MMUSIC Working Group G. Camarillo Internet-Draft Ericsson Expires: April 25, 2005 J. Rosenberg dynamicsoft October 25, 2004 The Alternative Network Address Types Semantics (ANAT) for the Session Description Protocol (SDP) Grouping Framework draft-ietf-mmusic-anat-02.txt Status of this Memo This document is an Internet-Draft and is subject to all provisions of section 3 of RFC 3667. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668. 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/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 25, 2005. Copyright Notice Copyright (C) The Internet Society (2004). Abstract This document defines the Alternative Network Address Types (ANAT) semantics for the SDP grouping framework. The ANAT semantics allow offering alternative types of network addresses to establish a particular media stream. Camarillo & Rosenberg Expires April 25, 2005 [Page 1] Internet-Draft ANAT Semantics October 2004 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Scope and Relation with Interactive Connectivity Establishment . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. ANAT Semantics . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Preference . . . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Offer/Answer and ANAT . . . . . . . . . . . . . . . . . . . . 4 6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 7. Security Considerations . . . . . . . . . . . . . . . . . . . 5 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 9.1 Normative References . . . . . . . . . . . . . . . . . . . . 6 9.2 Informational References . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 6 Intellectual Property and Copyright Statements . . . . . . . . 8 Camarillo & Rosenberg Expires April 25, 2005 [Page 2] Internet-Draft ANAT Semantics October 2004 1. Introduction An SDP [2] session description contains the media parameters to be used to establish a number of media streams. For a particular media stream, an SDP session description contains, among other parameters, the network addresses and the codec to be used to transfer media. SDP allows providing a set of codecs per media stream, but only one network address. Being able to offer a set of network addresses to establish a media stream is useful in environments with both IPv4-only hosts and IPv6-only hosts, for instance. This document defines the Alternative Network Address Types (ANAT) semantics for the SDP grouping framework [4]. The ANAT semantics allow expressing alternative network addresses (e.g., different IP versions) for a particular media stream. 1.1 Scope and Relation with Interactive Connectivity Establishment The ANAT semantics are intended to address scenarios that involve different network address types (e.g., different IP versions). They are not intended to provide alternative transport addresses with the same network type. Systems that need to provide different transport addresses with the same network type should use the SDP format defined in ICE (Interactive Connectivity Establishment) [6] instead. ICE is used by systems that cannot determine their own transport address as seen from the remote end but that can provide several possible alternatives. ICE encodes the address that is most likely to be valid in an 'm' line and the rest of addresses as a= lines after that 'm' line. This way, systems that do not support ICE simply ignore the a= lines and only use the address in the 'm' line. This achieves good backwards compatibility. We have chosen to group 'm' lines with different IP versions at the 'm' level (ANAT semantics) rather than at the a= level (ICE format) in order to keep the IPv6 syntax free from ICE parameters used for legacy (IPv4) NATs (Network Address Translators). This yields a syntax much closer to vanilla SDP, where IPv6 addresses are defined in their own 'm' line, rather than in parameters belonging to a different 'm' line. Additionally, ICE only allows us to provide a single primary address when the peer does not support ICE. The ANAT semantics avoids relegating addresses of a certain type (e.g., IPv6 addresses) to just be a secondary alternate to another address type (e.g., IPv4 addresses). Camarillo & Rosenberg Expires April 25, 2005 [Page 3] Internet-Draft ANAT Semantics October 2004 Furthermore, the separation between ANAT and ICE helps systems that support IPv4 and IPv6 but that do not need to support ICE (e.g., a multicast server). 2. Terminology In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119 [1] and indicate requirement levels for compliant implementations. 3. ANAT Semantics We define a new ``semantics'' attribute within the SDP grouping framework [4]: ANAT (Alternative Network Address Types). Media lines grouped using ANAT semantics provide alternative network addresses of different types for a single logical media stream. The entity creating a session description with an ANAT group MUST be ready to receive (or send) media over any of the grouped 'm' lines. The ANAT semantics MUST NOT be used to group media streams whose network addresses are of the same type. 4. Preference The entity generating a session description may have an order of preference for the alternative network address types offered. The identifiers of the media streams MUST be listed in order of preference in the group line. For an example where the 'm- line with mid=1 has a higher preference than the 'm' line with mid=2, see Section 6. 5. Offer/Answer and ANAT An offerer using SIP [3] to send its offer SHOULD place the sdp-anat option-tag [5] in a Require header field. An answerer receiving a session description that uses the ANAT semantics SHOULD use the address with highest priority it understands and set the ports of the rest of the 'm' lines of the group to zero. 6. Example The session description below contains an IPv4 address and an IPv6 address grouped using ANAT. The format correspoding to the mapping of ICE into SDP [6] is used in both 'm' lines to provide extra addresses. Camarillo & Rosenberg Expires April 25, 2005 [Page 4] Internet-Draft ANAT Semantics October 2004 v=0 o=bob 280744730 28977631 IN IP4 host.example.com s= t=0 0 a=group:ANAT 1 2 m=audio 25000 RTP/AVP 0 c=IN IP6 2001:DB8::1 a=alt:1 1.0 : user1 9kksj== 2001:DB8::1 25000 a=alt:2 0.8 : user2 9kksk== 2001:DB8::2 20000 a=alt:3 0.4 : user3 9kksl== 2001:DB8::3 30000 a=mid:1 m=audio 22334 RTP/AVP 0 c=IN IP4 192.0.2.1 a=alt:1 1.0 : user4 9kksm== 10.0.1.1 1010 a=alt:2 0.8 : user5 9kksn== 192.0.2.2 20000 a=alt:3 0.4 : user6 9kkso== 192.0.2.1 22334 a=mid:2 7. Security Considerations An attacker adding group lines using the ANAT semantics to an SDP session description could make an end-point use only one out of all the streams offered by the remote end, when the intention of the remote-end might have been to establish all the streams. An attacker removing group lines using ANAT semantics could make and end-point establish a higher number of media streams. If the end-point sends media over all of them, the session bandwidth may increase dramatically. It is thus STRONGLY RECOMMENDED that integrity protection be applied to the SDP session descriptions. For session descriptions carried in SIP [3], S/MIME is the natural choice to provide such end-to-end integrity protection, as described in RFC 3261. Other applications MAY use a different form of integrity protection. 8. IANA Considerations IANA needs to register the following new 'semantics' attribute for the SDP grouping framework [4]: Semantics Token Reference --------------------------------- ----- --------- Alternative Network Address Types ANAT [RFCxxxx] It should be registered in the SDP parameters registry Camarillo & Rosenberg Expires April 25, 2005 [Page 5] Internet-Draft ANAT Semantics October 2004 (http://www.iana.org/assignments/sdp-parameters) under Semantics for the "group" SDP Attribute. 9. References 9.1 Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Handley, M. and V. Jacobson, "SDP: Session Description Protocol", RFC 2327, April 1998. [3] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [4] Camarillo, G., Eriksson, G., Holler, J. and H. Schulzrinne, "Grouping of Media Lines in the Session Description Protocol (SDP)", RFC 3388, December 2002. [5] Camarillo, G. and J. Rosenberg, "The sdp-anat Session Initiation Protocol (SIP) Option-Tag", draft-camarillo-sip-anat-option-tag-00.txt (work in progress), April 2004. 9.2 Informational References [6] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A Methodology for Network Address Translator (NAT) Traversal for Multimedia Session Establishment Protocols", draft-ietf-mmusic-ice-02 (work in progress), July 2004. Authors' Addresses Gonzalo Camarillo Ericsson Hirsalantie 11 Jorvas 02420 Finland EMail: Gonzalo.Camarillo@ericsson.com Camarillo & Rosenberg Expires April 25, 2005 [Page 6] Internet-Draft ANAT Semantics October 2004 Jonathan Rosenberg dynamicsoft 600 Lanidex Plaza Parsippany, NJ 07054 US EMail: jdrosen@dynamicsoft.com Camarillo & Rosenberg Expires April 25, 2005 [Page 7] Internet-Draft ANAT Semantics October 2004 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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