Medias Mediatrix 1204, Справочное руководство

Страница: 243 / 390

T.38 Fax Reference Manual (SIP Version)
Mediatrix 1204 217
Mediatrix suggests to use pcma if you are located in Europe and pcmu anywhere else. However,
you should check first which codec is supported in your telephone network.
T.38 Fax
T.38 fax relay is a real-time fax transmission; that is, two fax machines communicating with each other as if
there were a direct phone line between the two. T.38 is called a fax relay, which means that instead of sending
inband fax signals, which implies a loss of signal quality, it sends those fax signals out-of-band in a T.38
payload, so that the remote end can reproduce the signal locally.
The Mediatrix 1204 can send faxes in T.38 mode over UDP or TCP. T.38 is used for fax if both units are T.38
capable; otherwise, transmission in clear channel over G.711 as defined is used (if
G.711 µ-law and/or G.711
A-law are enabled). If no clear channel codecs are enabled and the other endpoint is not T.38 capable, the fax
transmission fails.
The following is a T.38 fax call flow:
Figure 64: T.38 Fax Call Flow
Standards Supported • Based on draft-ietf-sipping-realtimefax-01.txt
• Recommendation ITU T.38 version 0
Caution:
The Mediatrix 1204 opens the T.38 channel only after receiving the “200 OK” message from the
peer. This means that the Mediatrix 1204 cannot receive T.38 packets before receiving the “200 OK”. Based
on RFC 3264, the T.38 channel should be opened as soon as the unit sends the “INVITE” message. See
“Fax Issues” on page 285 for more details.
In the Unit Manager Network Administration Manual , refer to chapter Ports Parameters , section Port
Configuration Window .
INVITE
Ringing/Trying
ACK
INVITE
Trying
ACK
INVITE
[…]
m=audio 5006 RTP/AVP 0 18 4 8 13
a=rtpmap:0 PCMU/8000
a=rtpmap:18 G729/8000
a=rtpmap:4 G723/8000
a=rtpmap:8 PCMA/8000 […]
m=audio 5004 RTP/AVP 0 18 4 8 13
a=rtpmap:0 PCMU/8000
a=rtpmap:18 G729/8000
a=rtpmap:4 G723/8000
a=rtpmap:8 PCMA/8000
User
Agent
#1
User
Agent
#2
Trying
ACK
BYE
200 OK
200 OK
Fax Tone Detected
[…]
m=image 6006 udptl t38
a=T38MaxBitRate:14400
a=T38FaxRateManagement:transferredTCF
a=T38FaxFillBitRemoval:0
a=T38FaxTranscodingMMR:0
a=T38FaxTranscodingJBIG:0
a=T38FaxVersion:0
a=T38FaxUdpEC:t38UDPRedundancy
[…]
m=image 6006 udptl t38
a=T38MaxBitRate:14400
a=T38FaxRateManagement:transferredTCF
a=T38FaxFillBitRemoval:0
a=T38FaxTranscodingMMR:0
a=T38FaxTranscodingJBIG:0
a=T38FaxVersion:0
a=T38FaxUdpEC:t38UDPRedundancy
200 OK
Fax is terminated
[…]
m=audio 5006 RTP/AVP 0 18 4 8 13
a=rtpmap:0 PCMU/8000
a=rtpmap:18 G729/8000
a=rtpmap:4 G723/8000
a=rtpmap:8 PCMA/8000 […]
m=audio 5004 RTP/AVP 0 18 4 8 13
a=rtpmap:0 PCMU/8000
a=rtpmap:18 G729/8000
a=rtpmap:4 G723/8000
a=rtpmap:8 PCMA/8000
200 OK