SIPPING Working Group Jean-Francois Mule Internet Engineering Task Force CableLabs Internet Draft Document: draft-ietf-sipping-realtimefax-01.txt Category: Informational Jieying Li Expires: February 2003 August 2003 SIP Support for Real-time Fax: Call Flow Examples And Best Current Practices Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 [1]. 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. 1. Abstract The Session Initiation Protocol (SIP) allows the establishment of real-time Internet fax communications. Real-time facsimile communications over IP may follow 2 modes of operation: T.38 fax relay as defined by the ITU-T T.38 recommendation or fax pass- through. This document clarifies the options available to Internet telephony gateway vendors to handle real-time fax calls using SIP. While our primary focus is to address the more reliable real-time T.38 Group 3 fax mode, we briefly cover the fax pass-through mode to enable fallback operations and super G3 fax communications using SIP. We also give examples of SIP call flows for real-time Internet fax gateways or SIP proxy redirect servers. Elements in these call flows include SIP User Agents, SIP Proxy Servers, and Gateways to the PSTN (Public Switch Telephone Network). This document introduces best current practices for SIP T.38 fax and SIP fax pass-through sessions. A session starts with audio capabilities, and, upon fax tone detection, T.38 fax capabilities are negotiated; upon successful negotiation, the session continues J-F. Mule/J. Li SIPPING WG 1 SIP T.38 Call Flows February 2003 with fax capabilities and the media termination hosts exchange T.38 Internet fax packets. The T.38 fax call scenarios include various aspects of the call sequence: the detection of fax transmission, the usage of the T.38 session description attributes, the optional fallback into fax pass-through mode and the session termination. The fax pass-through call scenarios involve some specific SDP media attributes to enable proper fax transmission. Fax transmission can be detected by the receiving side, the emitting side or both (in the latter case, a 'glare' effect may appear). This document only covers the case when the fax transmission is detected by the receiving side: it is the most common practice and the other cases do not represent any particular challenges and are therefore left for future discussions). Call flow diagrams and message details are shown. A list of IANA defined SDP attribute names for T.38 is summarized in section 7. J-F. Mule/J. Li 2 SIP T.38 Call Flows February 2003 Table of Contents Status of this Memo...................................................1 1. Abstract...........................................................1 2. Conventions used in this document..................................4 3. Overview...........................................................4 3.1. General Assumptions.............................................4 3.2 Legend for Message Flows..........................................4 3.3 Changes to previous drafts........................................5 4 Handling of real-time fax communication using SIP...................5 4.1 Internet telephony gateways and fax detection.....................6 4.2 Internet telephony gateways and T.38 fax media connections........6 4.3 SIP session and fax termination...................................7 4.4 Internet telephony gateways and fax pass-through mode.............7 4.5 Responses to SIP OPTIONS request..................................8 4.6 Beyond Internet telephony gateways................................8 5 Successful SIP T.38 fax Call Scenarios..............................8 5.1 Internet fax device - fax only support............................8 5.1.1 Sequence Diagram................................................8 5.1.2 Message Details.................................................9 5.2 SIP T.38 fax call -fax stream replaces voice stream..............14 5.2.1 Sequence Diagram...............................................15 5.2.2 Message Details................................................17 5.3 SIP T.38 fax call - fax stream added to voice stream.............26 5.3.1 Sequence Diagram...............................................27 5.3.2 Message Details................................................29 5.4 SIP T.38 fax call - fax stream forced to replace voice stream....38 5.4.1 Sequence Diagram...............................................39 5.4.2 Message Details................................................39 6. Unsuccessful Scenarios............................................42 6.1. Unsuccessful T.38 fax scenario - no support for T.38............42 6.1.1. Sequence Diagram..............................................42 6.1.2. Message Details...............................................43 6.2. Unsuccessful T.38 fax scenario -488/606 rsp & G.711 fallback....45 6.2.1. Sequence Diagram..............................................46 6.2.2. Message Details...............................................47 7. SDP Attribute Table for T.38 sessions.............................52 8. Considerations....................................................53 8.1. Level of requirements for Internet gateways.....................53 8.2. Negotiation of UDP ports for T.38 transmission..................53 8.3. Adding a fax stream to SIP session vs. Replacing audio stream...53 8.4. Adding text to make use of SIP OPTIONS: in progress in draft-02.53 8.5. Use of IP addresses in SDP connection information...............54 8.6. Unsuccessful scenario: 606 or 488...............................54 8.7. SIP re-INVITE or UPDATE?........................................54 9. Security Considerations...........................................54 10. References.......................................................54 11. Acknowledgments..................................................55 12. Author's Addresses...............................................55 Full Copyright Statement.............................................56 Acknowledgement......................................................56 J-F. Mule/J. Li 3 SIP T.38 Call Flows February 2003 2. Conventions used in this document 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 [2]. 3. Overview The Session Initiation Protocol (SIP) is defined by RFC3261 [3] and T.38 is the ITU-T Recommendation defining the procedures for real- time Group 3 facsimile communications over IP networks [4]. This document deals with the handling of real-time fax communications using the SIP protocol for T.38 fax and fax pass-through modes. For T.38, this document deals primarily with one transport protocol for the media: T.38 over UDP/UDPTL; T.38 fax packet transport over TCP using SIP session establishment can easily be extrapolated. These T.38 call flows were developed in the design of carrier-class SIP Telephony products supporting voice and real-time fax traffic. It is the hope of the authors that this document will be useful for the SIP community, SIP implementors of T.38 fax products, designers. Call flows shown in this document complement the main SIP call flow Internet-Draft [5]. These call flows are based on the current version 2.0 of SIP in RFC3261[3], the ITU-T T.38 Amendment 2 [6] and an ITU-T SG8 liaison to IANA. Note: IANA registration of the T.38 SDP attributes is currently a work in progress. 3.1. General Assumptions Internet telephony gateways with T.38 support MAY pass various fax tones (T.30 CNG, CED, etc.) or flag sequence (like V.21 Preamble) in the RTP audio streams before those tones or flag sequence are detected. Once detected by the DSP resources, T.38 fax-capable devices switch from audio to fax mode and initiate a T.38 fax packet transmission. These best current practices MAY apply to "Network Gateway", "Enterprise Gateway" and Internet-aware fax devices or terminals. 3.2 Legend for Message Flows The legend defined [5] also applies in this document. Dashed lines (---) represent control messages that are mandatory to the call scenario. These control messages can be SIP or PSTN signaling. Double dashed lines (===) represent media paths between network elements. Messages with parenthesis around name represent optional control messages. Messages are identified in the Figures as F1, F2, etc. This references the message details in the table that follows the Figure. Comments in the message details are shown in the following form: /* Comments. */ J-F. Mule/J. Li 4 SIP T.38 Call Flows February 2003 3.3 Changes to previous drafts o Changes to sipping-draft-01 The changes between the current draft and the expired sipping draft- 00 are: - removed ecan which is a local param and removed all text - started realignment with rfc3261 (tags, branch, Max-Forward): this remains unfinished and it has not been proof-read; look for more rigorous updates in the next draft - realigned with T.38 recommendation from 3/2002 + corrected T38FaxFillBitRemoval, T38FaxTranscodingMMR, T38FaxTranscodingJBIG - edits: updated reference section (to do: need to split it into normative vs. informative) o Changes to draft-01 The changes between the current draft and draft-01 are: - Major updates: + additions based on SIPit fax testing event 8/2001: added text regarding the negotiation of T38MaxBitRate in 4.2, + added more general text for the handling of real-time fax pass-through, + added of echo cancellation & silence suppression SDP attributes and usage recommendations in 6.2, + correction of the session version number in SDP when issuing re-INVITE with updated SDP information as per draft-ietf-sip-rfc2543bis-05, + started a section on the use of the OPTIONS method to determine the support of T.38 capabilities (work-in- progress), - Minor editorial updates (added tag fields in To and From header lines as well as Contact header lines as per draft-ietf-sip- rfc2543bis-05, added proper reference to T.38 Amendment 2 pre- published version, exact case matching for T38MaxBitRate, etc.) o Changes to draft-00 The major changes between draft-01 and draft-00 are listed below: - Major updates: + new text in fax handling section 4.2 based on sip list: clarified text for fax detection, capability negotiation and termination + additions of new successful call flows in section 5 + additions of unsuccessful call flows in section 6 - Added Record-Route header, modified Cseq numbers, - Added T38FaxMaxDatagram attribute in SDP and corrected the sample value for T38FaxMaxBuffer, - Minor editorial changes (e.g. removed references in Abstract). 4 Handling of real-time fax communication using SIP The handling of real-time fax sessions using SIP involves the initial session establishment, the modification or negotiation of J-F. Mule/J. Li 5 SIP T.38 Call Flows February 2003 session capabilities upon fax detection, the optional fallback into fax pass-through mode and the session termination. Some variants of these best current practices MAY apply depending on the nature or the configuration of Internet telephony gateways. Two distinct cases are considered in this document: o The Internet telephony gateway only supports T.38 real-time fax communications (by design or by configuration). In this case, the Internet fax gateway SHOULD initiate the SIP session with T.38 SDP capabilities (this is typically the case of Internet fax terminals, also called Internet-aware fax devices or the case of gateways statically configured to support T.38 fax calls only); o The Internet telephony gateway supports voice and real-time fax communications. In this case, the Internet telephony gateway initiates the SIP session with audio capabilities, and, upon fax detection, the switchover to T.38 fax capabilities is triggered. The fax media connection may replace or be added to the audio connection depending on the target applications. 4.1 Internet telephony gateways and fax detection Two possible ways exist for an Internet telephony gateway to detect a facsimile communication: 1. On the emitting gateway (the one sending the facsimile document), the T.30 calling tone (CNG) is detected. The CNG tone is however an optional signal [7]; 2. On the receiving gateway, the V.21 Preamble flag sequence is detected. The Preamble is always present and follows the called station identification tone (CED) when CED is present. Note that even though the CED tone may be detected on the receiving gateway, since the fax CED tone is similar to V.25 ANS modem tones, it SHOULD NOT be used to trigger the fax switchover. In conclusion, several conditions can trigger fax detection. Internet telephony gateways supporting T.38 real-time facsimile MUST support the detection of fax transmission on the V.21 Preamble flag sequence; Internet telephony gateways MAY support the detection of fax on CNG tone. The authors recommend that a facsimile transmission SHOULD be detected on the receiving Internet telephony gateway. 4.2 Internet telephony gateways and T.38 fax media connections Upon successful fax detection, the description of the media connection(s) is modified using the SDP protocol [8] as described in SIP (see sections in chapter 5). Several cases should be considered: - In the case of Internet fax devices (supporting T.38 fax only communications), the SIP session is established with SDP description J-F. Mule/J. Li 6 SIP T.38 Call Flows February 2003 containing the T.38 media attributes; refer to section 5.1 for a sample call flow for Internet fax devices. - In the case of Internet telephony gateways, the SIP/SDP session is modified and the T.38 fax media connection SHOULD replace the existing audio media connection. The SIP UAC triggering the modification of the session description MUST indicate all of its T.38 media attributes in SDP. This is the recommended behavior for gateways; refer to section 5.2 for a sample call flow illustrating this scenario. Some implementations MAY choose to add the fax media connection to the existing audio connection and in that case, they SHOULD mute the audio connection while fax is transmitted. Refer to section 5.3 for a sample call flow illustrating this optional scenario. Note: Among the SDP T.38 media attributes being exchanged after fax detection, implementors should particularly pay attention to T38MaxBitRate, the maximum T.38 bit rate for the media connection. It is recommended to implement the following rule when responding to a maximum bit rate proposal. If the remote peer's SDP description contains a maximum fax bit rate of X and the local host is set to a maximum bit rate of Y (either by fax protocol detection or configuration), the local host MUST propose a maximum fax rate of min (X,Y) in the SIP response to the re-INVITE in order to facilitate the negotiation. This note is exemplified in section 5.2.1. in messages F11-F14. Failures to implement this rule MAY imply call teardown in some cases. 4.3 SIP session and fax termination Upon completion of the fax transmission, any audio connection successfully established prior to fax detection SHOULD be restored or the session MUST be terminated. 4.4 Internet telephony gateways and fax pass-through mode This section deals real-time facsimile communications over IP using fax pass-through instead of T.38 fax relay. In this mode, the facsimile communication is handled as a PCM audio call (PCMA/PCMU as specified in ITU-T recommendation G.711). The fax pass-through mode is important to prevent call failures, for example in cases when one of the SIP communication peers does not support T.38. For Internet telephony gateways with support for PCM/G.711 audio but no support for T.38 real-time fax, it is recommended to switch the session to fax pass-through mode. Internet telephony gateways SHOULD handle the fall back mode to fax pass-through by recognizing the SDP T.38 connection and proposing to switch to a new audio connection. The new audio connection SHOULD have the following characteristics: at a minimum, specify PCM G.711 codec, silence suppression OFF. The telephony gateway that J-F. Mule/J. Li 7 SIP T.38 Call Flows February 2003 originated the failed T.38 re-INVITE SHOULD initiate the subsequent re-INVITE to fax pass-through mode. Refer to section 6.2 for a sample call flow illustrating this scenario. 4.5 Responses to SIP OPTIONS request Suggestion currently logged in section 8.4, just a placeholder for now; <<work in progress >> 4.6 Beyond Internet telephony gateways This document may also serve to vendors of SIP redirect servers or other SIP UA types like SIP phones. Such SIP entities may recognize the fax nature of the sessions and redirect the flows to the proper real-time fax-capable devices or to other fax service providers. 5 Successful SIP T.38 fax Call Scenarios 5.1 Internet fax device - - fax only support This section represents a SIP call flow for a T.38 fax session between 2 Internet fax terminals. It is also applicable to Internet telephony gateways when telephony ports are statically configured to support fax only (case of analog IP telephony gateways where a specific port is connected to a fax terminal). A session starts with fax capabilities (t.38/udptl). The mechanism for supporting T.38 in SIP & SDP is detailed in T.38 Annex D [9], a temporary document that proposes an amendment to T.38 describing SIP call establishment procedures. 5.1.1 Sequence Diagram Internet Fax UA Proxy IFTGW UA Fax | | | ------->| F1 INVITE | | emitted |------------------->| | | | F2 INVITE | | |------------------->| | F3 100 Trying | | |<-------------------| F4 100 Trying | | |<-------------------| | | | | | F5 180 Ringing | | F6 180 Ringing |<-------------------| |<-------------------| | | | F7 200 OK | J-F. Mule/J. Li 8 SIP T.38 Call Flows February 2003 | F8 200 OK |<-------------------| |<-------------------| | | F9 ACK | | |------------------->| F10 ACK | | |------------------->| | | | T.38/UDPTL Fax Flow Established | |<=======================================>| End of | | fax | | | detected| | | ------->| | | | F11 BYE | | |------------------->| | | | F12 BYE | | |------------------->| | | F13 200 OK | | |<-------------------| | F14 200 OK | | |<-------------------| | 5.1.2 Message Details F1 INVITE I.FAX UA -> PROXY INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70 From: iFax <sip:+1-303-555-1111@ifax.here.com;user=phone> ;tag=ab111 To: fax Bob <sip:+1-650-555-2222@obelix.banyuls.com;user=phone> Call-ID: 1717@ifax.here.com CSeq: 17 INVITE Contact: <sip:+1-303-555-1111@ifax.here.com> Content-Type: application/sdp Content-Length: 320 v=0 o=ifaxgw1 2890846527 2890846527 IN IP4 ifax.here.com s=Session SDP c=IN IP4 ifaxmg.here.com t=0 0 m=image 15002 udptl t38 a=T38FaxVersion:0 a=T38MaxBitRate:14400 a=T38FaxRateManagement:transferredTCF a=T38FaxMaxBuffer:72 a=T38FaxMaxDatagram:316 a=T38FaxUdpEC:t38UDPFEC a=T38FaxUdpEC:t38UDPRedundancy J-F. Mule/J. Li 9 SIP T.38 Call Flows February 2003 F2 INVITE PROXY -> IFTGW UA INVITE sip:+1-650-555-2222@iftgw.there.com;user=phone SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@iftgw.there.com; maddr=obelix.banyuls.com> From: iFax <sip:+1-303-555-1111@ifax.here.com;user=phone> ;tag=ab111 To: fax Bob <sip:+1-650-555-2222@obelix.banyuls.com;user=phone> Call-ID: 1717@ifax.here.com CSeq: 17 INVITE Contact: <sip:+1-303-555-1111@ifax.here.com> Content-Type: application/sdp Content-Length: 320 v=0 o=ifaxgw1 2890846527 2890846527 IN IP4 ifax.here.com s=Session SDP c=IN IP4 ifaxmg.here.com t=0 0 m=image 15002 udptl t38 a=T38FaxVersion:0 a=T38MaxBitRate:14400 a=T38FaxRateManagement:transferredTCF a=T38FaxMaxBuffer:72 a=T38FaxMaxDatagram:316 a=T38FaxUdpEC:t38UDPFEC a=T38FaxUdpEC:t38UDPRedundancy F3 (100 Trying) PROXY -> I.FAX UA SIP/2.0 100 Trying Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 From: iFax <sip:+1-303-555-1111@ifax.here.com;user=phone> ;tag=ab111 To: fax Bob <sip:+1-650-555-2222@obelix.banyuls.com;user=phone> Call-ID: 1717@ifax.here.com CSeq: 17 INVITE Content-Length: 0 F4 (100 Trying) IFTGW UA -> PROXY SIP/2.0 100 Trying Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 Via: SIP/2.0/UDP ifax.here.com:5060 J-F. Mule/J. Li 10 SIP T.38 Call Flows February 2003 From: iFax <sip:+1-303-555-1111@ifax.here.com;user=phone> ;tag=ab111 To: fax Bob <sip:+1-650-555-2222@obelix.banyuls.com;user=phone> Call-ID: 1717@ifax.here.com CSeq: 17 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Length: 0 F5 180 Ringing IFTGW UA -> PROXY SIP/2.0 180 Ringing Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 From: iFax <sip:+1-303-555-1111@ifax.here.com;user=phone> ;tag=ab111 To: fax Bob <sip:+1-650-555-2222@obelix.banyuls.com;user=phone> Call-ID: 1717@ifax.here.com CSeq: 17 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Length: 0 F6 180 Ringing PROXY -> I.FAX UA SIP/2.0 180 Ringing Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 From: iFax <sip:+1-303-555-1111@ifax.here.com;user=phone> ;tag=ab111 To: fax Bob <sip:+1-650-555-2222@obelix.banyuls.com;user=phone> Call-ID: 1717@ifax.here.com CSeq: 17 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Length: 0 F7 200 OK IFTGW UA -> PROXY SIP/2.0 200 OK Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 From: iFax <sip:+1-303-555-1111@ifax.here.com;user=phone> ;tag=ab111 To: fax Bob <sip:+1-650-555-2222@obelix.banyuls.com;user=phone> Call-ID: 1717@ifax.here.com CSeq: 17 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Type: application/sdp Content-Length: 320 v=0 J-F. Mule/J. Li 11 SIP T.38 Call Flows February 2003 o=faxgw1 2890844527 2890844527 IN IP4 iftgw.there.com s=Session SDP c=IN IP4 iftmg.there.com t=0 0 m=image 49172 udptl t38 a=T38FaxVersion:0 a=T38MaxBitRate:14400 a=T38FaxRateManagement:transferredTCF a=T38FaxMaxBuffer:72 a=T38FaxMaxDatagram:316 a=T38FaxUdpEC:t38UDPRedundancy F8 200 OK PROXY -> I.FAX UA SIP/2.0 200 OK Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 Record-Route: <sip:+1-650-555-2222@iftgw.there.com; maddr=obelix.banyuls.com> From: iFax <sip:+1-303-555-1111@ifax.here.com;user=phone> ;tag=ab111 To: fax Bob <sip:+1-650-555-2222@obelix.banyuls.com;user=phone> Call-ID: 1717@ifax.here.com CSeq: 17 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Type: application/sdp Content-Length: 320 v=0 o=faxgw1 2890844527 2890844527 IN IP4 iftgw.there.com s=Session SDP c=IN IP4 iftmg.there.com t=0 0 m=image 49172 udptl t38 a=T38FaxVersion:0 a=T38MaxBitRate:14400 a=T38FaxRateManagement:transferredTCF a=T38FaxMaxBuffer:72 a=T38FaxMaxDatagram:316 a=T38FaxUdpEC:t38UDPRedundancy F9 ACK I.FAX UA -> PROXY ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70 Route: <sip:+1-650-555-2222@iftgw.there.com; maddr=obelix.banyuls.com> From: iFax <sip:+1-303-555-1111@ifax.here.com;user=phone> ;tag=ab111 To: fax Bob <sip:+1-650-555-2222@obelix.banyuls.com;user=phone> Call-ID: 1717@ifax.here.com J-F. Mule/J. Li 12 SIP T.38 Call Flows February 2003 CSeq: 17 ACK Content-Length: 0 F10 ACK PROXY -> IFTGW UA ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 69 Route: <sip:+1-650-555-2222@iftgw.there.com; maddr=obelix.banyuls.com> From: iFax <sip:+1-303-555-1111@ifax.here.com;user=phone> ;tag=ab111 To: fax Bob <sip:+1-650-555-2222@obelix.banyuls.com;user=phone> Call-ID: 1717@ifax.here.com CSeq: 17 ACK Content-Length: 0 /* T.38 fax streams are established. */ F11 BYE I.FAX UA -> PROXY BYE sip:+1-650-555-2222@obelix.banyuls.com SIP/2.0 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70 Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: iFax <sip:+1-303-555-1111@ifax.here.com;user=phone> ;tag=ab22 To: fax Bob <sip:+1-650-555-2222@obelix.banyuls.com;user=phone> ;tag=cde34 Call-ID: 1717@ifax.here.com CSeq: 18 BYE Content-Length: 0 F12 BYE PROXY -> IFTGW UA BYE sip:+1-650-555-2222@obelix.banyuls.com SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d009.1 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: iFax <sip:+1-303-555-1111@ifax.here.com;user=phone> ;tag=ab22 To: fax Bob <sip:+1-650-555-2222@obelix.banyuls.com;user=phone> ;tag=cde34 Call-ID: 1717@ifax.here.com CSeq: 18 BYE J-F. Mule/J. Li 13 SIP T.38 Call Flows February 2003 Content-Length: 0 F13 200 OK IFTGW UA -> PROXY SIP/2.0 200 OK Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 From: iFax <sip:+1-303-555-1111@ifax.here.com;user=phone> ;tag=ab22 To: fax Bob <sip:+1-650-555-2222@obelix.banyuls.com;user=phone> ;tag=cde34 Call-ID: 1717@ifax.here.com CSeq: 18 BYE Content-Type: application/sdp Content-Length: 0 F14 200 OK PROXY -> I.FAX UA SIP/2.0 200 OK Via: SIP/2.0/UDP ifax.here.com:5060;branch=z9hG4bK74bf9 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: iFax <sip:+1-303-555-1111@ifax.here.com;user=phone> ;tag=ab22 To: fax Bob <sip:+1-650-555-2222@obelix.banyuls.com;user=phone> ;tag=cde34 Call-ID: 1717@ifax.here.com CSeq: 18 BYE Content-Type: application/sdp Content-Length: 0 5.2 SIP T.38 fax call - - fax stream replaces voice stream This section represents the SIP call flow for a T.38 fax session between 2 Internet telephony gateways (fax detection on terminating side). A session starts with audio capabilities, and then the session is modified to switch to t38 fax mode (t.38/udptl). Scenario: 1. A SIP INVITE is sent to the called party requesting a voice connection per RFC3261; our scenario involves 1 SIP proxy. An audio connection is established, 2. Upon detection of Preamble by the terminating gateway, a SIP re- INVITE request is sent to the emitting gateway to modify the parameters of the session to allow a T.38 fax media connection. J-F. Mule/J. Li 14 SIP T.38 Call Flows February 2003 This INVITE request contains new SDP information detailing T.38 capabilities, 3. Upon successful acknowledgments, T.38 IFP fax packets are sent/received on UDP ports, which may be the same UDP ports used for audio RTP, 4. Once the fax transmission is terminated, audio capabilities are æærestoredÆÆ or the call is terminated. 5.2.1 Sequence Diagram In our example, we illustrate the fact that Internet telephony gateways may use multiple network interfaces for signaling and/or media streaming or one network interface with multiple IP addresses. Typically, our example shows: - one interface for SIP signaling (ingress gateway = ift.here.com, egress gateway = iftgw.there.com) - one or multiple interface(s) for media transport: (ingress gateway = iftmg.here.com, egress gateway = iftmg.there.com) A proxy is acting as a pure SIP signaling proxy (obelix.banyuls.com). IFT UA Proxy IFTGW UA | | | | F1 INVITE | | |------------------->| | | | F2 INVITE | | |------------------->| | F3 100 Trying | | |<-------------------| F4 100 Trying | | |<-------------------| | | | | | F5 180 Ringing | | F6 180 Ringing |<-------------------| |<-------------------| | | | F7 200 OK | | F8 200 OK |<-------------------| |<-------------------| | | | | | F9 ACK | | |------------------->| F10 ACK | | ------------------->| | | | Both Way RTP Media Established | Fax |<=======================================>| ------->| | emitted | | | | | | Preamble | | |<--------- | | F11 INVITE | detected | |<-------------------| J-F. Mule/J. Li 15 SIP T.38 Call Flows February 2003 | F12 INVITE | | |<-------------------| | | | | | F13 200 OK | | |------------------->| | | | F14 200 OK | | |------------------->| | | | | | F15 ACK | | |<-------------------| | F16 ACK | | |<-------------------| | | | | T.38/UDPT Fax Flow Established | |<=======================================>| End of | | fax | | | detected| | | ------->| | | | | | End of fax | | |<---------- | | | detected | | F17 INVITE | | |<-------------------| | F18 INVITE | | |<-------------------| | | | | | F19 200 OK | | |------------------->| | | | F20 200 OK | | |------------------->| | | | | | F21 ACK | | |<-------------------| | F22 ACK | | |<-------------------| | | Both Way RTP Media Re-Established | |<=======================================>| | F23 BYE | | |------------------->| | | | F24 BYE | | |------------------->| | | | | | F25 200 OK | | |<-------------------| | F26 200 OK | | |<-------------------| | J-F. Mule/J. Li 16 SIP T.38 Call Flows February 2003 5.2.2 Message Details << NOTE: WIP - ALIGNMENT with RFC3261 req. incomplete for the rest of the document.>> F1 INVITE IFT UA -> PROXY INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP ift.here.com:5060 Max-Forwards: 70 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone Call-ID: 1717@ift.here.com CSeq: 17 INVITE Contact: <sip:+1-303-555-1111@ift.here.com> Content-Type: application/sdp Content-Length: 146 v=0 o=IFAXTERMINAL01 2890844527 2890844527 IN IP4 ift.here.com s=Session SDP c=IN IP4 iftmg.here.com t=0 0 m=audio 3456 RTP/AVP 0 a=rtpmap:0 PCMU/8000 F2 INVITE PROXY -> IFTGW UA INVITE sip:+1-650-555-2222@iftgw.there.com;user=phone SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 Via: SIP/2.0/UDP ift.here.com:5060 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@iftgw.there.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone Call-ID: 1717@ift.here.com CSeq: 17 INVITE Contact: <sip:+1-303-555-1111@ift.here.com> Content-Type: application/sdp Content-Length: 146 v=0 o=IFAXTERMINAL01 2890844527 2890844527 IN IP4 ift.here.com s=Session SDP c=IN IP4 iftmg.here.com t=0 0 m=audio 3456 RTP/AVP 0 a=rtpmap:0 PCMU/8000 F3 (100 Trying) PROXY -> IFT UA J-F. Mule/J. Li 17 SIP T.38 Call Flows February 2003 SIP/2.0 100 Trying Via: SIP/2.0/UDP ift.here.com:5060 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone Call-ID: 1717@ift.here.com CSeq: 17 INVITE Content-Length: 0 F4 100 Trying IFTGW UA -> PROXY SIP/2.0 100 Trying Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 Via: SIP/2.0/UDP ift.here.com:5060 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 17 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Length: 0 F5 180 Ringing IFTGW UA -> PROXY SIP/2.0 180 Ringing Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 Via: SIP/2.0/UDP ift.here.com:5060 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 17 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Length: 0 F6 180 Ringing PROXY -> IFT UA SIP/2.0 180 Ringing Via: SIP/2.0/UDP ift.here.com:5060 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 17 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Length: 0 F7 200 OK IFTGW UA -> PROXY SIP/2.0 200 OK Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 Via: SIP/2.0/UDP ift.here.com:5060 J-F. Mule/J. Li 18 SIP T.38 Call Flows February 2003 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 17 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Type: application/sdp Content-Length: 150 v=0 o=IFAXTERMINAL01 2890844527 171089 IN IP4 iftgw.there.com s=Session SDP c=IN IP4 iftmg.there.com t=0 0 m=audio 12322 RTP/AVP 0 a=rtpmap:0 PCMU/8000 F8 200 OK PROXY -> IFT UA SIP/2.0 200 OK Via: SIP/2.0/UDP ift.here.com:5060 Record-Route: <sip:+1-650-555-2222@iftgw.there.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 17 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Type: application/sdp Content-Length: 150 v=0 o=IFAXTERMINAL01 2890844527 171089 IN IP4 iftgw.there.com s=Session SDP c=IN IP4 iftmg.there.com t=0 0 m=audio 12322 RTP/AVP 0 a=rtpmap:0 PCMU/8000 F9 ACK IFT UA -> PROXY ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP ift.here.com:5060 Max-Forwards: 70 Route: <sip:+1-650-555-2222@iftgw.there.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 17 ACK Content-Length: 0 J-F. Mule/J. Li 19 SIP T.38 Call Flows February 2003 F10 ACK PROXY -> IFTGW UA ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 Via: SIP/2.0/UDP ift.here.com:5060 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@iftgw.there.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 17 ACK Content-Length: 0 /* RTP streams are established. The CNG fax tone is sent in-band if it is present. The receiving side IFT gateway DSP detects the Preamble sequence. A new UDP port is open on IFTGW for T.38 IFP packets and the IFTGW signals the switch over to fax mode by send a re-INVITE with the new UDP port in the SDP. Note: the IFTGW has a T38MaxBitRate configured to 9600 */ F11 INVITE IFTGW UA -> PROXY INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 70 Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Type: application/sdp Content-Length: 320 v=0 o=faxgw1 2890844527 171090 IN IP4 iftgw.there.com s=Session SDP c=IN IP4 iftmg.there.com t=0 0 m=image 49172 udptl t38 a=T38FaxVersion:0 a=T38MaxBitRate:9600 a=T38FaxRateManagement:transferredTCF a=T38FaxMaxBuffer:72 J-F. Mule/J. Li 20 SIP T.38 Call Flows February 2003 a=T38FaxMaxDatagram:316 a=T38FaxUdpEC:t38UDPFEC a=T38FaxUdpEC:t38UDPRedundancy F12 INVITE PROXY -> IFT UA INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Type: application/sdp Content-Length: 320 v=0 o=faxgw1 2890844527 171090 IN IP4 iftgw.there.com s=Session SDP c=IN IP4 iftmg.there.com t=0 0 m=image 49172 udptl t38 a=T38FaxVersion:0 a=T38MaxBitRate:9600 a=T38FaxRateManagement:transferredTCF a=T38FaxMaxBuffer:72 a=T38FaxMaxDatagram:316 a=T38FaxUdpEC:t38UDPFEC a=T38FaxUdpEC:t38UDPRedundancy /* Note: the IFT has a T38MaxBitRate configured to 14400 but since it received a T38MaxBitRate proposal of 9600, it replies with T38MaxBitRate = min (9600,14400) */ F13 200 OK IFT UA -> PROXY SIP/2.0 200 OK Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 INVITE Contact: <sip:+1-303-555-1111@ift.here.com> Content-Type: application/sdp Content-Length: 320 v=0 J-F. Mule/J. Li 21 SIP T.38 Call Flows February 2003 o=faxgw1 2890846527 2890846528 IN IP4 ift.here.com s=Session SDP c=IN IP4 iftmg.here.com t=0 0 m=image 15002 udptl t38 a=T38FaxVersion:0 a=T38MaxBitRate:9600 a=T38FaxRateManagement:transferredTCF a=T38FaxMaxBuffer:72 a=T38FaxMaxDatagram:316 a=T38FaxUdpEC:t38UDPRedundancy F14 200 OK PROXY -> IFT UA SIP/2.0 200 OK Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 INVITE Contact: <sip:+1-303-555-1111@ift.here.com> Content-Type: application/sdp Content-Length: 320 v=0 o=faxgw1 2890846527 2890846528 IN IP4 ift.here.com s=Session SDP c=IN IP4 iftmg.here.com t=0 0 m=image 15002 udptl t38 a=T38FaxVersion:0 a=T38MaxBitRate:9600 a=T38FaxRateManagement:transferredTCF a=T38FaxMaxBuffer:72 a=T38FaxMaxDatagram:316 a=T38FaxUdpEC:t38UDPRedundancy F15 ACK IFTGW UA -> PROXY ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 70 Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 ACK Content-Length: 0 J-F. Mule/J. Li 22 SIP T.38 Call Flows February 2003 F16 ACK PROXY -> IFT UA ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 ACK Content-Length: 0 /* T.38 fax transmission established both ways */ /* Then, the end of the fax transmission is detected on ingress side and sent to the egress side (IFTGW). IFTGW initiates the switch back to voice communication */ F17 INVITE IFTGW UA -> PROXY INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 70 Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 19 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Type: application/sdp Content-Length: 181 v=0 o=faxgw1 2890844527 171091 IN IP4 iftgw.there.com s=Session SDP c=IN IP4 iftmg.there.com t=0 0 m=audio 12322 RTP/AVP 0 a=rtpmap:0 PCMU/8000 F18 INVITE PROXY -> IFT UA INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d009.1 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 J-F. Mule/J. Li 23 SIP T.38 Call Flows February 2003 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 19 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Type: application/sdp Content-Length: 181 v=0 o=faxgw1 2890844527 171091 IN IP4 iftgw.there.com s=Session SDP c=IN IP4 iftmg.there.com t=0 0 m=audio 12322 RTP/AVP 0 a=rtpmap:0 PCMU/8000 F19 200 OK IFT UA -> PROXY SIP/2.0 200 OK Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 19 INVITE Contact: <sip:+1-303-555-1111@ift.here.com> Content-Type: application/sdp Content-Length: 150 v=0 o=faxgw1 2890844527 2890844529 IN IP4 ift.here.com s=Session SDP c=IN IP4 iftmg.here.com t=0 0 m=audio 3456 RTP/AVP 0 a=rtpmap:0 PCMU/8000 F20 200 OK PROXY -> IFTGW UA SIP/2.0 200 OK Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 19 INVITE Contact: <sip:+1-303-555-1111@ift.here.com> J-F. Mule/J. Li 24 SIP T.38 Call Flows February 2003 Content-Type: application/sdp Content-Length: 150 v=0 o=faxgw1 2890844527 2890844529 IN IP4 ift.here.com s=Session SDP c=IN IP4 iftmg.here.com t=0 0 m=audio 3456 RTP/AVP 0 a=rtpmap:0 PCMU/8000 F21 ACK IFTGW UA -> PROXY ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 70 Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 19 ACK Content-Length: 0 F22 ACK PROXY -> IFT UA ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d009.1 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 19 ACK Content-Length: 0 /* Voice streams re-established both ways */ F23 BYE IFT UA -> PROXY BYE sip:+1-650-555-2222@obelix.banyuls.com SIP/2.0 Via: SIP/2.0/UDP ift.here.com:5060 Max-Forwards: 70 Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> J-F. Mule/J. Li 25 SIP T.38 Call Flows February 2003 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone Call-ID: 1717@ift.here.com CSeq: 20 BYE Content-Length: 0 F24 BYE PROXY -> IFTGW UA BYE sip:+1-650-555-2222@obelix.banyuls.com SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d009.1 Via: SIP/2.0/UDP ift.here.com:5060 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone Call-ID: 1717@ift.here.com CSeq: 20 BYE Content-Length: 0 F25 200 OK IFTGW UA -> PROXY SIP/2.0 200 OK Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 Via: SIP/2.0/UDP ift.here.com:5060 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde24 Call-ID: 1717@ift.here.com CSeq: 20 BYE Content-Type: application/sdp Content-Length: 0 F26 200 OK PROXY -> IFT UA SIP/2.0 200 OK Via: SIP/2.0/UDP ift.here.com:5060 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde24 Call-ID: 1717@ift.here.com CSeq: 20 BYE Content-Type: application/sdp Content-Length: 0 5.3 SIP T.38 fax call - - fax stream added to voice stream J-F. Mule/J. Li 26 SIP T.38 Call Flows February 2003 This section represents the SIP call flow for a T.38 fax session between 2 Internet telephony gateways. It shows the detection of the fax communication on terminating or receiving side. A session starts with one audio stream in SDP, and, upon detection of fax, an additional fax stream is added to the session while the voice stream is muted. After the fax communication is terminated, the fax stream is terminated and the voice stream is restored. Scenario: 1. A SIP INVITE is sent to the called party requesting a voice connection per RFC3261; our scenario involves 1 SIP proxy. An audio connection is established, 2. Upon detection of Preamble by the terminating gateway, a SIP re¡INVITE request is sent to the emitting gateway to modify the parameters of the session to add a T.38 fax connection. The connection data is specified per media description and not at the session-level. This allows the audio stream and t.38 fax stream to be controlled independently (i.e., placing the audio on hold while the t.38 fax transmission is active). Also note that the t.38 fax media stream has been added to the session. This re-INVITE request contains SDP information detailing the additional T.38 capabilities, 3. It is suggested that the voice pipe be muted while the fax session is in progress. Upon successful acknowledgments, T.38 IFP fax packets are sent/received on different UDP ports than the one used for audio RTP, 4. Once the fax transmission is terminated, audio capabilities are æærestoredÆÆ or the call is terminated. 5.3.1 Sequence Diagram IFT UA Proxy IFTGW UA | | | | F1 INVITE | | |------------------->| | | | F2 INVITE | | |------------------->| | F3 100 Trying | | |<-------------------| F4 100 Trying | | |<-------------------| | | | | | F5 180 Ringing | | F6 180 Ringing |<-------------------| |<-------------------| | | | F7 200 OK | | F8 200 OK |<-------------------| |<-------------------| | | | | | F9 ACK | | |------------------->| F10 ACK | | ------------------->| | | J-F. Mule/J. Li 27 SIP T.38 Call Flows February 2003 | Both Way RTP Media Established | Fax |<=======================================>| ------->| | emitted | | | | | | Preamble | | |<--------- | | F11 INVITE | detected | |<-------------------| | F12 INVITE | | |<-------------------| | | | | | F13 200 OK | | |------------------->| | | | F14 200 OK | | |------------------->| | | F15 ACK | | |<-------------------| | F16 ACK | | |<-------------------| | | | | T.38/UDPT Fax Flow Established | | Voice connection muted | |<=======================================>| End of | | fax | | | detected| | | ------->| | | | | | | | End of fax | | |<---------- | | | detected | | F17 INVITE | | |<-------------------| | F18 INVITE | | |<-------------------| | | | | | F19 200 OK | | |------------------->| | | | F20 200 OK | | |------------------->| | | | | | F21 ACK | | |<-------------------| | F22 ACK | | |<-------------------| | | | | Both way RTP Flow restored | |<=======================================>| | | | F23 BYE | | |------------------->| | | | F24 BYE | J-F. Mule/J. Li 28 SIP T.38 Call Flows February 2003 | |------------------->| | | | | | F25 200 OK | | |<-------------------| | F26 200 OK | | |<-------------------| | 5.3.2 Message Details F1 INVITE IFT UA -> PROXY INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP ift.here.com:5060 Max-Forwards: 70 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone Call-ID: 1717@ift.here.com CSeq: 17 INVITE Contact: <sip:+1-303-555-1111@ift.here.com> Content-Type: application/sdp Content-Length: 146 v=0 o=IFAXTERMINAL01 2890844527 2890844527 IN IP4 ift.here.com s=Session SDP c=IN IP4 iftmg.here.com t=0 0 m=audio 3456 RTP/AVP 0 a=rtpmap:0 PCMU/8000 F2 INVITE PROXY -> IFTGW UA INVITE sip:+1-650-555-2222@iftgw.there.com;user=phone SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 Via: SIP/2.0/UDP ift.here.com:5060 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@iftgw.there.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone Call-ID: 1717@ift.here.com CSeq: 17 INVITE Contact: <sip:+1-303-555-1111@ift.here.com> Content-Type: application/sdp Content-Length: 146 v=0 o=IFAXTERMINAL01 2890844527 2890844527 IN IP4 ift.here.com s=Session SDP J-F. Mule/J. Li 29 SIP T.38 Call Flows February 2003 c=IN IP4 iftmg.here.com t=0 0 m=audio 3456 RTP/AVP 0 a=rtpmap:0 PCMU/8000 F3 (100 Trying) PROXY -> IFT UA SIP/2.0 100 Trying Via: SIP/2.0/UDP ift.here.com:5060 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone Call-ID: 1717@ift.here.com CSeq: 17 INVITE Content-Length: 0 F4 100 Trying IFTGW UA -> PROXY SIP/2.0 100 Trying Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 Via: SIP/2.0/UDP ift.here.com:5060 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 17 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Length: 0 F5 180 Ringing IFTGW UA -> PROXY SIP/2.0 180 Ringing Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 Via: SIP/2.0/UDP ift.here.com:5060 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 17 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Length: 0 F6 180 Ringing PROXY -> IFT UA SIP/2.0 180 Ringing Via: SIP/2.0/UDP ift.here.com:5060 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 17 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Length: 0 J-F. Mule/J. Li 30 SIP T.38 Call Flows February 2003 F7 200 OK IFTGW UA -> PROXY SIP/2.0 200 OK Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 Via: SIP/2.0/UDP ift.here.com:5060 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 17 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Type: application/sdp Content-Length: 150 v=0 o=IFAXTERMINAL01 2890844527 171089 IN IP4 iftgw.there.com s=Session SDP c=IN IP4 iftmg.there.com t=0 0 m=audio 12322 RTP/AVP 0 a=rtpmap:0 PCMU/8000 F8 200 OK PROXY -> IFT UA SIP/2.0 200 OK Via: SIP/2.0/UDP ift.here.com:5060 Record-Route: <sip:+1-650-555-2222@iftgw.there.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 17 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Type: application/sdp Content-Length: 150 v=0 o=IFAXTERMINAL01 2890844527 171089 IN IP4 iftgw.there.com s=Session SDP c=IN IP4 iftmg.there.com t=0 0 m=audio 12322 RTP/AVP 0 a=rtpmap:0 PCMU/8000 F9 ACK IFT UA -> PROXY ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP ift.here.com:5060 Max-Forwards: 70 J-F. Mule/J. Li 31 SIP T.38 Call Flows February 2003 Route: <sip:+1-650-555-2222@iftgw.there.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 17 ACK Content-Length: 0 F10 ACK PROXY -> IFTGW UA ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 Via: SIP/2.0/UDP ift.here.com:5060 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@iftgw.there.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 17 ACK Content-Length: 0 /* RTP streams are established. The CNG fax tone is sent in-band if it is present. The receiving side IFT gateway DSP detects the Preamble. A new UDP port is open on IFTGW for T.38 IFP packets and the IFTGW signals the switch over to fax mode by send a re-INVITE with the new UDP port in the SDP */ F11 INVITE IFTGW UA -> PROXY INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 70 Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Type: application/sdp Content-Length: 320 v=0 o=faxgw1 2890844527 171090 IN IP4 iftgw.there.com s=Session SDP t=0 0 m=audio 12322 RTP/AVP 0 c=IN IP4 0.0.0.0 m=image 49172 udptl t38 c=IN IP4 iftmg.there.com J-F. Mule/J. Li 32 SIP T.38 Call Flows February 2003 a=T38FaxVersion:0 a=T38MaxBitRate:14400 a=T38FaxRateManagement:transferredTCF a=T38FaxMaxBuffer:72 a=T38FaxMaxDatagram:316 a=T38FaxUdpEC:t38UDPFEC a=T38FaxUdpEC:t38UDPRedundancy F12 INVITE PROXY -> IFT UA INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Type: application/sdp Content-Length: 320 v=0 o=faxgw1 2890844527 171090 IN IP4 iftgw.there.com s=Session SDP t=0 0 m=audio 12322 RTP/AVP 0 c=IN IP4 0.0.0.0 m=image 49172 udptl t38 c=IN IP4 iftmg.there.com a=T38FaxVersion:0 a=T38MaxBitRate:14400 a=T38FaxRateManagement:transferredTCF a=T38FaxMaxBuffer:72 a=T38FaxMaxDatagram:316 a=T38FaxUdpEC:t38UDPFEC a=T38FaxUdpEC:t38UDPRedundancy F13 200 OK IFT UA -> PROXY SIP/2.0 200 OK Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 INVITE Contact: <sip:+1-303-555-1111@ift.here.com> Content-Type: application/sdp J-F. Mule/J. Li 33 SIP T.38 Call Flows February 2003 Content-Length: 320 v=0 o=faxgw1 2890846527 2890846528 IN IP4 ift.here.com s=Session SDP t=0 0 m=audio 3456 RTP/AVP 0 c=IN IP4 0.0.0.0 m=image 15002 udptl t38 c=IN IP4 iftmg.here.com a=T38FaxVersion:0 a=T38MaxBitRate:14400 a=T38FaxRateManagement:transferredTCF a=T38FaxMaxBuffer:72 a=T38FaxMaxDatagram:316 a=T38FaxUdpEC:t38UDPRedundancy F14 200 OK PROXY -> IFT UA SIP/2.0 200 OK Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 INVITE Contact: <sip:+1-303-555-1111@ift.here.com> Content-Type: application/sdp Content-Length: 320 v=0 o=faxgw1 2890846527 2890846528 IN IP4 ift.here.com s=Session SDP t=0 0 m=audio 3456 RTP/AVP 0 c=IN IP4 0.0.0.0 m=image 15002 udptl t38 c=IN IP4 iftmg.here.com a=T38FaxVersion:0 a=T38MaxBitRate:14400 a=T38FaxRateManagement:transferredTCF a=T38FaxMaxBuffer:72 a=T38FaxMaxDatagram:316 a=T38FaxUdpEC:t38UDPRedundancy F15 ACK IFTGW UA -> PROXY ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 70 J-F. Mule/J. Li 34 SIP T.38 Call Flows February 2003 Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 ACK Content-Length: 0 F16 ACK PROXY -> IFT UA ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 ACK Content-Length: 0 /* T.38 fax transmission established both ways and the voice stream is muted */ /* Then, the end of the fax transmission is detected on ingress side and sent to the egress side (IFTGW). IFTGW initiates the switch back to voice communication */ F17 INVITE IFTGW UA -> PROXY INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 70 Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 19 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Type: application/sdp Content-Length: 181 v=0 o=faxgw1 2890844527 171091 IN IP4 iftgw.there.com s=Session SDP c=IN IP4 iftmg.there.com t=0 0 m=audio 12322 RTP/AVP 0 a=rtpmap:0 PCMU/8000 J-F. Mule/J. Li 35 SIP T.38 Call Flows February 2003 F18 INVITE PROXY -> IFT UA INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d009.1 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 19 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Type: application/sdp Content-Length: 181 v=0 o=faxgw1 2890844527 171091 IN IP4 iftgw.there.com s=Session SDP c=IN IP4 iftmg.there.com t=0 0 m=audio 12322 RTP/AVP 0 a=rtpmap:0 PCMU/8000 F19 200 OK IFT UA -> PROXY SIP/2.0 200 OK Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 19 INVITE Contact: <sip:+1-303-555-1111@ift.here.com> Content-Type: application/sdp Content-Length: 150 v=0 o=faxgw1 2890844527 2890844529 IN IP4 ift.here.com s=Session SDP c=IN IP4 iftmg.here.com t=0 0 m=audio 3456 RTP/AVP 0 a=rtpmap:0 PCMU/8000 F20 200 OK PROXY -> IFTGW UA SIP/2.0 200 OK Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 J-F. Mule/J. Li 36 SIP T.38 Call Flows February 2003 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 19 INVITE Contact: <sip:+1-303-555-1111@ift.here.com> Content-Type: application/sdp Content-Length: 150 v=0 o=faxgw1 2890844527 2890844529 IN IP4 ift.here.com s=Session SDP c=IN IP4 iftmg.here.com t=0 0 m=audio 3456 RTP/AVP 0 a=rtpmap:0 PCMU/8000 F21 ACK IFTGW UA -> PROXY ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 70 Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 19 ACK Content-Length: 0 F22 ACK PROXY -> IFT UA ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d009.1 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 19 ACK Content-Length: 0 F23 BYE IFT UA -> PROXY BYE sip:+1-650-555-2222@obelix.banyuls.com SIP/2.0 Via: SIP/2.0/UDP ift.here.com:5060 Max-Forwards: 70 Route: <sip:+1-650-555-2222@obelix.banyuls.com; J-F. Mule/J. Li 37 SIP T.38 Call Flows February 2003 maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone Call-ID: 1717@ift.here.com CSeq: 20 BYE Content-Length: 0 F24 BYE PROXY -> IFTGW UA BYE sip:+1-650-555-2222@obelix.banyuls.com SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d009.1 Via: SIP/2.0/UDP ift.here.com:5060 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone Call-ID: 1717@ift.here.com CSeq: 20 BYE Content-Length: 0 F25 200 OK IFTGW UA -> PROXY SIP/2.0 200 OK Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 Via: SIP/2.0/UDP ift.here.com:5060 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde24 Call-ID: 1717@ift.here.com CSeq: 20 BYE Content-Type: application/sdp Content-Length: 0 F26 200 OK PROXY -> IFT UA SIP/2.0 200 OK Via: SIP/2.0/UDP ift.here.com:5060 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde24 Call-ID: 1717@ift.here.com CSeq: 20 BYE Content-Type: application/sdp Content-Length: 0 5.4 SIP T.38 fax call - - fax stream forced to replace voice stream This section illustrates the following scenario: J-F. Mule/J. Li 38 SIP T.38 Call Flows February 2003 1. A SIP INVITE is sent to the called party requesting a voice connection per RFC3261; our scenario involves 1 SIP proxy. An audio connection is established, 2. Upon detection of Preamble by the terminating gateway, a SIP re¡INVITE request is sent to the emitting gateway to modify the parameters of the session to add a T.38 fax connection. This re- INVITE request contains SDP information detailing the additional T.38 capabilities. It is also suggested that the voice pipe be muted while the fax session is in progress. 3. The emitting gateway does not have the resources to maintain both the audio & fax streams and replies by allowing the fax media stream. Upon successful acknowledgments, the audio stream is terminated and T.38 IFP fax packets are exchanged, 4. Once the fax transmission is terminated, audio capabilities are æære-negotiatedÆÆ and the call is terminated. 5.4.1 Sequence Diagram Refer to section 5.3.1; sequence diagram is unchanged. 5.4.2 Message Details See section 5.3.2 for the complete set of messages. We only indicate the changed messages based on the emitting gatewayÆs decline to support both voice and fax streams. ... F11 INVITE IFTGW UA -> PROXY INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 70 Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Type: application/sdp Content-Length: 320 v=0 o=faxgw1 2890844527 171090 IN IP4 iftgw.there.com s=Session SDP t=0 0 m=audio 12322 RTP/AVP 0 c=IN IP4 0.0.0.0 m=image 49172 udptl t38 c=IN IP4 iftmg.there.com a=T38FaxVersion:0 a=T38MaxBitRate:14400 J-F. Mule/J. Li 39 SIP T.38 Call Flows February 2003 a=T38FaxRateManagement:transferredTCF a=T38FaxMaxBuffer:72 a=T38FaxMaxDatagram:316 a=T38FaxUdpEC:t38UDPFEC a=T38FaxUdpEC:t38UDPRedundancy F12 INVITE PROXY -> IFT UA INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Type: application/sdp Content-Length: 320 v=0 o=faxgw1 2890844527 171090 IN IP4 iftgw.there.com s=Session SDP t=0 0 m=audio 12322 RTP/AVP 0 c=IN IP4 0.0.0.0 m=image 49172 udptl t38 c=IN IP4 iftmg.there.com a=T38FaxVersion:0 a=T38MaxBitRate:14400 a=T38FaxRateManagement:transferredTCF a=T38FaxMaxBuffer:72 a=T38FaxMaxDatagram:316 a=T38FaxUdpEC:t38UDPFEC a=T38FaxUdpEC:t38UDPRedundancy F13 200 OK IFT UA -> PROXY SIP/2.0 200 OK Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555- 2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 INVITE Contact: <sip:+1-303-555-1111@ift.here.com> J-F. Mule/J. Li 40 SIP T.38 Call Flows February 2003 Content-Type: application/sdp Content-Length: 320 v=0 o=faxgw1 2890846527 2890846528 IN IP4 ift.here.com s=Session SDP t=0 0 m=audio 0 RTP/AVP 0 c=IN IP4 0.0.0.0 m=image 15002 udptl t38 c=IN IP4 iftmg.here.com a=T38FaxVersion:0 a=T38MaxBitRate:14400 a=T38FaxRateManagement:transferredTCF a=T38FaxMaxBuffer:72 a=T38FaxMaxDatagram:316 a=T38FaxUdpEC:t38UDPRedundancy F14 200 OK PROXY -> IFT UA SIP/2.0 200 OK Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555- 2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 INVITE Contact: <sip:+1-303-555-1111@ift.here.com> Content-Type: application/sdp Content-Length: 320 v=0 o=faxgw1 2890846527 2890846528 IN IP4 ift.here.com s=Session SDP t=0 0 m=audio 0 RTP/AVP 0 c=IN IP4 0.0.0.0 m=image 15002 udptl t38 c=IN IP4 iftmg.here.com a=T38FaxVersion:0 a=T38MaxBitRate:14400 a=T38FaxRateManagement:transferredTCF a=T38FaxMaxBuffer:72 a=T38FaxMaxDatagram:316 a=T38FaxUdpEC:t38UDPRedundancy F15 ACK IFTGW UA -> PROXY ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 J-F. Mule/J. Li 41 SIP T.38 Call Flows February 2003 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 70 Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555- 2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 ACK Content-Length: 0 F16 ACK PROXY -> IFT UA ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555- 2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 ACK Content-Length: 0 6. Unsuccessful Scenarios 6.1. Unsuccessful T.38 fax scenario - - no support for T.38 This section represents a SIP T.38 call failure because the emitting gateway does not support T.38. Scenario: 1. A SIP INVITE is sent to the called party requesting a voice connection per RFC3261; our scenario involves 1 SIP proxy. An audio connection is established, 2. Upon detection of Preamble by the terminating gateway, a SIP re¡INVITE request is sent to the emitting gateway to modify the parameters of the session to allow a T.38 fax connection. This re- INVITE request contains SDP information detailing T.38 capabilities, 3. The emitting gateway rejects the re¡INVITE with a 415 Unsupported Media Type response. 4. Upon reception of the reject, the call is terminated. 6.1.1. Sequence Diagram The messages F1 to F12 are identical to section 5.2. J-F. Mule/J. Li 42 SIP T.38 Call Flows February 2003 IFT UA Proxy IFTGW UA | | | | F1 INVITE | | |------------------->| | | | F2 INVITE | | |------------------->| | F3 100 Trying | | |<-------------------| F4 100 Trying | | |<-------------------| | | | | | F5 180 Ringing | | F6 180 Ringing |<-------------------| |<-------------------| | | | F7 200 OK | | F8 200 OK |<-------------------| |<-------------------| | | F9 ACK | | |------------------->| F10 ACK | | ------------------->| | | | Both Way RTP Media Established | Fax |<=======================================>| ------->| | emitted | | | | | | Preamble | | |<--------- | | F11 INVITE | detected | |<-------------------| | F12 INVITE | | |<-------------------| | | | | | F13 415 | | |------------------->| | | | F14 415 | | |------------------->| | | | | | F15 BYE | | |<-------------------| | F16 BYE | | |<-------------------| | | | | | F17 200 OK | | |------------------->| | | | F18 200 OK | | |------------------->| 6.1.2. Message Details Messages F1 to F12 are identical to section 5.2; refer to 5.2. F13 415 Unsupported Media Type IFT UA -> PROXY J-F. Mule/J. Li 43 SIP T.38 Call Flows February 2003 SIP/2.0 415 Unsupported Media Type Via: SIP/2.0/UDP ift.here.com:5060 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 INVITE Contact: <sip:+1-303-555-1111@ift.here.com> Content-Length: 0 F14 415 Unsupported Media Type PROXY -> IFTGW UA SIP/2.0 415 Unsupported Media Type Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=2d010.1 Via: SIP/2.0/UDP ift.here.com:5060 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 INVITE Contact: <sip:+1-303-555-1111@ift.here.com> Content-Length: 0 F15 BYE IFTGW UA -> PROXY BYE sip:+1-650-555-2222@obelix.banyuls.com SIP/2.0 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 70 Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde34 Call-ID: 1717@ift.here.com CSeq: 19 BYE Content-Length: 0 F16 BYE PROXY -> IFT UA BYE sip:+1-650-555-2222@obelix.banyuls.com SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=2d010.1 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde34 Call-ID: 1717@ift.here.com CSeq: 19 BYE Content-Length: 0 J-F. Mule/J. Li 44 SIP T.38 Call Flows February 2003 F17 200 OK IFT UA -> PROXY SIP/2.0 200 OK Via: SIP/2.0/UDP ift.here.com:5060 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde34 Call-ID: 1717@ift.here.com CSeq: 19 BYE Content-Type: application/sdp Content-Length: 0 F18 200 OK PROXY -> IFTGW UA SIP/2.0 200 OK Via: SIP/2.0/UDP obelix.banyuls.com:5060 Via: SIP/2.0/UDP ift.here.com:5060 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde34 Call-ID: 1717@ift.here.com CSeq: 19 BYE Content-Type: application/sdp Content-Length: 0 6.2. Unsuccessful T.38 fax scenario - - 488/606 rsp & G.711 fallback This section represents an unsuccessful SIP T.38 fax call: when the emitting gateway does not support T.38 fax relay, it SHOULD respond with either a ææ488 Not Acceptable HereÆÆ response or a ææ606 Not AcceptableÆÆ response to indicate that some aspects of the session description are not acceptable. The terminating gateway SHOULD react by proposing a fallback to G.711 fax pass-through with special codec characteristics - -silence suppression OFF. The message details in this section make use of the generic SDP attribute silenceSupp defined in RFC3108 [10]. Scenario: 1. A SIP INVITE is sent to the called party requesting a voice connection per RFC3261; our scenario involves 1 SIP proxy. An audio connection is established, 2. Upon detection of Preamble by the terminating gateway, a SIP re¡INVITE request is sent to the emitting gateway to modify the parameters of the session to allow a T.38 fax connection. This re- INVITE request contains SDP information detailing T.38 capabilities, 3. The emitting gateway rejects the re-INVITE with a 488 or 606 response. Upon reception of the reject, the terminating gateway proposes to use plain G.711 to carry the fax stream. 4. The call is terminated. J-F. Mule/J. Li 45 SIP T.38 Call Flows February 2003 6.2.1. Sequence Diagram The messages F1 to F12 are identical to section 5.2. IFT UA Proxy IFTGW UA | | | | F1 INVITE | | |------------------->| | | | F2 INVITE | | |------------------->| | F3 100 Trying | | |<-------------------| F4 100 Trying | | |<-------------------| | | | | | F5 180 Ringing | | F6 180 Ringing |<-------------------| |<-------------------| | | | F7 200 OK | | F8 200 OK |<-------------------| |<-------------------| | | F9 ACK | | |------------------->| F10 ACK | | ------------------->| | | | Both Way RTP Media Established | Fax |<=======================================>| ------->| | emitted | | | | | | Preamble | | |<--------- | | F11 INVITE | detected | |<-------------------| | F12 INVITE | | |<-------------------| | | | | | F13 606 | | |------------------->| | | | F14 606 (or 488) | | |------------------->| | | F15 INVITE | | |<-------------------| | F16 INVITE | | |<-------------------| | | F17 200 OK | | |------------------->| | | | F18 200 OK | | |------------------->| | | | | | F19 ACK | | |<-------------------| | F20 ACK | | |<-------------------| | | | J-F. Mule/J. Li 46 SIP T.38 Call Flows February 2003 | G.711 RTP Flow Established | |<=======================================>| | for fax pass-through | | | | F21 BYE | | |------------------->| | | | F22 BYE | | |------------------->| | | | | | F23 200 OK | | |<-------------------| | F24 200 OK | | |<-------------------| | 6.2.2. Message Details Messages F1 to F12 are identical to section 5.2; refer to 5.2. F13 606 Not Acceptable IFT UA -> PROXY SIP/2.0 606 Not Acceptable Via: SIP/2.0/UDP ift.here.com:5060 Warning: 304 Media type not available: One or more media types contained in the session description are not available. From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 INVITE Content-Length: 0 F14 606 Not Acceptable PROXY -> IFTGW UA SIP/2.0 606 Not Acceptable Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=2d010.1 Via: SIP/2.0/UDP ift.here.com:5060 Warning: 304 Media type not available: One or more media types contained in the session description are not available. From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 18 INVITE Content-Length: 0 F15 INVITE IFTGW UA -> PROXY INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 70 Route: <sip:+1-650-555-2222@obelix.banyuls.com; J-F. Mule/J. Li 47 SIP T.38 Call Flows February 2003 maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 19 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Type: application/sdp Content-Length: 181 v=0 o=faxgw1 2890844527 171091 IN IP4 iftgw.there.com s=Session SDP c=IN IP4 iftmg.there.com t=0 0 m=audio 12322 RTP/AVP 0 a=rtpmap:0 PCMU/8000 a=silenceSupp:off - - - - F16 INVITE PROXY -> IFT UA INVITE sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d009.1 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 19 INVITE Contact: <sip:+1-650-555-2222@iftgw.there.com> Content-Type: application/sdp Content-Length: 181 v=0 o=faxgw1 2890844527 171091 IN IP4 iftgw.there.com s=Session SDP c=IN IP4 iftmg.there.com t=0 0 m=audio 12322 RTP/AVP 0 a=rtpmap:0 PCMU/8000 a=silenceSupp:off - - - - F17 200 OK IFT UA -> PROXY SIP/2.0 200 OK Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d008.1 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 J-F. Mule/J. Li 48 SIP T.38 Call Flows February 2003 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 19 INVITE Contact: <sip:+1-303-555-1111@ift.here.com> Content-Type: application/sdp Content-Length: 150 v=0 o=faxgw1 2890844527 2890844528 IN IP4 ift.here.com s=Session SDP c=IN IP4 iftmg.here.com t=0 0 m=audio 3456 RTP/AVP 0 a=rtpmap:0 PCMU/8000 a=silenceSupp:off - - - - F18 200 OK PROXY -> IFTGW UA SIP/2.0 200 OK Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 19 INVITE Contact: <sip:+1-303-555-1111@ift.here.com> Content-Type: application/sdp Content-Length: 150 v=0 o=faxgw1 2890844527 2890844528 IN IP4 ift.here.com s=Session SDP c=IN IP4 iftmg.here.com t=0 0 m=audio 3456 RTP/AVP 0 a=rtpmap:0 PCMU/8000 a=silenceSupp:off - - - - F19 ACK IFTGW UA -> PROXY ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 70 Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 19 ACK Content-Length: 0 J-F. Mule/J. Li 49 SIP T.38 Call Flows February 2003 F20 ACK PROXY -> IFT UA ACK sip:+1-650-555-2222@obelix.banyuls.com;user=phone SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d009.1 Via: SIP/2.0/UDP iftgw.there.com:5060;branch=z9hG4bK2d017.1 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab11 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde17 Call-ID: 1717@ift.here.com CSeq: 19 ACK Content-Length: 0 /* G.711 audio streams established both ways for fax pass through */ F21 BYE IFT UA -> PROXY BYE sip:+1-650-555-2222@obelix.banyuls.com SIP/2.0 Via: SIP/2.0/UDP ift.here.com:5060 Max-Forwards: 70 Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde34 Call-ID: 1717@ift.here.com CSeq: 20 BYE Content-Length: 0 F22 BYE PROXY -> IFTGW UA BYE sip:+1-650-555-2222@obelix.banyuls.com SIP/2.0 Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d009.1 Via: SIP/2.0/UDP ift.here.com:5060 Max-Forwards: 69 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde34 Call-ID: 1717@ift.here.com CSeq: 20 BYE Content-Length: 0 F23 200 OK IFTGW UA -> PROXY SIP/2.0 200 OK Via: SIP/2.0/UDP obelix.banyuls.com:5060; branch=z9hG4bK2d007.1 J-F. Mule/J. Li 50 SIP T.38 Call Flows February 2003 Via: SIP/2.0/UDP ift.here.com:5060 From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde34 Call-ID: 1717@ift.here.com CSeq: 20 BYE Content-Type: application/sdp Content-Length: 0 F24 200 OK PROXY -> IFT UA SIP/2.0 200 OK Via: SIP/2.0/UDP ift.here.com:5060 Record-Route: <sip:+1-650-555-2222@obelix.banyuls.com; maddr=obelix.banyuls.com> From: sip:+1-303-555-1111@ift.here.com;user=phone;tag=ab22 To: sip:+1-650-555-2222@obelix.banyuls.com;user=phone;tag=cde34 Call-ID: 1717@ift.here.com CSeq: 20 BYE Content-Type: application/sdp Content-Length: 0 J-F. Mule/J. Li 51 SIP T.38 Call Flows February 2003 7. SDP Attribute Table for T.38 sessions For a detailed description of these attributes, refer to IANAÆs SDP parameters registration page. The tables below are replicated here for information only. +-----------------------+---------------------+---------------+ | SDP Attribute Name | Appropriate values | Example | | ("att-field") | | | +-----------------------+---------------------+---------------+ | | | | | T38FaxVersion | 1*DIGIT | 0 | | | | | | T38MaxBitRate | 1*(DIGIT) | 14400 | | | | | | T38FaxFillBitRemoval | boolean |true if present| | | | | | T38FaxTranscodingMMR | boolean |true if present| | | | | | T38FaxTranscodingJBIG | boolean |true if present| | | | | | T38FaxRateManagement | localTCF | |transferredTCF | | | transferredTCF | | | | | | | T38FaxMaxBuffer | 1*(DIGIT); optional | 72 | | | | (bytes) | | | | | | T38FaxMaxDatagram | 1*(DIGIT); | Depends on | | | optional | redundancy; | | | | 316 (bytes) | | | | | | T38FaxUdpEC | t38UDPFEC | | T38UDPRedund | | | t38UDPRedundancy | ancy | +-----------------------+---------------------+---------------+ Registered SDP Protocol ææprotoÆÆ for T.38: +-----------------+ | Name | | | +-----------------+ | | | UDPTL | | | | TCP | | | +-----------------+ Registered SDP Protocol ææfmtÆÆ, MIME media type image/t38: Registered Real-time Facsimile (T.38) - image/t38 MIME Sub-type is defined in [11]; MIME media type name: image MIME subtype name: t38 J-F. Mule/J. Li 52 SIP T.38 Call Flows February 2003 8. Considerations In this temporary section, we log the open items for discussion as well as issues that have been solved on the mailing list: 8.1. Level of requirements for Internet gateways --- Status: closed, solved by old draft01 text in section 4.2 Based on the comments received on old draft-00, the authors recommend that: T.38 Internet fax gateways MUST trigger a SIP re- INVITE upon detection of the V.21 Preamble flag sequence on the receiving side. Emitting gateways MAY trigger session modification upon CNG. 8.2. Negotiation of UDP ports for T.38 transmission --- Status: not an issue, just logged here When switching to T.38 mode, Internet fax gateways specify a new set of parameters for the media connection in SDP. Some gateways may choose the UDP/RTP port used in audio mode for UDP/UDPTL/T.38 traffic. Some gateways may choose to open a new UDP port for UDPTL/T.38 fax (and keep the previous UDP/RTP port open for the switch back to audio). SDP provides the mechanism to precisely define in SIP all cases: - if an Internet Fax gateway desires to re-use the UDP/RTP port for UDP/UDPTL/T.38, put 1 ææm=ÆÆ line in the re-INVITE. m=image <original_RTP_port> udptl t38 - if an Internet Fax gateway desires to release the RTP port and open a new UDP port for T.38: m=image <new_UDP_port> udptl t38 - if an Internet Fax gateway desires to keep the RTP port for future use in the session and open a new UDP port for T.38, we need to repeat the RTP/AVP port: m=audio <original_RTP_port> RTP/AVP 0 m=image <new_UDP_port> udptl t38 8.3. Adding a fax stream to SIP session vs. Replacing audio stream --- Status: closed, see flows 5.2 and 5.3 Based on the mailing list discussion, it is recommended in section 5.2 to replace an existing audio media connection with a fax one. We however kept section 5.3 to illustrate what adding a fax stream would entail. 8.4. Adding text to make use of SIP OPTIONS: in progress in draft-02 --- Status: Open for discussion As discussed with Bill Sulzen, the SIP OPTIONS response could be used to assert that real-time fax communications using either T.38 or fax-passthrough are supported. This could certainly improve the negotiation phases and reduce the number of SIP messages. It is also key to get the capabilities of the Internet-aware fax device or gateway other than on a per call basis. What needs to be added: J-F. Mule/J. Li 53 SIP T.38 Call Flows February 2003 - add text in sub-section in section 4.5 - specify how the Accept header line should be populated (do we want to specify t.38 and/or fax pass-through (meaning ability to support silencesuppression), and within t.38, do we want to specify whether it is t.38 over tcp, udptl, both, etc. 8.5. Use of IP addresses in SDP connection information --- Status: Closed, remains unchanged per sipping call flow ID Comment from Christer Holmberg: SDP connection information should use IP addresses instead of domain names (as per draft-ietf-mmusic- sdp-new-03) 8.6. Unsuccessful scenario: 606 or 488 --- Status: Closed Comment from Bill Sulzen: it is acceptable or even preferable to reject with a 488 Not Acceptable Media? Resolution: treat 606 and 488 as equally appropriate. 8.7. SIP re-INVITE or UPDATE? --- Status: open with the following recommendation In most cases, the SIP dialog is established when the codec changes occur so the use of UPDATE is not required. Also the re-INVITE is more standard so we propose to use re-INVITE. 9. Security Considerations This document contains examples of SIP session establishment of particular media types. The security considerations in RFC 3261 [3] apply. There is no known additional security threats because of the nature of the media descriptors exchanged in these call flows. RFC 3261 describes the basic threats including server impersonation, message body tampering, session modifying or teardown, and denial of service and amplification attacks. The use of TLS and the Secure SIP (sips) URI scheme provides a better level of security including two-way authentication. IPsec can also improve security. S/MIME can provide end-to-end confidentiality and integrity protection of message bodies, as described in RFC 3261. 10. References 1 S. Bradner, "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. 2 S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 3 Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and Schooler, E., "SIP: J-F. Mule/J. Li 54 SIP T.38 Call Flows February 2003 Session Initiation Protocol", RFC 3261, June 2002. 4 ITU-T Recommendation T.38, ææProcedures for real-time Group 3 facsimile communication over IP networksÆÆ, June 1998. 5 Johnston, et al, ææSIP Basic Call Flow ExamplesÆÆ, Internet-Draft draft-ietf-sipping-basic-call-flows-01.txt, October 2002. 6 ITU-T Recommendation T.38, ææProcedures for real-time Group 3 facsimile communication over IP networksÆÆ, March 2002. 7 ITU-T Recommendation T.30, ææProcedures for document facsimile transmission in the general switched telephone networkÆÆ, March 1993. 8 M. Handley, V. Jacobson, "SDP: session description protocol", RFC 2327, April 1998. 9 ITU-T Recommendation T.38 Amendment 2 Annex D, ææSIP/SDP Call Establishment ProceduresÆÆ, February 2000. 10 R. Kumar, M. Mostafa, ææConventions for the use of the Session Description Protocol (SDP) for ATM Bearer ConnectionsÆÆ, RFC3108, May 2001. 11 G. Parsons, ææReal-time Facsimile (T.38) - image/t38 MIME Sub-type RegistrationÆÆ, RFC3362, August 2002. 1. Acknowledgments This document would not have been possible without the help of the following development engineers and fax experts, in particular Stanley Khouw, Bill Michalek, and George Maphis of Clarent Corporation. The authors would like to thank Bill Sulzen of Cisco Systems for his continued support and critical comments. We also acknowledge the valuable contributions from Flemming Andreasen of Cisco Systems, Christer Holmberg of Ericsson, and Bert Culpepper of InterVoice- Brite. Many thanks to the reviewers of the previous document for their comments: Jim Renkel of 3COM, Sudipto Mukherjee of Cisco Systems, Arjun Roychowdhury of Hughes Software Systems. 2. Author's Addresses Jieying Li email:jieying.li@ivoxnetworks.com Jean-Francois MuleÆ CableLabs J-F. Mule/J. Li 55 SIP T.38 Call Flows February 2003 400 Centennial Parkway Louisville, CO 80027 USA email: jfm@cablelabs.com ull Copyright Statement "Copyright (C) The Internet Society 2003. All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. cknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. -F. Mule/J. Li 56
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