Network Working Group Kutscher Internet-Draft Ott Expires: October 18, 2001 Bormann TZI, Universitaet Bremen April 19, 2001 Session Description and Capability Negotiation draft-ietf-mmusic-sdpng-00.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on October 18, 2001. Copyright Notice Copyright (C) The Internet Society (2001). All Rights Reserved. Abstract This document defines a language for describing multimedia sessions with respect to configuration parameters and capabilities of end systems. This document is a product of the Multiparty Multimedia Session Control (MMUSIC) working group of the Internet Engineering Task Force. Comments are solicited and should be addressed to the working group's mailing list at confctrl@isi.edu and/or the authors. Document Revision $Revision: 1.8 $ Kutscher, et. al. Expires October 18, 2001 [Page 1] Internet-Draft SDPng April 2001 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology and System Model . . . . . . . . . . . . . . . . 5 3. SDPng . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.1 Conceptual Outline . . . . . . . . . . . . . . . . . . . . . 8 3.1.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . . 8 3.1.2 Components & Configurations . . . . . . . . . . . . . . . . 10 3.1.3 Constraints . . . . . . . . . . . . . . . . . . . . . . . . 11 3.1.4 Session . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.2 Syntax Proposal . . . . . . . . . . . . . . . . . . . . . . 12 3.3 External Definition Packages . . . . . . . . . . . . . . . . 14 3.3.1 Profile Definitions . . . . . . . . . . . . . . . . . . . . 15 3.3.2 Library Definitions . . . . . . . . . . . . . . . . . . . . 15 3.4 Mappings . . . . . . . . . . . . . . . . . . . . . . . . . . 17 4. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . 18 References . . . . . . . . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 19 Full Copyright Statement . . . . . . . . . . . . . . . . . . 21 Kutscher, et. al. Expires October 18, 2001 [Page 2] Internet-Draft SDPng April 2001 1. Introduction Multiparty multimedia conferencing is one application that requires the dynamic interchange of end system capabilities and the negotiation of a parameter set that is appropriate for all sending and receiving end systems in a conference. For some applications, e.g. for loosely coupled conferences, it may be sufficient to simply have session parameters be fixed by the initiator of a conference. In such a scenario no negotiation is required because only those participants with media tools that support the predefined settings can join a media session and/or a conference. This approach is applicable for conferences that are announced some time ahead of the actual start date of the conference. Potential participants can check the availability of media tools in advance and tools like session directories can configure media tools on startup. This procedure however fails to work for conferences initiated spontaneously like Internet phone calls or ad-hoc multiparty conferences. Fixed settings for parameters like media types, their encoding etc. can easily inhibit the initiation of conferences, for example in situations where a caller insists on a fixed audio encoding that is not available at the callee's end system. To allow for spontaneous conferences, the process of defining a conference's parameter set must therefore be performed either at conference start (for closed conferences) or maybe (potentially) even repeatedly every time a new participant joins an active conference. The latter approach may not be appropriate for every type of conference without applying certain policies: For conferences with TV-broadcast or lecture characteristics (one main active source) it is usually not desired to re-negotiate parameters every time a new participant with an exotic configuration joins because it may inconvenience existing participants or even exclude the main source from media sessions. But conferences with equal "rights" for participants that are open for new participants on the other hand would need a different model of dynamic capability negotiation, for example a telephone call that is extended to a 3-parties conference at some time during the session. SDP [1] allows to specify multimedia sessions (i.e. conferences, "session" as used here is not to be confused with "RTP session"!) by providing general information about the session as a whole and specifications for all the media streams (RTP sessions and others) to be used to exchange information within the multimedia session. Currently, media descriptions in SDP are used for two purposes: o to describe session parameters for announcements and invitations Kutscher, et. al. Expires October 18, 2001 [Page 3] Internet-Draft SDPng April 2001 (the original purpose of SDP) o to describe the capabilities of a system (and possibly provide a choice between a number of alternatives). Note that SDP was not designed to facilitate this. A distinction between these two "sets of semantics" is only made implicitly. In the following we first introduce a model for session description and capability negotiation and define some terms that are later used to express some requirements. Note that this list of requirements is possibly incomplete. The purpose of this document is to initiate the development of a session description and capability negotiation framework. Kutscher, et. al. Expires October 18, 2001 [Page 4] Internet-Draft SDPng April 2001 2. Terminology and System Model Any (computer) system has, at a time, a number of rather fixed hardware as well as software resources. These resources ultimately define the limitations on what can be captured, displayed, rendered, replayed, etc. with this particular device. We term features enabled and restricted by these resources "system capabilities". Example: System capabilities may include: a limitation of the screen resolution for true color by the graphics board; available audio hardware or software may offer only certain media encodings (e.g. G.711 and G.723.1 but not GSM); and CPU processing power and quality of implementation may constrain the possible video encoding algorithms. In multiparty multimedia conferences, participants employ different "components" in conducting the conference. Example: In lecture multicast conferences one component might be the voice transmission for the lecturer, another the transmission of video pictures showing the lecturer and the third the transmission of presentation material. Depending on system capabilities, user preferences and other technical and political constraints, different configurations can be chosen to accomplish the "deployment" of these components. Each component can be characterized at least by (a) its intended use (i.e. the function it shall provide) and (b) a one or more possible ways to realize this function. Each way of realizing a particular function is referred to as a "configuration". Example: A conference component's intended use may be to make transparencies of a presentation visible to the audience on the Mbone. This can be achieved either by a video camera capturing the image and transmitting a video stream via some video tool or by loading a copy of the slides into a distributed electronic whiteboard. For each of these cases, additional parameters may exist, variations of which lead to additional configurations (see below). Two configurations are considered different regardless of whether they employ entirely different mechanisms and protocols (as in the previous example) or they choose the same and differ only in a single parameter. Example: In case of video transmission, a JPEG-based still image protocol may be used, H.261 encoded CIF images could be sent as could H.261 encoded QCIF images. All three cases constitute Kutscher, et. al. Expires October 18, 2001 [Page 5] Internet-Draft SDPng April 2001 different configurations. Of course there are many more detailed protocol parameters. Each component's configurations are limited by the participating system's capabilities. In addition, the intended use of a component may constrain the possible configurations further to a subset suitable for the particular component's purpose. Example: In a system for highly interactive audio communication the component responsible for audio may decide not to use the available G.723.1 audio codec to avoid the additional latency but only use G.711. This would be reflected in this component only showing configurations based upon G.711. Still, multiple configurations are possible, e.g. depending on the use of A-law or u-Law, packetization and redundancy parameters, etc. In this system model, we distinguish two types of configurations: o potential configurations (a set of any number of configurations per component) indicating a system's functional capabilities as constrained by the intended use of the various components; o actual configurations (exactly one per instance of a component) reflecting the mode of operation of this component's particular instantiation. Example: The potential configuration of the aforementioned video component may indicate support for JPEG, H.261/CIF, and H.261/QCIF. A particular instantiation for a video conference may use the actual configuration of H.261/CIF for exchanging video streams. In summary, the key terms of this model are: o A multimedia session (streaming or conference) consists of one or more conference components for multimedia "interaction". o A component describes a particular type of interaction (e.g. audio conversation, slide presentation) that can be realized by means of different applications (possibly using different protocols). o A configuration is a set of parameters that are required to implement a certain variation (realization) of a certain component. There are actual and potential configurations. * Potential configurations describe possible configurations that are supported by an end system. Kutscher, et. al. Expires October 18, 2001 [Page 6] Internet-Draft SDPng April 2001 * An actual configuration is an "instantiation" of one of the potential configurations, i.e. a decision how to realize a certain component. In less abstract words, potential configurations describe what a system can do ("capabilities") and actual configurations describe how a system is configured to operate at a certain point in time (media stream spec). To decide on a certain actual configuration, a negotiation process needs to take place between the involved peers: 1. to determine which potential configuration(s) they have in common, and 2. to select one of this shared set of common potential configurations to be used for information exchange (e.g. based upon preferences, external constraints, etc.). In SAP [9] -based session announcements on the Mbone, for which SDP was originally developed, the negotiation procedure is non-existent. Instead, the announcement contains the media stream description sent out (i.e. the actual configurations) which implicitly describe what a receiver must understand to participate. In point-to-point scenarios, the negotiation procedure is typically carried out implicitly: each party informs the other about what it can receive and the respective sender chooses from this set a configuration that it can transmit. Capability negotiation must not only work for 2-party conferences but is also required for multi-party conferences. Especially for the latter case it is required that the process of determining the subset of allowable potential configurations is deterministic to reduce the number of required round trips before a session can be established. In the following, we elaborate on requirements for an SDPng specification, subdivided into general requirements and requirements for session descriptions, potential and actual configurations as well as negotiation rules. Kutscher, et. al. Expires October 18, 2001 [Page 7] Internet-Draft SDPng April 2001 3. SDPng This section outlines a proposed solution for describing capabilities that meets most of the above requirements. Note that at this early point in time not all of the details are completely filled in; rather, the focus is on the concepts of such a capability description and negotiation language. 3.1 Conceptual Outline Our concept for the description language follows the system model introduced in the beginning of this document. We use a rather abstract language to avoid misinterpretations due to different intuitive understanding of terms as far as possible. Our concept of a capability description language addresses various pieces of a full description of system and application capabilities in four separate "sections": Definitions (elementary and compound) Potential or Actual Configurations Constraints Session attributes 3.1.1 Definitions The definition section specifies a number of basic abstractions that are later referenced to avoid repetitions in more complex specifications and allow for a concise representation. Definition elements are labelled with an identifier by which they may be referenced. They may be elementary or compound (i.e. combinations of elementary entities). Examples of definitions of that sections include (but are not limited to) codec definitions, redundancy schemes, transport mechanisms and payload formats. Elementary definition elements do not reference other elements. Each elementary entity only consists of one of more attributes and their values. Default values specified in the definition section may be overridden in descriptions for potential (and later actual) configurations. The concrete mechanisms for overriding definitions are still to be defined. For the moment, elementary elements are defined for media types (i.e. codecs) and for media transports. For each transport and for each codec to be used, the respective attributes need to be defined. This definition may either be provided within the "Definition" Kutscher, et. al. Expires October 18, 2001 [Page 8] Internet-Draft SDPng April 2001 section itself or in an external document (similar to the audio-video profile or an IANA registry that define payload types and media stream identifiers. Examples for elementary definitions: The element type "audio-codec" is used in these examples to define audio codec configurations. The configuration parameters are given as attribute values. Compound elements combine a number of elementary and/or other compound elements for more complex descriptions. This mechanism can be used for simple standard configurations such as G.711 over RTP/AVP as well as to express more complex coding schemes including e.g. FEC schemes, redundancy coding, and layered coding. Again, such definitions may be standardized and externalized so that there is no need to repeat them in every specification. An example for the definition of a audio-redundancy format: In this example, the element type "audio-red" is used to define a redundant audio configuration that is labelled "red-pcm-gsm-fec" for later referencing. In the definition itself, the element type "use" is used to reference other definitions. Definitions may have default values specified along with them for each attribute. Some of these default values may be overridden so that a codec definition can easily be re-used in a different context (e.g. by specifying a different sampling rate) without the need for a large number of base specifications. This approach allows to have simple as well as more complex definitions which are commonly used be available in an extensible set of reference documents. Section 3.3 specifies the mechanisms for external references. Note: For negotiation between endpoints, it may be helpful to define two modes of operation: explicit and implicit. Implicit specifications may refer to externally defined entities to minimize traffic volume, explicit specifications would list all external Kutscher, et. al. Expires October 18, 2001 [Page 9] Internet-Draft SDPng April 2001 definitions used in a description in the "Definitions" section. Again, please see Section 3.3 for complete discussion of external definitions. 3.1.2 Components & Configurations The "Configurations" section contains all the components that constitute the multimedia conference (IP telephone call, multiplayer gaming session etc.). For each of these components, the potential and, later, the actual configurations are given. Potential configurations are used during capability exchange and/or negotiation, actual configurations to configure media streams after negotiation or in session announcements (e.g. via SAP). A potential and the actual configuration of a component may be identical. Each component is labelled with an identifier so that it can be referenced, e.g. to associate semantics with a particular media stream. For such a component, any number of configurations may be given with each configuration describing an alternate way to realize the functionality of the respective component. Each configuration (potential as well as actual) is labelled with an identifier. A configuration combines one or more (elementary and/or compound) entities from the "Definitions" section to describe a potential or an actual configuration. Within the specification of the configuration, default values from the referenced entities may be overwritten. 239.239.239.239 30000 239.239.239.239 30000 For example, an IP telephone call may require just a single Kutscher, et. al. Expires October 18, 2001 [Page 10] Internet-Draft SDPng April 2001 component id=interactive-audio with two possible ways of implementing it. The two corresponding configurations are "AVP-audio-0" without modification, the other ("AVP-audio-11") uses linear 16-bit encoding. Typically, transport address parameters such as the port number would also be provided. In this example, this information is given by the "addr" element. During/after the negotiation phase, an actual configuration is chosen out of a number of alternative potential configurations, the actual configuration may refer to the potential configuration just by its "id", possibly allowing for some parameter modifications. Alternatively, the full actual configuration may be given. 3.1.3 Constraints Definitions specify media, transport, and other capabilities, whereas configurations indicate which combinations of these could be used to provide the desired functionality in a certain setting. There may, however, be further constraints within a system (such as CPU cycles, DSP available, dedicated hardware, etc.) that limit which of these configurations can be instantiated in parallel (and how many instances of these may exist). We deliberately do not couple this aspect of system resource limitations to the various application semantics as the constraints exist across application boundaries. Also, in many cases, expressing such constraints is simply not necessary (as many uses of the current SDP show), so additional overhead can be avoided where this is not needed. Therefore, we introduce a "Constraints" section to contain these additional limitations. Constraints refer to potential configurations and to entity definitions and express and use simple logic to express mutual exclusion, limit the number of instantiations, and allow only certain combinations. The following example shows the definition of a constraints that restricts the maximum number of instantiation of two alternatives (that would have to be defined in the configuration section before) when they are used in parallel: As the example shows, contraints are defined by defining limits on simultaneous instantiations of alternatives. They are not defined by expressing abstract endsystem resources, such as CPU speed or memory size. Kutscher, et. al. Expires October 18, 2001 [Page 11] Internet-Draft SDPng April 2001 By default, the "Constraints" section is empty (or missing) which means that no further restrictions apply. 3.1.4 Session The "Session" section is used to describe general meta-information parameters of the communication relationship to be invoked or modified. It contains most (if not all) of the general parameters of SDP (and thus will easily be usable with SAP for session announcements). In addition to the session description parameters, the "Session" section also ties the various components to certain semantics. If, in current SDP, two audio streams were specified (possibly even using the same codecs), there was little way to differentiate between their uses (e.g. live audio from an event broadcast vs. the commentary from the TV studio). This section also allows to tie together different media streams or provide a more elaborate description of alternatives (e.g. subtitles or not, which language, etc.). SDPng test joe@example.com A test conference Video stream for the different speakers Further uses are envisaged but need to be defined in future versions of this document. 3.2 Syntax Proposal In order to allow for the possibility to validate session descriptions and in order to allow for structured extensibility it is proposed to rely on a syntax framework that provides concepts as well as concrete procedures for document validation and extending the set of allows syntax elements. SGML/XML technologies allow for the preparation of Document Type Definitions (DTDs) that can define the allowed content models for the elements of conforming documents. Documents can be formally validated against a given DTD to check their conformance and correctness. For XML, mechanisms have been defined that allow for structured extensibility of a model of allowed syntax: XML Namespace and XML Schema. Kutscher, et. al. Expires October 18, 2001 [Page 12] Internet-Draft SDPng April 2001 XML Schema mechanisms allows to constrain the allowed document content, e.g. for documents that contain structured data and also provide the possibility that document instances can conform to several XML Schema definitions at the same time, while allowing Schema validators to check the conformance of these documents. Extensions of the session description language, say for allowing to express the parameters of a new media type, would require the creation of a corresponding XML schema definition that contains the specification of element types that can be used to describe configurations of components for the new media type. Session description documents have to reference the non-standard Schema module, thus enabling parsers and validators to identify the elements of the new extension module and to either ignore them (if they are not supported) or to consider them for processing the session/capability description. It is important to note that the functionality of validating capability and session description documents is not necessarily required to generate or process them. For example, endpoints would be configured to understand only those parts of description documents that are conforming to the baseline specification and simply ignore extensions they cannot support. The usage of XML and XML Schema is thus rather motivated by the need to allow for extensions being defined and added to the language in a structured way that does not preclude the possibility to have applications to identify and process the extensions elements they might support. The baseline specification of XML Schema definitions and profiles must be well-defined and targeted to the set of parameters that are relevant for the protocols and algorithms of the Internet Multimedia Conferencing Architecture, i.e. transport over RTP/UDP/IP, the audio video profile of RFC1890 etc. The example below shows how the definition of codecs, transport-variants and configuration of components could be realized. Please note that this is not a complete example and that identifiers have been chosen arbitrarily. Kutscher, et. al. Expires October 18, 2001 [Page 13] Internet-Draft SDPng April 2001 239.239.239.239 30000 239.239.239.239 30000 SDPng test joe@example.com A test conference Video stream for the different speakers The example does also not include specifications of XML Schema definitions or references to such definitions. This will be provided in a future version of this draft. A real-world capability description would likely be shorter than the presented example because the codec and transport definitions can be factored-out to profile definition documents that would only be referenced in capability description documents. 3.3 External Definition Packages Kutscher, et. al. Expires October 18, 2001 [Page 14] Internet-Draft SDPng April 2001 3.3.1 Profile Definitions In order to allow for extensibility it must be possible to define extensions to the basic SDPng configuration options. For example if some application requires the use of a new esoteric transport protocol endpoints must be able describe their configuration with respect to the parameters of that transport protocol. The mandatory and optional parameters that can be configured and negotiated when using the transport protocol will be specified in a definition document. Such a definition document is called a "profile". A profile contains rules that specify how SDPng is used to describe conferences or endsystem capabilities with respect to the parameters of the profile. The concrete properties of the profile definitions mechanism are still to be defined. An example of such a profile would be the RTP profile that defines how to specify RTP parameters. Another example would be the audio codec profiles that defines how specify audio codec parameters. SDPng document can reference profiles and provide concrete definitions, for example the definition for the GSM audio codec. (This would be done in the "Definitions" section of a SDPng document.) A SDPng document that references a profile and provides concrete defintions of configurations can be validated against the profile definition. 3.3.2 Library Definitions While profile definitions specify the allowed parameters for a given profile SDPng definition sections refer to profile definitions and define concrete configurations based on a specific profile. In order to such definitions to be imported into SDPng documents, there will be the notion of "SDPng libraries". A library is a set of definitions that is conforming to a certain profile definition (or to more than one profile definition -- this needs to be defined). The purpose of the library concept is to allow certain common definitions to be factored-out so that not every SDPng document has to include the basic definitions, for example the PCMU codec definition. SDP [1] uses a similar concept by relying on the well known static payload types (defined in RFC1890 [3]) that are also just referenced but never defined in SDP documents. An SPDng document that references definitions from an external library has to declare the use of the external library. The external Kutscher, et. al. Expires October 18, 2001 [Page 15] Internet-Draft SDPng April 2001 library, being a set of configuration definitions for a given profile, again needs to declare the use of the profile that it is conformant to. There are different possibilities of how profiles definitions and libraries can be used in SDPng documents: o In an SPDng document a profile definition can be referenced and all the configuration definitions are provided within the document itself. The SDPng document is self-contained with respect to the definitions it uses. o In an SPDng document the use of an external library can be declared. The library references a profile definition and the SDPng document references the library. There are two alternatives how external libraries can be referenced: by name: Referencing libraries by names implies the use of a registration authority where definitions and reference names can be registered with. It is conceivable that the most common SDPng definitions be registered that way and that there will be a baseline set of definitions that minimal implementations must understand. Secondly, a registration procedure will be defined, that allows vendors to register frequently used definitions with a registration authority (e.g., IANA) and to declare the use of registered definition packages in conforming SDPng documents. Of course, care should be taken though not to make the external references too complex and thus require too much a priori knowledge in a protocol engine implementing SDPng. Relying on this mechanism in general is also problematic because it impedes the extensiblity, because it requires implementors to provide support for new extensions in their products before they can interoperate. Registration is not useful for spontaneous or experimental extensions that are defined in an SDPng library. by address: An alternative to referencing libraries by name is to declare the use of an external library by providing an address, i.e., an URL, that specifies where the library can be obtained. While is allows the use of arbitrary third-party libraries that can extend the basic SDPng set of configuration options in many ways there are problems if the referenced libraries cannot be accessed by all communication partners. o Because of these problematic properties of external libraries, the final SDPng specification will have to provide a set of recommendations under which circumstances the different mechanisms of externalizing definitions should be used. Kutscher, et. al. Expires October 18, 2001 [Page 16] Internet-Draft SDPng April 2001 3.4 Mappings A mapping needs to be defined in particular to SDP that allows to translate final session descriptions (i.e. the result of capability negotiation processes) to SDP documents. In principle, this can be done in a rather schematic fashion. Furthermore, to accommodate SIP-H.323 gateways, a mapping from SDPng to H.245 needs to be specified at some point. Kutscher, et. al. Expires October 18, 2001 [Page 17] Internet-Draft SDPng April 2001 4. Open Issues Overriding Sytnax for referencing profiles and libraries Registry (reuse of SDP mechanisms and names etc.) Negotiation Kutscher, et. al. Expires October 18, 2001 [Page 18] Internet-Draft SDPng April 2001 References [1] Handley, M. and V. Jacobsen, "SDP: Session Description Protocol", RFC 2327, April 1998. [2] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobsen, "RTP: A Transport Protocol for Real-Time Applications", RFC 1889, January 1996. [3] Schulzrinne, H., "RTP Profile for Audio and Video Conferences with Minimal Control", RFC 1890, January 1996. [4] Perkins, C., Kouvelas, I., Hodson, O., Hardman, V., Handley, M., Bolot, J., Vega-Garcia, A. and S. Fosse-Parisis, "RTP Payload for Redundant Audio Data", RFC 2198, September 1997. [5] Klyne, G., "A Syntax for Describing Media Feature Sets", RFC 2533, March 1999. [6] Klyne, G., "Protocol-independent Content Negotiation Framework", RFC 2703, September 1999. [7] Rosenberg, J. and H. Schulzrinne, "An RTP Payload Format for Generic Forward Error Correction", RFC 2733, December 1999. [8] Perkins, C. and O. Hodson, "Options for Repair of Streaming Media", RFC 2354, June 1998. [9] Handley, M., Perkins, C. and E. Whelan, "Session Announcement Protocol", RFC 2974, October 2000. Authors' Addresses Dirk Kutscher TZI, Universitaet Bremen Bibliothekstr. 1 Bremen 28359 Germany Phone: +49.421.218-7595 Fax: +49.421.218-7000 EMail: dku@tzi.uni-bremen.de Kutscher, et. al. Expires October 18, 2001 [Page 19] Internet-Draft SDPng April 2001 Joerg Ott TZI, Universitaet Bremen Bibliothekstr. 1 Bremen 28359 Germany Phone: +49.421.201-7028 Fax: +49.421.218-7000 EMail: jo@tzi.uni-bremen.de Carsten Bormann TZI, Universitaet Bremen Bibliothekstr. 1 Bremen 28359 Germany Phone: +49.421.218-7024 Fax: +49.421.218-7000 EMail: cabo@tzi.org Kutscher, et. al. Expires October 18, 2001 [Page 20] Internet-Draft SDPng April 2001 Full Copyright Statement Copyright (C) The Internet Society (2001). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implmentation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgement Funding for the RFC editor function is currently provided by the Internet Society. Kutscher, et. al. Expires October 18, 2001 [Page 21]