cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
683
Views
0
Helpful
1
Replies

T.38 to SIP

dvanzee
Level 2
Level 2

Does anyone know if SIP supports T.38 faxing?

1 Reply 1

vmoopeung
Level 5
Level 5

SIP T.38 Fax Relay

"The transport protocols specified in the ITU-T recommendation for T.38 are Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). However, for T.38 fax relay on Cisco gateways, only UDP is supported for the transport layer.

"If SIP T.38 fax relay is not supported by both gateways, the T.38 negotiation fails and the call reverts to an audio codec.

"T.38 fax relay requires a 64-kbps transmission rate, the same amount of bandwidth as a voice call with the G.711 codec.

"Fax Calling Tones (CNG) are optional and are not used to initiate a switch to T.38 mode. Instead, Called Station Identifier (CED) tones or preamble flags are used.

"SIP fax relay does not rely on NSEs to signal a switch to T.38 mode. Standard RFC 2543 and RFC 2327 SIP and SDP signaling are used instead.

"If the fax rate disable command is configured on a dial peer, neither the originating nor the terminating gateway can enter into Cisco fax relay mode, T.38 fax relay mode, or fax pass-through mode. The fax rate disable command disables fax transfer support.

http://www.cisco.com/en/US/docs/ios/12_3/vvf_c/cisco_ios_fax_services_over_ip_application_guide/t38.html#wp1158490

Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: