Internet Engineering Task Force John Veizades INTERNET DRAFT @Home Network 10 June 1996 Erik Guttman Sun Microsystems Charles Perkins IBM Research Scott Kaplan Service Location Protocol draft-ietf-svrloc-protocol-13.txt Status of This Memo This draft document is a product of the Service Location Working Group of the Internet Engineering Task Force (IETF); it will be submitted to the RFC editor as a standards document. Please respond with comments to the srvloc@tgv.com mailing list. Distribution of this memo is unlimited. This document is an Internet-Draft. 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.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). Abstract The Service Location protocol provides a scalable framework for the discovery and selection of network services. Using this protocol, computers using the Internet no longer need so much static configuration of network services for network based applications. This is especially important as computers become more portable, and users less tolerant or able to fulfill the demands of network system administration. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page i]
Internet Draft Service Location Protocol 10 June 1996 Contents Status of This Memo i Abstract i 1. Recent Changes 2 2. Introduction 5 3. Terminology 5 3.1. Notation Conventions . . . . . . . . . . . . . . . . . . 6 3.2. Service Information and Predicate Representation . . . . 7 3.3. Specification Language . . . . . . . . . . . . . . . . . 7 4. Protocol Overview 8 4.1. Protocol Transactions . . . . . . . . . . . . . . . . . . 9 4.2. Schemes . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.2.1. The 'service:' URL scheme . . . . . . . . . . . 11 4.3. Standard Attribute Definitions . . . . . . . . . . . . . 11 4.4. Naming Authority . . . . . . . . . . . . . . . . . . . . 12 4.5. Interpretation of Service Location Replies . . . . . . . 12 4.6. Use of TCP, UDP and Multicast in Service Location . . . . 13 4.6.1. Multicast vs. Broadcast . . . . . . . . . . . . 13 4.7. Service Location Scaling, and Multicast Operating Modes . 14 5. Service Location General Message Format 15 5.1. Use of Transaction IDs (XIDs) . . . . . . . . . . . . . . 17 5.2. URL Entry Lifetime . . . . . . . . . . . . . . . . . . . 18 6. Service Request Message Format 18 6.1. Service Request Usage . . . . . . . . . . . . . . . . . . 20 6.2. Directory Agent Discovery Request . . . . . . . . . . . . 21 6.3. Explanation of Terms of Predicate Grammar . . . . . . . . 22 6.4. Service Request Predicate Grammar . . . . . . . . . . . . 24 6.5. String Matching for Requests . . . . . . . . . . . . . . 25 7. Service Reply Message Format 26 8. Service Type Request Message Format 27 9. Service Type Reply Message Format 29 10. Service Registration Message Format 30 11. Service Acknowledgement Message Format 33 Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page ii]
Internet Draft Service Location Protocol 10 June 1996 12. Service Deregister 34 13. Attribute Request Message Format 35 14. Attribute Reply Message Format 37 15. Directory Agent Advertisement Message Format 39 16. Directory Agents 40 16.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 40 16.2. Finding Directory Agents . . . . . . . . . . . . . . . . 40 17. Scope Discovery and Use 42 18. Language and Character Encoding Issues 43 18.1. Character Encoding and String Issues . . . . . . . . . . 44 18.1.1. Substitution of Character Escape Sequences . . . 45 18.2. Language Dialect . . . . . . . . . . . . . . . . . . . . 45 18.3. Language-Independent Strings . . . . . . . . . . . . . . 46 19. Service Location Transactions 46 19.1. Service Location Connections . . . . . . . . . . . . . . 46 20. Security Considerations 47 21. String Formats used with Service Location Messages 48 21.1. Previous Responders' Address Specification . . . . . . . 49 21.2. Reply and Registration Information . . . . . . . . . . . 49 21.3. Attribute Information . . . . . . . . . . . . . . . . . . 50 21.3.1. Service Type String . . . . . . . . . . . . . . . 50 21.4. Address Specification in Service Location . . . . . . . . 50 21.5. Attribute Value encoding rules . . . . . . . . . . . . . 51 22. Implementation Requirements 52 23. Configurable Parameters and Default Values 55 23.1. Service Agent: Use Predefined Directory Agent(s) . . . . 56 23.2. Time Out Intervals . . . . . . . . . . . . . . . . . . . 57 24. Non-configurable Parameters 58 25. Acknowledgments 58 A. Appendix: Technical contents of ISO 639:1988 (E/F): "Code for the representation of names of languages" 59 B. Appendix: For Further Reading 60 Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 1]
Internet Draft Service Location Protocol 10 June 1996 1. Recent Changes After much thought, we decided to change the way service attributes are requested by clients. Whereas before we specified a /Select/ clause within the Service Request as well as another Attribute Request message type, now attributes will be requested only by use of the Attribute Request message type. The Service Request will not have a /Select/ clause, and will return URLs only. Conceptually, this is fairly minor change to the protocol, but it has had a pretty substantial effect on the wording in the document. In addition, we have broken out the Service Type message as a different message type, and the Directory Agent now can make use of an Advertisement message. All of these changes have been made to simplify the protocol as well as the description of the protocol. We reached the decision only after much hand-wringing. We believe that the gain in protocol quality is worth the cost of making modifications at this late date, and that the resulting protocol is powerful yet simple enough that no further such changes will be needed. In addition, and as part of the abovementioned modifications, we have addressed all of the language, consistency, and security concerns that have been brought during the recent last call period. 1. The predicate grammar has changed: - To disambiguate the grammar, parentheses are required for keywords in where-list queries. - The predicate query no longer contains a SELECT clause. The select list has been moved to the AttrRqst. This simplifies the query grammar and functionality of the SrvRqst. 2. The header has changed: - Error codes have been removed from the header. This shrinks the header, and since only half of the PDUs need to carry an Error field: DAAdvert, SrvTypeRply, SrvRply, AttrRply, SrvAck. - TTL has been removed from the header. It has been renamed Lifetime. The name TTL was confusing to people for whom it had other associations. Having the TTL in the header did not allow multiple services which were returned to be given distinct lifetime values. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 2]
Internet Draft Service Location Protocol 10 June 1996 3. SrvRqst changed quite a bit. It now merely returns a URL, not attributes. SrvRqst had too much functionality. It allowed Service Type discovery, DA Discovery, Service Discovery and Attribute selection. This made it complex to explain and subtle to specify and code. The elements have been broken into clear and distinct interactions. - The SELECT of the predicate clause has been removed. Attribute information is no longer returned with the SrvRply therefore SELECT is unneeded. It was complex to explain how this feature worked. Removing all attribute information from the SrvRqst <---> SrvRply transaction greatly simplifies the protocol and predicate syntax. - WILD CARD Service Types are no longer possible. This was used to allow Service Type discovery and constituted a special case. This was not at all elegant. One might even use the word kludge here. 4. AttrRqst changed quite a bit. It now does all attribute functions. SrvRqst and the grammar it used were very complicated. This change takes on the attribute functions in a clean and simple fashion which increases the clarity of the protocol. It also makes it possible to ignore attributes entirely if one wishes. - There are more fields. AttrRqst used to have only a ServiceType. It returned all the attributes and values of that Service Type. Now a URL String, Scope String and Select String are included. The URL String can be either merely a Service Type or it can be a complete URL. This returns all attributes and values as before, THAT SATISFY THE PROVIDED SCOPE AND SELECT CLAUSE. - This mechanism is more powerful than the original AttrRqst, in that it allows a Selection of WHICH attributes are to be returned. It also simplifies the protocol by combining all attribute requests into one function. 5. SrvRply changed as a result of changes to SrvReq. It now contains an Error field and it returns URL Entries not URL Strings and Attribute information for each Service in the reply. - An error field included, to make it clear how to handle errors. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 3]
Internet Draft Service Location Protocol 10 June 1996 - URL Entries used, no attributes included. Lifetime had to be associated with each entry in the reply not with the entire reply. Attribute info may now only be obtained with the AttrRqst. 6. SrvTypeRqst and SrvTypeRply were created in order to further simplify (and rationalize) SrvReq. - This request now has weaker semantics than before, since it is impossible to specify a SELECT clause in the SrvTypeRqst. This means that you can't say "Give me all service types that start with the letter Q" or "Give me all service types except the following list". Such things are not really needed and add complexity to the wrong part of the protocol. - There is no longer any special case or wild card necessary for doing service type requests. - The Naming Authority and Scope field for the SrvTypeRqst are still included. 7. Created DAAdvert for the reply for a SrvRqst for Service Type "directory-agent". The reply for a DA must include the Scope of the DA. Since Attributes are no longer included in SrvRply messages, a distinct message type was required. This message is also periodically transmitted even if unsolicited. 8. There is now a character escape mechanism almost exactly as used in HTML, so that characters which are part of service location protocol syntax can appear in attribute tags and values. 9. Added rules and conditions for use of multiple character sets to satisfy Harald Alverstrand's rejection of slp draft 12. 10. Added security comments and requirements to satisfy last call issues raised. 11. The SrvDereg message now includes a list of attributes to deregister. In the previous version of the protocol the service had to be deregistered as a whole, which was deemed to coarse and easily correctible. If this field is excluded, the SrvDereg functions exactly as before. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 4]
Internet Draft Service Location Protocol 10 June 1996 2. Introduction Traditionally, users find services by using the name of a network host (a human readable text string) which is an alias for a network address. The service location protocol eliminates the need for a user to know the name of a network host supporting a service. Rather, the user supplies a set of attributes which describe the service. The service location protocol allows the user to bind this description to the network address of the service. Service Location provides a dynamic configuration mechanism for applications in local area networks. It is not a global resolution system for the entire Internet; rather it is intended to serve enterprise networks with shared services. Applications are modeled as clients that need to find servers attached to the enterprise network at a possibly distant location. For cases where there are many different clients and/or services available, the protocol is adapted to make use of nearby Directory Agents that offer a centralized repository for advertised services. 3. Terminology User Agent (UA) A process working on the user's behalf to acquire service attributes and configuration. The User Agent retrieves service information from the Service Agents or Directory Agents. Service Agent (SA) A process working on the behalf of one or more services to advertise service attributes and configuration. Service Information A collection of attributes and configuration information associated with a single service. The Service Agents advertise service information for a collection of service instances. Service The service is a process or system providing a facility to the network. The service itself is accessed using a communication mechanism external to the the service location protocol. Directory Agent (DA) A process which collects information from Service Agents to provide a single repository of service information Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 5]
Internet Draft Service Location Protocol 10 June 1996 in order to centralize it for efficient access by User Agents. There can only be one DA present per given host. Service Type Each type of service has a unique Service Type string. The Service Type defines a template including expected attributes, values and protocol behavior. Naming Authority The agency or group which catalogues given Service Types and Attributes. The default Naming Authority is IANA. Keyword A string describing a characteristic of a service. Attribute A (class, value-list) pair of strings describing a characteristic of a service. The value string may be interpreted as a boolean, integer or opaque value if it takes specific forms (see section 21.5). Predicate A boolean expression of attributes, relations and logical operators. The predicate is used to find services which satisfy particular requirements. See section 6.3. Scope A collection of services that make up a logical group. See sections 17 and 4.7. Site Network All the hosts accessible within the Agent's multicast radius, which defaults to a value appropriate for reaching all hosts within a site (see section 23). If the site does not support multicast, the agent's site network is restricted to a single subnet. Address Specification This is the network layer protocol dependent mechanism for specifying an Agent. For Internet systems this is part of a URL (Universal Resource Locator - see [7]). 3.1. Notation Conventions CAPS Strings which appear in all capital letters are protocol literal. All string comparison is case insensitive, however, (see section 6.5). Some strings are quoted in Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 6]
Internet Draft Service Location Protocol 10 June 1996 this document to indicate they should be used literally. Single characters inside apostrophes should be included literally. <> Values set off in this manner are fully described in section 21. In general, all definitions of items in messages are described in section 21 or immediately following their first use. | | \ \ Message layouts with this notation indicate a variable | | length field. 3.2. Service Information and Predicate Representation Service information is represented in a text format. The goal is that the format be human readable and transmissible via email. The location of network services is encoded as a Universal Resource Locator (URL) which is also human readable and well defined. Only the datagram headers are encoded in a form which is not human readable. Predicates are expressed in a simple boolean notation using keywords, attributes, and logical connectives, as described in Section 6.4. The logical connectives and subexpressions are presented in prefix-order, so that the connective comes first and the expressions it operates on follow afterwards. 3.3. Specification Language In this document, several words are used to signify the requirements of the specification. These words are often capitalized. MUST This word, or the adjective "required", means that the definition is an absolute requirement of the specification. MUST NOT This phrase means that the definition is an absolute prohibition of the specification. SHOULD This word, or the adjective "recommended", means that, in some circumstances, valid reasons may exist to ignore this item, but the full implications must be understood and carefully weighed before choosing a different course. Unexpected results may result otherwise. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 7]
Internet Draft Service Location Protocol 10 June 1996 MAY This word, or the adjective "optional", means that this item is one of an allowed set of alternatives. An implementation which does not include this option MUST be prepared to interoperate with another implementation which does include the option. silently discard The implementation discards the datagram without further processing, and without indicating an error to the sender. The implementation SHOULD provide the capability of logging the error, including the contents of the discarded datagram, and SHOULD record the event in a statistics counter. 4. Protocol Overview The basic operation in Service Location is that a client attempts to discover the location of a Service. In smaller installations, each service will be configured to respond individually to each client. In larger installations, services will register their services with one or more Directory Agents, and clients will contact the Directory Agent to fulfill requests for Service Location information. Clients may discover the whereabouts of a Directory Agent by preconfiguration, DHCP [2, 10], or by issuing queries to the Directory Agent Discovery multicast address. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 8]
Internet Draft Service Location Protocol 10 June 1996 4.1. Protocol Transactions The diagram below illustrates the relationships described below: +---------------+ we want this info: +-----------+ | Application | - - - - - - - - - - - -> | Service | +---------------+ +-----------+ /|\ | | | +-------------+ | | | | \|/ \|/ \|/ +---------------+ +-----------+ +----------------+ | User Agent |<-------->| Service | | Service | +---------------+ | Agent | | Agent which | | +-----------+ | does not reply | | | | to UA requests | | \|/ +----------------+ | +-------------+ | +------------------>| Directory |<----------+ | Agent | +-------------+ ___________ /|\ / Many other\ +------------>| SA's | \___________/ The following describes the operations a User Agent would employ to find services on the site's network. The User Agent needs no configuration to begin network interaction. The User Agent can acquire information to construct predicates which describe the services that match the user's needs. The User Agent may build on the information received in earlier network requests to find the Service Agents advertising service information. A User Agent will operate two ways: If the User Agent has already obtained the location of a Directory Agent, the User Agent will unicast a request to it in order to resolve a particular request. The Directory Agent will unicast a reply to the User Agent. The User Agent will retry a request to a Directory Agent until it gets a reply, so if the Directory Agent cannot service the request (say it has no information) it must return an response with zero values, possibly with an error code set. If the User Agent does not have knowledge of a Directory Agent or if there are no Directory Agents available on the site network, a second mode of discovery is used. The User Agent multicasts a request to the service-specific multicast address, to which the service it wishes to locate will respond. All the Service Agents which are listening to this multicast address will respond, provided they can Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 9]
Internet Draft Service Location Protocol 10 June 1996 satisfy the User Agent's request. A similar mechanism is used for Directory Agent discovery; see section 6.2. Service Agents which have no information for the User Agent MUST NOT respond. When a User Agent wishes to obtain an enumeration of ALL services which satisfy the query, a retransmission/convergence algorithm is used. The User Agent resends the request, together with a list of previous responders. Only those Service Agents which are not on the list respond. Once there are no new responses to the request the accumulation of responses is deemed complete. Depending on the length of the request, around 60 previous responders may be listed in a single datagram. If there are more responders than this, the scaling mechanisms described in section 4.7 should be used. While the multicast/convergence model may be important for discovering services (such as Directory Agents) it is the exception rather than the rule. Once a User Agent knows of the location of a Directory Agent, it will use a unicast request/response transaction. The Service Agent SHOULD listen for multicast requests on the service-specific multicast address, and MUST register with an available Directory Agent. This Directory Agent will resolve requests from User Agents as described above. This means that a Directory Agent must first be discovered, using the multicast mechanism described above. A Service Agent which does not respond to multicast requests will not be useful in the absence of Directory Agents. Some Service Agents may not include this functionality, if an especially light-weight implementation is required. If the service is to become unavailable, it should be deregistered with the Directory Agent. The Directory Agent responds with an acknowledgment to either a registration or deregistration. Service Registrations include a Lifetime value and will eventually expire. Service Registrations need to be refreshed by the Service Agent before their Lifetime runs out. 4.2. Schemes The Service Location Protocol, designed as a way for clients to access resources on the network, is a natural application for Universal Resource Locators (URLs). It is intended that by re-using URL specification and technology from the World Wide Web, clients and servers will be more flexible and able to be written using already existing code. Moreover, it is hoped that browsers will be written to take advantage of the similarity in locator format, so that a Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 10]
Internet Draft Service Location Protocol 10 June 1996 client can dynamically formulate requests for services that are resolved differently depending upon the circumstances. There is the possibility for beneficial interaction between Directory Agents and Web Browsers which we wish to facilitate by means of compatible locator format. 4.2.1. The 'service:' URL scheme The service URL scheme is used by Service Location. It is used to specify a Service Location. Many Service Types will be named by including a scheme name after the 'service:' scheme name. Service Types are used by SAs to register and deregister Services with DAs. It is also used by SAs and DAs to return Service Replies to UAs. The formal definition of the 'service:' URL scheme is in section 21. The format of the information which follows the 'service:' scheme should as closely as possible follow the URL structure and semantics as formalized by the IETF standardization process. Well known Service Types are registered with the IANA and templates are available as RFCs. Private Service Types may also be supported. 4.3. Standard Attribute Definitions Service Types used with the service location protocol must describe the following: Service Type string of the service Service-specific multicast address, if used Attributes and Keywords Attribute Descriptions and interpretations Service Types note registered with IANA will use their own Naming Authority string and, possibly, a service-specific multicast address from the unassigned range. This is only an option for a site-specific deployment, as there may be conflicts with this multicast address somewhere, in some other site. If a service-specific multicast address is not supplied by a standards document registered with IANA, nor is a site specific address being used, the Service Location General Multicast address is the default. All Service Agents SHOULD listen to this address, especially if they have not registered their service information with any Directory Agent. The service-specific multicast address is merely used for efficiency and is not strictly needed for correct operation. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 11]
Internet Draft Service Location Protocol 10 June 1996 Services which advertise a particular Service Type must support the complete set of standardized attributes. They may support additional attributes, beyond the standardized set. Unrecognized attributes MUST be ignored by User Agents. Service Type names which begin with "x-" are guaranteed not to conflict with any officially registered Service Type names. It is suggested that this prefix be used for experimental or private Service Type names. Similarly, attribute names which begin with "x-" are guaranteed not to be used for any officially registered attribute names. A service of a given Service Type should accept the networking protocol which is implied in its definition. If a Service Type can accept multiple protocols, configuration information SHOULD be included in the Service Type attribute information. This configuration information will enable an application to use the results of a Service Request and Attribute Request to directly connect to a service. See section 21.3.1 for the format of a Service Type String as used in the Service Location Protocol. 4.4. Naming Authority The Naming Authority of a service defines the meaning of the Service Types and attributes registered with and provided by Service Location. The Naming Authority itself is a string which uniquely identifies an organization. If no string is provided IANA is the default. Naming Authorities may define Service Types which are experimental, proprietary or for private use. The procedure to use is to create a 'unique' Naming Authority string and then specify the Standard Attribute Definitions as described above. This Naming Authority will accompany registration and queries, as described in sections 10 and 6. 4.5. Interpretation of Service Location Replies Replies should be considered to be valid at the time of delivery. The service may, however, fail or change between the time of the reply and the moment an application seeks to make use of the service. The application making use of service location SHOULD be prepared for the possibility that the service information provided is either stale or incomplete. In the case where the service information provided Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 12]
Internet Draft Service Location Protocol 10 June 1996 does not allow a User Agent to connect to a service as desired, the Service Request may be resubmitted. Service specific configuration information (such as which protocol to use) should be included as attribute information in Service Registrations. These configuration attributes will be used by applications which interpret the Service Location Reply. 4.6. Use of TCP, UDP and Multicast in Service Location The service location protocol requires the implementation of connectionless and a connection oriented transport protocols. The latter is used for bulk transfer, only when necessary. Connections are always initiated by an agent request or registration, not by a replying Directory Agent. The Service Location discovery mechanisms use possibly internetwork-wide multicast. The protocol will operate in a broadcast environment with limitations detailed in section 4.6.1. 4.6.1. Multicast vs. Broadcast The service location protocol was designed for use in networks where multicast at the network layer is supported; in some instances multicast may not be supported. To support this protocol in networks where multicast is not supported the following modifications are made to support the protocol in an environment where network layer broadcast is supported. 4.6.1.1. Single Subnet If a network is not connected to any other networks simple network layer broadcasts will work in place of multicast. 4.6.1.2. Multiple Subnets The Directory Agent provides a central clearing house of information for User Agents. If the network is designed so that a Directory Agent address is statically configured with each User Agent, the Directory Agent will act as a bridge for information that resides on different subnets. The Directory Agent address can be dynamically configured with Agents using DHCP or staticly configured, but Agents will not be able to discover DAs on non-bridged subnets. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 13]
Internet Draft Service Location Protocol 10 June 1996 As dynamic discovery is not feasible in a broadcast environment with multiple subnets and manual configuration is difficult, deploying multiple DAs in multiple subnets will require use of multicast discovery with multiple hops (i.e., TTL > 1 in the IP header). 4.6.1.3. Service-Specific Multicast Address Each service type MAY have a unique multicast address which is expected to be used for discovering services of that type. This multicast address may be obtained from the naming authority (e.g., IANA). This mechanism is used so that the number of datagrams any one service agent receives is minimized. The Service Location General Multicast Address may be used to query for any service, though one should use the service-specific multicast address if it exists. If the site network does not support multicast then the query should be broadcast to the Service Location port. If the underlying hardware will not support the number of needed multicast addresses the service location general multicast address may be used. Service Agents which have not registered with a Directory Agent listen on this multicast address as well as the service-specific multicast addresses for the service types they advertise. 4.7. Service Location Scaling, and Multicast Operating Modes In a very small network, with few nodes, no DA is required. A User Agent can detect services by multicasting requests. Service Agents will then reply to them. Further, Service Agents which respond to user requests must be used to make service information available. This does not scale to environments with many hosts and services. When scaling service location systems to intermediate sized networks, a central repository (Directory Agent) may be added to reduce the number of Service Location messages transmitted in the network infrastructure. Since the central repository can respond to all Service Requests, fewer Service Replies will be needed; for the same reason, there is no need to differentiate between Directory Agents. Service Agents should register with this DA even if they are configured to specifically register with DAs which have a specific scope or set of scopes. User Agents may query DAs without scopes, even if they are configured to use DAs with a certain scope. This is because any DA with no Scope will have all the available service information. A site may also grow to such a size that it is not feasible to maintain only one central repository of service information. In this Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 14]
Internet Draft Service Location Protocol 10 June 1996 case more Directory Agents are needed. The services (and service agents) advertised by the several Directory Agents are collected together into logical groupings called "scopes". All Service Registrations that have a scope must be registered with all DAs (within the appropriate multicast radius) of that scope which have been or are subsequently discovered. Unscoped services should be registered with all DAs as they are implicitly Global in scope. User Agents make requests of DAs whose Scope they are configured to use. It is possible to specially configure Service Agents to register only with a specific set of DAs (see Section 23.1). In that case, services may not be available to User Agents via all Directory Agents, but some network administrators may deem this appropriate. There are thus 3 distinct operating modes. The first requires no administrative intervention. The second requires only that a DA be run. The last requires that all DAs be configured to have Scope and that a coherent strategy of assigning Scopes to services be followed. Users must be instructed which Scopes are appropriate for them to use. This administrative effort will allow users and applications to subsequently dynamically discover services without assistance. A subsequent protocol document will describe mechanisms for supporting a service discovery protocol for the global Internet. 5. Service Location General Message Format The following header is used in all of the message descriptions below and is abbreviated by using "Service location header =" followed by the function being used. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Version | Function | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |O|M| rsvd | Dialect | Language Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Char Encoding | XID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Version This protocol document defines version 1 of the service location protocol. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 15]
Internet Draft Service Location Protocol 10 June 1996 Function Service location datagrams can be identified as to their operation by the function field. The following are the defined operations: Message Type Abbreviation Function Value Service Request SrvReq 1 Service Reply SrvRply 2 Service Registration SrvReg 3 Service Deregister SrvDereg 4 Service Acknowledge SrvAck 5 Attribute Request AttrRqst 6 Attribute Reply AttrRply 7 DA Advertisement DAAdvert 8 Service Type Request SrvTypeRqst 9 Service Type Reply SrvTypeRply 10 Length The number of bytes in the message, including the Service Location Header. O The 'Overflow' bit. See Section 19 for the use of this field. M The 'Monolingual' bit. Requests with this bit set indicate the User Agent will only accept responses in the language (see section 18) that is indicated by the Service or Attribute Request. rsvd MUST be zero. Dialect Dialect tags are used in Service Location messages to indicate a variant of vocabulary used. Language Code Strings within the remainder of the message which follows are to be interpreted in the language encoded (see appendix A) in this field. See also section 18. Character Encoding The characters making up strings within the remainder of the message may be encoded in any standardized encoding (see section 18.1). Transaction Identifier (XID) The XID (transaction ID) field allows the requester to match replies to individual requests (see section 5.1). Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 16]
Internet Draft Service Location Protocol 10 June 1996 When URLs are registered, they have lengths and lifetimes. These two values are associated with the URL for the duration of the registration. The triplet (length, lifetime, URL) is known as a "URL-entry", and has the following format when used in Service Replies and Service Registrations: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Lifetime | Length of URL String | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ <URL String> \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The URL string conforms to RFC 1738 [7]. If the scheme used in the URL does not have a standardized representation, the minimal requirement is: service:<srvtype>://<addr-spec> The "SERVICE" string is the URL scheme of all Service Location Information included in Service Registrations and Service Replies. Each entry in the Reply will always have a <srvtype>. It may also include an <addr-spec> except in the case of a reply to a Service Type request (see section 8). 5.1. Use of Transaction IDs (XIDs) Retransmission is used to ensure reliable transactions in the Service Location Protocol. If a User Agent or Service Agent sends a message and fails to receive an expected response, the message will be sent again. Retransmission of the same service location datagram should not contain an updated XID. It is quite possible the original request reached the DA or SA, but reply failed to reach the requester. Using the same XID allows the DA or SA to cache its reply to the original request and then send it again, should a duplicate request arrive. This cached information should only be held very briefly (CONFIG_INTERVAL_0.) Any registration or deregistration at a Directory Agent, or change of service information at a SA should flush this cache so that the information returned to the client is always valid. The requester creates the XID from an initial random seed and increments it by one for each request it makes. The XIDs will eventually wrap back to zero and continue incrementing from there. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 17]
Internet Draft Service Location Protocol 10 June 1996 Directory Agents use XID values in their DA Advertisements to indicate their state (see section 16.2). 5.2. URL Entry Lifetime The Lifetime field is set to the number of minutes the reply can be cached by any agent. A value of 0 means the information must not be cached. User Agents MAY cache service information, but if they do, they must provide a way for applications to flush this cached information and issue the request directly onto the network. Services should be registered with DAs with a Lifetime, the suggested value being CONFIG_INTERVAL_1. The service must be reregistered before this interval elapses, or the service advertisement will no longer be available. Thus, services which vanish and fail to deregister eventually become automatically deregistered. 6. Service Request Message Format The Service Request is used to obtain URLs from a Directory Agent or Service Agents. The format of the Service Request is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service location header (function = SrvReq) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of prev responder list |<Previous Responders Addr Spec>| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ <Previous Responders Addr Spec> \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ Service Request <predicate> \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The <Previous Responders Addr Spec> is described in sections 8 and 21.1. After a User Agent restarts (say, after rebooting of a system, loading of the network kernel), Service Requests should be delayed for some random time uniformly distributed within a one second Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 18]
Internet Draft Service Location Protocol 10 June 1996 interval centered about a configured delay value (by default, CONFIG_INTERVAL_4). The Service Request allows the User Agent to specify the Service Type of the service and a Predicate in a specific language. The general form of a Service Request is shown below: <srvtype>[.<na>]/[<scope>]/[<where>]/ The punctuation is necessary even where the fields are omitted. - The <srvtype> refers to the Service Type. For each type of service available, there is a unique Service type name string. See section 21.3.1. - The <na> is the Naming Authority. This string determines the semantic interpretation of the attribute information in the <where> part of the Service Request. - The <scope> is a string used to restrict the range of the query. Scope is determined administratively, at a given site. It is not necessarily related to network topology (see Section 17). Leaving this field out means that the request can be satisfied under any scope. - The <where> string is the Where Clause of the request. It contains query which specify which service instances the User Agent is interested in. The query includes attributes, boolean operators and relations. (See section 6.3.) In the case of a multicast request, a list of previous responders is sent. This list will prevent those in the list from responding, to be sure that responses from other sources are not drowned out. The request is multicast repeatedly (with a recommended wait interval of CONFIG_INTERVAL_2) until there are no new responses, or a certain time (CONFIG_INTERVAL_3) has elapsed. In order for a request to succeed in matching registered information, the following conditions must be met: 1. The result must have the same Service Type as the request. 2. It must have the same Naming Authority. 3. It must have the same Scope (unless the <scope> of the request was omitted.) Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 19]
Internet Draft Service Location Protocol 10 June 1996 4. The conditions specified in the Where Clause must match the attributes and keywords registered for the service. 6.1. Service Request Usage The User Agent may form Service Requests using preconfigured knowledge of a Service Type's attributes. It may also issue Attribute Requests to obtain the attribute values for a Service Type before issuing Service Requests (see Section 13). Having obtained the attributes which describe a particular kind of service from an Attribute Request, (or using configured knowledge of a service's attributes,) the User Agent can build a predicate that describes the service needs of the user. Service Requests may be sent directly to a Directory Agent. Suppose a printer supporting the lpr protocol is needed on the 12th floor which has UNRESTRICTED_ACCESS and prints 12 pages per minute. Suppose further that a Attribute Request indicates that there is a printer on the 12th floor, a printer that prints 12 pages per minute, and a printer that offers UNRESTRICTED_ACCESS. To check whether they are same printer, issue the following request: lpr://(& (PAGES PER MINUTE==12) (UNRESTRICTED_ACCESS) (LOCATION==12TH FLOOR))/ Suppose there is no such printer. The Directory Agent responds with a Service Reply with 0 in the number of responses and no reply values. The User Agent then tries a less restrictive query to find a printer, using the 12th floor as "where" criteria. lpr://(LOCATION==12TH FLOOR)/ In this case, there is now only one reply: Returned URL: service:lpr://igore.wco.ftp.com:515 Returned Attrs: ((PAGES PER MINUTE = 3),(PROTOCOL=LPR,PCNFS)) The Address Specification for the printer is: igore.wco.ftp.com:515. This is the location of the printer. Files would be printed by spooling to that port on that host. In the absence of a Directory Agent, the request above could be multicast. In this case it would be sent to the printer Multicast Address and not to the Directory Agent. Service Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 20]
Internet Draft Service Location Protocol 10 June 1996 Agents that can satisfy the predicate will reply. Service Agents which cannot support the character set of the request MUST return CHARSET_NOT_UNDERSTOOD in the SrvTypeRply. In all other circumstances, Service Agents which cannot satisfy the reply do not send any reply at all. The only way a User Agent can be sure there are no services which match the query is by retrying the request (CONFIG_INTERVAL_8). If no response comes, the User Agent gives up and assumes there are no such printers. Another form of query is a simpler 'join' query. Its syntax has no parentheses or logical operators. Each term is conjoined (AND-ed together.) Rewriting the initial query provides an example: lpr://PAGES PER MINUTE==12, UNRESTRICTED_ACCESS, LOCATION==12TH FLOOR/ 6.2. Directory Agent Discovery Request Normally a Service Request returns a Service Reply. The sole exception to this is a Service Request for the Service Type "directory-agent". This Service Request is answered with a DA Advertisement. Without configured knowledge of a Directory Agent (DA), a User Agent or Service Agent uses a Service Request to discover a DA. (See section 16.1 for mechanisms by which a client may be configured to have knowledge of a DA.) Such a Service Request used for Directory Agent Discovery includes a predicate of the form: directory-agent:/// This query is always sent to the Directory Agent Discovery multicast address. The Service Type of a Directory Agent is "directory-agent", hence it is the Service Type used in the request. No scope is included in the request, since the query is global in scope. No Naming Authority is included, so "IANA" is assumed. We want to reach all the available directory agents. If the scope were supplied, only DAs supporting that scope would reply. Replies may arrive from different sources, similar in form to: URL returned: directory-agent://slp-resolver.catch22.com Scope returned: ACCOUNTING Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 21]
Internet Draft Service Location Protocol 10 June 1996 URL returned: directory-agent://204.182.15.66 Scope returned: JANITORIAL SERVICES If the goal is merely to discover any Directory Agent, the first reply will do. If the goal, however, is to discover all reachable DAs, the request must be retransmitted after an interval (the recommended time is CONFIG_INTERVAL_5). This retransmitted request will include a list of DAs which have already responded. See sections 8 and 21.1. Directory Agents which receive the request will only respond if they are not on this list. After there are no new replies, all DAs are presumed to have been discovered. If a DA fails to respond after CONFIG_INTERVAL_6 seconds, the UA or Service Agent should use a different DA. DA addresses may be cached from previous discovery attempts, preconfigured, or by use of DHCP (see section 16.2). If no such DA responds, DA discovery should be used to find a new DA. Only after CONFIG_INTERVAL_7 seconds should it be assumed that no DA exists and multicast based Service Requests should be used. 6.3. Explanation of Terms of Predicate Grammar A predicate has a simple structure, which depends on parentheses, commas and slashes to delimit the elements. Examples of proper usage are given throughout this document. The terms used in the grammar are as follows: predicate: Placed in a Service Request, this is interpreted by a Service Agent or Directory Agent to determine what information to return. scope: If this is absent in a Service Request, the request will match any service regardless of scope. If it is present, only services registered under that scope will match the request. where-clause: This determines which services the request matches. An empty where-clause will match all services. The request will be limited to services which have the specified Service Type, so the where-clause is not the sole factor in picking out which services match the request. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 22]
Internet Draft Service Location Protocol 10 June 1996 where-list: The where-list is a logical expression. It can be a single expression, a disjunction or a conjunction. A single expression must apply for the where-clause to match. A disjunction matches if any expression in the OR list matches. A conjunction matches only if all elements in the AND list match. Note that there is no logical negation operator: This is because there is no notion of returning "everything except" what matches a given criteria. A where-list can be nested and complex. For example, the following requires that three subexpressions must all be true: (& (| <query-item> <query-item>) <query-item> (& <query-item> <query-item> <query-item>) ) Notice that white space, tabs or carriage returns can be added anywhere outside query-items. Each list has 2 or more items in it, and lists can be nested. Services which fulfill the entire logical expression match the where-clause. '(' '|' <query-item> ')' and '(' '&' <query-item> ')' are degenerate expressions but they should be tolerated. They are equivalent to <query-item>. query-item: A query item has the form: '(' <attr-tag> <comp-op> <attr-val> ')' or '(' <keyword> ')' Examples of this would be: (SOME ATTRIBUTE == SOME VALUE) (RESERVED) (QUEUE LENGTH <= 234) Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 23]
Internet Draft Service Location Protocol 10 June 1996 query-join: The query-join is a comma delimited list of conditions which the service must satisfy in order to match the query. The items are considered to be logically conjoined. Thus the query-join: ATTR1=VALUE1, KEYWORD1, KEYWORD2, ATTR2>=34 is equivalent to the where-list: (& (ATTR1=VALUE1) (KEYWORD1) (KEYWORD2) (ATTR2>=34)) The query-join cannot be mixed with a where-list. It is provided as a convenient mechanism to provide a statement of necessary conditions without building a logical expression. 6.4. Service Request Predicate Grammar Service Requests can precisely describe the services they need by including a Predicate the body of the Request. This Predicate must be constructed according to the grammar below. <predicate> ::= <srvtype>['.'<na>]'/'<scope>'/'<where>'/' <srvtype> ::= string representing type of service. Only 'a' to 'z', 'A' to 'Z', '+' and '-' are allowed. <na> ::= string representing the Naming Authority. Only characters from 'a' to 'z', 'A' to 'z', '+' and '-' are allowed. If this field is omitted then "IANA" is assumed. <scope> ::= string representing the directory agent scope. '/', ',' (comma) and ':' are not allowed in this string. The scopes "LOCAL" and "REMOTE" are reserved. <attr-tag> ::= class name of an attribute of a given Service Type. This tag cannot include the following characters: '(', ')', ',', '=', '!', '>', '<', '/', '*', except where escaped (see 18.1.) <keyword> ::= a class name of an attribute which will have no values. This string has the same limits as the <attr-tag>. In addition white space internal to the keyword is illegal. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 24]
Internet Draft Service Location Protocol 10 June 1996 <where> ::= <where-any> | <where-list> | <query-join> <where-any> ::= That is NOTHING or white space. <where-list> ::= '(' '&' <where-list> <query-list> ')' | '(' '|' <where-list> <query-list> ')' | '(' <keyword> ')' '(' <attr-tag> <comp-op> <attr-val> ')' <query-list> ::= <where-list> | <where-list> <query-list> <query-join> ::= <keyword> | <join-item> | <query-join> ',' <keyword> | <query-join> ',' <join-item> <join-item> ::= <attr-tag> <comp-op> <attr-val> <comp-op> ::= "!=" | "==" | '<' | "<=" | '>' | ">=" <attr-val> ::= any string (see Section 21.5 for the ways in which attr-vals are interpreted.) Value strings may not contain '/', ',' '=', '<', '>', except where escaped (see 18.1.). '(' and ')' may be used in attribute values for the purpose of encoding a binary values. Binary encodings (See Section 10.3) may include the above reserved characters. 6.5. String Matching for Requests All strings are case insensitive, with respect to string matching on queries. All preceding or trailing blanks should not be considered for a match, but blanks internal to a string are relevant. For example " Some String " matches "SOME STRING" but not "some string". String matching may only be performed over the same character sets. If a query cannot be satisfied due to a lack of service information in the character set of the request a CHARSET_NOT_SUPPORTED error is returned. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 25]
Internet Draft Service Location Protocol 10 June 1996 String comparisons (using comparison operators such as '<' or '>=') are done using lexical ordering in the character set of the registration, not using any language specific rules. The ordering is strictly by the character value, i.e. "0" < "A" is true when the character set is US-ASCII, since "0" has the value of 48 and "A" has the value 65. String matching is done after escape sequences have been substituted. See sections 18, 6.3, 18.1. 7. Service Reply Message Format The format of the Service Reply Message is: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service location header (function = SrvRply) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error Code | number of replies returned | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | <URL Entry>-1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . | \ . \ | . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | <URL Entry>-N | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Each Service Reply message is composed of a list of URL Entries. The Error Code may have one of the following values: 0 Success LANGUAGE_NOT_SUPPORTED A SA or DA returns this when a request is received from a UA which is in a language for which there is no registered Service Information and the request arrived with the Monolingual bit set. See Section 18. PROTOCOL_PARSE_ERROR A SA or DA returns this error when a SrvReq is received which cannot be parsed. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 26]
Internet Draft Service Location Protocol 10 June 1996 SCOPE_NOT_SUPPORTED A DA which is configured to have a scope will return this error if it receives a request which is set to have a scope which it does not support. An SA will not return this error, it will simply not reply to the multicast request. CHARSET_NOT_UNDERSTOOD If the DA or SA receives a request or registration in a character set which it does not support, it will return this error. Each <URL Entry> in the list has the form defined at the end of Section 5. The URL strings in the reply have no delimiters between them, other than the length fields. The length fields indicate where the strings end. 8. Service Type Request Message Format The Service Type Request is used to determine all the types of services supported on a network. The request should be sent directly to a DA (though it may also be sent to the Service Location General Multicast Address), in order to find out all services available on the site network (which are advertised by Directory Agents and Service Agents.) If no DA is available, a User Agent MAY issue more than one request to insure that all replies have been received. In each subsequent request, a User Agent included those Service Types that it is aware of. When no new replies arrive within CONFIG_INTERVAL_3 from a request, the User Agent can presume that it has acquired a complete set of available Service Types. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 27]
Internet Draft Service Location Protocol 10 June 1996 The format of a Service Type Request is: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service location header (function = SrvTypeRqst) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of prev resp string |<Previous Responders Addr Spec>| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ <Previous Responders Addr Spec> \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of naming authority | <Naming Authority String> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ <Naming Authority String>, continued \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of scope string | <Scope String> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ <Scope String>, continued \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Note that the <Previous Responders Addr Spec> is a comma delimited list. (See section 21.1.) The 'length of prev responder list' field indicates the length of the comma delimited list string. A previous responder list with 3 elements takes this form: <addr-spec>,<addr-spec>,<addr-spec> The Naming Authority, if included, will limit the replies to Service Type Requests to Service Types which have the specified Naming Authority. If this field is omitted (i.e., the length field is zero), the default Naming Authority ("IANA") is assumed. If the length field is -1, service types from all naming authorities are requested. The Scope String Field, if included, will limit replies to Service Types which have the specified Scope. If this field is omitted, all Service Types (from the specified Naming Authority) are returned. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 28]
Internet Draft Service Location Protocol 10 June 1996 9. Service Type Reply Message Format The Service Type Reply has the following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service location header (function = SrvTypeRply) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Multicast Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error Code | number of service types | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ <Service Type Item>-1 \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . . . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ <Service Type Item>-N \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The format of a Service Type Item is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of Service Type String | <Service Type String> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ <Service Type String>, continued \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of addr spec string | <addr spec> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ <addr spec>, continued \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Error Code may have one of the following values: 0 Success Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 29]
Internet Draft Service Location Protocol 10 June 1996 PROTOCOL_PARSE_ERROR A SA or DA returns this error when a SrvTypeRqst is received which cannot be parsed. SCOPE_NOT_SUPPORTED A DA which is configured to have a scope will return this error if it receives a SrvTypeRqst which is set to have a scope which it does not support. An SA will not return this error, it will simply silently discard the multicast request. CHARSET_NOT_UNDERSTOOD If the DA receives a SrvTypeRqst in a character set which it does not support, it MUST this error. The service type's name is provided in the <Service Type String>. See section 21.3.1 for the formal definition of this field. The <addr spec> format is described in 21.4. This field provides the service specific multicast address. If the service specific multicast address is omitted, the General Service Location Multicast Address is assumed. User Agents may then use this multicast address for issuing Service and Attribute Requests directly to SAs. Example Service Type Replies might be: Multicast Address Service Type String 224.0.3.10 service:lpr:// 224.0.3.24 service:http:// 224.0.3.115 service:nfs:// NOTE: These multicast addresses are examples only, the official numbers have not yet been assigned. 10. Service Registration Message Format After a Service Agent has found a Directory Agent, it begins to register its advertised services one at a time. A Service Agent must wait for some random time uniformly distributed within the range specified by CONFIG_INTERVAL_11 before registering again. Registration is done using the Service Registration message specifying all attributes for a service. A Directory Agent must acknowledge each service registration request. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 30]
Internet Draft Service Location Protocol 10 June 1996 The format of a Service Registration is: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service location header (function = SrvReg) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ <URL-Entry> \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length of Attr List String | <attr-list> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ <attr-list>, Continued. \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The <URL-Entry> is defined at the end of Section 5. The <attr-list> is defined in Section 21.2. Service registration may use a connectionless protocol (e.g. UDP), or a connection oriented protocol (e.g. TCP). If the registration operation may contain more information than can be sent in one datagram, the Service Agent MUST use a connection oriented protocol to register itself with the DA. When a Service Agent registers the same attribute class more than once for a service instance, the Directory Agent overwrites the all the values associated with that attribute class for that service instance. Separate registrations must be made for each language that the service is to be advertised in. An example of Service Registration information is: Lifetime (minutes): 16-bit unsigned integer URL (at least): service:<srvtype>://<addr-spec> Attributes (if any): (ATTR1=VALUE),KEYWORD,(ATTR2 = VAL1, VAL2) In order to offer continuously advertised services, Service Agents should start the reregistration process before the Lifetime they used in the registration expires. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 31]
Internet Draft Service Location Protocol 10 June 1996 An example of a service registration (valid for one day) is as follows: Lifetime: 1440 URL: service:lpr://igore.wco.ftp.com:515 Attributes: (SCOPE=DEVELOPMENT), (PAPER COLOR=WHITE), (PAPER SIZE=LETTER), UNRESTRICTED_ACCESS, (LANGUAGE=POSTSCRIPT, HPGCL), (LOCATION=12 FLOOR) The same registration could be done again, as shown below, in German; however, note that "lpr", "service", and "SCOPE" are reserved terms and will remain in the language they were originally registered (English). Lifetime: 1440 URL: service:lpr://igore.wco.ftp.com:515 Attributes: (SCOPE=ENTWICKLUNG), (PAPIERFARBE=WEISS), (PAPIERFORMAT=BRIEF), UNBEGRENTZTER_ZUGANG, (DRUECKERSPRACHE=POSTSCRIPT,HPGCL), (STANDORT=11 ETAGE) Registrations must contain an Attribute of SCOPE unless they are unscoped and then they must be registered with all directory agents. In the example above, the SCOPE is set to DEVELOPMENT (in English) and ENTWICKLUNG (in German). Recall that all strings in a message must be in one language, which is specified in the header. The string SCOPE is *not* translated, as it is one of the reserved strings in the Service Location Protocol (see section 4.3.) The Directory Agent may return a server error in the acknowledgment. This error is carried in the Error Codes field of the service location message header. A Directory Agent MUST decline to register a service if it is specified with an unsupported Scope. A Directory Agent SHOULD always accept Service Registrations which have no Scope. In this case a SCOPE_NOT_SUPPORTED error is returned in the SrvAck. An unscoped service registration will match all requests. A request which specifies a certain scope will therefore return services which have that scope and services which are unscoped. It is strongly suggested that one should use scopes in all registrations or none. See Sections 17 and 4.7 for details. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 32]
Internet Draft Service Location Protocol 10 June 1996 11. Service Acknowledgement Message Format A Service Acknowledgement is sent as the result of a DA receiving and processing a Service Registration or Service Deregistration. An acknowledgment indicating success must have the error code set to zero. Once a DA acknowledges a service registration it makes the information available to clients. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service location header (function = SrvAck) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Error Code may have one of the following values: 0 Success PROTOCOL_PARSE_ERROR A DA returns this error when the SrvReg or SrvDereg could not be parsed. INVALID_REGISTRATION A DA returns this error when a SrvReg is invalid (it parses badly or is poorly formed in some way.) SCOPE_NOT_SUPPORTED A DA which is configured to have a scope will return this error if it receives a SrvReq which is set to have a scope which it does not support. CHARSET_NOT_UNDERSTOOD If the DA receives a SrvReg or SrvDereg in a character set which it does not support, it will return this error. AUTHENTICATION_FAILED If the DA uses IP Security Authentication and the SA sending a SrvReg or SrvDereg message fails to be authenticated, the DA will return this error. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 33]
Internet Draft Service Location Protocol 10 June 1996 12. Service Deregister When a service is no longer available for use, the Service Agent must deregister itself from Directory Agents that it has been registered with. A service uses the following PDU to deregister itself. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service location header (function = SrvDereg) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ <URL> of Service to Deregister \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of tag spec string | <tag spec> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ <tag spec>, continued \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Service Agent should retry this operation if there is no response from the Directory Agent. The Directory Agent acknowledges this operation with a service acknowledgment. Once the Service Agent receives an acknowledgment indicating success, it can assume that the service is no longer advertised by the Directory Agent. The Error Code in the Acknowledgment of the Service Deregistration may have the same values as described in section 11. The Service Deregister Information sent to the Directory Agent is a URL followed by a <tag-list>, where a <tag-list> is described by the following grammar: <tag-list> ::= <attr-tag> | <keyword> | <attr-tag> ',' <tag-list> | <keyword> ',' <tag-list> For definitions of <attr-tag> and <keyword> see 6.4. This will deregister the specified attributes from the service information from the Directory Agent. If no attribute tags are included, the entire service information is deregistered in every language and every scope it was registered in. To deregister the printer, use: service:lpr://igore.wco.ftp.com:515 Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 34]
Internet Draft Service Location Protocol 10 June 1996 13. Attribute Request Message Format The Attribute Request is used to obtain attribute information. The UA supplies a request and the appropriate attribute information is returned. If the UA supplies only a Service Type, and the reply includes all attributes and all values for that Service Type. The reply includes only those attributes for which services exist and are advertised by the DA or SA which received the Attribute Request. Since different instances of a given service can, and very likely will, have different values for the attributes defined by the Service Type, the User Agent must form a union of all attributes returned by all service Agents. The Attribute information will be used to form Service Requests. If the UA supplies a URL, the reply will contain service information corresponding to that URL. Attribute Requests include a 'select clause'. This may be used to limit the amount of information returned. If the select clause is empty, all information is returned. Otherwise, the UA supplies a comma delimited list of attribute tags and keywords. If the attribute or keyword is defined for a service, it will be returned in the Attribute Reply, along with all registered values for that attribute. If the attribute selected has not ben registered for that URL or Service Type, the attribute or keyword information is simply not returned. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 35]
Internet Draft Service Location Protocol 10 June 1996 The Attribute Request message has the following form: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service location header (function = AttrRqst) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |length of prev responders list |<Previous Responders Addr Spec>| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ <Previous Responders Addr Spec>, continued \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of URL | <URL> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ <URL>, continued \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of <scope> | <scope> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ <Scope>, continued \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | length of <select-list> | <select-list> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ <select-list>, continued \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The <Previous Responder Address List> functions exactly as introduced in Section 8. See also Section 21.1. The URL String can take two forms: Either it is simply a Service Type, such as "service:http:", or it can be a URL, such as "service:lpr://igore.wco.ftp.com:515". In the former case, all attributes and the full range of values for each attribute for the Service Type is returned. In the latter case, only the attributes for the service whose URL is defined are returned. The Scope String is provided so that Attribute Requests for Service Types can be made so that only the Attribute information pertaining to a specific scope will be returned. This field is ignored in the case when a full URL is sent in the Attribute Request. The rules for encoding of the Scope String are given in Section 6.4. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 36]
Internet Draft Service Location Protocol 10 June 1996 The select list takes the form: <select-list> ::= <select-item> | <select-item> ',' <select-list> <select-item> ::= <keyword> | <attr-tag> | <partial-tag> '*' <partial-tag> ::= the partial class name of an attribute followed by an '*' matches all class names which begin with the characters preceding the '*' For definitions of <attr-tag> and <keyword> see 6.4. An example of a select-list following the printer example is: PAGES PER MINUTE, UNRESTRICTED_ACCESS, LOCATION If sent to a Directory Agent, the number of previous responders is zero and there are no Previous Responder Address Specification. These fields are only used for repeated multicasting, exactly as for the Service Request. 14. Attribute Reply Message Format An Attribute Reply Message takes the form: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service location header (function = AttrRply) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error Code | length of <attr-list> string | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ <attr-list> \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Error Code may have the following values: 0 Success LANGUAGE_NOT_SUPPORTED A SA or DA returns this when a request is received Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 37]
Internet Draft Service Location Protocol 10 June 1996 from a UA which is in a language for which there is no registered Service Information and the request arrived with the Monolingual bit set. See Section 18. PROTOCOL_PARSE_ERROR A DA or SA returns this error when the AttrRqst could not be parsed. SCOPE_NOT_SUPPORTED A DA which is configured to have a scope will return this error if it receives an AttrRqst which is set to have a scope which it does not support. SAs will silently discard multicast AttrRqst messages for scopes they do not support. CHARSET_NOT_UNDERSTOOD If the DA receives an AttrRqst in a character set which it does not support, it will return this error. SAs will silently discard multicast AttrRqst messages which arrive using character sets they do not support. The <attr-list> (attribute list) has the same form as the attribute list at the end of a reply, see Section 21.2 for a formal definition of this field. An Attribute Request for "lpr" might elicit the following reply (UNRESTRICTED_ACCESS is a keyword): (PAPER COLOR=WHITE,BLUE), (PAPER SIZE=LEGAL,LETTER,ENVELOPE,TRACTOR FEED), UNRESTRICTED_ACCESS, (PAGES PER MINUTE=1,3,12), (LOCATION=12TH, NEAR ARUNA'S OFFICE), (QUEUES=LEGAL,LETTER,ENVELOPE,LETTER HEAD) Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 38]
Internet Draft Service Location Protocol 10 June 1996 15. Directory Agent Advertisement Message Format Directory Agent Advertisement Messages have the following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Service location header (function = DAAdvert) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error Code | Length of URL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ <URL> \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length of <scope-list> | <scope-list> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | \ <scope-list>, continued \ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Error Code is set when a DA Advertisement is returned as the result of a Service Request. It will always be set to 0 in the case of an unsolicited DA Advertisement. The Error Code may take the values specified in Section 7. The URL corresponds to the Directory Agent's location. The <scope-list> is a comma delimited list of Scopes which the DA supports, in the following format: <scope-list> ::= <scope> | <scope-list> ',' <scope> <scope> ::= String representing a scope See Section 6.4 for the lexical rules regarding <scope>. DA Advertisements sent in reply to a Directory Agent Discovery Request has the same format as the unsolicited DA Advertisement, for example: URL: directory-agent://SLP-RESOLVER.CATCH22.COM SCOPE List: ADMIN The Directory Agent can be reached at the Address Specification returned, and supports the SCOPE called "ADMIN". Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 39]
Internet Draft Service Location Protocol 10 June 1996 16. Directory Agents 16.1. Introduction A Directory Agent acts on behalf of many Service Agents. It acquires information from them and acts as a single point of contact to supply that information to User Agents. The queries that a User Agent multicasts to Service Agents (in an environment without a Directory Agent) are the same as queries that the User Agent might unicast to a Directory Agent. A User Agent may cache information about the presence of alternate Directory Agents to use in case a selected Directory Agent fails. Aside from enhancing the scalability of the protocol (see section 4.7), running multiple DAs provides robustness of operation. The DAs have replicated service information which remain accessible even when one of the DAs fail. Directory Agents, in the future, may use mechanisms outside of this protocol to coordinate the maintenance of a distributed database of service location information, and thus scale to enterprise networks or larger administrative domains. Each Service Agent must register with all DAs they are configured to use. UAs may choose among DAs they are configured to use. Locally, Directory Agent consistency is guaranteed using mechanisms in the protocol. There isn't any Directory to Directory Agent protocol yet. Rather, passive detection of DAs by SAs ensures that eventually service information will be registered consistently between DAs. Invalid data will age out of the Directory Agents leaving only transient stale registrations even in the case of a failure of a Service Agent. 16.2. Finding Directory Agents A User or Service Agent may be statically configured to use a particular DA. This is discouraged unless the application resides on a network where any form of multicast or broadcast is impossible. Alternatively, a host which uses DHCP [2, 10] may use it to obtain a Directory Agent's address. A DHCP option will be assigned for this purpose. It has not yet been, at the time this document was written. The third way to discover DAs is dynamically. This occurs actively by sending out a Directory Agent Discovery request (see Section 6.2). Lastly, the agent may be informed passively as follows: Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 40]
Internet Draft Service Location Protocol 10 June 1996 When a Directory Agent first comes on-line it sends an unsolicited DA Advertisement to the service location general multicast address. If a DA supports a particular scope or set of scopes these are placed in the reply. The class for this attribute is 'SCOPE'. Every CONFIG_INTERVAL_9 a Directory Agent will send an unsolicited DA Advertisement again. This will ensure that eventually it will be discovered by all applications which are concerned. When a Directory Agent first comes up it begins with 0 as its XID, and increments this by one each time it sends an unsolicited DA Advertisement. When the counter wraps, it should go from 0xFFFF to 0x0100, not 0. If the Directory Agent has stored all of the service information in a nonvolatile store, it should initially set the XID to 0x100, as it is not coming up 'stateless.' If it stores service registrations in memory only, it will restart without any state. It should indicate this by resetting its XID to 0. All Service Agents which receive the unsolicited DA Advertisement should examine its XID. If the Directory Agent has never before been heard from or if the XID is less than it was previously and less than 256, the Service Agent should assume the DA does not have its service registration, even if it once did. If this is the case and the DA has the proper Scope, the SA should register all service information with the Directory Agent, after waiting a random interval CONFIG_INTERVAL_10. When a Service Agent or User Agent first comes on-line it must issue a Directory Agent Discovery Request unless it is using static or DHCP configuration, as described in 6.2. A Service Agent registers information with ALL newly discovered Directory Agents when either of the above two events take place. When scopes are being used, a Service Agent may choose a set of scopes to be advertised in and need only register with Directory Agents that support the scopes in which they wish to be registered. Services MUST be registered with DAs that support their scope and those which have no scope, unless specifically configured not to do so (see section 23.1.) Once a User Agent becomes aware of a Directory Agent it will unicast its queries there. In the event that more than one Directory Agent is detected, it will select one to communicate with. When scopes are supported, the User Agent will direct its queries to different Directory Agents depending on which scopes are appropriate domains for the query to be answered in. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 41]
Internet Draft Service Location Protocol 10 June 1996 The protocol will cause all DAs (of the same scope) to eventually obtain consistent information. Thus one DA should be as good as any other for obtaining service information. There may be temporary inconsistencies between DAs. 17. Scope Discovery and Use The scope mechanism in the service location protocol enhances its scalability. The primary use of scopes is to provide the capability to organize a site network along administrative lines. A set of services can be assigned to a given department of an organization, to a certain building or geographical area or for a certain purpose. The users of the system can be presented with these organizational elements as a top level selection, before services within this domain are sought. A site network that has grown beyond a size that can be reasonably serviced by a few DAs can use the Scope mechanism. DAs have the attribute class "SCOPE". The values for this attribute are a list of strings that represent the administrative areas for which this Directory Agent is an authority. The semantics and language of the strings used to describe the Scope are almost entirely the choice of the administrative entity of the particular domain in which these Scopes exist. The values of SCOPE should be configurable, so the system administrator can set its value. The scopes "LOCAL" and "REMOTE" are reserved and SHOULD NOT be used. Use of these reserved values is to be defined in a future protocol document. Services with the attribute SCOPE should only be registered with DAs which support the same scope or DAs which have no Scope. Directory Agents advertise the available scopes. A Service Agent may then choose a scope in which to register, and SHOULD register with all Directory Agents in that scope, as well as all DAs which have no scope. Failure to be comprehensive in registration according to this rule will mean that the service advertisement may not be discoverable by all User Agents. A Directory Agent which has a Scope will send replies to Directory Agent Discovery requests with the scope information included. Note that the directory-agent Service Type is registered with the IANA naming authority (which is automatically selected by leaving the Naming Authority field empty.) The query: directory-agent:/MATH DEPT// Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 42]
Internet Draft Service Location Protocol 10 June 1996 Could receive the following DA Advertisement: Returned URL: directory-agent://diragent.blah.edu Returned SCOPE: MATH DEPT The same Directory Agent if it had no Scope value would reply: Returned URL: directory-agent://diragent.void.com Returned SCOPE: If a Directory Agent supported more than one scope it would reply as: Returned URL: directory-agent://srv.domain.org Returned SCOPE: MATH DEPT,ENGLISH DEPT,CS DEPT A DA which has no scope will reply to any Directory Agent Discovery Request. Being a member of a scope means that an agent may use those Directory Agents that support its scope. User Agents send all requests to DAs which support the indicated scope. Services are registered with the DA(s) in their scope. For a UA to find a service that is registered in a particular scope they must send requests to a DA which supports the indicated scope. There is no limitation on scope membership built into the protocol; that is to say, a User Agent or Service Agent may be a member of more than one scope. Membership is open to all, unless some external authorization mechanism is added to limit access. 18. Language and Character Encoding Issues All Service Registrations declare the language in which the strings in the service attributes are written by specifying the appropriate code in the message header. For each language the Service advertises a separate registration takes place. The Service needs to be deregistered only once since the information associated with it will be unique. There can only be one service of a given type at a given address specification even if it is registered in multiple languages. Service Registrations in different languages are mutually unintelligible. They share no information except for their service type and URL string with which they were registered. No attempt is made to match queries with "language independence." Instead, queries are handled using string matching against registrations in the same language as the query. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 43]
Internet Draft Service Location Protocol 10 June 1996 Service Types which are standardized will have definitions for all attributes and value strings. Official translations to other languages of the attribute tags and values may be created and submitted as part of the standard; this is not feasible for all languages. For those languages which are not defined as part of the Service Type, a best effort translation of the standard definitions of the Service type's attribute strings MAY be used. All Service Requests specify a requested language in the message header. The Directory Agent or Service Agent will respond in the same language as the request, if it has a registration in the same language as the request. If this language is not supported, and the Monolingual bit is not specified, a reply can be sent in the default language (which is English.) If the 'monolingual bit' flag in the header is set and the requested language is not supported, a SrvRply is returned with the error field set to LANGUAGE_NOT_SUPPORTED. If a query is in a supported language on a SA or DA, but has a different dialect than the available service information, the query MUST be serviced on a best-effort basis. If possible, the query should be matched against the same dialect. If that is not possible, it MAY be matched against any dialect of the same language. 18.1. Character Encoding and String Issues Values for character encoding can be found in the Internet Assigned Numbers Authority's (IANA) database (http://www.isi.edu/in-notes/iana/assignments/character-sets), and have the values referred by the MIBEnum value. The encoding will determine the interpretation of all character data which follows the Service Location protocol header. There is no way to mix ASCII and UNICODE, for example. All responses must be in the character set of the request or use US-ASCII. If a request is sent to a DA or SA or a registration is sent to a DA, which is unable to manipulate or store the character set of the incoming message, the request will fail. The SA or DA returns a CHARSET_NOT_UNDERSTOOD error in a SrvAck message in this case. Requests using US-ASCII will never fail for this reason, since all SAs and DAs must be able to accept this character set. Certain characters are illegal in certain contexts of the protocol. Since the protocol is largely character string based, in some contexts characters are used as protocol delimiters. In these cases the delimiter characters must not be used as 'data text.' Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 44]
Internet Draft Service Location Protocol 10 June 1996 18.1.1. Substitution of Character Escape Sequences The Service Location Protocol has an 'escape mechanism' which is consistent with HTTP 2.0 [6] and SGML [13]. If the character sequence "&#" is followed by one or more digits, followed by a semicolon ';' the entire sequence is interpreted as a single character. The digits are interpreted as a decimal value in the character set of the request, as specified by the header. Thus, in US-ASCII , would be interpreted as a comma. Substitution of these escape strings must be done in all <attr-list> and strings present in SrvReq and AttrRqst messages. Only numerical character references are accepted, not 'Entity References,' as defined in HTML. These escape values should only be used to provide a mechanism for including reserved characters in attribute tag and value strings. The interpretation of these escape values is different than in HTML in one respect: In HTML the escape values are considered to be in the ISO Latin-1 character set. In Service Location they are interpreted in the character set defined in the header of the message. This escape mechanism allows characters like commas to be included in attribute tags and values, which would otherwise be illegal as the comma is a protocol delimiter. Attribute tags and values of different languages are considered to be mutually unintelligible. A query in one language SHOULD use service information registered in that language. 18.2. Language Dialect Dialect tags are used in Service Location messages to indicate a variant of vocabulary used. If one service is registered in more than one dialect, a DA or SA SHOULD return the one with the same dialect tag as in the query, but MAY choose to return any registered service that matches the criteria. Dialects (unlike languages) are assumed to be mutually intelligible, but may have variations in spelling. Since string matching is used, it is advantageous in some cases to register service information in multiple dialects. Dialect tags will be assigned as enumerated values to correspond to the official dialects registered with the IANA. There are as of this writing no enumerated dialect values; they will be created as needed. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 45]
Internet Draft Service Location Protocol 10 June 1996 18.3. Language-Independent Strings Some strings, such as Service Type names, have standard definitions. These strings should be considered as tokens and not as words in a language to be translated. Reserved String Section Definition --------------- ------- -------------------------------------- SCOPE 4, 16 Used to limit the scope of requests. SERVICE TYPE 8 Used in Service Type requests. SERVICE 10, 7 The URL scheme of all Service Location information registered with a DA or returned from a Service Request. <srvtype> 21.3.1 Used in all service registrations and replies. domain names 21.4 A fully qualified domain name, used in registrations and replies. SA MULTICAST ADDRESS 8 An attribute whose value is the service-specific multicast address. IANA 4.3 The default naming authority. LOCAL 17 Reserved. REMOTE 17 Reserved. TRUE 21.5 Boolean true. FALSE 21.5 Boolean false. 19. Service Location Transactions 19.1. Service Location Connections When a Service Location Request or Attribute Request results in a UDP reply from a Service or Directory Agent that will overflow a datagram, the User Agent can open a connection to the Agent and reissue the request over the connection. The reply will be returned with the overflow bit set (see section 5). The reply will contain as much data as will fit into a single datagram. If no MTU information is available for the route, assume that the MTU is 1400; this value is configurable (see section 23). When a request results in overflowed data that cannot be correctly parsed (say, because of duplicate or dropped IP datagrams), a User Agent that wishes to reliably obtain the overflowed data must establish a TCP connection with the Directory Agent or Service Agent with the data. The request is sent again with a new XID. The reply is returned over the connection stream. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 46]
Internet Draft Service Location Protocol 10 June 1996 When registration data exceeds one datagram in length, the Service Registration should be made by establishing a connection with a Directory Agent and sending the registration over the connection stream. Directory Agents and Service Agents must respond to connection requests; services whose registration data can overflow a datagram must be able to use TCP to send the registration. User Agents should be able to make Service Requestsequests using TCP. If they fail to implement this, they must be able to interpret partial replies and/or reissue requests with more selective criteria to reduce the size of the replies. A connection initiated by an Agent may be used for a single transaction. It may also be used for multiple transactions. Since there are length fields in the message headers, the Agents may send multiple requests along a connection and read the return stream for acknowledgments and replies. The initiating agent is responsible for closing the TCP connection. The DA should wait at least CONFIG_INTERVAL_12 before closing an idle connection. DAs and SAs SHOULD eventually close idle connections to ensure robust operation, even when the agent which opened a connection neglects to close it. There is no requirement that one transaction complete before a given host begins another. An agent may have multiple outstanding transactions, initiated either using UDP or TCP. All Service Location actions are idempotent. Of course registration and deregistration will change the state of a DA, but repeating these actions will have exactly the same effect each time. 20. Security Considerations The Service Location protocol does not provide authentication, integrity or confidentiality. Because the objective of this protocol is to advertise services to a community of users, confidentiality might not generally be needed when this protocol is used in non-sensitive environments. Authentication and integrity are functionally equivalent in the context of this protocol. Authentication is generally needed with this protocol. An adversary can easily use this protocol to advertise services on servers controlled by the adversary and thereby gain access to users' private information. Further, an adversary using this protocol will find it much easier to engage in selective denial of service Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 47]
Internet Draft Service Location Protocol 10 June 1996 attacks. Sites that are in potentially hostile environments (e.g. are directly connected to the Internet) should consider the security risks of deploying this protocol prior to deploying it. The security risks in this protocol can be significantly reduced or eliminated by using the IP Authentication Header [5, 3] with all Service Location messages. It is recommended that sites use the IP Authentication header with all Service Location messages. For the security considerations listed above, it is recommended that all nodes which implement Service Location also implement the IP Authentication Header. Sites requiring confidentiality should implement the IP Encapsulating Security Payload (ESP) [4] to provide confidentiality for Service Location messages. Service Location is useful as a bootstrap protocol. It may be used in environments in which no preconfiguration is possible. In such situations, a certain amount of "blind faith" is required: Without any prior configuration it is impossible to use any of the security mechanisms described above. Service Location will make use of the mechanisms provided by the Security Area of the IETF for key distribution as they become available. At this point it would only be possible to deploy the IP Authentication Header if some certificate information can be preconfigured with the end systems before they use Service Location. 21. String Formats used with Service Location Messages The following section supplies formal definitions for fields and protocol elements introduced in the sections indicated. Protocol Element Defined in Used in ----------------------------------- ------------ ------------ <Previous Responders' Addr Spec> 21.1 SrvReq Service Request <predicate> 6.4 SrvReq <URL-String> 21.2 SrvReg, SrvDereg, SrvRply <attr-list> 21.3 SrvReg, SrvRply, AttrRply <Service Registration Information> 10 SrvReg <Service Deregister Information> 12 SrvDereg <Service Type String> 21.3.1 AttrRqst Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 48]
Internet Draft Service Location Protocol 10 June 1996 21.1. Previous Responders' Address Specification The previous responders' Address Specification is specified as <Previous Responders' Address Specification> ::= <addr-spec>, | <addr-spec>, <Previous Responders' Address Specification> i.e., a list separated and terminated by commas with no intervening white space. The Address Specification is the address of the Directory Agent or Service Agent which supplied the previous response. The format for Address Specifications in Service Location is defined in section 21.4. The comma delimiter is required between each <addr-spec>. The use of dotted decimal IP address notation should only be used in environments which have no Domain Name Service. Example: RESOLVO.NEATO.ORG,128.127.203.63 21.2. Reply and Registration Information Service Replies and Service Registrations have two fields -- a URL and an attribute list. URLs are defined in RFC 1738 [7]. They should contain at least: <url> ::= service:<srvtype>://<addr-spec> where: service the URL scheme for service location, to return Replies. <srvtype> a string; Service Types may be standardized by developing a specification for the "service type"-specific part and registering it with the IANA. See section 18. <addr-spec> the service access point of the service. It is the network address or domain name where the service can be accessed. See section 21.4. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 49]
Internet Draft Service Location Protocol 10 June 1996 21.3. Attribute Information The <attr-list> is returned in the Attribute Reply if the Attribute Request does not result in an empty result. <attr-list> ::= <attribute> | <attribute>, <attr-list> <attribute> ::= (<attr-tag>=<attr-val-list>) | <keyword> <attr-val-list> ::= <attr-val> | <attr-val>, <attr-val-list> An <attr-list> must be scanned prior to evaluation for all occurrences of the string "&#" followed by one or more digit followed by ';'. See Section 18.1 and specifically Section 18.1.1. A keyword has only an <attr-tag>, and no values. A comma cannot appear in an <attr-val>, as the comma is used as the multiple value delimiter. Examples of an <attr-list> are: (SCOPE=ADMINISTRATION) (COLOR=RED, WHITE, BLUE) (DELAY=10 MINS),BUSY,(LATEST BUILD=10-5-95),(PRIORITY=L,M,H) The third example has three attributes in the list. Color can take on the values red, white and blue. There are several other examples of replies throughout the document. 21.3.1. Service Type String The Service Type is a string describing the type of service. These strings may only be comprised of 'a' through 'z', '+' and '-'. Upper case is considered equivalent to lower case in Service Type names. If the Service Type name is followed by a '.' and a string (which has the same limitations) the 'suffix' is considered to be the Naming Authority of the service. If the Naming Authority is omitted, IANA is assumed to be the Naming Authority. Service Types developed for in-house or experimental use may have any name and attribute semantics provided that they do not conflict with the standardized Service Types. The Service Type's Service specific Multicast Address used should taken from the range of experimental multicast addresses reserved by the IANA. 21.4. Address Specification in Service Location The address specification used in Service Location is: Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 50]
Internet Draft Service Location Protocol 10 June 1996 <addr-spec> ::= [<user>:<password>@]<host>[:<port>] <host> ::= Fully qualified domain name | dotted decimal IP address notation It is preferable to use a fully qualified domain name wherever possible as renumbering of host addresses will make IP addresses invalid over time. When no Domain Name Server is available SAs and DAs must use dotted decimal conventions for IP addresses. Generally, just the host domain name (or address) is sufficient to return. When there is a non-standard port for the protocol, that should be returned as well. Some applications may make use of the <user>:<password>@ syntax, but its use is not encouraged in this context until mechanisms are established to maintain confidentiality. Address specification in Service Location is consistent with standard URL format [7]. 21.5. Attribute Value encoding rules Attribute values, and attribute tags are CASE INSENSITIVE for purposes of lexical comparison. Attribute values can have be any string with the exception of '(', ')', '=', '>', '<', '/' and ',' (the comma) except in the case described below where opaque values are encoded. These characters may be included using the character value escape mechanism described in section 18.1. While an attribute can take any value, there are three types of values which differentiate themselves from general strings: Booleans, Integers and Opaque values. - Boolean values are either "TRUE" or "FALSE". This is the case regardless of the language (i.e. in French or Telugu, Boolean TRUE is "TRUE", as well as in English.) Boolean attributes can take only one value. - Integer values are expressed as a sequence of numbers. The range of allowable values, for this 32 bit quantity, is "-2147483648" to "2147483647". Note: No other form of numeric representation is interpreted as such, save integers. For example, hexadecimal numbers such as "0x342" are not interpreted as integers, but as strings. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 51]
Internet Draft Service Location Protocol 10 June 1996 - Opaque values (i.e. binary values) are expressed in radix-64 notation. The syntax is: <opaque-val> ::= (<len>:<radix-64-data>) <len> ::= number of bytes of the original data <radix-64-data> ::= radix-64 encoding of the original data Radix-64 encodes every 3 bytes of binary data into 4 bytes of ASCII data which is in the range of characters which are fully printable and transferable by mail. For a formal definition of the Radix-64 format see RFC 1521 [8], MIME Part One, Section 5.2 Base64 Content Transfer Encoding, page 21. 22. Implementation Requirements A User Agent MAY: - Provide a way for the application to configure the default DA, so that it can be used without needing to find it each initially. - Be able to request the address of a DA from DHCP, if configured to do so. - Ignore any unauthenticated Service Reply or Attribute Reply. - Be able to issue requests in any language or character set provided that it can switch to the default language and character set if the request can not be serviced by DAs and SAs at the site. A User Agent SHOULD: - Listen on the Service Location General Multicast address for unsolicited DA Advertisements. This will increase the set of Directory Agents available to it for making replies. See Section 16.2. If this is not done, new DAs will not be passively detected. A UA which does not have a configured DA and has not yet discovered one and is not listening for unsolicited DA Advertisements will remain ignorant of DAs. It may then do a DA discovery before each query performed or it may simply use multicasted queries to Service Agents. A User Agent MUST: - Be able to unicast requests and receive replies from a DA. Transactions should be made reliable by using retransmission Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 52]
Internet Draft Service Location Protocol 10 June 1996 of the request if the reply does not arrive within a timeout interval. - Be able to detect DAs using a Directory Agent Discovery request issued when the UA starts up. - Be able to send requests to a multicast address. If the multicast address is not known, the UA must be able to use a Service Type query to obtain the multicast address for the Service Type of the request. - Be able to handle numerous replies after a multicast request. The implementation may be configurable so it will either return the first reply, all replies until a timeout or keep trying till the results converge. - Ignore any unauthenticated Service Reply or Attribute Reply when an appropriate IPSec Security Association for that Reply exists. - Use the IP Authentication Header or IP Encapsulating Payload in all Service Location messages, whenever an appropriate IPSec Security Association exists. - Be able to issue requests using the US-ASCII character set. A Service Agent MAY be able to: - Get the address of a local Directory Agent by way of DHCP. - Accept requests in non-US-ASCII character encodings. This is encouraged, especially for UNICODE [1] and UTF-8 [17] encodings. - Register services with a DA in non-US-ASCII character encodings. This is encouraged, especially for UNICODE [1] and UTF-8 [17] encodings. A Service Agent SHOULD be able to: - Listen to the service-specific multicast address of the service it is advertising. The incoming requests should be filtered: If the Address Specification of the SA is in the Previous Responders Address Specification list, the SA SHOULD NOT respond. Otherwise, a response to the multicast query SHOULD be unicast to the UA which sent the request. - Listen for and respond to broadcast requests and TCP connection requests, to the Service Location port. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 53]
Internet Draft Service Location Protocol 10 June 1996 - Listen to the Service Location General Multicast address for queries (e.g., Service Type Requests). If the query can be replied to by the Service Agent, the Service Agent must do so. It MUST check first to make sure it is not on the list of 'previous responders.' A Service Agent MUST be able to: - Listen to the Service Location General Multicast address for unsolicited DA Advertisements. If one is detected, and the DA has the right scope, all services which are currently being advertised MUST be registered with the DA (unless configured to only use a single DA (see section 23.1), or the DA has already been detected, subject to certain rules (see section 16.2)). - Unicast registrations and deregistrations to a DA. Transactions should be made reliable by using retransmission of the request if the reply does not arrive within a timeout interval. - Be able to detect DAs using a Directory Agent Discovery request issued when the SA starts up (unless configured to only use a single DA, see section 23.1.) - Use the IP Authentication Header or IP Encapsulating Payload in all Service Location messages, whenever an appropriate IPSec Security Association exists. - Be able to register service information with a DA using US-ASCII character encoding. It must also be able to reply to requests from UAs which use US-ASCII character encoding. - Reregister with a DA before the Lifetime of registered service information elapses. A Directory Agent MAY: - Ignore any unauthenticated Service Registration or Service Deregistration. - Accept registrations and requests in non-US-ASCII character encodings. This is encouraged, especially for UNICODE [1] and UTF-8 [17] encodings. A Directory Agent MUST be able to: - Send an unsolicited DA Advertisements to the Service Location General Multicast address on startup and repeat it periodically. This reply has an XID which is incremented by one each time. If Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 54]
Internet Draft Service Location Protocol 10 June 1996 the DA starts with state, it initializes the XID to 0x0100. If it starts up stateless, it initializes the XID to 0x0000. - Listen on the Directory Agent Discovery Multicast Address for Directory agent discovery requests. Filter these requests if the Previous Responder Address Specification list includes the DA's Address Specification. - Listen for broadcast requests to the Service Location port. - Listen on the TCP and UDP Service Location Ports for unicast requests, registrations and deregistrations and service them. - Provide a way in which Scope information can be used to configure the Directory Agent. - Age out the services which have been registered so that when the service registration's Lifetime expires, the service advertisement is withdrawn. - Ignore any unauthenticated Service Location messages when an appropriate IPSec Security Association exists for that request. - Use the IP Authentication and IP Encapsulating Security Payload in Service Location messages whenever an appropriate IPSec Security Association exists. - Accept requests and registrations in US-ASCII. NOTE: Service Agents and User Agents use ephemeral ports for transmitting information to the service location port. 23. Configurable Parameters and Default Values There are several configuration parameters for Service Location. The protocol will work fine if only default values are used. Due to the nature of the protocol, it may be deployed in many different environments. The configuration options parameters will allow an implementation of Service Location to be useful in a variety of different scenarios. Multicast vs. Broadcast All Service Location entities must use multicast by default. The ability to use broadcast messages must be configurable. Broadcast messages are to be used in environments where not all Service Location entities have hardware or software which supports multicast. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 55]
Internet Draft Service Location Protocol 10 June 1996 Multicast Radius Multicast requests should be sent to all subnets in a site. The default multicast radius for a site is 32. This value must be configurable. The value for the site's multicast TTL may be obtained from DHCP. The DHCP option has not yet been assigned. Directory Agent Address The Directory Agent address discovery mechanism must be configurable. There are three possibilities for this configuration: A default address, no default address and the use of DHCP to locate a DA as described in section 16.2. The default value should be "no default address." In this case the UA or SA must do a Directory Agent Discovery query. Directory Agent Scope Assignment The scope or scopes of a DA must be configurable. The default value for a DA is to have no scope if not otherwise configured. Default Path MTU The default path MTU is assumed to be 1400. This value may be too large for the infrastructure of some sites. For this reason this value MUST be configurable for all SAs and DAs. If a UA issues a request which will result in a reply which is too large, the SA or DA will return an abbreviated response (in a datagram the size of the site's MTU) which has the 'Overflow' bit flag set. The UA must then issue the request again using a tcp connection. Similarly, if a SA attempts to register a service with a DA and the registration is larger than the site path MTU the DA will reply with a SrvAck, with the error set to INVALID_REGISTRATION and the 'Overflow' byte set. 23.1. Service Agent: Use Predefined Directory Agent(s) A Service Agent's default configuration is to do passive and active DA discovery and to register with all DAs which are properly scoped. A Service Agent SHOULD be configurable to allow a special mode of operation: They will use only preconfigured DAs. This means they will *NOT* actively or passively detect DAs. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 56]
Internet Draft Service Location Protocol 10 June 1996 If a Service Agent is configured this way, knowledge of the DA must come through another channel, either static configuration or by the use of DHCP. The availability of the Service information will not be consistent between DAs. The mechanisms which achieve eventual consistency between DAs are ignored by the SA, so their service information will not be distributed. This leaves the SA open to failure if the DA they are configured to use fails. 23.2. Time Out Intervals These values should be configurable in case the site deploying Service Location has special requirements (such as very slow links.) Interval name Section Default Value Meaning ----------------- ------- ------------- ----------------------- CONFIG_INTERVAL_0 5.1 1 minute Cache replies by XID. CONFIG_INTERVAL_1 5.2 1440 minutes registration Lifetime, (ie. 1 day) after which ad expires CONFIG_INTERVAL_2 6 each second, Retry multicast query backing off until no new values gradually arrive. CONFIG_INTERVAL_3 6 15 seconds Max time to wait for a complete multicast query response (all values.) CONFIG_INTERVAL_4 10 3 seconds Wait to register on reboot. CONFIG_INTERVAL_5 6.2 3 seconds Retransmit DA discovery, try it 3 times. CONFIG_INTERVAL_6 6.2 5 seconds Give up on requests sent to a DA. CONFIG_INTERVAL_7 6.2 15 seconds Give up on DA discovery CONFIG_INTERVAL_8 6.1 15 seconds Give up on requests sent to SAs. CONFIG_INTERVAL_9 16.2 3 hours DA Heartbeat, so that SAs will passively detect new DAs. CONFIG_INTERVAL_10 16.2 1-3 seconds Wait to register services on passive DA discovery. CONFIG_INTERVAL_11 10 1-3 seconds Wait to register services on active DA discovery. CONFIG_INTERVAL_12 19.1 5 minutes DAs and SAs close idle connections. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 57]
Internet Draft Service Location Protocol 10 June 1996 A note on CONFIG_INTERVAL_9: While it might seem advantageous to have frequent heartbeats, this poses a significant risk of generating a lot of overhead traffic. This value should be kept high to prevent routine protocol operations from using any significant bandwidth. 24. Non-configurable Parameters IP Port number for unicast requests to Directory Agents: UDP and TCP Port Number: 427 Multicast Addresses Service Location General Multicast Address: 224.0.1.22 Directory Agent Discovery Multicast Address: 224.0.1.35 Further service-specific multicast address will be assigned for specific types of service through the IANA. Error Codes: No Error 0 LANGUAGE_NOT_SUPPORTED 1 PROTOCOL_PARSE_ERROR 2 INVALID_REGISTRATION 3 SCOPE_NOT_SUPPORTED 4 CHARSET_NOT_UNDERSTOOD 5 AUHENTICATION_FAILED 6 25. Acknowledgments This protocol owes some of the original ideas to other service location protocols found in many other networking protocols. Leo McLaughlin and Mike Ritter (Metricom) provided much input into early version of this document. Thanks also to Steve Deering (Xerox) for providing his insight into distributed multicast protocols. Harry Harjono and Charlie Perkins supplied the basis for the URL based wire protocol in their Resource Discovery Protocol. Thanks also to Peerlogic, Inc. for supporting this work. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 58]
Internet Draft Service Location Protocol 10 June 1996 A. Appendix: Technical contents of ISO 639:1988 (E/F): "Code for the representation of names of languages" Two-letter lower-case symbols are used. The Registration Authority for ISO 639 [12] is Infoterm, Osterreiches Normungsinstitut (ON), Postfach 130, A-1021 Vienna, Austria. Contains additions from ISO 639/RA Newsletter No.1/1989 aa Afar gn Guarani mr Marathi ab Abkhazian gu Gujarati ms Malay af Afrikaans mt Maltese am Amharic ha Hausa my Burmese ar Arabic he Hebrew as Assamese hi Hindi na Nauru ay Aymara hr Croatian ne Nepali az Azerbaijani hu Hungarian nl Dutch hy Armenian no Norwegian ba Bashkir be Byelorussian ia Interlingua oc Occitan bg Bulgarian in Indonesian om (Afan) Oromo bh Bihari ie Interlingue or Oriya bi Bislama ik Inupiak bn Bengali; Bangla is Icelandic pa Punjabi bo Tibetan it Italian pl Polish br Breton ps Pashto, Pushto pt Portuguese ca Catalan ja Japanese co Corsican jw Javanese qu Quechua cs Czech cy Welsh ka Georgian rm Rhaeto-Romance kk Kazakh rn Kirundi da Danish kl Greenlandic ro Romanian de German km Cambodian ru Russian dz Bhutani kn Kannada rw Kinyarwanda ko Korean el Greek ks Kashmiri sa Sanskrit en English ku Kurdish sd Sindhi eo Esperanto ky Kirghiz sg Sangro es Spanish sh Serbo-Croatian et Estonian la Latin si Singhalese eu Basque ln Lingala sk Slovak lo Laothian sl Slovenian fa Persian lt Lithuanian sm Samoan fi Finnish lv Latvian, Lettish sn Shona fj Fiji so Somali fo Faeroese sq Albanian fr French mg Malagasy sr Serbian fy Frisian mi Maori ss Siswati Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 59]
Internet Draft Service Location Protocol 10 June 1996 mk Macedonian st Sesotho ga Irish ml Malayalam su Sundanese gd Scots Gaelic mn Mongolian sv Swedish gl Galician mo Moldavian sw Swahili ta Tamil ug Uigar te Telugu uk Ukrainian tg Tajik ur Urdu th Thai uz Uzbek ti Tigrinya tk Turkmen vi Vietnamese tl Tagalog vo Volapuk tn Setswana to Tonga wo Wolof tr Turkish ts Tsonga xh Xhosa tt Tatar tw Twi yi Yiddish yo Yoruba za Zhuang zh Chinese zu Zulu B. Appendix: For Further Reading Three related resource discovery protocols are NBP and ZIP which are part of the AppleTalk protocol family [11], the Legato Resource Administration Platform [18], and the Xerox Clearinghouse system [16]. Domain names and representation of addresses are used extensively in the Service Location Protocol. The references for these are RFCs 1034 and 1035 [14, 15]. An example of service discovery protocol for a specific service is Router Discovery [9]. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 60]
Internet Draft Service Location Protocol 10 June 1996 References [1] Unicode Technical Report #4. The unicode standard, version 1.1 (volumes 1 and 2). Technical Report (ISBN 0-201-56788-1) and (ISBN 0-201-60845-6), Unicode Consortium, 1994. [2] S. Alexander and R. Droms. DHCP Options and BOOTP Vendor Extensions. RFC 1533, October 1993. [3] R. Atkinson. IP Authentication Header. RFC 1826, August 1995. [4] R. Atkinson. IP Encapsulating Security Payload. RFC 1827, August 1995. [5] R. Atkinson. Security Architecture for the Internet Protocol. RFC 1825, August 1995. [6] T. Berners-Lee and D. Connolly. Hypertext Markup Language - 2.0. RFC 1866, November 1995. [7] T. Berners-Lee, L. Masinter, and M. McCahill. Uniform Resource Locators (URL). RFC 1738, December 1994. [8] N. Borenstein and N. Freed. MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies. RFC 1521, September 1993. [9] Stephen E. Deering, editor. ICMP Router Discovery Messages. RFC 1256, September 1991. [10] Ralph Droms. Dynamic Host Configuration Protocol. RFC 1541, October 1993. [11] S. Gursharan, R. Andrews, and A. Oppenheimer. Inside AppleTalk. Addison-Wesley, 1990. [12] Geneva ISO. Code for the representation of names of languages. ISO 639:1988 (E/F), 1988. [13] Geneva ISO 8879. Information Processing -- Text and Office Systems - Standard Generalized Markup Language (SGML). <URL:http://www.iso.ch/cate/d16387.html>, 1986. [14] P. Mockapetris. Domain Names - Concepts and Facilities. RFC 1034, November 1987. Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 61]
Internet Draft Service Location Protocol 10 June 1996 [15] P. Mockapetris. DOMAIN NAMES - IMPLEMENTATION AND SPECIFICATION. RFC 1035, November 1987. [16] D. Oppen and Y. Dalal. The clearinghouse: A decentralized agent for locating named objects in a distributed environment. Technical Report Tech. Rep. OPD-78103, Xerox Office Products Division, 1981. [17] X/Open Preliminary Specification. File System Safe UCS Transformation Format (FSS_UTF). Technical Report Document Number: P316, X/Open Company Ltd., 1994. [18] Legato Systems. The Legato Resource Administration Platform. Legato Systems, 1991. Authors' Addresses Questions about this memo can be directed to: John Veizades Erik Guttman @Home Network Sun Microsystems 385 Ravendale Dr. 2550 Garcia Avenue, MS PAL01-550 Mountain View, CA 94043 Mountain View, CA 94043-1100 Phone: +1 415 944 7332 Phone: +1 415 336 6697 Fax: +1 415 944 8500 Email: veizades@home.com Email: Erik.Guttman@eng.sun.com Charles Perkins Scott Kaplan IBM Corporation P.O. Box 704 346 Fair Oaks St. Yorktown Heights NY 10598 San Francisco, CA 94110 Phone: +1 914 784 7350 Phone: +1 415 285 4526 Fax: +1 914 784 6205 EMail: perk@watson.ibm.com Email: scott@catch22.com Veizades,Guttman,Perkins,Kaplan Expires 10 December 1996 [Page 62]
