Ok, like I stated before if you have only a-law (8) or mu-law (0) set then the output you see in the 200ok SDP is correct:
v=0
o=Dialogic_SIP_CCLIB 0 1 IN IP4 172.18.180.10
s=Dialogic_SIP_CCLIB
i=session information
c=IN IP4 172.18.180.10
t=0 0
m=audio 49152 RTP/AVP 8
a=ptime:20
There will not be a= line as per specification as its stated in the 8 (for a-law) only needs to be present in the m= line.
Jeff