RMT Working Group R.Kermode/Motorola Internet Engineering Task Force L.Vicisano/Cisco INTERNET-DRAFT draft-ietf-rmt-author-guidelines-01.txt 02 March 2001 Expires 02 September 2001 Author Guidelines for RMT Building Blocks and Protocol Instantiation documents 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 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 a "work in progress". To view the list Internet-Draft Shadow Directories, see http://www.ietf.org/shadow.html. Abstract This document provides general guidelines to assist the authors of reliable multicast transport (RMT) building block and protocol instantiation definitions. The purpose of these guidelines is to ensure that any building block and protocol instantiation definitions produced contain sufficient information to fully explain their operation and use. In addition these guidelines provide directions to specify modular and clearly defined RMT building blocks and protocol instantiations that can be refined and augmented to safely create new protocols for use in new scenarios for which any existing protocols were not designed. Copyright Notice Copyright (C) The Internet Society (2001). All Rights Reserved. Draft RMT Draft Author Guidelines 02 March 2001 1. Introduction Reliable Multicast Transport (RMT) protocols can be constructed in a variety of ways, some of which will work better for certain situations then others. It is believed that the requirements space for reliable multicast transport is sufficiently diverse that no one protocol can meet all the requirements [RFC2887]. However, it is also believed that there is sufficient commonality between the various approaches that it should be possible to define a number of building blocks [RFC3048] from which the various RMT protocols can be constructed. One key benefit of this approach is that the same building block can be used multiple times in different protocol instantiations. Another key benefit is that building blocks may be upgraded as experience and understanding is gained. For this operation to be possible the building block needs to be clearly defined in terms of what it does, how interacts with other building blocks and how fits into the overall architecture of a protocol instantiation. This description should also be sufficiently detailed so that those wishing to improve upon a particular building block or protocol instantiation can do with a full understanding of the design decisions and tradeoffs were made earlier. The building block approach presents also some dangers that must be well understood in order to avoid potential specification flaws. The most important danger is related to inappropriate usage of building blocks. Although any effort should be made in order to produce a modular and reusable specification of building blocks, for practical reasons this goal is not always fully achievable. This results in the specification of building blocks whose applicability is context dependent, which in turn creates the potential for the risk of co- dependence incompatibilities between building blocks. An example of such an incompatibility would be situation where the combinations of building blocks A and B works, the combination of building blocks B and C works, however the combination of building blocks A, B, and C does not work. In order to avoid misusage of and incompatibilities between building blocks, any external dependency must be highlighted in the building block specification. Furthermore, the specification must contain a precise applicability statement for the building block. Conversely, any protocol instantiation specification must state how any building block being used in it meets the protocol instantiation's applicability requirements. Expires 02 September 2001 [Page 2] Draft RMT Draft Author Guidelines 02 March 2001 1.1. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and"OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 2. The Guidelines This document provides guidelines for authors of the two main kinds of RMT drafts; building block drafts and protocol instantiation drafts. The guidelines for each are as follows. 2.1. Building Block Draft Guidelines All RMT Building block drafts MUST contain sections that cover the following. 2.1.1. Rationale Individual building blocks SHOULD be reusable within multiple protocols and MUST provide functionality not present within other building blocks. If a building block is currently used in a single protocol instantiation, then it MUST specify some functionality that is likely to be reused in another (future) protocol instantiation. The rational section of a building block draft must clearly define why the particular level of granularity for the functional decomposition that resulted in the building block was chosen. If the granularity is too small it is highly likely that the building blocks will be trivial, and therefore require excessive additional effort to realize a working protocol. Conversely, if the level of granularity is too large building blocks will only usable within a single protocol instantiation. This section MUST show that level of granularity is appropriate so that neither problem occurs. 2.1.2. Functionality The functionality section within a building block draft MUST describe all algorithms and functions contained within the building block. In addition, the external interfaces for accessing these algorithms and functions must be fully specified so that the building block can be Expires 02 September 2001 [Page 3] Draft RMT Draft Author Guidelines 02 March 2001 combined with other building blocks and any additional functionality specified within a protocol instantiation draft to realize a working protocol. 2.1.3. Applicability Statement One of the most important sections of a building block draft will be the Applicability Statement. The purpose of this section is to provide sufficient details about the intended use of the building block so that potential authors of protocol instantiation will be able to use the building block in conformance to its applicability constraints. Also the Applicability Statement section will enable future building blocks drafts authors to quickly be able to determine whether or not their particular need can be met with an existing building block. For this to be possible the Applicability Statement MUST describe o Intended scenarios for the building block's use o The building blocks known failure modes, why they occur, and how they can be detected. o A list of environmental considerations that includes but is not limited to whether the building block requires multi-source multicast or can be used in single-source only multicast networks, satellite networks, asymmetric networks, and wireless networks. o A list of potential areas of conflict or incompatibilities with other building blocks 2.1.4. Packet-Header Fields If a building block implements a functionality whose realization requires an exchange of protocol messages between multiple agents, then the building block specification MUST state what kind of information is required and how this is exchanged. This includes detailed description the data format and various communication requirements, such as timing constraints, and network requirement (e.g. multicast vs. unicast delivery). Typically the data format specification is at the level of "generic header fields" without a full bit-level header specification. Generic header fields MAY specify additional requirement, such as representation precision or preferred position within the packet header (this last Expires 02 September 2001 [Page 4] Draft RMT Draft Author Guidelines 02 March 2001 constraint might be dictated by efficiency concerns). A building block specification MAY specify "abstract messages" that carry particular information for exclusive use within the building block, however, more frequently, it will rely on the protocol messages specified in the protocol instantiation to carry the information it needs. The building block that provides Generic Router Assist functionality is and exception to the rule state above. For efficiency reason, this building block may fully specify header fields and position of these fields within the packet-header. 2.1.5. Requirements from other Building Blocks Each building block will encapsulate a specific well defined piece of functionality that is common to multiple protocol instantiations. However, this does not mean that building block definitions will be generated in isolation from other building blocks. For example, a congestion control building block will have specific requirements regarding loss notification from either a NACK or ACK building block. The "Requirements from other Building Blocks" section is included to capture these requirements so that the authors of related building blocks can determine what functionality they need to provide in order to use a particular building block. Specifically, the "Requirements from other Building Blocks section" MUST provide a complete and exhaustive enumeration of all the requirements that will be made upon other building blocks in order for the building block being specified to operate in its intended manner. Requirements that SHOULD be enumerated include but are not limited to o Event generation for and responses to other building blocks o Message ordering relative to messages from other building blocks. 2.1.6. Security Considerations Protocol instantiations have the ultimate responsibility of addressing security requirements, in conformance to RFC2357. Security consideration may not be applicable to generic building blocks other than a specific "security" building block. Some building blocks, however, may raise special security issues, either due to the nature of Expires 02 September 2001 [Page 5] Draft RMT Draft Author Guidelines 02 March 2001 communication required by the building block or due to the intended usage of the building block in a protocol instantiation. When special security issues are present in a building block, its specification MUST address them explicitly. An example of this might be a building block that involves exchange of data that is particularly sensitive to security attacks. 2.1.7. Codepoint Considerations Certain Building Blocks will specify general frameworks for describing functionality while leaving the detail open for implementation specific algorithms. One example of such a building block is the Forward Error Correction (FEC) building block which describes how the framing aspects for FEC message fragments but not the algorithms used to generate the redundant data. 2.1.8. Summary Checklist Rationale _ Provide justification for the building block's existence _ Provide rationale for the building block's granularity Functionality _ Functionality contained within the building block _ External interfaces Applicability Statement _ Intended usage _ Failure modes (including means of detection if known) _ Environmental considerations _ Incompatibilities / Conflicts with other building blocks Packet Header Fields _ Specification of logical packet-header fields (*) _ Abstract messages specifications (*) Requirements from other building blocks; _ Mandatory needs from other building blocks Security Considerations _ Specify as much as possible (w.r.t. procedures, algorithms and data encoding), without affecting the general applicability of Expires 02 September 2001 [Page 6] Draft RMT Draft Author Guidelines 02 March 2001 the building block. (*) May not be applicable to some building blocks. Expires 02 September 2001 [Page 7] Draft RMT Draft Author Guidelines 02 March 2001 2.2. Protocol Instantiation Draft Guidelines Protocol Instantiation drafts have one purpose: to specify how one can combine multiple building blocks to construct a new fully specified working protocol. To that end RMT Protocol Instantiation drafts MUST contain the following four sections. 2.2.1. Applicability Statement The applicability statement's purpose is to frame the design space in which the fully realized protocol will operate and to thereby enable subsequent would be RMT protocol designers to determine whether or not an existing protocol already meets their needs. For this to be possible the applicability statement MUST adhere to the following guidelines 1) The target application space for which the protocol is intended MUST be clearly identified. For example; is the protocol to be used for real-time delivery or not, or non-real time file transfer. 2) The target scale, in terms of maximum number of receivers per session, for which the protocol is intended MUST be clearly specified. If the protocol has an architectural limitation resulting from the optimization of another feature, say per packet acknowledgment, this SHOULD be included. 3) The applicability statement MUST identify the intended environment's for the protocols use AND list any environments in which the protocol should not be used. Example environments that should be considered include asymmetric networks, wireless networks, and satellite networks. 4) Finally, all protocols have inherent weaknesses that stem from the optimization for a specific feature. These weaknesses can manifest in spectacular failure modes when certain conditions occur. When known these conditions and the nature of how the subsequent failure can be detected MUST be included in the applicability statement. 2.2.2. Architecture Definition Protocol Instantiations define how to combine one or more building blocks to create a working protocol. The Architecture Definition lays out the framework for how this take place. For this framework to be complete, it MUST contain the following information: Expires 02 September 2001 [Page 8] Draft RMT Draft Author Guidelines 02 March 2001 1) An overview of the major facets of the protocols operation. 2) Full enumeration and overview of which Building Blocks with explicit references to their documents that define them. 3) An overview of how the aforementioned building blocks are to be joined. 4) A discussion of the design tradeoffs made in the selection of the chosen architecture. 2.2.3. Conformance Statement The conformance statement below MUST be included and adhered to "This Protocol Instantiation document, in conjunction with the following Building Block documents identified in [list of relevant building block references] completely specifies a working reliable multicast transport protocol that conforms to the requirements described in RFC 2357." Protocol instantiation document authors are specifically reminded that RFC2357 requires that any RMT protocol put forward for standardization with the IETF is required to protect the network in as much as is possible. This does not mean that RMT protocols will be held to a higher standard than unicast transport protocols, merely that they should be designed to perform at least as well as unicast transport protocols when it comes to the possibility of protocol failure. 2.2.4. Functionality Definition Building Block documents will be incomplete in that they will specify an abstract framework of a building block's functionality. Complete algorithmic specifications for each building block along with any additional functionality MUST provided within the Protocol Instantiation document's functionality definition. Furthermore, this description must show that each building block is used in accordance with its respective applicability statement. Finally the functionality description must provide a description of the abstract programming interface for interfacing the protocol instantiation with the applications that will use it. Expires 02 September 2001 [Page 9] Draft RMT Draft Author Guidelines 02 March 2001 2.2.5. Packet Formats Once all the functionality has been fully defined, the Protocol Instantiation document must defined the packet formats that will be used by the protocol. Each message part and the rules for their concatenation MUST be specified for both IPv4 [RFC791] and IPv6 [RFC2460]. Support for IPSEC [RFC2401] MUST be explicitly shown. In recognition of the fact that protocols will evolve and that IP protocol numbers are a scarce resource, protocol instantiations MUST initially define packet formats for use over UDP [RFC768]. Whether or not a particular Reliable Multicast Transport protocol instantiation becomes sufficiently popular to warrant its own protocol number is an issue which will be deferred until such time that the protocol has been sufficiently widely deployed and understood. 2.2.6. Summary Checklist Applicability Statement _ Target application space _ Target scale _ Intended environment _ Weaknesses and known failure modes Architecture Definition _ Operational overview _ Building blocks used _ Details on how building blocks are joined Conformance Statement _ Inclusion of mandatory paragraph Functionality Definition _ Building block algorithmic specification _ Addition functionality specification _ Compliance with building block applicability statements _ Abstract program interface Packet Formats _ IPv4 message parts _ IPv6 message parts _ IPSEC support _ Message ordering Expires 02 September 2001 [Page 10] Draft RMT Draft Author Guidelines 02 March 2001 3. IANA Considerations There are no explicit IANA considerations for this document. 4. Acknowledgments This document represents an overview of the mandatory elements required for the specification of building blocks and protocol instantiations within the the for RMT working group. The requirements presented are a summarization of discussions held between the RMT Working Group chairs and the participants in the IRTF Reliable Multicast Research Group. Although the name of these participants are too numerous to list here, the Working Group chairs would like to thank everyone who has participated in these discussions for their contributions. 5. References [RFC768] J. Postel, "User Datagram Protocol", RFC768, August 1980. [RFC791] J. Postel, "Darpa Internet Protocol Specification", ST5, RFC791, September 1981. [RFC2401] S. Kent, R. Atkinson, "Security Architecture for the Internet Protocol", RFC2401, November 1998. [RFC2460] S. Deering, R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC2460, December 1998. [RFC2887] M. Handley, B.Whetten, R. Kermode, S.Floyd, L. Vicisano, and M. Luby, "The Reliable Multicast Design Space for Bulk Data Transfer," Internet Draft, Internet Engineering Task Force, August 2000. [RFC3048] B.Whetten, L. Vicisano, R. Kermode, M. Handley, S.Floyd, and M. Luby, "Reliable Multicast Transport Building Blocks for One-to-Many Bulk-Data Transfer," Internet Draft, Internet Engineering Task Force, January 2001. Expires 02 September 2001 [Page 11] Draft RMT Draft Author Guidelines 02 March 2001 6. Authors' Addresses Roger Kermode Motorola Australian Research Centre Locked Bag 5028 Botany NSW 1455, Australia. Roger.Kermode@motorola.com Lorenzo Vicisano Cisco Systems, 170 West Tasman Dr. San Jose, CA 95134, USA lorenzo@cisco.com 7. 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 implementation 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 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." Expires 02 September 2001 [Page 12] Draft RMT Draft Author Guidelines 02 March 2001 Table of Contents 1 Introduction .................................................... 2 1.1 Terminology ................................................... 3 2 The Guidelines .................................................. 3 2.1 Building Block Draft Guidelines ............................... 3 2.1.1 Rationale ................................................... 3 2.1.2 Functionality ............................................... 3 2.1.3 Applicability Statement ..................................... 4 2.1.4 Packet-Header Fields ........................................ 4 2.1.5 Requirements from other Building Blocks ..................... 5 2.1.6 Security Considerations ..................................... 5 2.1.7 Codepoint Considerations .................................... 6 2.1.8 Summary Checklist ........................................... 6 2.2 Protocol Instantiation Draft Guidelines ....................... 8 2.2.1 Applicability Statement ..................................... 8 2.2.2 Architecture Definition ..................................... 8 2.2.3 Conformance Statement ....................................... 9 2.2.4 Functionality Definition .................................... 9 2.2.5 Packet Formats .............................................. 10 2.2.6 Summary Checklist ........................................... 10 3 IANA Considerations ............................................. 11 4 Acknowledgments ................................................. 11 5 References ...................................................... 11 6 Authors' Addresses .............................................. 12 7 Full Copyright Statement ........................................ 12 Expires 02 September 2001 [Page 13]