--- 1/draft-ietf-tsvwg-udp-lite-00.txt 2006-02-05 02:06:08.000000000 +0100 +++ 2/draft-ietf-tsvwg-udp-lite-01.txt 2006-02-05 02:06:08.000000000 +0100 @@ -1,338 +1,454 @@ -INTERNET-DRAFT Lars-Ake Larzon -TSV WG Lulea University of Technology, Sweden -January 24, 2002 Mikael Degermark -Expires: July 24, 2002 Stephen Pink - The University of Arizona, USA +Network Working Group L-A. Larzon +INTERNET-DRAFT Lulea University of Technology +Expires: June 2003 M. Degermark + S. Pink + The University of Arizona + L-E. Jonsson (editor) + Ericsson + G. Fairhurst (editor) + University of Aberdeen + December 5, 2002 - The UDP Lite Protocol - + The UDP-Lite Protocol + -Status of this Memo +Status of this memo This document is an Internet-Draft and is in full conformance with - all provisions of Section 10 of [RFC-2026]. + all provisions of Section 10 of RFC2026. - 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 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.'' + material or cite them other than as "work in progress". The list of current Internet-Drafts can be accessed at - http://www.ietf.org/ietf/1id-abstracts.txt + http://www.ietf.org/ietf/lid-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at - http://www.ietf.org/shadow.html. + http://www.ietf.org/shadow.html Please direct comments to the TSV WG mailing list: tsvwg@ietf.org Abstract - This document describes the UDP Lite protocol, which is similar to - classic UDP [RFC-768], but can also serve applications which in lossy + This document describes the UDP-Lite protocol, which is similar to + UDP [RFC-768], but can also serve applications that in error-prone network environments prefer to have partially damaged payloads - delivered rather than discarded. If this feature is not used, UDP - Lite is semantically identical to classic UDP. + delivered rather than discarded. If this feature is not used, UDP- + Lite is semantically identical to UDP. -Conventions +Table of Contents - 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]. + 1. Introduction...................................................2 + 2. Terminology....................................................3 + 3. Protocol Description...........................................3 + 3.1. Fields....................................................3 + 3.2. Pseudo Header.............................................4 + 3.3. Application Interface.....................................4 + 3.4. IP Interface..............................................5 + 3.5. Jumbograms................................................5 + 4. Lower Layer Considerations.....................................5 + 5. Compatibility with UDP.........................................6 + 6. Security Considerations........................................7 + 7. IANA Considerations............................................7 + 8. References.....................................................8 + 8.1. Normative References......................................8 + 8.2. Informative References....................................8 + 9. Acknowledgements...............................................8 + 10. Authors' Addresses............................................9 -Introduction +1. Introduction Why another transport protocol? - First, there is a class of applications which prefer to have damaged + First, there is a class of applications that prefer to have damaged data delivered rather than discarded by the network. A number of codecs for voice and video fall into this class. These codecs are designed to cope better with errors in the payload than with loss of entire packets. Second, there are a number of link technologies where data can be partially damaged. Several radio technologies exhibit this behavior - when operating at a point where cost and delay is sufficiently low. + when operating at a point where cost and delay are sufficiently low. - Third, intermediate layers should not prevent such applications to - run well over such links. The intermediate layers are IP and the - transport layer. IP is not a problem in this regard since the IP - header has no checksum which covers the IP payload. The generally - available transport protocol best suited for these applications is - UDP, since it has no overhead for retransmission of erroneous - packets, in-order delivery or error correction. However, the UDP - checksum either covers the entire datagram or nothing at all. - Moreover, in the next version of IP, IPv6 [RFC-2460], the UDP - checksum is mandatory and must not be disabled. The IPv6 header does - not have a header checksum and it was deemed necessary to always - protect the IP addressing information by making the UDP checksum - mandatory. + Third, intermediate layers should not prevent error-tolerant + applications to run well in the presence of such links. The + intermediate layers are IP and the transport layer. IP is not a + problem in this regard since the IP header has no checksum that + covers the IP payload. The generally available transport protocol + best suited for these applications is UDP, since it has no overhead + for retransmission of erroneous packets, in-order delivery, or error + correction. In IPv4 [RFC-791], the UDP checksum covers either the + entire packet or nothing at all. In IPv6 [RFC-2460], the UDP checksum + is mandatory and must not be disabled. The IPv6 header does not have + a header checksum and it was deemed necessary to always protect the + IP addressing information by making the UDP checksum mandatory. - A transport protocol is needed that conforms with the properties of - link layers and applications described above. The error-detection - mechanism of the transport layer must be able to protect vital - information such as headers, but also to optionally ignore errors - best dealt with by the application. What should be verified by the - checksum is best specified by the sending application. + A transport protocol is needed that conforms to the properties of + link layers and applications described above [UDP-LITE]. The error- + detection mechanism of the transport layer must be able to protect + vital information such as headers, but also to optionally ignore + errors best dealt with by the application. What should be verified by + the checksum is best specified by the sending application. - UDP Lite provides a checksum with optionally partial coverage. When - using this option, a datagram is divided into a sensitive part - (covered by checksum) and an insensitive part (not covered by - checksum). Errors in the insensitive part will not cause the - datagram to be discarded. When the checksum covers the entire - datagram, which SHOULD be the default, UDP Lite is semantically - identical to UDP. + UDP-Lite provides a checksum with an optional partial coverage. When + using this option, a packet is divided into a sensitive part (covered + by the checksum) and an insensitive part (not covered by the + checksum). Errors in the insensitive part will not cause the packet + to be discarded by the transport layer at the receiving end host. + When the checksum covers the entire packet, which should be the + default, UDP-Lite is semantically identical to UDP. - Compared to UDP (hereafter referred to as "classic UDP"), the partial - checksum provides extra flexibility for applications with partially - insensitive data. + Compared to UDP, the UDP-Lite partial checksum provides extra + flexibility for applications that want to define the payload as + partially insensitive to bit errors. -Protocol description +2. Terminology - The UDP Lite header is shown in figure 1. Its format differs from - classic UDP in that the Length field has been replaced with a - Checksum Coverage field. This can be done since information about UDP - packet length can be provided by the IP module in the same manner as - for TCP [rfc-793]. + 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]. + +3. Protocol Description + + The UDP-Lite header is shown in figure 1. Its format differs from + UDP in that the Length field has been replaced with a Checksum + Coverage field. This can be done since information about UDP packet + length can be provided by the IP module in the same manner as for TCP + [RFC-793]. 0 15 16 31 +--------+--------+--------+--------+ | Source | Destination | | Port | Port | +--------+--------+--------+--------+ | Checksum | | | Coverage | Checksum | +--------+--------+--------+--------+ | | - | data bytes ... | - +---------------- ...---------------+ + : Payload : + | | + +-----------------------------------+ - Figure 1: New UDP Header Format + Figure 1: UDP-Lite Header Format -Fields +3.1. Fields - The fields ``Source Port'' and ``Destination port'' are defined as in - the UDP specification [RFC-768]. + The fields Source Port and Destination Port are defined as in the UDP + specification [RFC-768]. UDP-Lite uses the same set of port number + values as those assigned by the IANA for use by UDP. - Checksum Coverage is the number of bytes, counting from the first - byte of the new UDP header, that are covered by the checksum. The UDP - Lite header MUST always be included in the checksum. Despite this - requirement, the Checksum Coverage is expressed in bytes from the - beginning of the UDP Lite header in order to preserve compatibility - with classic UDP. A Checksum Coverage of zero indicates that the - entire new UDP packet is included in the checksum. This means that - the value of the Checksum Coverage field MUST be either zero or at - least eight. + Checksum Coverage is the number of octets, counting from the first + octet of the UDP-Lite header, that are covered by the checksum. The + UDP-Lite header MUST always be covered by the checksum. Despite this + requirement, the Checksum Coverage is expressed in octets from the + beginning of the UDP-Lite header, in the same way as for UDP. A + Checksum Coverage of zero indicates that the entire UDP-Lite packet + is covered by the checksum. This means that the value of the Checksum + Coverage field MUST be either 0 or at least 8. A UDP-Lite packet with + a Checksum Coverage value of 1 to 7 MUST be discarded by the + receiver. UDP-Lite packets with a Checksum Coverage greater than the + IP length MUST also be discarded. Checksum is the 16-bit one's complement of the one's complement sum of a pseudo-header of information from the IP header, the number of - bytes specified by the Checksum Coverage (starting at the first byte - in the new UDP header), virtually padded with zero bytes at the end - (if necessary) to make a multiple of two bytes. If the computed - checksum is zero, it is transmitted as all ones (the equivalent in - one's complement arithmetic). The transmitted checksum MUST NOT be - all zeroes. + octets specified by the Checksum Coverage (starting at the first + octet in the UDP-Lite header), virtually padded with a zero octet at + the end (if necessary) to make a multiple of two octets [RFC-1071]. + If the computed checksum is 0, it is transmitted as all ones (the + equivalent in one's complement arithmetic). -Pseudo header + The transmitted checksum MUST NOT be all zeroes. If an application + using UDP-Lite wishes to have no protection of the packet payload, it + should use a Checksum Coverage value of 8. This differs from the use + of UDP over IPv4, in that the minimal UDP-Lite checksum always covers + the UDP-Lite protocol header, which includes the Checksum Coverage + field. - Similar to classic UDP, UDP Lite uses a conceptually prefixed pseudo - header from the IP layer for checksumming purposes. The format of - the pseudo header is the same as for classic UDP, and differs for - different versions of IP. The pseudo header of UDP Lite is different - from the pseudo header of classic UDP in one way: The value of the - length field of the pseudo header is not taken from the UDP Lite - header, but rather from information provided by the IP module. This - computation is done in the same manner as for TCP [RFC-793], and - implies that the length field of the pseudo header includes the UDP - Lite header and all subsequent bytes in the IP payload. +3.2. Pseudo Header -User Interface + UDP and UDP-Lite use the same conceptually prefixed pseudo header + from the IP layer for the checksum. This pseudo header is different + for IPv4 and IPv6. The pseudo header of UDP-Lite is different from + the pseudo header of UDP in one way: The value of the Length field of + the pseudo header is not taken from the UDP-Lite header, but rather + from information provided by the IP module. This computation is done + in the same manner as for TCP [RFC-793], and implies that the Length + field of the pseudo header includes the UDP-Lite header and all + subsequent octets in the IP payload. - A user interface should allow the same operations as for classic UDP. - In addition to this, it SHOULD provide a way for the sending - application to pass the checksum coverage value to the UDP Lite - module. There SHOULD also be a way to pass the checksum coverage +3.3. Application Interface + + An application interface should allow the same operations as for + UDP. In addition to this, it should provide a way for the sending + application to pass the checksum coverage value to the UDP-Lite + module. There should also be a way to pass the checksum coverage value to the receiving application, or at least let the receiving application block delivery of packets with coverage values less than a value provided by the application. - We RECOMMEND that the default behaviour of UDP Lite is to mimic - classic UDP by having the coverage field match the length of the UDP - Lite datagram and verifying the entire packet. Applications that want - to define the payload as partially insensitive to bit errors SHOULD - do that by a separate system call on the sender side. Applications - that wish to receive payloads which were only partially covered by a - checksum SHOULD inform the system by a separate system call. + It is RECOMMENDED that the default behavior of UDP-Lite be to mimic + UDP by having the Checksum Coverage field match the length of the + UDP-Lite packet, and verify the entire packet. Applications that want + to define the payload as partially insensitive to bit errors (e.g. + error tolerant codecs using RTP [RFC-1889]) should do that by an + explicit system call on the sender side. Applications that wish to + receive payloads that were only partially covered by a checksum + should inform the receiving system by an explicit system call. -IP Interface + The characteristics of the links forming an Internet path may vary + greatly. It is therefore difficult to make assumptions about the + level or patterns of errors that may occur in the insensitive part of + the UDP-Lite payload. Applications that use UDP-Lite should not make + any assumptions regarding the correctness of the received data beyond + the indicated checksum coverage, and should if necessary introduce + their own appropriate validity checks. - As for classic UDP, the UDP Lite module must pass the pseudo header - to the UDP Lite module. The UDP Lite pseudo header contains the IP - addresses and protocol fields of the IP header, and also the length - of the IP payload which is derived from the length field of the IP - header. +3.4. IP Interface - The IP module MUST NOT pad the IP payload with extra bytes since the - length of the UDP Lite payload delivered to the receiver depends on - the length of the IP payload. + As for UDP, the IP module must provide the pseudo header to the UDP- + Lite module. The UDP-Lite pseudo header contains the IP addresses and + protocol fields of the IP header, and also the length of the IP + payload, which is derived from the Length field of the IP header. -Lower layer considerations + The sender IP module MUST NOT pad the IP payload with extra octets + since the length of the UDP-Lite payload delivered to the receiver + depends on the length of the IP payload. - Since UDP Lite can deliver packets with damaged payloads to an - application that wants them, frames carrying UDP Lite packets need - not be discarded by lower layers when there are errors only in the - insensitive part. For a link layer that supports partial error - detection, the Coverage field in the UDP Lite header MAY be used as a - hint of where errors should be detected. Link layers that do not - support partial checksums SHOULD detect errors in the entire frame. - In general, lower layers SHOULD detect errors at least in the - sensitive part of the frame using strong error detection mechanisms, - but need not do so for the insensitive part. +3.5. Jumbograms - Note that it is usually only over links where errors are frequent - that the partial checksum feature of UDP Lite can make a difference - to the application. On links where errors are infrequent it is - RECOMMENDED that lower layeers detect errors in the entire packet. + The Checksum Coverage field is 16 bits and can represent a checksum + coverage of up to 65535 octets. This allows arbitrary checksum + coverage for IP packets, unless they are Jumbograms. For Jumbograms, + the checksum can cover either the entire payload (when the Checksum + Coverage field has the value zero), or else at most the initial 65535 + octets of the UDP-Lite packet. -Jumbograms +4. Lower Layer Considerations - The Checksum Coverage field is 16 bits and can represent checksum - coverage up to 65535 octets. This allows arbitrary checksum coverage - for IP datagrams, unless they are Jumbograms. For Jumbograms, the - Checksum can cover either the entire payload (when the Checksum - Coverage field has the value zero), or else at most the initial 65535 - octets of the UDP Lite datagram. + Since UDP-Lite can deliver packets with damaged payloads to an + application that wants them, frames carrying UDP-Lite packets need + not be discarded by lower layers when there are errors only in the + insensitive part. For a link that supports partial error detection, + the Checksum Coverage field in the UDP-Lite header MAY be used as a + hint of where errors do not need to be detected. Lower layers MUST + use a strong error detection mechanism to detect at least errors that + occur in the sensitive part of the packet, and discard damaged + packets. The sensitive part consists of the octets between the first + octet of the IP header and the last octet identified by the Checksum + Coverage field. At least the sensitive part would thus be treated in + exactly the same way as UDP packets. -Backwards compatibility + Link layers that do not support partial error detection suitable for + UDP-Lite, as described above, MUST detect errors in the entire UDP- + Lite packet, and discard damaged packets. The whole UDP-Lite packet + is thus treated in exactly the same way as a UDP packet. - The syntactic and semantic similarity between UDP Lite and classic - UDP suggests that they might share the same protocol identifier. - This section explores some consequences of doing so. + It should be noted that UDP-Lite would only make a difference to the + application if partial error detection, based on the partial checksum + feature of UDP-Lite, is implemented also by link layers, as discussed + above. Obviously, partial error detection at the link layer would + only make a difference when implemented over error-prone links. - There are no known interoperability problems between classic UDP and - UDP Lite if they were to share the protocol identifier of classic - UDP. To be more precise: there is no case where a potentially - problematic packet is delivered to an unsuspecting application; a UDP - Lite payload with partial checksum coverage cannot be delivered to - UDP applications, and UDP datagrams which only partially fills the IP - payload cannot be delivered to UDP Lite applications. +5. Compatibility with UDP - If the protocol identifier was shared between UDP and UDP Lite and a - UDP Lite implementation sends UDP Lite packets with partial checksums - to a classic UDP implementation, the classic UDP implementation would - silently discard them because a mismatching pseudo header would cause - the UDP checksum to mismatch. Neither the sending nor the receiving - application would be notified. The obvious solutions to this include + UDP and UDP-Lite have similar syntax and semantics. Applications + designed for UDP may therefore use UDP-Lite instead, and will by + default receive the same full packet coverage. The similarities also + ease implementation of UDP-Lite, since only minor modifications are + needed to an existing UDP implementation. - 1) explicit application in-band signaling (not using the partial - checksum coverage option) to enable the sender to learn whether the - receiver is UDP Lite enabled or not, or + UDP-Lite has been allocated a separate IP protocol identifier, XXXX + [INSERT IANA NUMBER BEFORE PUBLICATION], that allows a receiver to + identify whether UDP or UDP-Lite is used. A system unaware of UDP- + Lite will in general return an ICMP Protocol Unreachable error + message to the sender. This simple method of detecting UDP-Lite + unaware systems is the primary benefit of having separate protocol + identifiers. - 2) use of out-of-band signaling such as H.323, SIP, or RTCP to convey - whether the receiver is UDP Lite enabled. + The remainder of this section provides the rationale for allocating a + separate IP protocol identifier for UDP-Lite, rather than sharing the + IP protocol identifier with UDP. - If UDP Lite has its own separate protocol identifier, on the other - hand, a system unaware of UDP Lite would return ICMP Protocol - Unreachable error messages to the sender. This simple method of - detecting UDP Lite unaware systems is the primary benefit of having - separate protocol identifiers. + There are no known interoperability problems between UDP and UDP-Lite + if they were to share the protocol identifier with UDP. Specifically, + there is no case where a potentially problematic packet is delivered + to an unsuspecting application; a UDP-Lite payload with partial + checksum coverage cannot be delivered to UDP applications, and UDP + packets that only partially fill the IP payload cannot be delivered + to applications using UDP-Lite. - Therefore, this draft proposes to allocate a new protocol identifier - for UDP Lite. + However, if the protocol identifier were to be shared between UDP and + UDP-Lite, and a UDP-Lite implementation was to send a UDP-Lite packet + using a partial checksum to a UDP implementation, the UDP + implementation would silently discard the packet, because a + mismatching pseudo header would cause the UDP checksum to fail. + Neither the sending nor the receiving application would be notified. + Potential solutions to this could have been: -Security considerations + 1) explicit application in-band signaling (while not using the + partial checksum coverage option) to enable the sender to learn + whether the receiver is UDP-Lite enabled or not, or + 2) use of out-of-band signaling such as H.323, SIP, or RTCP to + convey whether the receiver is UDP-Lite enabled. - The security impact of UDP Lite is twofold. First, applications who - do not expect damaged payloads are bound to malfunction if damaged - payloads are delivered to them. To avoid this, we RECOMMEND that the - sending and the receiving side application both explicitly enable the - partial checksum option. Packets with partial checksums SHOULD NOT - be delivered to applications that have not enabled the partial - checksum option. + Anyway, since UDP-Lite has now been assigned its own protocol + identifier, there is no need to consider the possibility of delivery + of a UDP-Lite packet to an unsuspecting UDP port. - Second, there is the question of how UDP Lite interacts with +6. Security Considerations + + The security impact of UDP-Lite is related to its interaction with authentication and encryption mechanisms. When the partial checksum - option of UDP Lite is enabled, it is fine with the application if the - insensitive part of a packet changes in transit. This is contrary to - the idea behind most authentication mechanisms; authentication - succeeds when the packet has not changed in transit. Unless - authentication mechanisms that operate only on the sensitive part of - packets are developed, authentication will always fail on UDP Lite - packets where the insensitive part has been damaged. + option of UDP-Lite is enabled, the insensitive portion of a packet + may change in transit. This is contrary to the idea behind most + authentication mechanisms: authentication succeeds if the packet has + not changed in transit. Unless authentication mechanisms that operate + only on the sensitive part of packets are developed and used, + authentication will always fail on UDP-Lite packets where the + insensitive part has been damaged. - Encryption is also an issue when using UDP Lite. If a few bits of an + The IPSec integrity check (Encapsulation Security Protocol, ESP, or + Authentication Header, AH) is applied (at least) to the entire IP + packet payload. Corruption of any bit within the protected area will + then result in the discarding of the UDP-Lite packet by the IP + receiver. + + Encryption is also an issue when using UDP-Lite. If a few bits of an encrypted packet are damaged, the decryption transform will typically - spread this error so that the packet becomes too damaged to be of - use. Most strong encryption transforms today exhibit this behaviour, - for good reason. It might be possible to develop encryption - transforms which would not spread damage in this way when the damage - occurs in the insensitive part of the packet. A class of such - transforms would be transforms where the sensitive part is encrypted - using a strong transform as usual, and the insensitive part is - encrypted by XORing it with a cryptographic hash computed over the - cleartext of the sensitive part. However, it is clear that with most - transforms in use today, encryption eliminates the benefits that the - partial checksum coverage option of the UDP Lite might bring. + spread errors so that the packet becomes too damaged to be of use. + Many strong encryption transforms today exhibit this behavior, for + reasons obvious from a security point of view. There exist encryption + transforms, stream ciphers, which do not spread errors in this way + when the damage occurs in the insensitive part of the packet. -IANA considerations +7. IANA Considerations - We request that a new ip protocol identifier is allocated for UDP - Lite. + A new IP protocol number, XXXX [INSERT NUMBER BEFORE PUBLICATION], + has been assigned for UDP-Lite. -Conclusions + [NOTE, REMOVE BEFORE PUBLICATION] - We have presented the UDP Lite protocol. The main motivation for this - new variant of the classic UDP transport protocol is decreased packet - error rates for damage-tolerant applications today using classic UDP - in harsh network environments. UDP Lite provides optionally partial - checksum coverage which increases the flexibility of classic UDP by - making it possible to define a packet as partially insensitive to bit - errors on a per-packet basis. If no part of a packet is defined as - insensitive, UDP Lite is semantically identical to classic UDP. + IANA assignment instruction: + - The IANA must reserve an IP protocol number for UDP-Lite. -Contact info + [END OF NOTE] + +8. References + +8.1. Normative References + + [RFC-768] Postel, J., "User Datagram Protocol", RFC 768 (STD6), + August 1980. + + [RFC-791] Postel, J., "Internet Protocol", RFC 791 (STD5), + September 1981. + + [RFC-793] Postel, J., "Transmission Control Protocol", RFC 793 + (STD7), September 1981. + + [RFC-1071] Braden, R., Borman, D., and C. Partridge, "Computing the + Internet Checksum", RFC 1071, September 1988. + + [RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", RFC 2119 (BCP15), March 1997. + + [RFC-2460] Deering, S., and R. Hinden, "Internet Protocol, Version 6 + (IPv6) Specification", RFC 2460, December 1998. + +8.2. Informative References + + [RFC-1889] Schulzrinne, H., Casner, S., Frederick, R., and + V. Jacobson, "RTP: A Transport Protocol for Real-Time + Applications", RFC 1889, January 1996. + + [RFC-2026] Bradner, S., "The Internet Standards Process", RFC 2026, + October 1996. + + [RFC-2402] Kent, S., and R. Atkinson, "IP Authentication Header", + RFC 2402, November 1998. + + [RFC-2406] Kent, S., and R. Atkinson, "IP Encapsulating Security + Payload (ESP)", RFC 206, November 1998. + + [UDP-LITE] Larzon, L-A., Degermark, M., and S. Pink, "UDP Lite for + Real-Time Multimedia Applications", Proceedings of the + IEEE International Conference of Communications (ICC), + 1999. + +9. Acknowledgements + + Thanks to Ghyslain Pelletier for significant technical and editorial + comments. Thanks also to Elisabetta Carrara and Mats Naslund for + reviewing the security considerations chapter, and to Peter Eriksson + for doing a language review and thereby improving the clarity of this + document. + +10. Authors' Addresses Lars-Ake Larzon Department of CS & EE Lulea University of Technology S-971 87 Lulea, Sweden Email: lln@cdt.luth.se Mikael Degermark Department of Computer Science The University of Arizona P.O. Box 210077 - Tucson, AZ 85721-0077 + Tucson, AZ 85721-0077, USA Email: micke@cs.arizona.edu Stephen Pink The University of Arizona P.O. Box 210077 - Tucson, AZ 85721-0077 + Tucson, AZ 85721-0077, USA Email: steve@cs.arizona.edu -Normative References + Lars-Erik Jonsson + Ericsson AB + Box 920 + S-971 28 Lulea, Sweden + Email: lars-erik.jonsson@ericsson.com - [RFC-768] Postel, J., "User Datagram Protocol," RFC 768, - Information Sciences Institute, August 1980. + Godred Fairhurst + Department of Engineering + University of Aberdeen + Aberdeen, AB24 3UE, UK + Email: gorry@erg.abdn.ac.uk - [RFC-793] Postel, J., "Transmission Control Protocol," RFC 793, - Information Sciences Institute, September 1981. +Full Copyright Statement - [RFC-2460] Deering, S., Hinden, R., "Internet Protocol, Version 6 - (IPv6) Specification," RFC 2460, IETF, December 1998. + Copyright (C) The Internet Society (2002). All Rights Reserved. -Informative References + 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 Standards process must be + followed, or as required to translate it into languages other than + English. - [RFC-2026] Bradner, S., "The Internet Standards Process," RFC 2026, - Harvard University, October 1996. + The limited permissions granted above are perpetual and will not be + revoked by the Internet Society or its successors or assigns. - [RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate - Requirement Levels," Harvard University, March 1997. + 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. -This draft expires July 24, 2002 +This Internet-Draft expires June 5, 2003.