This post is to list common issues Brooktrout customers may encounter and how to alleviate them.

1. Using a Comma in a SIP call

- The SIP protocol does not allow commas to appear in a dialstring. Commas are restricted characters.
- The SR140 will report an error a comma appears in the SIP dialstring and the call will not go out.
- Note that SIP is out-of-band signaling and there is no such thing as a pause.
- If an application wants to pass in-band DTMF, possibly for a “long distance access code”, it should use the SR140’s post-dial feature.
  -- The ampersand symbol (&) is used for this feature. (e.g. 7814339600@10.20.30.40&12345)
2. SR140 rejects gateway’s T.38 re-INVITE
- When the SR140 is set for G.711 Fallback (t38_first in callctrl.cfg), if the T.38 re-INVITE arrives too late, the SR140 will reject it with a SIP 488 Not Acceptable Here message and remain in G.711 mode. Some gateways will hang up the call at this point instead.
- media_passthrough_timeout_outbound controls the amount of time the SR140 waits for the re-INVITE. This may need to be extended if the re-INVITE takes longer than expected.
3. Firewall issues
- Firewalls can block either call control (SIP/H.323) or media (T.38/RTP) packets.
- Calls and fax messages appear in debug log/ECC log but not in a Wireshark trace or vice versa
- By default, SR140 uses port 5060 for SIP, 1728 for H.323, and 56000-56999 for media. The firewall should allow these ports.
4. T4 timer issues
- When a fax device sends a command, e.g. MPS, EOP, it waits for a response. The wait time is defines as the fax T4 timer.
- If no response arrives within the T4 timer, the message is re-sent up to 3 times.
- Delays in receiving responses can cause them not to be seen if the sender is already re-sending its command.
- The T4 timer can be increased with the t4_xmit_timer parameter in btcall.cfg. Can be set up to 15000 ms.
  -- Note this cannot be set from Configtool