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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 St. Edwards University 4 Intended status: Informational P. Matthews 5 Expires: January 13, 2014 Alcatel-Lucent 6 E. Shim 7 Samsung Electronics Co., Ltd. 8 D. Willis 9 Softarmor Systems 10 S. Dawkins 11 Huawei (USA) 12 July 12, 2013 14 Concepts and Terminology for Peer to Peer SIP 15 draft-ietf-p2psip-concepts-05 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 mechanisms 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 January 13, 2014. 48 Copyright Notice 49 Copyright (c) 2013 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 . . . . . . . . . . . . . . . . . . . . 18 97 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19 99 1. Editor's Notes and Changes To This Version 101 This version of the draft represents a minor revision of version -04 102 and is intended to restart conversation on this draft in the group, 103 to identify open issues, address them, and complete work on the 104 document. 106 Version -03 represented a substantial revision from the previous 107 version. Until -02, this work was tracking open questions and being 108 used to help reach consensus on a draft. With the selection of 109 RELOAD as the protocol for this WG, the focus of the group turned to 110 completing the RELOAD drafts, and the WG directed the editors to 111 update the document to reflect the decisions made in RELOAD upon 112 completion. 114 Please see Section 7 for the list of major open issues. 116 2. Background 118 One of the fundamental problems in multimedia communication between 119 Internet nodes is discovering the host at which a given user can be 120 reached. In the Session Initiation Protocol (SIP) [RFC3261] this 121 problem is expressed as the problem of mapping an Address of Record 122 (AoR) for a user into one or more Contact URIs [RFC3986]. The AoR is 123 a name for the user that is independent of the host or hosts where 124 the user can be contacted, while a Contact URI indicates the host 125 where the user can be contacted. 127 In the common SIP-using architectures that we refer to as 128 "Conventional SIP" or "Client/Server SIP", there is a relatively 129 fixed hierarchy of SIP routing proxies and SIP user agents. To 130 deliver a SIP INVITE to the host or hosts at which the user can be 131 contacted, a SIP UA follows the procedures specified in [RFC3263] to 132 determine the IP address of a SIP proxy, and then sends the INVITE to 133 that proxy. The proxy will then, in turn, deliver the SIP INVITE to 134 the hosts where the user can be contacted. 136 This document gives a high-level description of an alternative 137 solution to this problem. In this alternative solution, the 138 relatively fixed hierarchy of Client/Server SIP is replaced by a 139 peer-to-peer overlay network. In this peer-to-peer overlay network, 140 the various AoR to Contact URI mappings are not centralized at proxy/ 141 registrar nodes but are instead distributed amongst the peers in the 142 overlay. 144 The details of this alternative solution are specified by the RELOAD 145 protocol. The RELOAD base draft [I-D.ietf-p2psip-base] defines a 146 mechanism to distribute using a Distributed Hash Table (DHT) and 147 specifies the wire protocol, security, and authentication mechanisms 148 needed to convey this information. This DHT protocol was designed 149 specifically with the purpose of enabling a distributed SIP registrar 150 in mind. While designing the protocol other applications were 151 considered, and when possible design decisions were made that allow 152 RELOAD to be used in other instances where a DHT is desirable, but 153 only when making such decisions did not add undue complexity to the 154 RELOAD protocol. The RELOAD sip draft [I-D.ietf-p2psip-sip] 155 specifies how RELOAD is used with the SIP protocol to enable a 156 distributed, server-less SIP solution. 158 3. High-Level Description 160 A P2PSIP Overlay is a collection of nodes organized in a peer-to-peer 161 fashion for the purpose of enabling real-time communication using the 162 Session Initiation Protocol (SIP). Collectively, the nodes in the 163 overlay provide a distributed mechanism for mapping names to overlay 164 locations. This provides for the mapping of Addresses of Record 165 (AoRs) to Contact URIs, thereby providing the "location server" 166 function of [RFC3261]. An Overlay also provides a transport function 167 by which SIP messages can be transported between any two nodes in the 168 overlay. 170 A P2PSIP Overlay consists of one or more nodes called Peers. The 171 nodes in the overlay collectively run a distributed database 172 algorithm. This distributed database algorithm allows data to be 173 stored on nodes and retrieved in an efficient manner. It may also 174 ensure that a copy of a data item is stored on more than one node, so 175 that the loss of a node does not result in the loss of the data item 176 to the overlay. 178 One use of this distributed database is to store the information 179 required to provide the mapping between AoRs and Contact URIs for the 180 distributed location function. This provides a location function 181 within each overlay that is an alternative to the location functions 182 described in [RFC3263]. However, the model of [RFC3263] is used 183 between overlays. 185 3.1. Services 187 The nature of peer-to-peer computing is that each peer offers 188 services to other peers to allow the overlay to collectively provide 189 larger functions. In P2PSIP, peers offer both distributed storage 190 and distributed message routing services, allowing these functions to 191 be implemented across the overlay. Additionally, the RELOAD protocol 192 offers a simplistic discovery mechanism specific to the TURN 194 [RFC5766] protocol used for NAT traversal. Individual peers may also 195 offer other services as an enhancement to P2PSIP functionality (for 196 example to support voicemail) or to support other applications beyond 197 SIP. To support these additional services, peers may need to store 198 additional information in the overlay. 199 [I-D.ietf-p2psip-service-discovery] describes the mechanism used in 200 P2PSIP for resource discovery. 202 3.2. Clients 204 An overlay may or may not also include one or more nodes called 205 clients. Clients are supported in the RELOAD protocol as peers that 206 have not joined the overlay, and therefore do not route messages or 207 store information. Clients access the services of the RELOAD 208 protocol by connecting to a peer which performs operations on the 209 behalf of the client. Note that in RELOAD there is no distinct 210 client protocol. Instead, a client connects using the same protocol, 211 but never joins the overlay as a peer. For more information, see 212 [I-D.ietf-p2psip-base]. 214 Note that in the context of P2PSIP, there is an additional entity 215 that is sometimes referred to as a client. A special peer may be a 216 member of the in the P2PSIP overlay and may present the functionality 217 of one or all of a SIP registrar, proxy or redirect server to 218 conventional SIP devices (SIP clients). In this way, existing, non- 219 modified SIP clients may connect to the network. These unmodified 220 SIP devices do not speak the RELOAD protocol, and this is a distinct 221 concept from the notion of client discussed in the previous 222 paragraph. 224 3.3. Relationship Between P2PSIP and RELOAD 226 The RELOAD protocol defined by the P2PSIP working group implements a 227 DHT primarily for use by server-less, peer-to-peer SIP deployments. 228 However, the RELOAD protocol could be used for other applications as 229 well. As such, a "P2PSIP" deployment is generally assumed to be a 230 use of RELOAD to implement distributed SIP, but it is possible that 231 RELOAD is used as a mechanism to distribute other applications, 232 completely unrelated to SIP. 234 3.4. Relationship Between P2PSIP and SIP 236 Since P2PSIP is about peer-to-peer networks for real-time 237 communication, it is expected that most peers and clients will be 238 coupled with SIP entities (although RELOAD may be used for other 239 applications than P2PSIP). For example, one peer might be coupled 240 with a SIP UA, another might be coupled with a SIP proxy, while a 241 third might be coupled with a SIP-to-PSTN gateway. For such nodes, 242 the peer or client portion of the node is logically distinct from the 243 SIP entity portion. However, there is no hard requirement that every 244 P2PSIP node (peer or client) be coupled to a SIP entity. As an 245 example, additional peers could be placed in the overlay to provide 246 additional storage or redundancy for the RELOAD overlay, but might 247 not have any direct SIP capabilities. 249 3.5. Relationship Between P2PSIP and Other AoR Dereferencing Approaches 251 OPEN ISSUE: Many of the "decisions" made have been moved out of the 252 main document. This one, however, seems to point out a difference. 253 Should this section be moved or removed? 255 As noted above, the fundamental task of P2PSIP is turning an AoR into 256 a Contact. This task might be approached using zeroconf techniques 257 such as multicast DNS and DNS Service Discovery (as in Apple's 258 Bonjour protocol), link-local multicast name resolution [RFC4795], 259 and dynamic DNS [RFC2136]. 261 These alternatives were discussed in the P2PSIP Working Group, and 262 not pursued as a general solution for a number of reasons related to 263 scalability, the ability to work in a disconnected state, partition 264 recovery, and so on. However, there does seem to be some continuing 265 interest in the possibility of using DNS-SD and mDNS for 266 bootstrapping of P2PSIP overlays. 268 3.6. NAT Issues 270 Network Address Translators (NATs) are impediments to establishing 271 and maintaining peer-to-peer networks, since NATs hinder direct 272 communication between nodes. Some peer-to-peer network architectures 273 avoid this problem by insisting that all nodes exist in the same 274 address space. However, RELOAD provides capabilities that allow 275 nodes to be located in multiple address spaces interconnected by 276 NATs, to allow RELOAD messages to traverse NATs, and to assist in 277 transmitting application-level messages (for example SIP messages) 278 across NATs. 280 4. Reference Model 282 The following diagram shows a P2PSIP Overlay consisting of a number 283 of Peers, one Client, and an ordinary SIP UA. It illustrates a 284 typical P2PSIP overlay but does not limit other compositions or 285 variations; for example, Proxy Peer P might also talk to a ordinary 286 SIP proxy as well. The figure is not intended to cover all possible 287 architecture variations, but simply to show a deployment with many 288 common P2PSIP elements. 290 --->PSTN 291 +------+ N +------+ +---------+ / 292 | | A | | | Gateway |-/ 293 | UA |####T#####| UA |#####| Peer |######## 294 | Peer | N | Peer | | G | # RELOAD 295 | E | A | F | +---------+ # P2PSIP 296 | | T | | # Protocol 297 +------+ N +------+ # | 298 # A # | 299 NATNATNATNAT # | 300 # # | \__/ 301 NATNATNATNAT +-------+ v / \ 302 # N | |#####/ UA \ 303 +------+ A P2PSIP Overlay | Peer | /Client\ 304 | | T | Q | |___C__| 305 | UA | N | | 306 | Peer | A +-------+ 307 | D | T # 308 | | N # 309 +------+ A # RELOAD 310 # T # P2PSIP 311 # N +-------+ +-------+ # Protocol 312 # A | | | | # 313 #########T####| Proxy |########| Redir |####### 314 N | Peer | | Peer | 315 A | P | | R | 316 T +-------+ +-------+ 317 | / 318 | SIP / 319 \__/ / / 320 /\ / ______________/ SIP 321 / \/ / 322 / UA \/ 323 /______\ 324 SIP UA A 326 Figure: P2PSIP Overlay Reference Model 328 Here, the large perimeter depicted by "#" represents a stylized view 329 of the Overlay (the actual connections could be a mesh, a ring, or 330 some other structure). Around the periphery of the Overlay 331 rectangle, we have a number of Peers. Each peer is labeled with its 332 coupled SIP entity -- for example, "Proxy Peer P" means that peer P 333 which is coupled with a SIP proxy. In some cases, a peer or client 334 might be coupled with two or more SIP entities. In this diagram we 335 have a PSTN gateway coupled with peer "G", three peers ("D", "E" and 336 "F") which are each coupled with a UA, a peer "P" which is coupled 337 with a SIP proxy, an ordinary peer "Q" with no SIP capabilities, and 338 one peer "R" which is coupled with a SIP Redirector. Note that 339 because these are all Peers, each is responsible for storing Resource 340 Records and transporting messages around the Overlay. 342 To the left, two of the peers ("D" and "E") are behind network 343 address translators (NATs). These peers are included in the P2PSIP 344 overlay and thus participate in storing resource records and routing 345 messages, despite being behind the NATs. 347 On the right side, we have a client "C", which uses the RELOAD 348 Protocol to communicate with Proxy Peer "Q". The Client "C" uses 349 RELOAD to obtain information from the overlay, but has not inserted 350 itself into the overlay, and therefore does not participate in 351 routing messages or storing information. 353 Below the Overlay, we have a conventional SIP UA "A" which is not 354 part of the Overlay, either directly as a peer or indirectly as a 355 client. It does not speak the RELOAD P2PSIP protocol, and is not 356 participating in the overlay as either a Peer nor Client. Instead, 357 it uses SIP to interact with the Overlay via an adapter peer or peers 358 which communicate with the overlay using RELOAD. 360 Both the SIP proxy coupled with peer "P" and the SIP redirector 361 coupled with peer "R" can serve as adapters between ordinary SIP 362 devices and the Overlay. Each accepts standard SIP requests and 363 resolves the next-hop by using the P2PSIP protocol to interact with 364 the routing knowledge of the Overlay, then processes the SIP requests 365 as appropriate (proxying or redirecting towards the next-hop). Note 366 that proxy operation is bidirectional - the proxy may be forwarding a 367 request from an ordinary SIP device to the Overlay, or from the 368 P2PSIP overlay to an ordinary SIP device. 370 The PSTN Gateway at peer "G" provides a similar sort of adaptation to 371 and from the public switched telephone network (PSTN). 373 5. Definitions 375 This section defines a number of concepts that are key to 376 understanding the P2PSIP work. 378 Overlay Network: An overlay network is a computer network which is 379 built on top of another network. Nodes in the overlay can be 380 thought of as being connected by virtual or logical links, each of 381 which corresponds to a path, perhaps through many physical links, 382 in the underlying network. For example, many peer-to-peer 383 networks are overlay networks because they run on top of the 384 Internet. Dial-up Internet is an overlay upon the telephone 385 network. 387 P2P Network: A peer-to-peer (or P2P) computer network is a network 388 that relies primarily on the computing power and bandwidth of the 389 participants in the network rather than concentrating it in a 390 relatively low number of servers. P2P networks are typically used 391 for connecting nodes via largely ad hoc connections. Such 392 networks are useful for many purposes. Sharing content files (see 393 ) containing audio, 394 video, data or anything in digital format is very common, and 395 real-time data, such as telephony traffic, is also exchanged using 396 P2P technology. . A 397 P2P Network may also be called a "P2P Overlay" or "P2P Overlay 398 Network" or "P2P Network Overlay", since its organization is not 399 at the physical layer, but is instead "on top of" an existing 400 Internet Protocol network. 402 P2PSIP: A suite of communications protocols related to the Session 403 Initiation Protocol (SIP) [RFC3261] that enable SIP to use peer- 404 to-peer techniques for resolving the targets of SIP requests, 405 providing SIP message transport, and providing other SIP-related 406 functions. At present, these protocols include 407 [I-D.ietf-p2psip-base], [I-D.ietf-p2psip-sip], 408 [I-D.ietf-p2psip-diagnostics], [I-D.ietf-p2psip-service-discovery] 409 and [I-D.ietf-p2psip-self-tuning]. 411 User: A human that interacts with the overlay through SIP UAs 412 located on peers and clients (and perhaps other ways). 414 The following terms are defined here only within the scope of 415 P2PSIP. These terms may have conflicting definitions in other 416 bodies of literature. Some earlier versions of this document 417 prefixed each term with "P2PSIP" to clarify the term's scope. 418 This prefixing has been eliminated from the text; however the 419 scoping still applies. 421 Overlay Name: A human-friendly name that identifies a specific 422 P2PSIP Overlay. This is in the format of (a portion of) a URI, 423 but may or may not have a related record in the DNS. 425 Peer: A node participating in a P2PSIP Overlay that provides storage 426 and transport services to other nodes in that P2PSIP Overlay. 427 Each Peer has a unique identifier, known as a Peer-ID, within the 428 Overlay. Each Peer may be coupled to one or more SIP entities. 429 Within the Overlay, the peer is capable of performing several 430 different operations, including: joining and leaving the overlay, 431 transporting SIP messages within the overlay, storing information 432 on behalf of the overlay, putting information into the overlay, 433 and getting information from the overlay. 435 Node-ID: Information that uniquely identifies each Node within a 436 given Overlay. This value is not human-friendly -- in a DHT 437 approach, this is a numeric value in the hash space. These Node- 438 IDs are completely independent of the identifier of any user of a 439 user agent associated with a peer. 441 Client: A node participating in a P2PSIP Overlay but that does not 442 store information or forward messages. A client can also be 443 thought of as a peer that has not joined the overlay. Clients can 444 store and retrieve information from the overlay. 446 User Name: A human-friendly name for a user. This name must be 447 unique within the overlay, but may be unique in a wider scope. 448 User Names are formatted so that they can be used within a URI 449 (likely a SIP URI), perhaps in combination with the Overlay Name. 451 Service: A capability contributed by a peer to an overlay or to the 452 members of an overlay. Not all peers and clients will offer the 453 same set of services, and P2PSIP provides service discovery 454 mechanisms to locate services. 456 Service Name: A unique, human-friendly, name for a service. 458 Resource: Anything about which information can be stored in the 459 overlay. Both Users and Services are examples of Resources. 461 Resource-ID: A non-human-friendly value that uniquely identifies a 462 resource and which is used as a key for storing and retrieving 463 data about the resource. One way to generate a Resource-ID is by 464 applying a mapping function to some other unique name (e.g., User 465 Name or Service Name) for the resource. The Resource-ID is used 466 by the distributed database algorithm to determine the peer or 467 peers that are responsible for storing the data for the overlay. 469 Resource Record: A block of data, stored using distributed database 470 mechanism of the Overlay, that includes information relevant to a 471 specific resource. We presume that there may be multiple types of 472 resource records. Some may hold data about Users, and others may 473 hold data about Services, and the working group may define other 474 types. The types, usages, and formats of the records are a 475 question for future study. 477 Responsible Peer The Peer that is responsible for storing the 478 Resource Record for a Resource. In the literature, the term "Root 479 Peer" is also used for this concept. 481 Peer Protocol: The protocol spoken between P2PSIP Overlay peers to 482 share information and organize the P2PSIP Overlay Network. In 483 P2PSIP, this is implemented using the RELOAD 484 [I-D.ietf-p2psip-base] protocol. 486 Client Protocol: The protocol spoken between Clients and Peers. In 487 P2PSIP and RELOAD, this is the same protocol syntactically as the 488 Peer Protocol. The only difference is that Clients are not 489 routing messages or routing information, and have not (or can not) 490 insert themselves into the overlay. 492 Peer Protocol Connection / P2PSIP Client Protocol Connection: The 493 TLS, DTLS, TCP, UDP or other transport layer protocol connection 494 over which the RELOAD Peer Protocol messages are transported. 496 Neighbors: The set of P2PSIP Peers that a Peer or Client know of 497 directly and can reach without further lookups. 499 Joining Peer: A node that is attempting to become a Peer in a 500 particular Overlay. 502 Bootstrap Peer: A Peer in the Overlay that is the first point of 503 contact for a Joining Peer. It selects the peer that will serve 504 as the Admitting Peer and helps the joining peer contact the 505 admitting peer. 507 Admitting Peer: A Peer in the Overlay which helps the Joining Peer 508 join the Overlay. The choice of the admitting peer may depend on 509 the joining peer (e.g., depend on the joining peer's Peer-ID). 510 For example, the admitting peer might be chosen as the peer which 511 is "closest" in the logical structure of the overlay to the future 512 position of the joining peer. The selection of the admitting peer 513 is typically done by the bootstrap peer. It is allowable for the 514 bootstrap peer to select itself as the admitting peer. 516 Bootstrap Server: A network node used by Joining Peers to locate a 517 Bootstrap Peer. A Bootstrap Server may act as a proxy for 518 messages between the Joining Peer and the Bootstrap Peer. The 519 Bootstrap Server itself is typically a stable host with a DNS name 520 that is somehow communicated (for example, through configuration, 521 specification on a web page, or using DHCP) to peers that want to 522 join the overlay. A Bootstrap Server is NOT required to be a peer 523 or client, though it may be if desired. 525 Peer Admission: The act of admitting a node (the "Joining Peer") 526 into an Overlay as a Peer. After the admission process is over, 527 the joining peer is a fully-functional peer of the overlay. 528 During the admission process, the joining peer may need to present 529 credentials to prove that it has sufficient authority to join the 530 overlay. 532 Resource Record Insertion: The act of inserting a P2PSIP Resource 533 Record into the distributed database. Following insertion, the 534 data will be stored at one or more peers. The data can be 535 retrieved or updated using the Resource-ID as a key. 537 6. Discussion 539 6.1. The Distributed Database Function 541 A P2PSIP Overlay functions as a distributed database. The database 542 serves as a way to store information about Resources. A piece of 543 information, called a Resource Record, can be stored by and retrieved 544 from the database using a key associated with the Resource Record 545 called its Resource-ID. Each Resource must have a unique 546 Resource-ID. In addition to uniquely identifying the Resource, the 547 Resource-ID is also used by the distributed database algorithm to 548 determine the peer or peers that store the Resource Record in the 549 overlay. 551 Users are humans that can use the overlay to do things like making 552 and receiving calls. Information stored in the resource record 553 associated with a user can include things like the full name of the 554 user and the location of the UAs that the user is using (the users 555 SIP AoR). Full details of how this is implemented using RELOAD are 556 provided in [I-D.ietf-p2psip-sip] 558 Before information about a user can be stored in the overlay, a user 559 needs a User Name. The User Name is a human-friendly identifier that 560 uniquely identifies the user within the overlay. In RELOAD, users 561 are issued certificates, which in the case of centrally signed 562 certificates, identify the User Name as well as a certain number of 563 Resource-IDs where the user may store their information. For more 564 information, see [I-D.ietf-p2psip-base]. 566 The P2PSIP suite of protocols also standardizes information about how 567 to locate services. Services represent actions that a peer (and 568 perhaps a client) can do to benefit other peers and clients in the 569 overlay. Information that might be stored in the resource record 570 associated with a service might include the peers (and perhaps 571 clients) offering the service. Service discovery for P2PSIP is 572 defined in [I-D.ietf-p2psip-service-discovery]. 574 Each service has a human-friendly Service Name that uniquely 575 identifies the service. Like User Names, the Service Name is not a 576 resource-id, rather the resource-id is derived from the service name 577 using some function defined by the distributed database algorithm 578 used by the overlay. 580 A class of algorithms known as Distributed Hash Tables 581 are one way to implement 582 the Distributed Database. The RELOAD protocol is extensible and 583 allows many different DHTs to be implemented, but specifies a 584 mandatory to implement DHT in the form of a modified Chord DHT. For 585 more information, see [Chord] 587 6.2. Using the Distributed Database Function 589 While there are a number of ways the distributed database described 590 in the previous section can be used to establish multimedia sessions 591 using SIP, the basic mechanism defined in the RELOAD base draft and 592 SIP usage is summarized below. This is a very simplistic overview. 593 For more detailed information, please see the RELOAD base draft. 595 Contact information for a user is stored in the resource record for 596 that user. Assume that a user is using a device, here called peer A, 597 which serves as the contact point for this user. The user adds 598 contact information to this resource record, as authorized by the 599 RELOAD certificate mechanism. The resource record itself is stored 600 with peer Z in the network, where peer Z is chosen by the particular 601 distributed database algorithm in use by the overlay. 603 When the SIP entity coupled with peer B has an INVITE message 604 addressed to this user, it retrieves the resource record from peer Z. 605 It then extracts the contact information for the various peers that 606 are a contact point for the user, including peer A, and uses the 607 overlay to establish a connection to peer A, including any 608 appropriate NAT traversal (the details of which are not shown). 610 Note that RELOAD is used only to establish the connection. Once the 611 connection is established, messages between the peers are sent using 612 ordinary SIP. 614 This exchange is illustrated in the following figure. The notation 615 "Store(U@A)" is used to show the distributed database operation of 616 updating the resource record for user U with the contract A, and 617 "Fetch(U)" illustrates the distributed database operation of 618 retrieving the resource record for user U. Note that the messages 619 between the peers A, B and Z may actually travel via intermediate 620 peers (not shown) as part of the distributed lookup process or so as 621 to traverse intervening NATs. 623 Peer B Peer Z Peer A 624 | | | 625 | | Store(U@Y)| 626 | |<------------------| 627 | |Store-Resp(OK) | 628 | |------------------>| 629 | | | 630 |Fetch(U) | | 631 |------------------->| | 632 | Fetch-Resp(U@Y)| | 633 |<-------------------| | 634 | | | 635 (RELOAD IS USED TO ESTABLISH CONNECTION) 636 | | | 637 | SIP INVITE(To:U) | | 638 |--------------------------------------->| 639 | | | 641 6.3. NAT Traversal 643 NAT Traversal in P2PSIP using RELOAD treats all peers as equal and 644 establishes a partial mesh of connections between them. Messages 645 from one peer to another are routed along the edges in the mesh of 646 connections until they reach their destination. To make the routing 647 efficient and to avoid the use of standard Internet routing 648 protocols, the partial mesh is organized in a structured manner. If 649 the structure is based on any one of a number of common DHT 650 algorithms, then the maximum number of hops between any two peers is 651 log N, where N is the number of peers in the overlay. Existing 652 connections, along with the ICE NAT traversal techniques [RFC5245], 653 are used to establish new connections between peers, and also to 654 allow the applications running on peers to establish a connection to 655 communicate with one another. 657 6.4. Locating and Joining an Overlay 659 Before a peer can attempt to join a P2PSIP overlay, it must first 660 obtain a Node-ID, configuration information, and optionally a set of 661 credentials. The Node-ID is an identifier that will uniquely 662 identify the peer within the overlay, while the credentials show that 663 the peer is allowed to join the overlay. 665 The P2PSIP WG does not impose a particular mechanism for how the 666 peer-ID and the credentials are obtained, but the RELOAD base draft 667 does specify the format for the configuration information, and 668 specifies how this information may be obtained, along with 669 credentials and a Node-ID, from an offline enrollment server. 671 Once the configuration information is obtained, the RELOAD base draft 672 specifies a mechanism whereby a peer may obtain a multicast-bootstrap 673 address in the configuration file, and can broadcast to this address 674 to attempt to locate a bootstrap peer. Additionally, the peer may 675 store previous peers it has seen and attempt to use these as 676 bootstrap peers, or may obtain an address for a bootstrap peer by 677 some other mechanism. For more information, see the RELOAD base 678 draft. 680 The job of the bootstrap peer is simple: refer the joining peer to a 681 peer (called the "admitting peer") that will help the joining peer 682 join the network. The choice of admitting peer will often depend on 683 the joining node - for example, the admitting peer may be a peer that 684 will become a neighbor of the joining peer in the overlay. It is 685 possible that the bootstrap peer might also serve as the admitting 686 peer. 688 The admitting peer will help the joining peer learn about other peers 689 in the overlay and establish connections to them as appropriate. The 690 admitting peer and/or the other peers in the overlay will also do 691 whatever else is required to help the joining peer become a fully- 692 functional peer. The details of how this is done will depend on the 693 distributed database algorithm used by the overlay. 695 At various stages in this process, the joining peer may be asked to 696 present its credentials to show that it is authorized to join the 697 overlay. Similarly, the various peers contacted may be asked to 698 present their credentials so the joining peer can verify that it is 699 really joining the overlay it wants to. 701 6.5. Clients and Connecting Unmodified SIP Devices 703 As mentioned above, in RELOAD, from the perspective of the protocol, 704 clients are simply peers that do not store information, do not route 705 messages, and which have not inserted themselves into the overlay. 706 The same protocol is used for the actual message exchanged. Note 707 that while the protocol is the same, the client need not implement 708 all the capabilities of a peer. If, for example, it never routes 709 messages, it will not need to be capable of processing such messages, 710 or understanding a DHT. 712 For SIP devices, another way to realize this functionality is for a 713 Peer to behave as a [RFC3261] proxy/registrar. SIP devices then use 714 standard SIP mechanisms to add, update, and remove registrations and 715 to send SIP messages to peers and other clients. The authors here 716 refer to these devices simply as a "SIP UA", not a "P2PSIP Client", 717 to distinguish it from the concept described above. 719 6.6. Architecture 721 The architecture adopted by RELOAD to implement P2PSIP is shown 722 below. An application, for example SIP (or another application using 723 RELOAD) uses RELOAD to locate other peers and (optionally) to 724 establish connections to those peers, potentially across NATs. 725 Messages may still be exchanged directly between the peers. The 726 overall block diagram for the architecture is as follows: 728 __________________________ 729 | | 730 | SIP, other apps... | 731 | ___________________| 732 | | RELOAD Layer | 733 |______|___________________| 734 | Transport Layer | 735 |__________________________| 737 7. Open Issues 739 MAJOR OPEN ISSUE: The initial wording in the high-level description 740 about proving AoR to contact mapping reflects a very long and 741 contentious debate about the role of the protocol, and reflected a 742 pretense that this was an overlay only for P2PSIP. That is 743 explicitly not true in base anymore (see last paragraph of 744 introduction) and the language has been very much genericized in 745 base. Should we make this text more abstract and then use 746 AoR->contact mapping as an example of the (original) use? On a 747 related note, see the last paragraph of the Background section -- do 748 we want to reword this? 750 OPEN ISSUE: Should we include a section that documents previous 751 decisions made, to preserve the historical debate and prevent past 752 issues from being raised in the future, or simply rely on the mailing 753 list to address these concerns? 755 OPEN ISSUE: Should we include the use cases from 756 draft-bryan-p2psip-app-scenarios-00 (now long expired)? There was 757 some interest in doing so in previous versions, but no conclusion was 758 reached. 760 8. Informative References 762 [Chord] Singh, K., Stoica, I., Morris, R., Karger, D., Kaashock, 763 M., Dabek, F., and H. Balakrishman, "Chord: A scalable 764 peer-to-peer lookup protocol for internet applications", 765 IEEE/ACM Transactions on Neworking Volume 11 Issue 1, pp. 766 17-32, Feb. 2003. 768 Copy available at 769 http://pdos.csail.mit.edu/chord/papers/paper-ton.pdf 771 [I-D.ietf-p2psip-base] 772 Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and 773 H. Schulzrinne, "REsource LOcation And Discovery (RELOAD) 774 Base Protocol", draft-ietf-p2psip-base-26 (work in 775 progress), February 2013. 777 [I-D.ietf-p2psip-diagnostics] 778 Song, H., Jiang, X., Even, R., and D. Bryan, "P2P Overlay 779 Diagnostics", draft-ietf-p2psip-diagnostics-11 (work in 780 progress), March 2013. 782 [I-D.ietf-p2psip-self-tuning] 783 Maenpaa, J. and G. Camarillo, "A Self-tuning Distributed 784 Hash Table (DHT) for REsource LOcation And Discovery 785 (RELOAD)", draft-ietf-p2psip-self-tuning-08 (work in 786 progress), February 2013. 788 [I-D.ietf-p2psip-service-discovery] 789 Maenpaa, J. and G. Camarillo, "Service Discovery Usage for 790 REsource LOcation And Discovery (RELOAD)", 791 draft-ietf-p2psip-service-discovery-08 (work in progress), 792 February 2013. 794 [I-D.ietf-p2psip-sip] 795 Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., 796 Schulzrinne, H., and T. Schmidt, "A SIP Usage for RELOAD", 797 draft-ietf-p2psip-sip-09 (work in progress), 798 February 2013. 800 [RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, 801 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 802 RFC 2136, April 1997. 804 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 805 A., Peterson, J., Sparks, R., Handley, M., and E. 806 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 807 June 2002. 809 [RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation 810 Protocol (SIP): Locating SIP Servers", RFC 3263, 811 June 2002. 813 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 814 Resource Identifier (URI): Generic Syntax", STD 66, 815 RFC 3986, January 2005. 817 [RFC4795] Aboba, B., Thaler, D., and L. Esibov, "Link-local 818 Multicast Name Resolution (LLMNR)", RFC 4795, 819 January 2007. 821 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 822 (ICE): A Protocol for Network Address Translator (NAT) 823 Traversal for Offer/Answer Protocols", RFC 5245, 824 April 2010. 826 [RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using 827 Relays around NAT (TURN): Relay Extensions to Session 828 Traversal Utilities for NAT (STUN)", RFC 5766, April 2010. 830 Authors' Addresses 832 David A. Bryan 833 St. Edwards University 834 Austin, Texas 835 USA 837 Email: bryan@ethernot.org 839 Philip Matthews 840 Alcatel-Lucent 841 600 March Road 842 Ottawa, Ontario K2K 2E6 843 Canada 845 Phone: +1 613 784 3139 846 Email: philip_matthews@magma.ca 847 Eunsoo Shim 848 Samsung Electronics Co., Ltd. 849 San 14, Nongseo-dong, Giheung-gu, 850 Yongin-si, Gyeonggi-do, 446-712 851 South Korea 853 Email: eunsooshim@gmail.com 855 Dean Willis 856 Softarmor Systems 857 3100 Independence Pkwy #311-164 858 Plano, Texas 75075 859 USA 861 Phone: +1 214 504 1987 862 Email: dean.willis@softarmor.com 864 Spencer Dawkins 865 Huawei Technologies (USA) 867 Phone: +1 214 755 3870 868 Email: spencerdawkins.ietf@gmail.com