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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. 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. 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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: December 6, 2014 Independent 6 H. Tschofenig 7 Nokia Siemens Networks 8 June 4, 2014 10 Diameter Applications Design Guidelines 11 draft-ietf-dime-app-design-guide-24 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. Futhermore, this document provides guidelines to 20 Diameter application designers reusing/defining Diameter applications 21 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 December 6, 2014. 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3 71 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4 72 4. Reusing Existing Diameter Applications . . . . . . . . . . . 5 73 4.1. Adding a New Command . . . . . . . . . . . . . . . . . . 5 74 4.2. Deleting an Existing Command . . . . . . . . . . . . . . 6 75 4.3. Reusing Existing Commands . . . . . . . . . . . . . . . . 7 76 4.3.1. Adding AVPs to a Command . . . . . . . . . . . . . . 7 77 4.3.2. Deleting AVPs from a Command . . . . . . . . . . . . 9 78 4.4. Reusing Existing AVPs . . . . . . . . . . . . . . . . . . 9 79 4.4.1. Setting of the AVP Flags . . . . . . . . . . . . . . 10 80 4.4.2. Reuse of AVP of Type Enumerated . . . . . . . . . . . 10 81 5. Defining New Diameter Applications . . . . . . . . . . . . . 10 82 5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 10 83 5.2. Defining New Commands . . . . . . . . . . . . . . . . . . 11 84 5.3. Use of Application-Id in a Message . . . . . . . . . . . 11 85 5.4. Application-Specific Session State Machines . . . . . . . 12 86 5.5. Session-Id AVP and Session Management . . . . . . . . . . 12 87 5.6. Use of Enumerated Type AVPs . . . . . . . . . . . . . . . 13 88 5.7. Application-Specific Message Routing . . . . . . . . . . 15 89 5.8. Translation Agents . . . . . . . . . . . . . . . . . . . 15 90 5.9. End-to-End Application Capabilities Exchange . . . . . . 16 91 5.10. Diameter Accounting Support . . . . . . . . . . . . . . . 17 92 5.11. Diameter Security Mechanisms . . . . . . . . . . . . . . 18 93 6. Defining Generic Diameter Extensions . . . . . . . . . . . . 19 94 7. Guidelines for Registrations of Diameter Values . . . . . . . 20 95 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 96 9. Security Considerations . . . . . . . . . . . . . . . . . . . 22 97 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 22 98 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23 99 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 23 100 12.1. Normative References . . . . . . . . . . . . . . . . . . 23 101 12.2. Informative References . . . . . . . . . . . . . . . . . 23 102 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25 104 1. Introduction 106 The Diameter base protocol provides facilities to extend Diameter 107 (see Section 1.3 of [RFC6733]) to support new functionality. In the 108 context of this document, extending Diameter means one of the 109 following: 111 1. Addition of new functionality to an existing Diameter application 112 without defining a new application. 114 2. Addition of new functionality to an existing Diameter application 115 that requires the definition of a new application. 117 3. The definition of an entirely new Diameter application to offer 118 functionality not supported by existing applications. 120 4. The definition of a new generic functionality that can be reused 121 across different applications. 123 All of these choices are design decisions that can be done by any 124 combination of reusing existing or defining new commands, AVPs or AVP 125 values. However, application designers do not have complete freedom 126 when making their design. A number of rules have been defined in 127 [RFC6733] that place constraints on when an extension requires the 128 allocation of a new Diameter application identifier or a new command 129 code value. The objective of this document is the following: 131 o Clarify the Diameter extensibility rules as defined in the 132 Diameter base protocol. 134 o Discuss design choices and provide guidelines when defining new 135 applications. 137 o Present trade-off choices. 139 2. Terminology 141 This document reuses the terminology defined in [RFC6733]. 142 Additionally, the following terms and acronyms are used in this 143 application: 145 Application Extension of the Diameter base protocol [RFC6733] via 146 the addition of new commands or AVPs. Each application is 147 uniquely identified by an IANA-allocated application identifier 148 value. 150 Command Diameter request or answer carrying AVPs between Diameter 151 endpoints. Each command is uniquely identified by a IANA- 152 allocated command code value and is described by a Command Code 153 Format (CCF) for an application. 155 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 156 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 157 document are to be interpreted as described in [RFC2119]. 159 3. Overview 161 As designed, the Diameter base protocol [RFC6733] can be seen as a 162 two-layer protocol. The lower layer is mainly responsible for 163 managing connections between neighboring peers and for message 164 routing. The upper layer is where the Diameter applications reside. 165 This model is in line with a Diameter node having an application 166 layer and a peer-to-peer delivery layer. The Diameter base protocol 167 document defines the architecture and behavior of the message 168 delivery layer and then provides the framework for designing Diameter 169 applications on the application layer. This framework includes 170 definitions of application sessions and accounting support (see 171 Section 8 and Section 9 of [RFC6733]). Accordingly, a Diameter node 172 is seen in this document as a single instance of a Diameter message 173 delivery layer and one or more Diameter applications using it. 175 The Diameter base protocol is designed to be extensible and the 176 principles are described in the Section 1.3 of [RFC6733]. As a 177 summary, Diameter can be extended by: 179 1. Defining new AVP values 181 2. Creating new AVPs 183 3. Creating new commands 185 4. Creating new applications 187 As a main guiding principle, application designers SHOULD follow the 188 following recommendation: "try to re-use as much as possible!". It 189 will reduce the time to finalize specification writing, and it will 190 lead to a smaller implementation effort as well as reduce the need 191 for testing. In general, it is clever to avoid duplicate effort when 192 possible. 194 However, re-use is not appropriate when the existing functionality 195 does not fit the new requirement and/or the re-use leads to 196 ambiguity. 198 The impact on extending existing applications can be categorized into 199 two groups: 201 Minor Extension: Enhancing the functional scope of an existing 202 application by the addition of optional features to support. Such 203 enhancement has no backward compatibility issue with the existing 204 application. 206 A typical example would be the definition of a new optional AVP 207 for use in an existing command. Diameter implementations 208 supporting the existing application but not the new AVP will 209 simply ignore it, without consequences for the Diameter message 210 handling, as described in [RFC6733]. The standardization effort 211 will be fairly small. 213 Major Extension: Enhancing an application that requires the 214 definition of a new Diameter application. Such enhancement causes 215 backward compatibility issue with existing implementations 216 supporting the application. 218 Typical examples would be the creation of a new command for 219 providing functionality not supported by existing applications or 220 the definition of a new AVP to be carried in an existing command 221 with the M-bit set in the AVP flags (see Section 4.1 of [RFC6733] 222 for definition of the "M-bit"). For such extension, a significant 223 specification effort is required and a careful approach is 224 recommended. 226 4. Reusing Existing Diameter Applications 228 An existing application may need to be enhanced to fulfill new 229 requirements and these modifications can be at the command level and/ 230 or at the AVP level. The following sections describe the possible 231 modifications that can be performed on existing applications and 232 their related impact. 234 4.1. Adding a New Command 236 Adding a new command to an existing application is considered as a 237 major extension and requires a new Diameter application to be 238 defined, as stated in the Section 1.3.4 of [RFC6733]. Adding a new 239 command means either defining a completely new command or importing 240 the command's Command Code Format (CCF) syntax from another 241 application whereby the new application inherits some or all of the 242 functionality of the application where the command came from. In the 243 former case, the decision to create a new application is 244 straightforward since this is typically a result of adding a new 245 functionality that does not exist yet. For the latter, the decision 246 to create a new application will depend on whether importing the 247 command in a new application is more suitable than simply using the 248 existing application as it is in conjunction with any other 249 application. Therefore, a case by case study of each application 250 requirement SHOULD be applied. 252 An example considers the Diameter EAP application [RFC4072] and the 253 Diameter Network Access Server application [RFC7155]. When network 254 access authentication using EAP is required, the Diameter EAP 255 commands (Diameter-EAP-Request/Diameter-EAP-Answer) are used; 256 otherwise the Diameter Network Access Server application will be 257 used. When the Diameter EAP application is used, the accounting 258 exchanges defined in the Diameter Network Access Server may be used. 260 However, in general, it is difficult to come to a hard guideline, and 261 so a case-by-case study of each application requirement should be 262 applied. Before adding or importing a command, application designers 263 should consider the following: 265 o Can the new functionality be fulfilled by creating a new command 266 independent from any existing command? In this case, the 267 resulting new application and the existing application can work 268 independent of, but cooperating with each other. 270 o Can the existing command be reused without major extensions and 271 therefore without the need for the definition of a new 272 application, e.g. new functionality introduced by the creation of 273 new optional AVPs. 275 Note: Importing commands too liberally could result in a monolithic 276 and hard to manage application supporting too many different 277 features. 279 4.2. Deleting an Existing Command 281 Although this process is not typical, removing a command from an 282 application requires a new Diameter application to be defined and 283 then it is considered as a major extension. This is due to the fact 284 that the reception of the deleted command would systematically result 285 in a protocol error (i.e., DIAMETER_COMMAND_UNSUPPORTED). 287 It is unusual to delete an existing command from an application for 288 the sake of deleting it or the functionality it represents. This 289 normally indicates of a flawed design. An exception might be if the 290 intent of the deletion is to create a newer variance of the same 291 application that is somehow simpler than the application initially 292 specified. 294 4.3. Reusing Existing Commands 296 This section discusses rules in adding and/or deleting AVPs from an 297 existing command of an existing application. The cases described in 298 this section may not necessarily result in the creation of new 299 applications. 301 From a historical point of view, it is worth to note that there was a 302 strong recommendation to re-use existing commands in the [RFC3588] to 303 prevent rapid depletion of code values available for vendor-specific 304 commands. However, [RFC6733] has relaxed the allocation policy and 305 enlarged the range of available code values for vendor-specific 306 applications. Although reuse of existing commands is still 307 RECOMMENDED, protocol designers MAY consider defining a new command 308 when it provides a solution more suitable than the twisting of an 309 existing command's use and applications. 311 4.3.1. Adding AVPs to a Command 313 Based on the rules in [RFC6733], AVPs that are added to an existing 314 command can be categorized into: 316 o Mandatory (to understand) AVPs. As defined in [RFC6733], these 317 are AVPs with the M-bit flag set in this command, which means that 318 a Diameter node receiving them is required to understand not only 319 their values but also their semantics. Failure to do so will 320 cause an message handling error. 322 o Optional (to understand) AVPs. As defined in [RFC6733], these are 323 AVPs with the M-bit flag cleared in this command. A Diameter node 324 receiving these AVPs can simply ignore them if it does not support 325 them. 326 It is important to note that the definition given above are 327 independent of whether these AVPs are required or optional in the 328 command as specified by the command's Command Code Format (CCF) 329 syntax [RFC6733]. 331 NOTE: As stated in [RFC6733], the M-bit setting for a given AVP is 332 relevant to an application and each command within that 333 application that includes the AVP. 335 The rules are strict in the case where the AVPs to be added in an 336 exiting command are mandatory to understand, i.e., they have the 337 M-bit set. A mandatory AVP MUST NOT be added to an existing command 338 without defining a new Diameter application, as stated in [RFC6733]. 339 This falls into the "Major Extensions" category. Despite the clarity 340 of the rule, ambiguity still arises when evaluating whether a new AVP 341 being added should be mandatory to begin with. Application designers 342 SHOULD consider the following questions when deciding about the M-bit 343 for a new AVP: 345 o Would it be required for the receiving side to be able to process 346 and understand the AVP and its content? 348 o Would the new AVPs change the state machine of the application? 350 o Would the presence of the new AVP lead to a different number of 351 round-trips, effectively changing the state machine of the 352 application? 354 o Would the new AVP be used to differentiate between old and new 355 variances of the same application whereby the two variances are 356 not backward compatible? 358 o Would the new AVP have duality in meaning, i.e., be used to carry 359 application-related information as well as to indicate that the 360 message is for a new application? 362 If the answer to at least one of the questions is "yes" then the 363 M-bit MUST be set for the new AVP. This list of questions is non- 364 exhaustive and other criteria MAY be taken into account in the 365 decision process. 367 If application designers are instead contemplating the use of 368 optional AVPs, i.e., with the M-bit cleared, then the following are 369 some of the pitfalls that SHOULD be avoided: 371 o Use of optional AVPs with intersecting meaning. One AVP has 372 partially the same usage and meaning as another AVP. The presence 373 of both can lead to confusion. 375 o An optional AVPs with dual purpose, i.e., to carry application 376 data as well as to indicate support for one or more features. 377 This has a tendency to introduce interpretation issues. 379 o Adding one or more optional AVPs and indicating (usually within 380 descriptive text for the command) that at least one of them has to 381 be present in the command. This essentially circumventing the 382 ABNF and is equivalent to adding a mandatory AVP to the command. 384 These practices generally result in interoperability issues and 385 SHOULD be avoided. 387 4.3.2. Deleting AVPs from a Command 389 Application designers may want to reuse an existing command but some 390 of the AVP present in the command's CCF syntax specification may be 391 irrelevant for the functionality foreseen to be supported by this 392 command. It may be then tempting to delete those AVPs from the 393 command. 395 The impacts of deleting an AVP from a command depends on its command 396 code format specification and M-bit setting: 398 o Deleting an AVP that is indicated as a required AVP (noted as 399 {AVP}) in the command's CCF syntax specification (regardless of 400 the M-bit setting). 402 In this case, a new command code and subsequently a new Diameter 403 application MUST be specified. 405 o Deleting an AVP, which has the M-bit set, and is indicated as 406 optional AVP (noted as [AVP]) in the command CCF) in the command's 407 CCF syntax specification. 409 No new command code has to be specified but the definition of a 410 new Diameter application is REQUIRED. 412 o Deleting an AVP, which has the M-bit cleared, and is indicated as 413 [ AVP ] in the command's CCF syntax specification. 415 In this case, the AVP can be deleted without consequences. 417 Application designers SHOULD attempt the reuse the command's CCF 418 syntax specification without modification and simply ignore (but not 419 delete) any optional AVP that will not be used. This is to maintain 420 compatibility with existing applications that will not know about the 421 new functionality as well as maintain the integrity of existing 422 dictionaries. 424 4.4. Reusing Existing AVPs 426 This section discusses rules in reusing existing AVP when reusing an 427 existing command or defining a new command in a new application. 429 4.4.1. Setting of the AVP Flags 431 When reusing existing AVPs in a new application, application 432 designers MUST specify the setting of the M-bit flag for a new 433 Diameter application and, if necessary, for every command of the 434 application that can carry these AVPs. In general, for AVPs defined 435 outside of the Diameter base protocol, the characteristics of an AVP 436 are tied to its role within a given application and the commands used 437 in this application. 439 All other AVP flags (V-bit, P-bit, reserved bits) MUST remain 440 unchanged. 442 4.4.2. Reuse of AVP of Type Enumerated 444 When reusing an AVP of type Enumerated in a command for a new 445 application, it is RECOMMENDED to avoid modifying the set of valid 446 values defined for this AVP. Modifying the set of Enumerated values 447 includes adding a value or deprecating the use of a value defined 448 initially for the AVP. Modifying the set of values will impact the 449 application defining this AVP and all the applications using this 450 AVP, causing potential interoperability issues. When the full range 451 of values defined for this Enumerated AVP is not suitable for the new 452 application, it is RECOMMENDED to define a new AVP to avoid backwards 453 compatibility issues with existing implementations. 455 5. Defining New Diameter Applications 457 5.1. Introduction 459 This section discusses the case where new applications have 460 requirements that cannot be fulfilled by existing applications and 461 would require definition of completely new commands, AVPs and/or AVP 462 values. Typically, there is little ambiguity about the decision to 463 create these types of applications. Some examples are the interfaces 464 defined for the IP Multimedia Subsystem of 3GPP, e.g., Cx/Dx 465 ([TS29.228] and [TS29.229]), Sh ([TS29.328] and [TS29.329]) etc. 467 Application designers SHOULD try to import existing AVPs and AVP 468 values for any newly defined commands. In certain cases where 469 accounting will be used, the models described in Section 5.10 SHOULD 470 also be considered. 472 Additional considerations are described in the following sections. 474 5.2. Defining New Commands 476 As a general recommendation, commands SHOULD not be defined from 477 scratch. It is instead RECOMMENDED to re-use an existing command 478 offering similar functionality and use it as a starting point. Code 479 re-use lead to a smaller implementation effort as well as reduce the 480 need for testing. 482 Moreover, the new command's CCF syntax specification SHOULD be 483 carefully defined when considering applicability and extensibility of 484 the application. If most of the AVPs contained in the command are 485 indicated as fixed or required, it might be difficult to reuse the 486 same command and therefore the same application in a slightly changed 487 environment. Defining a command with most of the AVPs indicated as 488 optional MUST NOT be seen as a sub-optimal design introducing too 489 much flexibility in the protocol. The protocol designers SHOULD only 490 clearly state the condition of presence of these AVPs and properly 491 define the corresponding behaviour of the Diameter nodes when these 492 AVPs are absent from the command. 494 NOTE: As a hint for protocol designers, it is not sufficient to just 495 look at the command's CCF syntax specification. It is also 496 necessary to carefully read through the accompanying text in the 497 specification. 499 In the same way, the CCF syntax specification SHOULD be defined such 500 that it will be possible to add any arbitrary optional AVPs with the 501 M-bit cleared (including vendor-specific AVPs) without modifying the 502 application. For this purpose, "* [AVP]" SHOULD be added in the 503 command's CCF, which allows the addition of any arbitrary number of 504 optional AVPs as described in [RFC6733]. 506 5.3. Use of Application-Id in a Message 508 When designing new applications, application designers SHOULD specify 509 that the Application Id carried in all session-level messages is the 510 Application Id of the application using those messages. This 511 includes the session-level messages defined in Diameter base 512 protocol, i.e., RAR/RAA, STR/STA, ASR/ASA and possibly ACR/ACA in the 513 coupled accounting model, see Section 5.10. Some existing 514 specifications do not adhere to this rule for historical reasons. 515 However, this guidance SHOULD be followed by new applications to 516 avoid routing problems. 518 When a new application has been allocated with a new Application Id 519 and it also reuses existing commands with or without modifications, 520 the commands SHOULD use the newly allocated Application Id in the 521 header and in all relevant Application Id AVPs (Auth-Application-Id 522 or Acct-Application-Id) present in the commands message body. 524 Additionally, application designers using Vendor-Specific- 525 Application-Id AVP SHOULD not use the Vendor-Id AVP to further 526 dissect or differentiate the vendor-specification Application Id. 527 Diameter routing is not based on the Vendor-Id. As such, the Vendor- 528 Id SHOULD not be used as an additional input for routing or delivery 529 of messages. The Vendor-Id AVP is an informational AVP only and kept 530 for backward compatibility reasons. 532 5.4. Application-Specific Session State Machines 534 Section 8 of [RFC6733] provides session state machines for 535 authentication, authorization and accounting (AAA) services and these 536 session state machines are not intended to cover behavior outside of 537 AAA. If a new application cannot clearly be categorized into any of 538 these AAA services, it is RECOMMENDED that the application defines 539 its own session state machine. Support for server-initiated request 540 is a clear example where an application-specific session state 541 machine would be needed, for example, the Rw interface for ITU-T push 542 model (cf.[Q.3303.3]). 544 5.5. Session-Id AVP and Session Management 546 Diameter applications are usually designed with the aim of managing 547 user sessions (e.g., Diameter network access session (NASREQ) 548 application [RFC4005]) or specific service access session (e.g., 549 Diameter SIP application [RFC4740]). In the Diameter base protocol, 550 session state is referenced using the Session-Id AVP. All Diameter 551 messages that use the same Session-Id will be bound to the same 552 session. Diameter-based session management also implies that both 553 Diameter client and server (and potentially proxy agents along the 554 path) maintain session state information. 556 However, some applications may not need to rely on the Session-Id to 557 identify and manage sessions because other information can be used 558 instead to correlate Diameter messages. Indeed, the User-Name AVP or 559 any other specific AVP can be present in every Diameter message and 560 used therefore for message correlation. Some applications might not 561 require the notion of Diameter session concept at all. For such 562 applications, the Auth-Session-State AVP is usually set to 563 NO_STATE_MAINTAINED in all Diameter messages and these applications 564 are therefore designed as a set of stand-alone transactions. Even if 565 an explicit access session termination is required, application- 566 specific commands are defined and used instead of the Session- 567 Termination-Request/Answer (STR/STA) or Abort-Session-Request/Answer 568 (ASR/ASA) defined in the Diameter base protocol [RFC6733]. In such a 569 case, the Session-Id is not significant. 571 Based on these considerations, protocol designers SHOULD carefully 572 appraise whether the application currently defined relies on its own 573 session management concept or whether the Session-Id defined in the 574 Diameter base protocol would be used for correlation of messages 575 related to the same session. If not, the protocol designers MAY 576 decide to define application commands without the Session-Id AVP. If 577 any session management concept is supported by the application, the 578 application documentation MUST clearly specify how the session is 579 handled between client and server (as possibly Diameter agents in the 580 path). 582 5.6. Use of Enumerated Type AVPs 584 The type Enumerated was initially defined to provide a list of valid 585 values for an AVP with their respective interpretation described in 586 the specification. For instance, AVPs of type Enumerated can be used 587 to provide further information on the reason for the termination of a 588 session or a specific action to perform upon the reception of the 589 request. 591 As described in the section 4.4.2 above, defining an AVP of type 592 Enumerated presents some limitations in term of extensibility and 593 reusability. Indeed, the finite set of valid values defined at the 594 definition of the AVP of type Enumerated cannot be modified in 595 practice without causing backward compatibility issues with existing 596 implementations. As a consequence, AVPs of Type Enumerated MUST NOT 597 be extended by adding new values to support new capabilities. 598 Diameter protocol designers SHOULD carefully consider before defining 599 an Enumerated AVP whether the set of values will remain unchanged or 600 new values may be required in a near future. If such extension is 601 foreseen or cannot be avoided, it is RECOMMENED to rather define AVPs 602 of type Unsigned32 or Unsigned64 in which the data field would 603 contain an address space representing "values" that would have the 604 same use of Enumerated values. 606 For illustration, an AVP describing possible access networks would be 607 defined as follow: 609 Access-Network-Type AVP (XXX) is of type Unsigned32 and contains a 610 32-bit address space representing types of access networks. This 611 application defines the following classes of access networks, all 612 identified by the thousands digit in the decimal notation: 614 o 1xxx (Mobile Access Networks) 616 o 2xxx (Fixed Access Network) 618 o 3xxx (Wireless Access Networks) 620 Values that fall within the Mobile Access Networks category are used 621 to inform a peer that a request has been sent for a user attached to 622 a mobile access networks. The following values are defined in this 623 application: 625 1001: 3GPP-GERAN 627 TBD. 629 1002: 3GPP-UTRAN-FDD 631 TBD. 633 Unlike Enumerated AVP, any new value can be added in the address 634 space defined by this Unsigned32 AVP without modifying the definition 635 of the AVP. There is therefore no risk of backward compatibility 636 issue, especially when intermediate nodes may be present between 637 Diameter endpoints. 639 In the same line, AVPs of type Enumerated are too often used as a 640 simple Boolean flag, indicating for instance a specific permission or 641 capability, and therefore only two values are defined, e.g., TRUE/ 642 FALSE, AUTORIZED/UNAUTHORIZED or SUPPORTED/UNSUPPORTED. This is a 643 sub-optimal design since it limits the extensibility of the 644 application: any new capability/permission would have to be supported 645 by a new AVP or new Enumerated value of the already defined AVP, with 646 the backward compatibility issues described above. Instead of using 647 an Enumerated AVP for a Boolean flag, protocol designers SHOULD use 648 AVPs of type Unsigned32 or Unsigned64 AVP in which the data field 649 would be defined as bit mask whose bit settings are described in the 650 relevant Diameter application specification. Such AVPs can be reused 651 and extended without major impact on the Diameter application. The 652 bit mask SHOULD leave room for future additions. Examples of AVPs 653 that use bit masks are the Session-Binding AVP defined in [RFC6733] 654 and the MIP6-Feature-Vector AVP defined in [RFC5447]. 656 5.7. Application-Specific Message Routing 658 As described in [RFC6733], a Diameter request that needs to be sent 659 to a home server serving a specific realm, but not to a specific 660 server (such as the first request of a series of round trips), will 661 contain a Destination-Realm AVP and no Destination-Host AVP. 663 For such a request, the message routing usually relies only on the 664 Destination-Realm AVP and the Application Id present in the request 665 message header. However, some applications may need to rely on the 666 User-Name AVP or any other application-specific AVP present in the 667 request to determine the final destination of a request, e.g., to 668 find the target AAA server hosting the authorization information for 669 a given user when multiple AAA servers are addressable in the realm. 671 In such a context, basic routing mechanisms described in [RFC6733] 672 are not fully suitable, and additional application-level routing 673 mechanisms MUST be described in the application documentation to 674 provide such specific AVP-based routing. Such functionality will be 675 basically hosted by an application-specific proxy agent that will be 676 responsible for routing decisions based on the received specific 677 AVPs. 679 Examples of such application-specific routing functions can be found 680 in the Cx/Dx applications ([TS29.228] and [TS29.229]) of the 3GPP IP 681 Multimedia Subsystem, in which the proxy agent (Subscriber Location 682 Function aka SLF) uses specific application-level identities found in 683 the request to determine the final destination of the message. 685 Whatever the criteria used to establish the routing path of the 686 request, the routing of the answer MUST follow the reverse path of 687 the request, as described in [RFC6733], with the answer being sent to 688 the source of the received request, using transaction states and hop- 689 by-hop identifier matching. In particular, this ensures that the 690 Diameter Relay or Proxy agents in the request routing path will be 691 able to release the transaction state upon receipt of the 692 corresponding answer, avoiding unnecessary failover. Application 693 designers SHOULD NOT modify the answer-routing principles described 694 in [RFC6733] when defining a new application. 696 5.8. Translation Agents 698 As defined in [RFC6733], a translation agent is a device that 699 provides interworking between Diameter and another AAA protocol, such 700 as RADIUS . 702 In the case of RADIUS, it was initially thought that defining the 703 translation function would be straightforward by adopting few basic 704 principles, e.g., by the use of a shared range of code values for 705 RADIUS attributes and Diameter AVPs. Guidelines for implementing a 706 RADIUS-Diameter translation agent were put into the Diameter NASREQ 707 Application ([RFC4005]). 709 However, it was acknowledged that such translation mechanism was not 710 so obvious and deeper protocol analysis was required to ensure 711 efficient interworking between RADIUS and Diameter. Moreover, the 712 interworking requirements depend on the functionalities provided by 713 the Diameter application under specification, and a case-by-case 714 analysis is required. As a consequence, all the material related to 715 RADIUS-to-Diameter translation is removed from the new version of the 716 Diameter NASREQ application specification [RFC4005bis], (see 717 [RFC7155]) which deprecates the RFC4005 ([RFC4005]). 719 Therefore, protocol designers SHOULD NOT assume the availability of a 720 "standard" Diameter-to-RADIUS gateways agent when planning to 721 interoperate with the RADIUS infrastructure. They SHOULD specify the 722 required translation mechanism along with the Diameter application, 723 if needed. This recommendation applies for any kind of translation. 725 5.9. End-to-End Application Capabilities Exchange 727 Diameter applications can rely on optional AVPs to exchange 728 application-specific capabilities and features. These AVPs can be 729 exchanged on an end-to-end basis at the application layer. Examples 730 of this can be found with the MIP6-Feature-Vector AVP in [RFC5447] 731 and the QoS-Capability AVP in [RFC5777]. 733 End-to-end capabilities AVPs can be added as optional AVPs with the 734 M-bit cleared to existing applications to announce support of new 735 functionality. Receivers that do not understand these AVPs or the 736 AVP values can simply ignore them, as stated in [RFC6733]. When 737 supported, receivers of these AVPs can discover the additional 738 functionality supported by the Diameter end-point originating the 739 request and behave accordingly when processing the request. Senders 740 of these AVPs can safely assume the receiving end-point does not 741 support any functionality carried by the AVP if it is not present in 742 corresponding response. This is useful in cases where deployment 743 choices are offered, and the generic design can be made available for 744 a number of applications. 746 When used in a new application, these end-to-end capabilities AVPs 747 SHOULD be added as optional AVP into the CCF of the commands used by 748 the new application. Protocol designers SHOULD clearly specify this 749 end-to-end capabilities exchange and the corresponding behaviour of 750 the Diameter nodes supporting the application. 752 It is also important to note that this end-to-end capabilities 753 exchange relying on the use of optional AVPs is not meant as a 754 generic mechanism to support extensibility of Diameter applications 755 with arbitrary functionality. When the added features drastically 756 change the Diameter application or when Diameter agents must be 757 upgraded to support the new features, a new application SHOULD be 758 defined, as recommended in [RFC6733]. 760 5.10. Diameter Accounting Support 762 Accounting can be treated as an auxiliary application that is used in 763 support of other applications. In most cases, accounting support is 764 required when defining new applications. This document provides two 765 possible models for using accounting: 767 Split Accounting Model: 769 In this model, the accounting messages will use the Diameter base 770 accounting Application Id (value of 3). The design implication 771 for this is that the accounting is treated as an independent 772 application, especially for Diameter routing. This means that 773 accounting commands emanating from an application may be routed 774 separately from the rest of the other application messages. This 775 may also imply that the messages end up in a central accounting 776 server. A split accounting model is a good design choice when: 778 * The application itself does not define its own accounting 779 commands. 781 * The overall system architecture permits the use of centralized 782 accounting for one or more Diameter applications. 784 Centralizing accounting may have advantages but there are also 785 drawbacks. The model assumes that the accounting server can 786 differentiate received accounting messages. Since the received 787 accounting messages can be for any application and/or service, the 788 accounting server MUST have a method to match accounting messages 789 with applications and/or services being accounted for. This may 790 mean defining new AVPs, checking the presence, absence or contents 791 of existing AVPs, or checking the contents of the accounting 792 record itself. One of these means could be to insert into the 793 request sent to the accounting server an Auth-Application-Id AVP 794 containing the identifier of the application for which the 795 accounting request is sent. But in general, there is no clean and 796 generic scheme for sorting these messages. Therefore, the use of 797 this model is NOT RECOMMENDED when all received accounting 798 messages cannot be clearly identified and sorted. For most cases, 799 the use of Coupled Accounting Model is RECOMMENDED. 801 Coupled Accounting Model: 803 In this model, the accounting messages will use the Application Id 804 of the application using the accounting service. The design 805 implication for this is that the accounting messages are tightly 806 coupled with the application itself; meaning that accounting 807 messages will be routed like the other application messages. It 808 would then be the responsibility of the application server 809 (application entity receiving the ACR message) to send the 810 accounting records carried by the accounting messages to the 811 proper accounting server. The application server is also 812 responsible for formulating a proper response (ACA). A coupled 813 accounting model is a good design choice when: 815 * The system architecture or deployment does not provide an 816 accounting server that supports Diameter. Consequently, the 817 application server MUST be provisioned to use a different 818 protocol to access the accounting server, e.g., via LDAP, SOAP 819 etc. This case includes the support of older accounting 820 systems that are not Diameter aware. 822 * The system architecture or deployment requires that the 823 accounting service for the specific application should be 824 handled by the application itself. 826 In all cases above, there will generally be no direct Diameter 827 access to the accounting server. 829 These models provide a basis for using accounting messages. 830 Application designers may obviously deviate from these models 831 provided that the factors being addressed here have also been taken 832 into account. An application MAY define a new set of commands to 833 carry application-specific accounting records but it is NOT 834 RECOMMENDED to do so. 836 5.11. Diameter Security Mechanisms 838 As specified in [RFC6733], the Diameter message exchange SHOULD be 839 secured between neighboring Diameter peers using TLS/TCP or DTLS/ 840 SCTP. However, IPsec MAY also be deployed to secure communication 841 between Diameter peers. When IPsec is used instead of TLS or DTLS, 842 the following recommendations apply. 844 IPsec ESP [RFC4301] in transport mode with non-null encryption and 845 authentication algorithms MUST be used to provide per-packet 846 authentication, integrity protection and confidentiality, and support 847 the replay protection mechanisms of IPsec. IKEv2 [RFC5996] SHOULD be 848 used for performing mutual authentication and for establishing and 849 maintaining security associations (SAs). 851 IKEv1 [RFC2409] was used with RFC 3588 [RFC3588] and for easier 852 migration from IKEv1 based implementations both RSA digital 853 signatures and pre-shared keys SHOULD be supported in IKEv2. 854 However, if IKEv1 is used, implementers SHOULD follow the guidelines 855 given in Section 13.1 of RFC 3588 [RFC3588]. 857 6. Defining Generic Diameter Extensions 859 Generic Diameter extensions are AVPs, commands or applications that 860 are designed to support other Diameter applications. They are 861 auxiliary applications meant to improve or enhance the Diameter 862 protocol itself or Diameter applications/functionality. Some 863 examples include the extensions to support realm-based redirection of 864 Diameter requests (see [RFC7075]), convey a specific set of priority 865 parameters influencing the distribution of resources (see [RFC6735]), 866 and the support for QoS AVPs (see [RFC5777]). 868 Since generic extensions may cover many aspects of Diameter and 869 Diameter applications, it is not possible to enumerate all scenarios. 870 However, some of the most common considerations are as follows: 872 Backward Compatibility: 874 When defining generic extensions designed to be supported by 875 existing Diameter applications, protocol designers MUST consider 876 the potential impacts of the introduction of the new extension on 877 the behavior of node that would not be yet upgraded to support/ 878 understand this new extension. Designers MUST also ensure that 879 new extensions do not break expected message delivery layer 880 behavior. 882 Forward Compatibility: 884 Protocol designers MUST ensure that their design will not 885 introduce undue restrictions for future applications. 887 Trade-off in Signaling: 889 Designers may have to choose between the use of optional AVPs 890 piggybacked onto existing commands versus defining new commands 891 and applications. Optional AVPs are simpler to implement and may 892 not need changes to existing applications. However, this ties the 893 sending of extension data to the application's transmission of a 894 message. This has consequences if the application and the 895 extensions have different timing requirements. The use of 896 commands and applications solves this issue, but the trade-off is 897 the additional complexity of defining and deploying a new 898 application. It is left up to the designer to find a good balance 899 among these trade-offs based on the requirements of the extension. 901 In practice, generic extensions often use optional AVPs because they 902 are simple and non-intrusive to the application that would carry 903 them. Peers that do not support the generic extensions need not 904 understand nor recognize these optional AVPs. However, it is 905 RECOMMENDED that the authors of the extension specify the context or 906 usage of the optional AVPs. As an example, in the case that the AVP 907 can be used only by a specific set of applications then the 908 specification MUST enumerate these applications and the scenarios 909 when the optional AVPs will be used. In the case where the optional 910 AVPs can be carried by any application, it SHOULD be sufficient to 911 specify such a use case and perhaps provide specific examples of 912 applications using them. 914 In most cases, these optional AVPs piggybacked by applications would 915 be defined as a Grouped AVP and it would encapsulate all the 916 functionality of the generic extension. In practice, it is not 917 uncommon that the Grouped AVP will encapsulate an existing AVP that 918 has previously been defined as mandatory ('M'-bit set) e.g., 3GPP IMS 919 Cx/Dx interfaces ([TS29.228] and [TS29.229]). 921 7. Guidelines for Registrations of Diameter Values 923 As summarized in the Section 3 of this document and further described 924 in the Section 1.3 of [RFC6733], there are four main ways to extend 925 Diameter. The process for defining new functionality slightly varies 926 based on the different extensions. This section provides protocol 927 designers with some guidance regarding the definition of values for 928 possible Diameter extensions and the necessary interaction with IANA 929 to register the new functionality. 931 a. Defining new AVP values 933 The specifications defining AVPs and AVP values MUST provide 934 guidance for defining new values and the corresponding policy for 935 adding these values. For example, the RFC 5777 [RFC5777] defines 936 the Treatment-Action AVP which contains a list of valid values 937 corresponding to pre-defined actions (drop, shape, mark, permit). 938 This set of values can be extended following the Specification 939 Required policy defined in [RFC5226]. As a second example, the 940 Diameter base specification [RFC6733] defines the Result-Code AVP 941 that contains a 32-bit address space used to identity possible 942 errors. According to the Section 11.3.2 of [RFC6733], new values 943 can be assigned by IANA via an IETF Review process [RFC5226]. 945 b. Creating new AVPs 947 Two different types of AVP Codes namespaces can be used to create 948 a new AVPs: 950 * IETF AVP Codes namespace; 952 * Vendor-specific AVP Codes namespace. 954 In the latter case, a vendor needs to be first assigned by IANA 955 with a private enterprise number, which can be used within the 956 Vendor-Id field of the vendor-specific AVP. This enterprise 957 number delimits a private namespace in which the vendor is 958 responsible for vendor-specific AVP code value assignment. The 959 absence of a Vendor-Id or a Vendor-Id value of zero (0) in the AVP 960 header identifies standard AVPs from the IETF AVP Codes namespace 961 managed by IANA. The allocation of code values from the IANA- 962 managed namespace is conditioned by an Expert Review of the 963 specification defining the AVPs or an IETF review if a block of 964 AVPs needs to be assigned. Moreover, the remaining bits of the 965 AVP Flags field of the AVP header are also assigned via Standard 966 Action if the creation of new AVP Flags is desired. 968 c. Creating new commands 970 Unlike the AVP Code namespace, the Command Code namespace is flat 971 but the range of values is subdivided into three chunks with 972 distinct IANA registration policies: 974 * A range of standard Command Code values that are allocated via 975 IETF review; 977 * A range of vendor-specific Command Code values that are 978 allocated on a First-Come/First-Served basis; 980 * A range of values reserved only for experimental and testing 981 purposes. 983 As for AVP Flags, the remaining bits of the Command Flags field of 984 the Diameter header are also assigned via a Standards Action to 985 create new Command Flags if required. 987 d. Creating new applications 988 Similarly to the Command Code namespace, the Application-Id 989 namespace is flat but divided into two distinct ranges: 991 * A range of values reserved for standard Application-Ids 992 allocated after Expert Review of the specification defining the 993 standard application; 995 * A range for values for vendor specific applications, allocated 996 by IANA on a First-Come/First-Serve basis. 998 The IANA AAA parameters page can be found at http://www.iana.org/ 999 assignments/aaa-parameters/aaa-parameters.xml and the enterprise 1000 number IANA page is available at http://www.iana.org/assignments/ 1001 enterprise-numbers. More details on the policies followed by IANA 1002 for namespace management (e.g. First-Come/First-Served, Expert 1003 Review, IETF Review, etc.) can be found in [RFC5226]. 1005 NOTE: 1006 When the same functionality/extension is used by more than one 1007 vendor, it is RECOMMENDED to define a standard extension. 1008 Moreover, a vendor-specific extension SHOULD be registered to 1009 avoid interoperability issues in the same network. With this aim, 1010 the registration policy of vendor-specific extension has been 1011 simplified with the publication of [RFC6733] and the namespace 1012 reserved for vendor-specific extensions is large enough to avoid 1013 exhaustion. 1015 8. IANA Considerations 1017 This document does not require actions by IANA. 1019 9. Security Considerations 1021 This document provides guidelines and considerations for extending 1022 Diameter and Diameter applications. Although such an extension may 1023 be related to a security functionality, the document does not 1024 explicitly give guidance on enhancing Diameter with respect to 1025 security. 1027 10. Contributors 1029 The content of this document was influenced by a design team created 1030 to revisit the Diameter extensibility rules. The team was formed in 1031 February 2008 and finished its work in June 2008. Except the 1032 authors, the design team members were: 1034 o Avi Lior 1035 o Glen Zorn 1037 o Jari Arkko 1039 o Jouni Korhonen 1041 o Mark Jones 1043 o Tolga Asveren 1045 o Glenn McGregor 1047 o Dave Frascone 1049 We would like to thank Tolga Asveren, Glenn McGregor, and John 1050 Loughney for their contributions as co-authors to earlier versions of 1051 this document. 1053 11. Acknowledgments 1055 We greatly appreciate the insight provided by Diameter implementers 1056 who have highlighted the issues and concerns being addressed by this 1057 document. The authors would also like to thank Jean Mahoney, Ben 1058 Campbell, Sebastien Decugis and Benoit Claise for their invaluable 1059 detailed reviews and comments on this document. 1061 12. References 1063 12.1. Normative References 1065 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1066 Requirement Levels", BCP 14, RFC 2119, March 1997. 1068 [RFC6733] Fajardo, V., Arkko, J., Loughney, J., and G. Zorn, 1069 "Diameter Base Protocol", RFC 6733, October 2012. 1071 12.2. Informative References 1073 [Q.3303.3] 1074 3rd Generation Partnership Project, "ITU-T Recommendation 1075 Q.3303.3, "Resource control protocol no. 3 (rcp3): 1076 Protocol at the Rw interface between the Policy Decision 1077 Physical Entity (PD-PE) and the Policy Enforcement 1078 Physical Entity (PE-PE): Diameter"", 2008. 1080 [RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange 1081 (IKE)", RFC 2409, November 1998. 1083 [RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. 1084 Arkko, "Diameter Base Protocol", RFC 3588, September 2003. 1086 [RFC4005] Calhoun, P., Zorn, G., Spence, D., and D. Mitton, 1087 "Diameter Network Access Server Application", RFC 4005, 1088 August 2005. 1090 [RFC4072] Eronen, P., Hiller, T., and G. Zorn, "Diameter Extensible 1091 Authentication Protocol (EAP) Application", RFC 4072, 1092 August 2005. 1094 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 1095 Internet Protocol", RFC 4301, December 2005. 1097 [RFC4740] Garcia-Martin, M., Belinchon, M., Pallares-Lopez, M., 1098 Canales-Valenzuela, C., and K. Tammi, "Diameter Session 1099 Initiation Protocol (SIP) Application", RFC 4740, November 1100 2006. 1102 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1103 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 1104 May 2008. 1106 [RFC5447] Korhonen, J., Bournelle, J., Tschofenig, H., Perkins, C., 1107 and K. Chowdhury, "Diameter Mobile IPv6: Support for 1108 Network Access Server to Diameter Server Interaction", RFC 1109 5447, February 2009. 1111 [RFC5777] Korhonen, J., Tschofenig, H., Arumaithurai, M., Jones, M., 1112 and A. Lior, "Traffic Classification and Quality of 1113 Service (QoS) Attributes for Diameter", RFC 5777, February 1114 2010. 1116 [RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, 1117 "Internet Key Exchange Protocol Version 2 (IKEv2)", RFC 1118 5996, September 2010. 1120 [RFC6735] Carlberg, K. and T. Taylor, "Diameter Priority Attribute- 1121 Value Pairs", RFC 6735, October 2012. 1123 [RFC7075] Tsou, T., Hao, R., and T. Taylor, "Realm-Based Redirection 1124 In Diameter", RFC 7075, November 2013. 1126 [RFC7155] Zorn, G., "Diameter Network Access Server Application", 1127 RFC 7155, April 2014. 1129 [TS29.228] 1130 3rd Generation Partnership Project, "3GPP TS 29.228; 1131 Technical Specification Group Core Network and Terminals; 1132 IP Multimedia (IM) Subsystem Cx and Dx Interfaces; 1133 Signalling flows and message contents", 1134 . 1136 [TS29.229] 1137 3rd Generation Partnership Project, "3GPP TS 29.229; 1138 Technical Specification Group Core Network and Terminals; 1139 Cx and Dx interfaces based on the Diameter protocol; 1140 Protocol details", 1141 . 1143 [TS29.328] 1144 3rd Generation Partnership Project, "3GPP TS 29.328; 1145 Technical Specification Group Core Network and Terminals; 1146 IP Multimedia (IM) Subsystem Sh interface; signalling 1147 flows and message content", 1148 . 1150 [TS29.329] 1151 3rd Generation Partnership Project, "3GPP TS 29.329; 1152 Technical Specification Group Core Network and Terminals; 1153 Sh Interface based on the Diameter protocol; Protocol 1154 details", 1155 . 1157 Authors' Addresses 1159 Lionel Morand (editor) 1160 Orange Labs 1161 38/40 rue du General Leclerc 1162 Issy-Les-Moulineaux Cedex 9 92794 1163 France 1165 Phone: +33145296257 1166 Email: lionel.morand@orange.com 1168 Victor Fajardo 1169 Independent 1171 Email: vf0213@gmail.com 1172 Hannes Tschofenig 1173 Nokia Siemens Networks 1174 Linnoitustie 6 1175 Espoo 02600 1176 Finland 1178 Phone: +358 (50) 4871445 1179 Email: Hannes.Tschofenig@gmx.net 1180 URI: http://www.tschofenig.priv.at