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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-22) exists of draft-ietf-p2psip-diagnostics-19 == Outdated reference: A later version (-21) exists of draft-ietf-p2psip-sip-16 -- Obsolete informational reference (is this intentional?): RFC 5245 (Obsoleted by RFC 8445, RFC 8839) -- Obsolete informational reference (is this intentional?): RFC 5766 (Obsoleted by RFC 8656) Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 5 comments (--). 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: August 14, 2016 Alcatel-Lucent 6 E. Shim 7 Samsung Electronics Co., Ltd. 8 D. Willis 9 Softarmor Systems 10 S. Dawkins 11 Huawei (USA) 12 February 11, 2016 14 Concepts and Terminology for Peer to Peer SIP 15 draft-ietf-p2psip-concepts-08 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 document defined by the working 29 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 August 14, 2016. 48 Copyright Notice 50 Copyright (c) 2016 IETF Trust and the persons identified as the 51 document authors. All rights reserved. 53 This document is subject to BCP 78 and the IETF Trust's Legal 54 Provisions Relating to IETF Documents 55 (http://trustee.ietf.org/license-info) in effect on the date of 56 publication of this document. Please review these documents 57 carefully, as they describe your rights and restrictions with respect 58 to this document. Code Components extracted from this document must 59 include Simplified BSD License text as described in Section 4.e of 60 the Trust Legal Provisions and are provided without warranty as 61 described in the Simplified BSD License. 63 This document may contain material from IETF Documents or IETF 64 Contributions published or made publicly available before November 65 10, 2008. The person(s) controlling the copyright in some of this 66 material may not have granted the IETF Trust the right to allow 67 modifications of such material outside the IETF Standards Process. 68 Without obtaining an adequate license from the person(s) controlling 69 the copyright in such materials, this document may not be modified 70 outside the IETF Standards Process, and derivative works of it may 71 not be created outside the IETF Standards Process, except to format 72 it for publication as an RFC or to translate it into languages other 73 than English. 75 Table of Contents 77 1. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3 78 2. High-Level Description . . . . . . . . . . . . . . . . . . . 4 79 2.1. Services . . . . . . . . . . . . . . . . . . . . . . . . 4 80 2.2. Clients . . . . . . . . . . . . . . . . . . . . . . . . . 4 81 2.3. Relationship Between P2PSIP and RELOAD . . . . . . . . . 5 82 2.4. Relationship Between P2PSIP and SIP . . . . . . . . . . . 5 83 2.5. Relationship Between P2PSIP and Other AoR Dereferencing 84 Approaches . . . . . . . . . . . . . . . . . . . . . . . 5 85 2.6. NAT Issues . . . . . . . . . . . . . . . . . . . . . . . 6 86 3. Reference Model . . . . . . . . . . . . . . . . . . . . . . . 6 87 4. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 8 88 5. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 12 89 5.1. The Distributed Database Function . . . . . . . . . . . . 12 90 5.2. Using the Distributed Database Function . . . . . . . . . 13 91 5.3. NAT Traversal . . . . . . . . . . . . . . . . . . . . . . 14 92 5.4. Locating and Joining an Overlay . . . . . . . . . . . . . 14 93 5.5. Clients and Connecting Unmodified SIP Devices . . . . . . 15 94 5.6. Architecture . . . . . . . . . . . . . . . . . . . . . . 16 95 6. Security Considerations . . . . . . . . . . . . . . . . . . . 16 96 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 97 8. Informative References . . . . . . . . . . . . . . . . . . . 16 98 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 100 1. Background 102 One of the fundamental problems in multimedia communication between 103 Internet nodes is discovering the host at which a given user can be 104 reached. In the Session Initiation Protocol (SIP) [RFC3261] this 105 problem is expressed as the problem of mapping an Address of Record 106 (AoR) for a user into one or more Contact URIs [RFC3986]. The AoR is 107 a name for the user that is independent of the host or hosts where 108 the user can be contacted, while a Contact URI indicates the host 109 where the user can be contacted. 111 In the common SIP-using architectures that we refer to as 112 "Conventional SIP" or "Client/Server SIP", there is a relatively 113 fixed hierarchy of SIP routing proxies and SIP user agents. To 114 deliver a SIP INVITE to the host or hosts at which the user can be 115 contacted, a SIP UA follows the procedures specified in [RFC3263] to 116 determine the IP address of a SIP proxy, and then sends the INVITE to 117 that proxy. The proxy will then, in turn, deliver the SIP INVITE to 118 the hosts where the user can be contacted. 120 This document gives a high-level description of an alternative 121 solution to this problem. In this alternative solution, the 122 relatively fixed hierarchy of Client/Server SIP is replaced by a 123 peer-to-peer overlay network. In this peer-to-peer overlay network, 124 the various AoR to Contact URI mappings are not centralized at proxy/ 125 registrar nodes but are instead distributed amongst the peers in the 126 overlay. 128 The details of this alternative solution are specified by the RELOAD 129 protocol [RFC6940], which defines a mechanism to distribute using a 130 Distributed Hash Table (DHT) and specifies the wire protocol, 131 security, and authentication mechanisms needed to convey this 132 information. This DHT protocol was designed specifically with the 133 purpose of enabling a distributed SIP registrar in mind. While 134 designing the protocol other applications were considered, and when 135 possible design decisions were made that allow RELOAD to be used in 136 other instances where a DHT is desirable, but only when making such 137 decisions did not add undue complexity to the RELOAD protocol. The 138 RELOAD sip draft [I-D.ietf-p2psip-sip] specifies how RELOAD is used 139 with the SIP protocol to enable a distributed, server-less SIP 140 solution. 142 2. High-Level Description 144 A P2PSIP Overlay is a collection of nodes organized in a peer-to-peer 145 fashion for the purpose of enabling real-time communication using the 146 Session Initiation Protocol (SIP). Collectively, the nodes in the 147 overlay provide a distributed mechanism for mapping names to overlay 148 locations. This provides for the mapping of Addresses of Record 149 (AoRs) to Contact URIs, thereby providing the "location server" 150 function of [RFC3261]. An Overlay also provides a transport function 151 by which SIP messages can be transported between any two nodes in the 152 overlay. 154 A P2PSIP Overlay consists of one or more nodes called Peers. The 155 nodes in the overlay collectively run a distributed database 156 algorithm. This distributed database algorithm allows data to be 157 stored on nodes and retrieved in an efficient manner. It may also 158 ensure that a copy of a data item is stored on more than one node, so 159 that the loss of a node does not result in the loss of the data item 160 to the overlay. 162 One use of this distributed database is to store the information 163 required to provide the mapping between AoRs and Contact URIs for the 164 distributed location function. This provides a location function 165 within each overlay that is an alternative to the location functions 166 described in [RFC3263]. However, the model of [RFC3263] is used 167 between overlays. 169 2.1. Services 171 The nature of peer-to-peer computing is that each peer offers 172 services to other peers to allow the overlay to collectively provide 173 larger functions. In P2PSIP, peers offer both distributed storage 174 and distributed message routing services, allowing these functions to 175 be implemented across the overlay. Additionally, the RELOAD protocol 176 offers a simplistic discovery mechanism specific to the TURN 177 [RFC5766] protocol used for NAT traversal. Individual peers may also 178 offer other services as an enhancement to P2PSIP functionality (for 179 example to support voicemail) or to support other applications beyond 180 SIP. To support these additional services, peers may need to store 181 additional information in the overlay. [RFC7374] describes the 182 mechanism used in P2PSIP for resource discovery. 184 2.2. Clients 186 An overlay may or may not also include one or more nodes called 187 clients. Clients are supported in the RELOAD protocol as peers that 188 have not joined the overlay, and therefore do not route messages or 189 store information. Clients access the services of the RELOAD 190 protocol by connecting to a peer which performs operations on the 191 behalf of the client. Note that in RELOAD there is no distinct 192 client protocol. Instead, a client connects using the same protocol, 193 but never joins the overlay as a peer. For more information, see 194 [RFC6940]. 196 Note that in the context of P2PSIP, there is an additional entity 197 that is sometimes referred to as a client. A special peer may be a 198 member of the in the P2PSIP overlay and may present the functionality 199 of one or all of a SIP registrar, proxy or redirect server to 200 conventional SIP devices (SIP clients). In this way, existing, non- 201 modified SIP clients may connect to the network. These unmodified 202 SIP devices do not speak the RELOAD protocol, and this is a distinct 203 concept from the notion of client discussed in the previous 204 paragraph. 206 2.3. Relationship Between P2PSIP and RELOAD 208 The RELOAD protocol defined by the P2PSIP working group implements a 209 DHT primarily for use by server-less, peer-to-peer SIP deployments. 210 However, the RELOAD protocol could be used for other applications as 211 well. As such, a "P2PSIP" deployment is generally assumed to be a 212 use of RELOAD to implement distributed SIP, but it is possible that 213 RELOAD is used as a mechanism to distribute other applications, 214 completely unrelated to SIP. 216 2.4. Relationship Between P2PSIP and SIP 218 Since P2PSIP is about peer-to-peer networks for real-time 219 communication, it is expected that most peers and clients will be 220 coupled with SIP entities (although RELOAD may be used for other 221 applications than P2PSIP). For example, one peer might be coupled 222 with a SIP UA, another might be coupled with a SIP proxy, while a 223 third might be coupled with a SIP-to-PSTN gateway. For such nodes, 224 the peer or client portion of the node is logically distinct from the 225 SIP entity portion. However, there is no hard requirement that every 226 P2PSIP node (peer or client) be coupled to a SIP entity. As an 227 example, additional peers could be placed in the overlay to provide 228 additional storage or redundancy for the RELOAD overlay, but might 229 not have any direct SIP capabilities. 231 2.5. Relationship Between P2PSIP and Other AoR Dereferencing Approaches 233 As noted above, the fundamental task of P2PSIP is turning an AoR into 234 a Contact. This task might be approached using zeroconf techniques 235 such as multicast DNS and DNS Service Discovery [RFC6762][RFC6763], 236 link-local multicast name resolution [RFC4795], and dynamic DNS 237 [RFC2136]. 239 These alternatives were discussed in the P2PSIP Working Group, and 240 not pursued as a general solution for a number of reasons related to 241 scalability, the ability to work in a disconnected state, partition 242 recovery, and so on. However, there does seem to be some continuing 243 interest in the possibility of using DNS-SD and mDNS for 244 bootstrapping of P2PSIP overlays. 246 2.6. NAT Issues 248 Network Address Translators (NATs) are impediments to establishing 249 and maintaining peer-to-peer networks, since NATs hinder direct 250 communication between nodes. Some peer-to-peer network architectures 251 avoid this problem by insisting that all nodes exist in the same 252 address space. However, RELOAD provides capabilities that allow 253 nodes to be located in multiple address spaces interconnected by 254 NATs, to allow RELOAD messages to traverse NATs, and to assist in 255 transmitting application-level messages (for example SIP messages) 256 across NATs. 258 3. Reference Model 260 The following diagram shows a P2PSIP Overlay consisting of a number 261 of Peers, one Client, and an ordinary SIP UA. It illustrates a 262 typical P2PSIP overlay but does not limit other compositions or 263 variations; for example, Proxy Peer P might also talk to a ordinary 264 SIP proxy as well. The figure is not intended to cover all possible 265 architecture variations, but simply to show a deployment with many 266 common P2PSIP elements. 268 --->PSTN 269 +------+ N +------+ +---------+ / 270 | | A | | | Gateway |-/ 271 | UA |####T#####| UA |#####| Peer |######## 272 | Peer | N | Peer | | G | # RELOAD 273 | E | A | F | +---------+ # P2PSIP 274 | | T | | # Protocol 275 +------+ N +------+ # | 276 # A # | 277 NATNATNATNAT # | 278 # # | \__/ 279 NATNATNATNAT +-------+ v / \ 280 # N | |#####/ UA \ 281 +------+ A P2PSIP Overlay | Peer | /Client\ 282 | | T | Q | |___C__| 283 | UA | N | | 284 | Peer | A +-------+ 285 | D | T # 286 | | N # 287 +------+ A # RELOAD 288 # T # P2PSIP 289 # N +-------+ +-------+ # Protocol 290 # A | | | | # 291 #########T####| Proxy |########| Redir |####### 292 N | Peer | | Peer | 293 A | P | | R | 294 T +-------+ +-------+ 295 | / 296 | SIP / 297 \__/ / / 298 /\ / ______________/ SIP 299 / \/ / 300 / UA \/ 301 /______\ 302 SIP UA A 304 Figure: P2PSIP Overlay Reference Model 306 Here, the large perimeter depicted by "#" represents a stylized view 307 of the Overlay (the actual connections could be a mesh, a ring, or 308 some other structure). Around the periphery of the Overlay 309 rectangle, we have a number of Peers. Each peer is labeled with its 310 coupled SIP entity -- for example, "Proxy Peer P" means that peer P 311 which is coupled with a SIP proxy. In some cases, a peer or client 312 might be coupled with two or more SIP entities. In this diagram we 313 have a PSTN gateway coupled with peer "G", three peers ("D", "E" and 314 "F") which are each coupled with a UA, a peer "P" which is coupled 315 with a SIP proxy, an ordinary peer "Q" with no SIP capabilities, and 316 one peer "R" which is coupled with a SIP Redirector. Note that 317 because these are all Peers, each is responsible for storing Resource 318 Records and transporting messages around the Overlay. 320 To the left, two of the peers ("D" and "E") are behind network 321 address translators (NATs). These peers are included in the P2PSIP 322 overlay and thus participate in storing resource records and routing 323 messages, despite being behind the NATs. 325 On the right side, we have a client "C", which uses the RELOAD 326 Protocol to communicate with Proxy Peer "Q". The Client "C" uses 327 RELOAD to obtain information from the overlay, but has not inserted 328 itself into the overlay, and therefore does not participate in 329 routing messages or storing information. 331 Below the Overlay, we have a conventional SIP UA "A" which is not 332 part of the Overlay, either directly as a peer or indirectly as a 333 client. It does not speak the RELOAD P2PSIP protocol, and is not 334 participating in the overlay as either a Peer nor Client. Instead, 335 it uses SIP to interact with the Overlay via an adapter peer or peers 336 which communicate with the overlay using RELOAD. 338 Both the SIP proxy coupled with peer "P" and the SIP redirector 339 coupled with peer "R" can serve as adapters between ordinary SIP 340 devices and the Overlay. Each accepts standard SIP requests and 341 resolves the next-hop by using the P2PSIP protocol to interact with 342 the routing knowledge of the Overlay, then processes the SIP requests 343 as appropriate (proxying or redirecting towards the next-hop). Note 344 that proxy operation is bidirectional - the proxy may be forwarding a 345 request from an ordinary SIP device to the Overlay, or from the 346 P2PSIP overlay to an ordinary SIP device. 348 The PSTN Gateway at peer "G" provides a similar sort of adaptation to 349 and from the public switched telephone network (PSTN). 351 4. Definitions 353 This section defines a number of concepts that are key to 354 understanding the P2PSIP work. 356 Overlay Network: An overlay network is a computer network which is 357 built on top of another network. Nodes in the overlay can be 358 thought of as being connected by virtual or logical links, each of 359 which corresponds to a path, perhaps through many physical links, 360 in the underlying network. For example, many peer-to-peer 361 networks are overlay networks because they run on top of the 362 Internet. Dial-up Internet is an overlay upon the telephone 363 network. 365 P2P Network: A peer-to-peer (or P2P) computer network is a network 366 that relies primarily on the computing power and bandwidth of the 367 participants in the network rather than concentrating it in a 368 relatively low number of servers. P2P networks are typically used 369 for connecting nodes via largely ad hoc connections. Such 370 networks are useful for many purposes. Sharing content files 371 containing audio, video, data or anything in digital format is 372 very common, and real-time data, such as telephony traffic, is 373 also exchanged using P2P technology. A P2P Network may also be 374 called a "P2P Overlay" or "P2P Overlay Network" or "P2P Network 375 Overlay", since its organization is not at the physical layer, but 376 is instead "on top of" an existing Internet Protocol network. 378 P2PSIP: A suite of communications protocols related to the Session 379 Initiation Protocol (SIP) [RFC3261] that enable SIP to use peer- 380 to-peer techniques for resolving the targets of SIP requests, 381 providing SIP message transport, and providing other SIP-related 382 functions. At present, these protocols include [RFC6940], 383 [I-D.ietf-p2psip-sip], [I-D.ietf-p2psip-diagnostics], [RFC7374] 384 and [RFC7363]. 386 User: A human that interacts with the overlay through SIP UAs 387 located on peers and clients (and perhaps other ways). 389 The following terms are defined here only within the scope of 390 P2PSIP. These terms may have conflicting definitions in other 391 bodies of literature. Some earlier versions of this document 392 prefixed each term with "P2PSIP" to clarify the term's scope. 393 This prefixing has been eliminated from the text; however the 394 scoping still applies. 396 Overlay Name: A human-friendly name that identifies a specific 397 P2PSIP Overlay. This is in the format of (a portion of) a URI, 398 but may or may not have a related record in the DNS. 400 Peer: A node participating in a P2PSIP Overlay that provides storage 401 and transport services to other nodes in that P2PSIP Overlay. 402 Each Peer has a unique identifier, known as a Peer-ID, within the 403 Overlay. Each Peer may be coupled to one or more SIP entities. 404 Within the Overlay, the peer is capable of performing several 405 different operations, including: joining and leaving the overlay, 406 transporting SIP messages within the overlay, storing information 407 on behalf of the overlay, putting information into the overlay, 408 and getting information from the overlay. 410 Node-ID: Information that uniquely identifies each Node within a 411 given Overlay. This value is not human-friendly -- in a DHT 412 approach, this is a numeric value in the hash space. These Node- 413 IDs are completely independent of the identifier of any user of a 414 user agent associated with a peer. 416 Client: A node participating in a P2PSIP Overlay but that does not 417 store information or forward messages. A client can also be 418 thought of as a peer that has not joined the overlay. Clients can 419 store and retrieve information from the overlay. 421 User Name: A human-friendly name for a user. This name must be 422 unique within the overlay, but may be unique in a wider scope. 423 User Names are formatted so that they can be used within a URI 424 (likely a SIP URI), perhaps in combination with the Overlay Name. 426 Service: A capability contributed by a peer to an overlay or to the 427 members of an overlay. Not all peers and clients will offer the 428 same set of services, and P2PSIP provides service discovery 429 mechanisms to locate services. 431 Service Name: A unique, human-friendly, name for a service. 433 Resource: Anything about which information can be stored in the 434 overlay. Both Users and Services are examples of Resources. 436 Resource-ID: A non-human-friendly value that uniquely identifies a 437 resource and which is used as a key for storing and retrieving 438 data about the resource. One way to generate a Resource-ID is by 439 applying a mapping function to some other unique name (e.g., User 440 Name or Service Name) for the resource. The Resource-ID is used 441 by the distributed database algorithm to determine the peer or 442 peers that are responsible for storing the data for the overlay. 444 Resource Record: A block of data, stored using distributed database 445 mechanism of the Overlay, that includes information relevant to a 446 specific resource. We presume that there may be multiple types of 447 resource records. Some may hold data about Users, and others may 448 hold data about Services, and the working group may define other 449 types. The types, usages, and formats of the records are a 450 question for future study. 452 Responsible Peer The Peer that is responsible for storing the 453 Resource Record for a Resource. In the literature, the term "Root 454 Peer" is also used for this concept. 456 Peer Protocol: The protocol spoken between P2PSIP Overlay peers to 457 share information and organize the P2PSIP Overlay Network. In 458 P2PSIP, this is implemented using the RELOAD [RFC6940] protocol. 460 Client Protocol: The protocol spoken between Clients and Peers. In 461 P2PSIP and RELOAD, this is the same protocol syntactically as the 462 Peer Protocol. The only difference is that Clients are not 463 routing messages or routing information, and have not (or can not) 464 insert themselves into the overlay. 466 Peer Protocol Connection / P2PSIP Client Protocol Connection: 467 The TLS, DTLS, TCP, UDP or other transport layer protocol 468 connection over which the RELOAD Peer Protocol messages are 469 transported. 471 Neighbors: The set of P2PSIP Peers that a Peer or Client know of 472 directly and can reach without further lookups. 474 Joining Peer: A node that is attempting to become a Peer in a 475 particular Overlay. 477 Bootstrap Peer: A Peer in the Overlay that is the first point of 478 contact for a Joining Peer. It selects the peer that will serve 479 as the Admitting Peer and helps the joining peer contact the 480 admitting peer. 482 Admitting Peer: A Peer in the Overlay which helps the Joining Peer 483 join the Overlay. The choice of the admitting peer may depend on 484 the joining peer (e.g., depend on the joining peer's Peer-ID). 485 For example, the admitting peer might be chosen as the peer which 486 is "closest" in the logical structure of the overlay to the future 487 position of the joining peer. The selection of the admitting peer 488 is typically done by the bootstrap peer. It is allowable for the 489 bootstrap peer to select itself as the admitting peer. 491 Bootstrap Server: A network node used by Joining Peers to locate a 492 Bootstrap Peer. A Bootstrap Server may act as a proxy for 493 messages between the Joining Peer and the Bootstrap Peer. The 494 Bootstrap Server itself is typically a stable host with a DNS name 495 that is somehow communicated (for example, through configuration, 496 specification on a web page, or using DHCP) to peers that want to 497 join the overlay. A Bootstrap Server is NOT required to be a peer 498 or client, though it may be if desired. 500 Peer Admission: The act of admitting a node (the "Joining Peer") 501 into an Overlay as a Peer. After the admission process is over, 502 the joining peer is a fully-functional peer of the overlay. 503 During the admission process, the joining peer may need to present 504 credentials to prove that it has sufficient authority to join the 505 overlay. 507 Resource Record Insertion: The act of inserting a P2PSIP Resource 508 Record into the distributed database. Following insertion, the 509 data will be stored at one or more peers. The data can be 510 retrieved or updated using the Resource-ID as a key. 512 5. Discussion 514 5.1. The Distributed Database Function 516 A P2PSIP Overlay functions as a distributed database. The database 517 serves as a way to store information about Resources. A piece of 518 information, called a Resource Record, can be stored by and retrieved 519 from the database using a key associated with the Resource Record 520 called its Resource-ID. Each Resource must have a unique Resource- 521 ID. In addition to uniquely identifying the Resource, the Resource- 522 ID is also used by the distributed database algorithm to determine 523 the peer or peers that store the Resource Record in the overlay. 525 Users are humans that can use the overlay to do things like making 526 and receiving calls. Information stored in the resource record 527 associated with a user can include things like the full name of the 528 user and the location of the UAs that the user is using (the users 529 SIP AoR). Full details of how this is implemented using RELOAD are 530 provided in [I-D.ietf-p2psip-sip] 532 Before information about a user can be stored in the overlay, a user 533 needs a User Name. The User Name is a human-friendly identifier that 534 uniquely identifies the user within the overlay. In RELOAD, users 535 are issued certificates, which in the case of centrally signed 536 certificates, identify the User Name as well as a certain number of 537 Resource-IDs where the user may store their information. For more 538 information, see [RFC6940]. 540 The P2PSIP suite of protocols also standardizes information about how 541 to locate services. Services represent actions that a peer (and 542 perhaps a client) can do to benefit other peers and clients in the 543 overlay. Information that might be stored in the resource record 544 associated with a service might include the peers (and perhaps 545 clients) offering the service. Service discovery for P2PSIP is 546 defined in [RFC7374]. 548 Each service has a human-friendly Service Name that uniquely 549 identifies the service. Like User Names, the Service Name is not a 550 resource-id, rather the resource-id is derived from the service name 551 using some function defined by the distributed database algorithm 552 used by the overlay. 554 A class of algorithms known as Distributed Hash Tables are one way to 555 implement the Distributed Database. The RELOAD protocol is 556 extensible and allows many different DHTs to be implemented, but 557 specifies a mandatory to implement DHT in the form of a modified 558 Chord DHT. For more information, see [Chord] 560 5.2. Using the Distributed Database Function 562 While there are a number of ways the distributed database described 563 in the previous section can be used to establish multimedia sessions 564 using SIP, the basic mechanism defined in the RELOAD protocol and SIP 565 usage is summarized below. This is a very simplistic overview. For 566 more detailed information, please see the RELOAD protocol document. 568 Contact information for a user is stored in the resource record for 569 that user. Assume that a user is using a device, here called peer A, 570 which serves as the contact point for this user. The user adds 571 contact information to this resource record, as authorized by the 572 RELOAD certificate mechanism. The resource record itself is stored 573 with peer Z in the network, where peer Z is chosen by the particular 574 distributed database algorithm in use by the overlay. 576 When the SIP entity coupled with peer B has an INVITE message 577 addressed to this user, it retrieves the resource record from peer Z. 578 It then extracts the contact information for the various peers that 579 are a contact point for the user, including peer A, and uses the 580 overlay to establish a connection to peer A, including any 581 appropriate NAT traversal (the details of which are not shown). 583 Note that RELOAD is used only to establish the connection. Once the 584 connection is established, messages between the peers are sent using 585 ordinary SIP. 587 This exchange is illustrated in the following figure. The notation 588 "Store(U@A)" is used to show the distributed database operation of 589 updating the resource record for user U with the contract A, and 590 "Fetch(U)" illustrates the distributed database operation of 591 retrieving the resource record for user U. Note that the messages 592 between the peers A, B and Z may actually travel via intermediate 593 peers (not shown) as part of the distributed lookup process or so as 594 to traverse intervening NATs. 596 Peer B Peer Z Peer A 597 | | | 598 | | Store(U@Y)| 599 | |<------------------| 600 | |Store-Resp(OK) | 601 | |------------------>| 602 | | | 603 |Fetch(U) | | 604 |------------------->| | 605 | Fetch-Resp(U@Y)| | 606 |<-------------------| | 607 | | | 608 (RELOAD IS USED TO ESTABLISH CONNECTION) 609 | | | 610 | SIP INVITE(To:U) | | 611 |--------------------------------------->| 612 | | | 614 5.3. NAT Traversal 616 NAT Traversal in P2PSIP using RELOAD treats all peers as equal and 617 establishes a partial mesh of connections between them. Messages 618 from one peer to another are routed along the edges in the mesh of 619 connections until they reach their destination. To make the routing 620 efficient and to avoid the use of standard Internet routing 621 protocols, the partial mesh is organized in a structured manner. If 622 the structure is based on any one of a number of common DHT 623 algorithms, then the maximum number of hops between any two peers is 624 log N, where N is the number of peers in the overlay. Existing 625 connections, along with the ICE NAT traversal techniques [RFC5245], 626 are used to establish new connections between peers, and also to 627 allow the applications running on peers to establish a connection to 628 communicate with one another. 630 5.4. Locating and Joining an Overlay 632 Before a peer can attempt to join a P2PSIP overlay, it must first 633 obtain a Node-ID, configuration information, and optionally a set of 634 credentials. The Node-ID is an identifier that will uniquely 635 identify the peer within the overlay, while the credentials show that 636 the peer is allowed to join the overlay. 638 The P2PSIP WG does not impose a particular mechanism for how the 639 peer-ID and the credentials are obtained, but the RELOAD protocol 640 does specify the format for the configuration information, and 641 specifies how this information may be obtained, along with 642 credentials and a Node-ID, from an offline enrollment server. 644 Once the configuration information is obtained, RELOAD specifies a 645 mechanism whereby a peer may obtain a multicast-bootstrap address in 646 the configuration file, and can broadcast to this address to attempt 647 to locate a bootstrap peer. Additionally, the peer may store 648 previous peers it has seen and attempt to use these as bootstrap 649 peers, or may obtain an address for a bootstrap peer by some other 650 mechanism. For more information, see the RELOAD protocol. 652 The job of the bootstrap peer is simple: refer the joining peer to a 653 peer (called the "admitting peer") that will help the joining peer 654 join the network. The choice of admitting peer will often depend on 655 the joining node - for example, the admitting peer may be a peer that 656 will become a neighbor of the joining peer in the overlay. It is 657 possible that the bootstrap peer might also serve as the admitting 658 peer. 660 The admitting peer will help the joining peer learn about other peers 661 in the overlay and establish connections to them as appropriate. The 662 admitting peer and/or the other peers in the overlay will also do 663 whatever else is required to help the joining peer become a fully- 664 functional peer. The details of how this is done will depend on the 665 distributed database algorithm used by the overlay. 667 At various stages in this process, the joining peer may be asked to 668 present its credentials to show that it is authorized to join the 669 overlay. Similarly, the various peers contacted may be asked to 670 present their credentials so the joining peer can verify that it is 671 really joining the overlay it wants to. 673 5.5. Clients and Connecting Unmodified SIP Devices 675 As mentioned above, in RELOAD, from the perspective of the protocol, 676 clients are simply peers that do not store information, do not route 677 messages, and which have not inserted themselves into the overlay. 678 The same protocol is used for the actual message exchanged. Note 679 that while the protocol is the same, the client need not implement 680 all the capabilities of a peer. If, for example, it never routes 681 messages, it will not need to be capable of processing such messages, 682 or understanding a DHT. 684 For SIP devices, another way to realize this functionality is for a 685 Peer to behave as a [RFC3261] proxy/registrar. SIP devices then use 686 standard SIP mechanisms to add, update, and remove registrations and 687 to send SIP messages to peers and other clients. The authors here 688 refer to these devices simply as a "SIP UA", not a "P2PSIP Client", 689 to distinguish it from the concept described above. 691 5.6. Architecture 693 The architecture adopted by RELOAD to implement P2PSIP is shown 694 below. An application, for example SIP (or another application using 695 RELOAD) uses RELOAD to locate other peers and (optionally) to 696 establish connections to those peers, potentially across NATs. 697 Messages may still be exchanged directly between the peers. The 698 overall block diagram for the architecture is as follows: 700 __________________________ 701 | | 702 | SIP, other apps... | 703 | ___________________| 704 | | RELOAD Layer | 705 |______|___________________| 706 | Transport Layer | 707 |__________________________| 709 6. Security Considerations 711 This specification is an overview of existing specifications and does 712 not introduce any security considerations on its own. Please refer 713 to the security considerations of the respective specifications, 714 particularly the RELOAD protocol specification ([RFC6940]) for 715 further details. 717 7. IANA Considerations 719 This document has no actions for IANA. 721 8. Informative References 723 [Chord] Singh, K., Stoica, I., Morris, R., Karger, D., Kaashock, 724 M., Dabek, F., and H. Balakrishman, "Chord: A scalable 725 peer-to-peer lookup protocol for internet applications", 726 IEEE/ACM Transactions on Neworking Volume 11 Issue 1, pp. 727 17-32, Feb. 2003, August 2001. 729 Copy available at http://pdos.csail.mit.edu/chord/papers/ 730 paper-ton.pdf 732 [I-D.ietf-p2psip-diagnostics] 733 Song, H., Xingfeng, J., Even, R., Bryan, D., and Y. Sun, 734 "P2P Overlay Diagnostics", draft-ietf-p2psip- 735 diagnostics-19 (work in progress), November 2015. 737 [I-D.ietf-p2psip-sip] 738 Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., 739 Schulzrinne, H., and T. Schmidt, "A SIP Usage for RELOAD", 740 draft-ietf-p2psip-sip-16 (work in progress), December 741 2015. 743 [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, 744 "Dynamic Updates in the Domain Name System (DNS UPDATE)", 745 RFC 2136, DOI 10.17487/RFC2136, April 1997, 746 . 748 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 749 A., Peterson, J., Sparks, R., Handley, M., and E. 750 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 751 DOI 10.17487/RFC3261, June 2002, 752 . 754 [RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation 755 Protocol (SIP): Locating SIP Servers", RFC 3263, 756 DOI 10.17487/RFC3263, June 2002, 757 . 759 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 760 Resource Identifier (URI): Generic Syntax", STD 66, 761 RFC 3986, DOI 10.17487/RFC3986, January 2005, 762 . 764 [RFC4795] Aboba, B., Thaler, D., and L. Esibov, "Link-local 765 Multicast Name Resolution (LLMNR)", RFC 4795, 766 DOI 10.17487/RFC4795, January 2007, 767 . 769 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 770 (ICE): A Protocol for Network Address Translator (NAT) 771 Traversal for Offer/Answer Protocols", RFC 5245, 772 DOI 10.17487/RFC5245, April 2010, 773 . 775 [RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using 776 Relays around NAT (TURN): Relay Extensions to Session 777 Traversal Utilities for NAT (STUN)", RFC 5766, 778 DOI 10.17487/RFC5766, April 2010, 779 . 781 [RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, 782 DOI 10.17487/RFC6762, February 2013, 783 . 785 [RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service 786 Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013, 787 . 789 [RFC6940] Jennings, C., Lowekamp, B., Ed., Rescorla, E., Baset, S., 790 and H. Schulzrinne, "REsource LOcation And Discovery 791 (RELOAD) Base Protocol", RFC 6940, DOI 10.17487/RFC6940, 792 January 2014, . 794 [RFC7363] Maenpaa, J. and G. Camarillo, "Self-Tuning Distributed 795 Hash Table (DHT) for REsource LOcation And Discovery 796 (RELOAD)", RFC 7363, DOI 10.17487/RFC7363, September 2014, 797 . 799 [RFC7374] Maenpaa, J. and G. Camarillo, "Service Discovery Usage for 800 REsource LOcation And Discovery (RELOAD)", RFC 7374, 801 DOI 10.17487/RFC7374, October 2014, 802 . 804 Authors' Addresses 806 David A. Bryan 807 Cogent Force, LLC 808 Cedar Park, TX, Texas 809 USA 811 Email: dbryan@ethernot.org 813 Philip Matthews 814 Alcatel-Lucent 815 600 March Road 816 Ottawa, Ontario K2K 2E6 817 Canada 819 Phone: +1 613 784 3139 820 Email: philip_matthews@magma.ca 822 Eunsoo Shim 823 Samsung Electronics Co., Ltd. 824 San 14, Nongseo-dong, Giheung-gu, 825 Yongin-si, Gyeonggi-do, 446-712 826 South Korea 828 Email: eunsooshim@gmail.com 829 Dean Willis 830 Softarmor Systems 831 3100 Independence Pkwy #311-164 832 Plano, Texas 75075 833 USA 835 Phone: +1 214 504 1987 836 Email: dean.willis@softarmor.com 838 Spencer Dawkins 839 Huawei Technologies (USA) 841 Phone: +1 214 755 3870 842 Email: spencerdawkins.ietf@gmail.com