McDewey

CUBE Third-Party Interoperability Fax Guidelines

Contents Introduction Prerequisites Requirements Components Used Background Information CUBE Fax Call Flows FoIP Transport Methods Fax Pass-Through T.38 Fax Relay CUBE Configuration CUBE Pass-Through Configuration CUBE T.38 Configuration Time-Division Multiplexing (TDM) Gateway Configuration for Interworking with CUBE Verify Troubleshoot SIP T.38 Switchover Fax Pass-Through Switchover H323 T.38 Switchover Fax Pass-Through Switchover Symptom 1: CUBE Rejects ReINVITE with 488 Symptom 2: CUBE Rejects RequestMode with RequestModeReject Vendor Specific Information Verizon Related Information Introduction This document describes how Fax over IP (FoIP) operates in Cisco Unified Border Element (CUBE) call flows with IP Service Providers. Prerequisites Requirements Cisco recommends that you have knowledge of these topics:

CUBE Enterprise G Media Gateway Control Protocol (MGCP) G Session Initiation Protocol (SIP) G H323 Protocol Suite G T30 Signaling G Components Used The information in this document is based on these software and hardware versions: Cisco IOS® Releases 12.4T, 15.0M, 15.0T, 15.1M, 15.1T, 15.2M, 15.2T, 15.3T on Cisco Integrated Services Routers (ISR) Series 2800, 3800, 2900, 3900, 3900e or the Cisco AS5400XM Universal Gateway Note: This configuration example is not limited to the software versions and hardware platforms listed here. The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command. Background Information FoIP with CUBE operates in a multitude of environments and is implemented in order to leverage current VoIP networks for reliable fax services. There are multiple fax protocols that CUBE supports along with a multitude of switchover mechanisms. However, in the context of IP service providers, you must adhere to fax protocols and switchover methods that are supported by vendors outside of Cisco. In FoIP call flows, CUBE is between the Terminating Gateway (TGW) and the Originating Gateway (OGW). From a signaling perspective, the CUBE configuration either permits, or denies, the switchover from a voice call to a fax call. Due to the fact that FoIP protocols are negotiated end-to-end in a VoIP environment, it is essential that everything from the OGW to the TGW are configured in order to use the same FoIP protocol. It is important to know what FoIP flows are supported and what configuration is necessary on CUBE, as well as the TGWs and OGWs, in order to ensure reliable fax communication. CUBE Fax Call Flows

Due to the fact that IP Service Providers typically have a mixed environment of Cisco and non- Cisco equipment, it is essential that you use an industry-standard method in order to switch from a voice call to a fax call. This means that the Named Signaling Event (NSE) cannot be used, since NSEs are Cisco-proprietary. There are exceptions to this rule, but they are extremely infrequent. Note: The inability to use a protocol-based switchover means that Skinny Call Control Protocol (SCCP) is only used in fax call flows to IP Service Providers with G711ulaw and is a "best effort." FoIP Transport Methods This document discusses two FoIP transport methods, Fax Pass-Through and T.38 Fax Relay. Fax Pass-Through Fax Pass-Through is a fax transport method where the T30 signals and page data are transported through the IP network as Pulse-Code Modulation (PCM)-encoded data, wrapped in Real-time Transport Protocol (RTP) frames. The Fax Pass-Through switchover is triggered by the detection of the V.21 Preamble on the TGW. The resultant INVITE (for SIP) or Request Mode (for H323) is sent through the CUBE and the rest of the call signaling path to the OGW. The Fax Pass-Through switchover switches over from any voice codec to the codec defined under the Fax Pass-Through configuration (this process is outlined later in this document). Note: An MGCP gateway cannot be configured in order to initiate upspeed to G.711 for Fax Pass-Through. Therefore, any fax that uses pass-through on the CUBE that terminates to an MGCP gateway must be routed with G.711 codec. Note: Fax Pass-Through should not be configured with H.323 if the initial codec is G.711. This causes a H.245 request mode to be sent to switch to G.711 when G.711 is already negotiated. CUCM responds with a H.245 request mode rejection.

T.38 Fax Relay Fax Relay is a fax transport method where the TGWs and OGWs detect the T30 signals and page data. The gateways take those signals and convert them into relay messages, which are digital representations of the analog signals. Those relay messages are then sent through the IP network.
The T.38 Fax Relay switchover is also triggered by the detection of the V.21 preamble on the TGW. When the TGW operates with SIP, detection of the V.21 preamble triggers a T.38 ReINVITE (similar to what was previously described). G When the TGW operates with H323, detection of the V.21 preamble triggers a T.38 Request Mode. G When the TGW operates with MGCP, detection of the V.21 preamble triggers a notify (NTFY), which is sent to the Call Agent. The Call Agent then responds with a 200 OK, and sends either a Request Mode or a ReINVITE to CUBE, which depends on the VoIP protocol used. G

Debug examples are in the Troubleshoot section of this document. CUBE Configuration CUBE can be configured for FoIP in two places: globally under voice service voip as well as under the dial-peer. Configuration at the dial-peer matched for a given call always takes precedence over the global configuration. Configuration for T.38 and Fax Pass-Through can be configured at the same time if under different dial-peers, so that both protocols are simultaneously supported. CUBE Pass-Through Configuration In order to configure Fax Pass-Through under voice service voip, use this command (in bold): voice service voip no ip address trusted authenticate allow-connections h323 to h323 allow-connections h323 to sip allow-connections sip to h323 allow-connections sip to sip fax protocol pass-through g711ulaw In order to configure Fax Pass-Through at the dial-peer, use this command (in bold): dial-peer voice 1 voip description T38 Test destination-pattern ^1000$ session protocol sipv2 session target ipv4:192.168.0.1 dtmf-relay rtp-nte

fax protocol pass-through g711ulaw no vad Note: Fax Pass-through is not the same as Fax Passthrough. Fax Passthrough leverages Cisco Network Services Engines (NSEs) in order to switch over from a voice call to a fax call. CUBE T.38 Configuration Note: T.38 Version 3 (Super G3 fax speeds) is supported in Cisco IOS Versions 15.1(1)T and later. In order to configure T.38 Version 0 (G3 fax speed) under voice service voip, use this command (in bold): voice service voip no ip address trusted authenticate allow-connections h323 to h323 allow-connections h323 to sip allow-connections sip to h323 allow-connections sip to sip fax protocol t38 version 0 ls-redundancy 0 hs-redundancy 0 fallback none In order to configure T.38 at the dial-peer, use this command (in bold): dial-peer voice 1 voip description T38 Test destination-pattern ^1000$ session protocol sipv2 session target ipv4:192.168.0.1 dtmf-relay rtp-nte fax protocol t38 version 0 ls-redundancy 0 hs-redundancy 0 fallback none no vad In order to configure T.38 Version 3, either under voice service VoIP or at the dial-peer, use this command: fax protocol t38 version 3 ls-redundancy 0 hs-redundancy 0 fallback none If a Media Transfer Protocol (MTP) is used when interworking through a CUBE, it must support codec passthrough. Cisco Unified Communications Manager (CUCM) MTP supports codec passthrough for Version 8.6.1 and later. Cisco IOS MTP must have codec pass-through in the Digital Signal Processor (DSP) Farm configuration: dspfarm profile 2 mtp
codec pass-through codec g729r8 maximum sessions software 50 associate application SCCP Time-Division Multiplexing (TDM) Gateway Configuration for Interworking with CUBE For an SCCP controlled TDM gateway, this configuration is used for Fax Pass-Through.

voice service voip no modem passthrough fax protocol none no fax-relay sg3-to-g3 Note: The codec in the regions setting for this interworking must be G.711. As noted previously, an SCCP gateway cannot be set to use T.38 when interworking with CUBE. In order to configure Fax Pass-Through for SIP and H.323 TDM gateways interworking with CUBE, enter: voice service voip no modem passthrough no fax-relay sg3-to-g3 fax protocol pass-through g711ulaw In order to configure T.38 for SIP and H.323 TDM gateways interworking with CUBE, enter: voice service voip no modem passthrough fax protocol t38 version 0 ls-redundancy 0 hs-redundancy 0 fallback none Note: T.38 Version 3 can be used if it is configured on the CUBE and is supported by the SIP service provider. In order to configure an MGCP TDM gateway for Fax Pass-Through inteworking with CUBE, enter: no mgcp fax-relay sg3-to-g3 no mgcp package fxr-package mgcp fax t38 inhibit no mgcp modem passthrough voip mode nse Note: Since a MGCP gateway does not support upspeeding for Fax Pass-Through, the regions in CUCM between the MGCP gateway and the CUBE must have a codec of G.711. Verify There is currently no verification procedure available for this configuration. Troubleshoot In order to troubleshoot this issue on CUBE, these debugs must be enabled. SIP Enable these debugs for SIP:

no mgcp fax-relay sg3-to-g3 no mgcp package fxr-package mgcp fax t38 inhibit no mgcp modem passthrough voip mode nse After the voice call is set up, the TGW sends a SIP ReINVITE to the OGW through CUBE. If the switchover is successful, the OGW responds with a SIP 200 OK with the correct Session Description Protocol (SDP) parameters. T.38 Switchover INVITE sip:2101@10.0.0.1:5060 SIP/2.0 Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bK171D71 Remote-Party-ID: sip:1101@10.0.0.2;party=calling;screen=no;privacy=off From: sip:8141101@10.0.0.2;tag=8D815D8-646 To: sip:2101@10.0.0.1;tag=DD4D344-21B2 Date: Fri, 25 Feb 2011 19:25:15 GMT Call-ID: 32395B08-403E11E0-818C9D5B-499FBE40@10.0.0.1 Supported: 100rel,timer,resource-priority,replaces,sdp-anat Min-SE: 1800 Cisco-Guid: 786980147-1077809632-2173148507-1235205696 User-Agent: Cisco-SIPGateway/IOS-12.x Allow: INVITE, OPTIONS, BYE, CANCEL, ACK, PRACK, UPDATE, REFER, SUBSCRIBE, NOTIFY, INFO, REGISTER CSeq: 101 INVITE Max-Forwards: 70 Timestamp: 1298661915 Contact: sip:8141101@10.0.0.2:5060 Expires: 180 Allow-Events: telephone-event Content-Type: application/sdp Content-Length: 384 v=0 o=CiscoSystemsSIP-GW-UserAgent 3745 9509 IN IP4 10.0.0.2 s=SIP Call c=IN IP4 10.0.0.2 t=0 0 m=image 17682 udptl t38 c=IN IP4 10.0.0.2 a=T38FaxVersion:0 a=T38MaxBitRate:7200 a=T38FaxFillBitRemoval:0 a=T38FaxTranscodingMMR:0 a=T38FaxTranscodingJBIG:0 a=T38FaxRateManagement:transferredTCF a=T38FaxMaxBuffer:200 a=T38FaxMaxDatagram:180 a=T38FaxUdpEC:t38UDPRedundancy !!NOTE!! Not all of the above bolded fields are required. The above is an example of how Cisco implements T38. SIP/2.0 100 Trying Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bK171D71 From: sip:8141101@10.0.0.2;tag=8D815D8-646 To: sip:2101@10.0.0.1;tag=DD4D344-21B2 Date: Fri, 25 Feb 2011 17:48:05 GMT Call-ID: 32395B08-403E11E0-818C9D5B-499FBE40@10.0.0.1 CSeq: 101 INVITE

Allow-Events: telephone-event Server: Cisco-SIPGateway/IOS-12.x Content-Length: 0 176443: Feb 25 17:48:05.360: //134/2EE85D338187/SIP/Msg/ccsipDisplayMsg: Sent: SIP/2.0 200 OK Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bK171D71 From: sip:8141101@10.0.0.2;tag=8D815D8-646 To: sip:2101@10.0.0.1;tag=DD4D344-21B2 Date: Fri, 25 Feb 2011 17:48:05 GMT Call-ID: 32395B08-403E11E0-818C9D5B-499FBE40@10.0.0.1 CSeq: 101 INVITE Allow: INVITE, OPTIONS, BYE, CANCEL, ACK, PRACK, UPDATE, REFER, SUBSCRIBE, NOTIFY, INFO, REGISTER Allow-Events: telephone-event Remote-Party-ID: sip:2101@10.0.0.1 ;party=called;screen=no;privacy=off Contact: sip:2101@10.0.0.1:5060 Supported: replaces Supported: sdp-anat Server: Cisco-SIPGateway/IOS-12.x Supported: timer Content-Type: application/sdp Content-Length: 384 v=0 o=CiscoSystemsSIP-GW-UserAgent 5552 9399 IN IP4 10.0.0.1 s=SIP Call c=IN IP4 10.0.0.1 t=0 0 m=image 16710 udptl t38 c=IN IP4 10.0.0.1 a=T38FaxVersion:0 a=T38MaxBitRate:7200 a=T38FaxFillBitRemoval:0 a=T38FaxTranscodingMMR:0 a=T38FaxTranscodingJBIG:0 a=T38FaxRateManagement:transferredTCF a=T38FaxMaxBuffer:200 a=T38FaxMaxDatagram:320 a=T38FaxUdpEC:t38UDPRedundancy ACK sip:2101@10.0.0.1:5060 SIP/2.0 Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bK181B79 From: sip:8141101@10.0.0.2;tag=8D815D8-646 To: sip:2101@10.0.0.1;tag=DD4D344-21B2 Date: Fri, 25 Feb 2011 19:25:15 GMT Call-ID: 32395B08-403E11E0-818C9D5B-499FBE40@10.0.0.1 Max-Forwards: 70 CSeq: 101 ACK Allow-Events: telephone-event Content-Length: 0 Fax Pass-Through Switchover INVITE sip:2101@10.0.0.1:5060 SIP/2.0 Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bK154F2 Remote-Party-ID: sip:1101@10.0.0.2;party=calling;screen=no;privacy=off From: sip:8131101@10.0.0.2;tag=8D66B94-7BF To: sip:2101@10.0.0.1;tag=DD32900-5D4 Date: Fri, 25 Feb 2011 19:23:25 GMT

Call-ID: F12F0BBB-403D11E0-81869D5B-499FBE40@10.0.0.1 Supported: 100rel,timer,resource-priority,replaces,sdp-anat Min-SE: 1800 Cisco-Guid: 3990792353-1077744096-2172755291-1235205696 User-Agent: Cisco-SIPGateway/IOS-12.x Allow: INVITE, OPTIONS, BYE, CANCEL, ACK, PRACK, UPDATE, REFER, SUBSCRIBE, NOTIFY, INFO, REGISTER CSeq: 101 INVITE Max-Forwards: 70 Timestamp: 1298661805 Contact: sip:8131101@10.0.0.2:5060 Expires: 180 Allow-Events: telephone-event Content-Type: application/sdp Content-Length: 174 v=0 o=CiscoSystemsSIP-GW-UserAgent 107 1892 IN IP4 10.0.0.2 s=SIP Call c=IN IP4 10.0.0.2 t=0 0 m=audio 16464 RTP/AVP 0 a=rtpmap:0 PCMU/8000 a=silenceSupp:off - - - - SIP/2.0 100 Trying Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bK154F2 From: sip:8131101@10.0.0.2;tag=8D66B94-7BF To: sip:2101@10.0.0.1;tag=DD32900-5D4 Date: Fri, 25 Feb 2011 17:46:16 GMT Call-ID: F12F0BBB-403D11E0-81869D5B-499FBE40@10.0.0.1 CSeq: 101 INVITE Allow-Events: telephone-event Server: Cisco-SIPGateway/IOS-12.x Content-Length: 0 SIP/2.0 200 OK Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bK154F2 From: sip:8131101@10.0.0.2;tag=8D66B94-7BF To: sip:2101@10.0.0.1;tag=DD32900-5D4 Date: Fri, 25 Feb 2011 17:46:16 GMT Call-ID: F12F0BBB-403D11E0-81869D5B-499FBE40@10.0.0.1 CSeq: 101 INVITE Allow: INVITE, OPTIONS, BYE, CANCEL, ACK, PRACK, UPDATE, REFER, SUBSCRIBE, NOTIFY, INFO, REGISTER Allow-Events: telephone-event Remote-Party-ID: sip:2101@10.0.0.1;party=called;screen=no;privacy=off Contact: sip:2101@10.0.0.1:5060 Supported: replaces Supported: sdp-anat Server: Cisco-SIPGateway/IOS-12.x Supported: timer Content-Type: application/sdp Content-Length: 194 v=0 o=CiscoSystemsSIP-GW-UserAgent 4896 2709 IN IP4 10.0.0.1 s=SIP Call c=IN IP4 10.0.0.1 t=0 0 m=audio 19054 RTP/AVP 0 c=IN IP4 10.0.0.1 a=rtpmap:0 PCMU/8000 a=silenceSupp:off - - - -

ACK sip:2101@10.0.0.1:5060 SIP/2.0 Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bK16A56 From: sip:8131101@10.0.0.2;tag=8D66B94-7BF To: sip:2101@10.0.0.1;tag=DD32900-5D4 Date: Fri, 25 Feb 2011 19:23:25 GMT Call-ID: F12F0BBB-403D11E0-81869D5B-499FBE40@10.0.0.1 Max-Forwards: 70 CSeq: 101 ACK Allow-Events: telephone-event Content-Length: 0 H323 Enable these debugs for H323: INVITE sip:2101@10.0.0.1:5060 SIP/2.0 Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bK154F2 Remote-Party-ID: sip:1101@10.0.0.2;party=calling;screen=no;privacy=off From: sip:8131101@10.0.0.2;tag=8D66B94-7BF To: sip:2101@10.0.0.1;tag=DD32900-5D4 Date: Fri, 25 Feb 2011 19:23:25 GMT Call-ID: F12F0BBB-403D11E0-81869D5B-499FBE40@10.0.0.1 Supported: 100rel,timer,resource-priority,replaces,sdp-anat Min-SE: 1800 Cisco-Guid: 3990792353-1077744096-2172755291-1235205696 User-Agent: Cisco-SIPGateway/IOS-12.x Allow: INVITE, OPTIONS, BYE, CANCEL, ACK, PRACK, UPDATE, REFER, SUBSCRIBE, NOTIFY, INFO, REGISTER CSeq: 101 INVITE Max-Forwards: 70 Timestamp: 1298661805 Contact: sip:8131101@10.0.0.2:5060 Expires: 180 Allow-Events: telephone-event Content-Type: application/sdp Content-Length: 174 v=0 o=CiscoSystemsSIP-GW-UserAgent 107 1892 IN IP4 10.0.0.2 s=SIP Call c=IN IP4 10.0.0.2 t=0 0 m=audio 16464 RTP/AVP 0 a=rtpmap:0 PCMU/8000 a=silenceSupp:off - - - - SIP/2.0 100 Trying Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bK154F2 From: sip:8131101@10.0.0.2;tag=8D66B94-7BF To: sip:2101@10.0.0.1;tag=DD32900-5D4 Date: Fri, 25 Feb 2011 17:46:16 GMT Call-ID: F12F0BBB-403D11E0-81869D5B-499FBE40@10.0.0.1 CSeq: 101 INVITE Allow-Events: telephone-event Server: Cisco-SIPGateway/IOS-12.x Content-Length: 0 SIP/2.0 200 OK Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bK154F2 From: sip:8131101@10.0.0.2;tag=8D66B94-7BF To: sip:2101@10.0.0.1;tag=DD32900-5D4

Date: Fri, 25 Feb 2011 17:46:16 GMT Call-ID: F12F0BBB-403D11E0-81869D5B-499FBE40@10.0.0.1 CSeq: 101 INVITE Allow: INVITE, OPTIONS, BYE, CANCEL, ACK, PRACK, UPDATE, REFER, SUBSCRIBE, NOTIFY, INFO, REGISTER Allow-Events: telephone-event Remote-Party-ID: sip:2101@10.0.0.1;party=called;screen=no;privacy=off Contact: sip:2101@10.0.0.1:5060 Supported: replaces Supported: sdp-anat Server: Cisco-SIPGateway/IOS-12.x Supported: timer Content-Type: application/sdp Content-Length: 194 v=0 o=CiscoSystemsSIP-GW-UserAgent 4896 2709 IN IP4 10.0.0.1 s=SIP Call c=IN IP4 10.0.0.1 t=0 0 m=audio 19054 RTP/AVP 0 c=IN IP4 10.0.0.1 a=rtpmap:0 PCMU/8000 a=silenceSupp:off - - - - ACK sip:2101@10.0.0.1:5060 SIP/2.0 Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bK16A56 From: sip:8131101@10.0.0.2;tag=8D66B94-7BF To: sip:2101@10.0.0.1;tag=DD32900-5D4 Date: Fri, 25 Feb 2011 19:23:25 GMT Call-ID: F12F0BBB-403D11E0-81869D5B-499FBE40@10.0.0.1 Max-Forwards: 70 CSeq: 101 ACK Allow-Events: telephone-event Content-Length: 0 After the voice call is set up, the TGW sends a H245 RequestMode to the OGW through CUBE. If the switchover is successful, the OGW responds with a RequestModeAck. T.38 Switchover INVITE sip:2101@10.0.0.1:5060 SIP/2.0 Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bK154F2 Remote-Party-ID: sip:1101@10.0.0.2;party=calling;screen=no;privacy=off From: sip:8131101@10.0.0.2;tag=8D66B94-7BF To: sip:2101@10.0.0.1;tag=DD32900-5D4 Date: Fri, 25 Feb 2011 19:23:25 GMT Call-ID: F12F0BBB-403D11E0-81869D5B-499FBE40@10.0.0.1 Supported: 100rel,timer,resource-priority,replaces,sdp-anat Min-SE: 1800 Cisco-Guid: 3990792353-1077744096-2172755291-1235205696 User-Agent: Cisco-SIPGateway/IOS-12.x Allow: INVITE, OPTIONS, BYE, CANCEL, ACK, PRACK, UPDATE, REFER, SUBSCRIBE, NOTIFY, INFO, REGISTER CSeq: 101 INVITE Max-Forwards: 70 Timestamp: 1298661805 Contact: sip:8131101@10.0.0.2:5060 Expires: 180 Allow-Events: telephone-event Content-Type: application/sdp Content-Length: 174

v=0 o=CiscoSystemsSIP-GW-UserAgent 107 1892 IN IP4 10.0.0.2 s=SIP Call c=IN IP4 10.0.0.2 t=0 0 m=audio 16464 RTP/AVP 0 a=rtpmap:0 PCMU/8000 a=silenceSupp:off - - - - SIP/2.0 100 Trying Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bK154F2 From: sip:8131101@10.0.0.2;tag=8D66B94-7BF To: sip:2101@10.0.0.1;tag=DD32900-5D4 Date: Fri, 25 Feb 2011 17:46:16 GMT Call-ID: F12F0BBB-403D11E0-81869D5B-499FBE40@10.0.0.1 CSeq: 101 INVITE Allow-Events: telephone-event Server: Cisco-SIPGateway/IOS-12.x Content-Length: 0 SIP/2.0 200 OK Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bK154F2 From: sip:8131101@10.0.0.2;tag=8D66B94-7BF To: sip:2101@10.0.0.1;tag=DD32900-5D4 Date: Fri, 25 Feb 2011 17:46:16 GMT Call-ID: F12F0BBB-403D11E0-81869D5B-499FBE40@10.0.0.1 CSeq: 101 INVITE Allow: INVITE, OPTIONS, BYE, CANCEL, ACK, PRACK, UPDATE, REFER, SUBSCRIBE, NOTIFY, INFO, REGISTER Allow-Events: telephone-event Remote-Party-ID: sip:2101@10.0.0.1;party=called;screen=no;privacy=off Contact: sip:2101@10.0.0.1:5060 Supported: replaces Supported: sdp-anat Server: Cisco-SIPGateway/IOS-12.x Supported: timer Content-Type: application/sdp Content-Length: 194 v=0 o=CiscoSystemsSIP-GW-UserAgent 4896 2709 IN IP4 10.0.0.1 s=SIP Call c=IN IP4 10.0.0.1 t=0 0 m=audio 19054 RTP/AVP 0 c=IN IP4 10.0.0.1 a=rtpmap:0 PCMU/8000 a=silenceSupp:off - - - - ACK sip:2101@10.0.0.1:5060 SIP/2.0 Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bK16A56 From: sip:8131101@10.0.0.2;tag=8D66B94-7BF To: sip:2101@10.0.0.1;tag=DD32900-5D4 Date: Fri, 25 Feb 2011 19:23:25 GMT Call-ID: F12F0BBB-403D11E0-81869D5B-499FBE40@10.0.0.1 Max-Forwards: 70 CSeq: 101 ACK Allow-Events: telephone-event Content-Length: 0 Fax Pass-Through Switchover

INVITE sip:2101@10.0.0.1:5060 SIP/2.0 Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bK154F2 Remote-Party-ID: sip:1101@10.0.0.2;party=calling;screen=no;privacy=off From: sip:8131101@10.0.0.2;tag=8D66B94-7BF To: sip:2101@10.0.0.1;tag=DD32900-5D4 Date: Fri, 25 Feb 2011 19:23:25 GMT Call-ID: F12F0BBB-403D11E0-81869D5B-499FBE40@10.0.0.1 Supported: 100rel,timer,resource-priority,replaces,sdp-anat Min-SE: 1800 Cisco-Guid: 3990792353-1077744096-2172755291-1235205696 User-Agent: Cisco-SIPGateway/IOS-12.x Allow: INVITE, OPTIONS, BYE, CANCEL, ACK, PRACK, UPDATE, REFER, SUBSCRIBE, NOTIFY, INFO, REGISTER CSeq: 101 INVITE Max-Forwards: 70 Timestamp: 1298661805 Contact: sip:8131101@10.0.0.2:5060 Expires: 180 Allow-Events: telephone-event Content-Type: application/sdp Content-Length: 174 v=0 o=CiscoSystemsSIP-GW-UserAgent 107 1892 IN IP4 10.0.0.2 s=SIP Call c=IN IP4 10.0.0.2 t=0 0 m=audio 16464 RTP/AVP 0 a=rtpmap:0 PCMU/8000 a=silenceSupp:off - - - - SIP/2.0 100 Trying Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bK154F2 From: sip:8131101@10.0.0.2;tag=8D66B94-7BF To: sip:2101@10.0.0.1;tag=DD32900-5D4 Date: Fri, 25 Feb 2011 17:46:16 GMT Call-ID: F12F0BBB-403D11E0-81869D5B-499FBE40@10.0.0.1 CSeq: 101 INVITE Allow-Events: telephone-event Server: Cisco-SIPGateway/IOS-12.x Content-Length: 0 SIP/2.0 200 OK Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bK154F2 From: sip:8131101@10.0.0.2;tag=8D66B94-7BF To: sip:2101@10.0.0.1;tag=DD32900-5D4 Date: Fri, 25 Feb 2011 17:46:16 GMT Call-ID: F12F0BBB-403D11E0-81869D5B-499FBE40@10.0.0.1 CSeq: 101 INVITE Allow: INVITE, OPTIONS, BYE, CANCEL, ACK, PRACK, UPDATE, REFER, SUBSCRIBE, NOTIFY, INFO, REGISTER Allow-Events: telephone-event Remote-Party-ID: sip:2101@10.0.0.1;party=called;screen=no;privacy=off Contact: sip:2101@10.0.0.1:5060 Supported: replaces Supported: sdp-anat Server: Cisco-SIPGateway/IOS-12.x Supported: timer Content-Type: application/sdp Content-Length: 194 v=0 o=CiscoSystemsSIP-GW-UserAgent 4896 2709 IN IP4 10.0.0.1 s=SIP Call

c=IN IP4 10.0.0.1 t=0 0 m=audio 19054 RTP/AVP 0 c=IN IP4 10.0.0.1 a=rtpmap:0 PCMU/8000 a=silenceSupp:off - - - - ACK sip:2101@10.0.0.1:5060 SIP/2.0 Via: SIP/2.0/UDP 10.0.0.2:5060;branch=z9hG4bK16A56 From: sip:8131101@10.0.0.2;tag=8D66B94-7BF To: sip:2101@10.0.0.1;tag=DD32900-5D4 Date: Fri, 25 Feb 2011 19:23:25 GMT Call-ID: F12F0BBB-403D11E0-81869D5B-499FBE40@10.0.0.1 Max-Forwards: 70 CSeq: 101 ACK Allow-Events: telephone-event Content-Length: 0 Symptom 1: CUBE Rejects ReINVITE with 488 If you encounter this problem, complete these steps: Enable debugs and collect for a test call. 1. Verify that T.38 or Fax Pass-Through is configured globally. 2. If T.38 or Fax Pass-Through is not configured globally, ensure that T.38 or Fax Pass- Through is configured under both the incoming and outgoing dial-peers based on the Call Control Application Programming Interface (CCAPI) debugs. 3. If the problem is still not resolved, enable debug ccsip all (in a logging buffer with logging buffered 5000000 debug) in order to determine why SIP rejects this ReINVITE. 4. Symptom 2: CUBE Rejects RequestMode with RequestModeReject If you encounter this problem, complete these steps: Enable debugs and collect for a test call. 1. Verify that T.38 or Fax Pass-Through is configured globally. 2. If T.38 or Fax Pass-Through is not configured globally, ensure that T.38 or Fax Pass- Through is configured under both the incoming and outgoing dial-peers based on the CCAPI debugs. 3. If the problem is still not resolved, enable debug h225 events, debug h225 q931, and debug h245 events in order to determine why H323 rejects this RequestMode. 4. Vendor Specific Information Verizon The Cisco Technical Assistance Center (TAC) has noticed that, although Verizon claims support for T.38 over SIP, they never initiate a switchover from a voice call to T.38 when they operate at the TGW. G This is a known limitation in their environment, and it does not appear that they are going to fix it. G When the OGW is a FoIP server, you can usually set the server to initiate a switchover even G

when it is the OGW. When a Cisco GW is the OGW, there is currently no way to force the switchover when the Cisco GW acts as the OGW. G Cisco bug ID CSCud72998 is the enhancement request to support the T.38 switchover when the Cisco GW is the OGW. G Related Information Configuring Fax Pass-Through G Configuring T.38 Fax Relay G Understanding Inbound and Outbound Dial-peer Matching on IOS Platforms G Technical Support & Documentation - Cisco Systems G