Page 128 - Asterisk™: The Future of Telephony

Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
Supported: replaces
Content-Type: application/sdp
Content-Length: 265
With the fromuser:

Audio is at 66.135.99.122 port 11700
Adding codec 0x2 (gsm) to SDP
Adding codec 0x4 (ulaw) to SDP
Adding non-codec 0x1 (telephone-event) to SDP
Reliably Transmitting (no NAT) to 10.251.55.100:5060:
INVITE sip:15195915119@10.251.55.100 SIP/2.0
Via: SIP/2.0/UDP 66.135.99.122:5060;branch=z9hG4bK635b0b1b;rport
From: "asterisk" <sip:my_unique_id@66.135.99.122>;tag=as3186c1ba
To: <sip:15195915119@10.251.55.100>
Contact: <sip:my_unique_id@66.135.99.122>
Call-ID: 0c7ad6156f92e70b1fecde903550a12f@66.135.99.122
CSeq: 102 INVITE
User-Agent: Asterisk PBX
Max-Forwards: 70
Date: Fri, 20 Apr 2007 15:00:30 GMT
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
Supported: replaces
Content-Type: application/sdp
Content-Length: 265
The deny and permit statements are used to deny all incoming calls to this peer except
the IP address defined by the permit parameter. This is simply a security measure used
to make sure nothing else matches on this peer except traffic coming from the IP address
we expect.
At the end is insecure=invite, which may be required for your provider. This is because
the source of the INVITE may originate from its backend platform, but could be di-
rected through its SIP proxy server. Basically what this means is that the IP address that
the peer is coming from, and which you are matching on, may not be the IP address
that is in the Contact line: field of the INVITE message when you are accepting a call
from your provider. This tells Asterisk to ignore this inconsistency and to accept the
INVITE anyway.

You may need to set invite=invite,port if the port address is also in-
consistent with what Asterisk is expecting.

Now we need one additional parameter set in the [general] section of our sip.conf file:
register. register is going to tell the service provider where to send calls when it has
a call to deliver to us. This is Asterisk’s way of saying to the service provider, “Hey! If
you’ve got a call for me, send it to me at IP address 10.251.55.100.” The register
parameter takes the following form:

100 | Chapter 4: Initial Configuration of Asterisk