----------------------
SDP in initial INVITE:
----------------------
v=0.
o=- 0 270673746 IN IP4 xxx.xxx.xxx.xxx.
s=IMSS.
c=IN IP4 xxx.xxx.xxx.xxx.
t=0 0.
m=audio 10360 RTP/AVP 8 101 18 106.
a=rtpmap:101 G726-32/8000.
a=rtpmap:106 telephone-event/8000.
a=sendrecv.
a=ptime:20.

-------------------------------
SDP in 200 OK from Asterisk 11:
-------------------------------
v=0.
o=root 422714547 422714547 IN IP4 xxx.xxx.xxx.xxx.
s=Asterisk PBX 11.5.1.
c=IN IP4 xxx.xxx.xxx.xxx.
t=0 0.
m=audio 15366 RTP/AVP 8 101 101.
a=rtpmap:8 PCMA/8000.
a=rtpmap:101 G726-32/8000.
a=rtpmap:101 telephone-event/8000.
a=fmtp:101 0-16.
a=ptime:20.
a=sendrecv.