P2PSIP Working Group D. Bryan Internet-Draft
SIPeerior TechnologiesCogent Force, LLC Intended status: Informational P. Matthews Expires: January 8, 2009 UnaffiliatedApril 28, 2011 Alcatel-Lucent E. Shim Locus TelecommunicationsAvaya, Inc. D. Willis Softarmor Systems S. Dawkins Huawei (USA) July 7, 2008October 25, 2010 Concepts and Terminology for Peer to Peer SIP draft-ietf-p2psip-concepts-02 Statusdraft-ietf-p2psip-concepts-03 Abstract This document defines concepts and terminology for the use of this Memo By submitting this Internet-Draft, each author represents that any applicable patentthe Session Initiation Protocol in a peer-to-peer environment where the traditional proxy-registrar and message routing functions are replaced by a distributed mechanism. These mechansims may be implemented using a distributed hash table or other IPR claimsdistributed data mechanism with similar external properties. This document includes a high-level view of which he or she is aware have been or will be disclosed,the functional relationships between the network elements defined herein, a conceptual model of operations, and anyan outline of which he or she becomes aware will be disclosed,the related problems addressed by the P2PSIP working group and the RELOAD protocol ([I-D.ietf-p2psip-base], [I-D.ietf-p2psip-sip]) defined by the working group. Status of this Memo This Internet-Draft is submitted in accordancefull conformance with Section 6the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups.(IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts.Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html.This Internet-Draft will expire on January 8, 2009. AbstractApril 28, 2011. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document defines conceptsis subject to BCP 78 and terminology for use ofthe Session Initiation ProtocolIETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in a peer-to-peer environment whereeffect on the traditional proxy-registrardate of publication of this document. Please review these documents carefully, as they describe your rights and message routing functions are replaced by a distributed mechanism implemented using a distributed hash table or other distributed data mechanismrestrictions with similar external properties. Thisrespect to this document. Code Components extracted from this document includes a high-level viewmust include Simplified BSD License text as described in Section 4.e of the functional relationships between the network elements defined herein, a conceptual model of operations,Trust Legal Provisions and an outlineare provided without warranty as described in the Simplified BSD License. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the related open problems being addressed byIETF Trust the P2PSIP working group. Asright to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document matures,may not be modified outside the IETF Standards Process, and derivative works of it is expected to definemay not be created outside the general frameworkIETF Standards Process, except to format it for P2PSIP.publication as an RFC or to translate it into languages other than English. Table of Contents 1. Author'sEditor's Notes and Changes To This Version . . . . . . . . . . 4 1.1. Author's Notes . . . . . . . . . . . . . . . . . . . . . . 4 1.2. Changes from Previous Version . . . . . . . . . . . . . . 42. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. High Level Description . . . . . . . . . . . . . . . . . . . . 5 3.1. Services . . . . . . . . . . . . . . . . . . . . . . . . . 65 3.2. Clients . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.3. Protocol . . . . . . . . . . . . . . .Relationship Between P2PSIP and RELOAD . . . . . . . . . . 6 3.4. Relationship of Peer and Client Protocols . . . . . . . . 7 3.5. RelationshipBetween P2PSIP and SIP . . . . . . . . . . . 7 3.6.6 3.5. Relationship Between P2PSIP and Other AoR Dereferencing Approaches . . . . . . . . . . . . . . . . . 7 22.214.171.124. NAT Issues . . . . . . . . . . . . . . . . . . . . . . . . 7 4. Reference Model . . . . . . . . . . . . . . . . . . . . . . . 87 5. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 109 6. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 1413 6.1. The Distributed Database Function . . . . . . . . . . . . 1413 6.2. Using the Distributed Database Function . . . . . . . . . 1614 6.3. NAT Traversal . . . . . . . . . . . . . . . . . . . . . . 1915 6.4. Locating and Joining an Overlay . . . . . . . . . . . . . 2115 6.5. Possible Client Behavior . . . . . . . . . . .Clients and Connecting Unmodified SIP Devices . . . . . . 2216 6.6. Interacting with non-P2PSIP entities . . . . . . . . . . . 22 6.7.Architecture . . . . . . . . . . . . . . . . . . . . . . . 2317 7. Additional Questions .Open Issues . . . . . . . . . . . . . . . . . . . . 24 7.1. Selecting between Multiple Peers offering the Same Service. . . . . 17 8. Informative References . . . . . . . . . . . . . . . . . . . . 24 7.2. Visibility of Messages to Intermediate Peers17 Authors' Addresses . . . . . . . 25 7.3. Using C/S SIP and P2PSIP Simultaneously in a Single UA. . 25 7.4. Clients, Peers, and Services. . . . . . . . . . . . . . . 25 7.5. Relationships19 1. Editor's Notes and Changes To This Version This version of Domains to Overlays . . . . . . . . . . . 25 8. Security Considerations . . . . . . . . . . . . . . . . . . . 26 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 26 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26 11.1. Normative References . . . . . . . . . . . . . . . . . . . 26 11.2. Informative References . . . . . . . . . . . . . . . . . . 27 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28 Intellectual Property and Copyright Statements . . . . . . . . . . 30 1. Author's Notes and Changes To This Version 1.1. Author's Notes The editors are currently consideringthe draft represents a rathersubstantial revision tofrom the previous version. Until -02, this documentwork was tracking open questions and being used to better reflecthelp reach consensus on a draft. With the evolving directioneselection of RELOAD as the working group. This version incorporates only minor revisions fromprotocol for this WG, the -01 versionfocus of the document. In particular, the authors intendgroup turned to makecompleting the following more substantial changes,RELOAD drafts, and solicit the opinion ofthe WG on these changes, as well as to solicit suggestions for text for the new sections: o Documentdirected the current view ofeditors to update the working group thatdocument to reflect the protocols being developeddecisions made in P2PSIP should be more broadly applicable than just for peer-to-peer networks of SIP endpoints. o The authors plan to add a section that documents the history of various design decisions, and at the same time remove this discussion from other parts of the text. The authors feel that this historical information is important, but also feel that a reader needs to be able to quicklyRELOAD upon completion. Please see what the current state of the P2PSIP work is today. An exception would be an early explanation of the fact that P2PSIP doesn't use SIPSection 7 for the peer protocol, a frequent source of confusion to many people new to the WG. o The definition text is somewhat out of date, and should be revised (with some terms added and others eliminated, as appropriate) o Incorporate the descriptions of the applications scenarios currently described in draft-bryan-p2psip-app-scenarios-00 into this document. 1.2. Changes from Previous Version Changes to this version include removal of the prefix "P2PSIP" before each definition, and clarification on the issue of clients, reflecting the consensuslist of the WG.major open issues. 2. Background One of the fundamental problems in multimedia communication between Internet nodes is that ofdiscovering the host at which a given user can be reached. In the Session Initiation Protocol (SIP) [RFC3261] this problem is expressed as the problem of mapping an Address of Record (AoR) for a user into one or more Contact URIs [RFC3986]. The AoR is a name for the user that is independent of the host or hosts where the user can be contacted, while a Contact URI indicates the host where the user can be contacted. In the common SIP-using architectures that we refer to as "Conventional SIP" or "Client/Server SIP", there is a relatively fixed hierarchy of SIP routing proxies and SIP user agents. To deliver a SIP INVITE to the host or hosts at which the user can be contacted, a SIP UA follows the procedures specified in [RFC3263] to determine the IP address of a SIP proxy, and then sends the INVITE to that proxy. The proxy will then, in turn, deliver the SIP INVITE to the hosts where the user can be contacted. This document gives a high-level description of an alternative solution to this problem. In this alternative solution, the relatively fixed hierarchy of Client/Server SIP is replaced by a peer-to-peer overlay network. In this peer-to-peer overlay network, the various AoR to Contact URI mappings are not centralized at proxy/ registrar nodes but are instead distributed amongst the peers in the overlay. The details of this alternative solution are currently being worked out inspecified by the P2PSIP working group.RELOAD protocol. The RELOAD base draft [I-D.ietf-p2psip-base] defines a mechanism to distribute using a Distributed Hash Table (DHT) and specifies the wire protocol, security, and authentication mechanisms needed to convey this information. This document describesDHT protocol was designed specifically with the basic conceptspurpose of suchenabling a peer-to-peer overlay, and listsdistributed SIP registrar in mind. While designing the open questionsprotocol other applications were considered, and when possible design decisions were made that still needallow RELOAD to be resolved. Asused in other instances where a DHT is desirable, but only when making such decisions did not add undue complexity to the work proceeds, itRELOAD protocol. The RELOAD sip draft [I-D.ietf-p2psip-sip] specifies how RELOAD is expected that this document will develop into a high-level architecture document forused with the SIP protocol to enable a distributed, server-less SIP solution. 3. High Level Description A P2PSIP Overlay is a collection of nodes organized in a peer-to-peer fashion for the purpose of enabling real-time communication using the Session Initiation Protocol (SIP). Collectively, the nodes in the overlay provide a distributed mechanism for mapping names to overlay locations. This provides for the mapping of Addresses of Record (AoRs) to Contact URIs, thereby providing the "location server" function of [RFC3261]. An Overlay also provides a transport function by which SIP messages can be transported between any two nodes in the overlay. A P2PSIP Overlay consists of one or more nodes called Peers. The peers in the overlay collectively run a distributed database algorithm. This distributed database algorithm allows data to be stored on peers and retrieved in an efficient manner. It may also ensure that a copy of a data item is stored on more than one peer, so that the loss of a peer does not result in the loss of the data item to the overlay. One use of this distributed database is to store the information required to provide the mapping between AoRs and Contact URIs for the distributed location function. This provides a location function within each overlay that is an alternative to the location functions described in [RFC3263]. However, the model of [RFC3263] is used between overlays. 3.1. Services The nature of peer-to-peer computing is that each peer offers services to other peers to allow the overlay to collectively provide larger functions. In P2PSIP, peers offer storage and transport services to allow the distributed database function and distributed transport function to be implemented. Additionally, the RELOAD protocol offers a simplistic discovery mechanism specific to the TURN [RFC5766] protocol used for NAT traversal. It is expected that individual peers may also offer other services. Some of these additionalservices as an enhancement to P2PSIP functionality (for example, a STUN server service [I-D.ietf-behave-rfc3489bis]) may be requiredexample to allow the overlay to form and operate, while others (for example, a voicemail service) may be enhancementssupport voicemail) or to the basic P2PSIP functionality.support other applications beyond SIP. To allow peers to offersupport these additional services, the distributed database may need to store information about services. For example, itpeers may need to store additional information about which peers offer which services, and perhaps what sort of capacity each peer hasin the overlay. [I-D.ietf-p2psip-service-discovery] describes the mechanism used in P2PSIP for delivering each listed service.resource discovery. 3.2. Clients An overlay may or may not also include one or more nodes called clients. The role of a clientClients are supported in the P2PSIP model is still under discussion, with a number of suggestions for roles being put forth. The group has reached consensusRELOAD protocol as peers that clients will be able to storehave not joined the overlay, and retrieve information fromtherefore do not route messages or store information. Clients access the overlay. Section 6.5 discussesservices of the possible rolesRELOAD protocol by connecting to a peer which performs operations on the behalf of the client. Note that in RELOAD there is no distinct client protocol. Instead, a client inconnects using the same protocol, but never joins the overlay as a peer. For more detail. 3.3. Protocol Peersinformation, see [I-D.ietf-p2psip-base]. Note that in an overlay need to speak some protocol between themselves to maintainthe overlay andcontext of P2PSIP, there is an additional entity that is sometimes referred to store and retrieve data. Untilas a better name is found, this protocol has been dubbedclient. A special peer may be a member of the in the P2PSIP Peer Protocol. Whileoverlay and may present the usefunctionality of one or all of a SIP forregistrar, proxy or redirect server to conventional SIP devices (SIP clients). In this protocol was proposed asway, existing, non- modified SIP clients may connect to the working group was forming,network. These unmodified SIP devices do not speak the groupRELOAD protocol, and this is currently working towarda new protocol. 3.4. Relationshipdistinct concept from the notion of Peerclient discussed in the previous paragraph. 3.3. Relationship Between P2PSIP and Client Protocols To allow clients to communicate with peers, another protocol is required. Until a better name is found, thisRELOAD The RELOAD protocol has been dubbeddefined by the P2PSIP Client Protocol. The details of this protocol are also very much under debate.working group implements a DHT primarily for use by server-less, peer-to-peer SIP deployments. However, ifthe clientRELOAD protocol exists, then itcould be used for other applications as well. As such, a "P2PSIP" deployment is agreed that it shouldgenerally assumed to be a logical subset of the peer protocol. In other words, the syntaxuse of the peer and client protocols may be completely different,RELOAD to implement distributed SIP, but any operation supported by client protocolit is also supported by the peer protocol. This implies that clients cannot do anythingpossible that peers cannot also do. 3.5.RELOAD is used as a mechanism to distribute other applications, completely unrelated to SIP. 3.4. Relationship Between P2PSIP and SIP Since P2PSIP is about peer-to-peer networks for real-time communication, it is expected that most (if not all)peers and clients will be coupled with SIP entities.entities (although RELOAD may be used for other applications than P2PSIP). For example, one peer might be coupled with a SIP UA, another might be coupled with a SIP proxy, while a third might be coupled with a SIP-to-PSTN gateway. For such nodes, we think ofthe peer or client portion of the node as beingis logically distinct from the SIP entity portion. However, there is no hard requirement that every P2PSIP node (peer or client) be coupled to a SIP entity, and some proposed architectures include peer nodes thatentity. As an example, additional peers could be placed in the overlay to provide additional storage or redundancy for the RELOAD overlay, but might not have noany direct SIP function whatsoever. 3.6.capabilities. 3.5. Relationship Between P2PSIP and Other AoR Dereferencing Approaches OPEN ISSUE: Many of the "decisions" made have been moved out of the main document. This one, however, seems to point out a difference. Should this section be moved or removed? As noted above, the fundamental task of P2PSIP is turning an AoR into a Contact. This task might be approached using zeroconf techniques such as multicast DNS and DNS Service Discovery (as in Apple's Bonjour protocol), link-local multicast name resolution [RFC4795], and dynamic DNS [RFC2136]. These alternatives were discussed in the P2PSIP Working Group, and not pursued as a general solution for a number of reasons related to scalability, the ability to work in a disconnected state, partition recovery, and so on. However, there does seem to be some continuing interest in the possibility of using DNS-SD and mDNS for bootstrapping of P2PSIP overlays. 126.96.36.199. NAT Issues Network Address Translators (NATs) are impediments to establishing and maintaining peer-to-peer networks, since NATs hinder direct communication between peers. Some peer-to-peer network architectures avoid this problem by insisting that all peers exist in the same address space. However, in the P2PSIP model, it has been agreedRELOAD provides capabilities that allow peers can liveto be located in multiple address spaces interconnected by NATs. This implies that Peer Protocol connections must be ableNATs, to allow RELOAD messages to traverse NATs, and to assist in transmitting application-level messages (for example SIP messages) across NATs. It also means that the peers must collectively provide a distributed transport function that allows4. Reference Model The following diagram shows a peer to sendP2PSIP Overlay consisting of a SIP message to any other peer in the overlay - without this function two peers in different IP address spaces might not be able to exchange SIP messages. 4. Reference Model The following diagram shows a P2PSIP Overlay consisting of a number of Peers, one Client, and an ordinarynumber of Peers, one Client, and an ordinary SIP UA. It illustrates a typical P2PSIP overlay but does not limit other compositions or variations; for example, Proxy Peer P might also talk to a ordinary SIP proxy as well. The figure is not intended to cover all possible architecture variations in this document.variations, but simply to show a deployment with many common P2PSIP elements. --->PSTN +------+ N +------+ +---------+ / | | A | | | Gateway |-/ | UA |####T#####| UA |#####| Peer |######## | Peer | N | Peer | | G | # P2PSIPRELOAD | E | A | F | +---------+ # ClientP2PSIP | | T | | # Protocol +------+ N +------+ # | # A # | NATNATNATNAT # | # # | \__/ NATNATNATNAT +-------+ v / \ # N | |=====/|#####/ UA \ +------+ A P2PSIP Overlay | Peer | /Client\ | | T | Q | |___C__| | UA | N | | | Peer | A +-------+ | D | T # | | N # +------+ A # P2PSIPRELOAD # T # PeerP2PSIP # N +-------+ +-------+ # Protocol # A | | | | # #########T####| Proxy |########| Redir |####### N | Peer | | Peer | A | P | | R | T +-------+ +-------+ | / | SIP / \__/ / / /\ / ______________/ SIP / \/ / / UA \/ /______\ SIP UA A Figure: P2PSIP Overlay Reference Model Here, the large perimeter depicted by "#" represents a stylized view of the Overlay (the actual connections could be a mesh, a ring, or some other structure). Around the periphery of the Overlay rectangle, we have a number of Peers. Each peer is labeled with its coupled SIP entity -- for example, "Proxy Peer P" means that peer P which is coupled with a SIP proxy. In some cases, a peer or client might be coupled with two or more SIP entities. In this diagram we have a PSTN gateway coupled with peer "G", three peers ("D", "E" and "F") which are each coupled with a UA, a peer "P" which is coupled with a SIP proxy, an ordinary peer "Q","Q" with no SIP capabilities, and one peer "R" which is coupled with a SIP Redirector. Note that because these are all Peers, each is responsible for storing Resource Records and transporting messages around the Overlay. To the left, two of the peers ("D" and "E") are behind network address translators (NATs). These peers are included in the P2PSIP overlay and thus participate in storing resource records and routing messages, despite being behind the NATs. On the right side, we have a client "C", which uses the RELOAD Protocol to communicate with Proxy Peer "Q". The Client "C" uses RELOAD to obtain information from the overlay, but has not inserted itself into the overlay, and therefore does not participate in routing messages or storing information. Below the Overlay, we have a conventional SIP UA "A" which is not part of the Overlay, either directly as a peer or indirectly as a client. It speaks neitherdoes not speak the RELOAD P2PSIP protocol, and is not participating in the overlay as either a Peer nor Client protocols.Client. Instead, it uses SIP to interact with the Overlay. On the right side, we have a client "C",Overlay via an adapter peer or peers which uses the Client Protocol depicted by "=" to communicate with Proxy Peer "Q". The Client "C" couldcommunicate with a different peer, for example peer "F", if it establishes a connection to "F" instead of or in addition to "Q". The exact role that this client plays inthe network is still under discussion (see Section 6.5).overlay using RELOAD. Both the SIP proxy coupled with peer "P" and the SIP redirector coupled with peer "R" can serve as adapters between ordinary SIP devices and the Overlay. Each accepts standard SIP requests and resolves the next-hop by using the P2PSIP overlay Peer Protocolprotocol to interact with the routing knowledge of the Overlay, then processes the SIP requests as appropriate (proxying or redirecting towards the next-hop). Note that proxy operation is bidirectional - the proxy may be forwarding a request from an ordinary SIP device to the Overlay, or from the P2PSIP overlay to an ordinary SIP device. The PSTN Gateway at peer "G" provides a similar sort of adaptation to and from the public switched telephone network (PSTN). 5. Definitions This section defines a number of concepts that are key to understanding the P2PSIP work. Overlay Network: An overlay network is a computer network which is built on top of another network. Nodes in the overlay can be thought of as being connected by virtual or logical links, each of which corresponds to a path, perhaps through many physical links, in the underlying network. For example, many peer-to-peer networks are overlay networks because they run on top of the Internet. Dial-up Internet is an overlay upon the telephone network. <http://en.wikipedia.org/wiki/P2P_overlay> P2P Network: A peer-to-peer (or P2P) computer network is a network that relies primarily on the computing power and bandwidth of the participants in the network rather than concentrating it in a relatively low number of servers. P2P networks are typically used for connecting nodes via largely ad hoc connections. Such networks are useful for many purposes. Sharing content files (see <http://en.wikipedia.org/wiki/File_sharing>) containing audio, video, data or anything in digital format is very common, and realtimereal-time data, such as telephony traffic, is also exchanged using P2P technology. <http://en.wikipedia.org/wiki/Peer-to-peer>. A P2P Network may also be called a "P2P Overlay" or "P2P Overlay Network" or "P2P Network Overlay", since its organization is not at the physical layer, but is instead "on top of" an existing Internet Protocol network. P2PSIP: A suite of communications protocols related to the Session Initiation Protocol (SIP) [RFC3261] that enable SIP to use peer- to-peer techniques for resolving the targets of SIP requests, providing SIP message transport, and providing other SIP-related functions. The exact contents of this protocol suite are still under discussion, but is likely toAt present, these protocols include the P2PSIP Peer Protocol[I-D.ietf-p2psip-base], [I-D.ietf-p2psip-sip], [I-D.ietf-p2psip-diagnostics], [I-D.ietf-p2psip-service-discovery] and may include a P2PSIP Client Protocol (see definitions below).[I-D.ietf-p2psip-self-tuning]. User: A human that interacts with the overlay through SIP UAs located on peers and clients (and perhaps other ways). The following terms are defined here only within the scope of P2PSIP. These terms may have conflicting definitions in other bodies of literature. Some earlier versions of this document prefixed each term with "P2PSIP" to clarify the term's scope. This prefixing has been eliminated from the text; however the scoping still applies. Overlay Name: A human-friendly name that identifies a specific P2PSIP Overlay. This is in the format of (a portion of) a URI, but may or may not have a related record in the DNS. Peer: A node participating in a P2PSIP Overlay that provides storage and transport services to other nodes in that P2PSIP Overlay. Each Peer has a unique identifier, known as a Peer-ID, within the Overlay. Each Peer may be coupled to one or more SIP entities. Within the Overlay, the peer is capable of performing several different operations, including: joining and leaving the overlay, transporting SIP messages within the overlay, storing information on behalf of the overlay, putting information into the overlay, and getting information from the overlay. Peer-ID: Information that uniquely identifies each Peer within a given Overlay. This value is not human-friendly -- in a DHT approach, this is a numeric value in the hash space. These Peer- IDs are completely independent of the identifier of any user of a user agent associated with a peer. (Note: This is often called a "Node-ID" in the P2P literature). Client: A node participating in a P2PSIP Overlay that is less capable than a Peer in some way. The role of a Client is still under debate, with a number of competing proposals (see the discussion on this later in the document). It has been agreed that they do have the ability to add, modify, inspect, and delete information in the overlay. Note that the term client does not imply that this node is a SIP UAC. Some have suggested that the word 'client' be changed to something else to avoid both this confusion and the implication of a client-server relationship. User Name: A human-friendly name for a user. This name must be unique within the overlay, but may be unique in a wider scope. User Names are formatted so that they can be used within a URI (likely a SIP URI), perhaps in combination with the Overlay Name. Service: A capability contributed by a peer to an overlay or to the members of an overlay. It is expected that not all peers and clients will offer the same set of services, so a means of finding peers (and perhaps clients) that offer a particular service is required. Services might include routing of requests, storing of routing data, storing of other data, STUN discovery, STUN relay, and many other things. This model posits a requirement for a service locator function, possibly including supporting information such as the capacity of a peer to provide a specific service or descriptions of the policies under which a peer will provide that service. We currently expect that we will need to be able to search for available service providers within each overlay. We think we might need to be able to make searches based on network locality or path minimalization. Service Name: A unique, human-friendly, name for a service. Resource: Anything about which information can be stored in the overlay. Both Users and Services are examples of Resources. Resource-ID: A non-human-friendly value that uniquely identifies a resource and which is used as a key for storing and retrieving data about the resource. One way to generate a Resource-ID is by applying a mapping function to some other unique name (e.g., User Name or Service Name) for the resource. The Resource-ID is used by the distributed database algorithm to determine the peer or peers that are responsible for storing the data for the overlay. Resource Record: A block of data, stored using distributed database mechanism of the Overlay, that includes information relevant to a specific resource. We presume that there may be multiple types of resource records. Some may hold data about Users, and others may hold data about Services, and the working group may define other types. The types, usages, and formats of the records are a question for future study. Responsible Peer The Peer that is responsible for storing the Resource Record for a Resource. In the literature, the term "Root Peer" is also used for this concept. Peer Protocol: The protocol spoken between P2PSIP Overlay peers to share information and organize the P2PSIP Overlay Network. Client Protocol: The protocol spoken between Clients and Peers. It is used to store and retrieve information from the P2P Overlay. The nature of this protocol, and even its existence, is under discussion. However, if it exists, it has been agreed that the Client Protocol is a functional subset of the P2P Peer Protocol, but may differ in syntax and protocol implementation (i.e., may not be syntactically related). Peer Protocol Connection / P2PSIP Client Protocol Connection: The TCP, UDP or other transport layer protocol connection over which the Peer Protocol (or respectively the Client protocol) is transported. Neighbors: The set of P2PSIP Peers that either a Peer or Client know of directly and can reach without further lookups. Joining Peer: A node that is attempting to become a Peer in a particular Overlay. Bootstrap Peer: A Peer in the Overlay that is the first point of contact for a Joining Peer. It selects the peer that will serve as the Admitting Peer and helps the joining peer contact the admitting peer. Admitting Peer: A Peer in the Overlay which helps the Joining Peer join the Overlay. The choice of the admitting peer may depend on the joining peer (e.g., depend on the joining peer's Peer-ID). For example, the admitting peer might be chosen as the peer which is "closest" in the logical structure of the overlay to the future position of the joining peer. The selection of the admitting peer is typically done by the bootstrap peer. It is allowable for the bootstrap peer to select itself as the admitting peer. Bootstrap Server: A network node used by Joining Peers to locate a Bootstrap Peer. A Bootstrap Server may act as a proxy for messages between the Joining Peer and the Bootstrap Peer. The Bootstrap Server itself is typically a stable host with a DNS name that is somehow communicated (for example, through configuration) to peers that want to join the overlay. A Bootstrap Server is NOT required to be a peer or client, though it may be if desired. Peer Admission: The act of admitting a node (the "Joining Peer") into an Overlay as a Peer. After the admission process is over, the joining peer is a fully-functional peer of the overlay. During the admission process, the joining peer may need to present credentials to prove that it has sufficient authority to join the overlay. Resource Record Insertion: The act of inserting a P2PSIP Resource Record into the distributed database. Following insertion, the data will be stored at one or more peers. The data can be retrieved or updated using the Resource-ID as a key. 6. Discussion 6.1. The Distributed Database Function A P2PSIP Overlay functions as a distributed database. The database serves as a way to store information about things called Resources. A piece of information, called a Resource Record, can be stored by and retrieved from the database using a key associated with the Resource Record called its Resource-ID. Each Resource must have a unique Resource-ID. In addition to uniquely identifying the Resource, the Resource-ID is also used by the distributed database algorithm to determine the peer or peers that store the Resource Record in the overlay. It is expected that the P2PSIP working group will standardize the way(s) certain types of resources are represented in the distributed database. One type of resource representation that the working group is expected to standardize is information about users. Users are humans that can use the overlay to do things like making and receiving calls. Information stored in the resource record associated with a user might include things like the full name of the user and the location of the UAs that the user is using. Before information about a user can be stored in the overlay, a user needs a User Name. The User Name is a human-friendly identifier that uniquely identifies the user within the overlay. The User Name is not a Resource-ID, rather the Resource-ID is derived from the User Name using some mapping function (often a cryptographic hash function) defined by the distributed database algorithm used by the overlay. The overlay may also require that the user have a set of credentials. Credentials may be required to authenticate the user and/or to show that the user is authorized to use the overlay. Another type of resource representation that the working group is expected to standardize is information about services. Services represent actions that a peer (and perhaps a client) can do to benefit other peers and clients in the overlay. Information that might be stored in the resource record associated with a service might include the peers (and perhaps clients) offering the service. Each service has a human-friendly Service Name that uniquely identifies the service. Like User Names, the Service Name is not a resource-id, rather the resource-id is derived from the service name using some function defined by the distributed database algorithm used by the overlay. It is expected that the working group will standardize at least one service. For each standardized service, the working group will likely specify the service name, the nature and format of the information stored in the resource record associated with the service, and the protocol used to access the service. The overlay may require that the peer (or client) have a set of credentials for a service. For example, credentials might be required to show that the peer (or client) is authorized to offer the service, or to show that the peer (or client) is a providing a trustworthy implementation of the service. It is expected that the P2PSIP WG will not standardize how a User Name is obtained, nor how the credentials associated with a User Name or a Service Name are obtained, but merely standardize at least one acceptable format for each. To ensure interoperability, it is expected that at least one of these formats will be specified as "mandatory-to-implement". A class of algorithms known as Distributed Hash Tables <http://en.wikipedia.org/wiki/P2P_overlay> are one way to implement the Distributed Database. In particular, both the Chord and Bamboo algorithms have been suggested as good choices for the distributed database algorithm. However, no decision has been taken so far. 6.2. Using the Distributed Database Function There are a number of ways the distributed database described in the previous section might be used to establish multimedia sessions using SIP. In this section, we give four possibilities as examples. It seems likely that the working group will standardize at least one way (not necessarily one of the four listed here), but no decisions have been taken yet. The first option is to store the contact information for a user in the resource record for the user. A peer Y that is a contact point for this user adds contact information to this resource record. The resource record itself is stored with peer Z in the network, where peer Z is chosen by the distributed database algorithm. When the SIP entity coupled with peer X has an INVITE message addressed to this user, it retrieves the resource record from peer Z. It then extracts the contact information for the various peers that are a contact point for the user, including peer Y, and forwards the INVITE onward. This exchange is illustrated in the following figure. The notation "Put(U@Y)" is used to show the distributed database operation of updating the resource record for user U with the contract Y, and "Get(U)" illustrates the distributed database operation of retrieving the resource record for user U. Note that the messages between the peers X, Y and Z may actually travel via intermediate peers (not shown) as part of the distributed lookup process or so as to traverse intervening NATs. Peer X Peer Z Peer Y | | | | | Put(U@Y) | | |<---------------| | | Put-Resp(OK) | | |--------------->| | | | | Get(U) | | |---------------->| | | Get-Resp(U@Y)| | |<----------------| | | INVITE(To:U) | | |--------------------------------->| | | | The second option also involves storing the contact information for a user in the resource record of the user. However, SIP entity at peer X, rather than retrieving the resource record from peer Z, instead forwards the INVITE message to the proxy at peer Z. The proxy at peer Z then uses the information in the resource record and forwards the INVITE onwards to the SIP entity at peer Y and the other contacts. Peer X Peer Z Peer Y | | | | | Put(U@Y) | | |<---------------| | | Put-Resp(OK) | | |--------------->| | | | | INVITE(To:U) | | |-----------------| INVITE(To:U) | | |--------------->| | | | The third option is for a single peer W to place its contact information into the resource record for the user (stored with peer Z). A peer Y that is a contact point for the user retrieves the resource record from peer Z, extracts the contact information for peer W, and then uses the standard SIP registration mechanism [RFC3261] to register with peer W. When the SIP entity at peer X has to forward an INVITE request, it retrieves the resource record and extracts the contact information for W. It then forwards the INVITE to the proxy at peer W, which proxies it onward to peer Y and the other contacts. Peer X Peer Z Peer Y Peer W | | | | | | Put(U@W) | | | |<---------------------------------| | | Put-Resp(OK) | | | |--------------------------------->| | | | | | | | | | | | REGISTER(To:U) | | | |---------------->| | | | 200 | | | |<----------------| | | | | | | | | | Get(U) | | | |---------------->| | | | Get-Resp(U@W)| | | |<----------------| | | | INVITE(To:U) | | | |--------------------------------------------------->| | | | INVITE(To:U) | | | |<----------------| | | | | The fourth option works as in option 3, with the exception that, rather than X retrieving the resource record from Z, peer X forwards the INVITE to a SIP proxy at Z, which proxies it onward to W and hence to Y. Peer X Peer Z Peer Y Peer W | | | | | | Put(U@W) | | | |<---------------------------------| | | Put-Resp(OK) | | | |--------------------------------->| | | | | | | | | | | | REGISTER(To:U) | | | |---------------->| | | | 200 | | | |<----------------| | | | | | | | | | INVITE(To:U) | | | |---------------->| INVITE(To:U) | | | |--------------------------------->| | | | INVITE(To:U) | | | |<----------------| | | | | The pros and cons of option 1 and 3 are briefly discussed in [Using-an-External-DHT]. 6.3. NAT Traversal Two approaches to NAT Traversal for P2PSIP Peer Protocol have been suggested. The working group has not made any decision yet on the approach that will be selected. The first, the traditional approach adopted by most peer-to-peer networks today, divides up the peers in the network into two groups: those with public IP addresses and those without. The networks then select a subset of the former group and elevate them to "super peer" status, leaving the remaining peers as "ordinary peers". Since super peers all have public IP addresses, there are no NAT problems when communicating between them. The network then associates each ordinary peer with (usually just one) super peer in a client-server relationship. Once this is done, an ordinary peer X can communicate with another ordinary peer Y by sending the message to X's super peer, which forwards it to Y's super peer, which forwards it to Y. The connection between an ordinary peer and its super peer is initiated by the ordinary peer, which makes it easy to traverse any intervening NATs. In this approach, the number of hops between two peers is at most 3. The second approach treats all peers as equal and establishes a partial meshclients (and perhaps other ways). The following terms are defined here only within the scope of connections between them. Messages from one peerP2PSIP. These terms may have conflicting definitions in other bodies of literature. Some earlier versions of this document prefixed each term with "P2PSIP" to another are then routed alongclarify the edgesterm's scope. This prefixing has been eliminated from the text; however the scoping still applies. Overlay Name: A human-friendly name that identifies a specific P2PSIP Overlay. This is in the meshformat of connections until they reach their destination. To make(a portion of) a URI, but may or may not have a related record in the routing efficientDNS. Peer: A node participating in a P2PSIP Overlay that provides storage and transport services to avoid the use of standard Internet routing protocols, the partial mesh is organizedother nodes in that P2PSIP Overlay. Each Peer has a structured manner. Ifunique identifier, known as a Peer-ID, within the structure is based on anyOverlay. Each Peer may be coupled to one of a number of common DHT algorithms, thenor more SIP entities. Within the maximum number of hops between any two peers is log N, where NOverlay, the peer is capable of performing several different operations, including: joining and leaving the numberoverlay, transporting SIP messages within the overlay, storing information on behalf of peers inthe overlay, putting information into the overlay, and getting information from the overlay. The first approachPeer-ID: Information that uniquely identifies each Peer within a given Overlay. This value is not human-friendly -- in a DHT approach, this is significantly more efficient than the seconda numeric value in overlays with large numbers of peers. However,the first approach assumes therehash space. These Peer- IDs are a sufficient number of peers with public IP addresses to serve as super peers. In some usage scenarios envisioned for P2PSIP, this assumption does not hold. For example, this approach failscompletely inindependent of the case where every peer is behindidentifier of any user of a distinct NAT. The second approach, while less efficient in overlaysuser agent associated with larger numbers of peers,a peer. (Note: This is efficientoften called a "Node-ID" in smaller overlays andthe P2P literature). Client: A node participating in a P2PSIP Overlay but that does not store information or forward messages. A client can also be made to work in many use cases where the first approach fails. Boththought of these approaches assumeas a method of setting up Peer Protocol connections between peers. Many such methods exist;peer that has not joined the now expired [I-D.iab-nat-traversal-considerations] is an attempt to giveoverlay User Name: A human-friendly name for a fairly comprehensive list along withuser. This name must be unique within the overlay, but may be unique in a discussion of their pros and cons. Afterwider scope. User Names are formatted so that they can be used within a consideration of the various techniques,URI (likely a SIP URI), perhaps in combination with the P2PSIP working group has decidedOverlay Name. Service: A capability contributed by a peer to an overlay or to selectthe Unilateral Self-Address Fixing method [RFC3424]members of NAT Traversal,an overlay. Not all peers and in particularclients will offer the ICE [I-D.ietf-mmusic-ice] implementationsame set of this approach. The above discussion covers NAT traversalservices, and P2PSIP provides service discovery mechanisms to locate services. Service Name: A unique, human-friendly, name for Peer Protocol connections. For Client Protocol connections, the approach depends ona service. Resource: Anything about which information can be stored in the role adopted for clientsoverlay. Both Users and we defer the discussion onServices are examples of Resources. Resource-ID: A non-human-friendly value that point until the role becomes clearer. In addition to Peer Protocol and Client Protocol messages,uniquely identifies a P2PSIP Overlay must also provideresource and which is used as a solution to the NAT Traversal problemkey for SIP messages. If it does not, there is no reliablestoring and retrieving data about the resource. One way for a peer behind one NATto sendgenerate a SIP INVITE toResource-ID is by applying a peer behind another NAT. One waymapping function to solve this problemsome other unique name (e.g., User Name or Service Name) for the resource. The Resource-ID is to transport SIP messages along Peer and Client Protocol connections: this could be done eitherused by encapsulatingthe SIP messages inside Peer and Client Protocol messages or by multiplexing SIP withdistributed database algorithm to determine the Peer (resp.Client) Protocol on a Peer (resp. Client) Protocol connection. Finally, it should be notedpeer or peers that are responsible for storing the NAT traversal problemdata for media connections signaled using SIP is outsidethe scopeoverlay. Resource Record: A block of data, stored using distributed database mechanism of the P2PSIP working group. As discussed in [I-D.ietf-sipping-nat-scenarios], the current recommendation is to use ICE. 6.4. Locating and Joining an Overlay Before a peer can attemptOverlay, that includes information relevant to join a P2PSIP overlay, it must first obtaina Peer-IDspecific resource. We presume that there may be multiple types of resource records. Some may hold data about Users, and optionally a setothers may hold data about Services, and the working group may define other types. The types, usages, and formats of credentials.the records are a question for future study. Responsible Peer The Peer-ID is an identifierPeer that will uniquely identify the peer withinis responsible for storing the overlay, whileResource Record for a Resource. In the credentials show thatliterature, the peerterm "Root Peer" is allowedalso used for this concept. Peer Protocol: The protocol spoken between P2PSIP Overlay peers to joinshare information and organize the overlay. TheP2PSIP WG will not standardize howOverlay Network. In P2PSIP, this is implemented using the peer-IDRELOAD [I-D.ietf-p2psip-base] protocol. Client Protocol: The protocol spoken between Clients and Peers. In P2PSIP and RELOAD, this is the credentials are obtained, but merely standardize at least one acceptable format for each. To ensure interoperability, itsame protocol syntactically as the Peer Protocol. The only difference is expectedthat at least one of these formats will be specified as "mandatory-to-implement". Once a peer (the "joining peer") has a peer-IDClients are not routing messages or routing information, and optionally a set of credentials, ithave not (or can attempt to joinnot) insert themselves into the overlay. To do this, it needs to locate a bootstrap peer for the Overlay. A bootstrap peer is a peer that serves as the first point of contact forPeer Protocol Connection / P2PSIP Client Protocol Connection: The TLS, DTLS, TCP, UDP or other transport layer protocol connection over which the joining peer.RELOAD Peer Protocol messages are transported. Neighbors: The joining peer uses a bootstrap mechanism to locate a bootstrap peer. Locating a bootstrap peer might be done in any one of a numberset of different ways: o By remembering peersP2PSIP Peers that were part of the overlay the last time the peer was part of the overlay; o Through a multicast discovery mechanism; o Through manual configuration; or o By contactinga P2PSIP Bootstrap Server, and using its helpPeer or Client know of directly and can reach without further lookups. Joining Peer: A node that is attempting to locatebecome a bootstrap peer. The joining peer might reasonably try each of the methods (and perhaps others) in some order or in parallel until it succeedsPeer in findinga bootstrap peer. The job ofparticular Overlay. Bootstrap Peer: A Peer in the bootstrap peerOverlay that is simple: referthe joining peer tofirst point of contact for a peer (calledJoining Peer. It selects the "admitting peer")peer that will helpserve as the Admitting Peer and helps the joining peer contact the admitting peer. Admitting Peer: A Peer in the Overlay which helps the Joining Peer join the network.Overlay. The choice of the admitting peer will oftenmay depend on the joining node - forpeer (e.g., depend on the joining peer's Peer-ID). For example, the admitting peer maymight be achosen as the peer that will become a neighborwhich is "closest" in the logical structure of the overlay to the future position of the joining peer. The selection of the admitting peer inis typically done by the overlay.bootstrap peer. It is possible thatallowable for the bootstrap peer might also serveto select itself as the admitting peer. The admitting peer will helpBootstrap Server: A network node used by Joining Peers to locate a Bootstrap Peer. A Bootstrap Server may act as a proxy for messages between the joining peer learn about otherJoining Peer and the Bootstrap Peer. The Bootstrap Server itself is typically a stable host with a DNS name that is somehow communicated (for example, through configuration, specification on a web page, or using DHCP) to peers inthat want to join the overlay and establish connectionsoverlay. A Bootstrap Server is NOT required to them as appropriate.be a peer or client, though it may be if desired. Peer Admission: The act of admitting peer and/or the other peers ina node (the "Joining Peer") into an Overlay as a Peer. After the overlay will also do whatever elseadmission process is required to helpover, the joining peer becomeis a fully- functional peer. The detailsfully-functional peer of how this is done will depend on the distributed database algorithm used inthe overlay. At various stages in thisDuring the admission process, the joining peer may be askedneed to present itscredentials to showprove that it is authorizedhas sufficient authority to join the overlay. Similarly,Resource Record Insertion: The act of inserting a P2PSIP Resource Record into the various peers contacted maydistributed database. Following insertion, the data will be askedstored at one or more peers. The data can be retrieved or updated using the Resource-ID as a key. 6. Discussion 6.1. The Distributed Database Function A P2PSIP Overlay functions as a distributed database. The database serves as a way to present their credentials sostore information about Resources. A piece of information, called a Resource Record, can be stored by and retrieved from the database using a key associated with the Resource Record called its Resource-ID. Each Resource must have a unique Resource-ID. In addition to uniquely identifying the Resource, the Resource-ID is also used by the distributed database algorithm to determine the joiningpeer can verifyor peers that it is really joiningstore the Resource Record in the overlay. Users are humans that can use the overlay it wants to. 6.5. Possible Client Behavior As mentioned above, a number of people have proposedto do things like making and receiving calls. Information stored in the resource record associated with a second typeuser can include things like the full name of P2PSIP entity, known as a "P2PSIP client". The consensusthe user and the location of the group isUAs that the need for entities to store and retrieveuser is using (the users SIP AoR). Full details of how this is implemented using RELOAD are provided in [I-D.ietf-p2psip-sip] Before information fromabout a user can be stored in the Overlay without participatingoverlay, a user needs a User Name. The User Name is recognized, buta human-friendly identifier that for now, little time will spent. This section presents some ofuniquely identifies the alternatives that have been suggested foruser within the possible role of a client.overlay. In one approach,RELOAD, users are issued certificates, which in the case of centrally signed certificates, identify the User Name as well as a client interacts withcertain number of Resource-IDs where the user may store their information. For more information, see [I-D.ietf-p2psip-base]. The P2PSIP overlay through an associatedsuite of protocols also standardizes information about how to locate services. Services represent actions that a peer (or(and perhaps several such peers) using the Client Protocol. The client does not run the distributed database algorithm, does not store resource records, and is not involved in routing messagesa client) can do to benefit other peers or clients. Through interactions with its associated peer, a client can insert, modify, examine,and remove resource records. A client may also send SIP messages to its associated peer for routing throughclients in the overlay. In this approach,Information that might be stored in the resource record associated with a clientservice might include the peers (and perhaps clients) offering the service. Service discovery for P2PSIP is defined in [I-D.ietf-p2psip-service-discovery]. Each service has a nodehuman-friendly Service Name that wants to take advantage ofuniquely identifies the overlay, butservice. Like User Names, the Service Name is not a resource-id, rather the resource-id is unable or unwilling to contribute resources back toderived from the overlay. This may be achievedservice name using a subset ofsome function defined by the Peer Protocol. Such a device need not speak SIP. For SIP devices, anotherdistributed database algorithm used by the overlay. A class of algorithms known as Distributed Hash Tables <http://en.wikipedia.org/wiki/P2P_overlay> are one way to realize this functionalityimplement the Distributed Database. The RELOAD protocol is for a Peer to behave as a [RFC3261] proxy/registrar. SIP devices then use standard SIP mechanisms to add, update, and remove registrations and to send SIP messages to peersextensible and other clients. The authors here referallows many different DHTs to these devices simply as a "SIP UA", notbe implemented, but specifies a "P2PSIP Client",mandatory to distinguish it fromimplement DHT in the concept described above. 6.6. Interacting with non-P2PSIP entities It is possible for network nodes that are not peers or clients to interact withform of a P2PSIP overlay. Such nodes would do this through mechanisms not defined bymodified Chord DHT. For more information, see [Chord] 6.2. Using the P2PSIP working group provided they can findDistributed Database Function While there are a peer or client that supports that mechanism and which will do any related P2PSIP operations necessary. In this section, we briefly describe twonumber of ways this mightthe distributed database described in the previous section can be done. (Note that these are just examples andused to establish multimedia sessions using SIP, the descriptions here are not recommendations). One examplebasic mechanism defined in the RELOAD base draft and SIP usage is summarized below. This is a peer that also acts asvery simplistic overview. For more detailed information, please see the RELOAD base draft. Contact information for a standard SIP proxy and registrar. SIP UAs can interact with it using mechanisms defineduser is stored in [RFC3261]. The peer inserts registrationsthe resource record for users learned from these UAs intothat user. Assume that a user is using a device, here called peer A, which serves as the distributed database, and retrievescontact point for this user. The user adds contact information when proxying INVITE messages. Another exampleto this resource record, as authorized by the RELOAD certificate mechanism. The resource record itself is astored with peer that has a fully-qualified domain name (FQDN) that matchesZ in the name ofnetwork, where peer Z is chosen by the overlay and acts as a SIP proxy for calls coming intoparticular distributed database algorithm in use by the overlay. AWhen the SIP entity coupled with peer B has an INVITE message addressed to "user@overlay-name" arrives atthis user, it retrieves the resource record from peer (usingZ. It then extracts the mechanisms in [RFC3263])contact information for the various peers that are a contact point for the user, including peer A, and thisuses the overlay to establish a connection to peer then looks upA, including any appropriate NAT traversal (the details of which are not shown). Note that RELOAD is used only to establish the userconnection. Once the connection is established, messages between the peers are sent using ordinary SIP. This exchange is illustrated in the following figure. The notation "Store(U@A)" is used to show the distributed database operation of updating the resource record for user U with the contract A, and proxies"Fetch(U)" illustrates the call onto it. 6.7. Architecture There has been much debate indistributed database operation of retrieving the group over what an appropriate architectureresource record for P2PSIP should be. Currently, the group is investigating architectures that involve a P2P layeruser U. Note that is distinct fromthe applications that run onmessages between the overlay. __________________________peers A, B and Z may actually travel via intermediate peers (not shown) as part of the distributed lookup process or so as to traverse intervening NATs. Peer B Peer Z Peer A | | | SIP, other apps...| | ___________________|Store(U@Y)| | |<------------------| | P2P Layer|Store-Resp(OK) | |______|___________________|| Transport Layer|------------------>| | |__________________________| The P2P layer implements the Peer Protocol (and the Client Protocol, if such a protocol exists). Applications access this P2P layer for various overlay-related services. Applications are also free to bypass this layer| | |Fetch(U) | | |------------------->| | | Fetch-Resp(U@Y)| | |<-------------------| | | | | (RELOAD IS USED TO ESTABLISH CONNECTION) | | | | SIP INVITE(To:U) | | |--------------------------------------->| | | | 6.3. NAT Traversal NAT Traversal in P2PSIP using RELOAD treats all peers as equal and access the existing transport layer protocols (e.g., TCP, UDP, etc.) directly. A notable featureestablishes a partial mesh of this architecture is that it envisionsconnections between them. Messages from one peer to another are routed along the use of protocols other than SIPedges in the overlay. Though the working group is primarily focused on the usemesh of SIP in peer-to-peer overlays, this architecture envisions a future in which other protocols can play a role. The group initially considered another architecture. In this alternative architecture, the Peer Protocol was defined as an extension to SIP. That is, thatconnections until they reach their destination. To make the necessary operations for formingrouting efficient and maintainingto avoid the overlay and for storing and retrieving resource records inuse of standard Internet routing protocols, the distributed database were defined as extensions to SIP. Each peerpartial mesh is organized in the overlay was viewed asa SIP proxy that would forwardstructured manner. If the overlay maintenance and distributed database query messages (expressed in SIP)structure is based on behalfany one of other peers. This architecture was eventually rejected bya number of common DHT algorithms, then the working group formaximum number of hops between any two peers is log N, where N is the following reasons: o The architecture was totally focused on SIP, and made it difficult to use other protocolsnumber of peers in the overlay. o In SIP, proxies are assumed to be trusted parties. Relying onExisting connections, along with the peersICE NAT traversal techniques [RFC5245], are used to route the message as proxies exposes the SIP messagesestablish new connections between peers, and also to attacks from untrusted proxies that SIP's design does not anticipate. A design that does notallow the applications running on peers to modify the SIP message and ideally prevents them from reading it is preferable. o SIP was seen as a "heavy-weight" protocol for this task. SIP usesestablish a text-based encoding which is very flexible, but leadsconnection to both large messagescommunicate with one another. 6.4. Locating and slow processing times at proxies. This was seenJoining an Overlay Before a peer can attempt to bejoin a poor match for P2PSIP, whereP2PSIP overlay, it must first obtain a distributed database lookup operation requires O(log N) peers to receive, process and forward the message. More discussion on this alternate approachPeer-ID, configuration information, and why it was rejected can be found on the P2PSIP mailing list inoptionally a thread that started on 20 March 2007. 7. Additional Questions This section lists some additional questionsset of credentials. The Peer-ID is an identifier that will uniquely identify the proposed P2PSIP Working Group may need to consider in the process of definingpeer within the Peer and Client protocols. 7.1. Selecting between Multiple Peers offeringoverlay, while the Same Service If a P2PSIP network contains two or more peerscredentials show that offerthe same service, then how does apeer or client that wishesis allowed to use that service selectjoin the peer to use? This question comes up in a number of contexts: o When two or more peers are willing to serve asoverlay. The P2PSIP WG does not impose a STUN Relay,particular mechanism for how do we select a peer that is close inthe netpath sense and is otherwise appropriatepeer-ID and the credentials are obtained, but the RELOAD base draft does specify the format for the call? o When two or more peers are willing to serve as PSTN gateways,configuration information, and specifies how do we select an appropriate gateway forthis information may be obtained, along with credentials and a call thatPeer-ID, from an offline enrollment server. Once the configuration information is both netpath efficient and provides good quality or inexpensive PSTN routing? It has been suggested that, at least initially,obtained, the working group should restrict itself to definingRELOAD base draft specifies a mechanism that can returnwhereby a list of peers offeringpeer may obtain a servicemulticast-bootstrap address in the configuration file, and not definecan broadcast to this address to attempt to locate a bootstrap peer. Additionally, the mechanismpeer may store previous peers it has seen and attempt to use these as bootstrap peers, or may obtain an address for selectinga bootstrap peer from that list. 7.2. Visibility of Messages to Intermediate Peers When transporting SIP messages through the overlay, areby some other mechanism. For more information, see the headers and/or bodiesRELOAD base draft. The job of the SIP messages visiblebootstrap peer is simple: refer the joining peer to a peer (called the peers"admitting peer") that will help the messages happen to pass through? If they are, what types of security risks does this pose injoining peer join the presence of peers that have been compromised in some way? 7.3. Using C/S SIP and P2PSIP Simultaneously in a Single UA If a given UA is capablenetwork. The choice of operating in both P2PSIP and conventional SIP modalities (especially simultaneously), is it possibleadmitting peer will often depend on the joining node - for it to use and respond toexample, the same AOR using both conventional and P2PSIP? An example of such a topology mightadmitting peer may be a UA that registers an AOR (say, "sip:email@example.com") conventionally with a registrar and then inserts a resource record for that resource into a P2PSIP topology, suchpeer that both conventional SIP users and P2PSIP users (within the overlay orwill become a federation thereof) would be able to contact the user without necessarily traversing some sortneighbor of gateway. Is this somethingthe joining peer in the overlay. It is possible that we want to make work? 7.4. Clients, Peers, and Services 1. Do allthe bootstrap peer might also serve as the admitting peer. The admitting peer will help the joining peer learn about other peers providing routing, storage,in the overlay and allestablish connections to them as appropriate. The admitting peer and/or the other services, or do only some peers provide certain services? 2. What services, if any, must allpeers provide? 3. How we can we describein the capacity of aoverlay will also do whatever else is required to help the joining peer for deliveringbecome a given service? 7.5. Relationshipsfully- functional peer. The details of Domains to Overlays 1. Can there be names from more than one domainhow this is done will depend on the distributed database algorithm used by the overlay. At various stages in a single overlay? 2. Can therethis process, the joining peer may be names from one domain in more than a single overlay? If so, how do we route Client/Server SIP requestsasked to present its credentials to show that it is authorized to join the right overlay? 3. Canoverlay. Similarly, the domain of an AoRvarious peers contacted may be in more than one overlay? 4. Should we have a "default overlay"asked to search for peerspresent their credentials so the joining peer can verify that it is really joining the overlay it wants to. 6.5. Clients and Connecting Unmodified SIP Devices As mentioned above, in many domains? 8. Security Considerations Building a P2PSIP system has many security considerations, manyRELOAD, from the perspective of the protocol, clients are simply peers that do not store information, do not route messages, and which wehave only begun to consider. We anticipatenot inserted themselves into the overlay. The same protocol is used for the actual message exchanged. Note that while the protocol documents describingis the actual protocols will deal more thoroughly with security topics. One critical security issue thatsame, the client need not implement all the capabilities of a peer. If, for example, it never routes messages, it will not need to be addressedcapable of processing such messages, or understanding a DHT. For SIP devices, another way to realize this functionality is providingfor the privacya Peer to behave as a [RFC3261] proxy/registrar. SIP devices then use standard SIP mechanisms to add, update, and integrity ofremove registrations and to send SIP messages being routed by peer nodes, when those peer nodes might well be hostile. This isto peers and other clients. The authors here refer to these devices simply as a "SIP UA", not a departure"P2PSIP Client", to distinguish it from Client/Server SIP, wherethe proxies are generally operatedconcept described above. 6.6. Architecture The architecture adopted by enterprises or service providers with whom the users ofRELOAD to implement P2PSIP is shown below. An application, for example SIP UAs have(or another application using RELOAD) uses RELOAD to locate other peers and (optionally) to establish connections to those peers, potentially across NATs. Messages may still be exchanged directly between the peers. The overall block diagram for the architecture is as follows: __________________________ | | | SIP, other apps... | | ___________________| | | RELOAD Layer | |______|___________________| | Transport Layer | |__________________________| 7. Open Issues OPEN ISSUE: Should we include a trust relationship. 9. IANA Considerations This document presently raises no IANA considerations. 10. Acknowledgements This document draws heavily fromsection that documents previous decisions made, to preserve the contributions of many participantshistorical debate and prevent past issues from being raised in the P2PSIP Mailing List. Particular thanks to Henning Schulzrinne and Cullen Jennings who spent timefuture, or simply rely on phone calls relatedthe mailing list to this text. 11. References 11.1. Normative References [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks,address these concerns? OPEN ISSUE: Should we include the use cases from draft-bryan-p2psip-app-scenarios-00 (now expired)? There was some interest in doing so in previous versions, but no conclusion was reached. 8. Informative References [Chord] Singh, K., Stoica, I., Morris, R., Handley,Karger, D., Kaashock, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [RFC3263] Rosenberg, J.Dabek, F., and H. Schulzrinne, "Session Initiation Protocol (SIP): Locating SIP Servers", RFC 3263, June 2002. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. 11.2. Informative References [I-D.bryan-p2psip-reload]Balakrishman, "Chord: A scalable peer-to-peer lookup protocol for internet applications", IEEE/ACM Transactions on Neworking Volume 11 Issue 1, pp. 17-32, Feb. 2003. Copy available at http://pdos.csail.mit.edu/chord/papers/paper-ton.pdf [I-D.ietf-p2psip-base] Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and H. Schulzrinne, "REsource LOcation And Discovery (RELOAD)", draft-bryan-p2psip-reload-04 (work in progress), June 2008. [I-D.camarillo-hip-bone] Camarillo, G., Nikander, P., and J. Hautakorpi, "HIP BONE: Host Identity Protocol (HIP) Based Overlay Networking Environment", draft-camarillo-hip-bone-01 (work in progress), February 2008. [I-D.iab-nat-traversal-considerations] Rosenberg, J., "Considerations for Selection of Techniques for NAT Traversal", draft-iab-nat-traversal-considerations-00(RELOAD) Base Protocol", draft-ietf-p2psip-base-11 (work in progress), October 2005. [I-D.ietf-behave-rfc3489bis] Rosenberg, J., Mahy,2010. [I-D.ietf-p2psip-diagnostics] Yongchao, S., Jiang, X., Even, R., Matthews, P.,and D. Wing, "Session Traversal Utilities for (NAT) (STUN)", draft-ietf-behave-rfc3489bis-16Bryan, "P2PSIP Overlay Diagnostics", draft-ietf-p2psip-diagnostics-04 (work in progress), July 2008. [I-D.ietf-mmusic-ice] Rosenberg,2010. [I-D.ietf-p2psip-self-tuning] Maenpaa, J., "Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) TraversalCamarillo, G., and J. Hautakorpi, "A Self- tuning Distributed Hash Table (DHT) for Offer/Answer Protocols", draft-ietf-mmusic-ice-19REsource LOcation And Discovery (RELOAD)", draft-ietf-p2psip-self-tuning-02 (work in progress), October 2007. [I-D.ietf-sipping-nat-scenarios] Boulton, C., Rosenberg, J.,July 2010. [I-D.ietf-p2psip-service-discovery] Maenpaa, J. and G. Camarillo, "Best Current Practices for NAT Traversal for SIP", draft-ietf-sipping-nat-scenarios-08 (work in progress), April 2008. [I-D.jiang-p2psip-sep] Jiang, X. and H. Zhang,"Service Extensible P2P Peer Protocol", draft-jiang-p2psip-sep-01 (work in progress), February 2008. [I-D.li-p2psip-node-types] Wang, Y., "Different types of nodes in P2PSIP", draft-li-p2psip-node-types-00 (work in progress), December 2007. [I-D.matthews-p2psip-id-loc] Cooper, E., Johnston, A., and P. Matthews, "An ID/Locator ArchitectureDiscovery Usage for P2PSIP", draft-matthews-p2psip-id-loc-01REsource LOcation And Discovery (RELOAD)", draft-ietf-p2psip-service-discovery-01 (work in progress), February 2008. [I-D.pascual-p2psip-clients] Pascual, V., Matuszewski, M., Shim,July 2010. [I-D.ietf-p2psip-sip] Jennings, C., Lowekamp, B., Rescorla, E., Zhang, H., and S. Yongchao, "P2PSIP Clients", draft-pascual-p2psip-clients-01 (work in progress), February 2008. [I-D.zheng-p2psip-client-protocol] Yongchao,Baset, S., Jiang, X., Zhang, H.,and H. Deng, "P2PSIP Client Protocol", draft-zheng-p2psip-client-protocol-01Schulzrinne, "A SIP Usage for RELOAD", draft-ietf-p2psip-sip-05 (work in progress), February 2008.July 2010. [RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, "Dynamic Updates in the Domain Name System (DNS UPDATE)", RFC 2136, April 1997. [RFC3424] Daigle, L.[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and IAB, "IAB Considerations for UNilateral Self-Address Fixing (UNSAF) Across Network Address Translation",E. Schooler, "SIP: Session Initiation Protocol", RFC 3424, November3261, June 2002. [RFC4485][RFC3263] Rosenberg, J. and H. Schulzrinne, "Guidelines for Authors of Extensions to the Session"Session Initiation Protocol (SIP)",(SIP): Locating SIP Servers", RFC 3263, June 2002. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 4485, May 2006.3986, January 2005. [RFC4795] Aboba, B., Thaler, D., and L. Esibov, "Link-local Multicast Name Resolution (LLMNR)", RFC 4795, January 2007. [Using-an-External-DHT] Singh, K.[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols", RFC 5245, April 2010. [RFC5766] Mahy, R., Matthews, P., and H. Schulzrinne, "Using an External DHT as a SIP Location Service", Columbia University Computer Science Dept. Tech Report 388). Copy available at http://mice.cs.columbia.edu/ getTechreport.php?techreportID=388/J. Rosenberg, "Traversal Using Relays around NAT (TURN): Relay Extensions to Session Traversal Utilities for NAT (STUN)", RFC 5766, April 2010. Authors' Addresses David A. Bryan SIPeerior Technologies 3000 Easter CircleCogent Force, LLC Williamsburg, Virginia 23188USA Phone: +1 757 565 0101571 314 0256 Email: firstname.lastname@example.org@ethernot.org Philip Matthews UnaffiliatedAlcatel-Lucent 600 March Road Ottawa, Ontario K2K 2E6 Canada Phone: +1 613 592 4343 x224784 3139 Email: email@example.com Eunsoo Shim Locus Telecommunications 111 Sylvan Avenue Englewood Cliffs,Avaya, Inc. 233 Mt. Airy Road Basking Ridge, New Jersey 0763207920 USA Phone: unlistedEmail: firstname.lastname@example.org Dean Willis Softarmor Systems 3100 Independence Pkwy #311-164 Plano, Texas 75075 USA Phone: unlisted+1 214 504 1987 Email: email@example.com Spencer Dawkins Huawei Technologies (USA) Phone: +1 214 755 3870 Email: firstname.lastname@example.org Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at email@example.com.