[asterisk-users] Odd DTMF problem when receiving calls

[Christopher David Howie]

Hello,

I've been tinkering with Asterisk today for the fun of it, trying to set
up my own domain.  I've got pretty much everything working, including a
DID number that connects to my extension.

However, I'm having a problem receiving calls from a particular peer,
specifically my office's PBX, which allows dialing directly via SIP.
(So, just to clarify, the DID number is not involved in this problematic
scenario.)

The symptom is that my office PBX demands rfc2833 support, and will
immediately disconnect a call if the callee doesn't support it.  I've
tried resolving this a number of ways and the only way that actually
works is to create a peer definition in sip.conf for my office's
external SIP IP address.  Then calls from my office to my Asterisk
service work with no problems.

However, the peer section is bare:

[corp]
type=peer
host=corp.example.ip
port=5060
context=default

That's it.  That solves the problem.  Copying *every setting* in
[global] has no effect.  In other words, how I configure the peer
doesn't appear to matter very much, only that it has a specific
configuration at all.  This makes no sense to me.

I've attached sanitized SIP debug output, with the following replacements:

* corp.example.com and corp.example.ip refer to the SIP PBX at my
company.  (corp.example.com may refer to either the IP or the domain
name, due to an oversight while I was sanitizing.  This should not be
significant.  corp.example.ip always refers to the IP.)

* asterisk.tld refers to the domain name for my Asterisk install.

* asterisk.ip refers to the IP address my Asterisk install binds to
(public and static).

* NUMBER is my phone number at the company.

* phone.nated.ip refers to the public, NATed IP address of the softphone
that is registered with Asterisk for my account.

* phone.private.ip refers to the private IP address of the softphone.
Note that I have nat=yes and directmedia=no for this device in sip.conf,
and calls from my DID number work as well as calls to sip:echo at iptel.org.

Looking at the SDP negotiation, and at the telephone-event capability in
particular, here is what I see happening:

1. Asterisk advertises telephone-event to my softphone.
2. My softphone advertises telephone-event to Asterisk.
3. Asterisk does not offer telephone-event to the company PBX.
4. The company PBX offers telephone-event to Asterisk.

After the ACK represented by step 4, the company PBX immediately issues
a BYE to Asterisk.

If the company PBX has a peer defined in my Asterisk sip.conf file,
Asterisk does offer telephone-event to the company PBX in step 3.

I've been up and down this issue for a few hours and I cannot for the
life of me determine why simply defining a peer causes Asterisk to offer
telephone-event.  I have tried specifying dtmfmode=rfc2833 or
dtmfmode=auto in [global] and neither change has any effect.  As I said
above, I've copied every configuration directive in [global] into the
peer definition for the company PBX, and calls still work.

So I'm at a loss to explain this.  The problem does not seem to stem
from my configuration, but I'm not entirely sure what else could be the
problem... an Asterisk bug perhaps?  I don't want to jump to that
conclusion since this is my first day tinkering with the software.
Perhaps someone more knowledgeable can steer me in the right direction?

Thanks,

-- 
Chris Howie
http://www.chrishowie.com
http://en.wikipedia.org/wiki/User:Crazycomputers

If you correspond with me on a regular basis, please read this document:
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