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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 Cogent Force, LLC 4 Intended status: Informational P. Matthews 5 Expires: November 9, 2015 Alcatel-Lucent 6 E. Shim 7 Samsung Electronics Co., Ltd. 8 D. Willis 9 Softarmor Systems 10 S. Dawkins 11 Huawei (USA) 12 May 8, 2015 14 Concepts and Terminology for Peer to Peer SIP 15 draft-ietf-p2psip-concepts-07 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 and SIP usage ([RFC6940], 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 November 9, 2015. 48 Copyright Notice 49 Copyright (c) 2015 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 . . . . . . . . . . . . . . . . . . . . . . . . . 6 80 3.2. Clients . . . . . . . . . . . . . . . . . . . . . . . . . 6 81 3.3. Relationship Between P2PSIP and RELOAD . . . . . . . . . . 6 82 3.4. Relationship Between P2PSIP and SIP . . . . . . . . . . . 7 83 3.5. Relationship Between P2PSIP and Other AoR 84 Dereferencing Approaches . . . . . . . . . . . . . . . . . 7 85 3.6. NAT Issues . . . . . . . . . . . . . . . . . . . . . . . . 7 86 4. Reference Model . . . . . . . . . . . . . . . . . . . . . . . 8 87 5. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 10 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 . . . . . . . . . . . . . 16 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 almost no change from -06, which 102 itself was a very minor revision of version -05 and is intended to 103 restart conversation on this draft in the group, to identify open 104 issues, address them, and complete work on the document in light of 105 RELOAD being issued as an RFC. 107 It is currently believed this draft's terminology is inline with RFC 108 6940. Please report any discrepancies to the editors of this 109 document. 111 Version -03 represented a substantial revision from the previous 112 version. Until -02, this work was tracking open questions and being 113 used to help reach consensus on a draft. With the selection of 114 RELOAD as the protocol for this WG, the focus of the group turned to 115 completing the RELOAD draft, and the WG directed the editors to 116 update the document to reflect the decisions made in RELOAD upon 117 completion. 119 Please see Section 7 for the list of major open issues. 121 2. Background 123 One of the fundamental problems in multimedia communication between 124 Internet nodes is discovering the host at which a given user can be 125 reached. In the Session Initiation Protocol (SIP) [RFC3261] this 126 problem is expressed as the problem of mapping an Address of Record 127 (AoR) for a user into one or more Contact URIs [RFC3986]. The AoR is 128 a name for the user that is independent of the host or hosts where 129 the user can be contacted, while a Contact URI indicates the host 130 where the user can be contacted. 132 In the common SIP-using architectures that we refer to as 133 "Conventional SIP" or "Client/Server SIP", there is a relatively 134 fixed hierarchy of SIP routing proxies and SIP user agents. To 135 deliver a SIP INVITE to the host or hosts at which the user can be 136 contacted, a SIP UA follows the procedures specified in [RFC3263] to 137 determine the IP address of a SIP proxy, and then sends the INVITE to 138 that proxy. The proxy will then, in turn, deliver the SIP INVITE to 139 the hosts where the user can be contacted. 141 This document gives a high-level description of an alternative 142 solution to this problem. In this alternative solution, the 143 relatively fixed hierarchy of Client/Server SIP is replaced by a 144 peer-to-peer overlay network. In this peer-to-peer overlay network, 145 the various AoR to Contact URI mappings are not centralized at proxy/ 146 registrar nodes but are instead distributed amongst the peers in the 147 overlay. 149 The details of this alternative solution are specified by the RELOAD 150 protocol. The RELOAD base draft [RFC6940] defines a mechanism to 151 distribute using a Distributed Hash Table (DHT) and specifies the 152 wire protocol, security, and authentication mechanisms needed to 153 convey this information. This DHT protocol was designed specifically 154 with the purpose of enabling a distributed SIP registrar in mind. 155 While designing the protocol other applications were considered, and 156 when possible design decisions were made that allow RELOAD to be used 157 in other instances where a DHT is desirable, but only when making 158 such decisions did not add undue complexity to the RELOAD protocol. 159 The RELOAD sip draft [I-D.ietf-p2psip-sip] specifies how RELOAD is 160 used with the SIP protocol to enable a distributed, server-less SIP 161 solution. 163 3. High-Level Description 165 A P2PSIP Overlay is a collection of nodes organized in a peer-to-peer 166 fashion for the purpose of enabling real-time communication using the 167 Session Initiation Protocol (SIP). Collectively, the nodes in the 168 overlay provide a distributed mechanism for mapping names to overlay 169 locations. This provides for the mapping of Addresses of Record 170 (AoRs) to Contact URIs, thereby providing the "location server" 171 function of [RFC3261]. An Overlay also provides a transport function 172 by which SIP messages can be transported between any two nodes in the 173 overlay. 175 A P2PSIP Overlay consists of one or more nodes called Peers. The 176 nodes in the overlay collectively run a distributed database 177 algorithm. This distributed database algorithm allows data to be 178 stored on nodes and retrieved in an efficient manner. It may also 179 ensure that a copy of a data item is stored on more than one node, so 180 that the loss of a node does not result in the loss of the data item 181 to the overlay. 183 One use of this distributed database is to store the information 184 required to provide the mapping between AoRs and Contact URIs for the 185 distributed location function. This provides a location function 186 within each overlay that is an alternative to the location functions 187 described in [RFC3263]. However, the model of [RFC3263] is used 188 between overlays. 190 3.1. Services 192 The nature of peer-to-peer computing is that each peer offers 193 services to other peers to allow the overlay to collectively provide 194 larger functions. In P2PSIP, peers offer both distributed storage 195 and distributed message routing services, allowing these functions to 196 be implemented across the overlay. Additionally, the RELOAD protocol 197 offers a simplistic discovery mechanism specific to the TURN 198 [RFC5766] protocol used for NAT traversal. Individual peers may also 199 offer other services as an enhancement to P2PSIP functionality (for 200 example to support voicemail) or to support other applications beyond 201 SIP. To support these additional services, peers may need to store 202 additional information in the overlay. 203 [I-D.ietf-p2psip-service-discovery] describes the mechanism used in 204 P2PSIP for resource discovery. 206 3.2. Clients 208 An overlay may or may not also include one or more nodes called 209 clients. Clients are supported in the RELOAD protocol as peers that 210 have not joined the overlay, and therefore do not route messages or 211 store information. Clients access the services of the RELOAD 212 protocol by connecting to a peer which performs operations on the 213 behalf of the client. Note that in RELOAD there is no distinct 214 client protocol. Instead, a client connects using the same protocol, 215 but never joins the overlay as a peer. For more information, see 216 [RFC6940]. 218 Note that in the context of P2PSIP, there is an additional entity 219 that is sometimes referred to as a client. A special peer may be a 220 member of the in the P2PSIP overlay and may present the functionality 221 of one or all of a SIP registrar, proxy or redirect server to 222 conventional SIP devices (SIP clients). In this way, existing, non- 223 modified SIP clients may connect to the network. These unmodified 224 SIP devices do not speak the RELOAD protocol, and this is a distinct 225 concept from the notion of client discussed in the previous 226 paragraph. 228 3.3. Relationship Between P2PSIP and RELOAD 230 The RELOAD protocol defined by the P2PSIP working group implements a 231 DHT primarily for use by server-less, peer-to-peer SIP deployments. 232 However, the RELOAD protocol could be used for other applications as 233 well. As such, a "P2PSIP" deployment is generally assumed to be a 234 use of RELOAD to implement distributed SIP, but it is possible that 235 RELOAD is used as a mechanism to distribute other applications, 236 completely unrelated to SIP. 238 3.4. Relationship Between P2PSIP and SIP 240 Since P2PSIP is about peer-to-peer networks for real-time 241 communication, it is expected that most peers and clients will be 242 coupled with SIP entities (although RELOAD may be used for other 243 applications than P2PSIP). For example, one peer might be coupled 244 with a SIP UA, another might be coupled with a SIP proxy, while a 245 third might be coupled with a SIP-to-PSTN gateway. For such nodes, 246 the peer or client portion of the node is logically distinct from the 247 SIP entity portion. However, there is no hard requirement that every 248 P2PSIP node (peer or client) be coupled to a SIP entity. As an 249 example, additional peers could be placed in the overlay to provide 250 additional storage or redundancy for the RELOAD overlay, but might 251 not have any direct SIP capabilities. 253 3.5. Relationship Between P2PSIP and Other AoR Dereferencing Approaches 255 OPEN ISSUE: Many of the "decisions" made have been moved out of the 256 main document. This one, however, seems to point out a difference. 257 Should this section be moved or removed? 259 As noted above, the fundamental task of P2PSIP is turning an AoR into 260 a Contact. This task might be approached using zeroconf techniques 261 such as multicast DNS and DNS Service Discovery (as in Apple's 262 Bonjour protocol), link-local multicast name resolution [RFC4795], 263 and dynamic DNS [RFC2136]. 265 These alternatives were discussed in the P2PSIP Working Group, and 266 not pursued as a general solution for a number of reasons related to 267 scalability, the ability to work in a disconnected state, partition 268 recovery, and so on. However, there does seem to be some continuing 269 interest in the possibility of using DNS-SD and mDNS for 270 bootstrapping of P2PSIP overlays. 272 3.6. NAT Issues 274 Network Address Translators (NATs) are impediments to establishing 275 and maintaining peer-to-peer networks, since NATs hinder direct 276 communication between nodes. Some peer-to-peer network architectures 277 avoid this problem by insisting that all nodes exist in the same 278 address space. However, RELOAD provides capabilities that allow 279 nodes to be located in multiple address spaces interconnected by 280 NATs, to allow RELOAD messages to traverse NATs, and to assist in 281 transmitting application-level messages (for example SIP messages) 282 across NATs. 284 4. Reference Model 286 The following diagram shows a P2PSIP Overlay consisting of a number 287 of Peers, one Client, and an ordinary SIP UA. It illustrates a 288 typical P2PSIP overlay but does not limit other compositions or 289 variations; for example, Proxy Peer P might also talk to a ordinary 290 SIP proxy as well. The figure is not intended to cover all possible 291 architecture variations, but simply to show a deployment with many 292 common P2PSIP elements. 294 --->PSTN 295 +------+ N +------+ +---------+ / 296 | | A | | | Gateway |-/ 297 | UA |####T#####| UA |#####| Peer |######## 298 | Peer | N | Peer | | G | # RELOAD 299 | E | A | F | +---------+ # P2PSIP 300 | | T | | # Protocol 301 +------+ N +------+ # | 302 # A # | 303 NATNATNATNAT # | 304 # # | \__/ 305 NATNATNATNAT +-------+ v / \ 306 # N | |#####/ UA \ 307 +------+ A P2PSIP Overlay | Peer | /Client\ 308 | | T | Q | |___C__| 309 | UA | N | | 310 | Peer | A +-------+ 311 | D | T # 312 | | N # 313 +------+ A # RELOAD 314 # T # P2PSIP 315 # N +-------+ +-------+ # Protocol 316 # A | | | | # 317 #########T####| Proxy |########| Redir |####### 318 N | Peer | | Peer | 319 A | P | | R | 320 T +-------+ +-------+ 321 | / 322 | SIP / 323 \__/ / / 324 /\ / ______________/ SIP 325 / \/ / 326 / UA \/ 327 /______\ 328 SIP UA A 330 Figure: P2PSIP Overlay Reference Model 332 Here, the large perimeter depicted by "#" represents a stylized view 333 of the Overlay (the actual connections could be a mesh, a ring, or 334 some other structure). Around the periphery of the Overlay 335 rectangle, we have a number of Peers. Each peer is labeled with its 336 coupled SIP entity -- for example, "Proxy Peer P" means that peer P 337 which is coupled with a SIP proxy. In some cases, a peer or client 338 might be coupled with two or more SIP entities. In this diagram we 339 have a PSTN gateway coupled with peer "G", three peers ("D", "E" and 340 "F") which are each coupled with a UA, a peer "P" which is coupled 341 with a SIP proxy, an ordinary peer "Q" with no SIP capabilities, and 342 one peer "R" which is coupled with a SIP Redirector. Note that 343 because these are all Peers, each is responsible for storing Resource 344 Records and transporting messages around the Overlay. 346 To the left, two of the peers ("D" and "E") are behind network 347 address translators (NATs). These peers are included in the P2PSIP 348 overlay and thus participate in storing resource records and routing 349 messages, despite being behind the NATs. 351 On the right side, we have a client "C", which uses the RELOAD 352 Protocol to communicate with Proxy Peer "Q". The Client "C" uses 353 RELOAD to obtain information from the overlay, but has not inserted 354 itself into the overlay, and therefore does not participate in 355 routing messages or storing information. 357 Below the Overlay, we have a conventional SIP UA "A" which is not 358 part of the Overlay, either directly as a peer or indirectly as a 359 client. It does not speak the RELOAD P2PSIP protocol, and is not 360 participating in the overlay as either a Peer nor Client. Instead, 361 it uses SIP to interact with the Overlay via an adapter peer or peers 362 which communicate with the overlay using RELOAD. 364 Both the SIP proxy coupled with peer "P" and the SIP redirector 365 coupled with peer "R" can serve as adapters between ordinary SIP 366 devices and the Overlay. Each accepts standard SIP requests and 367 resolves the next-hop by using the P2PSIP protocol to interact with 368 the routing knowledge of the Overlay, then processes the SIP requests 369 as appropriate (proxying or redirecting towards the next-hop). Note 370 that proxy operation is bidirectional - the proxy may be forwarding a 371 request from an ordinary SIP device to the Overlay, or from the 372 P2PSIP overlay to an ordinary SIP device. 374 The PSTN Gateway at peer "G" provides a similar sort of adaptation to 375 and from the public switched telephone network (PSTN). 377 5. Definitions 379 This section defines a number of concepts that are key to 380 understanding the P2PSIP work. 382 Overlay Network: An overlay network is a computer network which is 383 built on top of another network. Nodes in the overlay can be 384 thought of as being connected by virtual or logical links, each of 385 which corresponds to a path, perhaps through many physical links, 386 in the underlying network. For example, many peer-to-peer 387 networks are overlay networks because they run on top of the 388 Internet. Dial-up Internet is an overlay upon the telephone 389 network. 391 P2P Network: A peer-to-peer (or P2P) computer network is a network 392 that relies primarily on the computing power and bandwidth of the 393 participants in the network rather than concentrating it in a 394 relatively low number of servers. P2P networks are typically used 395 for connecting nodes via largely ad hoc connections. Such 396 networks are useful for many purposes. Sharing content files (see 397 ) containing audio, 398 video, data or anything in digital format is very common, and 399 real-time data, such as telephony traffic, is also exchanged using 400 P2P technology. . A 401 P2P Network may also be called a "P2P Overlay" or "P2P Overlay 402 Network" or "P2P Network Overlay", since its organization is not 403 at the physical layer, but is instead "on top of" an existing 404 Internet Protocol network. 406 P2PSIP: A suite of communications protocols related to the Session 407 Initiation Protocol (SIP) [RFC3261] that enable SIP to use peer- 408 to-peer techniques for resolving the targets of SIP requests, 409 providing SIP message transport, and providing other SIP-related 410 functions. At present, these protocols include [RFC6940], 411 [I-D.ietf-p2psip-sip], [I-D.ietf-p2psip-diagnostics], 412 [I-D.ietf-p2psip-service-discovery] and 413 [I-D.ietf-p2psip-self-tuning]. 415 User: A human that interacts with the overlay through SIP UAs 416 located on peers and clients (and perhaps other ways). 418 The following terms are defined here only within the scope of 419 P2PSIP. These terms may have conflicting definitions in other 420 bodies of literature. Some earlier versions of this document 421 prefixed each term with "P2PSIP" to clarify the term's scope. 422 This prefixing has been eliminated from the text; however the 423 scoping still applies. 425 Overlay Name: A human-friendly name that identifies a specific 426 P2PSIP Overlay. This is in the format of (a portion of) a URI, 427 but may or may not have a related record in the DNS. 429 Peer: A node participating in a P2PSIP Overlay that provides storage 430 and transport services to other nodes in that P2PSIP Overlay. 431 Each Peer has a unique identifier, known as a Peer-ID, within the 432 Overlay. Each Peer may be coupled to one or more SIP entities. 433 Within the Overlay, the peer is capable of performing several 434 different operations, including: joining and leaving the overlay, 435 transporting SIP messages within the overlay, storing information 436 on behalf of the overlay, putting information into the overlay, 437 and getting information from the overlay. 439 Node-ID: Information that uniquely identifies each Node within a 440 given Overlay. This value is not human-friendly -- in a DHT 441 approach, this is a numeric value in the hash space. These Node- 442 IDs are completely independent of the identifier of any user of a 443 user agent associated with a peer. 445 Client: A node participating in a P2PSIP Overlay but that does not 446 store information or forward messages. A client can also be 447 thought of as a peer that has not joined the overlay. Clients can 448 store and retrieve information from the overlay. 450 User Name: A human-friendly name for a user. This name must be 451 unique within the overlay, but may be unique in a wider scope. 452 User Names are formatted so that they can be used within a URI 453 (likely a SIP URI), perhaps in combination with the Overlay Name. 455 Service: A capability contributed by a peer to an overlay or to the 456 members of an overlay. Not all peers and clients will offer the 457 same set of services, and P2PSIP provides service discovery 458 mechanisms to locate services. 460 Service Name: A unique, human-friendly, name for a service. 462 Resource: Anything about which information can be stored in the 463 overlay. Both Users and Services are examples of Resources. 465 Resource-ID: A non-human-friendly value that uniquely identifies a 466 resource and which is used as a key for storing and retrieving 467 data about the resource. One way to generate a Resource-ID is by 468 applying a mapping function to some other unique name (e.g., User 469 Name or Service Name) for the resource. The Resource-ID is used 470 by the distributed database algorithm to determine the peer or 471 peers that are responsible for storing the data for the overlay. 473 Resource Record: A block of data, stored using distributed database 474 mechanism of the Overlay, that includes information relevant to a 475 specific resource. We presume that there may be multiple types of 476 resource records. Some may hold data about Users, and others may 477 hold data about Services, and the working group may define other 478 types. The types, usages, and formats of the records are a 479 question for future study. 481 Responsible Peer The Peer that is responsible for storing the 482 Resource Record for a Resource. In the literature, the term "Root 483 Peer" is also used for this concept. 485 Peer Protocol: The protocol spoken between P2PSIP Overlay peers to 486 share information and organize the P2PSIP Overlay Network. In 487 P2PSIP, this is implemented using the RELOAD [RFC6940] protocol. 489 Client Protocol: The protocol spoken between Clients and Peers. In 490 P2PSIP and RELOAD, this is the same protocol syntactically as the 491 Peer Protocol. The only difference is that Clients are not 492 routing messages or routing information, and have not (or can not) 493 insert themselves into the overlay. 495 Peer Protocol Connection / P2PSIP Client Protocol Connection: The 496 TLS, DTLS, TCP, UDP or other transport layer protocol connection 497 over which the RELOAD Peer Protocol messages are transported. 499 Neighbors: The set of P2PSIP Peers that a Peer or Client know of 500 directly and can reach without further lookups. 502 Joining Peer: A node that is attempting to become a Peer in a 503 particular Overlay. 505 Bootstrap Peer: A Peer in the Overlay that is the first point of 506 contact for a Joining Peer. It selects the peer that will serve 507 as the Admitting Peer and helps the joining peer contact the 508 admitting peer. 510 Admitting Peer: A Peer in the Overlay which helps the Joining Peer 511 join the Overlay. The choice of the admitting peer may depend on 512 the joining peer (e.g., depend on the joining peer's Peer-ID). 513 For example, the admitting peer might be chosen as the peer which 514 is "closest" in the logical structure of the overlay to the future 515 position of the joining peer. The selection of the admitting peer 516 is typically done by the bootstrap peer. It is allowable for the 517 bootstrap peer to select itself as the admitting peer. 519 Bootstrap Server: A network node used by Joining Peers to locate a 520 Bootstrap Peer. A Bootstrap Server may act as a proxy for 521 messages between the Joining Peer and the Bootstrap Peer. The 522 Bootstrap Server itself is typically a stable host with a DNS name 523 that is somehow communicated (for example, through configuration, 524 specification on a web page, or using DHCP) to peers that want to 525 join the overlay. A Bootstrap Server is NOT required to be a peer 526 or client, though it may be if desired. 528 Peer Admission: The act of admitting a node (the "Joining Peer") 529 into an Overlay as a Peer. After the admission process is over, 530 the joining peer is a fully-functional peer of the overlay. 531 During the admission process, the joining peer may need to present 532 credentials to prove that it has sufficient authority to join the 533 overlay. 535 Resource Record Insertion: The act of inserting a P2PSIP Resource 536 Record into the distributed database. Following insertion, the 537 data will be stored at one or more peers. The data can be 538 retrieved or updated using the Resource-ID as a key. 540 6. Discussion 542 6.1. The Distributed Database Function 544 A P2PSIP Overlay functions as a distributed database. The database 545 serves as a way to store information about Resources. A piece of 546 information, called a Resource Record, can be stored by and retrieved 547 from the database using a key associated with the Resource Record 548 called its Resource-ID. Each Resource must have a unique 549 Resource-ID. In addition to uniquely identifying the Resource, the 550 Resource-ID is also used by the distributed database algorithm to 551 determine the peer or peers that store the Resource Record in the 552 overlay. 554 Users are humans that can use the overlay to do things like making 555 and receiving calls. Information stored in the resource record 556 associated with a user can include things like the full name of the 557 user and the location of the UAs that the user is using (the users 558 SIP AoR). Full details of how this is implemented using RELOAD are 559 provided in [I-D.ietf-p2psip-sip] 561 Before information about a user can be stored in the overlay, a user 562 needs a User Name. The User Name is a human-friendly identifier that 563 uniquely identifies the user within the overlay. In RELOAD, users 564 are issued certificates, which in the case of centrally signed 565 certificates, identify the User Name as well as a certain number of 566 Resource-IDs where the user may store their information. For more 567 information, see [RFC6940]. 569 The P2PSIP suite of protocols also standardizes information about how 570 to locate services. Services represent actions that a peer (and 571 perhaps a client) can do to benefit other peers and clients in the 572 overlay. Information that might be stored in the resource record 573 associated with a service might include the peers (and perhaps 574 clients) offering the service. Service discovery for P2PSIP is 575 defined in [I-D.ietf-p2psip-service-discovery]. 577 Each service has a human-friendly Service Name that uniquely 578 identifies the service. Like User Names, the Service Name is not a 579 resource-id, rather the resource-id is derived from the service name 580 using some function defined by the distributed database algorithm 581 used by the overlay. 583 A class of algorithms known as Distributed Hash Tables 584 are one way to implement 585 the Distributed Database. The RELOAD protocol is extensible and 586 allows many different DHTs to be implemented, but specifies a 587 mandatory to implement DHT in the form of a modified Chord DHT. For 588 more information, see [Chord] 590 6.2. Using the Distributed Database Function 592 While there are a number of ways the distributed database described 593 in the previous section can be used to establish multimedia sessions 594 using SIP, the basic mechanism defined in the RELOAD base draft and 595 SIP usage is summarized below. This is a very simplistic overview. 596 For more detailed information, please see the RELOAD base draft. 598 Contact information for a user is stored in the resource record for 599 that user. Assume that a user is using a device, here called peer A, 600 which serves as the contact point for this user. The user adds 601 contact information to this resource record, as authorized by the 602 RELOAD certificate mechanism. The resource record itself is stored 603 with peer Z in the network, where peer Z is chosen by the particular 604 distributed database algorithm in use by the overlay. 606 When the SIP entity coupled with peer B has an INVITE message 607 addressed to this user, it retrieves the resource record from peer Z. 608 It then extracts the contact information for the various peers that 609 are a contact point for the user, including peer A, and uses the 610 overlay to establish a connection to peer A, including any 611 appropriate NAT traversal (the details of which are not shown). 613 Note that RELOAD is used only to establish the connection. Once the 614 connection is established, messages between the peers are sent using 615 ordinary SIP. 617 This exchange is illustrated in the following figure. The notation 618 "Store(U@A)" is used to show the distributed database operation of 619 updating the resource record for user U with the contract A, and 620 "Fetch(U)" illustrates the distributed database operation of 621 retrieving the resource record for user U. Note that the messages 622 between the peers A, B and Z may actually travel via intermediate 623 peers (not shown) as part of the distributed lookup process or so as 624 to traverse intervening NATs. 626 Peer B Peer Z Peer A 627 | | | 628 | | Store(U@Y)| 629 | |<------------------| 630 | |Store-Resp(OK) | 631 | |------------------>| 632 | | | 633 |Fetch(U) | | 634 |------------------->| | 635 | Fetch-Resp(U@Y)| | 636 |<-------------------| | 637 | | | 638 (RELOAD IS USED TO ESTABLISH CONNECTION) 639 | | | 640 | SIP INVITE(To:U) | | 641 |--------------------------------------->| 642 | | | 644 6.3. NAT Traversal 646 NAT Traversal in P2PSIP using RELOAD treats all peers as equal and 647 establishes a partial mesh of connections between them. Messages 648 from one peer to another are routed along the edges in the mesh of 649 connections until they reach their destination. To make the routing 650 efficient and to avoid the use of standard Internet routing 651 protocols, the partial mesh is organized in a structured manner. If 652 the structure is based on any one of a number of common DHT 653 algorithms, then the maximum number of hops between any two peers is 654 log N, where N is the number of peers in the overlay. Existing 655 connections, along with the ICE NAT traversal techniques [RFC5245], 656 are used to establish new connections between peers, and also to 657 allow the applications running on peers to establish a connection to 658 communicate with one another. 660 6.4. Locating and Joining an Overlay 662 Before a peer can attempt to join a P2PSIP overlay, it must first 663 obtain a Node-ID, configuration information, and optionally a set of 664 credentials. The Node-ID is an identifier that will uniquely 665 identify the peer within the overlay, while the credentials show that 666 the peer is allowed to join the overlay. 668 The P2PSIP WG does not impose a particular mechanism for how the 669 peer-ID and the credentials are obtained, but the RELOAD base draft 670 does specify the format for the configuration information, and 671 specifies how this information may be obtained, along with 672 credentials and a Node-ID, from an offline enrollment server. 674 Once the configuration information is obtained, the RELOAD base draft 675 specifies a mechanism whereby a peer may obtain a multicast-bootstrap 676 address in the configuration file, and can broadcast to this address 677 to attempt to locate a bootstrap peer. Additionally, the peer may 678 store previous peers it has seen and attempt to use these as 679 bootstrap peers, or may obtain an address for a bootstrap peer by 680 some other mechanism. For more information, see the RELOAD base 681 draft. 683 The job of the bootstrap peer is simple: refer the joining peer to a 684 peer (called the "admitting peer") that will help the joining peer 685 join the network. The choice of admitting peer will often depend on 686 the joining node - for example, the admitting peer may be a peer that 687 will become a neighbor of the joining peer in the overlay. It is 688 possible that the bootstrap peer might also serve as the admitting 689 peer. 691 The admitting peer will help the joining peer learn about other peers 692 in the overlay and establish connections to them as appropriate. The 693 admitting peer and/or the other peers in the overlay will also do 694 whatever else is required to help the joining peer become a fully- 695 functional peer. The details of how this is done will depend on the 696 distributed database algorithm used by the overlay. 698 At various stages in this process, the joining peer may be asked to 699 present its credentials to show that it is authorized to join the 700 overlay. Similarly, the various peers contacted may be asked to 701 present their credentials so the joining peer can verify that it is 702 really joining the overlay it wants to. 704 6.5. Clients and Connecting Unmodified SIP Devices 706 As mentioned above, in RELOAD, from the perspective of the protocol, 707 clients are simply peers that do not store information, do not route 708 messages, and which have not inserted themselves into the overlay. 709 The same protocol is used for the actual message exchanged. Note 710 that while the protocol is the same, the client need not implement 711 all the capabilities of a peer. If, for example, it never routes 712 messages, it will not need to be capable of processing such messages, 713 or understanding a DHT. 715 For SIP devices, another way to realize this functionality is for a 716 Peer to behave as a [RFC3261] proxy/registrar. SIP devices then use 717 standard SIP mechanisms to add, update, and remove registrations and 718 to send SIP messages to peers and other clients. The authors here 719 refer to these devices simply as a "SIP UA", not a "P2PSIP Client", 720 to distinguish it from the concept described above. 722 6.6. Architecture 724 The architecture adopted by RELOAD to implement P2PSIP is shown 725 below. An application, for example SIP (or another application using 726 RELOAD) uses RELOAD to locate other peers and (optionally) to 727 establish connections to those peers, potentially across NATs. 728 Messages may still be exchanged directly between the peers. The 729 overall block diagram for the architecture is as follows: 731 __________________________ 732 | | 733 | SIP, other apps... | 734 | ___________________| 735 | | RELOAD Layer | 736 |______|___________________| 737 | Transport Layer | 738 |__________________________| 740 7. Open Issues 742 OPEN ISSUE: The initial wording in the high-level description about 743 proving AoR to contact mapping reflects a very long and contentious 744 debate about the role of the protocol, and reflected a pretense that 745 this was an overlay only for P2PSIP. That is not really true in base 746 anymore (see last paragraph of introduction) and the language has 747 been very much genericized in base. Should we make this text more 748 abstract and then use AoR->contact mapping as an example of the 749 (original) use? On a related note, see the last paragraph of the 750 Background section -- do we want to reword this? 752 At this point, the editors believe these additional two issues are 753 settled, but are left here for final debate on the document before 754 publication. 756 OPEN ISSUE: Should we include a section that documents previous 757 decisions made, to preserve the historical debate and prevent past 758 issues from being raised in the future, or simply rely on the mailing 759 list to address these concerns? (consensus seemed to be no) 761 OPEN ISSUE: Should we include the use cases from 762 draft-bryan-p2psip-app-scenarios-00 (now long expired)? (consensus 763 seemed to be no) 765 8. Informative References 767 [Chord] Singh, K., Stoica, I., Morris, R., Karger, D., Kaashock, 768 M., Dabek, F., and H. Balakrishman, "Chord: A scalable 769 peer-to-peer lookup protocol for internet applications", 770 IEEE/ACM Transactions on Neworking Volume 11 Issue 1, pp. 771 17-32, Feb. 2003. 773 Copy available at 774 http://pdos.csail.mit.edu/chord/papers/paper-ton.pdf 776 [I-D.ietf-p2psip-diagnostics] 777 Song, H., Jiang, X., Even, R., Bryan, D., and Y. Sun, "P2P 778 Overlay Diagnostics", draft-ietf-p2psip-diagnostics-14 779 (work in progress), February 2014. 781 [I-D.ietf-p2psip-self-tuning] 782 Maenpaa, J. and G. Camarillo, "Self-tuning Distributed 783 Hash Table (DHT) for REsource LOcation And Discovery 784 (RELOAD)", draft-ietf-p2psip-self-tuning-12 (work in 785 progress), June 2014. 787 [I-D.ietf-p2psip-service-discovery] 788 Maenpaa, J. and G. Camarillo, "Service Discovery Usage for 789 REsource LOcation And Discovery (RELOAD)", 790 draft-ietf-p2psip-service-discovery-12 (work in progress), 791 June 2014. 793 [I-D.ietf-p2psip-sip] 794 Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., 795 Schulzrinne, H., and T. Schmidt, "A SIP Usage for RELOAD", 796 draft-ietf-p2psip-sip-12 (work in progress), January 2014. 798 [RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, 799 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 800 RFC 2136, April 1997. 802 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 803 A., Peterson, J., Sparks, R., Handley, M., and E. 804 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 805 June 2002. 807 [RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation 808 Protocol (SIP): Locating SIP Servers", RFC 3263, 809 June 2002. 811 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 812 Resource Identifier (URI): Generic Syntax", STD 66, 813 RFC 3986, January 2005. 815 [RFC4795] Aboba, B., Thaler, D., and L. Esibov, "Link-local 816 Multicast Name Resolution (LLMNR)", RFC 4795, 817 January 2007. 819 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 820 (ICE): A Protocol for Network Address Translator (NAT) 821 Traversal for Offer/Answer Protocols", RFC 5245, 822 April 2010. 824 [RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using 825 Relays around NAT (TURN): Relay Extensions to Session 826 Traversal Utilities for NAT (STUN)", RFC 5766, April 2010. 828 [RFC6940] Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and 829 H. Schulzrinne, "REsource LOcation And Discovery (RELOAD) 830 Base Protocol", RFC 6940, January 2014. 832 Authors' Addresses 834 David A. Bryan 835 Cogent Force, LLC 836 Cedar Park, TX, Texas 837 USA 839 Email: dbryan@ethernot.org 840 Philip Matthews 841 Alcatel-Lucent 842 600 March Road 843 Ottawa, Ontario K2K 2E6 844 Canada 846 Phone: +1 613 784 3139 847 Email: philip_matthews@magma.ca 849 Eunsoo Shim 850 Samsung Electronics Co., Ltd. 851 San 14, Nongseo-dong, Giheung-gu, 852 Yongin-si, Gyeonggi-do, 446-712 853 South Korea 855 Email: eunsooshim@gmail.com 857 Dean Willis 858 Softarmor Systems 859 3100 Independence Pkwy #311-164 860 Plano, Texas 75075 861 USA 863 Phone: +1 214 504 1987 864 Email: dean.willis@softarmor.com 866 Spencer Dawkins 867 Huawei Technologies (USA) 869 Phone: +1 214 755 3870 870 Email: spencerdawkins.ietf@gmail.com