MMUSIC Albrecht Schwarz Internet Draft Juergen Stoetzer-Bradler Intended status: Informational ALCATEL-LUCENT Expires: December 2010 June 7, 2010 Session Description Protocol (SDP) - Revised Offer/Answer Protocol (SDPCapNeg & MediaCapNeg) - Offer/Answer Examples draft-schwarz-mmusic-sdp-offer-answer-examples-04.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. 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." 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Code Components extracted from this document must include Simplified BSD License text Schwarz Expires December 7, 2010 [Page 1] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Abstract This document gives examples of Session Description Protocol (SDP) offer/answer exchanges. The SDP offer/answer protocol was revised by [SDPCapNeg] and [MediaCapNeg] plus other extensions. Examples include the indication, negotiation and selection of media configurations ("codecs"). This document discusses primarily examples of IP bearer emulation scenarios for PSTN modem calls in SIP- controlled VoIP networks. Further may be highlighted the examples like for instance "autonomous state transitioning between Audio VoIP and T.38 FoIP" or "G.725 terminal emulation". The purpose of this document is thus the same as the list of examples by RFC 4317 [2] for the legacy SDP offer/answer protocol (RFC 3264 [1]). Table of Contents 1. Terminology...................................................3 1.1. Abbreviations............................................3 2. Overview......................................................4 3. Revised SDP Offer/Answer Protocol.............................5 4. Examples for "Emulating PSTN Modem Calls".....................5 4.1. Supported SDP capabilities by SIP devices................6 4.2. Audio VoIP, no V.152 VBDoIP and no T.38 FoIP (Example 1).7 4.3. Audio VoIP, V.152 VBDoIP, but no T.38 FoIP (Example 2)...8 4.3.1. Example 2.1 - Multiple audio & multiple VBD codecs..8 4.3.2. Example 2.2 - Single audio codec, two VBD codecs....9 4.3.3. Example 2.3 - Two audio codecs & one VBD codec (overlapping with audio)..................................10 4.3.4. Example 2.4 - Declaration of RTP packet redundancy.11 4.3.5. Example 2.5 - Forward Error Correction for V.152 with PCMU as VBD codec)........................................11 4.4. Audio VoIP, V.152 VBDoIP and T.38 FoIP (Example 3)......12 4.4.1. Example Offer......................................12 4.4.1.1. Capabilities (Media, Transport) by OFFERER....12 4.4.1.2. Offered Codec/Configuration List (OCL_A)......13 4.4.1.3. SDP Syntax....................................14 4.4.2. Example Answers....................................17 4.4.2.1. ANSWERER not compliant to SDP_R_O/A...........17 Schwarz Expires December 7, 2010 [Page 2] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 4.4.2.2. ANSWERER supports SDP_R_O/A and is V.152 compliant ......................................................18 4.4.2.3. ANSWERER supports SDP_R_O/A and is none-V.152 compliant..............................................18 4.5. T.38 FoIP only calls, no Audio VoIP, no V.152 VBDoIP (Example 4)...........................................................19 4.5.1. Example 4.1 - Agreement on T.38-over-UDPTL/UDP, multiple transport variants offered................................19 4.6. T.38 FoIP and Audio VoIP, no V.152 VBDoIP (Example 5)...20 4.6.1. Example 5.1 - Multiple audio codecs, single T.38 option .........................................................20 4.6.2. Example 5.2 - Autonomous state transitioning between Audio VoIP and T.38 FoIP..................................21 4.6.3. Example 5.3 - Single audio codec, three T.38 configurations concerning error correction methods........23 4.6.4. Example 5.4 - Single audio codec, three T.38 configurations concerning error correction methods, and pseudo- VBD mode as T.38 fallback option..........................24 4.7. Other examples: in ITU-T Recommendations V.152 and T.38.26 4.7.1. Revised SDP Offer/Answer examples for V.152 VBDoIP.26 4.7.2. Revised SDP Offer/Answer examples for T.38 FoIP....26 5. Example "G.711 A-law & G.711 u-law with preference on A-law".26 6. Example "G.711 in multiple format configurations"............26 7. Example "G.725 terminal emulation"...........................28 8. Other examples...............................................29 9. Security Considerations......................................30 10. IANA Considerations.........................................30 11. Changes from previous versions..............................30 11.1. Changes from version 00................................30 11.2. Changes from version 01................................30 11.3. Changes from version 02................................30 11.4. Changes from version 03................................31 12. References..................................................31 12.1. Normative References...................................31 12.2. Informative References.................................31 1. Terminology The scope of the examples in this document is related to offer/answer exchanges for 'media configurations'. The term 'codec' if often synonymously used for 'media configuration' in the context of capability indication, negotiation and selection. 1.1. Abbreviations ACL Answered Configuration (Codec) List ATA Analog Terminal Adaptor (= SIP residential gateway) Schwarz Expires December 7, 2010 [Page 3] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 FoIP Facsimile over IP according ITU-T T.38 [9] NCL Negotiated Configuration (Codec) List OCL Offered Configuration (Codec) List PBX Private Branch Exchange (here SIP PBX) PCL Preferred Configuration (Codec) List PSTN Public Switched Telephone Network SCL Supported Configuration (Codec) List SDP Session Description Protocol SDP O/A SDP Offer/Answer SDP_L Legacy SDP Offer/Answer (model and protocol) SDP_R Revised SDP Offer/Answer (model and protocol) SIP Session Initiation Protocol VBD Voiceband Data VBDoIP VBD over IP according ITU-T V.152 [8] VGW Voice Gateway (= SIP access/residential gateway) 2. Overview This document describes offer/answer examples of Session Description Protocol (SDP) based on revised Offer/Answer model according to [4] and [5]. The SDP in these examples is defined by o RFC 4566 [2] for the latest "core protocol" of SDP; o RFC xxxx 'SDPCapNeg' [4]: SDP syntax extension for revised SDP Offer/Answer framework and transport capabilities; o RFC yyyy 'MediaCapNeg' [5]: SDP syntax extension for revised SDP Offer/Answer negotiation of media capabilities; o ITU-T Rec. V.152 [8]: SDP syntax extension for V.152 VBDoIP pass- through service; o ITU-T Rec. T.38 [9]: SDP syntax extension for T.38 FoIP packet relay service; The offers and answers are assumed to be transported using a protocol such as Session Initiation Protocol (SIP). Examples include indication, negotiation and selection of media configurations for voice over IP (VoIP), and in particular, the emulation of PSTN modem calls via VoIP infrastructures. Schwarz Expires December 7, 2010 [Page 4] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 The following sections 4 ff. contain examples in which two parties, Anna and Ben, exchange SDP offers, answers, and, in some cases, additional offers and answers. Note that the subject line (s=) contains a single space character. 3. Revised SDP Offer/Answer Protocol The "Revised SDP Offer/Answer Protocol" shall replace the "Legacy SDP Offer/Answer Protocol" (according RFC 3264 [1]) and is defined by multiple SDP extensions: o RFC xxxx 'SDPCapNeg' [4]: framework for Revised SDP Offer/Answer model and SDP syntax extension concerning transport capabilities; o RFC yyyy 'MediaCapNeg' [5]: SDP syntax extension for media capabilities; o RFC zzzz 'ConnCapNeg' [6]: SDP syntax extension for connection type capabilities; o RFC wwww 'MiscCapNeg' [7]: SDP syntax extension for further capabilities concerning SDP lines "b=", "c=" and "i="; o other extensions may follow (due to the open design of the Revised SDP Offer/Answer model. It shall be recalled that the "Revised SDP Offer/Answer Protocol" is backward compatible (due to semantic of "ignore" of unknown SDP syntax) to the "Legacy SDP Offer/Answer Protocol", which ensures successful offer/answer exchanges between different SIP entities. NOTE - It is noted that the terms 'legacy' and 'revised' are not related to the SDP syntax as such, rather to the overall "application", i.e. the O/A negotiation protocol. It is not expected that the SDP syntax of RFC 3264 [1] will be made obsolete by the revised SDP Offer/Answer RFCs. It is expected that both SDP O/A protocol variants will be used in parallel. 4. Examples for "Emulating PSTN Modem Calls" NOTE - The term "PSTN modem call" refers to a voiceband data call originating/terminating in a PSTN domain (see clause 3.1 in [11]). Schwarz Expires December 7, 2010 [Page 5] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 Figure 1 illustrates a simple network configuration by two PSTN access networks, interconnected by an IP network and SIP-controlled PSTN services. This section provides some examples for codec indication, negotiation and selection of resources for PSTN modem calls via Voice-over-IP sessions. The SDP offer/answer exchanges are here in responsibility of SIP VoIP terminals, SIP voice gateways (VGW) or/and SIP private branch exchanges (SIP PBX). +---------------------------------------------------+ | | | | | | | /-----------\ | | SIP/SDP | | SIP/SDP | | +------| |------+ | | | | | | | |--- | | | | ----| | \ +---+--+ | | +--+---+ / | | \ | SIP | | IP | | SIP | / | |PSTN )-|Device|---| |---|Device|--( PSTN | | / | 'A' | | Network | | 'B' | \ | | / +------+ | | +--+---+ \ | |--- e.g. | | e.g. ----| | SIP VGW \-----------/ SIP ATA | | | | | +---------------------------------------------------+ Figure 1 PSTN access networks interconnected via a SIP-controlled IP network (providing emulation services for PSTN modem calls) The Offerer role is provided by 'A', the Answerer role by 'B'. 4.1. Supported SDP capabilities by SIP devices The examples for SDP offer/answer exchanges are dependent on supported SDP capabilities with regards to SDP offer/answer protocol and SDP for control of user plane interworking functions like V.152, T.38, V.151 and V.150.1. Table 1 provides the eight theoretical combinations for SIP devices, under consideration of just V.152 and T.38 only. Schwarz Expires December 7, 2010 [Page 6] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 Table 1: SDP Negotiation Capability support versus SDP V.152/T.38 support - Matrix of SIP device specific options +-------------------+-------------------------------------------+ | | Negotiation Capabilities: | | SDP Compatibility +-------------------------------------------+ | of | SDP_L_O/A: | SDP_R_O/A: | | SIP device: | Support of Legacy | Support of Revised | | | SDP O/A (RFC 3264) | SDP O/A (RFC 3264) | +-----+---+-----+---+--------------------+----------------------+ | | | SDP | N | no example in doc. | Example 1 (Sec. 4.2) | | SDP | N | for +---+--------------------+----------------------+ | | |T.38 | Y | no example in doc. | Example 4 (Sec. 4.5) | | for +---+-----+---+--------------------+----------------------+ | | | SDP | N | no example in doc. | Example 2 (Sec. 4.3) | |V.152| Y | for +---+--------------------+----------------------+ | | |T.38 | Y | no example in doc. | Example 3 (Sec. 4.4) | +-----+---+-----+---+--------------------+----------------------+ This document provides three example offers (indicated in Table 1) in below sub-clauses. There are then again eight options concerning SDP support from answerer side. Some candidate answers will be illustrated. 4.2. Audio VoIP, no V.152 VBDoIP and no T.38 FoIP (Example 1) There are two possible media configurations, offered in this example: o Preference 1: Audio (G729) & NTE (RFC 4733) o Preference 2: Audio (PCMU incl. silence suppression) & NTE Table 1 - SDP Offer for Example 1 +-------------------------------------------------------------------+ | SDP encoding (shortened SDP description) | ... ; ACTUAL CONFIGURATION (due to backward compatibility) m=audio 3456 RTP/AVP 18 0 13 96 a=rtpmap:96 telephone-event/8000 a=fmtp:96 0-15 ; ; POTENTIAL CONFIGURATIONs a=tcap:1 RTP/AVP ; transport for VoIP a=mcap:1 G729/8000 ; audio codec 1 a=mcap:2 PCMU/8000 ; audio codec 2 Schwarz Expires December 7, 2010 [Page 7] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 a=mcap:3 CN/8000 ; comfort noise for audio codec 2 a=mcap:4 telephone-event/8000 ; NTE codec a=mfcap:4 0-15 ; value range DTMF a=pcfg:1 t=1 a=-ms:1 m=1,4 pt=1:18,4:96 a=pcfg:2 t=1 a=-ms:2 m=2,3,4 pt=1:0,3:13,4:96 +-------------------------------------------------------------------+ 4.3. Audio VoIP, V.152 VBDoIP, but no T.38 FoIP (Example 2) 4.3.1. Example 2.1 - Multiple audio & multiple VBD codecs Reference: clause 7.1.0.3.1/V.152 [8]. This is an extension of example 1, by adding V.152 VBDoIP support to the audio modes. There are thus four possible media configurations, offered in this example: o Preference 1: Audio (G729), VBD (V.152 PCMU) & NTE (RFC 4733) o Preference 2: Audio (G729), VBD (V.152 G726-32) & NTE (RFC 4733) o Preference 3: Audio (PCMU incl. silence suppression), VBD (V.152 PCMU) & NTE (RFC 4733) o Preference 4: Audio (PCMU incl. silence suppression), VBD (V.152 G726-32) & NTE (RFC 4733) Table 2 - SDP Offer for Example 2.1 +-------------------------------------------------------------------+ | SDP encoding (shortened SDP description) | ... ; ACTUAL CONFIGURATION (due to backward compatibility) m=audio 3456 RTP/AVP 18 0 13 96 98 99 a=maxmptime:10 10 - - 20 20 a=rtpmap:96 telephone-event/8000 a=fmtp:96 0-15, 34, 35 a=rtpmap:98 PCMU/8000 a=gpmd:98 vbd=yes a=rtpmap:99 G726-32/8000 a=gpmd:99 vbd=yes ; ; POTENTIAL CONFIGURATIONs a=tcap:1 RTP/AVP ; transport for VoIP & VBDoIP Schwarz Expires December 7, 2010 [Page 8] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 a=acap:1 maxmptime:10 20 - a=acap:2 maxmptime:10 - 20 - ; due to media format order in 'pcfg' lines a=mcap:1 G729/8000 ; audio codec 1 a=mcap:2,5 PCMU/8000 ; audio codec 2 & VBD codec 1 a=mcap:3 CN/8000 ; comfort noise for audio c. 2 a=mcap:4 telephone-event/8000 ; NTE codec a=mcap:6 G726-32/8000 ; VBD codec 2 a=mfcap:4 0-15,32-35 ; value range DTMF & VBD stimuli a=mscap:5 gpmd vbd=yes ; for V.152 PCMU a=mscap:6 gpmd vbd=yes ; for V.152 G726-32 a=pcfg:1 t=1 a=-ms:1 m=1,5,4 pt=1:18,5:98,4:96 a=pcfg:2 t=1 a=-ms:1 m=1,6,4 pt=1:18,6:99,4:96 a=pcfg:3 t=1 a=-ms:2 m=2,3,5,4 pt=1:0,3:13,5:98,4:96 a=pcfg:4 t=1 a=-ms:2 m=2,3,6,4 pt=1:0,3:13,6:99,4:96 +-------------------------------------------------------------------+ 4.3.2. Example 2.2 - Single audio codec, two VBD codecs Reference: clause 7.1.0.3.2/V.152 [8]. There are two possible media configurations, offered in this example: o Preference 1: Audio (G729), VBD (V.152 PCMU) o Preference 2: Audio (G729), VBD (V.152 G726-32) Table 3 - SDP Offer for Example 2.2 +-------------------------------------------------------------------+ | SDP encoding (shortened SDP description) | ... ; ACTUAL CONFIGURATION (due to backward compatibility) m=audio 3456 RTP/AVP 0 18 98 a=gpmd:0 vbd=yes a=rtpmap:98 G726-32/8000 a=gpmd:98 vbd=yes a=ptime:20 ; ; POTENTIAL CONFIGURATIONs a=tcap:1 RTP/AVP ; transport for VoIP & VBDoIP a=acap:1 ptime:20 ; common packetization time a=mcap:1 G729/8000 ; audio codec a=mcap:2 PCMU/8000 ; VBD codec 1 Schwarz Expires December 7, 2010 [Page 9] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 a=mcap:3 G726-32/8000 ; VBD codec 2 a=mscap:2 gpmd vbd=yes ; for V.152 PCMU a=mscap:3 gpmd vbd=yes ; for V.152 G726-32 a=pcfg:1 t=1 a=-ms:1 m=1,2 pt=1:18,2:0 a=pcfg:2 t=1 a=-ms:1 m=1,3 pt=1:18,3:98 +-------------------------------------------------------------------+ 4.3.3. Example 2.3 - Two audio codecs & one VBD codec (overlapping with audio) Reference: clause 7.1.3.1/V.152 [8]. There are two media configurations, offered in this example: o Preference 1: Audio (G729), VBD (V.152 PCMU) o Preference 2: Audio (PCMU incl. silence suppression), VBD (V.152 PCMU) Table 4 - SDP Offer for Example 2.3 +-------------------------------------------------------------------+ | SDP encoding (shortened SDP description) | ... ; ACTUAL CONFIGURATION (due to backward compatibility) m=audio RTP/AVP 18 0 13 96 a=ptime:10 a=rtpmap:96 PCMU/8000 a=gpmd: 96 vbd=yes ; ; POTENTIAL CONFIGURATIONs a=tcap:1 RTP/AVP ; transport for VoIP & VBDoIP a=acap:1 ptime:10 ; common packetization time a=mcap:1 G729/8000 ; audio codec 1 a=mcap:2,4 PCMU/8000 ; audio codec 2 & VBD codec 1 a=mcap:3 CN/8000 ; comfort noise for audio codec 2 a=mscap:4 gpmd vbd=yes ; for V.152 PCMU a=pcfg:1 t=1 a=-ms:1 m=1,4 pt=1:18,4:96 a=pcfg:2 t=1 a=-ms:1 m=2,3,4 pt=1:0,3:13,4:96 +-------------------------------------------------------------------+ Schwarz Expires December 7, 2010 [Page 10] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 4.3.4. Example 2.4 - Declaration of RTP packet redundancy Reference: clause 7.1.4.1/V.152 [8]. Following media configuration shall be offered in this example: o Preference 1: Audio (G728), VBD (V.152 PCMU with packet redundancy) Table 5 - SDP Offer for Example 2.4 +-------------------------------------------------------------------+ | SDP encoding (shortened SDP description) | ... ; ACTUAL CONFIGURATION (due to backward compatibility) m=audio 3456 RTP/AVP 0 15 102 a=gpmd:0 vbd=yes a=rtpmap:102 red/8000 a=fmtp:102 0/0/0/0 ; ; POTENTIAL CONFIGURATIONs a=tcap:1 RTP/AVP ; transport for VoIP & VBDoIP a=mcap:1 G728/8000 ; audio codec a=mcap:2 PCMU/8000 ; VBD codec a=mcap:3 RED/8000 ; RTP RFC 2198 redundancy a=mfcap:3 %2%/%2%/%2%/%2% ; RFC 2198 redundancy format a=mscap:2 gpmd vbd=yes ; for V.152 PCMU a=pcfg:1 t=1 a=-ms m=2,1,3 pt=2:0,1:15,3:102 +-------------------------------------------------------------------+ 4.3.5. Example 2.5 - Forward Error Correction for V.152 with PCMU as VBD codec) Reference: clause 7.1.4.1.2/V.152 [8]. Following media configuration shall be offered in this example: o Preference 1: Audio (G728), VBD (V.152 PCMU forward error correction) Table 6 - SDP Offer for Example 2.5 +-------------------------------------------------------------------+ Schwarz Expires December 7, 2010 [Page 11] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 | SDP encoding (shortened SDP description) | ... ; ACTUAL CONFIGURATION (due to backward compatibility) c=IN IP4 224.2.17.12 t=0 0 m=audio 49170 RTP/AVP 0 15 78 a=gpmd:0 vbd=yes a=rtpmap:78 parityfec/8000 a=fmtp:78 49170 IN IP4 224.2.17.12 ; ; POTENTIAL CONFIGURATIONs a=tcap:1 RTP/AVP ; transport for VoIP & VBDoIP a=mcap:1 G728/8000 ; audio codec a=mcap:2 PCMU/8000 ; VBD codec a=mcap:3 parityfec/8000 ; RTP RFC 5109 FEC a=mscap:2 gpmd vbd=yes ; for V.152 PCMU a=pcfg:1 t=1 a=-ms m=2,1,3 pt=2:0,1:15,3:78 +-------------------------------------------------------------------+ 4.4. Audio VoIP, V.152 VBDoIP and T.38 FoIP (Example 3) The primary goal of the configuration exchanges in this section is the successful negotiation of o separate states for 'audio' and 'voiceband data'; o V.152 VBD as "generic VBD" codec for ALL PSTN modem call types; and o eventually, T.38 application in case of a fax/modem call type. 4.4.1. Example Offer 4.4.1.1. Capabilities (Media, Transport) by OFFERER The Offerer ('Anna', briefly A) provides following endpoint (gateway) capabilities, which may be summarized as Supported Codec/Configuration List (SCL): SCL_A = { Schwarz Expires December 7, 2010 [Page 12] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 o Audio codecs for VoIP modes: - G.711 with & without silence suppression, - G.729AB; o Auxiliary codecs for application control incl. VBD stimuli: - RFC 4733 NTE (network telephone events); o Voiceband data codecs: - V.152 G.711 for VBDoIP, - T.38 FoIP with UDPTL/UDP transport variant}. The SCL is converted to an Offered Codec/Configuration List (OCL) by the Offerer, by taking into account the application ("PSTN call"), local policies (like preferences), QoS considerations and eventually the present condition of the IP network. 4.4.1.2. Offered Codec/Configuration List (OCL_A) The generated OCL follows above order of the SCL, e.g. V.152 first before using T.38 in case of fax/modem. OCL_A = { o offered configuration o1 (= actual configuration): o1 = {audio(G.711 w/o silence suppression); voiceband data(V.152 G.711 non-assured transport); RFC 4733 telephone event codec} o offered configuration o2 (= potential configuration p1): o2 = o1 NOTE: 'o2' is required for a SDP_R_O/A compliant answerer, whereas 'o1' reflects the preferred configuration for legacy SDP_L_O/A devices. o offered configuration o3 (= potential configuration p2): o3 = {audio(G.729B); voiceband data(V.152 G.711 non-assured transport); RFC 4733 telephone event codec} o offered configuration o4 (= potential configuration p3): o4 = {audio(G.711 w/o silence suppression); voiceband data(V.152 G.711 assured transport using packet redundancy); RFC 4733 telephone event codec} Schwarz Expires December 7, 2010 [Page 13] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 o offered configuration o5 (= potential configuration p4): o5 = {audio(G.729B); fax/modem data(T.38 with UDPTL/UDP transport); RFC 4733 telephone event codec} NOTE: assumption is "simultaneous" audio & fax support by preparing separate IP transport connections for audio (= RTP session for G.729) and fax (= UDPTL/UDP connection for T.38 traffic), in order to serve the "alternate speech-fax" PSTN service. o offered configuration o6 (= potential configuration p5): o6 = {audio(G.711 w/o silence suppression); voiceband data(merged with audio mode, i.e. pseudo-VBD); RFC 4733 telephone event codec} NOTE: this configuration is considered to be the fallback option for remote devices without any V.152 support. } The structure of OCL_A is based on the assumption that V.152 is already supported by some SIP nodes and the preference of V.152 over T.38. 4.4.1.3. SDP Syntax The OCL_A is mapped on SDP, e.g. following the example of Table 7. The offered configuration with T.38 (o5) requires the usage of session configurations due to the separate "m=" line for T.38 configurations. The T.38 configuration is also announced as latent configuration due to the low priority of offered configuration o5. Table 7 - SDP Offer for Example 3 +-------------------------------------------------------------------+ | SDP lines | |No.| Syntax and Comments | +---+---------------------------------------------------------------+ | 1| v=0 | | 2| o=- 1234 0 IN IP4 11.9.19.65 | | 3| s=SIP Speech Call incl VBD support ; "PSTN modem call" | | 4| c=IN IP4 11.9.19.65 | | 5| t=0 0 | | 6| ; Indication of SDPCapNeg & MediaCapNeg support | | 7| a=creq:med-v0 ; explicit indication of MediaCapNeg | Schwarz Expires December 7, 2010 [Page 14] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 | | | | 8| ; SESSION CONFIGURATIONS (offered) | | 9| ; Session configurations allow to specify combinations of | | 10| ; monomedia' (VoIP + VBDoIP) and 'multimedia' (VoIP + FoIP) | | 11| ; media stream configurations | | 12| a=sescap:1 1 ; VoIP = G.711, VBDoIP = V.152(G.711) | | 13| a=sescap:2 2 ; VoIP = G.729, VBDoIP = V.152(G.711) | | 14| a=sescap:3 3 ; VoIP = G.711, VBDoIP = V.152(G.711+RED) | | 15| a=sescap:4 4,10 ; VoIP = G.729, FoIP = T.38 | | 16| a=sescap:5 5 ; {V&VBD}oIP = G.711 (=> pVBDoIP) | | | | | 17| ; LATENT CONFIGURATION (offered, session level) | | 18| ; Latent configuration: T.38 FoIP announcement in order to | | 19| ; a) indicate T.38 support and b) to indicate the supported | | 20| ; T.38 transport mode and configuration details. | | 21| ; transport capabilities: | | 22| a=tcap:20 udptl ; T.38 FoUDPTL/UDP transport variant | | 23| ; media encoding capabilities: | | 24| a=mcap:10 t38 ; T.38 FoIP codec (subtype = 't38' | | 25| ; according to RFC 3362 image/t38 MIME subtype registration)| | 26| ; attribute capabilities: | | 27| a=acap:11 T38FaxVersion:1 | | 28| a=acap:12 T38FaxRateManagement:transferredTCF | | 29| a=acap:13 T38FaxUdpEC:t38UDPFEC | | 30| a=acap:14 T38FaxMaxBufferSize:2000 | | 31| a=acap:15 T38MaxDatagram:512 | | 32| a=acap:16 T38MaxBitRate:14400 | | 33| a=acap:17 (...additional T.38 attributes may be included) | | 34| ; latent configuration (= T.38) | | 35| a=lcfg:10 mt=image t=20 m=10 a=11,12,13,14,15,16,17 | | | | | 36| ; ACTUAL CONFIGURATION (offered) | | 37| ; SDP o1 - Actual configuration (= p1) | | 38| m=audio 40000 RTP/AVP 8 101 120 | | 39| a=sendrecv | | 40| a=rtpmap:101 PCMA/8000 | | 41| a=gpmd:101 vbd=yes | | 42| a=rtpmap:120 telephone-event/8000 | | 43| a=fmtp:120 0-15,32-35 ; value range for DTMF and VBD stimuli | | 44| a=ptime:20 ; common packetization time for VoIP & | | 45| ; VBDoIP PCMoRTP packets | | | | | 46| ; POTENTIAL CONFIGURATION(S) (offered) | | 47| ; transport capabilities: | | 48| a=tcap:1 RTP/AVP ; RFC 3551 XoRTP transp. (for audio, | | 49| ; voiceband data & auxiliary) | | 50| ; attribute capabilities: | Schwarz Expires December 7, 2010 [Page 15] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 | 51| a=acap:1 ptime:20 ; for 20 ms packets for XoRTP media flows | | 52| a=acap:2 sendrecv ; | | 53| ; media encoding capabilities: | | 54| a=mcap:1 G729/8000 ; selected compressing voice codec | | 55| a=mcap:2,4 PCMA/8000 ; G.711 A-law (assuming an | | 56| ; A-law region) & VBD codec | | 57| a=mcap:3 telephone-event/8000 ; RFC 4733 codec for NTE | | 58| a=mcap:5 RED/8000 ; RTP packet with RFC 2198 redundancy | | 59| ; media format parameter capabilities: | | 60| a=mfcap:1 annexb=yes ; silence suppression mode for G.729 | | 61| a=mfcap:3 0-15,32-35 ; value range for DTMF and VBD stimuli | | 62| a=mfcap:5 %4%/%4% ; RFC 2198 redundancy format | | 63| ; for "VBD codec" | | 64| ; media specific capabilities: | | 65| a=mscap:2 gpmd vbd=yes ; for V.152 if RTP flow | | 66| ; potential configurations: | | 67| ; SDP o2 - Potential config p1 (= Actual Config): | | 68| ; Audio (G.711), VBD (V.152) & RFC 4733 / 20 ms | | 69| a=pcfg:1 | | 70| ; SDP o3 - Potential config p2: | | 71| ; Audio (G.729AB), VBD (V.152) & RFC 4733 / 20 ms | | 72| a=pcfg:2 t=1 a=-ms:1,2 m=1,2,3 pt=1:18,2:101,3:120 | | 73| ; SDP o4 - Potential config p3: | | 74| ; Audio (G.711), VBD (V.152 + RFC 2198 Red) & RFC 4733 / 20 ms| | 75| a=pcfg:3 t=1 a=-ms:1,2 m=4,2,5,3 pt=4:8,2:101,5:102,3:120 | | 76| ; SDP o5 - Potential config p4: | | 77| ; Audio (G.729AB) & RFC 4733 with 20 ms | | 78| a=pcfg:4 t=1 a=-ms:1,2 m=1,3 pt=1:18,3:120 | | 79| ; SDP o6 - Potential config p5: | | 80| ; pVBD = merged Audio&VBD (G.711), & RFC 4733 / 20 ms | | 81| a=pcfg:5 t=1 a=-ms:1,2 m=4,3 pt=4:8,3:120 | | 82| | | 83| | +---+---------------------------------------------------------------+ Some comments to SDP syntax: o line 15: the only session configuration with two media decriptions (due to requested two parallel IP transport connections for audio and T.38); o line 24: only subtype ('t38') is part of mcap, but not media type (here 'image'); o line 58: it shall be noted that there are two, case-sensitive registrations with IANA for RFC 2198 ('red', 'RED'); Schwarz Expires December 7, 2010 [Page 16] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 o line 62: the attribute indication for format parameter ('fmtp') is already inherent to the name 'mfcap'; o line 72: the "a=-ms" operator is used to remove all legacy attribute lines on session and media description level. 4.4.2. Example Answers Just some possible answers shall be indicated. 4.4.2.1. ANSWERER not compliant to SDP_R_O/A All unknown SDP syntax is removed ("ignored") by the SDP decoder. Following lines are remaining, representing the actual configuration. The answerer is supporting the requested capabilities, which may be acknowledged by following Answer. Table 8 - SDP Answer for legacy SDP_L_O/A device +-------------------------------------------------------------------+ | SDP lines | |No.| Syntax and Comments | +---+---------------------------------------------------------------+ | 1| v=0 | | 2| o=- 1234 0 IN IP4 19.65.11.9 | | 3| s=SIP Speech Call incl VBD support ; "PSTN modem call" | | 4| c=IN IP4 19.65.11.9 | | 5| t=0 0 | | | | | 36| ; ACTUAL CONFIGURATION (offered) | | 37| ; SDP o1 - Actual configuration (= p1) | | 38| m=audio 40000 RTP/AVP 8 101 120 | | 39| a=sendrecv | | 40| a=rtpmap:101 PCMA/8000 | | 41| a=gpmd:101 vbd=yes | | 42| a=rtpmap:120 telephone-event/8000 | | 43| a=fmtp:120 0-15,32-35 ; value range for DTMF and VBD stimuli | | 44| a=ptime:20 ; common packetization time for VoIP & | | 45| ; VBDoIP PCMoRTP packets | | | | +---+---------------------------------------------------------------+ Schwarz Expires December 7, 2010 [Page 17] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 4.4.2.2. ANSWERER supports SDP_R_O/A and is V.152 compliant Ben includes the "a=acfg" attribute in the answer to inform Anna that he based his answer on an offer using potential configuration 1. Table 9 - SDP Answer (SDP_R_O/A, V.152 compliant) +-------------------------------------------------------------------+ | SDP lines | |No.| Syntax and Comments | +---+---------------------------------------------------------------+ | 1| v=0 | | 2| o=- 1234 0 IN IP4 19.65.11.9 | | 3| s=SIP Speech Call incl VBD support ; "PSTN modem call" | | 4| c=IN IP4 19.65.11.9 | | 5| t=0 0 | | | | | 36| ; ACTUAL CONFIGURATION (offered) | | 37| ; SDP o1 - Actual configuration (= p1) | | 38| m=audio 40000 RTP/AVP 8 101 120 | | 39| a=sendrecv | | 40| a=rtpmap:101 PCMA/8000 | | 41| a=gpmd:101 vbd=yes | | 42| a=rtpmap:120 telephone-event/8000 | | 43| a=fmtp:120 0-15,32-35 ; value range for DTMF and VBD stimuli | | 44| a=ptime:20 ; common packetization time for VoIP & | | 45| ; VBDoIP PCMoRTP packets | | | | | 69| a=acfg:1 | +---+---------------------------------------------------------------+ 4.4.2.3. ANSWERER supports SDP_R_O/A and is none-V.152 compliant Ben includes the "a=acfg" attribute in the answer to inform Anna that he based his answer on an offer using potential configuration 5. Table 10 - SDP Answer (SDP_R_O/A, none-V.152 compliant) +-------------------------------------------------------------------+ | SDP lines | |No.| Syntax and Comments | +---+---------------------------------------------------------------+ Schwarz Expires December 7, 2010 [Page 18] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 | 1| v=0 | | 2| o=- 1234 0 IN IP4 19.65.11.9 | | 3| s=SIP Speech Call excluding VBD support | | 4| c=IN IP4 19.65.11.9 | | 5| t=0 0 | | 6| ; Indication of SDPCapNeg & MediaCapNeg support | | 7| a=csup:med-v0 ; explicit indication of MediaCapNeg | | | ;(optional but recommended (SDPCapNeg 3.3.1) | | | ; SESSION CONFIGURATIONS (Supported) | | | ; Only sescap:5 is supported, if other session caps had been | | | ; supported then they would have been selected as sescap:5 is | | | ; least preferred one | | 16| a=sescap:5 5 ; {V&VBD}oIP = G.711 (=> pVBDoIP) | | | | | 36| ; ACTUAL CONFIGURATION (offered) | | 37| ; SDP o6 - Actual configuration (= p5) | | 38| m=audio 40004 RTP/AVP 8 120 | | 39| a=rtpmap:8 PCMA/8000 | | 40| a=rtpmap:120 telephone-event/8000 | | 41| a=fmpt:120 0-15,32-35 | | 42| a=ptime:20 ; Before or after the rtpmap and fmtp attr lines? | | 43| a=sendrecv | | 81| a=acfg:5 | +---+---------------------------------------------------------------+ 4.5. T.38 FoIP only calls, no Audio VoIP, no V.152 VBDoIP (Example 4) 4.5.1. Example 4.1 - Agreement on T.38-over-UDPTL/UDP, multiple transport variants offered Reference: clause D.2.4.1.1/T.38 [9]. Following two media configurations shall be offered in this example: o Preference 1: T.38 FoUDPTL/UDP o Preference 2: T.38 FoTPKT/TCP Table 11 - SDP Offer for Example 4.1 +-------------------------------------------------------------------+ | SDP encoding (shortened SDP description) | ... 1) OFFER (embedded in SIP INVITE): ... Schwarz Expires December 7, 2010 [Page 19] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 ; ACTUAL CONFIGURATION (due to backward compatibility) m=image 49170 udptl t38 a=T38FaxRateManagement:transferredTCF a=T38FaxUdpEC:t38UDPFEC m=image 49172 tcp t38 a=T38FaxRateManagement:localTCF ; ; POTENTIAL CONFIGURATIONs a=tcap:1 udptl ; T.38 FoUDPTL/UDP transport variant a=tcap:2 tcp ; T.38 FoTPKT/TCP transport variant a=mcap:1 t38 ; T.38 FoIP codec (subtype = 't38') ; Transport-independent T.38 parameters a=acap:11 T38FaxVersion:4 ; Transport-dependent T.38 parameters for UDPTL/UDP a=acap:12 T38FaxUdpEC:t38UDPFEC a=acap:13 (... additional T.38 UDPTL attributes should be included) ; Transport-dependent T.38 parameters for TPKT/TCP a=acap:21 T38FaxRateManagement:localTCF a=acap:22 (... additional T.38 TPKT attributes should be included) ; Preferences a=pcfg:1 mt=image t=1 m=1 a=-ms:11,12,13,14,... a=pcfg:2 mt=image t=2 m=1 a=-ms:11,21,... 2) ANSWER (embedded in SIP 200 OK): ... a=acfg:1 +-------------------------------------------------------------------+ 4.6. T.38 FoIP and Audio VoIP, no V.152 VBDoIP (Example 5) 4.6.1. Example 5.1 - Multiple audio codecs, single T.38 option Reference: clause D.2.4.2.3/T.38 [9]. Following two media configurations shall be offered in this example: o Preference 1: Audio (G729) and Fax Relay (T.38 FoUDPTL/UDP) o Preference 2: Audio (PCMU) and Fax Relay (T.38 FoUDPTL/UDP) Schwarz Expires December 7, 2010 [Page 20] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 Table 12 - SDP Offer for Example 5.1 +-------------------------------------------------------------------+ | SDP encoding (shortened SDP description) | ... 1) OFFER (embedded in SIP INVITE): ... ; ACTUAL CONFIGURATION (due to backward compatibility) ... ommitted ... ; SESSION CONFIGURATIONs a=sescap:1 1,3 ; VoIP = G.729, FoIP = T.38 UDPTL/UDP a=sescap:2 2,3 ; VoIP = G.711, FoIP = T.38 UDPTL/UDP ; LATENT CONFIGURATION for T.38 a=tcap:2 udptl ; T.38 FoUDPTL/UDP transport variant a=mcap:5 t38 ; T.38 FoIP codec (subtype = 't38') a=acap:11 T38FaxVersion:4 a=acap:12 T38FaxRateManagement:transferredTCF a=acap:13 T38FaxUdpEC:t38UDPRedundancy a=acap:14 (... additional T.38 attributes may be incl.) a=lcfg:3 mt=image t=2 m=5 a=11,12,13,14,... ; POTENTIAL CONFIGURATIONs a=tcap:1 RTP/AVP ; transport for VoIP a=acap:1 ptime:20 ; for G.729 a=acap:2 ptime:10 ; for G.711 a=mcap:1 G729/8000 ; audio codec 1 a=mcap:2 PCMU/8000 ; audio codec 2 a=pcfg:1 t=1 a=-ms:1 m=1 pt=1:18 a=pcfg:2 t=1 a=-ms:1 m=2 pt=1:0 2) ANSWER (embedded in SIP 200 OK): ... a=sescap:2 +-------------------------------------------------------------------+ The Answerer does not support G.729 and agrees to the 2nd session configuration. 4.6.2. Example 5.2 - Autonomous state transitioning between Audio VoIP and T.38 FoIP Reference: clause D.2.2.4.3/T.38 [9]. A single media configuration shall be offered in this example: Schwarz Expires December 7, 2010 [Page 21] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 o Preference 1: Audio (G729) and Fax Relay (T.38 FoUDPTL/UDP) Table 13 - SDP Offer for Example 5.2 +-------------------------------------------------------------------+ | SDP encoding (shortened SDP description) | ... 1) OFFER (embedded in SIP INVITE): ... ; ACTUAL CONFIGURATION (due to backward compatibility) ... ommitted ... ; SESSION CONFIGURATIONs a=sescap:1 1,3 ; VoIP = G.729, FoIP = T.38 UDPTL/UDP ; LATENT CONFIGURATION for T.38 a=tcap:2 udptl ; T.38 FoUDPTL/UDP transport variant a=mcap:5 t38 ; T.38 FoIP codec (subtype = 't38') a=acap:11 T38FaxVersion:4 a=acap:12 T38FaxRateManagement:transferredTCF a=acap:13 T38FaxUdpEC:t38UDPRedundancy a=acap:14 (... additional T.38 attributes may be incl.) a=lcfg:3 mt=image t=2 m=5 a=11,12,13,14,... ; POTENTIAL CONFIGURATIONs a=tcap:1 RTP/AVP ; transport for VoIP a=acap:1 ptime:20 ; for G.729 a=mcap:1 G729/8000 ; audio codec 1 a=pcfg:1 t=1 a=-ms:1 m=1 pt=1:18 2) ANSWER (embedded in SIP 200 OK): ... a=sescap:1 +-------------------------------------------------------------------+ The Answerer agrees to the session configuration, i.e., support of T.38 Version 4, too. The agreement confirms the execution of autonomous state transitioning at both gateway locations (on-ramp and off-ramp gateway), see clause D.2.2.4.3/T.38 [9]. Schwarz Expires December 7, 2010 [Page 22] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 4.6.3. Example 5.3 - Single audio codec, three T.38 configurations concerning error correction methods Following three media configurations shall be offered in this example: o Preference 1: Audio (G729) and Fax Relay (T.38 FoUDPTL/UDP with error correction method "t38UDPRedundancy") i.e. T.38 using packet redundancy as error correction o Preference 2: Audio (G729) and Fax Relay (T.38 FoUDPTL/UDP with error correction method "t38UDPFEC") i.e. T.38 using Forward Error Correction as error correction o Preference 3: Audio (G729) and Fax Relay (T.38 FoUDPTL/UDP with error correction method "t38UDPNoEC") i.e. T.38 without any error correction Table x1 - SDP Offer for Example 5.3 +-------------------------------------------------------------------+ | SDP encoding (shortened SDP description) | ... 1) OFFER (embedded in SIP INVITE): ... ; ACTUAL CONFIGURATION (due to backward compatibility) ... ommitted ... ; SESSION CONFIGURATIONs a=sescap:1 1,3 ; VoIP = G.729, FoIP = T.38 UDPTL/UDP with packet red a=sescap:2 1,4 ; VoIP = G.729, FoIP = T.38 UDPTL/UDP with FEC a=sescap:3 1,5 ; VoIP = G.729, FoIP = T.38 UDPTL/UDP with NoEC ; LATENT CONFIGURATION for T.38 a=tcap:2 udptl ; T.38 FoUDPTL/UDP transport variant a=mcap:5 t38 ; T.38 FoIP codec (subtype = 't38') a=acap:11 T38FaxVersion:4 a=acap:12 T38FaxRateManagement:transferredTCF a=acap:13 (... all T.38 attributes shall be incl.) a=acap:21 T38FaxUdpEC:t38UDPRedundancy ; error correction scheme 1 a=acap:22 T38FaxUdpEC:t38UDPFEC ; error correction scheme 2 a=acap:23 T38FaxUdpEC:t38UDPNoEC ; error correction scheme 3 a=lcfg:3 mt=image t=2 m=5 a=11,12,13,...,21 ; T.38 configuration #1 a=lcfg:4 mt=image t=2 m=5 a=11,12,13,...,22 ; T.38 configuration #2 a=lcfg:5 mt=image t=2 m=5 a=11,12,13,...,23 ; T.38 configuration #3 Schwarz Expires December 7, 2010 [Page 23] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 ; POTENTIAL CONFIGURATIONs a=tcap:1 RTP/AVP ; transport for VoIP a=acap:1 ptime:10 ; for G.711 a=mcap:1 G729/8000 ; audio codec 1 a=pcfg:1 t=1 a=-ms:1 m=1 pt=1:18 2) ANSWER (embedded in SIP 200 OK): ... a=sescap:1 +-------------------------------------------------------------------+ The Answerer does support T.38 error correction scheme "packet redundancy" and agrees to the 1st session configuration. 4.6.4. Example 5.4 - Single audio codec, three T.38 configurations concerning error correction methods, and pseudo-VBD mode as T.38 fallback option This is an extension of example 5.3, considering the possibilities of o peer side is supporting T.38, but not supporting any of the three offered T.38 configurations; or o peer side is not supporting T.38 at all; and o Offerer is not supporting V.152 VBD, thus trying to offer pseudo- VBD mode. There would be then a fourth media configuration as fallback option to the three T.38 configurations. Following four media configurations shall be offered in this example: o Preference 1: Audio (G729) and Fax Relay (T.38 FoUDPTL/UDP with error correction method "t38UDPRedundancy") i.e. T.38 using packet redundancy as error correction o Preference 2: Audio (G729) and Fax Relay (T.38 FoUDPTL/UDP with error correction method "t38UDPFEC") i.e. T.38 using Forward Error Correction as error correction o Preference 3: Audio (G729) and Fax Relay (T.38 FoUDPTL/UDP with error correction method "t38UDPNoEC") i.e. T.38 without any error correction Schwarz Expires December 7, 2010 [Page 24] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 o Preference 4: pseudo-VBD mode: G.711 for audio and VBD traffic Table x2 - SDP Offer for Example 5.4 +-------------------------------------------------------------------+ | SDP encoding (shortened SDP description) | ... 1) OFFER (embedded in SIP INVITE): ... ; ACTUAL CONFIGURATION (due to backward compatibility) ... ommitted ... ; SESSION CONFIGURATIONs a=sescap:1 1,3 ; VoIP = G.729, FoIP = T.38 UDPTL/UDP with packet red a=sescap:2 1,4 ; VoIP = G.729, FoIP = T.38 UDPTL/UDP with FEC a=sescap:3 1,5 ; VoIP = G.729, FoIP = T.38 UDPTL/UDP with NoEC a=sescap:4 2 ; pseudo-VBD mode: G.711 for audio and VBD traffic ; LATENT CONFIGURATION for T.38 a=tcap:2 udptl ; T.38 FoUDPTL/UDP transport variant a=mcap:5 t38 ; T.38 FoIP codec (subtype = 't38') a=acap:11 T38FaxVersion:4 a=acap:12 T38FaxRateManagement:transferredTCF a=acap:13 (... all T.38 attributes shall be incl.) a=acap:21 T38FaxUdpEC:t38UDPRedundancy ; error correction scheme 1 a=acap:22 T38FaxUdpEC:t38UDPFEC ; error correction scheme 2 a=acap:23 T38FaxUdpEC:t38UDPNoEC ; error correction scheme 3 a=lcfg:3 mt=image t=2 m=5 a=11,12,13,...,21 ; T.38 configuration #1 a=lcfg:4 mt=image t=2 m=5 a=11,12,13,...,22 ; T.38 configuration #2 a=lcfg:5 mt=image t=2 m=5 a=11,12,13,...,23 ; T.38 configuration #3 ; POTENTIAL CONFIGURATIONs a=tcap:1 RTP/AVP ; transport for VoIP a=acap:1 ptime:20 ; for G.729 a=acap:2 ptime:10 ; for G.711 a=mcap:1 G729/8000 ; audio codec 1 a=mcap:2 PCMU/8000 ; audio codec 2 a=pcfg:1 t=1 a=-ms:1 m=1 pt=1:18 a=pcfg:2 t=1 a=-ms:1 m=2 pt=1:0 +-------------------------------------------------------------------+ Schwarz Expires December 7, 2010 [Page 25] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 4.7. Other examples: in ITU-T Recommendations V.152 and T.38 4.7.1. Revised SDP Offer/Answer examples for V.152 VBDoIP The latest Revision of ITU-T Recommendation V.152 [8] provides further signaling examples in clause 7, for various V.152 media configurations. 4.7.2. Revised SDP Offer/Answer examples for T.38 FoIP The latest Revision of ITU-T Recommendation T.38 [9] provides further signaling examples in Annex D.2.4, for various T.38 media configurations. 5. Example "G.711 A-law & G.711 u-law with preference on A-law" There are two possible media configurations, offered in this example: o Preference 1: Audio (PCMU) o Preference 2: Audio (PCMA) Table 14 - SDP Offer for Example +-------------------------------------------------------------------+ | SDP encoding (shortened SDP description) | ... ; ACTUAL CONFIGURATION (due to backward compatibility) m=audio 3456 RTP/AVP 0 8 ; ; POTENTIAL CONFIGURATIONs a=tcap:1 RTP/AVP ; transport for VoIP a=mcap:1 PCMU/8000 ; audio codec 1 a=mcap:2 PCMA/8000 ; audio codec 2 a=pcfg:1 t=1 a=-ms:1 m=1 pt=1:0 a=pcfg:2 t=1 a=-ms:2 m=2 pt=1:8 +-------------------------------------------------------------------+ 6. Example "G.711 in multiple format configurations" G.711 A-law with three different packetization times (5, 10 & 20 ms; preference 20 ms), combined with/without silence suppression (preference: w/o), combined with three RTP profiles (RFC 3551, RFC 5762, RFC 5764) as transport (preference: RFC 3551) Schwarz Expires December 7, 2010 [Page 26] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 There are 18 (= 3 x 2 x 3) possible media configurations, offered in this example, see Table 15: o Preference 1: Audio (PCMU w/o silence suppression), RTP-over-UDP, 20 ms packetization time o Preferences 2 to 6: RTP-over-UDP, other combinations of packetization times and silence suppression o Preferences 7 to 12: RTP-over-DCCP, combinations of packetization times and silence suppression o Preferences 13 to 18: SRTP-over-DTLS, combinations of packetization times and silence suppression Table 15 - SDP Offer for Example +-------------------------------------------------------------------+ | SDP encoding (shortened SDP description) | ... ; ACTUAL CONFIGURATION (due to backward compatibility) ... omitted [note: only a subset of the PCL would be offered due to the issue in specifying packetization times (see draft-garcia-mmusic-multiple-ptimes-problem)] ... ; ; POTENTIAL CONFIGURATIONs ; transport capabilities: a=tcap:1 RTP/AVP ; G.711-over-RTP transport via RFC 3551 a=tcap:2 DCCP/RTP/AVP ; G.711-over-RTP transport via RFC 5762 a=tcap:3 UDP/TLS/RTP/SAVP ; G.711-over-RTP transport via RFC 5764 ; attribute capabilities: a=acap:1 ptime:5 ; packetization time of 5 ms a=acap:2 ptime:10 ; packetization time of 10 ms a=acap:3 ptime:20 ; packetization time of 20 ms ; media capabilities: a=mcap:1 PCMU/8000 ; audio codec a=mcap:2 CN/8000 ; comfort noise for audio codec ; PCL (= Preferred Configuration (Codec) List): ; UDP transport, unencrypted G.711 audio a=pcfg:1 t=1 a=-ms:3 m=1 pt=1:0 a=pcfg:2 t=1 a=-ms:3 m=1,2 pt=1:0,2:13 a=pcfg:3 t=1 a=-ms:2 m=1 pt=1:0 a=pcfg:4 t=1 a=-ms:2 m=1,2 pt=1:0,2:13 a=pcfg:5 t=1 a=-ms:1 m=1 pt=1:0 a=pcfg:6 t=1 a=-ms:1 m=1,2 pt=1:0,2:13 ; DCCP transport, unencrypted G.711 audio a=pcfg:7 t=2 a=-ms:3 m=1 pt=1:0 Schwarz Expires December 7, 2010 [Page 27] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 a=pcfg:8 t=2 a=-ms:3 m=1,2 pt=1:0,2:13 a=pcfg:9 t=2 a=-ms:2 m=1 pt=1:0 a=pcfg:10 t=2 a=-ms:2 m=1,2 pt=1:0,2:13 a=pcfg:11 t=2 a=-ms:1 m=1 pt=1:0 a=pcfg:12 t=2 a=-ms:1 m=1,2 pt=1:0,2:13 ; UDP transport, encrypted G.711 audio, encrypted transport a=pcfg:13 t=3 a=-ms:3 m=1 pt=1:0 a=pcfg:14 t=3 a=-ms:3 m=1,2 pt=1:0,2:13 a=pcfg:15 t=3 a=-ms:2 m=1 pt=1:0 a=pcfg:16 t=3 a=-ms:2 m=1,2 pt=1:0,2:13 a=pcfg:17 t=3 a=-ms:1 m=1 pt=1:0 a=pcfg:18 t=3 a=-ms:1 m=1,2 pt=1:0,2:13 +-------------------------------------------------------------------+ 7. Example "G.725 terminal emulation" The ISDN terminal "G.725" provides advanced speech telephony services by support of narrowband voice (using either PCMA or PCMU) and wideband audio (using G722) and even the option of embedded data channels. G.725 [14] defines here four, so-called "transmission modes". Furthermore, three types of G.725 terminals are defined, according to their modes of operations A single 64 kbit/s bearer is used for transport in ISDN domains. Such an ISDN bearer is transported via CMD-over-RTP in IP networks (using RFC 4040), like in a "trunking scenario" ISDN-IP-ISDN using {G722|PCMx}-over-CMD/RTP/UDP/IP as common "framing" in IP domain (note: the Clearmode format represents a "1x64 Circuit Emulation Service"). Such ISDN terminals are still used by business customers like e.g. news reporters in live TV sessions (in order to get best speech quality as possible in case of ISDN access). This example focuses on G.725 "Type 1" terminals, which are capable of working in Mode 1 (7 kHz audio using G722) or in Mode 0 (here PCMA) as fallback. Such a terminal may be emulated by a SIP UA. Leading to "native RTP framings" in IP domain: either G722/RTP/UDP/IP or PCMx/RTP/UDP/IP, dependent on terminal emulation mode. This example is characterized by following properties: o single preferred configuration, here wideband audio; Schwarz Expires December 7, 2010 [Page 28] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 o narrowband speech must be prepared as fallback option, which leads to the specification of a single latent configuration; o a "G.725 terminal emulation" implies that both sides, Offerer and Answerer, commit to support both terminal modes, which leads to the specification of a single session configuration. Table 16 - SDP Offer for Example "G.725 emulation" +-------------------------------------------------------------------+ | SDP encoding (shortened SDP description) | ... 1) OFFER (embedded in SIP INVITE): ... ; ACTUAL CONFIGURATION (due to backward compatibility) ... ommitted ... ; SESSION CONFIGURATIONs a=sescap:1 1,2 ; for G.722 WB-VoIP and G.711 NB-VoIP as fallback ; LATENT CONFIGURATION for NB-VoIP a=lcfg:2 t=1 a=-ms:1 m=2 pt=1:0 ; POTENTIAL CONFIGURATION a=tcap:1 RTP/AVP ; transport for WB-VoIP and NB-VoIP a=acap:1 ptime:20 ; for WB G.722 and NB G.711 a=mcap:1 G722/8000 ; audio codec 1 (wideband, WB) a=mcap:2 PCMU/8000 ; audio codec 2 (narrowband, NB) a=pcfg:1 t=1 a=-ms:1 m=1 pt=1:9 2) ANSWER (embedded in SIP 200 OK): ... a=sescap:1 +-------------------------------------------------------------------+ The Answerer supports both codec types and agrees to autonomous mode transitioning between WB and NB voice. The call will start in G.722 WB-VoIP mode. 8. Other examples [-] Schwarz Expires December 7, 2010 [Page 29] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 9. Security Considerations Same security considerations as RFC 4317 [2]. 10. IANA Considerations This document introduces no IANA considerations. 11. Changes from previous versions 11.1. Changes from version 00 o Clarifications in clause Abstract and Overview o list of abbreviations o new Figure 1 11.2. Changes from version 01 o editorial corrections o reference to "PSTN modem call" definition o addition of clause 4.5 o update of references 11.3. Changes from version 02 o update of clause 3: note added concerning terms 'legacy' and 'revised' o update of clause 4.2: one example added o update of clause 4.3: five example2 added o update of clause 4.5: one example added o update of clause 4.6: two examples added o update of clause 5: missing example added o update of clause 6: missing example added Schwarz Expires December 7, 2010 [Page 30] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 o update of clause 7: missing example added o update of clause 12.2: further ref 11.4. Changes from version 03 o further T.38 example: clause 4.6.3, "Single audio codec, three T.38 configurations concerning error correction methods" o further T.38 example: clause 4.6.4, "Single audio codec, three T.38 configurations concerning error correction methods, and pseudo-VBD mode as T.38 fallback option" 12. References 12.1. Normative References None. 12.2. Informative References [1] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, June 2002. [2] Johnston, A. and R. Sparks, "Session Description Protocol (SDP) - Offer/Answer Examples", RFC 4317, December 2005. [3] Handley, M. and V. Jacobson, "SDP: Session Description Protocol", RFC 4566, July 2006. [4] Andreasen, F., "SDP Capability Negotiation", draft-ietf-mmusic- sdp-capability-negotiation (work in progress). [5] Gilman, R., et al., "SDP media capabilities Negotiation", draft-ietf-mmusic-sdp-media-capabilities (work in progress). [6] Garcia-Martin, M. and S. Veikkolainen, "Session Description Protocol (SDP) Extension For Setting Up Audio Media Streams Over Circuit-Switched Bearers In The Public Switched Telephone Network (PSTN)", draft-ietf-mmusic-sdp-cs (work in progress). [7] Garcia-Martin, M. et al., "Miscellaneous Capabilities Negotiation in the Session Description Protocol (SDP)", draft- ietf-mmusic-sdp-misc-cap (work in progress). Schwarz Expires December 7, 2010 [Page 31] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 [8] ITU-T Recommendation V.152, "Procedures for supporting voice- band data over IP networks". [9] ITU-T Recommendation T.38, "Procedures for real-time Group 3 facsimile communication over IP networks". [10] MultiService Forum (MSF), msf2009.046, April 2009, "Revised SDP Offer/Answer Model for Negotiations between SIP entities". [11] ETSI TR 183 072, "Telecommunications and Internet converged Services and Protocols for Advanced Networking (TISPAN); Emulation Services for PSTN Modem Calls". [12] SIP Forum, 2009, "FoIP Task Group Problem Statement". access via http://www.sipforum.org/ [13] SIP Forum, 2009, "FoIP Task Group Strawman Proposal". access via http://www.sipforum.org/ [14] ITU-T Recommendation G.725, "System aspects for the use of the 7 kHz audio codec within 64 kbit/s", 1988. Schwarz Expires December 7, 2010 [Page 32] Internet-Draft Examples for Revised SDP Offer/Answer June 2010 Authors' Addresses Albrecht Schwarz Alcatel-Lucent Lorenzstrasse 10 D-70435 Stuttgart Germany Email: Albrecht.Schwarz@alcatel-lucent.com Juergen Stoetzer-Bradler Alcatel-Lucent Lorenzstrasse 10 D-70435 Stuttgart Germany Email: Juergen.Stoetzer-Bradler@alcatel-lucent.com Schwarz Expires December 7, 2010 [Page 33]