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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 P2PSIP Working Group D. Bryan 3 Internet-Draft SIPeerior Technologies 4 Intended status: Informational P. Matthews 5 Expires: January 8, 2009 Unaffiliated 6 E. Shim 7 Locus Telecommunications 8 D. Willis 9 Softarmor Systems 10 S. Dawkins 11 Huawei (USA) 12 July 7, 2008 14 Concepts and Terminology for Peer to Peer SIP 15 draft-ietf-p2psip-concepts-02 17 Status of this Memo 19 By submitting this Internet-Draft, each author represents that any 20 applicable patent or other IPR claims of which he or she is aware 21 have been or will be disclosed, and any of which he or she becomes 22 aware will be disclosed, in accordance with Section 6 of BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF), its areas, and its working groups. Note that 26 other groups may also distribute working documents as Internet- 27 Drafts. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 The list of current Internet-Drafts can be accessed at 35 http://www.ietf.org/ietf/1id-abstracts.txt. 37 The list of Internet-Draft Shadow Directories can be accessed at 38 http://www.ietf.org/shadow.html. 40 This Internet-Draft will expire on January 8, 2009. 42 Abstract 44 This document defines concepts and terminology for use of the Session 45 Initiation Protocol in a peer-to-peer environment where the 46 traditional proxy-registrar and message routing functions are 47 replaced by a distributed mechanism implemented using a distributed 48 hash table or other distributed data mechanism with similar external 49 properties. This document includes a high-level view of the 50 functional relationships between the network elements defined herein, 51 a conceptual model of operations, and an outline of the related open 52 problems being addressed by the P2PSIP working group. As this 53 document matures, it is expected to define the general framework for 54 P2PSIP. 56 Table of Contents 58 1. Author's Notes and Changes To This Version . . . . . . . . . . 4 59 1.1. Author's Notes . . . . . . . . . . . . . . . . . . . . . . 4 60 1.2. Changes from Previous Version . . . . . . . . . . . . . . 4 62 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 3. High Level Description . . . . . . . . . . . . . . . . . . . . 5 65 3.1. Services . . . . . . . . . . . . . . . . . . . . . . . . . 6 66 3.2. Clients . . . . . . . . . . . . . . . . . . . . . . . . . 6 67 3.3. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . 6 68 3.4. Relationship of Peer and Client Protocols . . . . . . . . 7 69 3.5. Relationship Between P2PSIP and SIP . . . . . . . . . . . 7 70 3.6. Relationship Between P2PSIP and Other AoR 71 Dereferencing Approaches . . . . . . . . . . . . . . . . . 7 72 3.7. NAT Issues . . . . . . . . . . . . . . . . . . . . . . . . 7 74 4. Reference Model . . . . . . . . . . . . . . . . . . . . . . . 8 76 5. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 10 78 6. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 14 79 6.1. The Distributed Database Function . . . . . . . . . . . . 14 80 6.2. Using the Distributed Database Function . . . . . . . . . 16 81 6.3. NAT Traversal . . . . . . . . . . . . . . . . . . . . . . 19 82 6.4. Locating and Joining an Overlay . . . . . . . . . . . . . 21 83 6.5. Possible Client Behavior . . . . . . . . . . . . . . . . . 22 84 6.6. Interacting with non-P2PSIP entities . . . . . . . . . . . 22 85 6.7. Architecture . . . . . . . . . . . . . . . . . . . . . . . 23 87 7. Additional Questions . . . . . . . . . . . . . . . . . . . . . 24 88 7.1. Selecting between Multiple Peers offering the Same 89 Service . . . . . . . . . . . . . . . . . . . . . . . . . 24 90 7.2. Visibility of Messages to Intermediate Peers . . . . . . . 25 91 7.3. Using C/S SIP and P2PSIP Simultaneously in a Single UA . . 25 92 7.4. Clients, Peers, and Services . . . . . . . . . . . . . . . 25 93 7.5. Relationships of Domains to Overlays . . . . . . . . . . . 25 95 8. Security Considerations . . . . . . . . . . . . . . . . . . . 26 96 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 98 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 26 100 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26 101 11.1. Normative References . . . . . . . . . . . . . . . . . . . 26 102 11.2. Informative References . . . . . . . . . . . . . . . . . . 27 104 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28 105 Intellectual Property and Copyright Statements . . . . . . . . . . 30 107 1. Author's Notes and Changes To This Version 109 1.1. Author's Notes 111 The editors are currently considering a rather substantial revision 112 to this document to better reflect the evolving direction of the 113 working group. This version incorporates only minor revisions from 114 the -01 version of the document. 116 In particular, the authors intend to make the following more 117 substantial changes, and solicit the opinion of the WG on these 118 changes, as well as to solicit suggestions for text for the new 119 sections: 121 o Document the current view of the working group that the protocols 122 being developed in P2PSIP should be more broadly applicable than 123 just for peer-to-peer networks of SIP endpoints. 125 o The authors plan to add a section that documents the history of 126 various design decisions, and at the same time remove this 127 discussion from other parts of the text. The authors feel that 128 this historical information is important, but also feel that a 129 reader needs to be able to quickly see what the current state of 130 the P2PSIP work is today. An exception would be an early 131 explanation of the fact that P2PSIP doesn't use SIP for the peer 132 protocol, a frequent source of confusion to many people new to the 133 WG. 135 o The definition text is somewhat out of date, and should be revised 136 (with some terms added and others eliminated, as appropriate) 138 o Incorporate the descriptions of the applications scenarios 139 currently described in draft-bryan-p2psip-app-scenarios-00 into 140 this document. 142 1.2. Changes from Previous Version 144 Changes to this version include removal of the prefix "P2PSIP" before 145 each definition, and clarification on the issue of clients, 146 reflecting the consensus of the WG. 148 2. Background 150 One of the fundamental problems in multimedia communication between 151 Internet nodes is that of discovering the host at which a given user 152 can be reached. In the Session Initiation Protocol (SIP) [RFC3261] 153 this problem is expressed as the problem of mapping an Address of 154 Record (AoR) for a user into one or more Contact URIs [RFC3986]. The 155 AoR is a name for the user that is independent of the host or hosts 156 where the user can be contacted, while a Contact URI indicates the 157 host where the user can be contacted. 159 In the common SIP-using architectures that we refer to as 160 "Conventional SIP" or "Client/Server SIP", there is a relatively 161 fixed hierarchy of SIP routing proxies and SIP user agents. To 162 deliver a SIP INVITE to the host or hosts at which the user can be 163 contacted, a SIP UA follows the procedures specified in [RFC3263] to 164 determine the IP address of a SIP proxy, and then sends the INVITE to 165 that proxy. The proxy will then, in turn, deliver the SIP INVITE to 166 the hosts where the user can be contacted. 168 This document gives a high-level description of an alternative 169 solution to this problem. In this alternative solution, the 170 relatively fixed hierarchy of Client/Server SIP is replaced by a 171 peer-to-peer overlay network. In this peer-to-peer overlay network, 172 the various AoR to Contact URI mappings are not centralized at proxy/ 173 registrar nodes but are instead distributed amongst the peers in the 174 overlay. 176 The details of this alternative solution are currently being worked 177 out in the P2PSIP working group. This document describes the basic 178 concepts of such a peer-to-peer overlay, and lists the open questions 179 that still need to be resolved. As the work proceeds, it is expected 180 that this document will develop into a high-level architecture 181 document for the solution. 183 3. High Level Description 185 A P2PSIP Overlay is a collection of nodes organized in a peer-to-peer 186 fashion for the purpose of enabling real-time communication using the 187 Session Initiation Protocol (SIP). Collectively, the nodes in the 188 overlay provide a distributed mechanism for mapping names to overlay 189 locations. This provides for the mapping of Addresses of Record 190 (AoRs) to Contact URIs, thereby providing the "location server" 191 function of [RFC3261]. An Overlay also provides a transport function 192 by which SIP messages can be transported between any two nodes in the 193 overlay. 195 A P2PSIP Overlay consists of one or more nodes called Peers. The 196 peers in the overlay collectively run a distributed database 197 algorithm. This distributed database algorithm allows data to be 198 stored on peers and retrieved in an efficient manner. It may also 199 ensure that a copy of a data item is stored on more than one peer, so 200 that the loss of a peer does not result in the loss of the data item 201 to the overlay. 203 One use of this distributed database is to store the information 204 required to provide the mapping between AoRs and Contact URIs for the 205 distributed location function. This provides a location function 206 within each overlay that is an alternative to the location functions 207 described in [RFC3263]. However, the model of [RFC3263] is used 208 between overlays. 210 3.1. Services 212 The nature of peer-to-peer computing is that each peer offers 213 services to other peers to allow the overlay to collectively provide 214 larger functions. In P2PSIP, peers offer storage and transport 215 services to allow the distributed database function and distributed 216 transport function to be implemented. It is expected that individual 217 peers may also offer other services. Some of these additional 218 services (for example, a STUN server service 219 [I-D.ietf-behave-rfc3489bis]) may be required to allow the overlay to 220 form and operate, while others (for example, a voicemail service) may 221 be enhancements to the basic P2PSIP functionality. 223 To allow peers to offer these additional services, the distributed 224 database may need to store information about services. For example, 225 it may need to store information about which peers offer which 226 services, and perhaps what sort of capacity each peer has for 227 delivering each listed service. 229 3.2. Clients 231 An overlay may or may not also include one or more nodes called 232 clients. The role of a client in the P2PSIP model is still under 233 discussion, with a number of suggestions for roles being put forth. 234 The group has reached consensus that clients will be able to store 235 and retrieve information from the overlay. Section 6.5 discusses the 236 possible roles of a client in more detail. 238 3.3. Protocol 240 Peers in an overlay need to speak some protocol between themselves to 241 maintain the overlay and to store and retrieve data. Until a better 242 name is found, this protocol has been dubbed the P2PSIP Peer 243 Protocol. While the use of SIP for this protocol was proposed as the 244 working group was forming, the group is currently working toward a 245 new protocol. 247 3.4. Relationship of Peer and Client Protocols 249 To allow clients to communicate with peers, another protocol is 250 required. Until a better name is found, this protocol has been 251 dubbed the P2PSIP Client Protocol. The details of this protocol are 252 also very much under debate. However, if the client protocol exists, 253 then it is agreed that it should be a logical subset of the peer 254 protocol. In other words, the syntax of the peer and client 255 protocols may be completely different, but any operation supported by 256 client protocol is also supported by the peer protocol. This implies 257 that clients cannot do anything that peers cannot also do. 259 3.5. Relationship Between P2PSIP and SIP 261 Since P2PSIP is about peer-to-peer networks for real-time 262 communication, it is expected that most (if not all) peers and 263 clients will be coupled with SIP entities. For example, one peer 264 might be coupled with a SIP UA, another might be coupled with a SIP 265 proxy, while a third might be coupled with a SIP-to-PSTN gateway. 266 For such nodes, we think of the peer or client portion of the node as 267 being distinct from the SIP entity portion. However, there is no 268 hard requirement that every P2PSIP node (peer or client) be coupled 269 to a SIP entity, and some proposed architectures include peer nodes 270 that have no SIP function whatsoever. 272 3.6. Relationship Between P2PSIP and Other AoR Dereferencing Approaches 274 As noted above, the fundamental task of P2PSIP is turning an AoR into 275 a Contact. This task might be approached using zeroconf techniques 276 such as multicast DNS and DNS Service Discovery (as in Apple's 277 Bonjour protocol), link-local multicast name resolution [RFC4795], 278 and dynamic DNS [RFC2136]. 280 These alternatives were discussed in the P2PSIP Working Group, and 281 not pursued as a general solution for a number of reasons related to 282 scalability, the ability to work in a disconnected state, partition 283 recovery, and so on. However, there does seem to be some continuing 284 interest in the possibility of using DNS-SD and mDNS for 285 bootstrapping of P2PSIP overlays. 287 3.7. NAT Issues 289 Network Address Translators (NATs) are impediments to establishing 290 and maintaining peer-to-peer networks, since NATs hinder direct 291 communication between peers. Some peer-to-peer network architectures 292 avoid this problem by insisting that all peers exist in the same 293 address space. However, in the P2PSIP model, it has been agreed that 294 peers can live in multiple address spaces interconnected by NATs. 296 This implies that Peer Protocol connections must be able to traverse 297 NATs. It also means that the peers must collectively provide a 298 distributed transport function that allows a peer to send a SIP 299 message to any other peer in the overlay - without this function two 300 peers in different IP address spaces might not be able to exchange 301 SIP messages. 303 4. Reference Model 305 The following diagram shows a P2PSIP Overlay consisting of a number 306 of Peers, one Client, and an ordinary SIP UA. It illustrates a 307 typical P2PSIP overlay but does not limit other compositions or 308 variations; for example, Proxy Peer P might also talk to a ordinary 309 SIP proxy as well. The figure is not intended to cover all possible 310 architecture variations in this document. 312 --->PSTN 313 +------+ N +------+ +---------+ / 314 | | A | | | Gateway |-/ 315 | UA |####T#####| UA |#####| Peer |######## 316 | Peer | N | Peer | | G | # P2PSIP 317 | E | A | F | +---------+ # Client 318 | | T | | # Protocol 319 +------+ N +------+ # | 320 # A # | 321 NATNATNATNAT # | 322 # # | \__/ 323 NATNATNATNAT +-------+ v / \ 324 # N | |=====/ UA \ 325 +------+ A P2PSIP Overlay | Peer | /Client\ 326 | | T | Q | |___C__| 327 | UA | N | | 328 | Peer | A +-------+ 329 | D | T # 330 | | N # 331 +------+ A # P2PSIP 332 # T # Peer 333 # N +-------+ +-------+ # Protocol 334 # A | | | | # 335 #########T####| Proxy |########| Redir |####### 336 N | Peer | | Peer | 337 A | P | | R | 338 T +-------+ +-------+ 339 | / 340 | SIP / 341 \__/ / / 342 /\ / ______________/ SIP 343 / \/ / 344 / UA \/ 345 /______\ 346 SIP UA A 348 Figure: P2PSIP Overlay Reference Model 350 Here, the large perimeter depicted by "#" represents a stylized view 351 of the Overlay (the actual connections could be a mesh, a ring, or 352 some other structure). Around the periphery of the Overlay 353 rectangle, we have a number of Peers. Each peer is labeled with its 354 coupled SIP entity -- for example, "Proxy Peer P" means that peer P 355 which is coupled with a SIP proxy. In some cases, a peer or client 356 might be coupled with two or more SIP entities. In this diagram we 357 have a PSTN gateway coupled with peer "G", three peers ("D", "E" and 358 "F") which are each coupled with a UA, a peer "P" which is coupled 359 with a SIP proxy, an ordinary peer "Q", and one peer "R" which is 360 coupled with a SIP Redirector. Note that because these are all 361 Peers, each is responsible for storing Resource Records and 362 transporting messages around the Overlay. 364 To the left, two of the peers ("D" and "E") are behind network 365 address translators (NATs). These peers are included in the P2PSIP 366 overlay and thus participate in storing resource records and routing 367 messages, despite being behind the NATs. 369 Below the Overlay, we have a conventional SIP UA "A" which is not 370 part of the Overlay, either directly as a peer or indirectly as a 371 client. It speaks neither the Peer nor Client protocols. Instead, 372 it uses SIP to interact with the Overlay. 374 On the right side, we have a client "C", which uses the Client 375 Protocol depicted by "=" to communicate with Proxy Peer "Q". The 376 Client "C" could communicate with a different peer, for example peer 377 "F", if it establishes a connection to "F" instead of or in addition 378 to "Q". The exact role that this client plays in the network is 379 still under discussion (see Section 6.5). 381 Both the SIP proxy coupled with peer "P" and the SIP redirector 382 coupled with peer "R" can serve as adapters between ordinary SIP 383 devices and the Overlay. Each accepts standard SIP requests and 384 resolves the next-hop by using the P2PSIP overlay Peer Protocol to 385 interact with the routing knowledge of the Overlay, then processes 386 the SIP requests as appropriate (proxying or redirecting towards the 387 next-hop). Note that proxy operation is bidirectional - the proxy 388 may be forwarding a request from an ordinary SIP device to the 389 Overlay, or from the P2PSIP overlay to an ordinary SIP device. 391 The PSTN Gateway at peer "G" provides a similar sort of adaptation to 392 and from the public switched telephone network (PSTN). 394 5. Definitions 396 This section defines a number of concepts that are key to 397 understanding the P2PSIP work. 399 Overlay Network: An overlay network is a computer network which is 400 built on top of another network. Nodes in the overlay can be 401 thought of as being connected by virtual or logical links, each of 402 which corresponds to a path, perhaps through many physical links, 403 in the underlying network. For example, many peer-to-peer 404 networks are overlay networks because they run on top of the 405 Internet. Dial-up Internet is an overlay upon the telephone 406 network. 408 P2P Network: A peer-to-peer (or P2P) computer network is a network 409 that relies primarily on the computing power and bandwidth of the 410 participants in the network rather than concentrating it in a 411 relatively low number of servers. P2P networks are typically used 412 for connecting nodes via largely ad hoc connections. Such 413 networks are useful for many purposes. Sharing content files (see 414 ) containing audio, 415 video, data or anything in digital format is very common, and 416 realtime data, such as telephony traffic, is also exchanged using 417 P2P technology. . A 418 P2P Network may also be called a "P2P Overlay" or "P2P Overlay 419 Network" or "P2P Network Overlay", since its organization is not 420 at the physical layer, but is instead "on top of" an existing 421 Internet Protocol network. 423 P2PSIP: A suite of communications protocols related to the Session 424 Initiation Protocol (SIP) [RFC3261] that enable SIP to use peer- 425 to-peer techniques for resolving the targets of SIP requests, 426 providing SIP message transport, and providing other SIP-related 427 functions. The exact contents of this protocol suite are still 428 under discussion, but is likely to include the P2PSIP Peer 429 Protocol and may include a P2PSIP Client Protocol (see definitions 430 below). 432 User: A human that interacts with the overlay through SIP UAs 433 located on peers and clients (and perhaps other ways). 435 The following terms are defined here only within the scope of 436 P2PSIP. These terms may have conflicting definitions in other 437 bodies of literature. Some earlier versions of this document 438 prefixed each term with "P2PSIP" to clarify the term's scope. 439 This prefixing has been eliminated from the text; however the 440 scoping still applies. 442 Overlay Name: A human-friendly name that identifies a specific 443 P2PSIP Overlay. This is in the format of (a portion of) a URI, 444 but may or may not have a related record in the DNS. 446 Peer: A node participating in a P2PSIP Overlay that provides storage 447 and transport services to other nodes in that P2PSIP Overlay. 448 Each Peer has a unique identifier, known as a Peer-ID, within the 449 Overlay. Each Peer may be coupled to one or more SIP entities. 450 Within the Overlay, the peer is capable of performing several 451 different operations, including: joining and leaving the overlay, 452 transporting SIP messages within the overlay, storing information 453 on behalf of the overlay, putting information into the overlay, 454 and getting information from the overlay. 456 Peer-ID: Information that uniquely identifies each Peer within a 457 given Overlay. This value is not human-friendly -- in a DHT 458 approach, this is a numeric value in the hash space. These Peer- 459 IDs are completely independent of the identifier of any user of a 460 user agent associated with a peer. (Note: This is often called a 461 "Node-ID" in the P2P literature). 463 Client: A node participating in a P2PSIP Overlay that is less 464 capable than a Peer in some way. The role of a Client is still 465 under debate, with a number of competing proposals (see the 466 discussion on this later in the document). It has been agreed 467 that they do have the ability to add, modify, inspect, and delete 468 information in the overlay. Note that the term client does not 469 imply that this node is a SIP UAC. Some have suggested that the 470 word 'client' be changed to something else to avoid both this 471 confusion and the implication of a client-server relationship. 473 User Name: A human-friendly name for a user. This name must be 474 unique within the overlay, but may be unique in a wider scope. 475 User Names are formatted so that they can be used within a URI 476 (likely a SIP URI), perhaps in combination with the Overlay Name. 478 Service: A capability contributed by a peer to an overlay or to the 479 members of an overlay. It is expected that not all peers and 480 clients will offer the same set of services, so a means of finding 481 peers (and perhaps clients) that offer a particular service is 482 required. Services might include routing of requests, storing of 483 routing data, storing of other data, STUN discovery, STUN relay, 484 and many other things. This model posits a requirement for a 485 service locator function, possibly including supporting 486 information such as the capacity of a peer to provide a specific 487 service or descriptions of the policies under which a peer will 488 provide that service. We currently expect that we will need to be 489 able to search for available service providers within each 490 overlay. We think we might need to be able to make searches based 491 on network locality or path minimalization. 493 Service Name: A unique, human-friendly, name for a service. 495 Resource: Anything about which information can be stored in the 496 overlay. Both Users and Services are examples of Resources. 498 Resource-ID: A non-human-friendly value that uniquely identifies a 499 resource and which is used as a key for storing and retrieving 500 data about the resource. One way to generate a Resource-ID is by 501 applying a mapping function to some other unique name (e.g., User 502 Name or Service Name) for the resource. The Resource-ID is used 503 by the distributed database algorithm to determine the peer or 504 peers that are responsible for storing the data for the overlay. 506 Resource Record: A block of data, stored using distributed database 507 mechanism of the Overlay, that includes information relevant to a 508 specific resource. We presume that there may be multiple types of 509 resource records. Some may hold data about Users, and others may 510 hold data about Services, and the working group may define other 511 types. The types, usages, and formats of the records are a 512 question for future study. 514 Responsible Peer The Peer that is responsible for storing the 515 Resource Record for a Resource. In the literature, the term "Root 516 Peer" is also used for this concept. 518 Peer Protocol: The protocol spoken between P2PSIP Overlay peers to 519 share information and organize the P2PSIP Overlay Network. 521 Client Protocol: The protocol spoken between Clients and Peers. It 522 is used to store and retrieve information from the P2P Overlay. 523 The nature of this protocol, and even its existence, is under 524 discussion. However, if it exists, it has been agreed that the 525 Client Protocol is a functional subset of the P2P Peer Protocol, 526 but may differ in syntax and protocol implementation (i.e., may 527 not be syntactically related). 529 Peer Protocol Connection / P2PSIP Client Protocol Connection: The 530 TCP, UDP or other transport layer protocol connection over which 531 the Peer Protocol (or respectively the Client protocol) is 532 transported. 534 Neighbors: The set of P2PSIP Peers that either a Peer or Client know 535 of directly and can reach without further lookups. 537 Joining Peer: A node that is attempting to become a Peer in a 538 particular Overlay. 540 Bootstrap Peer: A Peer in the Overlay that is the first point of 541 contact for a Joining Peer. It selects the peer that will serve 542 as the Admitting Peer and helps the joining peer contact the 543 admitting peer. 545 Admitting Peer: A Peer in the Overlay which helps the Joining Peer 546 join the Overlay. The choice of the admitting peer may depend on 547 the joining peer (e.g., depend on the joining peer's Peer-ID). 548 For example, the admitting peer might be chosen as the peer which 549 is "closest" in the logical structure of the overlay to the future 550 position of the joining peer. The selection of the admitting peer 551 is typically done by the bootstrap peer. It is allowable for the 552 bootstrap peer to select itself as the admitting peer. 554 Bootstrap Server: A network node used by Joining Peers to locate a 555 Bootstrap Peer. A Bootstrap Server may act as a proxy for 556 messages between the Joining Peer and the Bootstrap Peer. The 557 Bootstrap Server itself is typically a stable host with a DNS name 558 that is somehow communicated (for example, through configuration) 559 to peers that want to join the overlay. A Bootstrap Server is NOT 560 required to be a peer or client, though it may be if desired. 562 Peer Admission: The act of admitting a node (the "Joining Peer") 563 into an Overlay as a Peer. After the admission process is over, 564 the joining peer is a fully-functional peer of the overlay. 565 During the admission process, the joining peer may need to present 566 credentials to prove that it has sufficient authority to join the 567 overlay. 569 Resource Record Insertion: The act of inserting a P2PSIP Resource 570 Record into the distributed database. Following insertion, the 571 data will be stored at one or more peers. The data can be 572 retrieved or updated using the Resource-ID as a key. 574 6. Discussion 576 6.1. The Distributed Database Function 578 A P2PSIP Overlay functions as a distributed database. The database 579 serves as a way to store information about things called Resources. 580 A piece of information, called a Resource Record, can be stored by 581 and retrieved from the database using a key associated with the 582 Resource Record called its Resource-ID. Each Resource must have a 583 unique Resource-ID. In addition to uniquely identifying the 584 Resource, the Resource-ID is also used by the distributed database 585 algorithm to determine the peer or peers that store the Resource 586 Record in the overlay. 588 It is expected that the P2PSIP working group will standardize the 589 way(s) certain types of resources are represented in the distributed 590 database. 592 One type of resource representation that the working group is 593 expected to standardize is information about users. Users are humans 594 that can use the overlay to do things like making and receiving 595 calls. Information stored in the resource record associated with a 596 user might include things like the full name of the user and the 597 location of the UAs that the user is using. 599 Before information about a user can be stored in the overlay, a user 600 needs a User Name. The User Name is a human-friendly identifier that 601 uniquely identifies the user within the overlay. The User Name is 602 not a Resource-ID, rather the Resource-ID is derived from the User 603 Name using some mapping function (often a cryptographic hash 604 function) defined by the distributed database algorithm used by the 605 overlay. 607 The overlay may also require that the user have a set of credentials. 608 Credentials may be required to authenticate the user and/or to show 609 that the user is authorized to use the overlay. 611 Another type of resource representation that the working group is 612 expected to standardize is information about services. Services 613 represent actions that a peer (and perhaps a client) can do to 614 benefit other peers and clients in the overlay. Information that 615 might be stored in the resource record associated with a service 616 might include the peers (and perhaps clients) offering the service. 618 Each service has a human-friendly Service Name that uniquely 619 identifies the service. Like User Names, the Service Name is not a 620 resource-id, rather the resource-id is derived from the service name 621 using some function defined by the distributed database algorithm 622 used by the overlay. 624 It is expected that the working group will standardize at least one 625 service. For each standardized service, the working group will 626 likely specify the service name, the nature and format of the 627 information stored in the resource record associated with the 628 service, and the protocol used to access the service. 630 The overlay may require that the peer (or client) have a set of 631 credentials for a service. For example, credentials might be 632 required to show that the peer (or client) is authorized to offer the 633 service, or to show that the peer (or client) is a providing a 634 trustworthy implementation of the service. 636 It is expected that the P2PSIP WG will not standardize how a User 637 Name is obtained, nor how the credentials associated with a User Name 638 or a Service Name are obtained, but merely standardize at least one 639 acceptable format for each. To ensure interoperability, it is 640 expected that at least one of these formats will be specified as 641 "mandatory-to-implement". 643 A class of algorithms known as Distributed Hash Tables 644 are one way to implement 645 the Distributed Database. In particular, both the Chord and Bamboo 646 algorithms have been suggested as good choices for the distributed 647 database algorithm. However, no decision has been taken so far. 649 6.2. Using the Distributed Database Function 651 There are a number of ways the distributed database described in the 652 previous section might be used to establish multimedia sessions using 653 SIP. In this section, we give four possibilities as examples. It 654 seems likely that the working group will standardize at least one way 655 (not necessarily one of the four listed here), but no decisions have 656 been taken yet. 658 The first option is to store the contact information for a user in 659 the resource record for the user. A peer Y that is a contact point 660 for this user adds contact information to this resource record. The 661 resource record itself is stored with peer Z in the network, where 662 peer Z is chosen by the distributed database algorithm. 664 When the SIP entity coupled with peer X has an INVITE message 665 addressed to this user, it retrieves the resource record from peer Z. 666 It then extracts the contact information for the various peers that 667 are a contact point for the user, including peer Y, and forwards the 668 INVITE onward. 670 This exchange is illustrated in the following figure. The notation 671 "Put(U@Y)" is used to show the distributed database operation of 672 updating the resource record for user U with the contract Y, and 673 "Get(U)" illustrates the distributed database operation of retrieving 674 the resource record for user U. Note that the messages between the 675 peers X, Y and Z may actually travel via intermediate peers (not 676 shown) as part of the distributed lookup process or so as to traverse 677 intervening NATs. 679 Peer X Peer Z Peer Y 680 | | | 681 | | Put(U@Y) | 682 | |<---------------| 683 | | Put-Resp(OK) | 684 | |--------------->| 685 | | | 686 | Get(U) | | 687 |---------------->| | 688 | Get-Resp(U@Y)| | 689 |<----------------| | 690 | INVITE(To:U) | | 691 |--------------------------------->| 692 | | | 694 The second option also involves storing the contact information for a 695 user in the resource record of the user. However, SIP entity at peer 696 X, rather than retrieving the resource record from peer Z, instead 697 forwards the INVITE message to the proxy at peer Z. The proxy at peer 698 Z then uses the information in the resource record and forwards the 699 INVITE onwards to the SIP entity at peer Y and the other contacts. 701 Peer X Peer Z Peer Y 702 | | | 703 | | Put(U@Y) | 704 | |<---------------| 705 | | Put-Resp(OK) | 706 | |--------------->| 707 | | | 708 | INVITE(To:U) | | 709 |-----------------| INVITE(To:U) | 710 | |--------------->| 711 | | | 713 The third option is for a single peer W to place its contact 714 information into the resource record for the user (stored with peer 715 Z). A peer Y that is a contact point for the user retrieves the 716 resource record from peer Z, extracts the contact information for 717 peer W, and then uses the standard SIP registration mechanism 718 [RFC3261] to register with peer W. When the SIP entity at peer X has 719 to forward an INVITE request, it retrieves the resource record and 720 extracts the contact information for W. It then forwards the INVITE 721 to the proxy at peer W, which proxies it onward to peer Y and the 722 other contacts. 724 Peer X Peer Z Peer Y Peer W 725 | | | | 726 | | Put(U@W) | | 727 | |<---------------------------------| 728 | | Put-Resp(OK) | | 729 | |--------------------------------->| 730 | | | | 731 | | | | 732 | | | REGISTER(To:U) | 733 | | |---------------->| 734 | | | 200 | 735 | | |<----------------| 736 | | | | 737 | | | | 738 | Get(U) | | | 739 |---------------->| | | 740 | Get-Resp(U@W)| | | 741 |<----------------| | | 742 | INVITE(To:U) | | | 743 |--------------------------------------------------->| 744 | | | INVITE(To:U) | 745 | | |<----------------| 746 | | | | 748 The fourth option works as in option 3, with the exception that, 749 rather than X retrieving the resource record from Z, peer X forwards 750 the INVITE to a SIP proxy at Z, which proxies it onward to W and 751 hence to Y. 753 Peer X Peer Z Peer Y Peer W 754 | | | | 755 | | Put(U@W) | | 756 | |<---------------------------------| 757 | | Put-Resp(OK) | | 758 | |--------------------------------->| 759 | | | | 760 | | | | 761 | | | REGISTER(To:U) | 762 | | |---------------->| 763 | | | 200 | 764 | | |<----------------| 765 | | | | 766 | | | | 767 | INVITE(To:U) | | | 768 |---------------->| INVITE(To:U) | | 769 | |--------------------------------->| 770 | | | INVITE(To:U) | 771 | | |<----------------| 772 | | | | 774 The pros and cons of option 1 and 3 are briefly discussed in 775 [Using-an-External-DHT]. 777 6.3. NAT Traversal 779 Two approaches to NAT Traversal for P2PSIP Peer Protocol have been 780 suggested. The working group has not made any decision yet on the 781 approach that will be selected. 783 The first, the traditional approach adopted by most peer-to-peer 784 networks today, divides up the peers in the network into two groups: 785 those with public IP addresses and those without. The networks then 786 select a subset of the former group and elevate them to "super peer" 787 status, leaving the remaining peers as "ordinary peers". Since super 788 peers all have public IP addresses, there are no NAT problems when 789 communicating between them. The network then associates each 790 ordinary peer with (usually just one) super peer in a client-server 791 relationship. Once this is done, an ordinary peer X can communicate 792 with another ordinary peer Y by sending the message to X's super 793 peer, which forwards it to Y's super peer, which forwards it to Y. 794 The connection between an ordinary peer and its super peer is 795 initiated by the ordinary peer, which makes it easy to traverse any 796 intervening NATs. In this approach, the number of hops between two 797 peers is at most 3. 799 The second approach treats all peers as equal and establishes a 800 partial mesh of connections between them. Messages from one peer to 801 another are then routed along the edges in the mesh of connections 802 until they reach their destination. To make the routing efficient 803 and to avoid the use of standard Internet routing protocols, the 804 partial mesh is organized in a structured manner. If the structure 805 is based on any one of a number of common DHT algorithms, then the 806 maximum number of hops between any two peers is log N, where N is the 807 number of peers in the overlay. 809 The first approach is significantly more efficient than the second in 810 overlays with large numbers of peers. However, the first approach 811 assumes there are a sufficient number of peers with public IP 812 addresses to serve as super peers. In some usage scenarios 813 envisioned for P2PSIP, this assumption does not hold. For example, 814 this approach fails completely in the case where every peer is behind 815 a distinct NAT. 817 The second approach, while less efficient in overlays with larger 818 numbers of peers, is efficient in smaller overlays and can be made to 819 work in many use cases where the first approach fails. 821 Both of these approaches assume a method of setting up Peer Protocol 822 connections between peers. Many such methods exist; the now expired 823 [I-D.iab-nat-traversal-considerations] is an attempt to give a fairly 824 comprehensive list along with a discussion of their pros and cons. 825 After a consideration of the various techniques, the P2PSIP working 826 group has decided to select the Unilateral Self-Address Fixing method 827 [RFC3424] of NAT Traversal, and in particular the ICE 828 [I-D.ietf-mmusic-ice] implementation of this approach. 830 The above discussion covers NAT traversal for Peer Protocol 831 connections. For Client Protocol connections, the approach depends 832 on the role adopted for clients and we defer the discussion on that 833 point until the role becomes clearer. 835 In addition to Peer Protocol and Client Protocol messages, a P2PSIP 836 Overlay must also provide a solution to the NAT Traversal problem for 837 SIP messages. If it does not, there is no reliable way for a peer 838 behind one NAT to send a SIP INVITE to a peer behind another NAT. 839 One way to solve this problem is to transport SIP messages along Peer 840 and Client Protocol connections: this could be done either by 841 encapsulating the SIP messages inside Peer and Client Protocol 842 messages or by multiplexing SIP with the Peer (resp.Client) Protocol 843 on a Peer (resp. Client) Protocol connection. 845 Finally, it should be noted that the NAT traversal problem for media 846 connections signaled using SIP is outside the scope of the P2PSIP 847 working group. As discussed in [I-D.ietf-sipping-nat-scenarios], the 848 current recommendation is to use ICE. 850 6.4. Locating and Joining an Overlay 852 Before a peer can attempt to join a P2PSIP overlay, it must first 853 obtain a Peer-ID and optionally a set of credentials. The Peer-ID is 854 an identifier that will uniquely identify the peer within the 855 overlay, while the credentials show that the peer is allowed to join 856 the overlay. 858 The P2PSIP WG will not standardize how the peer-ID and the 859 credentials are obtained, but merely standardize at least one 860 acceptable format for each. To ensure interoperability, it is 861 expected that at least one of these formats will be specified as 862 "mandatory-to-implement". 864 Once a peer (the "joining peer") has a peer-ID and optionally a set 865 of credentials, it can attempt to join the overlay. To do this, it 866 needs to locate a bootstrap peer for the Overlay. 868 A bootstrap peer is a peer that serves as the first point of contact 869 for the joining peer. The joining peer uses a bootstrap mechanism to 870 locate a bootstrap peer. Locating a bootstrap peer might be done in 871 any one of a number of different ways: 873 o By remembering peers that were part of the overlay the last time 874 the peer was part of the overlay; 876 o Through a multicast discovery mechanism; 878 o Through manual configuration; or 880 o By contacting a P2PSIP Bootstrap Server, and using its help to 881 locate a bootstrap peer. 883 The joining peer might reasonably try each of the methods (and 884 perhaps others) in some order or in parallel until it succeeds in 885 finding a bootstrap peer. 887 The job of the bootstrap peer is simple: refer the joining peer to a 888 peer (called the "admitting peer") that will help the joining peer 889 join the network. The choice of admitting peer will often depend on 890 the joining node - for example, the admitting peer may be a peer that 891 will become a neighbor of the joining peer in the overlay. It is 892 possible that the bootstrap peer might also serve as the admitting 893 peer. 895 The admitting peer will help the joining peer learn about other peers 896 in the overlay and establish connections to them as appropriate. The 897 admitting peer and/or the other peers in the overlay will also do 898 whatever else is required to help the joining peer become a fully- 899 functional peer. The details of how this is done will depend on the 900 distributed database algorithm used in the overlay. 902 At various stages in this process, the joining peer may be asked to 903 present its credentials to show that it is authorized to join the 904 overlay. Similarly, the various peers contacted may be asked to 905 present their credentials so the joining peer can verify that it is 906 really joining the overlay it wants to. 908 6.5. Possible Client Behavior 910 As mentioned above, a number of people have proposed a second type of 911 P2PSIP entity, known as a "P2PSIP client". The consensus of the 912 group is that the need for entities to store and retrieve information 913 from the Overlay without participating is recognized, but that for 914 now, little time will spent. This section presents some of the 915 alternatives that have been suggested for the possible role of a 916 client. 918 In one approach, a client interacts with the P2PSIP overlay through 919 an associated peer (or perhaps several such peers) using the Client 920 Protocol. The client does not run the distributed database 921 algorithm, does not store resource records, and is not involved in 922 routing messages to other peers or clients. Through interactions 923 with its associated peer, a client can insert, modify, examine, and 924 remove resource records. A client may also send SIP messages to its 925 associated peer for routing through the overlay. In this approach, a 926 client is a node that wants to take advantage of the overlay, but is 927 unable or unwilling to contribute resources back to the overlay. 928 This may be achieved using a subset of the Peer Protocol. Such a 929 device need not speak SIP. 931 For SIP devices, another way to realize this functionality is for a 932 Peer to behave as a [RFC3261] proxy/registrar. SIP devices then use 933 standard SIP mechanisms to add, update, and remove registrations and 934 to send SIP messages to peers and other clients. The authors here 935 refer to these devices simply as a "SIP UA", not a "P2PSIP Client", 936 to distinguish it from the concept described above. 938 6.6. Interacting with non-P2PSIP entities 940 It is possible for network nodes that are not peers or clients to 941 interact with a P2PSIP overlay. Such nodes would do this through 942 mechanisms not defined by the P2PSIP working group provided they can 943 find a peer or client that supports that mechanism and which will do 944 any related P2PSIP operations necessary. In this section, we briefly 945 describe two ways this might be done. (Note that these are just 946 examples and the descriptions here are not recommendations). 948 One example is a peer that also acts as a standard SIP proxy and 949 registrar. SIP UAs can interact with it using mechanisms defined in 950 [RFC3261]. The peer inserts registrations for users learned from 951 these UAs into the distributed database, and retrieves contact 952 information when proxying INVITE messages. 954 Another example is a peer that has a fully-qualified domain name 955 (FQDN) that matches the name of the overlay and acts as a SIP proxy 956 for calls coming into the overlay. A SIP INVITE addressed to 957 "user@overlay-name" arrives at the peer (using the mechanisms in 958 [RFC3263]) and this peer then looks up the user in the distributed 959 database and proxies the call onto it. 961 6.7. Architecture 963 There has been much debate in the group over what an appropriate 964 architecture for P2PSIP should be. Currently, the group is 965 investigating architectures that involve a P2P layer that is distinct 966 from the applications that run on the overlay. 967 __________________________ 968 | | 969 | SIP, other apps... | 970 | ___________________| 971 | | P2P Layer | 972 |______|___________________| 973 | Transport Layer | 974 |__________________________| 976 The P2P layer implements the Peer Protocol (and the Client Protocol, 977 if such a protocol exists). Applications access this P2P layer for 978 various overlay-related services. Applications are also free to 979 bypass this layer and access the existing transport layer protocols 980 (e.g., TCP, UDP, etc.) directly. 982 A notable feature of this architecture is that it envisions the use 983 of protocols other than SIP in the overlay. Though the working group 984 is primarily focused on the use of SIP in peer-to-peer overlays, this 985 architecture envisions a future in which other protocols can play a 986 role. 988 The group initially considered another architecture. In this 989 alternative architecture, the Peer Protocol was defined as an 990 extension to SIP. That is, that the necessary operations for forming 991 and maintaining the overlay and for storing and retrieving resource 992 records in the distributed database were defined as extensions to 993 SIP. Each peer in the overlay was viewed as a SIP proxy that would 994 forward the overlay maintenance and distributed database query 995 messages (expressed in SIP) on behalf of other peers. 997 This architecture was eventually rejected by the working group for 998 the following reasons: 1000 o The architecture was totally focused on SIP, and made it difficult 1001 to use other protocols in the overlay. 1003 o In SIP, proxies are assumed to be trusted parties. Relying on the 1004 peers to route the message as proxies exposes the SIP messages to 1005 attacks from untrusted proxies that SIP's design does not 1006 anticipate. A design that does not allow the peers to modify the 1007 SIP message and ideally prevents them from reading it is 1008 preferable. 1010 o SIP was seen as a "heavy-weight" protocol for this task. SIP uses 1011 a text-based encoding which is very flexible, but leads to both 1012 large messages and slow processing times at proxies. This was 1013 seen to be a poor match for P2PSIP, where a distributed database 1014 lookup operation requires O(log N) peers to receive, process and 1015 forward the message. 1017 More discussion on this alternate approach and why it was rejected 1018 can be found on the P2PSIP mailing list in a thread that started on 1019 20 March 2007. 1021 7. Additional Questions 1023 This section lists some additional questions that the proposed P2PSIP 1024 Working Group may need to consider in the process of defining the 1025 Peer and Client protocols. 1027 7.1. Selecting between Multiple Peers offering the Same Service 1029 If a P2PSIP network contains two or more peers that offer the same 1030 service, then how does a peer or client that wishes to use that 1031 service select the peer to use? This question comes up in a number 1032 of contexts: 1034 o When two or more peers are willing to serve as a STUN Relay, how 1035 do we select a peer that is close in the netpath sense and is 1036 otherwise appropriate for the call? 1038 o When two or more peers are willing to serve as PSTN gateways, how 1039 do we select an appropriate gateway for a call that is both 1040 netpath efficient and provides good quality or inexpensive PSTN 1041 routing? 1043 It has been suggested that, at least initially, the working group 1044 should restrict itself to defining a mechanism that can return a list 1045 of peers offering a service and not define the mechanism for 1046 selecting a peer from that list. 1048 7.2. Visibility of Messages to Intermediate Peers 1050 When transporting SIP messages through the overlay, are the headers 1051 and/or bodies of the SIP messages visible to the peers that the 1052 messages happen to pass through? If they are, what types of security 1053 risks does this pose in the presence of peers that have been 1054 compromised in some way? 1056 7.3. Using C/S SIP and P2PSIP Simultaneously in a Single UA 1058 If a given UA is capable of operating in both P2PSIP and conventional 1059 SIP modalities (especially simultaneously), is it possible for it to 1060 use and respond to the same AOR using both conventional and P2PSIP? 1061 An example of such a topology might be a UA that registers an AOR 1062 (say, "sip:alice@example.com") conventionally with a registrar and 1063 then inserts a resource record for that resource into a P2PSIP 1064 topology, such that both conventional SIP users and P2PSIP users 1065 (within the overlay or a federation thereof) would be able to contact 1066 the user without necessarily traversing some sort of gateway. Is 1067 this something that we want to make work? 1069 7.4. Clients, Peers, and Services 1071 1. Do all peers providing routing, storage, and all other services, 1072 or do only some peers provide certain services? 1074 2. What services, if any, must all peers provide? 1076 3. How we can we describe the capacity of a peer for delivering a 1077 given service? 1079 7.5. Relationships of Domains to Overlays 1081 1. Can there be names from more than one domain in a single overlay? 1083 2. Can there be names from one domain in more than a single overlay? 1084 If so, how do we route Client/Server SIP requests to the right 1085 overlay? 1087 3. Can the domain of an AoR be in more than one overlay? 1089 4. Should we have a "default overlay" to search for peers in many 1090 domains? 1092 8. Security Considerations 1094 Building a P2PSIP system has many security considerations, many of 1095 which we have only begun to consider. We anticipate that the 1096 protocol documents describing the actual protocols will deal more 1097 thoroughly with security topics. 1099 One critical security issue that will need to be addressed is 1100 providing for the privacy and integrity of SIP messages being routed 1101 by peer nodes, when those peer nodes might well be hostile. This is 1102 a departure from Client/Server SIP, where the proxies are generally 1103 operated by enterprises or service providers with whom the users of 1104 SIP UAs have a trust relationship. 1106 9. IANA Considerations 1108 This document presently raises no IANA considerations. 1110 10. Acknowledgements 1112 This document draws heavily from the contributions of many 1113 participants in the P2PSIP Mailing List. Particular thanks to 1114 Henning Schulzrinne and Cullen Jennings who spent time on phone calls 1115 related to this text. 1117 11. References 1119 11.1. Normative References 1121 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 1122 A., Peterson, J., Sparks, R., Handley, M., and E. 1123 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 1124 June 2002. 1126 [RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation 1127 Protocol (SIP): Locating SIP Servers", RFC 3263, 1128 June 2002. 1130 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 1131 Resource Identifier (URI): Generic Syntax", STD 66, 1132 RFC 3986, January 2005. 1134 11.2. Informative References 1136 [I-D.bryan-p2psip-reload] 1137 Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and 1138 H. Schulzrinne, "REsource LOcation And Discovery 1139 (RELOAD)", draft-bryan-p2psip-reload-04 (work in 1140 progress), June 2008. 1142 [I-D.camarillo-hip-bone] 1143 Camarillo, G., Nikander, P., and J. Hautakorpi, "HIP BONE: 1144 Host Identity Protocol (HIP) Based Overlay Networking 1145 Environment", draft-camarillo-hip-bone-01 (work in 1146 progress), February 2008. 1148 [I-D.iab-nat-traversal-considerations] 1149 Rosenberg, J., "Considerations for Selection of Techniques 1150 for NAT Traversal", 1151 draft-iab-nat-traversal-considerations-00 (work in 1152 progress), October 2005. 1154 [I-D.ietf-behave-rfc3489bis] 1155 Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, 1156 "Session Traversal Utilities for (NAT) (STUN)", 1157 draft-ietf-behave-rfc3489bis-16 (work in progress), 1158 July 2008. 1160 [I-D.ietf-mmusic-ice] 1161 Rosenberg, J., "Interactive Connectivity Establishment 1162 (ICE): A Protocol for Network Address Translator (NAT) 1163 Traversal for Offer/Answer Protocols", 1164 draft-ietf-mmusic-ice-19 (work in progress), October 2007. 1166 [I-D.ietf-sipping-nat-scenarios] 1167 Boulton, C., Rosenberg, J., and G. Camarillo, "Best 1168 Current Practices for NAT Traversal for SIP", 1169 draft-ietf-sipping-nat-scenarios-08 (work in progress), 1170 April 2008. 1172 [I-D.jiang-p2psip-sep] 1173 Jiang, X. and H. Zhang, "Service Extensible P2P Peer 1174 Protocol", draft-jiang-p2psip-sep-01 (work in progress), 1175 February 2008. 1177 [I-D.li-p2psip-node-types] 1178 Wang, Y., "Different types of nodes in P2PSIP", 1179 draft-li-p2psip-node-types-00 (work in progress), 1180 December 2007. 1182 [I-D.matthews-p2psip-id-loc] 1183 Cooper, E., Johnston, A., and P. Matthews, "An ID/Locator 1184 Architecture for P2PSIP", draft-matthews-p2psip-id-loc-01 1185 (work in progress), February 2008. 1187 [I-D.pascual-p2psip-clients] 1188 Pascual, V., Matuszewski, M., Shim, E., Zhang, H., and S. 1189 Yongchao, "P2PSIP Clients", 1190 draft-pascual-p2psip-clients-01 (work in progress), 1191 February 2008. 1193 [I-D.zheng-p2psip-client-protocol] 1194 Yongchao, S., Jiang, X., Zhang, H., and H. Deng, "P2PSIP 1195 Client Protocol", draft-zheng-p2psip-client-protocol-01 1196 (work in progress), February 2008. 1198 [RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, 1199 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 1200 RFC 2136, April 1997. 1202 [RFC3424] Daigle, L. and IAB, "IAB Considerations for UNilateral 1203 Self-Address Fixing (UNSAF) Across Network Address 1204 Translation", RFC 3424, November 2002. 1206 [RFC4485] Rosenberg, J. and H. Schulzrinne, "Guidelines for Authors 1207 of Extensions to the Session Initiation Protocol (SIP)", 1208 RFC 4485, May 2006. 1210 [RFC4795] Aboba, B., Thaler, D., and L. Esibov, "Link-local 1211 Multicast Name Resolution (LLMNR)", RFC 4795, 1212 January 2007. 1214 [Using-an-External-DHT] 1215 Singh, K. and H. Schulzrinne, "Using an External DHT as a 1216 SIP Location Service", Columbia University Computer 1217 Science Dept. Tech Report 388). 1219 Copy available at http://mice.cs.columbia.edu/ 1220 getTechreport.php?techreportID=388/ 1222 Authors' Addresses 1224 David A. Bryan 1225 SIPeerior Technologies 1226 3000 Easter Circle 1227 Williamsburg, Virginia 23188 1228 USA 1230 Phone: +1 757 565 0101 1231 Email: bryan@sipeerior.com 1233 Philip Matthews 1234 Unaffiliated 1236 Phone: +1 613 592 4343 x224 1237 Email: philip_matthews@magma.ca 1239 Eunsoo Shim 1240 Locus Telecommunications 1241 111 Sylvan Avenue 1242 Englewood Cliffs, New Jersey 07632 1243 USA 1245 Phone: unlisted 1246 Email: eunsooshim@gmail.com 1248 Dean Willis 1249 Softarmor Systems 1250 3100 Independence Pkwy #311-164 1251 Plano, Texas 75075 1252 USA 1254 Phone: unlisted 1255 Email: dean.willis@softarmor.com 1257 Spencer Dawkins 1258 Huawei Technologies (USA) 1260 Phone: +1 214 755 3870 1261 Email: spencer@wonderhamster.org 1263 Full Copyright Statement 1265 Copyright (C) The IETF Trust (2008). 1267 This document is subject to the rights, licenses and restrictions 1268 contained in BCP 78, and except as set forth therein, the authors 1269 retain all their rights. 1271 This document and the information contained herein are provided on an 1272 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 1273 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 1274 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 1275 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 1276 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 1277 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 1279 Intellectual Property 1281 The IETF takes no position regarding the validity or scope of any 1282 Intellectual Property Rights or other rights that might be claimed to 1283 pertain to the implementation or use of the technology described in 1284 this document or the extent to which any license under such rights 1285 might or might not be available; nor does it represent that it has 1286 made any independent effort to identify any such rights. 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