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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: March 8, 2015 Fluke Networks 6 H. Tschofenig 8 September 4, 2014 10 Diameter Applications Design Guidelines 11 draft-ietf-dime-app-design-guide-27 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. Furthermore, this document provides guidelines 20 to Diameter application designers reusing/defining Diameter 21 applications or creating generic Diameter extensions. 23 Status of This Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at http://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on March 8, 2015. 40 Copyright Notice 42 Copyright (c) 2014 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 This document may contain material from IETF Documents or IETF 56 Contributions published or made publicly available before November 57 10, 2008. The person(s) controlling the copyright in some of this 58 material may not have granted the IETF Trust the right to allow 59 modifications of such material outside the IETF Standards Process. 60 Without obtaining an adequate license from the person(s) controlling 61 the copyright in such materials, this document may not be modified 62 outside the IETF Standards Process, and derivative works of it may 63 not be created outside the IETF Standards Process, except to format 64 it for publication as an RFC or to translate it into languages other 65 than English. 67 Table of Contents 69 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 70 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 71 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4 72 4. Reusing Existing Diameter Applications . . . . . . . . . . . 6 73 4.1. Adding a New Command . . . . . . . . . . . . . . . . . . 6 74 4.2. Deleting an Existing Command . . . . . . . . . . . . . . 7 75 4.3. Reusing Existing Commands . . . . . . . . . . . . . . . . 7 76 4.3.1. Adding AVPs to a Command . . . . . . . . . . . . . . 8 77 4.3.2. Deleting AVPs from a Command . . . . . . . . . . . . 9 78 4.3.3. Changing the Flags Setting of AVP in existing 79 Commands . . . . . . . . . . . . . . . . . . . . . . 10 80 4.4. Reusing Existing AVPs . . . . . . . . . . . . . . . . . . 10 81 4.4.1. Setting of the AVP Flags . . . . . . . . . . . . . . 11 82 4.4.2. Reuse of AVP of Type Enumerated . . . . . . . . . . . 11 83 5. Defining New Diameter Applications . . . . . . . . . . . . . 11 84 5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 11 85 5.2. Defining New Commands . . . . . . . . . . . . . . . . . . 12 86 5.3. Use of Application-Id in a Message . . . . . . . . . . . 12 87 5.4. Application-Specific Session State Machines . . . . . . . 13 88 5.5. Session-Id AVP and Session Management . . . . . . . . . . 13 89 5.6. Use of Enumerated Type AVPs . . . . . . . . . . . . . . . 14 90 5.7. Application-Specific Message Routing . . . . . . . . . . 16 91 5.8. Translation Agents . . . . . . . . . . . . . . . . . . . 17 92 5.9. End-to-End Application Capabilities Exchange . . . . . . 18 93 5.10. Diameter Accounting Support . . . . . . . . . . . . . . . 18 94 5.11. Diameter Security Mechanisms . . . . . . . . . . . . . . 20 95 6. Defining Generic Diameter Extensions . . . . . . . . . . . . 20 96 7. Guidelines for Registrations of Diameter Values . . . . . . . 22 97 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 98 9. Security Considerations . . . . . . . . . . . . . . . . . . . 24 99 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 24 100 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 25 101 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 25 102 12.1. Normative References . . . . . . . . . . . . . . . . . . 25 103 12.2. Informative References . . . . . . . . . . . . . . . . . 25 104 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27 106 1. Introduction 108 The Diameter base protocol [RFC6733] is intended to provide an 109 Authentication, Authorization, and Accounting (AAA) framework for 110 applications such as network access or IP mobility in both local and 111 roaming situations. This protocol provides the ability for Diameter 112 peers to exchange messages carrying data in the form of Attribute- 113 Value Pairs (AVPs). 115 The Diameter base protocol provides facilities to extend Diameter 116 (see Section 1.3 of [RFC6733]) to support new functionality. In the 117 context of this document, extending Diameter means one of the 118 following: 120 1. Addition of new functionality to an existing Diameter application 121 without defining a new application. 123 2. Addition of new functionality to an existing Diameter application 124 that requires the definition of a new application. 126 3. The definition of an entirely new Diameter application to offer 127 functionality not supported by existing applications. 129 4. The definition of a new generic functionality that can be reused 130 across different applications. 132 All of these choices are design decisions that can be done by any 133 combination of reusing existing or defining new commands, AVPs or AVP 134 values. However, application designers do not have complete freedom 135 when making their design. A number of rules have been defined in 136 [RFC6733] that place constraints on when an extension requires the 137 allocation of a new Diameter application identifier or a new command 138 code value. The objective of this document is the following: 140 o Clarify the Diameter extensibility rules as defined in the 141 Diameter base protocol. 143 o Discuss design choices and provide guidelines when defining new 144 applications. 146 o Present trade-off choices. 148 2. Terminology 150 This document reuses the terminology defined in [RFC6733]. 151 Additionally, the following terms and acronyms are used in this 152 application: 154 Application Extension of the Diameter base protocol [RFC6733] via 155 the addition of new commands or AVPs. Each application is 156 uniquely identified by an IANA-allocated application identifier 157 value. 159 Command Diameter request or answer carrying AVPs between Diameter 160 endpoints. Each command is uniquely identified by a IANA- 161 allocated command code value and is described by a Command Code 162 Format (CCF) for an application. 164 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 165 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 166 document are to be interpreted as described in [RFC2119]. 168 3. Overview 170 As designed, the Diameter base protocol [RFC6733] can be seen as a 171 two-layer protocol. The lower layer is mainly responsible for 172 managing connections between neighboring peers and for message 173 routing. The upper layer is where the Diameter applications reside. 174 This model is in line with a Diameter node having an application 175 layer and a peer-to-peer delivery layer. The Diameter base protocol 176 document defines the architecture and behavior of the message 177 delivery layer and then provides the framework for designing Diameter 178 applications on the application layer. This framework includes 179 definitions of application sessions and accounting support (see 180 Section 8 and Section 9 of [RFC6733]). Accordingly, a Diameter node 181 is seen in this document as a single instance of a Diameter message 182 delivery layer and one or more Diameter applications using it. 184 The Diameter base protocol is designed to be extensible and the 185 principles are described in the Section 1.3 of [RFC6733]. As a 186 summary, Diameter can be extended by: 188 1. Defining new AVP values 190 2. Creating new AVPs 191 3. Creating new commands 193 4. Creating new applications 195 As a main guiding principle, application designers SHOULD follow the 196 following recommendation: "try to re-use as much as possible!". It 197 will reduce the time to finalize specification writing, and it will 198 lead to a smaller implementation effort as well as reduce the need 199 for testing. In general, it is clever to avoid duplicate effort when 200 possible. 202 However, re-use is not appropriate when the existing functionality 203 does not fit the new requirement and/or the re-use leads to 204 ambiguity. 206 The impact on extending existing applications can be categorized into 207 two groups: 209 Minor Extension: Enhancing the functional scope of an existing 210 application by the addition of optional features to support. Such 211 enhancement has no backward compatibility issue with the existing 212 application. 214 A typical example would be the definition of a new optional AVP 215 for use in an existing command. Diameter implementations 216 supporting the existing application but not the new AVP will 217 simply ignore it, without consequences for the Diameter message 218 handling, as described in [RFC6733]. The standardization effort 219 will be fairly small. 221 Major Extension: Enhancing an application that requires the 222 definition of a new Diameter application. Such enhancement causes 223 backward compatibility issue with existing implementations 224 supporting the application. 226 Typical examples would be the creation of a new command for 227 providing functionality not supported by existing applications or 228 the definition of a new AVP to be carried in an existing command 229 with the M-bit set in the AVP flags (see Section 4.1 of [RFC6733] 230 for definition of the "M-bit"). For such extension, a significant 231 specification effort is required and a careful approach is 232 recommended. 234 4. Reusing Existing Diameter Applications 236 An existing application may need to be enhanced to fulfill new 237 requirements and these modifications can be at the command level and/ 238 or at the AVP level. The following sections describe the possible 239 modifications that can be performed on existing applications and 240 their related impact. 242 4.1. Adding a New Command 244 Adding a new command to an existing application is considered as a 245 major extension and requires a new Diameter application to be 246 defined, as stated in the Section 1.3.4 of [RFC6733]. The need for a 247 new application is because a Diameter node that is not upgraded to 248 support the new command(s) within the (existing) application would 249 reject any unknown command with the protocol error 250 DIAMETER_COMMAND_UNSUPPORTED and cause the failure of the 251 transaction. The new application ensures that Diameter nodes only 252 receive commands within the context of applications they support. 254 Adding a new command means either defining a completely new command 255 or importing the command's Command Code Format (CCF) syntax from 256 another application whereby the new application inherits some or all 257 of the functionality of the application where the command came from. 258 In the former case, the decision to create a new application is 259 straightforward since this is typically a result of adding a new 260 functionality that does not exist yet. For the latter, the decision 261 to create a new application will depend on whether importing the 262 command in a new application is more suitable than simply using the 263 existing application as it is in conjunction with any other 264 application. Therefore, a case by case study of each application 265 requirement SHOULD be applied. 267 An example considers the Diameter EAP application [RFC4072] and the 268 Diameter Network Access Server application [RFC7155]. When network 269 access authentication using EAP is required, the Diameter EAP 270 commands (Diameter-EAP-Request/Diameter-EAP-Answer) are used; 271 otherwise the Diameter Network Access Server application will be 272 used. When the Diameter EAP application is used, the accounting 273 exchanges defined in the Diameter Network Access Server may be used. 275 However, in general, it is difficult to come to a hard guideline, and 276 so a case-by-case study of each application requirement should be 277 applied. Before adding or importing a command, application designers 278 should consider the following: 280 o Can the new functionality be fulfilled by creating a new command 281 independent from any existing command? In this case, the 282 resulting new application and the existing application can work 283 independent of, but cooperating with each other. 285 o Can the existing command be reused without major extensions and 286 therefore without the need for the definition of a new 287 application, e.g. new functionality introduced by the creation of 288 new optional AVPs. 290 It is important to note that importing commands too liberally could 291 result in a monolithic and hard to manage application supporting too 292 many different features. 294 4.2. Deleting an Existing Command 296 Although this process is not typical, removing a command from an 297 application requires a new Diameter application to be defined and 298 then it is considered as a major extension. This is due to the fact 299 that the reception of the deleted command would systematically result 300 in a protocol error (i.e., DIAMETER_COMMAND_UNSUPPORTED). 302 It is unusual to delete an existing command from an application for 303 the sake of deleting it or the functionality it represents. An 304 exception might be if the intent of the deletion is to create a newer 305 variance of the same application that is somehow simpler than the 306 application initially specified. 308 4.3. Reusing Existing Commands 310 This section discusses rules in adding and/or deleting AVPs from an 311 existing command of an existing application. The cases described in 312 this section may not necessarily result in the creation of new 313 applications. 315 From a historical point of view, it is worth to note that there was a 316 strong recommendation to re-use existing commands in the [RFC3588] to 317 prevent rapid depletion of code values available for vendor-specific 318 commands. However, [RFC6733] has relaxed the allocation policy and 319 enlarged the range of available code values for vendor-specific 320 applications. Although reuse of existing commands is still 321 RECOMMENDED, protocol designers can consider defining a new command 322 when it provides a solution more suitable than the twisting of an 323 existing command's use and applications. 325 4.3.1. Adding AVPs to a Command 327 Based on the rules in [RFC6733], AVPs that are added to an existing 328 command can be categorized into: 330 o Mandatory (to understand) AVPs. As defined in [RFC6733], these 331 are AVPs with the M-bit flag set in this command, which means that 332 a Diameter node receiving them is required to understand not only 333 their values but also their semantics. Failure to do so will 334 cause an message handling error: either a error message with the 335 result-code set to DIAMETER_AVP_UNSUPPORTED if the AVP not 336 understood in a request or a application specific error handling 337 if the given AVP is in an answer. 339 o Optional (to understand) AVPs. As defined in [RFC6733], these are 340 AVPs with the M-bit flag cleared in this command. A Diameter node 341 receiving these AVPs can simply ignore them if it does not support 342 them. 343 It is important to note that the definition given above are 344 independent of whether these AVPs are required or optional in the 345 command as specified by the command's Command Code Format (CCF) 346 syntax [RFC6733]. 348 NOTE: As stated in [RFC6733], the M-bit setting for a given AVP is 349 relevant to an application and each command within that 350 application that includes the AVP. 352 The rules are strict in the case where the AVPs to be added in an 353 exiting command are mandatory to understand, i.e., they have the 354 M-bit set. A mandatory AVP MUST NOT be added to an existing command 355 without defining a new Diameter application, as stated in [RFC6733]. 356 This falls into the "Major Extensions" category. Despite the clarity 357 of the rule, ambiguity still arises when evaluating whether a new AVP 358 being added should be mandatory to begin with. Application designers 359 should consider the following questions when deciding about the M-bit 360 for a new AVP: 362 o Would it be required for the receiving side to be able to process 363 and understand the AVP and its content? 365 o Would the new AVPs change the state machine of the application? 367 o Would the presence of the new AVP lead to a different number of 368 round-trips, effectively changing the state machine of the 369 application? 371 o Would the new AVP be used to differentiate between old and new 372 variances of the same application whereby the two variances are 373 not backward compatible? 375 o Would the new AVP have duality in meaning, i.e., be used to carry 376 application-related information as well as to indicate that the 377 message is for a new application? 379 If the answer to at least one of the questions is "yes" then the 380 M-bit MUST be set for the new AVP and a new Diameter application MUST 381 be defined. This list of questions is non-exhaustive and other 382 criteria MAY be taken into account in the decision process. 384 If application designers are instead contemplating the use of 385 optional AVPs, i.e., with the M-bit cleared, there are still pitfalls 386 that will cause interoperability problems and therefore must be 387 avoided. Some examples of these pitfalls are : 389 o Use of optional AVPs with intersecting meaning. One AVP has 390 partially the same usage and meaning as another AVP. The presence 391 of both can lead to confusion. 393 o An optional AVPs with dual purpose, i.e., to carry application 394 data as well as to indicate support for one or more features. 395 This has a tendency to introduce interpretation issues. 397 o Adding one or more optional AVPs and indicating (usually within 398 descriptive text for the command) that at least one of them has to 399 be understood by the receiver of the command. This would be 400 equivalent to adding a mandatory AVP, i.e., an AVP with the M-bit 401 set, to the command. 403 4.3.2. Deleting AVPs from a Command 405 Application designers may want to reuse an existing command but some 406 of the AVP present in the command's CCF syntax specification may be 407 irrelevant for the functionality foreseen to be supported by this 408 command. It may be then tempting to delete those AVPs from the 409 command. 411 The impacts of deleting an AVP from a command depends on its command 412 code format specification and M-bit setting: 414 o Case 1: Deleting an AVP that is indicated as a required AVP (noted 415 as {AVP}) in the command's CCF syntax specification (regardless of 416 the M-bit setting). 418 In this case, a new command code and subsequently a new Diameter 419 application MUST be specified. 421 o Case 2: Deleting an AVP, which has the M-bit set, and is indicated 422 as optional AVP (noted as [AVP]) in the command CCF) in the 423 command's CCF syntax specification. 425 In this case, no new command code has to be specified but the 426 definition of a new Diameter application is REQUIRED. 428 o Case 3: Deleting an AVP, which has the M-bit cleared, and is 429 indicated as [AVP] in the command's CCF syntax specification. 431 In this case, the AVP can be deleted without consequences. 433 Application designers SHOULD attempt the reuse the command's CCF 434 syntax specification without modification and simply ignore (but not 435 delete) any optional AVP that will not be used. This is to maintain 436 compatibility with existing applications that will not know about the 437 new functionality as well as maintain the integrity of existing 438 dictionaries. 440 4.3.3. Changing the Flags Setting of AVP in existing Commands 442 Although unusual, implementors may want to change the setting of the 443 AVP flags a given AVP used in a command. 445 Into an existing command, a AVP that was initially defined as 446 mandatory AVP to understand, i.e., an AVP with the M-bit flag set in 447 the command, MAY be safely turned to an optional AVP, i.e., with the 448 M-bit cleared. Any node supporting the existing application will 449 still understand the AVP, whatever the setting of the M-bit. On the 450 contrary, an AVP initially defined as an optional AVP to understand, 451 i.e., an AVP with the M-bit flag cleared in the command, MUST NOT be 452 changed into a mandatory AVP with the M-bit flag set without defining 453 a new Diameter application. Setting the M-bit for an AVP that was 454 defined as an optional AVP is equivalent to adding a new mandatory 455 AVP to an existing command and the rules given in the section 4.3.1 456 apply. 458 All other AVP flags (V-bit, P-bit, reserved bits) MUST remain 459 unchanged. 461 4.4. Reusing Existing AVPs 463 This section discusses rules in reusing existing AVP when reusing an 464 existing command or defining a new command in a new application. 466 4.4.1. Setting of the AVP Flags 468 When reusing existing AVPs in a new application, application 469 designers MUST specify the setting of the M-bit flag for a new 470 Diameter application and, if necessary, for every command of the 471 application that can carry these AVPs. In general, for AVPs defined 472 outside of the Diameter base protocol, the characteristics of an AVP 473 are tied to its role within a given application and the commands used 474 in this application. 476 All other AVP flags (V-bit, P-bit, reserved bits) MUST remain 477 unchanged. 479 4.4.2. Reuse of AVP of Type Enumerated 481 When reusing an AVP of type Enumerated in a command for a new 482 application, it is RECOMMENDED to avoid modifying the set of valid 483 values defined for this AVP. Modifying the set of Enumerated values 484 includes adding a value or deprecating the use of a value defined 485 initially for the AVP. Modifying the set of values will impact the 486 application defining this AVP and all the applications using this 487 AVP, causing potential interoperability issues: a value used by a 488 peer that will not be recognized by all the nodes between the client 489 and the server will cause an error response with the Result-Code AVP 490 set to DIAMETER_INVALID_AVP_VALUE. When the full range of values 491 defined for this Enumerated AVP is not suitable for the new 492 application, it is RECOMMENDED to define a new AVP to avoid backwards 493 compatibility issues with existing implementations. 495 5. Defining New Diameter Applications 497 5.1. Introduction 499 This section discusses the case where new applications have 500 requirements that cannot be fulfilled by existing applications and 501 would require definition of completely new commands, AVPs and/or AVP 502 values. Typically, there is little ambiguity about the decision to 503 create these types of applications. Some examples are the interfaces 504 defined for the IP Multimedia Subsystem of 3GPP, e.g., Cx/Dx 505 ([TS29.228] and [TS29.229]), Sh ([TS29.328] and [TS29.329]) etc. 507 Application designers SHOULD try to import existing AVPs and AVP 508 values for any newly defined commands. In certain cases where 509 accounting will be used, the models described in Section 5.10 SHOULD 510 also be considered. 512 Additional considerations are described in the following sections. 514 5.2. Defining New Commands 516 As a general recommendation, commands SHOULD NOT be defined from 517 scratch. It is instead RECOMMENDED to re-use an existing command 518 offering similar functionality and use it as a starting point. Code 519 re-use lead to a smaller implementation effort as well as reduce the 520 need for testing. 522 Moreover, the new command's CCF syntax specification SHOULD be 523 carefully defined when considering applicability and extensibility of 524 the application. If most of the AVPs contained in the command are 525 indicated as fixed or required, it might be difficult to reuse the 526 same command and therefore the same application in a slightly changed 527 environment. Defining a command with most of the AVPs indicated as 528 optional is considered as a good design choice in many cases, despite 529 the flexibility it introduces in the protocol. Protocol designers 530 MUST clearly state the reasons why these optional AVPs might or might 531 not be present and properly define the corresponding behavior of the 532 Diameter nodes when these AVPs are absent from the command. 534 NOTE: As a hint for protocol designers, it is not sufficient to just 535 look at the command's CCF syntax specification. It is also 536 necessary to carefully read through the accompanying text in the 537 specification. 539 In the same way, the CCF syntax specification SHOULD be defined such 540 that it will be possible to add any arbitrary optional AVPs with the 541 M-bit cleared (including vendor-specific AVPs) without modifying the 542 application. For this purpose, "* [AVP]" SHOULD be added in the 543 command's CCF, which allows the addition of any arbitrary number of 544 optional AVPs as described in [RFC6733]. 546 5.3. Use of Application-Id in a Message 548 When designing new applications, application designers SHOULD specify 549 that the Application Id carried in all session-level messages is the 550 Application Id of the application using those messages. This 551 includes the session-level messages defined in Diameter base 552 protocol, i.e., RAR/RAA, STR/STA, ASR/ASA and possibly ACR/ACA in the 553 coupled accounting model, see Section 5.10. Some existing 554 specifications do not adhere to this rule for historical reasons. 555 However, this guidance SHOULD be followed by new applications to 556 avoid routing problems. 558 When a new application has been allocated with a new Application Id 559 and it also reuses existing commands with or without modifications, 560 the commands SHOULD use the newly allocated Application Id in the 561 header and in all relevant Application Id AVPs (Auth-Application-Id 562 or Acct-Application-Id) present in the commands message body. 564 Additionally, application designers using Vendor-Specific- 565 Application-Id AVP SHOULD NOT use the Vendor-Id AVP to further 566 dissect or differentiate the vendor-specification Application Id. 567 Diameter routing is not based on the Vendor-Id. As such, the Vendor- 568 Id SHOULD NOT be used as an additional input for routing or delivery 569 of messages. The Vendor-Id AVP is an informational AVP only and kept 570 for backward compatibility reasons. 572 5.4. Application-Specific Session State Machines 574 Section 8 of [RFC6733] provides session state machines for 575 authentication, authorization and accounting (AAA) services and these 576 session state machines are not intended to cover behavior outside of 577 AAA. If a new application cannot clearly be categorized into any of 578 these AAA services, it is RECOMMENDED that the application defines 579 its own session state machine. Support for server-initiated request 580 is a clear example where an application-specific session state 581 machine would be needed, for example, the Rw interface for ITU-T push 582 model (cf.[Q.3303.3]). 584 5.5. Session-Id AVP and Session Management 586 Diameter applications are usually designed with the aim of managing 587 user sessions (e.g., Diameter network access session (NASREQ) 588 application [RFC4005]) or specific service access session (e.g., 589 Diameter SIP application [RFC4740]). In the Diameter base protocol, 590 session state is referenced using the Session-Id AVP. All Diameter 591 messages that use the same Session-Id will be bound to the same 592 session. Diameter-based session management also implies that both 593 Diameter client and server (and potentially proxy agents along the 594 path) maintain session state information. 596 However, some applications may not need to rely on the Session-Id to 597 identify and manage sessions because other information can be used 598 instead to correlate Diameter messages. Indeed, the User-Name AVP or 599 any other specific AVP can be present in every Diameter message and 600 used therefore for message correlation. Some applications might not 601 require the notion of Diameter session concept at all. For such 602 applications, the Auth-Session-State AVP is usually set to 603 NO_STATE_MAINTAINED in all Diameter messages and these applications 604 are therefore designed as a set of stand-alone transactions. Even if 605 an explicit access session termination is required, application- 606 specific commands are defined and used instead of the Session- 607 Termination-Request/Answer (STR/STA) or Abort-Session-Request/Answer 608 (ASR/ASA) defined in the Diameter base protocol [RFC6733]. In such a 609 case, the Session-Id is not significant. 611 Based on these considerations, protocol designers SHOULD carefully 612 appraise whether the application currently defined relies on its own 613 session management concept or whether the Session-Id defined in the 614 Diameter base protocol would be used for correlation of messages 615 related to the same session. If not, the protocol designers MAY 616 decide to define application commands without the Session-Id AVP. If 617 any session management concept is supported by the application, the 618 application documentation MUST clearly specify how the session is 619 handled between client and server (as possibly Diameter agents in the 620 path). 622 Based on these considerations, protocol designers SHOULD carefully 623 appraise whether the Diameter application being defined relies on the 624 session management specified in the Diameter base protocol: 626 o If it is, the Diameter command defined for the new application 627 MUST include the Session-Id AVP defined in the Diameter base 628 protocol [RFC6733] and the Session-Id AVP MUST be used for 629 correlation of messages related to the same session. Guidance on 630 the use of the Auth-Session-State AVP is given in the Diameter 631 base protocol [RFC6733]. 633 o Otherwise, because session management is not required or the 634 application relies on its own session management mechanism, 635 Diameter commands for the application need not include the 636 Session-Id AVP. If any specific session management concept is 637 supported by the application, the application documentation MUST 638 clearly specify how the session is handled between client and 639 server (and possibly Diameter agents in the path). Moreover, 640 because the application is not maintaining session state at the 641 Diameter base protocol level, the Auth-Session-State AVP MUST be 642 included in all Diameter commands for the application and MUST be 643 set to NO_STATE_MAINTAINED. 645 5.6. Use of Enumerated Type AVPs 647 The type Enumerated was initially defined to provide a list of valid 648 values for an AVP with their respective interpretation described in 649 the specification. For instance, AVPs of type Enumerated can be used 650 to provide further information on the reason for the termination of a 651 session or a specific action to perform upon the reception of the 652 request. 654 As described in the section 4.4.2 above, defining an AVP of type 655 Enumerated presents some limitations in term of extensibility and 656 reusability. Indeed, the finite set of valid values defined at the 657 definition of the AVP of type Enumerated cannot be modified in 658 practice without causing backward compatibility issues with existing 659 implementations. As a consequence, AVPs of Type Enumerated MUST NOT 660 be extended by adding new values to support new capabilities. 661 Diameter protocol designers SHOULD carefully consider before defining 662 an Enumerated AVP whether the set of values will remain unchanged or 663 new values may be required in a near future. If such extension is 664 foreseen or cannot be avoided, it is RECOMMENED to rather define AVPs 665 of type Unsigned32 or Unsigned64 in which the data field would 666 contain an address space representing "values" that would have the 667 same use of Enumerated values. Whereas only the initial values 668 defined at the definition of the AVP of type Enumerated are valid as 669 described in section 4.4.2, any value from the address space from 0 670 to 2^32 - 1 for AVPs of type Unsigned32 or from 0 to 2^64 - 1 for 671 AVPs of type Unsigned64 is valid at the Diameter base protocol level 672 and will not interoperability issues for intermediary nodes between 673 clients and servers. Only clients and servers will be able to 674 process the values at the application layer. 676 For illustration, an AVP describing possible access networks would be 677 defined as follow: 679 Access-Network-Type AVP (XXX) is of type Unsigned32 and contains a 680 32-bit address space representing types of access networks. This 681 application defines the following classes of access networks, all 682 identified by the thousands digit in the decimal notation: 684 o 1xxx (Mobile Access Networks) 686 o 2xxx (Fixed Access Network) 688 o 3xxx (Wireless Access Networks) 690 Values that fall within the Mobile Access Networks category are used 691 to inform a peer that a request has been sent for a user attached to 692 a mobile access network. The following values are defined in this 693 application: 695 1001: 3GPP-GERAN 697 The user is attached to a GSM EDGE Radio Access Network. 699 1002: 3GPP-UTRAN-FDD 701 The user is attached to a UMTS access network that uses 702 frequency-division duplexing for duplexing. 704 Unlike Enumerated AVP, any new value can be added in the address 705 space defined by this Unsigned32 AVP without modifying the definition 706 of the AVP. There is therefore no risk of backward compatibility 707 issue, especially when intermediate nodes may be present between 708 Diameter endpoints. 710 In the same line, AVPs of type Enumerated are too often used as a 711 simple Boolean flag, indicating for instance a specific permission or 712 capability, and therefore only two values are defined, e.g., TRUE/ 713 FALSE, AUTORIZED/UNAUTHORIZED or SUPPORTED/UNSUPPORTED. This is a 714 sub-optimal design since it limits the extensibility of the 715 application: any new capability/permission would have to be supported 716 by a new AVP or new Enumerated value of the already defined AVP, with 717 the backward compatibility issues described above. Instead of using 718 an Enumerated AVP for a Boolean flag, protocol designers SHOULD use 719 AVPs of type Unsigned32 or Unsigned64 AVP in which the data field 720 would be defined as bit mask whose bit settings are described in the 721 relevant Diameter application specification. Such AVPs can be reused 722 and extended without major impact on the Diameter application. The 723 bit mask SHOULD leave room for future additions. Examples of AVPs 724 that use bit masks are the Session-Binding AVP defined in [RFC6733] 725 and the MIP6-Feature-Vector AVP defined in [RFC5447]. 727 5.7. Application-Specific Message Routing 729 As described in [RFC6733], a Diameter request that needs to be sent 730 to a home server serving a specific realm, but not to a specific 731 server (such as the first request of a series of round trips), will 732 contain a Destination-Realm AVP and no Destination-Host AVP. 734 For such a request, the message routing usually relies only on the 735 Destination-Realm AVP and the Application Id present in the request 736 message header. However, some applications may need to rely on the 737 User-Name AVP or any other application-specific AVP present in the 738 request to determine the final destination of a request, e.g., to 739 find the target AAA server hosting the authorization information for 740 a given user when multiple AAA servers are addressable in the realm. 742 In such a context, basic routing mechanisms described in [RFC6733] 743 are not fully suitable, and additional application-level routing 744 mechanisms MUST be described in the application documentation to 745 provide such specific AVP-based routing. Such functionality will be 746 basically hosted by an application-specific proxy agent that will be 747 responsible for routing decisions based on the received specific 748 AVPs. 750 Examples of such application-specific routing functions can be found 751 in the Cx/Dx applications ([TS29.228] and [TS29.229]) of the 3GPP IP 752 Multimedia Subsystem, in which the proxy agent (Subscriber Location 753 Function aka SLF) uses specific application-level identities found in 754 the request to determine the final destination of the message. 756 Whatever the criteria used to establish the routing path of the 757 request, the routing of the answer MUST follow the reverse path of 758 the request, as described in [RFC6733], with the answer being sent to 759 the source of the received request, using transaction states and hop- 760 by-hop identifier matching. This ensures that the Diameter Relay or 761 Proxy agents in the request routing path will be able to release the 762 transaction state upon receipt of the corresponding answer, avoiding 763 unnecessary failover. Moreover, especially in roaming cases, proxy 764 agents in the path must be able to apply local policies when 765 receiving the answer from the server during authentication/ 766 authorization and/or accounting procedures, and maintain up-to-date 767 session state information by keeping track of all authorized active 768 sessions. Therefore, application designers MUST NOT modify the 769 answer-routing principles described in [RFC6733] when defining a new 770 application. 772 5.8. Translation Agents 774 As defined in [RFC6733], a translation agent is a device that 775 provides interworking between Diameter and another AAA protocol, such 776 as RADIUS . 778 In the case of RADIUS, it was initially thought that defining the 779 translation function would be straightforward by adopting few basic 780 principles, e.g., by the use of a shared range of code values for 781 RADIUS attributes and Diameter AVPs. Guidelines for implementing a 782 RADIUS-Diameter translation agent were put into the Diameter NASREQ 783 Application ([RFC4005]). 785 However, it was acknowledged that such translation mechanism was not 786 so obvious and deeper protocol analysis was required to ensure 787 efficient interworking between RADIUS and Diameter. Moreover, the 788 interworking requirements depend on the functionalities provided by 789 the Diameter application under specification, and a case-by-case 790 analysis is required. As a consequence, all the material related to 791 RADIUS-to-Diameter translation is removed from the new version of the 792 Diameter NASREQ application specification [RFC7155], which deprecates 793 the RFC4005 ([RFC4005]). 795 Therefore, protocol designers SHOULD NOT assume the availability of a 796 "standard" Diameter-to-RADIUS gateways agent when planning to 797 interoperate with the RADIUS infrastructure. They SHOULD specify the 798 required translation mechanism along with the Diameter application, 799 if needed. This recommendation applies for any kind of translation. 801 5.9. End-to-End Application Capabilities Exchange 803 Diameter applications can rely on optional AVPs to exchange 804 application-specific capabilities and features. These AVPs can be 805 exchanged on an end-to-end basis at the application layer. Examples 806 of this can be found with the MIP6-Feature-Vector AVP in [RFC5447] 807 and the QoS-Capability AVP in [RFC5777]. 809 End-to-end capabilities AVPs can be added as optional AVPs with the 810 M-bit cleared to existing applications to announce support of new 811 functionality. Receivers that do not understand these AVPs or the 812 AVP values can simply ignore them, as stated in [RFC6733]. When 813 supported, receivers of these AVPs can discover the additional 814 functionality supported by the Diameter end-point originating the 815 request and behave accordingly when processing the request. Senders 816 of these AVPs can safely assume the receiving end-point does not 817 support any functionality carried by the AVP if it is not present in 818 corresponding response. This is useful in cases where deployment 819 choices are offered, and the generic design can be made available for 820 a number of applications. 822 When used in a new application, these end-to-end capabilities AVPs 823 SHOULD be added as optional AVP into the CCF of the commands used by 824 the new application. Protocol designers SHOULD clearly specify this 825 end-to-end capabilities exchange and the corresponding behaviour of 826 the Diameter nodes supporting the application. 828 It is also important to note that this end-to-end capabilities 829 exchange relying on the use of optional AVPs is not meant as a 830 generic mechanism to support extensibility of Diameter applications 831 with arbitrary functionality. When the added features drastically 832 change the Diameter application or when Diameter agents must be 833 upgraded to support the new features, a new application SHOULD be 834 defined, as recommended in [RFC6733]. 836 5.10. Diameter Accounting Support 838 Accounting can be treated as an auxiliary application that is used in 839 support of other applications. In most cases, accounting support is 840 required when defining new applications. This document provides two 841 possible models for using accounting: 843 Split Accounting Model: 845 In this model, the accounting messages will use the Diameter base 846 accounting Application Id (value of 3). The design implication 847 for this is that the accounting is treated as an independent 848 application, especially for Diameter routing. This means that 849 accounting commands emanating from an application may be routed 850 separately from the rest of the other application messages. This 851 may also imply that the messages end up in a central accounting 852 server. A split accounting model is a good design choice when: 854 * The application itself does not define its own accounting 855 commands. 857 * The overall system architecture permits the use of centralized 858 accounting for one or more Diameter applications. 860 Centralizing accounting may have advantages but there are also 861 drawbacks. The model assumes that the accounting server can 862 differentiate received accounting messages. Since the received 863 accounting messages can be for any application and/or service, the 864 accounting server MUST have a method to match accounting messages 865 with applications and/or services being accounted for. This may 866 mean defining new AVPs, checking the presence, absence or contents 867 of existing AVPs, or checking the contents of the accounting 868 record itself. One of these means could be to insert into the 869 request sent to the accounting server an Auth-Application-Id AVP 870 containing the identifier of the application for which the 871 accounting request is sent. But in general, there is no clean and 872 generic scheme for sorting these messages. Therefore, this model 873 SHOULD NOT be used when all received accounting messages cannot be 874 clearly identified and sorted. For most cases, the use of Coupled 875 Accounting Model is RECOMMENDED. 877 Coupled Accounting Model: 879 In this model, the accounting messages will use the Application Id 880 of the application using the accounting service. The design 881 implication for this is that the accounting messages are tightly 882 coupled with the application itself; meaning that accounting 883 messages will be routed like the other application messages. It 884 would then be the responsibility of the application server 885 (application entity receiving the ACR message) to send the 886 accounting records carried by the accounting messages to the 887 proper accounting server. The application server is also 888 responsible for formulating a proper response (ACA). A coupled 889 accounting model is a good design choice when: 891 * The system architecture or deployment does not provide an 892 accounting server that supports Diameter. Consequently, the 893 application server MUST be provisioned to use a different 894 protocol to access the accounting server, e.g., via LDAP, SOAP 895 etc. This case includes the support of older accounting 896 systems that are not Diameter aware. 898 * The system architecture or deployment requires that the 899 accounting service for the specific application should be 900 handled by the application itself. 902 In all cases above, there will generally be no direct Diameter 903 access to the accounting server. 905 These models provide a basis for using accounting messages. 906 Application designers may obviously deviate from these models 907 provided that the factors being addressed here have also been taken 908 into account. As a general recommendation, application designers 909 SHOULD NOT define a new set of commands to carry application-specific 910 accounting records. 912 5.11. Diameter Security Mechanisms 914 As specified in [RFC6733], the Diameter message exchange SHOULD be 915 secured between neighboring Diameter peers using TLS/TCP or DTLS/ 916 SCTP. However, IPsec MAY also be deployed to secure communication 917 between Diameter peers. When IPsec is used instead of TLS or DTLS, 918 the following recommendations apply. 920 IPsec ESP [RFC4301] in transport mode with non-null encryption and 921 authentication algorithms MUST be used to provide per-packet 922 authentication, integrity protection and confidentiality, and support 923 the replay protection mechanisms of IPsec. IKEv2 [RFC5996] SHOULD be 924 used for performing mutual authentication and for establishing and 925 maintaining security associations (SAs). 927 IKEv1 [RFC2409] was used with RFC 3588 [RFC3588] and for easier 928 migration from IKEv1 based implementations both RSA digital 929 signatures and pre-shared keys SHOULD be supported in IKEv2. 930 However, if IKEv1 is used, implementers SHOULD follow the guidelines 931 given in Section 13.1 of RFC 3588 [RFC3588]. 933 6. Defining Generic Diameter Extensions 935 Generic Diameter extensions are AVPs, commands or applications that 936 are designed to support other Diameter applications. They are 937 auxiliary applications meant to improve or enhance the Diameter 938 protocol itself or Diameter applications/functionality. Some 939 examples include the extensions to support realm-based redirection of 940 Diameter requests (see [RFC7075]), convey a specific set of priority 941 parameters influencing the distribution of resources (see [RFC6735]), 942 and the support for QoS AVPs (see [RFC5777]). 944 Since generic extensions may cover many aspects of Diameter and 945 Diameter applications, it is not possible to enumerate all scenarios. 946 However, some of the most common considerations are as follows: 948 Backward Compatibility: 950 When defining generic extensions designed to be supported by 951 existing Diameter applications, protocol designers MUST consider 952 the potential impacts of the introduction of the new extension on 953 the behavior of node that would not be yet upgraded to support/ 954 understand this new extension. Designers MUST also ensure that 955 new extensions do not break expected message delivery layer 956 behavior. 958 Forward Compatibility: 960 Protocol designers MUST ensure that their design will not 961 introduce undue restrictions for future applications. 963 Trade-off in Signaling: 965 Designers may have to choose between the use of optional AVPs 966 piggybacked onto existing commands versus defining new commands 967 and applications. Optional AVPs are simpler to implement and may 968 not need changes to existing applications. However, this ties the 969 sending of extension data to the application's transmission of a 970 message. This has consequences if the application and the 971 extensions have different timing requirements. The use of 972 commands and applications solves this issue, but the trade-off is 973 the additional complexity of defining and deploying a new 974 application. It is left up to the designer to find a good balance 975 among these trade-offs based on the requirements of the extension. 977 In practice, generic extensions often use optional AVPs because they 978 are simple and non-intrusive to the application that would carry 979 them. Peers that do not support the generic extensions need not 980 understand nor recognize these optional AVPs. However, it is 981 RECOMMENDED that the authors of the extension specify the context or 982 usage of the optional AVPs. As an example, in the case that the AVP 983 can be used only by a specific set of applications then the 984 specification MUST enumerate these applications and the scenarios 985 when the optional AVPs will be used. In the case where the optional 986 AVPs can be carried by any application, it should be sufficient to 987 specify such a use case and perhaps provide specific examples of 988 applications using them. 990 In most cases, these optional AVPs piggybacked by applications would 991 be defined as a Grouped AVP and it would encapsulate all the 992 functionality of the generic extension. In practice, it is not 993 uncommon that the Grouped AVP will encapsulate an existing AVP that 994 has previously been defined as mandatory ('M'-bit set) e.g., 3GPP IMS 995 Cx/Dx interfaces ([TS29.228] and [TS29.229]). 997 7. Guidelines for Registrations of Diameter Values 999 As summarized in the Section 3 of this document and further described 1000 in the Section 1.3 of [RFC6733], there are four main ways to extend 1001 Diameter. The process for defining new functionality slightly varies 1002 based on the different extensions. This section provides protocol 1003 designers with some guidance regarding the definition of values for 1004 possible Diameter extensions and the necessary interaction with IANA 1005 to register the new functionality. 1007 a. Defining new AVP values 1009 The specifications defining AVPs and AVP values MUST provide 1010 guidance for defining new values and the corresponding policy for 1011 adding these values. For example, the RFC 5777 [RFC5777] defines 1012 the Treatment-Action AVP which contains a list of valid values 1013 corresponding to pre-defined actions (drop, shape, mark, permit). 1014 This set of values can be extended following the Specification 1015 Required policy defined in [RFC5226]. As a second example, the 1016 Diameter base specification [RFC6733] defines the Result-Code AVP 1017 that contains a 32-bit address space used to identity possible 1018 errors. According to the Section 11.3.2 of [RFC6733], new values 1019 can be assigned by IANA via an IETF Review process [RFC5226]. 1021 b. Creating new AVPs 1023 Two different types of AVP Codes namespaces can be used to create 1024 a new AVPs: 1026 * IETF AVP Codes namespace; 1028 * Vendor-specific AVP Codes namespace. 1030 In the latter case, a vendor needs to be first assigned by IANA 1031 with a private enterprise number, which can be used within the 1032 Vendor-Id field of the vendor-specific AVP. This enterprise 1033 number delimits a private namespace in which the vendor is 1034 responsible for vendor-specific AVP code value assignment. The 1035 absence of a Vendor-Id or a Vendor-Id value of zero (0) in the AVP 1036 header identifies standard AVPs from the IETF AVP Codes namespace 1037 managed by IANA. The allocation of code values from the IANA- 1038 managed namespace is conditioned by an Expert Review of the 1039 specification defining the AVPs or an IETF review if a block of 1040 AVPs needs to be assigned. Moreover, the remaining bits of the 1041 AVP Flags field of the AVP header are also assigned via Standard 1042 Action if the creation of new AVP Flags is desired. 1044 c. Creating new commands 1046 Unlike the AVP Code namespace, the Command Code namespace is flat 1047 but the range of values is subdivided into three chunks with 1048 distinct IANA registration policies: 1050 * A range of standard Command Code values that are allocated via 1051 IETF review; 1053 * A range of vendor-specific Command Code values that are 1054 allocated on a First-Come/First-Served basis; 1056 * A range of values reserved only for experimental and testing 1057 purposes. 1059 As for AVP Flags, the remaining bits of the Command Flags field of 1060 the Diameter header are also assigned via a Standards Action to 1061 create new Command Flags if required. 1063 d. Creating new applications 1065 Similarly to the Command Code namespace, the Application-Id 1066 namespace is flat but divided into two distinct ranges: 1068 * A range of values reserved for standard Application-Ids 1069 allocated after Expert Review of the specification defining the 1070 standard application; 1072 * A range for values for vendor specific applications, allocated 1073 by IANA on a First-Come/First-Serve basis. 1075 The IANA AAA parameters page can be found at 1076 http://www.iana.org/assignments/aaa-parameters and the enterprise 1077 number IANA page is available at http://www.iana.org/assignments/ 1078 enterprise-numbers. More details on the policies followed by IANA 1079 for namespace management (e.g. First-Come/First-Served, Expert 1080 Review, IETF Review, etc.) can be found in [RFC5226]. 1082 NOTE: 1083 When the same functionality/extension is used by more than one 1084 vendor, it is RECOMMENDED to define a standard extension. 1085 Moreover, a vendor-specific extension SHOULD be registered to 1086 avoid interoperability issues in the same network. With this aim, 1087 the registration policy of vendor-specific extension has been 1088 simplified with the publication of [RFC6733] and the namespace 1089 reserved for vendor-specific extensions is large enough to avoid 1090 exhaustion. 1092 8. IANA Considerations 1094 This document does not require actions by IANA. 1096 9. Security Considerations 1098 This document provides guidelines and considerations for extending 1099 Diameter and Diameter applications. Although such an extension may 1100 be related to a security functionality, the document does not 1101 explicitly give additional guidance on enhancing Diameter with 1102 respect to security. However, as a general guideline, it is 1103 recommended that any Diameter extension SHOULD NOT break the security 1104 concept given in the [RFC6733]. In particular, it is reminded here 1105 that any command defined or reused in a new Diameter application 1106 SHOULD be secured by using TLS [RFC5246] or DTLS/SCTP [RFC6083] and 1107 MUST NOT be used without one of TLS, DTLS, or IPsec [RFC4301]. When 1108 defining a new Diameter extension, any possible impact of the 1109 existing security principles described in the [RFC6733] MUST be 1110 carefully appraised and documented in the Diameter application 1111 specification. 1113 10. Contributors 1115 The content of this document was influenced by a design team created 1116 to revisit the Diameter extensibility rules. The team was formed in 1117 February 2008 and finished its work in June 2008. Except the 1118 authors, the design team members were: 1120 o Avi Lior 1122 o Glen Zorn 1124 o Jari Arkko 1126 o Jouni Korhonen 1128 o Mark Jones 1130 o Tolga Asveren 1132 o Glenn McGregor 1133 o Dave Frascone 1135 We would like to thank Tolga Asveren, Glenn McGregor, and John 1136 Loughney for their contributions as co-authors to earlier versions of 1137 this document. 1139 11. Acknowledgments 1141 We greatly appreciate the insight provided by Diameter implementers 1142 who have highlighted the issues and concerns being addressed by this 1143 document. The authors would also like to thank Jean Mahoney, Ben 1144 Campbell, Sebastien Decugis and Benoit Claise for their invaluable 1145 detailed reviews and comments on this document. 1147 12. References 1149 12.1. Normative References 1151 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1152 Requirement Levels", BCP 14, RFC 2119, March 1997. 1154 [RFC6733] Fajardo, V., Arkko, J., Loughney, J., and G. Zorn, 1155 "Diameter Base Protocol", RFC 6733, October 2012. 1157 12.2. Informative References 1159 [Q.3303.3] 1160 3rd Generation Partnership Project, "ITU-T Recommendation 1161 Q.3303.3, "Resource control protocol no. 3 (rcp3): 1162 Protocol at the Rw interface between the Policy Decision 1163 Physical Entity (PD-PE) and the Policy Enforcement 1164 Physical Entity (PE-PE): Diameter"", 2008. 1166 [RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange 1167 (IKE)", RFC 2409, November 1998. 1169 [RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. 1170 Arkko, "Diameter Base Protocol", RFC 3588, September 2003. 1172 [RFC4005] Calhoun, P., Zorn, G., Spence, D., and D. Mitton, 1173 "Diameter Network Access Server Application", RFC 4005, 1174 August 2005. 1176 [RFC4072] Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible 1177 Authentication Protocol (EAP) Application", RFC 4072, 1178 August 2005. 1180 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 1181 Internet Protocol", RFC 4301, December 2005. 1183 [RFC4740] Garcia-Martin, M., Belinchon, M., Pallares-Lopez, M., 1184 Canales-Valenzuela, C., and K. Tammi, "Diameter Session 1185 Initiation Protocol (SIP) Application", RFC 4740, November 1186 2006. 1188 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1189 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 1190 May 2008. 1192 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 1193 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 1195 [RFC5447] Korhonen, J., Bournelle, J., Tschofenig, H., Perkins, C., 1196 and K. Chowdhury, "Diameter Mobile IPv6: Support for 1197 Network Access Server to Diameter Server Interaction", RFC 1198 5447, February 2009. 1200 [RFC5777] Korhonen, J., Tschofenig, H., Arumaithurai, M., Jones, M., 1201 and A. Lior, "Traffic Classification and Quality of 1202 Service (QoS) Attributes for Diameter", RFC 5777, February 1203 2010. 1205 [RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, 1206 "Internet Key Exchange Protocol Version 2 (IKEv2)", RFC 1207 5996, September 2010. 1209 [RFC6083] Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram 1210 Transport Layer Security (DTLS) for Stream Control 1211 Transmission Protocol (SCTP)", RFC 6083, January 2011. 1213 [RFC6735] Carlberg, K. and T. Taylor, "Diameter Priority Attribute- 1214 Value Pairs", RFC 6735, October 2012. 1216 [RFC7075] Tsou, T., Hao, R., and T. Taylor, "Realm-Based Redirection 1217 In Diameter", RFC 7075, November 2013. 1219 [RFC7155] Zorn, G., "Diameter Network Access Server Application", 1220 RFC 7155, April 2014. 1222 [TS29.228] 1223 3rd Generation Partnership Project, "3GPP TS 29.228; 1224 Technical Specification Group Core Network and Terminals; 1225 IP Multimedia (IM) Subsystem Cx and Dx Interfaces; 1226 Signalling flows and message contents", 1227 . 1229 [TS29.229] 1230 3rd Generation Partnership Project, "3GPP TS 29.229; 1231 Technical Specification Group Core Network and Terminals; 1232 Cx and Dx interfaces based on the Diameter protocol; 1233 Protocol details", 1234 . 1236 [TS29.328] 1237 3rd Generation Partnership Project, "3GPP TS 29.328; 1238 Technical Specification Group Core Network and Terminals; 1239 IP Multimedia (IM) Subsystem Sh interface; signalling 1240 flows and message content", 1241 . 1243 [TS29.329] 1244 3rd Generation Partnership Project, "3GPP TS 29.329; 1245 Technical Specification Group Core Network and Terminals; 1246 Sh Interface based on the Diameter protocol; Protocol 1247 details", 1248 . 1250 Authors' Addresses 1252 Lionel Morand (editor) 1253 Orange Labs 1254 38/40 rue du General Leclerc 1255 Issy-Les-Moulineaux Cedex 9 92794 1256 France 1258 Phone: +33145296257 1259 Email: lionel.morand@orange.com 1261 Victor Fajardo 1262 Fluke Networks 1264 Email: vf0213@gmail.com 1266 Hannes Tschofenig 1267 Hall in Tirol 6060 1268 Austria 1270 Email: Hannes.Tschofenig@gmx.net 1271 URI: http://www.tschofenig.priv.at