[Freeswitch-users] t.38 Call Flow Information

[Spencer Thomason]

Hello,
I've been analyzing some Wireshark traces to get a better grasp on the t.38 gateway process.  I'm using t38_gateway to convert SIP t38 to TDM audio on the receiving end.  I'm struggling to understand the following call flow.  I've excluded the audio portion for brevity but t38 is negotiated correctly by both endpoints (FS on our end and Acme on the other).  Note the absence of a DIS message and the PPS prior to CFR.  Can anyone shed any light on this?

Thanks in advance,
Spencer


Acme                                                                                FreeSWITCH
|1716.691635|         INVITE SDP (t38)               |                   |SIP Request
|         |(5060)   <------------------  (5070)   |                   |
|1716.719556|         100 trying -- your call is important to us          |                   |SIP Status
|         |(5060)   ------------------>  (5070)   |                   |
|1716.830431|                   |         no-signal |                   |t38:t30 Ind:no-signal
|         |                   |(21440)  <------------------  (15876)  |
|1716.906132|         200 OK SDP (t38)              |                   |SIP Status
|         |(5060)   ------------------>  (5070)   |                   |
|1716.912839|         ACK       |                   |                   |SIP Request
|         |(5060)   <------------------  (5070)   |                   |
|1716.973011|                   |         no-signal |                   |t38:t30 Ind:no-signal
|         |                   |(21440)  ------------------>  (15876)  |
|1717.450595|                   |         v21-preamble                  |t38:t30 Ind:v21-preamble
|         |                   |(21440)  <------------------  (15876)  |
|1717.730869|                   |         PPS       |                   |t38:v21:HDLC:Partial Page Signal
|         |                   |(21440)  <------------------  (15876)  |
|1717.780811|                   |         no-signal |                   |t38:t30 Ind:no-signal
|         |                   |(21440)  <------------------  (15876)  |
|1718.130798|                   |         v17-14400-long-training          |t38:t30 Ind:v17-14400-long-training
|         |                   |(21440)  <------------------  (15876)  |
|1719.541095|                   |         t4-non-ecm-data:v17-14400          |t38:t4-non-ecm-data:v17-14400 Duration: 1.51s No packet lost
|         |                   |(21440)  <------------------  (15876)  |
|1721.060850|                   |         no-signal |                   |t38:t30 Ind:no-signal
|         |                   |(21440)  <------------------  (15876)  |
|1722.573572|                   |         v21-preamble                  |t38:t30 Ind:v21-preamble
|         |                   |(21440)  ------------------>  (15876)  |
|1723.593652|                   |         CFR       |                   |t38:v21:HDLC:Confirmation To Receive