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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ECRIT H. Schulzrinne 3 Internet-Draft Columbia University 4 Intended status: Standards Track H. Tschofenig 5 Expires: September 20, 2013 Nokia Siemens Networks 6 C. Holmberg 7 Ericsson 8 M. Patel 9 InterDigital Communications 10 March 19, 2013 12 Public Safety Answering Point (PSAP) Callback 13 draft-ietf-ecrit-psap-callback-09.txt 15 Abstract 17 After an emergency call is completed (either prematurely terminated 18 by the emergency caller or normally by the call taker) it is possible 19 that the call taker feels the need for further communication. For 20 example, the call may have been dropped by accident without the call 21 taker having sufficient information about the current situation of a 22 wounded person. A call taker may trigger a callback towards the 23 emergency caller using the contact information provided with the 24 initial emergency call. This callback could, under certain 25 circumstances, be treated like any other call and as a consequence it 26 may get blocked by authorization policies or may get forwarded to an 27 answering machine. 29 The IETF emergency services architecture specification already offers 30 a solution approach for allowing PSAP callbacks to bypass 31 authorization policies to reach the caller without unnecessary 32 delays. Unfortunately, the specified mechanism only supports limited 33 scenarios. This document discusses shortcomings of the current 34 mechanisms and illustrates additional scenarios where better-than- 35 normal call treatment behavior would be desirable. A solution based 36 on a new header field value, called "psap-callback", for the SIP 37 Priority header field is specified to accomplish the PSAP callback 38 marking. 40 Status of This Memo 42 This Internet-Draft is submitted in full conformance with the 43 provisions of BCP 78 and BCP 79. 45 Internet-Drafts are working documents of the Internet Engineering 46 Task Force (IETF). Note that other groups may also distribute 47 working documents as Internet-Drafts. The list of current Internet- 48 Drafts is at http://datatracker.ietf.org/drafts/current/. 50 Internet-Drafts are draft documents valid for a maximum of six months 51 and may be updated, replaced, or obsoleted by other documents at any 52 time. It is inappropriate to use Internet-Drafts as reference 53 material or to cite them other than as "work in progress." 55 This Internet-Draft will expire on September 20, 2013. 57 Copyright Notice 59 Copyright (c) 2013 IETF Trust and the persons identified as the 60 document authors. All rights reserved. 62 This document is subject to BCP 78 and the IETF Trust's Legal 63 Provisions Relating to IETF Documents 64 (http://trustee.ietf.org/license-info) in effect on the date of 65 publication of this document. Please review these documents 66 carefully, as they describe your rights and restrictions with respect 67 to this document. Code Components extracted from this document must 68 include Simplified BSD License text as described in Section 4.e of 69 the Trust Legal Provisions and are provided without warranty as 70 described in the Simplified BSD License. 72 Table of Contents 74 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 75 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 76 3. Callback Scenarios . . . . . . . . . . . . . . . . . . . . . . 6 77 3.1. Routing Asymmetry . . . . . . . . . . . . . . . . . . . . 6 78 3.2. Multi-Stage Routing . . . . . . . . . . . . . . . . . . . 7 79 3.3. Call Forwarding . . . . . . . . . . . . . . . . . . . . . 8 80 3.4. Network-based Service URN Resolution . . . . . . . . . . . 10 81 3.5. PSTN Interworking . . . . . . . . . . . . . . . . . . . . 11 82 4. SIP PSAP Callback Indicator . . . . . . . . . . . . . . . . . 12 83 4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 12 84 4.2. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 12 85 4.3. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 12 86 4.3.1. General . . . . . . . . . . . . . . . . . . . . . . . 12 87 4.3.2. ABNF . . . . . . . . . . . . . . . . . . . . . . . . . 12 88 5. Security Considerations . . . . . . . . . . . . . . . . . . . 13 89 5.1. Security Threat . . . . . . . . . . . . . . . . . . . . . 13 90 5.2. Security Requirements . . . . . . . . . . . . . . . . . . 13 91 5.3. Security Solution . . . . . . . . . . . . . . . . . . . . 13 92 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 93 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 94 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17 95 8.1. Normative References . . . . . . . . . . . . . . . . . . . 17 96 8.2. Informative References . . . . . . . . . . . . . . . . . . 17 98 1. Introduction 100 Summoning police, the fire department or an ambulance in emergencies 101 is one of the fundamental and most-valued functions of the telephone. 102 As telephone functionality moves from circuit-switched telephony to 103 Internet telephony, its users rightfully expect that this core 104 functionality will continue to work at least as well as it has for 105 the legacy technology. New devices and services are being made 106 available that could be used to make a request for help, which are 107 not traditional telephones, and users are increasingly expecting them 108 to be used to place emergency calls. 110 An overview of the protocol interactions for emergency calling using 111 the IETF emergency services architecture are described in [RFC6443] 112 and [RFC6881] specifies the technical details. As part of the 113 emergency call setup procedure two important identifiers are conveyed 114 to the PSAP call taker's user agent, namely the Address-Of-Record 115 (AOR), and, if available, the Globally Routable User Agent (UA) URIs 116 (GRUU). RFC 3261 [RFC3261] defines the AOR as: 118 "An address-of-record (AOR) is a SIP or SIPS URI that points to a 119 domain with a location service that can map the URI to another URI 120 where the user might be available. Typically, the location 121 service is populated through registrations. An AOR is frequently 122 thought of as the "public address" of the user." 124 In SIP systems a single user can have a number of user agents 125 (handsets, softphones, voicemail accounts, etc.) which are all 126 referenced by the same AOR. There are a number of cases in which it 127 is desirable to have an identifier which addresses a single user 128 agent rather than the group of user agents indicated by an AOR. The 129 GRUU is such a unique user-agent identifier, which is still globally 130 routable. RFC 5627 [RFC5627] specifies how to obtain and use GRUUs. 131 [RFC6881] also makes use of the GRUU for emergency calls. 133 Regulatory requirements demand that the emergency call setup 134 procedure itself provides enough information to allow the call taker 135 to initiate a callback to the emergency caller. This is desirable in 136 those cases where the call got dropped prematurely or when further 137 communication need arises. The AOR and the GRUU serve this purpose. 139 The communication attempt by the PSAP call taker back to the 140 emergency caller is called 'PSAP callback'. 142 A PSAP callback may, however, be blocked by user configured 143 authorization policies or may be forwarded to an answering machine 144 since SIP entities (SIP proxies as well as the SIP user equipment 145 itself) cannot differentiate the PSAP callback from any other SIP 146 call. "Call barring", "do not disturb", or "call diversion"(aka call 147 forwarding) are features that prevent delivery of a call. It is 148 important to note that these features may be implemented by SIP 149 intermediaries as well as by the user agent. 151 Among the emergency services community there is the desire to offer 152 PSAP callbacks a treatment such that chances are increased that it 153 reaches the emergency caller. At the same time a design must deal 154 with the negative side-effects of allowing certain calls to bypass 155 call forwarding or other authorization policies. Ideally, the PSAP 156 callback has to relate to an earlier emergency call that was made 157 "not too long ago". An exact time interval is difficult to define in 158 a global IETF standard due to the variety of national regulatory 159 requirements. 161 To nevertheless meet the needs from the emergency services community 162 a basic mechanism for preferential treatment of PSAP callbacks was 163 defined in Section 13 of [RFC6443]. The specification says: 165 "A UA may be able to determine a PSAP callback by examining the 166 domain of incoming calls after placing an emergency call and 167 comparing that to the domain of the answering PSAP from the 168 emergency call. Any call from the same domain and directed to the 169 supplied Contact header or AOR after an emergency call should be 170 accepted as a callback from the PSAP if it occurs within a 171 reasonable time after an emergency call was placed." 173 This approach mimics a stateful packet filtering firewall and is 174 indeed helpful in a number of cases. It is also relatively simple to 175 implement even though it requires call state to be maintained by the 176 user agent as well as by SIP intermediaries. Unfortunately, the 177 solution does not work in all deployment scenarios. In Section 3 we 178 describe cases where the currently standardized approach is 179 insufficient. 181 2. Terminology 183 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 184 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 185 document are to be interpreted as described in [RFC2119]. 187 Emergency services related terminology is borrowed from [RFC5012]. 188 This includes terminology like emergency caller, user equipment, call 189 taker, Emergency Service Routing Proxy (ESRP), and Public Safety 190 Answering Point (PSAP). 192 3. Callback Scenarios 194 This section illustrates a number of scenarios where the currently 195 specified solution, as specified in [RFC6881], for preferential 196 treatment of callbacks fails. As explained in Section 1 a SIP entity 197 examines an incoming PSAP callback by comparing the domain of the 198 PSAP with the destination domain of the emergency call. 200 3.1. Routing Asymmetry 202 In some deployment environments it is common to have incoming and 203 outgoing SIP messaging routed through different SIP entities. 204 Figure 1 shows this graphically whereby a VoIP provider uses 205 different SIP proxies for inbound and for outbound call handling. 206 Unless the two devices are synchronized as to state the callback 207 hitting the inbound proxy would get treated like any other call since 208 the emergency call established state information at the outbound 209 proxy only. 211 ,-------. 212 ,' `. 213 ,-------. / Emergency \ 214 ,' `. | Services | 215 / VoIP \ I | Network | 216 | Provider | n | | 217 | | t | | 218 | | e | | 219 | +-------+ | r | | 220 +--+---|Inbound|<--+-----m | | 221 | | |Proxy | | e | +------+ | 222 | | +-------+ | d | |PSAP | | 223 | | | i | +--+---+ | 224 +----+ | | | a-+ | | | 225 | UA |<---+ | | t | | | | 226 | |----+ | | e | | | | 227 +----+ | | | | | | | 228 | | | P | | | | 229 | | | r | | | | 230 | | +--------+ | o | | | | 231 +--+-->|Outbound|--+---->v | | +--+---+ | 232 | |Proxy | | i | | +-+ESRP | | 233 | +--------+ | d | | | +------+ | 234 | | e || | | 235 | | r |+-+ | 236 \ / | | 237 `. ,' \ / 238 '-------' `. ,' 239 '-------' 241 Figure 1: Example for Routing Asymmetry. 243 3.2. Multi-Stage Routing 245 Consider the following emergency call routing scenario shown in 246 Figure 2 where routing towards the PSAP occurs in several stages. In 247 this scenario we consider a SIP UA that uses LoST to learn the next 248 hop destination closer to the PSAP. This call is then sent to the 249 user's VoIP provider. The user's VoIP provider receives the 250 emergency call and creates state based on the destination domain, 251 namely state.org. It then routes it to the indicated ESRP. When the 252 ESRP receives it it needs to decide what the next hop is to get it 253 closer to the PSAP. In our example the next hop is the PSAP with the 254 URI psap@town.com. 256 When a callback is sent from psap@town.com towards the emergency 257 caller the call will get normal treatment by the VoIP providers 258 inbound proxy since the domain of the PSAP does not match the stored 259 state information. 261 ,-------. 262 +----+ ,' `. 263 | UA |--- esrp1@foobar.com / Emergency \ 264 +----+ \ | Services | 265 \ ,-------. | Network | 266 ,' `. | | 267 / VoIP \ | +------+ | 268 ( Provider ) | |PSAP | | 269 \ / | +--+---+ | 270 `. ,' | | 271 '---+---' | | | 272 | |psap@town.com | 273 esrp@state.org | | | 274 | | | | 275 | | | | 276 | | +--+---+ | 277 +------------+---+ESRP | | 278 | +------+ | 279 | | 280 \ / 281 `. ,' 282 '-------' 284 Figure 2: Example for Multi-Stage Routing. 286 3.3. Call Forwarding 288 Imagine the following case where an emergency call enters an 289 emergency network (state.org) via an ESRP but then gets forwarded to 290 a different emergency services network (in our example to police- 291 town.org, fire-town.org or medic-town.org). The same considerations 292 apply when the police, fire and ambulance networks are part of the 293 state.org sub-domains (e.g., police.state.org). 295 Similarly to the previous scenario the problem here is with the wrong 296 state information being established during the emergency call setup 297 procedure. A callback would originate in the police-town.org, fire- 298 town.org or medic-town.org domain whereas the emergency caller's SIP 299 UA or the VoIP outbound proxy has stored state.org. 301 ,-------. 302 ,' `. 303 / Emergency \ 304 | Services | 305 | Network | 306 | (state.org) | 307 | | 308 | | 309 | +------+ | 310 | |PSAP +--+ | 311 | +--+---+ | | 312 | | | | 313 | | | | 314 | | | | 315 | | | | 316 | | | | 317 | +--+---+ | | 318 ------------------+---+ESRP | | | 319 esrp-a@state.org | +------+ | | 320 | | | 321 | Call Fwd | | 322 | +-+-+---+ | 323 \ | | | / 324 `. | | | ,' 325 '-|-|-|-' ,-------. 326 Police | | | Fire ,' `. 327 +------------+ | +----+ / Emergency \ 328 ,-------. | | | | Services | 329 ,' `. | | | | Network | 330 / Emergency \ | Ambulance | | fire-town.org | 331 | Services | | | | | | 332 | Network | | +----+ | | +------+ | 333 |police-town.org| | ,-------. | +----+---+PSAP | | 334 | | | ,' `. | | +------+ | 335 | +------+ | | / Emergency \ | | | 336 | |PSAP +----+--+ | Services | | | , 337 | +------+ | | Network | | `~~~~~~~~~~~~~~~ 338 | | |medic-town.org | | 339 | , | | | 340 `~~~~~~~~~~~~~~~ | +------+ | | 341 | |PSAP +----+ + 342 | +------+ | 343 | | 344 | , 345 `~~~~~~~~~~~~~~~ 347 Figure 3: Example for Call Forwarding. 349 3.4. Network-based Service URN Resolution 351 The IETF emergency services architecture also considers cases where 352 the resolution from the Service URN to the PSAP URI does not only 353 happen at the SIP UA itself but at intermediate SIP entities, such as 354 the user's VoIP provider. 356 Figure 4 shows this message exchange of the outgoing emergency call 357 and the incoming PSAP graphically. While the state information 358 stored at the VoIP provider is correct the state allocated at the SIP 359 UA is not. 361 ,-------. 362 ,' `. 363 / Emergency \ 364 | Services | 365 | Network | 366 |police-town.org| 367 | | 368 | +------+ | Invite to police.example.com 369 | |PSAP +<---+------------------------+ 370 | | +----+------------------+ ^ 371 | +------+ |Invite from | | 372 | ,police.example.com| | 373 `~~~~~~~~~~~~~~~ v | 374 +--------+ ++-----+-+ 375 | | query |VoIP | 376 | LoST |<-----------------------|Service | 377 | Server | police.example.com |Provider| 378 | |----------------------->| | 379 +--------+ +--------+ 380 | ^ 381 Invite| | Invite 382 from| | to 383 police.example.com| | urn:service:sos 384 V | 385 +-------+ 386 | SIP | 387 | UA | 388 | Alice | 389 +-------+ 391 Figure 4: Example for Network-based Service URN Resolution. 393 3.5. PSTN Interworking 395 In case an emergency call enters the PSTN, as shown in Figure 5, 396 there is no guarantee that the callback some time later does leave 397 the same PSTN/VoIP gateway or that the same end point identifier is 398 used in the forward as well as in the backward direction making it 399 difficult to reliably detect PSAP callbacks. 401 +-----------+ 402 | PSTN |-------------+ 403 | Calltaker | | 404 | Bob |<--------+ | 405 +-----------+ | v 406 ------------------- 407 //// \\\\ +------------+ 408 | | |PSTN / VoIP | 409 | PSTN |---->|Gateway | 410 \\\\ //// | | 411 ------------------- +----+-------+ 412 ^ | 413 | | 414 +-------------+ | +--------+ 415 | | | |VoIP | 416 | PSTN / VoIP | +->|Service | 417 | Gateway | |Provider| 418 | |<------Invite----| Y | 419 +-------------+ +--------+ 420 | ^ 421 | | 422 Invite Invite 423 | | 424 V | 425 +-------+ 426 | SIP | 427 | UA | 428 | Alice | 429 +-------+ 431 Figure 5: Example for PSTN Interworking. 433 Note: This scenario is considered outside the scope of this document. 434 The specified solution does not support this use case. 436 4. SIP PSAP Callback Indicator 438 4.1. General 440 This section defines a new header field value, called "psap- 441 callback", for the SIP Priority header field defined in [RFC3261]. 442 The value is used to inform SIP entities that the request is 443 associated with a PSAP callback SIP session. 445 4.2. Usage 447 SIP entities that receive the header field value within an initial 448 request for a SIP session can, depending on local policies, apply 449 PSAP callback specific procedures for the session or request. 451 The PSAP callback specific procedures may be applied by SIP-based 452 network entities and by the callee. The specific procedures taken 453 when receiving such a PSAP callback marked call, such as bypassing 454 services and barring procedures, are outside the scope of this 455 document. 457 4.3. Syntax 459 4.3.1. General 461 This section defines the ABNF for the new SIP Priority header field 462 value "psap-callback". 464 4.3.2. ABNF 466 priority-value /= "psap-callback" 468 Figure 6: ABNF 470 5. Security Considerations 472 5.1. Security Threat 474 The PSAP callback functionality described in this document allows 475 marked calls to bypass blacklists, ignore call forwarding procedures 476 and other similar features used to raise the attention of emergency 477 callers when attempting to contact them. In the case where the SIP 478 Priority header value, 'psap-callback', is supported by the SIP UA, 479 it would override user interface configurations, such as vibrate-only 480 mode, to alert the caller of the incoming call. 482 5.2. Security Requirements 484 The requirement is to ensure that the mechanisms described in this 485 document can not be used for malicious purposes, including 486 telemarketing. 488 Furthermore, if the newly defined extension is not recognized, not 489 verified adequately, or not obeyed by SIP intermediaries or SIP 490 endpoints then it must not lead to a failure of the call handling 491 procedure. Such call must be treated like a call that does not have 492 any marking attached. 494 5.3. Security Solution 496 Figure 7 shows the architecture that utilizes the identity of the 497 PSAP to decide whether a preferential treatment of callbacks should 498 be provided. To make this policy decision, the identity of the PSAP 499 is compared with a white list of valid PSAPs available to the SIP 500 entity. The identity assurance in SIP can come in different forms, 501 such as SIP Identity [RFC4474] or with P-Asserted-Identity [RFC3325]. 502 The former technique relies on a cryptographic assurance and the 503 latter on a chain of trust. Also the usage of TLS between 504 neighboring SIP entities may provide useful identity information. 506 +----------+ 507 | List of |+ 508 | valid || 509 | PSAPs || 510 +----------+| 511 +----------+ 512 * 513 * white list 514 * 515 V 516 Incoming +----------+ Normal 517 SIP Msg | SIP |+ Treatment 518 -------------->| Entity ||======================> 519 + Identity | ||(if not in white list) 520 Info +----------+| 521 +----------+ 522 || 523 || 524 || Preferential 525 || Treatment 526 ++========================> 527 (if successfully verified) 529 Figure 7: Identity-based Authorization 531 An important aspect from a security point of view is the relationship 532 between the emergency services network (containing PSAPs) and the 533 VoIP provider (assuming that the emergency call travels via the VoIP 534 provider and not directly between the SIP UA and the PSAP). 536 If there is some form of relationship between the emergency services 537 operator and the VoIP provider then the identification of a PSAP 538 callback is less problematic than in the case where the two entities 539 have not entered in some form of relationship that would allow the 540 VoIP provider to verify whether the marked callback message indeed 541 came from a legitimate source. 543 The establishment of a whitelist with PSAP identities maybe be 544 operationally complex. When there is a local relationship between 545 the VoIP provider and the PSAP then populating the whitelist is 546 fairly simple. For SIP UAs there is no need to maintain a list of 547 PSAPs. Instead SIP UAs are assumed to trust the correct processing 548 of their VoIP provider, i.e., the VoIP provider processes the PSAP 549 callback marking and, if it cannot be verified, the PSAP callback 550 marking is removed. If it is left untouched then the SIP UA should 551 assume that it has been verified successfully by the VoIP provider 552 and it should therefore be obeyed. 554 6. IANA Considerations 556 This document adds the "psap-callback" value to the SIP Priority 557 header IANA registry allocated by [RFC6878]. The semantic of the 558 newly defined "psap-callback" value is defined in Section 4. 560 7. Acknowledgements 562 We would like to thank the following persons for their feedback: Paul 563 Kyzivat, Martin Thomson, Robert Sparks, Keith Drage, Cullen Jennings 564 Brian Rosen, Martin Dolly, Bernard Aboba, Andrew Allen, Atle Monrad, 565 John-Luc Bakker, John Elwell, Geoff Thompson, Dan Romascanu, James 566 Polk, John Medland, Hadriel Kaplan, Kenneth Carlberg, Timothy Dwight, 567 Janet Gunn 569 Finally, we would like to thank the ECRIT working group chairs, Marc 570 Linsner and Roger Marshall, for their support. 572 8. References 574 8.1. Normative References 576 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 577 Requirement Levels", BCP 14, RFC 2119, March 1997. 579 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 580 A., Peterson, J., Sparks, R., Handley, M., and E. 581 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 582 June 2002. 584 [RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private 585 Extensions to the Session Initiation Protocol (SIP) for 586 Asserted Identity within Trusted Networks", RFC 3325, 587 November 2002. 589 [RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers", 590 RFC 3966, December 2004. 592 [RFC3969] Camarillo, G., "The Internet Assigned Number Authority 593 (IANA) Uniform Resource Identifier (URI) Parameter 594 Registry for the Session Initiation Protocol (SIP)", 595 BCP 99, RFC 3969, December 2004. 597 [RFC4474] Peterson, J. and C. Jennings, "Enhancements for 598 Authenticated Identity Management in the Session 599 Initiation Protocol (SIP)", RFC 4474, August 2006. 601 [RFC5627] Rosenberg, J., "Obtaining and Using Globally Routable User 602 Agent URIs (GRUUs) in the Session Initiation Protocol 603 (SIP)", RFC 5627, October 2009. 605 [RFC6878] Roach, A., "IANA Registry for the Session Initiation 606 Protocol (SIP) "Priority" Header Field", RFC 6878, 607 March 2013. 609 8.2. Informative References 611 [RFC4484] Peterson, J., Polk, J., Sicker, D., and H. Tschofenig, 612 "Trait-Based Authorization Requirements for the Session 613 Initiation Protocol (SIP)", RFC 4484, August 2006. 615 [RFC5012] Schulzrinne, H. and R. Marshall, "Requirements for 616 Emergency Context Resolution with Internet Technologies", 617 RFC 5012, January 2008. 619 [RFC5031] Schulzrinne, H., "A Uniform Resource Name (URN) for 620 Emergency and Other Well-Known Services", RFC 5031, 621 January 2008. 623 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 624 Specifications: ABNF", STD 68, RFC 5234, January 2008. 626 [RFC6443] Rosen, B., Schulzrinne, H., Polk, J., and A. Newton, 627 "Framework for Emergency Calling Using Internet 628 Multimedia", RFC 6443, December 2011. 630 [RFC6881] Rosen, B. and J. Polk, "Best Current Practice for 631 Communications Services in Support of Emergency Calling", 632 BCP 181, RFC 6881, March 2013. 634 Authors' Addresses 636 Henning Schulzrinne 637 Columbia University 638 Department of Computer Science 639 450 Computer Science Building 640 New York, NY 10027 641 US 643 Phone: +1 212 939 7004 644 EMail: hgs+ecrit@cs.columbia.edu 645 URI: http://www.cs.columbia.edu 647 Hannes Tschofenig 648 Nokia Siemens Networks 649 Linnoitustie 6 650 Espoo 02600 651 Finland 653 Phone: +358 (50) 4871445 654 EMail: Hannes.Tschofenig@gmx.net 655 URI: http://www.tschofenig.priv.at 657 Christer Holmberg 658 Ericsson 659 Hirsalantie 11 660 Jorvas 02420 661 Finland 663 EMail: christer.holmberg@ericsson.com 665 Milan Patel 666 InterDigital Communications 668 EMail: Milan.Patel@interdigital.com