1. i3 forum Fax over IP: achieving an industry solution Jerzy Sołdrowski Network Architect Telekomunikacja Polska S.A. i3 forum Technical Workshop Warsaw, 15–16 June, 2010

2. Objective of FoIP activity To make real time FoIP a viable alternative to TDM fax in IP-carrier networks Problems with fax over IP are observed by carriers and service providers all over the world. When voice over IP connections are usually set up and performed without problems, fax connections set up often fails or prematurely disconnected. In September 2009 i3 Forum started FoIP activity. The objectives are: Identify the reasons of FoIP poor performance Find appropriate remedies Issue the guidelines for carriers to establish reliable FoIP connections As most regulation authorities assume that fax is an indispensable part of Universal Services, the problems with its migration to IP may block whole migration of voice services to IP.

3. Surveys and their results # 1 Setup of voice connection Fax discrimination Voice to fax transition Capabilities negotiation Facsimile message transmission Post message procedure Call disconnection T.38, V.150.1 T.30 T.4 T.30 Fault rate Faults per connection chain section  Most often between gateways, then between gateway and terminal  Incoming from Third Party VoIP Networks  Less faults when incoming from TDM network Most often declared reasons:  Wrong implementation of SIP and H.248 (Error codes, user=phone)  Ambiguity of T.38 – different implementations e.g. fax call parameters, echo cancellers  Terminal – gateway incompatibility  Proprietary fax encoding methods  SG3 unstable or not supported

4. Standardization situation ITU-T.38 April 2007 June 1998 Sept. 2005 April 2004 March 2002 July 2010 78 p. Consolidation 1 Amendment, Addition of Vendor ID in SIP/SDP call setup Consolidation 1 Amendment, Addition of Vendor ID in SIP/SDP call setup 122 p. 125 p. 3 2 p. Consolidation 129 p. Revised SIP/SDP O/A [SDPCapNeg and MediaCapNeg], New parameter: T38ModemType, Signalled and provisioned T.38 protocol parameters (Annex H) 153 p. 3 Amendments 1. Half duplex V.34, V.150.1 Internetworking Annex F, Autonomous switchover 2. RTP encapsulation 3. Implementation guidelines 3 Amendments 1. Half duplex V.34, V.150.1 Internetworking Annex F, Autonomous switchover 2. RTP encapsulation 3. Implementation guidelines Consolidation 4 Amendments 1. H.323 setup. 2 SIP/SDP H.248 setup 3. IAF, TPKT 4. Improvements 4 Amendments 1. H.323 setup. 2 SIP/SDP H.248 setup 3. IAF, TPKT 4. Improvements *

5. Surveys and their results # 2 2002 1998 What can be neglected in this phase Cisco protocol and switchover Encryption – so far rarely used What is not possible SSE switchover – no Annex F T.38 Modem relay – V.150.1 not implemented.

6. Conclusions FoIP guidelines Only T.38 version 1998 can be used – lower common denominator What can improve interoperability Implement automatic speedup on fax tones - V.152 not implemented Implement G.711 without VAD/DTX Always declare RFC 2833 payload for VoIP call setup – fax tones transport Implement SG3 to G3 fallback procedure ECM to be negotiated by terminals General prerequisites Detailed technical guidelines Testing recommendations Target technical guidelines Testing recommendations I3 forum guidelines Surveys Valid standards SIP Forum New T.38 version, SDP extension Other standards, SIP Forum

7. Interoperability problems solutions PSTN VoIP GW-B Fax G3/SG3 VoIP GW-A PSTN Fax G3/SG3 ATA Fax G3/SG3 VoIP GW-A T.30FoIPT.30 Voice Call: Codec + RFC 2833 Auto speedup (G.711) CNG CED V.21 Re_INVITE (T.38) Switchover to T.38 ANSam CI CM block Fax SG3 V.21 Re_INVITE (T.38) Re- INVITE G.711 ? 415 Unsupported Media

8. Timing problems – SIP Forum investigation Examples: 1. Delay between the off-ramp/receiving gateway's 200OK to initial INVITE and the subsequent re-INVITE to T.38. When there are several TDM-network segments in a fax call the cumulative delay can exceed the T.4 (3 sec. +-15%) timer defined in T.30 for endpoint terminal. In this case the collision between repeated signals from the calling and called terminals can appear and a call will be disconnected.. 2. Suppression of audio during T.38 switchover When a Receiving Gateway sending T.38 re-INVITE will not suppress the audio stream fast enough the terminals will attempt to negotiate a T.30 session over the audio stream while the T.38 session is being established in the signalling path. If negotiation over voice path progress too far the switchover to T.38 is no more possible and the call will fail. Conclusions Delays can change and the faults may appear or not – identification problem Some faults may appear as a result of several causes coincidence T.30 and T.38 protocols are complex. Theoretical study must be complemented by practical verification in real, lossy networks

9. Next planned activities Target Guidelines with new standard version. T.38 version July/2010 draft-ietf-mmusic-sdp-capability-negotiation-13.txt draft-ietf-mmusic-sdp-media-capabilities-09.txt ITU-T V.152 “Amendment Annex B – Use of data signal detection and silence insertion in voiceband data, Annex C - Use of V.21 preamble for echo canceller control in a V.152 gateway”. 03/2009 draft-ietf-avt-dtls-srtp-07.txt. Verification tests list Equipment and network tests (also call flows, SIP O/A) Testing with SIP Forum.. Identification of interoperability problems and solution verification. Investigation of time dependencies problems – timer expire etc. Delay distribution measurement in tandem networks. Determination of an impact of different parameters on successful fax connection rate FoIP problems repository „ Knowledge database” gathering the description of known problems and solutions

10.  BACK-UP

11. Version Number Version Dependent Content Summary Original Documentation 01998 ASN.1 SyntaxInitial Publication (1998), Amendment 1 (1999), Amendment 2 (02/00) 11998 ASN.1 Syntax, TPKT, IAF support Amendment 3 (11/00) Note: Some early implementations supporting TPKT indicate version 0. 22002 ASN.1 SyntaxUpdated Recommendation (2002) 3V.34, V.33 support, 2002 Syntax extended 4Defined Defaults for negotiated parameters in Annex D. Draft T.38 version number (Amendment 1 (2003) * T38FaxVersion

12. I3 Forum guidelines for existing networks Assumptions: T.38 standard version implemented is Edition 1 from June 1998. Initially Fax call is always set up as voice call. Autonomous transitioning method is not used - it is defined in the next T.38 version. Cisco proprietary NSE* switchover method is not taken into consideration. CED CNG CED CNG Auto switch to VBD Auto Switch to VBD Service Provider A Service Provider B Carrier ACarrier B G3 Fax Border GWIngress SBCEgress SBC Ingress SBC Egress SBC Border GWG3 Fax Gateways in VBD mode

13. I3 Forum guidelines for existing networks Service Provider A Service Provider B Carrier ACarrier B Call in T.38 mode INVITE (T.38) ACK V.21 preamble 200 OK ACK G3 Fax Border GWIngress SBCEgress SBC Ingress SBC Egress SBC Border GWG3 Fax INVITE (T.38) Mute voice channel Service Provider A Carrier A Carrier B Call in VBD mode INVITE (T.38) ACK V.21 preamble 200 OK ACK G3 Fax Border GWIngress SBCEgress SBC Ingress SBC Egress SBC Border GWG3 Fax INVITE (T.38) Mute voice channel 415 INVITE G.711 Voice enable INVITE G.711 Service Provider B