JXTA v1.0 Protocols Specification From: http://www.ietf.org/internet-drafts/draft-duigou-jxta-protocols-00.txt --------------------------------------------------------------------------- not assigned M. Duigou Internet-Draft Project JXTA Expires: December 20, 2002 June 21, 2002 JXTA v1.0 Protocols Specification draft-duigou-jxta-protocols-00 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 except that the right to produce derivative works is not granted. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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 December 20, 2002. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract The JXTA protocols defines a suite of six XML-based protocols that standardize the manner in which peers self-organize into peergroups, publish and discover peer resources, communicate, and monitor each other. The Endpoint Routing Protocol (ERP) is the protocol by which a peer can discover a route (sequence of hops) to send a message to another peer potentially traversing firewalls and NATs. The Rendezvous Protocol (RVP) is used for propagating a message within a peergroup. The Peer Resolver Protocol (PRP) is the protocol used to send a generic query to one or more peers, and receive a response (or multiple responses) to the query. The Peer Discovery Protocol (PDP) is used to publish and discover resource advertisements. The Peer Duigou & Project JXTA Expires December 20, 2002 [Page 1] Internet-Draft JXTA v1.0 Protocols Specification June 2002 Information Protocol (PIP) is the protocol by a which a peer may obtain status information about another peers. The Pipe Binding Protocol (PBP) is the protocol by which a peer can establish a virtual communication channel or pipe between one or more peers. The JXTA protocols permit the establishment a virtual network overlay on top of physical networks allowing peers to directly interact and organize independently of their network location and connectivity. The JXTA protocols have been designed to be easily implemented on unidirectional links and asymmetric transports. Production Notes First Internet-Draft submission. This draft has been generated from a DocBook XML file which was transformed into an RFC 2629 XML source file. This draft does not include the tables from the original XML source as table conversion was not implemented by the IETF 54 submission deadline. To review the tables please access the XML source or HTML and PDF output versions source at http://spec.jxta.org Duigou & Project JXTA Expires December 20, 2002 [Page 2] Internet-Draft JXTA v1.0 Protocols Specification June 2002 1. Introduction 1.1 The JXTA Protocols The JXTA protocols are a set of six protocols that have been specifically designed for ad hoc, pervasive, and multi-hop peer-to- peer (P2P) network computing. Using the JXTA protocols, peers can cooperate to form self-organized and self-configured peer groups independent of their positions in the network (edges, firewalls, network address translators, public vs. private address spaces), and without the need of a centralized management infrastructure. The design of the JXTA protocols seeks to create a set of protocols that have very low overhead, make few assumptions about the underlying network transport and impose few requirements on the peer environment, and yet are able to be used to deploy a wide variety of P2P applications and services in a highly unreliable and changing network environment. Peers use the JXTA protocols to advertise their resources and to discover network resources (services, pipes, etc.) available from other peers. Peers form and join peergroups to create special relationships. Peers cooperate to route messages allowing for full peer connectivity. The JXTA protocols allow peers to communicate without the need to understand or manage the potentially complex and dynamic network topologies which are increasingly common. The JXTA protocols allow peers to dynamically route messages across multiple network hops to any destination in the network (potentially traversing firewalls). Each message carries with it either a complete or partial ordered list of gateway peers through which the message might be routed. If the routing information is incorrect, the intermediate peer can assist in dynamically finding a new route. The JXTA protocols are composed of six protocols that work together to allow the discovery, organization, monitoring and communication between peers: o Peer Resolver Protocol (Section 3.4.1) (PRP) is the mechanism by which a peer can send a query to one or more peers, and receive a response (or multiple responses) to the query. The PRP implements a query/response protocol. The response message is matched to the query via a unique id included in the message body. When a peer is discovered via PDP, a query can be sent to that peer. o Peer Discovery Protocol (Section 4.2.1) (PDP) is the mechanism by which a peer can advertise its own resources, and discover the resources from other peers (peer groups, services, pipes and Duigou & Project JXTA Expires December 20, 2002 [Page 3] Internet-Draft JXTA v1.0 Protocols Specification June 2002 additional peers). Every peer resource is described and published using an advertisement. Advertisements are programming language- neutral metadata structures that describe network resources. Advertisements are represented as XML documents. o Peer Information Protocol (Section 4.2.3) (PIP) is the mechanism by a which a peer may obtain status information about other peers, such as state, uptime, traffic load, capabilities, etc. o Pipe Binding Protocol (Section 4.2.4) (PBP) is the mechanism by which a peer can establish a virtual communication channel or pipe between one or more peers. The PBP is used by a peer to bind two or more ends of the connection (pipe endpoints). Pipes provide the foundation communication mechanism between peers. o Endpoint Routing Protocol (Section 3.4.2) (ERP) is the mechanism by which a peer can discover a route (sequence of hops) used to send a message to another peer. If a peer A wants to send a message to peer C, and there is no direct route between A and C, then peer A needs to find the intermediary peer(s) to route the message to C. ERP is used to determine the route information. When the network topology has changed such that the route to C can no longer be used, because a link along the route no longer works, the peer can use ERP to find any routes other peers know to construct a route to C. o Rendezvous Protocol (Section 4.2.2) (RVP) is the mechanism by which peers can subscribe or be a subscriber to a propagation service. Within a PeerGroup, peers can be rendezvous peers, or peers that are listening to rendezvous peers. The Rendezvous Protocol allows a peer to send messages to all the listening instances of the service. The RVP is used by the Peer Resolver Protocol and by the Pipe Binding Protocol in order to propagate messages. All of these protocols are implemented using a common messaging layer. This messaging layer is what binds the JXTA protocols to various network transports. (see Messages (Section 3.6)) Each of the JXTA protocols is independent of the others, and a peer is not required to implement all six protocols. A peer only implements the protocols that it needs to use. For example, a device may have all the advertisements it uses pre-stored in memory, so that peer does not need to implement the Peer Discovery Protocol. A peer may use a pre-configured set of peer routers to route all its messages, hence the peer does not need to implement the Endpoint Routing Protocol. It just sends messages to the routers to be forwarded. A peer may not need to obtain or wish to provide status Duigou & Project JXTA Expires December 20, 2002 [Page 4] Internet-Draft JXTA v1.0 Protocols Specification June 2002 information to other peers, hence the peer might not implement the Peer Information Protocol. The same can be said about all of the other protocols. --------------------------------------------------------------------- +------------------------+ +------------------------+ | +------------------+ | | +------------------+ | | | Peer Information | <-------> | Peer Information | | | +------------------+ | | +------------------+ | | | | | | +------------------+ | | +------------------+ | | | Peer Rendezvous | <-------> | Peer Rendezvous | | | +------------------+ | | +------------------+ | | | | | | +------------------+ | | +------------------+ | | | Pipe Binding | <-------> | Pipe Binding | | | +------------------+ | | +------------------+ | | | | | | +------------------+ | | +------------------+ | | | Peer Discovery | <-------> | Peer Discovery | | | +------------------+ | | +------------------+ | |Peer | |Peer | +------------------------+ +------------------------+ +------------------------+ +------------------------+ | +------------------+ | | +------------------+ | | | Peer Resolver | <-------> | Peer Resolver | | | +------------------+ | | +------------------+ | | | | | | +------------------+ | | +------------------+ | | | Endpoint Routing | <-------> | Endpoint Routing | | | +------------------+ | | +------------------+ | |Endpoint | |Endpoint | +------------------------+ +------------------------+ +------------------------+ +------------------------+ | Transport | | Transport | +------------------------+ +------------------------+ Figure 1: JXTA Protocols --------------------------------------------------------------------- The JXTA protocols do not require periodic messages of any kind at any level to be sent within the network. For example, JXTA does not require periodic polling, link status sensing, or neighbor detection Duigou & Project JXTA Expires December 20, 2002 [Page 5] Internet-Draft JXTA v1.0 Protocols Specification June 2002 messages, and does not rely on these functions from any underlying network transport in the network. This entirely on-demand behavior of the JXTA protocols and lack of periodic activity allows the number of overhead messages caused by JXTA to scale all the way down to zero, when all peers are stationary with respect to each other and all routes needed for current communication have already been discovered. A peer may decide to cache advertisements discovered via the Peer Discovery Protocol for later usage. It is important to point out that caching is not required by the JXTA architecture, but caching can be an important optimization. The caching of advertisements by a peers avoids performing a new discovery each time the peer is accessing a network resource. In highly-transient environment, performing the discovery is the only viable solution. In static environment, caching is more efficient. A unique characteristic of P2P networks, like JXTA, is their ability to spontaneously replicate information toward end-users. Popular advertisements are likely to be replicated more often, making them easier to find as more copies become available. Peers do not have to return to the same peer to obtain the advertisements they are interested in. Instead of querying the original source of an advertisement, peers may query neighboring peers that have already cached the information. Each peer may potentially become an advertisement provider to any other peer. The JXTA protocols have been designed to allow JXTA to be easily implemented on uni-directional links and asymmetric transports. In particular, many forms of wireless networking do not provide equal capability for devices to send and receive. JXTA permits any uni- directional link to be used when necessary, improving overall performance and network connectivity in the system. The intent is for the JXTA protocols to be as pervasive as possible, and easy to implement on any transport. Implementations on reliable and bi- directional transports such as TCP/IP or HTTP should lead to efficient bi-directional communications. The JXTA uni-directional and asymmetric transport also plays well in multi-hop network environments where the message latency may be difficult to predict. Furthermore, peers in a P2P network tend to have nondeterministic behaviours. They may join or leave the network on a very frequent basis. 1.2 JXTA Assumptions This section is a guide to the assumptions that inform the design of JXTA. There are two types of assumptions stated here, those which Duigou & Project JXTA Expires December 20, 2002 [Page 6] Internet-Draft JXTA v1.0 Protocols Specification June 2002 describe the requirements of JXTA implementations and those which describe the expected behavior of the JXTA network. The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL in this document are to be interpreted as described in "IETF RFC 2119" [bib- RFC2119 [2]]. A peer SHALL NOT make assumptions about the runtime environments or programming languages in use by another peer. The network of peers reachable by any peer is likely to be contain many peers with very heterogeneous implementations and capabilities. A peer SHOULD assume that the capabilities and complexity of the network peers supporting these protocols can range from a single light switch to a highly-available supercomputer cluster. A peer MUST implement the JXTA protocols such that all interaction with other peers is correct and conformant. A peer MAY implement only the JXTA protocols it requires for correct and conformant interaction with other peers. A peer MAY choose to partially implement protocols if unimplemented portions will never be used. (e.g. client-side or server-side only) Peers wishing to interact with other peers within the JXTA network SHOULD be willing to participate fully in the protocols. In particular, peers SHOULD cache advertisements and forward messages for other peers in the JXTA network. But, this participation is OPTIONAL. The JXTA protocols MAY be deployed over a wide variety of network configurations including the Internet, corporate intranets, a dynamic proximity network, or in a home networking environment. Applications should avoid assumptions about the underlying network environment. Peers receiving a corrupted or detectably compromised message MUST discard the message. Messages may be corrupted or intentionally altered during network transmission. Peers MAY appear, disappear and migrate at any time without notice. In particular, the JXTA protocols support very arbitrary environment changes allowing a peer to dynamically discover and reconnect to its changing environment. Communication ability between any pair of peers MAY at times not work equally well in both directions. That is, communications between two Duigou & Project JXTA Expires December 20, 2002 [Page 7] Internet-Draft JXTA v1.0 Protocols Specification June 2002 peers will in many cases be able to operate bi-directionally, but at times the connection between two peers may be only uni-directional, allowing one peer to successfully send messages to the other while no communication is possible in the reverse direction. The JXTA protocols MAY take advantage of additional optimizations, such as the easy ability to reverse a source route to obtain a route back to the origin of the original route. The JXTA protocols are defined as idempotent protocol exchanges. The same messages MAY be sent/received more than once during the course of a protocol exchange. No protocol states are required to be maintained at both ends. Due to unpredictability of P2P networks, assumptions MUST NOT be made about the time required for a message to reach a destination peer. The JXTA Core Protocols (Section 3.4) MUST NOT impose any timing requirements for message receipt. The JXTA Transport Protocols (see Core JXTA Transport Bindings (Section 3.5) and Standard JXTA Transport Bindings (Section 4.3)) MUST NOT impose any timing requirements on the JXTA Core Protocols (Section 3.4) but MAY have timing requirements internal to themselves. The Standard Protocols (Section 4.2) (e.g. Peer Discovery Protocol (Section 4.2.1), Peer Information Protocol (Section 4.2.3), Peer Discovery Protocol (Section 4.2.4), etc. ) and application defined protocols MAY impose timing requirements on message delivery and receipt. A JXTA protocol message which is routed through multiple hops SHOULD NOT be assumed to reliably delivered, even if only reliable transports such as TCP/IP are used through all hops. A congested peer MAY drop messages at any time rather than routing them. Message encodings for network transports MUST allow for the transmission of arbitrary numbers of message sections containing an arbitrary amount of data. While the JXTA protocol messages and advertisements are defined using XML messages, an XML parser is OPTIONAL. Small JXTA implementations MAY choose to use pre-built XML or XML templates for message and advertisement construction. The diameter of a multi-hops network is the minimum number of hops necessary for a message to reach from any peers located at one extreme edge of the network to another peer located at the opposite Duigou & Project JXTA Expires December 20, 2002 [Page 8] Internet-Draft JXTA v1.0 Protocols Specification June 2002 extreme. Empirical measurements on P2P networks such as Gnutella or Freenet shows this diameter to be around 5-7 hops. The JXTA protocols MUST NOT require a broadcast or multicast capability of the underlying network transport. Messages intended for receipt by multiple peers (propagation) MAY be implemented using point-to-point communications. A peer SHOULD make the assumption that if a destination address is not available at any time during the message transmission, the message will not be delivered. Each peer MUST be a member of the World Peergroup and Net Peergroups. Membership in these groups is automatic. Peers MUST be members of the same peer group in order to exchange messages. A peer MUST NOT assume that there is a guaranteed return route to a peer from which it has received communication. The lack of a return route may either be temporary or permanent. A peer MAY be assigned a unique string as a name. Any naming scheme can be used. Names are not unique unless a coordinated Naming service is used to guarantee name uniqueness. A Naming service is typically a service that guarantees, within a given scope, the uniqueness of name and can be used to register name mapping. Examples of Name services are DNS and LDAP. A naming service is OPTIONAL. JXTA does not define its own naming service. Once content has been published to the JXTA network, it MUST NOT be assumed that that the content can be later retrieved from the JXTA network. The content may be only available from peers that are not currently reachable or nowhere. Once a content has been published to the JXTA network, it MUST NOT be assumed that the content can be deleted. Republication of content by peers is unrestricted and the content may propagate to peers which are not reachable from the publishing peer. 1.3 Why JXTA? The JXTA Protocols are an open network computing platform designed for peer-to-peer (P2P) computing. The JXTA protocols standardize the manner in which peers: Duigou & Project JXTA Expires December 20, 2002 [Page 9] Internet-Draft JXTA v1.0 Protocols Specification June 2002 o Discover each others o Self-organize into peer groups o Advertise and discover network resources o Communicate with each others o Monitor each other The JXTA protocols DO NOT: o Require the use of any particular computer language or operating system. o Require the use of any particular network transport or topology. o Require the use of any particular authentication, security or encryption model. The JXTA protocols enable developers to build and deploy interoperable services and applications, further spring-boarding the peer to peer revolution on the Internet. JXTA intends to achieves this by providing a simple and generic P2P platform to host all types of network services o JXTA is defined by a small number of protocols. Each protocol is easy to implement and integrate into P2P services and applications. Thus service offerings from one vendor can be used transparently by the user community of another vendor's system. o The JXTA protocols are defined to be independent of programming languages, so that they can be implemented in C/C++, Java, Perl, and numerous other languages. Heterogeneous devices with completely different software stacks can interoperate with the JXTA protocols. o The JXTA protocols are designed to be independent of transport protocols. They can be implemented on top of TCP/IP, HTTP, Bluetooth, HomePNA, and many other protocols. 1.4 The JXTA Three Layer Cake The JXTA Project is divided in three layers. o Platform. This layer encapsulates minimal and essential Duigou & Project JXTA Expires December 20, 2002 [Page 10] Internet-Draft JXTA v1.0 Protocols Specification June 2002 primitives that are common to P2P networking, including peers, peergroups, discovery, communication, monitoring, and associated security primitives. This layer is ideally shared by all P2P devices so that interoperability becomes possible. o Services. This layer includes network services that may not be absolutely necessary for a P2P network to operate but are common or desirable to be available to the P2P environment. Examples of network services, include search and indexing, directory, storage systems, file sharing, distributed file systems, resource aggregation and renting, protocol translation, authentication and PKI services. o Applications. This layer includes P2P instant messaging, entertainment content management and delivery, P2P E-mail systems, distributed auction systems, and many others. Obviously, the boundary between services and applications is not rigid. An application to one customer can be viewed as a service to another customer. Duigou & Project JXTA Expires December 20, 2002 [Page 11] Internet-Draft JXTA v1.0 Protocols Specification June 2002 2. Conceptual Overview JXTA is intended to be a small system with a limited number of concepts at its core. This chapter introduces the concepts which are core to JXTA. 2.1 Peers A peer is any networked device (sensor, phone, PDA, PC, server, supercomputer, etc.) that implements the core JXTA protocols. Each peer operates independently and asynchronously of all other peers. Some peers MAY have more dependencies with other peers due to special relationships (gateways or routers). Peers spontaneously discover each other on the network to form transient or persistent relationships called peer groups. Peergroups are a collection of peers that have some common interests. Peergroups MAY also be statically predefined. Peers that provide the same set of services tend to be inter- changeable. It MAY not matter which peers a peer interact with. Peers MAY publish network resources (CPU, storage, routing) to other peers. A peer MAY cache information, but doing so is OPTIONAL. Peers MAY have persistent storage. Peers typically interact with a small number of other peers (network neighbors or buddy peers). Assumptions MUST NOT be made about peer reliability or connectivity. A peer MAY join or leave the network at any time. Peers MAY provide network services that can be used by other peers. Peers MAY have multiple network interfaces, though a peer does not need to publish all of its interfaces for use with the JXTA protocols. Each published interface is advertised as a peer endpoint. A peer endpoint is a URI that uniquely identify a peer network interface. Peer endpoints are used by peers to establish direct point-to-point connections between two peers. Communicating peers peers may not have direct point-to-point network connection between themselves, either due to lack of physical network connections, or network configuration (NATs, firewalls, proxies, etc.). A peer MAY have to use one or more intermediary peers to Duigou & Project JXTA Expires December 20, 2002 [Page 12] Internet-Draft JXTA v1.0 Protocols Specification June 2002 route a message to another peer. Each peer is uniquely identified by a unique Peer Id. 2.2 Peer Groups Peers self-organize into Peer Groups. A peer group is a collection of peers that have a common set of interests. Each peer group is uniquely identified by a unique PeerGroup Id. The JXTA protocols do not dictate when, where, or why peergroups are created. The JXTA protocols only describe how a peers may publish, discover, join, and monitor peergroups. JXTA recognizes three common motivations for creating peer groups: o To create a secure environment. Peergroup boundaries permit member peers to access and publish protected contents. Peergroups form logical regions whose boundaries limit access to the peergroup resources. A peergroup does not necessarily reflect the underlying physical network boundaries such as those imposed by routers and firewalls. Peergroups virtualize the notion of routers and firewalls, subdividing the network in secure regions without respect to actual physical network boundaries. o To create a scoping environment. Peergroups are typically formed and self-organized based upon the mutual interest of peers. No particular rules are imposed on the way peergroups are formed, but peers with the same interests will tend to join the same peergroups. Peergroups serve to subdivide the network into abstract regions providing an implicit scoping mechanism. Peergroup boundaries define the search scope when searching for a group's content. o To create a monitoring environment. Peergroups permit peers to monitor a set of peers for any special purpose (heartbeat, traffic introspection, accountability, etc.). A peergroup provides a set of services called peergroup services. JXTA defines a core set of peergroup services. The JXTA protocols specify the wire format for these core peergroup services. Additional peergroup services can be developed for delivering specific services. For example, a lookup service could be implemented to find active (running on some peer) and inactive (not yet running) service instances. The core peer group services are: Discovery Service : The Discovery service is used by member peers to search for peergroup resources (peers, peer groups, pipes, and services). Duigou & Project JXTA Expires December 20, 2002 [Page 13] Internet-Draft JXTA v1.0 Protocols Specification June 2002 Membership Service : The membership service is used by the current members to reject or accept a new group membership application. We expect that most peergroups will have at least a membership service, though it may be a "null" authenticator service which imposes no real membership policy. The membership service is used by a member peer to allow a new peer to join a peergroup. In order for a peer to join a peergroup, a peer MAY need to discover at least one member of the peergroup. Peers wishing to join a peer group MAY first have to locate a current member, and then request to join. The application to join is either rejected or accepted by the collective set of current members. The membership service MAY enforce a vote of peers or elect a designated group representative to accept or reject new membership applications. A peer MAY belong to more than one peergroup simultaneously. Access Service : The Access service is used to validate requests made by one peer to another. The peer receiving the request provides the requesting peer credentials and information about the request being made to the Access Service to determine if the access is permitted. Not all actions within the peer group need to be checked with the Access Service. Only those actions that are restricted to a subset of member peers must be checked. Pipe Service : The pipe service is used to manage and create pipe connections between the different peer group members. Resolver Service : The resolver service is used to address queries to services running on peers in the group and collect responses. Monitoring Service : The monitoring service is used to allow one peer to monitor other members of the same peer group. Not all the above services MUST be implemented by a peergroup. Each service MAY implement one or more of the JXTA protocols, the specifications for which are the main content of this document. A service will typically implement one protocol for simplicity and modularity reasons, but some services may not implement any protocols. 2.3 Network Services Peers cooperate and communicate to publish, discover and invoke network services. A peer can publish as many services that it can Duigou & Project JXTA Expires December 20, 2002 [Page 14] Internet-Draft JXTA v1.0 Protocols Specification June 2002 provide. Peers discover network services via the Peer Discovery Protocol. Network Service specifications are beyond the scope of this document. Upcoming standards such as WSDL, ebXML, SOAP, UPnP might be used within a JXTA Network. The JXTA protocols recognize two levels of network services: o Peer Services o PeerGroup Services A peer service is accessible only on the peer that is publishing the service. If that peer happens to fail, then the service also fails. Multiple instances of the service can be run on different peers, but each instance publishes its own advertisement. A peergroup service is composed of a collection of instances (potentially cooperating with each other) of the service running on multiple members of the peergroup. If any one peer fails, the collective peergroup service is not affected, because chances are the service is still available from another peer member. Peergroup services are published as part of the peergroup advertisement. Services can either be pre-installed into a peer or loaded from the network. The process of finding, downloading and installing a service from the network is similar to performing a search on the internet for a web page, retrieving the page, and then installing the required plug-in. In order to actually run a service, a peer may have to locate an implementation suitable for the peer's runtime environment. Multiple implementations of the same service may allow Java peers to use Java code implementations, and native peers to use native code implementations. 2.3.1 Service Invocation Service invocation is outside the scope of JXTA. JXTA is designed to interoperate and be compatible with any Web service standards; WSDL, uPnP, RMI, etc. The JXTA protocols define a generic framework to publish and discover Advertisements that may describe services. Peers publish and discover advertisements via the Peer Discovery Protocol. An advertisement for a service will typically contain all the necessary information to either invoke or instantiate the service being described. The JXTA protocols define Module Advertisements but any other form of service description may be introduced. Duigou & Project JXTA Expires December 20, 2002 [Page 15] Internet-Draft JXTA v1.0 Protocols Specification June 2002 2.3.2 JXTA-Enabled Service JXTA-Enabled services are services that are published by using the ModuleSpecAdvertisement. A module spec advertisement may specify a pipe advertisement that can be used by a peer to create output pipes to invoke the service. ModuleSpec Advertisement may be extended in the future to contain a list of pre-determined messages that can be sent by a peer to interact with the service. A ModuleSpecAdvertisement may also contain references to two other services which can be used as an authenticator for the service and as a local proxy for the service. Each Jxta-enabled service is uniquely identified by its ModuleSpecID. 2.4 Pipes Pipes are virtual communication channels used to send and receive messages between services or applications over endpoints. Pipes provide a network abstraction over the peer endpoint transport. Peer endpoints correspond to the available peer network interfaces that can be used to send and receive data from another peer. Pipes provide the illusion of a virtual in and out mailbox that is independent of any single peer location, and network topology (multi- hops route). Different quality of services can be implemented by a pipe. For example: Uni-directional asynchronous : The endpoint sends a message, no guarantee of delivery is made. Synchronous request-response : The endpoint sends a message, and receives a correlated answer. Bulk transfer : Bulk reliable data transfer of binary data. Streaming : Efficient control-flow data transfer. Secure : Secure reliable data streams. The uni-directional asynchronous pipe is REQUIRED by the JXTA protocols. Other pipe variations may be implemented for use by services and their associated protocols. Pipes connect one or more peer endpoints. At each endpoint software to send or receive, as well as to manage associated pipe message queues or streams, is assumed, but message queues are OPTIONAL. The pipe endpoints are referred to as input pipes (receiver) and output Duigou & Project JXTA Expires December 20, 2002 [Page 16] Internet-Draft JXTA v1.0 Protocols Specification June 2002 pipes (transmitter). Pipe endpoints are dynamically bounded to a peer endpoint at runtime, via the Pipe Binding Protocol (Section 4.2.4). The pipe binding process consists of searching for and connecting the two or more endpoints of a pipe. When a message is sent into an output pipe, the message is sent by the local peer endpoint to the peer endpoint(s) where the associated input pipe is located. The set of peer endpoints currently associated with the input pipes is discovered using the Pipe Binding Protocol (Section 4.2.4). A pipe offers two modes of communication: Point to Point : A point to point pipe connects exactly two pipe endpoints together, an input pipe that receives messages sent from an output pipe. No reply or acknowledgment operation is supported. Additional information in the message payload like a unique id may be required to thread message sequences. The message payload may also contain a pipe advertisement that can be used to open a pipe to reply to the sender (send/response). Propagate Pipe : A propagate pipe connects one output pipe to multiple input pipes together. Messages flow into the input pipes from the output pipe (propagation source). A propagate message is sent to all listening input pipes. This process may create multiple copies of the message to be sent. On TCP/IP, when the propagate scope maps an underlying physical subnet in a 1 to 1 fashion, IP multicast may be used as an implementation for propagate. Propagate can be implemented using point to point communication on transports that do not provide multicast such as HTTP. --------------------------------------------------------------------- Pipe Modes +-------+ (i) = Input Pipe | | (o) = Output Pipe | peer | | | +---+---+ Propagate | | | Pipe |(i)|(o)|-------------+ | | | | +---+---+ | | send | Duigou & Project JXTA Expires December 20, 2002 [Page 17] Internet-Draft JXTA v1.0 Protocols Specification June 2002 | | | | receive | receive V +------+-----+ | +-----+------+ | | (i) |<---------------+ | | (i) | | | peer +-----+ Point to Point | | +-----+ peer | | | (o) | Pipe | | | (o) | | +------+-----+ | | +-----+------+ | | | | send | V +---+---+ | | | |(o)|(i)| | | | +---+---+ | | | peer | | | +-------+ JXTA Pipe Types --------------------------------------------------------------------- Pipes may connect two peers that do not have a direct physical link. One or more intermediary peer endpoints are used to route messages between the two pipe endpoints. 2.5 Messages The information transmitted using pipes and between endpoints is packaged as messages. Messages define an envelope to transfer any kind of data. A message MAY contain an arbitrary number of named sub-sections which can hold any form of data. It is the intent that the JXTA protocols be compliant with W3C XML Protocol standards, so the JXTA protocols can be implemented on XML transports such as SOAP, XML-RPC, etc. The JXTA protocols are specified as a set of XML messages exchanged between peers. Each software platform binding describes how a message is converted to and from a native data structures such as Java objects or "C" structures. The use of XML messages to define protocols allows many different kinds of peers to participate in a protocol. Each peer is free to Duigou & Project JXTA Expires December 20, 2002 [Page 18] Internet-Draft JXTA v1.0 Protocols Specification June 2002 implement the protocol in a manner best suited to its abilities and role. 2.6 Advertisements All network resources, such as peers, peergroups, pipes and services are represented by advertisements. Advertisements are JXTA's language neutral metadata structures for describing resources. The JXTA Core Specification and Standard Services define, among others, the following advertisement types: o Peer Advertisement o PeerGroup Advertisement o ModuleClass Advertisement o ModuleSpec Advertisement o ModuleImpl Advertisement o Pipe Advertisement o Rendezvous Advertisement The complete specification of advertisements is given in the Advertisements (Section 3.3) chapter. The JXTA protocols make heavy reference to these advertisements, so the reader should be familiar with advertisements before moving on to the protocol specification chapters. Advertisements are, by far, the most common document exchanged in the protocol messages. Services or peer implementations can create their own advertisement types, either from scratch or by subtyping the existing types. 2.7 Credentials The need to support different levels of resource access in a dynamic and ad hoc P2P network leads to a role-based trust model in which an individual peer will act under the authority granted to it by another trusted peer to perform a particular task. Peer relationships MAY change quickly and the policies governing access control need to be flexible in allowing or denying access. Four basic security requirements MUST be provided: Confidentiality : guarantees that the contents of the message are not disclosed to unauthorized individuals. Duigou & Project JXTA Expires December 20, 2002 [Page 19] Internet-Draft JXTA v1.0 Protocols Specification June 2002 Authorization : guarantees that the sender is authorized to send a message. Data integrity : guarantees that the message was not modified accidentally or deliberately in transit. Refutability : guarantees the message was transmitted by a properly identified sender and is not a replay of a previously transmitted message. The structure of JXTA messages enables JXTA applications to add abitrary metadata information to messages such as credentials, digests, certificates, public keys, etc. A credential is a token that when presented in a message body is used to identify a sender and can be used to verify that sender's right to send the message to the specified endpoint. The credential is an opaque token that must be presented each time a message is sent. The sending address placed in the message envelope is cross-checked with the sender's identity in the credential. Each credential's implementation is specified as a plug-in configuration, which allows multiple authentication configurations to co-exist on the same network. Message digests guarantee the data integrity of messages. Messages may also be encrypted and signed for confidentiality and refutability. It is the intent of the JXTA protocols to be compatible with widely accepted transport-layer security mechanisms. Some JXTA implementations contain a virtualized TLS implementation that allows it to secure Endpoint to Endpoint communications regardless of the number of hops required to deliver each message. TLS and IPSec could also be used as JXTA transports. However, when used as transports they provide integrity and confidentiality of message transfer only between the two communicating peers. 2.8 IDs Within the JXTA protocols there are a number of entities that need to be uniquely identifiable. These are peers, peergroups, pipes and contents. A JXTA ID uniquely identifies an entity and serves as a canonical means of referring to that entity. URNs are used for the expression of JXTA IDs. Duigou & Project JXTA Expires December 20, 2002 [Page 20] Internet-Draft JXTA v1.0 Protocols Specification June 2002 2.9 Content The JXTA protocols assume that many types of contents may be shared, exchanged, and replicated between peers. A content can be a text file, a structured document (like a PDF or an XML file), a Java .jar or loadable library, code or even an executable process (checkpointed state). No size limitation is assumed. Content is published and shared amongst peer members of a peergroup. Content may only belong to one peergroup. If the same content must be published in two different peergroups, two different contents MUST be created. Each content is uniquely identified by a unique id. All contents make their existence known to other members by publishing a content advertisement. A content instance is a copy of a content. Each content copy may be replicated on different peers in the peergroup. Each copy has the same content id as well as a similar value. Replicating content within a peergroup helps to ensure that each item of content be more readily available. For example, if an item has two instances residing on two different peers, only one of the peers needs to be alive to respond to the content request. The JXTA protocols do not specify how contents are replicated. This decision is left to higher-level content service managers. Duigou & Project JXTA Expires December 20, 2002 [Page 21] Internet-Draft JXTA v1.0 Protocols Specification June 2002 3. JXTA Core Specification 3.1 Introduction JXTA is designed to be a small system with only a few required components and behaviours. The functionality that is required of all implementations is defined by the JXTA Core Specification and is documented in this section. Implementations that wish to be JXTA compliant MUST implement all of the JXTA Core Specification (Section 3). Implementation of the JXTA Core Specification (Section 3) does not guarantee or even necessarily provide interoperability with other JXTA implementations. There are a number of types of components and behaviours which need to be provided by JXTA implementation which are not part of the JXTA Core Specification (Section 3). Existing implementations of these components are described separately in JXTA Standard Services (Section 4) and JXTA Reference Implementations Information (Section 5). In order for a JXTA implementation to be interoperable with other implementations it may be necessary to implement some of the components described there. 3.2 IDs 3.2.1 Introduction The JXTA protocols often need to refer to peers, peer groups, pipes and other JXTA resources. These references are presented in the protocols as JXTA IDs. JXTA IDs are a means for uniquely identifying specific peer groups, peers, pipes, contents and service instances. JXTA IDs provide unambiguous references to the various JXTA entities. There are six types of JXTA entities which have JXTA ID types defined: peergroups, peers, pipes, content, module classes and module specifications. Additional JXTA ID types may be defined in the future. JXTA IDs are normally presented as URNs. URNs are a form of URI that "... are intended to serve as persistent, location-independent, resource identifiers". Like other forms of URI, JXTA IDs are presented as text. See "IETF RFC 2141" [bib-RFC2141 [3]] for more information on URNs. 3.2.2 Format of a JXTA ID URN A JXTA ID is a standard URN in the JXTA ID namespace. JXTA ID URNs are identified by the namespace identifier "jxta". Each JXTA ID URN also contains an ID Format keyword. The ID Format keyword indicates how the ID was created and may also allow JXTA bindings to extract Duigou & Project JXTA Expires December 20, 2002 [Page 22] Internet-Draft JXTA v1.0 Protocols Specification June 2002 additional information from the ID. Two ID formats have been defined which are identified by the "jxta" and "uuid" keywords. It is possible to define additional JXTA ID formats in order to refer to resources both within JXTA and to bridge to other technologies. The following format specifications use the ABNF syntax as defined in "IETF RFC 2234" [bib-RFC2234 [4]]. --------------------------------------------------------------------- ::= "urn:" ":" ::= "jxta" ::= "-" ::= 1 * ::= 1 * ::= | "%" ::= | | | | ::= "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" | "J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" | "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z" ::= "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z" ::= | "A" | "B" | "C" | "D" | "E" | "F" | "a" | "b" | "c" | "d" | "e" | "f" ::= "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ::= "(" | ")" | "+" | "," | "-" | "." | ":" | "=" | "@" | ";" | "$" | "_" | "!" | "*" | "'" ::= "%" | "/" | "?" | "#" Duigou & Project JXTA Expires December 20, 2002 [Page 23] Internet-Draft JXTA v1.0 Protocols Specification June 2002 Figure 3: JXTA ID ABNF --------------------------------------------------------------------- The jxta URN namespace does not currently define any special symbols from the "reserved" set. 3.2.3 Using JXTA IDs in Protocols When JXTA IDs are used within protocols they are manipulated as text string URIs. There are three operations available for URIs; compare, resolve, decompose. JXTA ID URIs may be compared for equality as strings. JXTA ID URIs can also be resolved to the resource they reference. Finally, JXTA ID URIs can be decomposed and interpreted by JXTA bindings. In order to interpret a JXTA ID, a JXTA binding must support the ID Format used by that JXTA ID. For many JXTA protocols and operations it is not necessary to decompose the JXTA IDs. 3.2.4 Example JXTA ID URNs The following examples demonstrate valid JXTA ID presentation forms. These examples are not necessarily valid JXTA IDs. --------------------------------------------------------------------- A. urn:jxta:idform-1234567890 B. URN:jxta:idform-1234567890 C. urn:JXTA:idform-1234567890 D. urn:JXTA:IDForm-1234567890 E. urn:jxta:idform2-ABCDEFG F. urn:jxta:idform3-31:08:66:42:67:::91:24::73 Figure 4: Sample JXTA IDs --------------------------------------------------------------------- In the preceding examples, A., B. and C. represent the same JXTA ID. Both the "URN" portion and the "JXTA" are case insensitive. Example D. is not equivalent to any of A., B. or C. because the data portion of the URN is case sensitive. In the six examples, four different JXTA ID Formats are used: "idform", "IDForm", "idform2" and "idform3". Definition of ID Format names that differ only in character case is NOT RECCOMENDED. The interpretation of the characters following the "-" is specific to each ID Format. Duigou & Project JXTA Expires December 20, 2002 [Page 24] Internet-Draft JXTA v1.0 Protocols Specification June 2002 3.2.5 JXTA ID Properties Every JXTA ID, regardless of format or type has the following properties: o Unambiguous. It MUST be a complete reference to the resource. o Relatively Unique. It MUST refer to a single resource. o Canonical. References to the same resource SHOULD encode to the same JXTA ID. This enables IDs to be compared to determine if they refer to the same resource, but understandably may not be achievable by all ID Formats. o Opacity. In their URN presentation JXTA IDs SHOULD be assumed to be opaque. The context of an ID within a protocol message generally is sufficient to establish its type. A JXTA binding may be able to interpret an ID if it supports the ID Format. Generally, only the immediate participants in a JXTA protocol need to understand the contents of a JXTA ID, if at all. 3.2.6 JXTA ID Formats JXTA IDs are designed to support multiple ID Formats. ID Formats allow JXTA developers to utilize existing naming and ID schemes within JXTA. In the JXTA ID presentation, the ID's "Format" follows the JXTA URN namespace. Any JXTA ID Format which follows the general requirements for URNs and the JXTA ID Properties will be usable by conformant JXTA implementations. 3.2.7 JXTA ID Types JXTA IDs may refer to many types of resources; pipes, peers, etc. Each JXTA ID format type may support references to one or more of these resource types. Currently, five standard resource types have been identified; peer groups, peers, pipes, content and service instances. Other types may be defined. Each of the individual ID Types MAY provide additional requirements specific to its type. 3.2.7.1 Peer Group IDs Peer Group IDs refer to peer groups. A peer group ID should canonically, uniquely and unambiguously refer to a peer group. Every ID Format MUST support this ID Type because all of the other ID Types refer to the peer group to which they belong. Every ID Format MUST Duigou & Project JXTA Expires December 20, 2002 [Page 25] Internet-Draft JXTA v1.0 Protocols Specification June 2002 support encoding of the World Peer Group. Support for other peer groups is OPTIONAL. Example: You are defining an ID Format for Peer IDs based upon driver's license number. Driver's licenses are not organized into groups. This can be considered equivalent to all driver's licenses belonging to the same group, the global "world peer group". 3.2.7.2 Peer IDs Peer IDs refer to peers. A Peer ID should canonically, uniquely and unambiguously refer to a peer. Support for this ID Type is OPTIONAL. If a JXTA binding recognizes the ID Format, it should be able to extract a Peer Group ID from a Peer ID. This Peer Group ID identifies the peer group of which the peer is a member. 3.2.7.3 Codat IDs Codat IDs refer to codats. A Codat ID should canonically, uniquely and unambiguously refer to a codat. Support for this ID Type is OPTIONAL. If a JXTA binding recognizes the ID Format, it should be able to extract a Peer Group ID from a Codat ID. This Peer Group ID identifies the peer group to which the codat belongs. 3.2.7.4 Pipe IDs Pipe IDs refer to pipes. A Pipe ID should canonically, uniquely and unambiguously refer to a pipe. Support for this ID Type is OPTIONAL. If a JXTA binding recognizes the ID Format, it should be able to extract a Peer Group ID from a Pipe ID. This Peer Group ID identifies the peer group to which the pipe belongs. 3.2.7.5 Module Class IDs A Module Class ID identifies a particular local behavior, that is, a specific API for each execution environment for which an implementation exists. A Module Class ID SHOULD canonically, uniquely and unambiguously refer to a module class as defined by an advertisement. Support for this ID Type is OPTIONAL. If a JXTA binding recognizes the ID Type, it should be able to extract a Base Class ID from a Module Class ID. The Base Class ID allows applications to determine if two Module Class IDs differ only in the "role" they perform. Module Spec ID's "roles" allow for the same module to be reused within a group and have instances distinguished. This is necessary when, for example, a common database service is used, with each "role" accessing a different data set. Duigou & Project JXTA Expires December 20, 2002 [Page 26] Internet-Draft JXTA v1.0 Protocols Specification June 2002 3.2.7.6 Module Spec IDs A ModuleSpecID uniquely identifies a particular network behavior (wire protocol and choreography) that may be embodied by a Jxta Module. There may be any number of implementations of a given Module Spec ID. A ModuleSpecID uniquely identifies an abstract module for which there may be multiple platform specific implementations. A ModuleSpecID is used to locate a compatible implementation such that it can be instantiated. All such implementations are assumed to be network compatible. A Module Spec ID SHOULD canonically, uniquely and unambiguously refer to a module specification. Support for this ID Type is OPTIONAL. If a JXTA binding recognizes the ID Type, it should be able to extract a Module Class ID from a Module Spec ID. 3.2.8 JXTA ID Formats : jxta ID Format The "jxta" ID Format is a REQUIRED ID Format that is used for encoding "well known" JXTA identifiers. All JXTA binding implementations MUST support this ID Format. There are three special reserved JXTA IDs; the Null ID, the World Peer Group ID and the Net Peer Group ID. The "jxta" ID Format exists so that for these few "well known" IDs only a single representation exists. --------------------------------------------------------------------- ::= "urn:" ":" "-" ::= "jxta" ::= | | ::= "Null" ::= "WorldGroup" ::= "NetGroup" Figure 5: JXTA ID : "jxta" ID Format ABNF --------------------------------------------------------------------- 3.3 Advertisements Duigou & Project JXTA Expires December 20, 2002 [Page 27] Internet-Draft JXTA v1.0 Protocols Specification June 2002 3.3.1 Introduction Advertisements are meta-data documents used by JXTA protocols to describe resources. Advertisements are used to describe peers, peer groups, pipes, content, services and many other types of resources. JXTA Advertisements are presented in XML. Many of the JXTA protocols depend on Advertisements to provide necessary information. JXTA protocols are used to pass Advertisements between peers. Services can define new Advertisement types by sub-typing existing Advertisement types or by defining completely new Advertisements. Advertisement sub-types allow for additional information to be provided as well as richer meta-data. Advertisements are composed of a series of hierarchically arranged elements. The elements may appear in any order within the advertisement. Each element can contain its data or additional elements. An element can also have attributes. Attributes are name- value string pairs. An attribute is used to store meta-data, which helps to describe the data within the element. The Core JXTA Protocols rely on the following advertisements: o Peer Advertisement (Section 3.3.3) o Peer Group Advertisement (Section 3.3.4) o Module Class Advertisement (Section 3.3.5) o Module Specification Advertisement (Section 3.3.6) o Module Implementation Advertisement (Section 3.3.7) 3.3.2 XML and JXTA Advertisements All JXTA advertisements are represented in XML. XML provides a powerful means of representing data and metadata throughout a distributed system. XML provides a universal (software-platform neutral) representation: o XML is programming language agnostic o XML is self-describing o XML content can be strongly-typed o XML ensures correct syntax Duigou & Project JXTA Expires December 20, 2002 [Page 28] Internet-Draft JXTA v1.0 Protocols Specification June 2002 These advantages allow peers to manage and use Advertisements safely and to be able to ensure correct interactions with other peers. The Advertisements defined by the JXTA Core Specification and the JXTA Standard Services are specified using the XML Schema Definition Language [bib-XSD2001-1 [6]][bib-XSD2001-2 [7]]. Use of XML Schemas allows the advertisement contents to be strongly type-checked and semanticly validated beyond the syntactical validation provided by XML with DTDs. Service and protocol authors are RECOMMENDED to specify their Advertisements or Advertisement sub-types using XML Schema Language. DTDs are normally prepared from the schema descriptions for use in environments which do not support XML schema. The other powerful feature of XML is its ability to be translated into other encodings such as HTML and WML. This feature allows peers that do not support XML to access advertised resources. --------------------------------------------------------------------- Figure 6: Common Advertisement Fragments Schemas --------------------------------------------------------------------- Duigou & Project JXTA Expires December 20, 2002 [Page 29] Internet-Draft JXTA v1.0 Protocols Specification June 2002 3.3.3 Peer Advertisement A Peer Advertisement describes a peer and the resources it provides to the group. The Peer Advertisement holds specific information about the peer such as its name, its unique id, its group id and descriptive information. It may also contain endpoint addresses and any run-time attributes that individual peer services want to publish (such as being a rendezvous peer for a group). --------------------------------------------------------------------- Figure 7: Peer Advertisement Schema --------------------------------------------------------------------- : This is a required element that uniquely identifies the peer. Each peer has a unique id. The peer id representation is given in the Id Chapter. : This element provides the Peer Group ID. This identifies canonically which Peer Group this peer belongs to.ftp : This is an optional string that can be associated with a peer. The name is not required to be unique unless the name is obtained from a centralized naming service that guarantees name uniqueness. : This is an optional string that can be used to index and search for a peer. The string is not guaranteed to be unique. Two peers may have the same keywords. The keywords string may contain spaces. : Any number of such elements may exist. Each of them describes the association between a group service denoted by its Class ID (the value of an MCID element), and arbitrary parameters Duigou & Project JXTA Expires December 20, 2002 [Page 30] Internet-Draft JXTA v1.0 Protocols Specification June 2002 encapsulated in a Parm element. For example, all accessible endpoint addresses are published in association with the Endpoint Service Class ID. The TLS Root certificate is published under the PeerGroup Class ID (There is a class ID for Peer Group as well). The flag that denotes that this peer is a rendezvous for this group is published under the Rendezvous Service Class ID. Ultimately, each service is responsible for what is published under its Class ID. The Service section may also optionally contain an element "isOff" meaning that this service is disabled. This element is used to convey a configuration choice made by the owner of the peer. 3.3.4 Peer Group Advertisement A Peer Group Advertisement describes peergroup specific resources: name, group id, description, specification, and service parameters. --------------------------------------------------------------------- Figure 8: Peer Group Advertisement Schema --------------------------------------------------------------------- : This element provides the Peer Group ID. The Peer Group ID is the canonical way of refering to a group and uniquely identifies the peer group. See Peer Group IDs (Section 3.2.7.1) for more information on peer group ids. : Peer group Specification ID. This designates the module that provides the peer group mechanism itself for that group. The spec ID designates an abstraction of that mechanism. This abstraction is optionally described by a ModuleSpecAdvertisement, and any number of implementations may exist, each described by a ModuleImplAdvertisement. These advertisements may all be searched Duigou & Project JXTA Expires December 20, 2002 [Page 31] Internet-Draft JXTA v1.0 Protocols Specification June 2002 by this SpecID. : This is an optional name that can be associated with a peergroup. The name is not required to be unique unless the name is obtained from a centralized naming service that guarantee name uniqueness. : This is an optional element provides descriptive information that may be used to index and search for a peergroup. The content of this element may not be unique. For example, two peergroups may have the same keywords. : Any number of such elements may exist. Each of them describes the association between a group service denoted by its Class ID (the value of an MCID element), and arbitrary parameters encapsulated in a Parm element. This optional parameter may only be meaningful to some services. It is used to configure a service specifically in relation with its use by this group. For example, a simple membership service may find an encrypted password list there. 3.3.5 Module Class Advertisement A Module Class Advertisement describes a class of modules. That is, an expected local behavior and and expected API for each JXTA binding (that supports such modules). The purpose of this advertisement is to provide a description of what a particular Module Class ID stands for. A Module Class ID is what other modules or other code running on JXTA uses to designate modules which it depends upon. The ModuleClassAdvertisement is not required to provide a completely formal description of the module's behavior and API. It is intended for humans who want to create modules with a similar functionality. It is not required to publish a Module Class Advertisement for a Module Class ID to be valid, although it is a good practice. Duigou & Project JXTA Expires December 20, 2002 [Page 32] Internet-Draft JXTA v1.0 Protocols Specification June 2002 --------------------------------------------------------------------- Figure 9: Module Class Advertisement Schema --------------------------------------------------------------------- : Module Class ID. This is a required element that uniquely identifies the class. Each module class has a unique id. The class id representation is given in the Id Chapter. : This is an optional name that can be associated with a class. The name is not required to be unique unless the name is obtained from a centralized naming service that guarantee name uniqueness. : Description. This is an optional string that can be used to describe and search for a class. 3.3.6 Module Specification Advertisement A Module Specification Advertisement describes the specification of a module. That is, an expected on-wire behavior and protocol. The purpose of this advertisement is to provide a description of what a particular Module Specification ID stands for. A Module Specification ID is what other modules or other code running on JXTA uses to designate a particular network-compatible family of implementations of a given class. It is more importantly how a group implementation may designate the components which provide the various services that this group supports. All the built-in core peergroup services (discovery, membership, resolver,...) are modules. It is not required to publish a Module Spec Advertisement for a Module Spec ID to be valid, although it is a good practice. A Module Spec Advertisement may also describe how to invoke and use a module. A Module may be used through its API, by locating an Duigou & Project JXTA Expires December 20, 2002 [Page 33] Internet-Draft JXTA v1.0 Protocols Specification June 2002 implementation, loading it and starting it, or a module may be usable through a pipe or through a proxy module. Modules which permit this include one or both of a Pipe Advertisement or the Module Spec ID of a proxy module, in their ModuleSpecID. Publication of the Module Spec Advertisement is of course required in that case. A Module Specification Advertisement is not required to provide a completely formal description of the module's network behavior or protocol, it is intended for humans who want to create compatible implementation of that specification. --------------------------------------------------------------------- Figure 10: Module Specification Advertisement Schema --------------------------------------------------------------------- : ModuleSpecID. This is a required element that uniquely identifies the specification. Each module specification has a unique id. The spec id representation is given in the Id Chapter. : The mandatory version of the specification that this advertises. : This is an optional name that can be associated with a spec. The name is not required to be unique unless the name is obtained from a centralized naming service that guarantee name uniqueness. : Description. This is an optional string that can be used Duigou & Project JXTA Expires December 20, 2002 [Page 34] Internet-Draft JXTA v1.0 Protocols Specification June 2002 to describe and search for a spec. : Creator. This optional element designates the creator of this specification. : Spec URI. This optional element is a URI that permits to retrieve a document containing the specification that this advertises. : Arbitrary parameters to be interpreted by each implementation. : Pipe advertisement. A pipe advertisement which this module binds to an input pipe and which thus may be used to establish a pipe to a nearby running implementation of this specification. Note that the element name is identical to the Pipe Advertisement document type since the entire element is an embedded pipe advertisement document. : Proxy Spec ID. Optional ModuleSpecID of a proxy module that may be used in order to communicate with modules of this specification. Note that the process may be recursive. The proxy module may be usable via pipes, or through a subsequent proxy module, and itself require a subsequent authenticator. However publishers of modules should probably avoid such designs. : Authenticator Spec ID. Optional ModuleSpecID of an authenticator module that may be required in order to communicate with modules of this specification. Note that the process may be recursive. The authenticator module may be usable via pipes, or through a subsequent proxy module, and itself require a subsequent authenticator. However publishers of modules should probably avoid such designs. 3.3.7 Module Implementation Advertisement A Module Implementation Advertisement describes one of the implementations of a module specification. Implementations of a given specification may be searched by the SpecID. An implementation may be selected by the type of environment in which it can be used (its compatibility statement) as well as by its name, description or the content of its parameters section. A Module Implementation Advertisement also provides a means to retrieve all the necessary data required in order to execute the implementation being described. This information is encapsulated in the Code and PURI elements. The interpretation of these elements are Duigou & Project JXTA Expires December 20, 2002 [Page 35] Internet-Draft JXTA v1.0 Protocols Specification June 2002 subject to the the module's compatibility. For example, the standard peer group implementation of the Java reference implementation expects the element to specify a fully qualified Java class name that designates a subclass of "net.jxta.platform.Module" and PURI to be the URI of a downloadable package (a .jar file). Other execution environments could expect the code to be inline within the element or even offer several options. --------------------------------------------------------------------- Figure 11: Module Implementation Advertisement Schema --------------------------------------------------------------------- : ModuleSpecID. This is a required element that uniquely identifies the specification being implemented. The SpecID representation is given in the Id Chapter. : Compatibility. A mandatory arbitrary element that describes the environment in with this implementation may be executed. Each framework capable of loading and executing module has its own requirement on the contents of this element. : This arbitrary element contains anything that is needed in addition to the package in order to load and execute the code of this implementation. In the case of a java implementation it contains the fully qualified class name containing the module's entry points. In other cases it may contain the entire code. : Package URI. This optional element is a URI that permits to retrieve a package containing the code of this implementation. : Provider. The provider of that implementation. Duigou & Project JXTA Expires December 20, 2002 [Page 36] Internet-Draft JXTA v1.0 Protocols Specification June 2002 : Description. This is an optional string that can be used to describe and search for a spec. : Parameter. Arbitrary parameters to be interpreted by the implementation's code. 3.4 JXTA Core Protocols 3.4.1 Peer Resolver Protocol 3.4.1.1 Introduction The Peer Resolver Protocol (PRP) permits the dissemination of generic queries to one or multiple handlers within a peer group and identigy matching responses. Each query is addressed to a specific handler name. This handler name defines the particular semantics of the query and its responses, but is not associated with any specific peer. A given query MAY be received by any number of peers in the peer group, possibly all, and processed according to the handler name if such a handler name is defined on that peer. The intent is for PRP to provide the essential generic query/response infrastructure for building high-level resolver services. In many situation, a higher level service may have a better knowledge of the group topology. The PRP uses the Rendezvous Service to disseminate a query to multiple peers or unicast messages to send queries to specified peers. 3.4.1.2 Resolver Query Message The resolver query message is used to send a resolver query to the named handler on one or more peers that are members of the peer group. The resolver query is sent as a query string to a specific handler. Each query has a unique Id. The query string can be any string that will be interpreted by the targeted handler. Duigou & Project JXTA Expires December 20, 2002 [Page 37] Internet-Draft JXTA v1.0 Protocols Specification June 2002 --------------------------------------------------------------------- Figure 12: Resolver Query Schema --------------------------------------------------------------------- : The credential of the sender. : A string that specifies the destination of this query. : The id of the peer originating the query (as a URN). : An opaque indentifier to be used by the querier to match replies. The SHOULD be included in the responses to this query. : Contains the query. --------------------------------------------------------------------- urn:jxta:uuid-DEADBEEFDEAFBABAFEEDBABE0000000305 JXTACRED Duigou & Project JXTA Expires December 20, 2002 [Page 38] Internet-Draft JXTA v1.0 Protocols Specification June 2002 0 urn:jxta:uuid-59616261646162614A7874615032503304BD268FA4764960AB93A53D7F15044503 <?xml version="1.0"?> <!DOCTYPE jxta:DiscoveryQuery> <jxta:DiscoveryQuery xmlns:jxta="http://jxta.org"> <Type> 0 </Type> <Threshold> 50 </Threshold> <PeerAdv> <?xml version="1.0"?> <!DOCTYPE jxta:PA> ... REMAINDER OMITTED FOR BREVITY ... </jxta:PA> </PeerAdv> <Attr> </Attr> <Value> </Value> </jxta:DiscoveryQuery> Figure 13: Resolver Query --------------------------------------------------------------------- 3.4.1.3 Resolver Response Message A resolver response message is used to send a response to a resolver query message. Duigou & Project JXTA Expires December 20, 2002 [Page 39] Internet-Draft JXTA v1.0 Protocols Specification June 2002 --------------------------------------------------------------------- Figure 14: Resolver Response Schema --------------------------------------------------------------------- : The credential of the respondent. : Specifies how to handle the response. : The query identifier of the query to which this is a response. : The responses. --------------------------------------------------------------------- urn:jxta:uuid-DEADBEEFDEAFBABAFEEDBABE0000000305 JXTACRED 0 <?xml version="1.0"?> <!DOCTYPE jxta:DiscoveryResponse> Duigou & Project JXTA Expires December 20, 2002 [Page 40] Internet-Draft JXTA v1.0 Protocols Specification June 2002 <jxta:DiscoveryResponse xmlns:jxta="http://jxta.org"> <Count> 1 </Count> <Type> 2 </Type> <PeerAdv> &lt;?xml version="1.0"?> &lt;!DOCTYPE jxta:PA> &lt;jxta:PA xmlns:jxta="http://jxta.org"> ... REMAINDER OMITTED FOR BREVITY ... &lt;/jxta:PA> </PeerAdv> <Response Expiration="7200000"> &lt;?xml version="1.0"?> &lt;!DOCTYPE jxta:PipeAdvertisement> &lt;jxta:PipeAdvertisement xmlns:jxta="http://jxta.org"> &lt;Id> urn:jxta:uuid-59616261646162614E50472050325033D1D1D1D1D1D1D1D1D1D1D1D1D1D1D1D104 &lt;/Id> &lt;Type> JxtaPropagate &lt;/Type> &lt;Name> JxtaTalkUserName.IP2PGRP &lt;/Name> &lt;/jxta:PipeAdvertisement> </Response> </jxta:DiscoveryResponse> Figure 15: Resolver Response --------------------------------------------------------------------- 3.4.1.4 Listener and Element Naming The PRP communicates by exchanging Endpoint Messages. Endpoint Addresses specify a handler name. The PRP attaches a listener by that name to the Endpoint Service. Endpoint Service (Section 3.5.1). Duigou & Project JXTA Expires December 20, 2002 [Page 41] Internet-Draft JXTA v1.0 Protocols Specification June 2002 All PRP implementations MUST use the same scheme for building their handler names. The convention used by all services of the world peer group is to use the concatenation of the service name, the peer group ID, and a value unique within the service. --------------------------------------------------------------------- ::= ::= ::= "ORes" ::= "IRes" ::= "jxta.service.resolver" ::= SEE Figure 16: Listener Naming Syntax ABNF --------------------------------------------------------------------- Thus, the listeners used by the PRP are currently named as follows: o QUERIES: jxta.service.resolver[group unique Id string]ORes (ORES is a literal string) o RESPONSES: jxta.service.resolver[group unique Id string]IRes (IRES is a literal string) Query and response messages are included in messages as elements named as follows: o QUERIES: [group unique Id string]ORes (ORES is a literal string) o RESPONSES: [group unique Id string]IRes (IRES is a literal string) 3.4.1.5 Behavior 3.4.1.5.1 Handler Name The Handler Name in PRP messages plays a role similar to that of the handler name in the Endpoint Message addresses: it is a demultiplexing key that specifies how, by which higher-level protocol, or by which module, the message is to be processed. Duigou & Project JXTA Expires December 20, 2002 [Page 42] Internet-Draft JXTA v1.0 Protocols Specification June 2002 In the Java and "C" reference implementations, the users of the PRP are typically services. Each instance of a given service (one per peer per group that uses this service) generates a handler name that is unique on its peer, but will be identical for the instances of this service on other peers. This is by convention achieved by concatenating the service name (which is unique in the group), the group id, which is unique in the peer, and a additional parameter which serves to discriminate between several handlers used by the same service, if needed. The handler name is used both to register the appropriate handler for incoming queries or responses, and as a destination for outgoing queries or responses. For convenience, most clients of the resolver do define two names: one for propagated messages (mostly queries), and one for unicast messages (mostly responses). The PRP SHOULD refuse, and the existing reference implementations SHALL refuse the registration of more than one handler with the same name. A service SHOULD register for any handler name that it uses as a destination, thereby preventing other services from registering themselves to receive these messages. This means that in principle a service or application that receives queries or responses from a service instance on another peer is de-facto the local instance of that service and SHOULD handle these messages as specified. PRP is designed for same-to-same communication, not client-server. 3.4.1.5.2 Policies and Quality of Service The PRP does not guarantee peers that define a query handler name will receive that query, nor does it mandate that all peers that define this handler name will receive it. Only a best effort is made at disseminating the query in a way that maximizes the chance of obtaining a response, if one can be obtained. There is no guarantee that a response to a resolver query request will be made. It is important to point that response to a ResolverQuery request is OPTIONAL. A peer is not required to respond. The PRP does not assume the presence of reliable message delivery. Multiple Resolver query messages may be sent--none, one, multiple or redundant responses may be received. The PRP provides a generic mechanism for services to send queries, and receive responses. As a service, the reference implementation helps other services by taking care of all messaging aspects, caching queries and responses and in forwarding queries, based on the invoker's decision. The PRP performs authentication, and Duigou & Project JXTA Expires December 20, 2002 [Page 43] Internet-Draft JXTA v1.0 Protocols Specification June 2002 verification of credentials and drops incorrect messages. The actual task of propagating a query to the next set of peers is delegated to the Rendezvous Protocol (Section 4.2.2). The Rendezvous service is responsible for determining the set of peers that should receive a message being propagated, but never automatically re- propagates an incoming propagated message. It is left to the service (query handler) handling the message to determine if further propogation should be performed. The PRP's policy is the following: if the query handler does not instruct the PRP to discard the query, and if the local peer is a rendezvous, then the query is re- propagated (within the limits of loop and TTL rules enforced by the Rendezvous service). In addition, if instructed by the query handler, an identical query may be issued with the local peer as the originator. 3.4.2 Endpoint Routing Protocol The JXTA network is ad hoc, multi-hop, and adaptive by nature. Connections in the network may be transient, and message routing is nondeterministic. Routes MAY be unidirectional and change rapidly. Peers MAY join and leave frequently. A peer inside a firewall can send a message directly to a peer outside a firewall. But a peer outside the firewall cannot establish a connection directly with a peer inside the firewall. The Endpoint Routing Protocol defines a set of request/query messages that are processed by a routing service to help a peer route messages to their destination. When a peer is asked to send a message to a given peer endpoint address, it looks in its local cache to see if it has a route to this peer. If it does not find a route, it sends a route resolver query message to its available peer routers asking for routing information. A peer can have as many peer routers as it can find or they can be pre-configured. Pre-configured routers are OPTIONAL. The peer routers provide the low-level infrastructure to route messages between two peers in the network. Any number of peers in a peergroup can elect themselves to become peer routers for other peers. Peers routers offer the ability to cache route information, as well as bridging different physical or logical networks. A peer can dynamically find its router peer via a qualified discovery search. A peer can find out if a peer it has discovered is a peer router via the peer advertisement element. When a peer router receives a route query, if it knows a route to the destination, it answers the query by returning the route information Duigou & Project JXTA Expires December 20, 2002 [Page 44] Internet-Draft JXTA v1.0 Protocols Specification June 2002 as an enumeration of hops. Once a route has been discovered, a message can be sent to the first router and that router will use the route information to route the message to the destination peer. The route is ordered from the next hop to the final destination peer. At any point the routing information MAY become obsolete requiring the current router to discover a new route in order to complete the message delivery. The peer endpoint adds extra routing information to the messages sent by a peer. When a message goes through a peer, the endpoint of that peers leaves its trace on the message. The trace can be used for loop detection, and to discard recurrent messages. The trace is also used to record new route information by peer routers. ERP provides last resort routing for a peer. More intelligent routing can be implemented by more sophisticated routing services in place of the core routing service. High-level routing services can manage and optimize routes more efficiently than the core service. JXTA intends is to provide the hooks necessary for user defined routing services to manipulate and update the route table information (route advertisements) used by the peer router. The intent is to have complex route analysis and discovery be performed above the core by high-level routing services, and have those routing services provide intelligent hints to the peer router to route messages. The Endpoint Routing Protocol (ERP) is used to find the available routes to send a message to a destination peer. This is accomplished through message exchanges between peer routers. Peer routing may be necessary to enable two peers to communicate depending on their location in the network. For instance, the two peers may be on different transports; the peers may be separated by a firewall; or may be using incompatible private IP address spaces. When necessary one or more peer routers can be used to deliver a message from the originating peer endpoint to the destination peer endpoint. 3.4.2.1 Route information Route information is represented as follow: Duigou & Project JXTA Expires December 20, 2002 [Page 45] Internet-Draft JXTA v1.0 Protocols Specification June 2002 --------------------------------------------------------------------- peer id of the source peer id of the destination time to live ordered sequence of gateway <...................> ordered sequence of gateway Figure 17: Endpoint Router --------------------------------------------------------------------- The time-to-live parameter is measured in hops and specifies how long this route is valid. The creator of the route can decide how long this route will be valid. The gateways are defined as an ordered sequence of peer IDs which define the route from the source peer to the destination peer. The sequence may not be complete, but at least the first gateway SHOULD be present. The first gateway is sufficient to initially route the messages. The remaining gateway sequence is OPTIONAL. --------------------------------------------------------------------- TABLES NOT CURRENTLY CONVERTED. Endpoint Route --------------------------------------------------------------------- Peer routers will typically cache route information. Any peer can query a peer router for route information. Any peer in a peer group MAY become a peer router. 3.4.2.2 Route Query Request This message is sent by a peer to a peer router to request route information. Route information may be cached or not. The query MAY indicate to bypass the cache content of a router, and search dynamically for a new route. Duigou & Project JXTA Expires December 20, 2002 [Page 46] Internet-Draft JXTA v1.0 Protocols Specification June 2002 --------------------------------------------------------------------- credential peer id of the destination true: if the reply can be a cached reply false: if the reply must not come from a cache Figure 19: Endpoint Router Query --------------------------------------------------------------------- --------------------------------------------------------------------- TABLES NOT CURRENTLY CONVERTED. Endpoint Router Query --------------------------------------------------------------------- 3.4.2.3 Route Answer Request This message is sent by a router peer to a peer in response to a route information request. Duigou & Project JXTA Expires December 20, 2002 [Page 47] Internet-Draft JXTA v1.0 Protocols Specification June 2002 --------------------------------------------------------------------- credential peer id of the destination Peer ID of the router that knows a route to DestPeer Advertisement of the routing peer ordered sequence of gateway < ...................> ordered sequence of gateway Figure 21: Endpoint Router Response --------------------------------------------------------------------- --------------------------------------------------------------------- TABLES NOT CURRENTLY CONVERTED. Endpoint Router Answer --------------------------------------------------------------------- 3.5 Core JXTA Transport Bindings 3.5.1 Endpoint Service 3.5.1.1 Description The Endpoint Service is responsible for performing end-to-end messaging between two JXTA peers, using one of the underlying JXTA transport protocols, such as the JXTA TCP or HTTP bindings. The Endpoint Service is primarily used by other services or applications that need to have an understanding of the network topology, such as the Resolver Service or the Propagation Service. The Endpoint Service is not responsible for routing messages for peers that are not directly connected to each other. This task is Duigou & Project JXTA Expires December 20, 2002 [Page 48] Internet-Draft JXTA v1.0 Protocols Specification June 2002 performed by the Endpoint Router Transport Protocol (Section 3.5.2) which provides the illusion that the source and destination peers are directly connected. 3.5.1.2 Protocol When the Endpoint Service transmits a message it MAY add a single element to the message: the source peer ID. The element name is : "jxta:EndpointHeaderSrcPeer" and its value is a textual UTF-8 representation of the peer ID at the point of emission of the message. This information is optional and is used by the emitter endpoint service itself to detect and eliminate progagated messages that loop back to the emitter. If this element is not present the message is assumed to not be looping back. The endpoint service expects incoming and outgoing messages to have a source address and a destination address. The encapsulation of that information is specified by the message wire format being used. 3.5.1.3 Behaviour The source and destination addresses of a message are represented as strings in URI format as follows: protocol://address_as_per_protocol/unique_name_of_recipient/ unique_name_in_recipient_context The Endpoint Service delegates the sending of outgoing messages to the enpoint protocol designated by the "protocol" part of the message's destination address. The Endpoint Service delivers incoming messages to the listener registered under the name that matches the concatenation of the "unique_name_of_recipient" and "unique_name_in_recipient_context" parts of the message's destination address. 3.5.2 Endpoint Router Transport Protocol 3.5.2.1 Description The Endpoint Router is a logical JXTA Transport Protocol that sits below the Endpoint Service and beside the other Transport Protocols such as the JXTA TCP and HTTP Transport Protocols. The Endpoint Router is responsible for exchanging messages between Duigou & Project JXTA Expires December 20, 2002 [Page 49] Internet-Draft JXTA v1.0 Protocols Specification June 2002 peers that do not have a direct connection between each other. The Endpoint Router provides a virtual direct connection to the peer's Endpoint Service. 3.5.2.2 Protocol The Endpoint Router protocol defines a set of queries and responses used to communicate with instances of the Endpoint Router on other peers. o Route Query: when the Endpoint Router is requested to send a message to a peer for which it does not have yet a route for, it sends a Route Query request to other peers. Peers that have an route for the given peer answers with Route Response. o Route Response: a peer that desires inform another peer about a give route sends a Route Response to the peer. A Route Response is replied following up a Route Query. o Ping Query: a Ping Query is sent to a peer in order to validate a route. The peer receiving a Ping Query is requested to answer with a Ping Response. o Ping Response: a Ping Response is sent back to the originator of a Ping Query. In addition, the Endpoint Router defines an informational message that requires no reply. o NACK: a NACK is sent by any peer that detects that a route used by another peer is not valid. Typically, this happens by a router peer that are requested to route a message to peer for which it does not have a route itself. NACK messages are optional: routers are not required to send them, and while a NACK is typically sent to the source peer of the message, peers can send NACK to other peers of their choice. Those messages are sent and received by the EndpointRouter using the JXTA Resolver Service. The Endpoint Router Transport Protocol appends its own message element to each message it transports. The name of the message element is "JxtaEndpointRouter" and contains an XML document containing the following: o Mandatory: o Duigou & Project JXTA Expires December 20, 2002 [Page 50] Internet-Draft JXTA v1.0 Protocols Specification June 2002 * Source: the original EndpointAddress of the source of the message. * Destination: the original EndpointAddress of the destination of the message. * LastHop: The EndpointRouter EndpointAddress of the last router that processed the incoming message to route. * NbOfHop: the number of the peers the incoming message to route has already been through. o Optional: o * ForwardRoute: the ordered list of EndpointRouter EndpointAddresses of the peers the message is supposed to go through in order to reach its destination. This list is optional since each router can use the QueryRoute request in order to find a route. However, JXTA EndpointRouter implementation are strongly encouraged to use it: it decreases the network traffic, by limiting the use of queries, which can be expensive. * ReverseRoute: the ordered list of EndpointRouter EndpointAddresses of the peers the message is supposed to go through in order to reach its source. This list is optional since each router can use the QueryRoute request in order to find a route. However, JXTA EndpointRouter implementation are strongly encouraged to use it: it decreases the network traffic, by limiting the use of queries, which can be expensive. 3.5.2.3 Wire Format 3.5.2.3.1 Queries And Responses All queries and responses defined by the Endpoint Router protocol are sent using the JXTA Resolver Service. The messages are represented by an XML document (passed to and by the Resolver Service) of the following type: Duigou & Project JXTA Expires December 20, 2002 [Page 51] Internet-Draft JXTA v1.0 Protocols Specification June 2002 --------------------------------------------------------------------- Figure 23: JXTA Endpoint Router DTD --------------------------------------------------------------------- While this DTD does not define the contents of the elements, the following defines what each element is expected to be: --------------------------------------------------------------------- TABLES NOT CURRENTLY CONVERTED. Router Query --------------------------------------------------------------------- Beside Version and Type, depending on the query or the response, only a subset of tags are used: o RouteQuery: DestPeer is set to the peer id (in its EndpointRouter definition) of the peer for which a route is requested. o RouteResponse: DestPeer is set to the peer id (in its EndpointRouter definition) of the peer for which a route was requested. o RoutingPeer is set to the EndpointAddress of the peer that knows how to route message to the destination peer. o RoutingPeerAdv can be optionally contain the Peer Advertisement of Duigou & Project JXTA Expires December 20, 2002 [Page 52] Internet-Draft JXTA v1.0 Protocols Specification June 2002 the routing peer. This allow the requesting peer to not have to search for the advertisement later on (optimization). o NbOfHops: is set to the number of hops of the route starting at the routing peer. o GatewayForward: contains the Endpoint Address of a routing peer within the route. The ordered list of GatewayForward defines the entire route to be used starting at the routing peer in order to reach the destination. Endpoint Routers are not required to fill up this list, however, this is required if the endpoint router desire to use the optimization of embedding the forward route within the message. JXTA Endpoint Routers implementations are strongly encouraged to fill up the Gateway Forward list. o PingQuery: DestPeer is set to the peer id (in its EndpointRouter definition) of the peer for which a ping is requested. o PingResponse: DestPeer is set to the peer id (in its EndpointRouter definition) of the peer for which a ping was requested. o NACK: DestPeer is set to the peer id (in its EndpointRouter definition) of the peer for which the route has failed. o GatewayForward: if the message for which the route has failed contained a list of GatewayForward, this list is included into the NACK message. 3.5.2.3.2 EndpointRouter Message Element The Endpoint Router transport protocol includes a message element named JxtaEndpointRouter. The format of the message element is an XML document defined as follows: Duigou & Project JXTA Expires December 20, 2002 [Page 53] Internet-Draft JXTA v1.0 Protocols Specification June 2002 --------------------------------------------------------------------- Figure 25: JXTA Endpoint Router Message DTD --------------------------------------------------------------------- While this DTD does not define the nature of contents of the tag, the following defines was is expected to be each tag: --------------------------------------------------------------------- TABLES NOT CURRENTLY CONVERTED. Router Element In Messages --------------------------------------------------------------------- The meaning of these elements is as follows: o jxta:Src contains the EndpointAdress of the original source of the message o jxta:Dest contains the EndpointAdress of the original destination of the message o jxta:Last contains the EndpointAdress of immediate previous peer that has received the message o jxta:NBOH contains the number of hops of the reverse route. 0 if there is no reverse route. o GatewayForward: contains the Endpoint Address of a routing peer within the forward route. The ordered list of GatewayForward Duigou & Project JXTA Expires December 20, 2002 [Page 54] Internet-Draft JXTA v1.0 Protocols Specification June 2002 defines the entire route to be used in order to reach the destination peer of the message. Endpoint Routers are not required to fill up this list, however, JXTA Endpoint Routers implementations are strongly encouraged to fill up the Gateway Forward list since it is an important optimization in order to decrease latency of communication between peers. o GatewayReverse: contains the Endpoint Address of a routing peer within the reverse route. The ordered list of GatewayForward defines the entire route to be used in order to reach the source peer of the message. Endpoint Routers are not required to fill up this list, however, JXTA Endpoint Routers implementations are strongly encouraged to fill up the Gateway Forward list since it is an important optimization in order to decrease latency of communication between peers. 3.5.2.3.3 EndpointRouter Endpoint Address format Since the EndpointRouter is a transport protocol, it has its own Endpoint Address format, which is: --------------------------------------------------------------------- jxta://uuid- Figure 27: JXTA Endpoint Router Address Format --------------------------------------------------------------------- 3.6 Messages Messages are the basic unit of data exchange between peers. Pipes send and receive messages to and from services; any protocol implemented by a service will send and receive messages. Messages are encoded using "wire" representations for transmission. Each JXTA transport will use the message representations most appropriate for its characteristics and the peers' preferences. See JXTA Message Wire Representations (Section 4.4) for information about representations. 3.6.1 Message A message is a set of named and typed contents called elements. Thus a message is essentially a set of name/value pairs. The content can be an arbitrary type. Many core services send XML advertisements as Duigou & Project JXTA Expires December 20, 2002 [Page 55] Internet-Draft JXTA v1.0 Protocols Specification June 2002 message element contents. As a message passes down a protocol stack (applications, services, endpoint and transports), each level may add one or more named elements to the message. As a message is passed back up the stack on the receiving peer, the protocol handlers SHOULD remove those elements. A message is an ordered sequence of message elements. The most recently added element appears at the end of the message. 3.6.2 Element A message element contains a namespace, an optional name, an optional type, an optional signature or digest and content. 3.6.2.1 Namespace Every element is assigned to a namespace. Namespaces are used to organize elements used by different message users and transports within the same message. Two namespaces names are considered equivalent if their representation in canonical UTF8 (NFC) (see Unicode Standard Annex #15 : Unicode Normalization Forms [USA15 [5]]) is byte-for-byte identical. Two message element namespaces are pre-defined, """" (empty string) and "jxta". The """" namespace is reserved for user applications and services--none of the JXTA protocols or services will use or modify elements in this namespace. The "jxta" namespace is reserved for internal use by the JXTA protocols and services. Applications SHOULD NOT create, manipulate or assume the interpretation of any of the content of elements in the "jxta" namespace. In some bindings, applications MAY be forbidden from accessing or creating elements in the "jxta" namespace. Use of namespaces by services and applications other than the "" namespace is OPTIONAL. Namespaces require no formal registration as the protocols used need only be agreed upon by the participants. 3.6.2.2 Name Elements may have an optional name. Elements in the same message MAY have the same name. Duigou & Project JXTA Expires December 20, 2002 [Page 56] Internet-Draft JXTA v1.0 Protocols Specification June 2002 3.6.2.3 Type A type is specified as a MIME type. See [bib-RFC2046 [1]]. MIME types are UTF8 strings. The type is used by the applications and services that process the element. There is no restriction on the set of MIME types that can be used by applications and services. In addition to the applications and services which use the particular element, the type of the element may also be examined by the JXTA transport to determine how to format the message element to ensure the most effcient transfer. If the type is not specified for an element "application/octet- stream" is assumed. 3.6.2.4 Content The contents of the Element data are opaque to except to the applications and services which use these elements. Duigou & Project JXTA Expires December 20, 2002 [Page 57] Internet-Draft JXTA v1.0 Protocols Specification June 2002 4. JXTA Standard Services 4.1 Introduction The JXTA Core Specification (Section 3) defines the required components and behaviours for all JXTA implementations. In order to create a complete JXTA implementation there are some additional components which all implementation SHOULD provide. The JXTA Standard Services are OPTIONAL JXTA components and behaviours. Implementations are not required to provide these services, but are strongly RECOMMENDED to do so. Implementing these services will provide greater interoperability with other implementations and broader functionality. 4.2 Standard Protocols 4.2.1 Peer Discovery Protocol 4.2.1.1 Introduction The Peer Discovery Protocol is used to discover any published peer resource. Resources are represented as advertisements. A resource can be a peer, a peergroup, a pipe, a module, or any resource that has an advertisement. Each resource MUST be represented by an advertisement. The Peer Discovery Protocol (PDP) enables a peer to find advertisements in its group. The PDP protocol is the discovery protocol of the world peergroup. Custom discovery services MAY choose to leverage PDP. If a peer group does not need to define its own discovery protocol, it may use the world peergroup PDP. The intent is for PDP to provide the essential discovery infrastructure for building and bootstrapping high-level discovery services. In many situation, discovery information is better known by a high-level service, because the service may have a better knowledge of the group topology. The PDP protocol provides a basic mechanism to discover advertisements while providing hooks so high-level services and applications can participate in the discovery process. Services SHOULD be able to give hints to improve discovery (i.e. decide which advertisements are the most valuable to cache). The PDP protocol utilizes the resolver protocol to route queries and responses. Duigou & Project JXTA Expires December 20, 2002 [Page 58] Internet-Draft JXTA v1.0 Protocols Specification June 2002 4.2.1.2 Discovery Query Message The discovery query message is used by peers to send discovery requests when searching for advertisements. --------------------------------------------------------------------- Figure 28: Discovery Query Schema --------------------------------------------------------------------- : Only advertisements of requested type will be matched. Possible values are: "0" : Peer Advertisements "1" : Peergroup Advertisements "2" : Any Advertisements : specifies the maximum number of advertisements that Duigou & Project JXTA Expires December 20, 2002 [Page 59] Internet-Draft JXTA v1.0 Protocols Specification June 2002 each responding peer SHOULD provide. The total number of results received depends on the number of peers that respond and the advertisements they have. If is "0" (Peer Advertisements) and is "0" , then the query has a special meaning: its objective is to collect Peer Advertisements of respondents. Therefore any peer SHOULD respond to such a query, e ven though no results are to be included. : If present, the advertisement of the requestor. , : Must either be both present or absent. If absent, then each respondent should supply a random set of advertisements of the appropriate type up to count. Only advertisements containing an element who's name matches and that also contains a value matching are eligible to be found. may begin or end with "*", or both. In that case will match all values that end with or beginning with, or contain the rest of the string. If contains only "*" the result is unspecified. Some implementations may choose not match any advertisement for "*". Duigou & Project JXTA Expires December 20, 2002 [Page 60] Internet-Draft JXTA v1.0 Protocols Specification June 2002 --------------------------------------------------------------------- 2 1 Name *sidus* <?xml version="1.0"?> <!DOCTYPE jxta:PA> <jxta:PA xmlns:jxta="http://jxta.org"> <PID> urn:jxta:uuid-59616261646162614A7874615032503304BD268FA4764960AB93A53D7F15044503 </PID> ... REMAINDER OMITTED FOR BREVITY ... </jxta:PA> Figure 29: Discovery Query --------------------------------------------------------------------- 4.2.1.3 Discovery Response Message A Discovery response message is used by a peer to respond to a discovery query message. Duigou & Project JXTA Expires December 20, 2002 [Page 61] Internet-Draft JXTA v1.0 Protocols Specification June 2002 --------------------------------------------------------------------- Figure 30: Discovery Response Schema --------------------------------------------------------------------- : The type of all the advertisements returned in the element(s). : If present, the number of element(s) included in this response. : If present, the advertisement of the respondent. The "Expiration" attribute is the associated relative expiration time in milliseconds. , : If present, reflects that of the Duigou & Project JXTA Expires December 20, 2002 [Page 62] Internet-Draft JXTA v1.0 Protocols Specification June 2002 DiscoveryQuery to which this is the response. : An advertisement.The "Expiration" attribute is the associated relative expiration time in milliseconds. --------------------------------------------------------------------- 2 1 Name *sidus* <?xml version="1.0"?> <!DOCTYPE jxta:PA> <jxta:PA xmlns:jxta="http://jxta.org"> <PID> urn:jxta:uuid-59616261646162614A7874615032503304BD268FA4764960AB93A53D7F15044503 </PID> ... OMITTED ... </jxta:PA> <?xml version="1.0"?> <!DOCTYPE jxta:PipeAdvertisement> <jxta:PipeAdvertisement xmlns:jxta="http://jxta.org"> <Id> urn:jxta:uuid-094AB61B99C14AB694D5BFD56C66E512FF7980EA1E6F4C238A26BB362B34D1F104 </Id> <Type> JxtaUnicastSecure </Type> <Name> JxtaTalkUserName.sidus </Name> </jxta:PipeAdvertisement> Figure 31: Discovery Response Duigou & Project JXTA Expires December 20, 2002 [Page 63] Internet-Draft JXTA v1.0 Protocols Specification June 2002 --------------------------------------------------------------------- 4.2.1.4 Behaviour 4.2.1.4.1 Policies and Quality of Service The PDP does not guarantee peers that receive a query will respond to the query, nor does it mandate that the number of advertisements requested will be honored. Only a best effort is made at matching the query to results in the respondant's cache. There is no guarantee that a response to a discovery query request will be made. It is important to point out that responding to a DiscoveryQuery request is OPTIONAL. A peer is not required to respond to a DiscoveryQuery request. A reliable transport is OPTIONAL with the PDP. Multiple Discovery query messages may be sent. None, one, multiple or redundant responses may be received. A peer may receive a DiscoveryResponse that is not a response to any DiscoveryQuery initiated by the peer, this mechanism provides the ability to remote publish a resource. The PDP provides a mechanism for services to query the network for JXTA resources, and receive responses. As a service, the reference implementation helps other services by taking care of all messaging aspects, caching, and expiring advertisements. The actual task of propagating, and re-propagating a query to the next set of peers is delegated to the Resolver Service. 4.2.2 Rendezvous Protocol 4.2.2.1 Introduction The Rendezvous Protocol (RVP) is responsible for propagating messages within a JXTA Peergroup. While different Peergroups may have different means to