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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 Polycom, Inc. 4 Intended status: Informational P. Matthews 5 Expires: May 3, 2012 Alcatel-Lucent 6 E. Shim 7 Avaya, Inc. 8 D. Willis 9 Softarmor Systems 10 S. Dawkins 11 Huawei (USA) 12 October 31, 2011 14 Concepts and Terminology for Peer to Peer SIP 15 draft-ietf-p2psip-concepts-04 17 Abstract 19 This document defines concepts and terminology for the use of the 20 Session Initiation Protocol in a peer-to-peer environment where the 21 traditional proxy-registrar and message routing functions are 22 replaced by a distributed mechanism. These mechansims may be 23 implemented using a distributed hash table or other distributed data 24 mechanism with similar external properties. This document includes a 25 high-level view of the functional relationships between the network 26 elements defined herein, a conceptual model of operations, and an 27 outline of the related problems addressed by the P2PSIP working group 28 and the RELOAD protocol ([I-D.ietf-p2psip-base], 29 [I-D.ietf-p2psip-sip]) defined by the working group. 31 Status of this Memo 33 This Internet-Draft is submitted in full conformance with the 34 provisions of BCP 78 and BCP 79. 36 Internet-Drafts are working documents of the Internet Engineering 37 Task Force (IETF). Note that other groups may also distribute 38 working documents as Internet-Drafts. The list of current Internet- 39 Drafts is at http://datatracker.ietf.org/drafts/current/. 41 Internet-Drafts are draft documents valid for a maximum of six months 42 and may be updated, replaced, or obsoleted by other documents at any 43 time. It is inappropriate to use Internet-Drafts as reference 44 material or to cite them other than as "work in progress." 46 This Internet-Draft will expire on May 3, 2012. 48 Copyright Notice 49 Copyright (c) 2011 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (http://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 This document may contain material from IETF Documents or IETF 63 Contributions published or made publicly available before November 64 10, 2008. The person(s) controlling the copyright in some of this 65 material may not have granted the IETF Trust the right to allow 66 modifications of such material outside the IETF Standards Process. 67 Without obtaining an adequate license from the person(s) controlling 68 the copyright in such materials, this document may not be modified 69 outside the IETF Standards Process, and derivative works of it may 70 not be created outside the IETF Standards Process, except to format 71 it for publication as an RFC or to translate it into languages other 72 than English. 74 Table of Contents 76 1. Editor's Notes and Changes To This Version . . . . . . . . . . 4 77 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 4 78 3. High Level Description . . . . . . . . . . . . . . . . . . . . 5 79 3.1. Services . . . . . . . . . . . . . . . . . . . . . . . . . 5 80 3.2. Clients . . . . . . . . . . . . . . . . . . . . . . . . . 6 81 3.3. Relationship Between P2PSIP and RELOAD . . . . . . . . . . 6 82 3.4. Relationship Between P2PSIP and SIP . . . . . . . . . . . 6 83 3.5. Relationship Between P2PSIP and Other AoR 84 Dereferencing Approaches . . . . . . . . . . . . . . . . . 7 85 3.6. NAT Issues . . . . . . . . . . . . . . . . . . . . . . . . 7 86 4. Reference Model . . . . . . . . . . . . . . . . . . . . . . . 7 87 5. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 9 88 6. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 13 89 6.1. The Distributed Database Function . . . . . . . . . . . . 13 90 6.2. Using the Distributed Database Function . . . . . . . . . 14 91 6.3. NAT Traversal . . . . . . . . . . . . . . . . . . . . . . 15 92 6.4. Locating and Joining an Overlay . . . . . . . . . . . . . 15 93 6.5. Clients and Connecting Unmodified SIP Devices . . . . . . 16 94 6.6. Architecture . . . . . . . . . . . . . . . . . . . . . . . 17 95 7. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 17 96 8. Informative References . . . . . . . . . . . . . . . . . . . . 17 97 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19 99 1. Editor's Notes and Changes To This Version 101 This version of the draft represents a substantial revision from the 102 previous version. Until -02, this work was tracking open questions 103 and being used to help reach consensus on a draft. With the 104 eselection of RELOAD as the protocol for this WG, the focus of the 105 group turned to completing the RELOAD drafts, and the WG directed the 106 editors to update the document to reflect the decisions made in 107 RELOAD upon completion. 109 Please see Section 7 for the list of major open issues. 111 2. Background 113 One of the fundamental problems in multimedia communication between 114 Internet nodes is discovering the host at which a given user can be 115 reached. In the Session Initiation Protocol (SIP) [RFC3261] this 116 problem is expressed as the problem of mapping an Address of Record 117 (AoR) for a user into one or more Contact URIs [RFC3986]. The AoR is 118 a name for the user that is independent of the host or hosts where 119 the user can be contacted, while a Contact URI indicates the host 120 where the user can be contacted. 122 In the common SIP-using architectures that we refer to as 123 "Conventional SIP" or "Client/Server SIP", there is a relatively 124 fixed hierarchy of SIP routing proxies and SIP user agents. To 125 deliver a SIP INVITE to the host or hosts at which the user can be 126 contacted, a SIP UA follows the procedures specified in [RFC3263] to 127 determine the IP address of a SIP proxy, and then sends the INVITE to 128 that proxy. The proxy will then, in turn, deliver the SIP INVITE to 129 the hosts where the user can be contacted. 131 This document gives a high-level description of an alternative 132 solution to this problem. In this alternative solution, the 133 relatively fixed hierarchy of Client/Server SIP is replaced by a 134 peer-to-peer overlay network. In this peer-to-peer overlay network, 135 the various AoR to Contact URI mappings are not centralized at proxy/ 136 registrar nodes but are instead distributed amongst the peers in the 137 overlay. 139 The details of this alternative solution are specified by the RELOAD 140 protocol. The RELOAD base draft [I-D.ietf-p2psip-base] defines a 141 mechanism to distribute using a Distributed Hash Table (DHT) and 142 specifies the wire protocol, security, and authentication mechanisms 143 needed to convey this information. This DHT protocol was designed 144 specifically with the purpose of enabling a distributed SIP registrar 145 in mind. While designing the protocol other applications were 146 considered, and when possible design decisions were made that allow 147 RELOAD to be used in other instances where a DHT is desirable, but 148 only when making such decisions did not add undue complexity to the 149 RELOAD protocol. The RELOAD sip draft [I-D.ietf-p2psip-sip] 150 specifies how RELOAD is used with the SIP protocol to enable a 151 distributed, server-less SIP solution. 153 3. High Level Description 155 A P2PSIP Overlay is a collection of nodes organized in a peer-to-peer 156 fashion for the purpose of enabling real-time communication using the 157 Session Initiation Protocol (SIP). Collectively, the nodes in the 158 overlay provide a distributed mechanism for mapping names to overlay 159 locations. This provides for the mapping of Addresses of Record 160 (AoRs) to Contact URIs, thereby providing the "location server" 161 function of [RFC3261]. An Overlay also provides a transport function 162 by which SIP messages can be transported between any two nodes in the 163 overlay. 165 A P2PSIP Overlay consists of one or more nodes called Peers. The 166 nodes in the overlay collectively run a distributed database 167 algorithm. This distributed database algorithm allows data to be 168 stored on nodes and retrieved in an efficient manner. It may also 169 ensure that a copy of a data item is stored on more than one node, so 170 that the loss of a node does not result in the loss of the data item 171 to the overlay. 173 One use of this distributed database is to store the information 174 required to provide the mapping between AoRs and Contact URIs for the 175 distributed location function. This provides a location function 176 within each overlay that is an alternative to the location functions 177 described in [RFC3263]. However, the model of [RFC3263] is used 178 between overlays. 180 3.1. Services 182 The nature of peer-to-peer computing is that each peer offers 183 services to other peers to allow the overlay to collectively provide 184 larger functions. In P2PSIP, peers offer storage and transport 185 services to allow the distributed database function and distributed 186 transport function to be implemented. Additionally, the RELOAD 187 protocol offers a simplistic discovery mechanism specific to the TURN 188 [RFC5766] protocol used for NAT traversal. It is expected that 189 individual peers may also offer other services as an enhancement to 190 P2PSIP functionality (for example to support voicemail) or to support 191 other applications beyond SIP. To support these additional services, 192 peers may need to store additional information in the overlay. 194 [I-D.ietf-p2psip-service-discovery] describes the mechanism used in 195 P2PSIP for resource discovery. 197 3.2. Clients 199 An overlay may or may not also include one or more nodes called 200 clients. Clients are supported in the RELOAD protocol as peers that 201 have not joined the overlay, and therefore do not route messages or 202 store information. Clients access the services of the RELOAD 203 protocol by connecting to a peer which performs operations on the 204 behalf of the client. Note that in RELOAD there is no distinct 205 client protocol. Instead, a client connects using the same protocol, 206 but never joins the overlay as a peer. For more information, see 207 [I-D.ietf-p2psip-base]. 209 Note that in the context of P2PSIP, there is an additional entity 210 that is sometimes referred to as a client. A special peer may be a 211 member of the in the P2PSIP overlay and may present the functionality 212 of one or all of a SIP registrar, proxy or redirect server to 213 conventional SIP devices (SIP clients). In this way, existing, non- 214 modified SIP clients may connect to the network. These unmodified 215 SIP devices do not speak the RELOAD protocol, and this is a distinct 216 concept from the notion of client discussed in the previous 217 paragraph. 219 3.3. Relationship Between P2PSIP and RELOAD 221 The RELOAD protocol defined by the P2PSIP working group implements a 222 DHT primarily for use by server-less, peer-to-peer SIP deployments. 223 However, the RELOAD protocol could be used for other applications as 224 well. As such, a "P2PSIP" deployment is generally assumed to be a 225 use of RELOAD to implement distributed SIP, but it is possible that 226 RELOAD is used as a mechanism to distribute other applications, 227 completely unrelated to SIP. 229 3.4. Relationship Between P2PSIP and SIP 231 Since P2PSIP is about peer-to-peer networks for real-time 232 communication, it is expected that most peers and clients will be 233 coupled with SIP entities (although RELOAD may be used for other 234 applications than P2PSIP). For example, one peer might be coupled 235 with a SIP UA, another might be coupled with a SIP proxy, while a 236 third might be coupled with a SIP-to-PSTN gateway. For such nodes, 237 the peer or client portion of the node is logically distinct from the 238 SIP entity portion. However, there is no hard requirement that every 239 P2PSIP node (peer or client) be coupled to a SIP entity. As an 240 example, additional peers could be placed in the overlay to provide 241 additional storage or redundancy for the RELOAD overlay, but might 242 not have any direct SIP capabilities. 244 3.5. Relationship Between P2PSIP and Other AoR Dereferencing Approaches 246 OPEN ISSUE: Many of the "decisions" made have been moved out of the 247 main document. This one, however, seems to point out a difference. 248 Should this section be moved or removed? 250 As noted above, the fundamental task of P2PSIP is turning an AoR into 251 a Contact. This task might be approached using zeroconf techniques 252 such as multicast DNS and DNS Service Discovery (as in Apple's 253 Bonjour protocol), link-local multicast name resolution [RFC4795], 254 and dynamic DNS [RFC2136]. 256 These alternatives were discussed in the P2PSIP Working Group, and 257 not pursued as a general solution for a number of reasons related to 258 scalability, the ability to work in a disconnected state, partition 259 recovery, and so on. However, there does seem to be some continuing 260 interest in the possibility of using DNS-SD and mDNS for 261 bootstrapping of P2PSIP overlays. 263 3.6. NAT Issues 265 Network Address Translators (NATs) are impediments to establishing 266 and maintaining peer-to-peer networks, since NATs hinder direct 267 communication between nodes. Some peer-to-peer network architectures 268 avoid this problem by insisting that all nodes exist in the same 269 address space. However, RELOAD provides capabilities that allow 270 nodes to be located in multiple address spaces interconnected by 271 NATs, to allow RELOAD messages to traverse NATs, and to assist in 272 transmitting application-level messages (for example SIP messages) 273 across NATs. 275 4. Reference Model 277 The following diagram shows a P2PSIP Overlay consisting of a number 278 of Peers, one Client, and an ordinary SIP UA. It illustrates a 279 typical P2PSIP overlay but does not limit other compositions or 280 variations; for example, Proxy Peer P might also talk to a ordinary 281 SIP proxy as well. The figure is not intended to cover all possible 282 architecture variations, but simply to show a deployment with many 283 common P2PSIP elements. 285 --->PSTN 286 +------+ N +------+ +---------+ / 287 | | A | | | Gateway |-/ 288 | UA |####T#####| UA |#####| Peer |######## 289 | Peer | N | Peer | | G | # RELOAD 290 | E | A | F | +---------+ # P2PSIP 291 | | T | | # Protocol 292 +------+ N +------+ # | 293 # A # | 294 NATNATNATNAT # | 295 # # | \__/ 296 NATNATNATNAT +-------+ v / \ 297 # N | |#####/ UA \ 298 +------+ A P2PSIP Overlay | Peer | /Client\ 299 | | T | Q | |___C__| 300 | UA | N | | 301 | Peer | A +-------+ 302 | D | T # 303 | | N # 304 +------+ A # RELOAD 305 # T # P2PSIP 306 # N +-------+ +-------+ # Protocol 307 # A | | | | # 308 #########T####| Proxy |########| Redir |####### 309 N | Peer | | Peer | 310 A | P | | R | 311 T +-------+ +-------+ 312 | / 313 | SIP / 314 \__/ / / 315 /\ / ______________/ SIP 316 / \/ / 317 / UA \/ 318 /______\ 319 SIP UA A 321 Figure: P2PSIP Overlay Reference Model 323 Here, the large perimeter depicted by "#" represents a stylized view 324 of the Overlay (the actual connections could be a mesh, a ring, or 325 some other structure). Around the periphery of the Overlay 326 rectangle, we have a number of Peers. Each peer is labeled with its 327 coupled SIP entity -- for example, "Proxy Peer P" means that peer P 328 which is coupled with a SIP proxy. In some cases, a peer or client 329 might be coupled with two or more SIP entities. In this diagram we 330 have a PSTN gateway coupled with peer "G", three peers ("D", "E" and 331 "F") which are each coupled with a UA, a peer "P" which is coupled 332 with a SIP proxy, an ordinary peer "Q" with no SIP capabilities, and 333 one peer "R" which is coupled with a SIP Redirector. Note that 334 because these are all Peers, each is responsible for storing Resource 335 Records and transporting messages around the Overlay. 337 To the left, two of the peers ("D" and "E") are behind network 338 address translators (NATs). These peers are included in the P2PSIP 339 overlay and thus participate in storing resource records and routing 340 messages, despite being behind the NATs. 342 On the right side, we have a client "C", which uses the RELOAD 343 Protocol to communicate with Proxy Peer "Q". The Client "C" uses 344 RELOAD to obtain information from the overlay, but has not inserted 345 itself into the overlay, and therefore does not participate in 346 routing messages or storing information. 348 Below the Overlay, we have a conventional SIP UA "A" which is not 349 part of the Overlay, either directly as a peer or indirectly as a 350 client. It does not speak the RELOAD P2PSIP protocol, and is not 351 participating in the overlay as either a Peer nor Client. Instead, 352 it uses SIP to interact with the Overlay via an adapter peer or peers 353 which communicate with the overlay using RELOAD. 355 Both the SIP proxy coupled with peer "P" and the SIP redirector 356 coupled with peer "R" can serve as adapters between ordinary SIP 357 devices and the Overlay. Each accepts standard SIP requests and 358 resolves the next-hop by using the P2PSIP protocol to interact with 359 the routing knowledge of the Overlay, then processes the SIP requests 360 as appropriate (proxying or redirecting towards the next-hop). Note 361 that proxy operation is bidirectional - the proxy may be forwarding a 362 request from an ordinary SIP device to the Overlay, or from the 363 P2PSIP overlay to an ordinary SIP device. 365 The PSTN Gateway at peer "G" provides a similar sort of adaptation to 366 and from the public switched telephone network (PSTN). 368 5. Definitions 370 This section defines a number of concepts that are key to 371 understanding the P2PSIP work. 373 Overlay Network: An overlay network is a computer network which is 374 built on top of another network. Nodes in the overlay can be 375 thought of as being connected by virtual or logical links, each of 376 which corresponds to a path, perhaps through many physical links, 377 in the underlying network. For example, many peer-to-peer 378 networks are overlay networks because they run on top of the 379 Internet. Dial-up Internet is an overlay upon the telephone 380 network. 382 P2P Network: A peer-to-peer (or P2P) computer network is a network 383 that relies primarily on the computing power and bandwidth of the 384 participants in the network rather than concentrating it in a 385 relatively low number of servers. P2P networks are typically used 386 for connecting nodes via largely ad hoc connections. Such 387 networks are useful for many purposes. Sharing content files (see 388 ) containing audio, 389 video, data or anything in digital format is very common, and 390 real-time data, such as telephony traffic, is also exchanged using 391 P2P technology. . A 392 P2P Network may also be called a "P2P Overlay" or "P2P Overlay 393 Network" or "P2P Network Overlay", since its organization is not 394 at the physical layer, but is instead "on top of" an existing 395 Internet Protocol network. 397 P2PSIP: A suite of communications protocols related to the Session 398 Initiation Protocol (SIP) [RFC3261] that enable SIP to use peer- 399 to-peer techniques for resolving the targets of SIP requests, 400 providing SIP message transport, and providing other SIP-related 401 functions. At present, these protocols include 402 [I-D.ietf-p2psip-base], [I-D.ietf-p2psip-sip], 403 [I-D.ietf-p2psip-diagnostics], [I-D.ietf-p2psip-service-discovery] 404 and [I-D.ietf-p2psip-self-tuning]. 406 User: A human that interacts with the overlay through SIP UAs 407 located on peers and clients (and perhaps other ways). 409 The following terms are defined here only within the scope of 410 P2PSIP. These terms may have conflicting definitions in other 411 bodies of literature. Some earlier versions of this document 412 prefixed each term with "P2PSIP" to clarify the term's scope. 413 This prefixing has been eliminated from the text; however the 414 scoping still applies. 416 Overlay Name: A human-friendly name that identifies a specific 417 P2PSIP Overlay. This is in the format of (a portion of) a URI, 418 but may or may not have a related record in the DNS. 420 Peer: A node participating in a P2PSIP Overlay that provides storage 421 and transport services to other nodes in that P2PSIP Overlay. 422 Each Peer has a unique identifier, known as a Peer-ID, within the 423 Overlay. Each Peer may be coupled to one or more SIP entities. 424 Within the Overlay, the peer is capable of performing several 425 different operations, including: joining and leaving the overlay, 426 transporting SIP messages within the overlay, storing information 427 on behalf of the overlay, putting information into the overlay, 428 and getting information from the overlay. 430 Node-ID: Information that uniquely identifies each Node within a 431 given Overlay. This value is not human-friendly -- in a DHT 432 approach, this is a numeric value in the hash space. These Node- 433 IDs are completely independent of the identifier of any user of a 434 user agent associated with a peer. 436 Client: A node participating in a P2PSIP Overlay but that does not 437 store information or forward messages. A client can also be 438 thought of as a peer that has not joined the overlay. Clients can 439 store and retrieve information from the overlay. 441 User Name: A human-friendly name for a user. This name must be 442 unique within the overlay, but may be unique in a wider scope. 443 User Names are formatted so that they can be used within a URI 444 (likely a SIP URI), perhaps in combination with the Overlay Name. 446 Service: A capability contributed by a peer to an overlay or to the 447 members of an overlay. Not all peers and clients will offer the 448 same set of services, and P2PSIP provides service discovery 449 mechanisms to locate services. 451 Service Name: A unique, human-friendly, name for a service. 453 Resource: Anything about which information can be stored in the 454 overlay. Both Users and Services are examples of Resources. 456 Resource-ID: A non-human-friendly value that uniquely identifies a 457 resource and which is used as a key for storing and retrieving 458 data about the resource. One way to generate a Resource-ID is by 459 applying a mapping function to some other unique name (e.g., User 460 Name or Service Name) for the resource. The Resource-ID is used 461 by the distributed database algorithm to determine the peer or 462 peers that are responsible for storing the data for the overlay. 464 Resource Record: A block of data, stored using distributed database 465 mechanism of the Overlay, that includes information relevant to a 466 specific resource. We presume that there may be multiple types of 467 resource records. Some may hold data about Users, and others may 468 hold data about Services, and the working group may define other 469 types. The types, usages, and formats of the records are a 470 question for future study. 472 Responsible Peer The Peer that is responsible for storing the 473 Resource Record for a Resource. In the literature, the term "Root 474 Peer" is also used for this concept. 476 Peer Protocol: The protocol spoken between P2PSIP Overlay peers to 477 share information and organize the P2PSIP Overlay Network. In 478 P2PSIP, this is implemented using the RELOAD 479 [I-D.ietf-p2psip-base] protocol. 481 Client Protocol: The protocol spoken between Clients and Peers. In 482 P2PSIP and RELOAD, this is the same protocol syntactically as the 483 Peer Protocol. The only difference is that Clients are not 484 routing messages or routing information, and have not (or can not) 485 insert themselves into the overlay. 487 Peer Protocol Connection / P2PSIP Client Protocol Connection: The 488 TLS, DTLS, TCP, UDP or other transport layer protocol connection 489 over which the RELOAD Peer Protocol messages are transported. 491 Neighbors: The set of P2PSIP Peers that a Peer or Client know of 492 directly and can reach without further lookups. 494 Joining Peer: A node that is attempting to become a Peer in a 495 particular Overlay. 497 Bootstrap Peer: A Peer in the Overlay that is the first point of 498 contact for a Joining Peer. It selects the peer that will serve 499 as the Admitting Peer and helps the joining peer contact the 500 admitting peer. 502 Admitting Peer: A Peer in the Overlay which helps the Joining Peer 503 join the Overlay. The choice of the admitting peer may depend on 504 the joining peer (e.g., depend on the joining peer's Peer-ID). 505 For example, the admitting peer might be chosen as the peer which 506 is "closest" in the logical structure of the overlay to the future 507 position of the joining peer. The selection of the admitting peer 508 is typically done by the bootstrap peer. It is allowable for the 509 bootstrap peer to select itself as the admitting peer. 511 Bootstrap Server: A network node used by Joining Peers to locate a 512 Bootstrap Peer. A Bootstrap Server may act as a proxy for 513 messages between the Joining Peer and the Bootstrap Peer. The 514 Bootstrap Server itself is typically a stable host with a DNS name 515 that is somehow communicated (for example, through configuration, 516 specification on a web page, or using DHCP) to peers that want to 517 join the overlay. A Bootstrap Server is NOT required to be a peer 518 or client, though it may be if desired. 520 Peer Admission: The act of admitting a node (the "Joining Peer") 521 into an Overlay as a Peer. After the admission process is over, 522 the joining peer is a fully-functional peer of the overlay. 523 During the admission process, the joining peer may need to present 524 credentials to prove that it has sufficient authority to join the 525 overlay. 527 Resource Record Insertion: The act of inserting a P2PSIP Resource 528 Record into the distributed database. Following insertion, the 529 data will be stored at one or more peers. The data can be 530 retrieved or updated using the Resource-ID as a key. 532 6. Discussion 534 6.1. The Distributed Database Function 536 A P2PSIP Overlay functions as a distributed database. The database 537 serves as a way to store information about Resources. A piece of 538 information, called a Resource Record, can be stored by and retrieved 539 from the database using a key associated with the Resource Record 540 called its Resource-ID. Each Resource must have a unique 541 Resource-ID. In addition to uniquely identifying the Resource, the 542 Resource-ID is also used by the distributed database algorithm to 543 determine the peer or peers that store the Resource Record in the 544 overlay. 546 Users are humans that can use the overlay to do things like making 547 and receiving calls. Information stored in the resource record 548 associated with a user can include things like the full name of the 549 user and the location of the UAs that the user is using (the users 550 SIP AoR). Full details of how this is implemented using RELOAD are 551 provided in [I-D.ietf-p2psip-sip] 553 Before information about a user can be stored in the overlay, a user 554 needs a User Name. The User Name is a human-friendly identifier that 555 uniquely identifies the user within the overlay. In RELOAD, users 556 are issued certificates, which in the case of centrally signed 557 certificates, identify the User Name as well as a certain number of 558 Resource-IDs where the user may store their information. For more 559 information, see [I-D.ietf-p2psip-base]. 561 The P2PSIP suite of protocols also standardizes information about how 562 to locate services. Services represent actions that a peer (and 563 perhaps a client) can do to benefit other peers and clients in the 564 overlay. Information that might be stored in the resource record 565 associated with a service might include the peers (and perhaps 566 clients) offering the service. Service discovery for P2PSIP is 567 defined in [I-D.ietf-p2psip-service-discovery]. 569 Each service has a human-friendly Service Name that uniquely 570 identifies the service. Like User Names, the Service Name is not a 571 resource-id, rather the resource-id is derived from the service name 572 using some function defined by the distributed database algorithm 573 used by the overlay. 575 A class of algorithms known as Distributed Hash Tables 576 are one way to implement 577 the Distributed Database. The RELOAD protocol is extensible and 578 allows many different DHTs to be implemented, but specifies a 579 mandatory to implement DHT in the form of a modified Chord DHT. For 580 more information, see [Chord] 582 6.2. Using the Distributed Database Function 584 While there are a number of ways the distributed database described 585 in the previous section can be used to establish multimedia sessions 586 using SIP, the basic mechanism defined in the RELOAD base draft and 587 SIP usage is summarized below. This is a very simplistic overview. 588 For more detailed information, please see the RELOAD base draft. 590 Contact information for a user is stored in the resource record for 591 that user. Assume that a user is using a device, here called peer A, 592 which serves as the contact point for this user. The user adds 593 contact information to this resource record, as authorized by the 594 RELOAD certificate mechanism. The resource record itself is stored 595 with peer Z in the network, where peer Z is chosen by the particular 596 distributed database algorithm in use by the overlay. 598 When the SIP entity coupled with peer B has an INVITE message 599 addressed to this user, it retrieves the resource record from peer Z. 600 It then extracts the contact information for the various peers that 601 are a contact point for the user, including peer A, and uses the 602 overlay to establish a connection to peer A, including any 603 appropriate NAT traversal (the details of which are not shown). 605 Note that RELOAD is used only to establish the connection. Once the 606 connection is established, messages between the peers are sent using 607 ordinary SIP. 609 This exchange is illustrated in the following figure. The notation 610 "Store(U@A)" is used to show the distributed database operation of 611 updating the resource record for user U with the contract A, and 612 "Fetch(U)" illustrates the distributed database operation of 613 retrieving the resource record for user U. Note that the messages 614 between the peers A, B and Z may actually travel via intermediate 615 peers (not shown) as part of the distributed lookup process or so as 616 to traverse intervening NATs. 618 Peer B Peer Z Peer A 619 | | | 620 | | Store(U@Y)| 621 | |<------------------| 622 | |Store-Resp(OK) | 623 | |------------------>| 624 | | | 625 |Fetch(U) | | 626 |------------------->| | 627 | Fetch-Resp(U@Y)| | 628 |<-------------------| | 629 | | | 630 (RELOAD IS USED TO ESTABLISH CONNECTION) 631 | | | 632 | SIP INVITE(To:U) | | 633 |--------------------------------------->| 634 | | | 636 6.3. NAT Traversal 638 NAT Traversal in P2PSIP using RELOAD treats all peers as equal and 639 establishes a partial mesh of connections between them. Messages 640 from one peer to another are routed along the edges in the mesh of 641 connections until they reach their destination. To make the routing 642 efficient and to avoid the use of standard Internet routing 643 protocols, the partial mesh is organized in a structured manner. If 644 the structure is based on any one of a number of common DHT 645 algorithms, then the maximum number of hops between any two peers is 646 log N, where N is the number of peers in the overlay. Existing 647 connections, along with the ICE NAT traversal techniques [RFC5245], 648 are used to establish new connections between peers, and also to 649 allow the applications running on peers to establish a connection to 650 communicate with one another. 652 6.4. Locating and Joining an Overlay 654 Before a peer can attempt to join a P2PSIP overlay, it must first 655 obtain a Node-ID, configuration information, and optionally a set of 656 credentials. The Node-ID is an identifier that will uniquely 657 identify the peer within the overlay, while the credentials show that 658 the peer is allowed to join the overlay. 660 The P2PSIP WG does not impose a particular mechanism for how the 661 peer-ID and the credentials are obtained, but the RELOAD base draft 662 does specify the format for the configuration information, and 663 specifies how this information may be obtained, along with 664 credentials and a Node-ID, from an offline enrollment server. 666 Once the configuration information is obtained, the RELOAD base draft 667 specifies a mechanism whereby a peer may obtain a multicast-bootstrap 668 address in the configuration file, and can broadcast to this address 669 to attempt to locate a bootstrap peer. Additionally, the peer may 670 store previous peers it has seen and attempt to use these as 671 bootstrap peers, or may obtain an address for a bootstrap peer by 672 some other mechanism. For more information, see the RELOAD base 673 draft. 675 The job of the bootstrap peer is simple: refer the joining peer to a 676 peer (called the "admitting peer") that will help the joining peer 677 join the network. The choice of admitting peer will often depend on 678 the joining node - for example, the admitting peer may be a peer that 679 will become a neighbor of the joining peer in the overlay. It is 680 possible that the bootstrap peer might also serve as the admitting 681 peer. 683 The admitting peer will help the joining peer learn about other peers 684 in the overlay and establish connections to them as appropriate. The 685 admitting peer and/or the other peers in the overlay will also do 686 whatever else is required to help the joining peer become a fully- 687 functional peer. The details of how this is done will depend on the 688 distributed database algorithm used by the overlay. 690 At various stages in this process, the joining peer may be asked to 691 present its credentials to show that it is authorized to join the 692 overlay. Similarly, the various peers contacted may be asked to 693 present their credentials so the joining peer can verify that it is 694 really joining the overlay it wants to. 696 6.5. Clients and Connecting Unmodified SIP Devices 698 As mentioned above, in RELOAD, from the perspective of the protocol, 699 clients are simply peers that do not store information, do not route 700 messages, and which have not inserted themselves into the overlay. 701 The same protocol is used for the actual message exchanged. Note 702 that while the protocol is the same, the client need not implement 703 all the capabilities of a peer. If, for example, it never routes 704 messages, it will not need to be capable of processing such messages, 705 or understanding a DHT. 707 For SIP devices, another way to realize this functionality is for a 708 Peer to behave as a [RFC3261] proxy/registrar. SIP devices then use 709 standard SIP mechanisms to add, update, and remove registrations and 710 to send SIP messages to peers and other clients. The authors here 711 refer to these devices simply as a "SIP UA", not a "P2PSIP Client", 712 to distinguish it from the concept described above. 714 6.6. Architecture 716 The architecture adopted by RELOAD to implement P2PSIP is shown 717 below. An application, for example SIP (or another application using 718 RELOAD) uses RELOAD to locate other peers and (optionally) to 719 establish connections to those peers, potentially across NATs. 720 Messages may still be exchanged directly between the peers. The 721 overall block diagram for the architecture is as follows: 723 __________________________ 724 | | 725 | SIP, other apps... | 726 | ___________________| 727 | | RELOAD Layer | 728 |______|___________________| 729 | Transport Layer | 730 |__________________________| 732 7. Open Issues 734 OPEN ISSUE: Should we include a section that documents previous 735 decisions made, to preserve the historical debate and prevent past 736 issues from being raised in the future, or simply rely on the mailing 737 list to address these concerns? 739 OPEN ISSUE: Should we include the use cases from 740 draft-bryan-p2psip-app-scenarios-00 (now expired)? There was some 741 interest in doing so in previous versions, but no conclusion was 742 reached. 744 8. Informative References 746 [Chord] Singh, K., Stoica, I., Morris, R., Karger, D., Kaashock, 747 M., Dabek, F., and H. Balakrishman, "Chord: A scalable 748 peer-to-peer lookup protocol for internet applications", 749 IEEE/ACM Transactions on Neworking Volume 11 Issue 1, pp. 750 17-32, Feb. 2003. 752 Copy available at 753 http://pdos.csail.mit.edu/chord/papers/paper-ton.pdf 755 [I-D.ietf-p2psip-base] 756 Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and 757 H. Schulzrinne, "REsource LOcation And Discovery (RELOAD) 758 Base Protocol", draft-ietf-p2psip-base-18 (work in 759 progress), August 2011. 761 [I-D.ietf-p2psip-diagnostics] 762 Haibin, S., Jiang, X., Even, R., and D. Bryan, "P2PSIP 763 Overlay Diagnostics", draft-ietf-p2psip-diagnostics-06 764 (work in progress), August 2011. 766 [I-D.ietf-p2psip-self-tuning] 767 Maenpaa, J., Camarillo, G., and J. Hautakorpi, "A Self- 768 tuning Distributed Hash Table (DHT) for REsource LOcation 769 And Discovery (RELOAD)", draft-ietf-p2psip-self-tuning-04 770 (work in progress), July 2011. 772 [I-D.ietf-p2psip-service-discovery] 773 Maenpaa, J. and G. Camarillo, "Service Discovery Usage for 774 REsource LOcation And Discovery (RELOAD)", 775 draft-ietf-p2psip-service-discovery-03 (work in progress), 776 July 2011. 778 [I-D.ietf-p2psip-sip] 779 Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and 780 H. Schulzrinne, "A SIP Usage for RELOAD", 781 draft-ietf-p2psip-sip-06 (work in progress), July 2011. 783 [RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, 784 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 785 RFC 2136, April 1997. 787 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 788 A., Peterson, J., Sparks, R., Handley, M., and E. 789 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 790 June 2002. 792 [RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation 793 Protocol (SIP): Locating SIP Servers", RFC 3263, 794 June 2002. 796 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 797 Resource Identifier (URI): Generic Syntax", STD 66, 798 RFC 3986, January 2005. 800 [RFC4795] Aboba, B., Thaler, D., and L. Esibov, "Link-local 801 Multicast Name Resolution (LLMNR)", RFC 4795, 802 January 2007. 804 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 805 (ICE): A Protocol for Network Address Translator (NAT) 806 Traversal for Offer/Answer Protocols", RFC 5245, 807 April 2010. 809 [RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using 810 Relays around NAT (TURN): Relay Extensions to Session 811 Traversal Utilities for NAT (STUN)", RFC 5766, April 2010. 813 Authors' Addresses 815 David A. Bryan 816 Polycom, Inc. 817 San Jose, California 818 USA 820 Phone: +1 408 883 5601 821 Email: bryan@ethernot.org 823 Philip Matthews 824 Alcatel-Lucent 825 600 March Road 826 Ottawa, Ontario K2K 2E6 827 Canada 829 Phone: +1 613 784 3139 830 Email: philip_matthews@magma.ca 832 Eunsoo Shim 833 Avaya, Inc. 834 233 Mt. Airy Road 835 Basking Ridge, New Jersey 07920 836 USA 838 Email: eunsooshim@gmail.com 839 Dean Willis 840 Softarmor Systems 841 3100 Independence Pkwy #311-164 842 Plano, Texas 75075 843 USA 845 Phone: +1 214 504 1987 846 Email: dean.willis@softarmor.com 848 Spencer Dawkins 849 Huawei Technologies (USA) 851 Phone: +1 214 755 3870 852 Email: spencer@wonderhamster.org