS29.229] 1135 3rd Generation Partnership Project, "3GPP TS 29.229; 1136 Technical Specification Group Core Network and Terminals; 1137 Cx and Dx interfaces based on the Diameter protocol; 1138 Protocol details", 1139 . 1141 [TS29.328] 1142 3rd Generation Partnership Project, "3GPP TS 29.328; 1143 Technical Specification Group Core Network and Terminals; 1144 IP Multimedia (IM) Subsystem Sh interface; signalling 1145 flows and message content", 1146 . 1148 [TS29.329] 1149 3rd Generation Partnership Project, "3GPP TS 29.329; 1150 Technical Specification Group Core Network and Terminals; 1151 Sh Interface based on the Diameter protocol; Protocol 1152 details", 1153 . 1155 Authors' Addresses 1157 Lionel Morand (editor) 1158 Orange Labs 1159 38/40 rue du General Leclerc 1160 Issy-Les-Moulineaux Cedex 9 92794 1161 France 1163 Phone: +33145296257 1164 Email: lionel.morand@orange.com 1166 Victor Fajardo 1167 Independent 1169 Email: vf0213@gmail.com 1170 Hannes Tschofenig 1171 Nokia Siemens Networks 1172 Linnoitustie 6 1173 Espoo 02600 1174 Finland 1176 Phone: +358 (50) 4871445 1177 Email: Hannes.Tschofenig@gmx.net 1178 URI: http://www.tschofenig.priv.at