Session Description Protocol (SDP) Format for Binary Floor Control Protocol (BFCP) Streams
RFC 8856
Document | Type |
RFC
- Proposed Standard
(January 2021)
Obsoletes RFC 4583
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|
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Authors | Gonzalo Camarillo , Tom Kristensen , Christer Holmberg | ||
Last updated | 2021-01-19 | ||
RFC stream | Internet Engineering Task Force (IETF) | ||
Formats | |||
Additional resources | Mailing list discussion | ||
IESG | Responsible AD | Adam Roach | |
Send notices to | (None) |
RFC 8856
#x27; attribute in offers and answers. The attribute value, if present, MUST be in accordance with the definition of the version ("Ver") field in [RFC8855]. If the attribute is not present, endpoints MUST assume a default value in accordance with [RFC8855]: when used over a reliable transport, the default attribute value is "1", and when used over an unreliable transport, the default attribute value is "2". The value is inferred from the transport specified in the "m=" line (Section 4) of the "m=" section associated with the stream. The SDP Offer/Answer procedures for the 'bfcpver' attribute are defined in Section 10. 6. Multiplexing Considerations [RFC8843] defines how multiplexing of multiple media streams can be negotiated. This specification does not define how BFCP streams can be multiplexed with other media streams. Therefore, a BFCP stream MUST NOT be associated with a BUNDLE group [RFC8843]. Note that BFCP-controlled media streams might be multiplexed with other media streams. [RFC8859] defines the mux categories for the SDP attributes defined in this specification, except for the 'bfcpver' attribute. Table 2 defines the mux category for the 'bfcpver' attribute: +=========+===========================+=======+==============+ | Name | Notes | Level | Mux Category | +=========+===========================+=======+==============+ | bfcpver | Needs further analysis in | M | TBD | | | a separate specification | | | +---------+---------------------------+-------+--------------+ Table 2: Multiplexing Attribute Analysis 7. BFCP Connection Management BFCP streams can use TCP or UDP as the underlying transport. Endpoints exchanging BFCP messages over UDP send the BFCP messages towards the peer using the connection address and port provided in the SDP "c=" and "m=" lines. TCP connection management is more complicated and is described in the following section. | Note: When using Interactive Connectivity Establishment (ICE) | [RFC8445], TCP/DTLS/BFCP, or UDP/TLS/BFCP, the straightforward | procedures for connection management via UDP/BFCP, as described | above, apply. TCP/TLS/BFCP follows the same procedures as | TCP/BFCP and is described below. 7.1. TCP Connection Management The management of the TCP connection used to transport BFCP messages is performed using the SDP 'setup' and 'connection' attributes [RFC4145]. The 'setup' attribute indicates which of the endpoints initiates the TCP connection. The 'connection' attribute handles TCP connection re-establishment. The BFCP specification [RFC8855] describes a number of situations when the TCP connection between a floor control client and the floor control server needs to be re-established. However, [RFC8855] does not describe the re-establishment process, because this process depends on how the connection was established in the first place. Endpoints using the offer/answer mechanism follow the following rules. When the existing TCP connection is closed and re-established following the rules in [RFC8855], the floor control client MUST send an offer towards the floor control server in order to re-establish the connection. If a TCP connection cannot deliver a BFCP message and times out, the endpoint that attempted to send the message (i.e., the one that detected the TCP timeout) MUST send an offer in order to re-establish the TCP connection. Endpoints that use the offer/answer mechanism to negotiate TCP connections MUST support the 'setup' and 'connection' attributes. 8. TLS/DTLS Considerations When DTLS is used with UDP, the generic procedures defined in Section 5 of [RFC8842] MUST be followed. When TLS is used with TCP, once the underlying connection is established, the answerer always acts as the TLS server. If the TCP connection is lost, the active endpoint [RFC4583] is responsible for re-establishing the TCP connection. Unless a new TLS connection is negotiated, subsequent SDP offers and answers will not impact the previously negotiated TLS roles. | Note: For TLS, it was decided to keep the original procedures | in [RFC4583] to determine which endpoint acts as the TLS | server, in order to retain backward compatibility. 9. ICE Considerations Generic SDP offer/answer procedures for ICE are defined in [RFC8839]. When BFCP is used with UDP-based ICE candidates [RFC8445], the procedures for UDP/TLS/BFCP are used. When BFCP is used with TCP-based ICE candidates [RFC6544], the procedures for TCP/DTLS/BFCP are used. Based on the procedures defined in [RFC8842], endpoints treat all ICE candidate pairs associated with a BFCP stream on top of a DTLS association as part of the same DTLS association. Thus, there will only be one BFCP handshake and one DTLS handshake even if there are multiple valid candidate pairs, and even if BFCP media is shifted between candidate pairs (including switching between UDP candidate pairs and TCP candidate pairs) prior to nomination. If new candidates are added, they will also be part of the same DTLS association. In order to maximize the likelihood of interoperability between the endpoints, all ICE-enabled BFCP-over-DTLS endpoints SHOULD implement support for UDP/TLS/BFCP. When an SDP offer or answer conveys multiple ICE candidates for a BFCP stream, UDP-based candidates SHOULD be included and the default candidate SHOULD be chosen from one of those UDP candidates. If UDP transport is used for the default candidate, then the "m=" line proto value MUST be 'UDP/TLS/BFCP'. If TCP transport is used for the default candidate, the "m=" line proto value MUST be 'TCP/DTLS/BFCP'. | Note: Usage of ICE with protocols other than UDP/TLS/BFCP and | TCP/DTLS/BFCP is out of scope for this specification. 10. SDP Offer/Answer Procedures This section defines the SDP offer/answer [RFC3264] procedures for negotiating and establishing a BFCP stream. Generic procedures for DTLS are defined in [RFC8842]. Generic procedures for TLS are defined in [RFC8122]. This section only defines the BFCP-specific procedures. Unless explicitly stated otherwise, the procedures apply to an "m=" section describing a BFCP stream. If an offer or answer contains multiple "m=" sections describing BFCP streams, the procedures are applied independently to each stream. Within this document, 'initial offer' refers to the first offer within an SDP session (e.g., a Session Initiation Protocol (SIP) dialog when SIP [RFC3261] is used to carry SDP) in which the offerer indicates that it wants to negotiate the establishment of a BFCP stream. If the "m=" line 'proto' value is 'TCP/TLS/BFCP', 'TCP/DTLS/BFCP', or 'UDP/TLS/BFCP', the offerer and answerer follow the generic procedures defined in [RFC8122]. If the "m=" line proto value is 'TCP/BFCP', 'TCP/TLS/BFCP', 'TCP/DTLS/TCP', or 'UDP/TLS/BFCP', the offerer and answerer use the SDP 'setup' attribute according to the procedures in [RFC4145]. If the "m=" line proto value is 'TCP/BFCP', 'TCP/TLS/BFCP', or 'TCP/DTLS/BFCP', the offerer and answerer use the SDP 'connection' attribute according to the procedures in [RFC4145]. | Note: The use of source-specific SDP parameters [RFC5576] is | not defined for BFCP streams. 10.1. Generating the Initial SDP Offer When the offerer creates an initial offer, the offerer MUST include an SDP 'floorctrl' attribute (Section 5.1) and an SDP 'bfcpver' attribute (Section 5.5) in the "m=" section. In addition, if the offerer includes an SDP 'floorctrl' attribute with "s-only" or "c-s" attribute values in the offer, the offerer * MUST include an SDP 'confid' attribute (Section 5.2) in the "m=" section, * MUST include an SDP 'userid' attribute (Section 5.3) in the "m=" section, * MUST include an SDP 'floorid' attribute (Section 5.4) in the "m=" section, and * MUST include an SDP 'label' attribute [RFC4574] with the "m=" section of each BFCP-controlled media stream. | Note: If the offerer includes an SDP 'floorctrl' attribute with | a "c-s" attribute value, or both a "c-only" and an "s-only" | attribute value in the offer, the attribute values above will | only be used if it is determined (Section 5.1) that the offerer | will act as a floor control server. 10.2. Generating the SDP Answer When the answerer receives an offer that contains an "m=" section describing a BFCP stream, the answerer MUST check whether it supports one or more of the BFCP versions supported by the offerer (Section 5.5). If the answerer does not support any of the BFCP versions, it MUST NOT accept the "m=" section. Otherwise, if the answerer accepts the "m=" section, the answerer * MUST insert a corresponding "m=" section in the answer, with an identical "m=" line proto value [RFC8866], * MUST include a 'bfcpver' attribute in the "m=" section; the versions indicated by the answer MUST be the same or a subset of the versions indicated by the offerer in the corresponding offer, and * MUST, if the offer contained an SDP 'floorctrl' attribute, include a 'floorctrl' attribute in the "m=" section. In addition, if the answerer includes an SDP 'floorctrl' attribute with an "s-only" attribute value in the answer, the answerer * MUST include an SDP 'confid' attribute in the "m=" section, * MUST include an SDP 'userid' attribute in the "m=" section, * MUST include an SDP 'floorid' attribute in the "m=" section, and * MUST include an SDP 'label' attribute in the "m=" section of each BFCP-controlled media stream. | Note: An offerer compliant with [RFC4583] might not include | 'floorctrl' and 'bfcpver' attributes in offers, in which case | the default values apply. Once the answerer has sent the answer, the answerer * MUST, if the answerer is the active endpoint and if a TCP connection associated with the "m=" section is to be established (or re-established), initiate the establishment of the TCP connection, and * MUST, if the answerer is the active endpoint and if a TLS/DTLS connection associated with the "m=" section is to be established (or re-established), initiate the establishment of the TLS/DTLS connection (by sending a ClientHello message). If the answerer does not accept the "m=" section in the offer, it MUST assign a zero port value to the "m=" line of the corresponding "m=" section in the answer. In addition, the answerer MUST NOT establish a TCP connection or a TLS/DTLS connection associated with the "m=" section. 10.3. Offerer Processing of the SDP Answer When the offerer receives an answer that contains an "m=" section describing a BFCP stream and with a non-zero port value in the "m=" line, the offerer * MUST, if the offerer is the active endpoint and if a TCP connection associated with the "m=" section is to be established (or re-established), initiate the establishment of the TCP connection, and * MUST, if the offerer is the active endpoint and if a TLS/DTLS connection associated with the "m=" section is to be established (or re-established), initiate the establishment of the TLS/DTLS connection (by sending a ClientHello message). | Note: An answerer compliant with [RFC4583] might not include | 'floorctrl' and 'bfcpver' attributes in answers, in which case | the default values apply. If the "m=" line in the answer contains a zero port value or if the offerer for some other reason does not accept the answer (e.g., if the answerer only indicates support of BFCP versions not supported by the offerer), the offerer MUST NOT establish a TCP connection or a TLS/DTLS connection associated with the "m=" section. 10.4. Modifying the Session When an offerer sends an updated offer, in order to modify a previously established BFCP stream, it follows the procedures in Section 10.1, with the following exceptions: * If the BFCP stream is carried on top of TCP and if the offerer does not want to re-establish an existing TCP connection, the offerer MUST include in the "m=" section an SDP 'connection' attribute with a value of "existing", and * If the offerer wants to disable a previously established BFCP stream, it MUST assign a zero port value to the "m=" line associated with the BFCP connection, following the procedures in [RFC3264]. 11. Examples For the purpose of brevity, the main portion of the session description is omitted in the examples, which only show "m=" sections and their "m=" lines and attributes. The following is an example of an offer sent by a conference server to a client. m=application 50000 TCP/TLS/BFCP * a=setup:actpass a=connection:new a=fingerprint:sha-256 \ 19:E2:1C:3B:4B:9F:81:E6:B8:5C:F4:A5:A8:D8:73:04: \ BB:05:2F:70:9F:04:A9:0E:05:E9:26:33:E8:70:88:A2 a=floorctrl:c-only s-only a=confid:4321 a=userid:1234 a=floorid:1 mstrm:10 a=floorid:2 mstrm:11 a=bfcpver:1 2 m=audio 50002 RTP/AVP 0 a=label:10 m=video 50004 RTP/AVP 31 a=label:11 Note that due to RFC formatting conventions, this document splits the SDP entries across lines whose content would exceed the maximum line length. A backslash character ("\") marks where this line folding has taken place. This backslash and its trailing CRLF and whitespace would not appear in actual SDP content. The following is the answer returned by the client. m=application 9 TCP/TLS/BFCP * a=setup:active a=connection:new a=fingerprint:sha-256 \ 6B:8B:F0:65:5F:78:E2:51:3B:AC:6F:F3:3F:46:1B:35: \ DC:B8:5F:64:1A:24:C2:43:F0:A1:58:D0:A1:2C:19:08 a=floorctrl:c-only a=bfcpver:1 m=audio 55000 RTP/AVP 0 m=video 55002 RTP/AVP 31 A similar example using an unreliable transport and DTLS is shown below, where the offer is sent from a client. m=application 50000 UDP/TLS/BFCP * a=setup:actpass a=dtls-id:abc3dl a=fingerprint:sha-256 \ 19:E2:1C:3B:4B:9F:81:E6:B8:5C:F4:A5:A8:D8:73:04: \ BB:05:2F:70:9F:04:A9:0E:05:E9:26:33:E8:70:88:A2 a=floorctrl:c-only s-only a=confid:4321 a=userid:1234 a=floorid:1 mstrm:10 a=floorid:2 mstrm:11 a=bfcpver:1 2 m=audio 50002 RTP/AVP 0 a=label:10 m=video 50004 RTP/AVP 31 a=label:11 The following is the answer returned by the server. m=application 55000 UDP/TLS/BFCP * a=setup:active a=dtls-id:abc3dl a=fingerprint:sha-256 \ 6B:8B:F0:65:5F:78:E2:51:3B:AC:6F:F3:3F:46:1B:35: \ DC:B8:5F:64:1A:24:C2:43:F0:A1:58:D0:A1:2C:19:08 a=floorctrl:s-only a=confid:4321 a=userid:1234 a=floorid:1 mstrm:10 a=floorid:2 mstrm:11 a=bfcpver:2 m=audio 55002 RTP/AVP 0 m=video 55004 RTP/AVP 31 12. Security Considerations The BFCP specification [RFC8855], SDP specification [RFC8866], and offer/answer specification [RFC3264] discuss security issues related to BFCP, SDP, and offer/answer, respectively. In addition, [RFC4145] and [RFC8122] discuss security issues related to the establishment of TCP and TLS connections using an offer/answer model. Furthermore, when using DTLS over UDP, the generic offer/answer considerations defined in [RFC8842] MUST be followed. The usage of certain proto values in the SDP offer/answer negotiation will result in a BFCP stream that is not protected by TLS or DTLS. Operators will need to provide integrity protection and confidentiality protection of the BFCP stream using other means. The generic security considerations associated with SDP attributes are defined in [RFC3264]. While the attributes defined in this specification do not reveal information about the content of individual BFCP-controlled media streams, they do reveal which media streams will be BFCP controlled. 13. IANA Considerations This document registers three new values in the "proto" subregistry within the "Session Description Protocol (SDP) Parameters" registry: 'TCP/DTLS/BFCP', 'UDP/BFCP', and 'UDP/TLS/BFCP' (see Section 13.1). This document also registers a new SDP attribute in the 'attribute- name (formerly "att-field")' subregistry within the "Session Description Protocol (SDP) Parameters" registry: 'bfcpver' (see Section 5.5). The remaining values are unchanged from [RFC4582], except that the references have been updated to refer to this document. 13.1. Registration of SDP 'proto' Values The IANA has registered three new values in the SDP 'proto' field under the "Session Description Protocol (SDP) Parameters" registry. +===============+===========+ | Value | Reference | +===============+===========+ | TCP/BFCP | RFC 8856 | +---------------+-----------+ | TCP/DTLS/BFCP | RFC 8856 | +---------------+-----------+ | TCP/TLS/BFCP | RFC 8856 | +---------------+-----------+ | UDP/BFCP | RFC 8856 | +---------------+-----------+ | UDP/TLS/BFCP | RFC 8856 | +---------------+-----------+ Table 3: Values for the SDP 'proto' Field 13.2. Registration of the SDP 'floorctrl' Attribute This document defines the SDP 'floorctrl' attribute. Details regarding this attribute are provided in Section 5.1. 13.3. Registration of the SDP 'confid' Attribute This document defines the SDP 'confid' attribute. Details regarding this attribute are provided in Section 5.2. 13.4. Registration of the SDP 'userid' Attribute This document defines the SDP 'userid' attribute. Details regarding this attribute are provided in Section 5.3. 13.5. Registration of the SDP 'floorid' Attribute This document defines the SDP 'floorid' attribute. Details regarding this attribute are provided in Section 5.4. 13.6. Registration of the SDP 'bfcpver' Attribute This document defines the SDP 'bfcpver' attribute. Details regarding this attribute are provided in Section 5.5. 14. Changes from RFC 4583 The technical changes and other fixes from [RFC4583] are listed below. The main purpose of this work was to add signaling support necessary to support BFCP over an unreliable transport, as described in [RFC8855], resulting in the following changes: * Fields in the "m=" Line (Section 4): This section has been rewritten to remove reference to the exclusivity of TCP as a transport for BFCP streams. The proto field values 'TCP/DTLS/BFCP', 'UDP/BFCP', and 'UDP/TLS/BFCP' have been added. * Security Considerations (Section 12): For the DTLS-over-UDP case, we direct the reader to existing considerations and requirements for the offer/answer exchange as provided in [RFC8842]. * Registration of SDP 'proto' Values (Section 13.1): This document registers the three new values 'TCP/DTLS/BFCP', 'UDP/BFCP', and 'UDP/TLS/BFCP' in the "Session Description Protocol (SDP) Parameters" registry. * SDP 'bfcpver' Attribute (Section 5.5): A new 'bfcpver' SDP media-level attribute has been added, in order to signal the supported version number. In addition to the changes associated with support of BFCP over an unreliable transport, the possibility that an endpoint can act as both a floor control client and a floor control server at the same time has been removed. An endpoint will now take the same role for all BFCP-controlled streams associated with the BFCP stream. Clarifications and bug fixes: * Erratum ID 712 (Sections 3 and 10 of [RFC4583]; see [Err712] for details): Do not use language such as 'used in an "m=" line' when discussing an SDP attribute; instead, make clear that the attribute is a media-level attribute. * Spelling corrected in the first SDP example in Section 9 of [RFC4583]: Do not use 'm-stream' as listed in the first SDP example in [RFC4583]; instead, use the correct 'mstrm' as specified in Section 11 of this document. However, we recommend continuing to interpret 'm-stream', if received, because it is still present in some implementations. * Assorted clarifications (throughout the document): Language clarifications were made as a result of reviews. Also, normative language was "tightened" where appropriate, i.e., changed from "SHOULD" strength to "MUST" in a number of places. 15. References 15.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>. [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, DOI 10.17487/RFC3261, June 2002, <https://www.rfc-editor.org/info/rfc3261>. [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, DOI 10.17487/RFC3264, June 2002, <https://www.rfc-editor.org/info/rfc3264>. [RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in the Session Description Protocol (SDP)", RFC 4145, DOI 10.17487/RFC4145, September 2005, <https://www.rfc-editor.org/info/rfc4145>. [RFC4571] Lazzaro, J., "Framing Real-time Transport Protocol (RTP) and RTP Control Protocol (RTCP) Packets over Connection- Oriented Transport", RFC 4571, DOI 10.17487/RFC4571, July 2006, <https://www.rfc-editor.org/info/rfc4571>. [RFC4574] Levin, O. and G. Camarillo, "The Session Description Protocol (SDP) Label Attribute", RFC 4574, DOI 10.17487/RFC4574, August 2006, <https://www.rfc-editor.org/info/rfc4574>. [RFC4582] Camarillo, G., Ott, J., and K. Drage, "The Binary Floor Control Protocol (BFCP)", RFC 4582, DOI 10.17487/RFC4582, November 2006, <https://www.rfc-editor.org/info/rfc4582>. [RFC4583] Camarillo, G., "Session Description Protocol (SDP) Format for Binary Floor Control Protocol (BFCP) Streams", RFC 4583, DOI 10.17487/RFC4583, November 2006, <https://www.rfc-editor.org/info/rfc4583>. [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008, <https://www.rfc-editor.org/info/rfc5234>. [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, January 2012, <https://www.rfc-editor.org/info/rfc6347>. [RFC6544] Rosenberg, J., Keranen, A., Lowekamp, B. B., and A. B. Roach, "TCP Candidates with Interactive Connectivity Establishment (ICE)", RFC 6544, DOI 10.17487/RFC6544, March 2012, <https://www.rfc-editor.org/info/rfc6544>. [RFC8122] Lennox, J. and C. Holmberg, "Connection-Oriented Media Transport over the Transport Layer Security (TLS) Protocol in the Session Description Protocol (SDP)", RFC 8122, DOI 10.17487/RFC8122, March 2017, <https://www.rfc-editor.org/info/rfc8122>. [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>. [RFC8445] Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal", RFC 8445, DOI 10.17487/RFC8445, July 2018, <https://www.rfc-editor.org/info/rfc8445>. [RFC8839] Petit-Huguenin, M., Nandakumar, S., Holmberg, C., Keränen, A., and R. Shpount, "Session Description Protocol (SDP) Offer/Answer Procedures for Interactive Connectivity Establishment (ICE)", RFC 8839, DOI 10.17487/RFC8839, January 2021, <https://www.rfc-editor.org/info/rfc8839>. [RFC8842] Holmberg, C. and R. Shpount, "Session Description Protocol (SDP) Offer/Answer Considerations for Datagram Transport Layer Security (DTLS) and Transport Layer Security (TLS)", RFC 8842, DOI 10.17487/RFC8842, January 2021, <https://www.rfc-editor.org/info/rfc8842>. [RFC8855] Camarillo, G., Drage, K., Kristensen, T., Ott, J., and C. Eckel, "The Binary Floor Control Protocol (BFCP)", RFC 8855, DOI 10.17487/RFC8855, January 2021, <https://www.rfc-editor.org/info/rfc8855>. [RFC8859] Nandakumar, S., "A Framework for Session Description Protocol (SDP) Attributes When Multiplexing", RFC 8859, DOI 10.17487/RFC8859, January 2021, <https://www.rfc-editor.org/info/rfc8859>. [RFC8866] Begen, A., Kyzivat, P., Perkins, C., and M. Handley, "SDP: Session Description Protocol", RFC 8866, DOI 10.17487/RFC8866, January 2021, <https://www.rfc-editor.org/info/rfc8866>. 15.2. Informative References [Err712] RFC Errata, Erratum ID 712, RFC 4583, <https://www.rfc-editor.org/errata/eid712>. [RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific Media Attributes in the Session Description Protocol (SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009, <https://www.rfc-editor.org/info/rfc5576>. [RFC8843] Holmberg, C., Alvestrand, H., and C. Jennings, "Negotiating Media Multiplexing Using the Session Description Protocol (SDP)", RFC 8843, DOI 10.17487/RFC8843, January 2021, <https://www.rfc-editor.org/info/rfc8843>. Acknowledgements Jörg Ott, Keith Drage, Alan Johnston, Eric Rescorla, Roni Even, and Oscar Novo provided useful ideas for the original [RFC4583]. The authors also acknowledge contributions to the revision of BFCP for use over an unreliable transport from Geir Arne Sandbakken, Charles Eckel, Alan Ford, Eoin McLeod, and Mark Thompson. Useful and important final reviews were done by Ali C. Begen, Mary Barnes, and Charles Eckel. In the final stages, Roman Shpount made a considerable effort in adding proper ICE support and considerations. Authors' Addresses Gonzalo Camarillo Ericsson Hirsalantie 11 FI-02420 Jorvas Finland Email: Gonzalo.Camarillo@ericsson.com Tom Kristensen Jotron AS Ringdalskogen 8 3270 Larvik Norway Email: tom.kristensen@jotron.com, tomkri@ifi.uio.no Christer Holmberg Ericsson Hirsalantie 11 FI-02420 Jorvas Finland Email: christer.holmberg@ericsson.com