Presence and IntComm WG

Hi all .
I have some questions about sipc.
1. Whether sipc supports a incoming request( i.e INVITE) without SDP?
In rfc 3261, it allows an offer in 200 OK and answer in ACK.

2. When an incoming INIVITE's SDP indicates  a multicast media, 
maybe like this:
 "m=audio 31616 RTP/AVP 0
  c=IN IP4 239.255.233.245/15"
sipc generates an successful reponse including such part:
 "c=IN IP4 10.10.136.128
 t=0 0
 m=audio 31616 RTP/AVP 0"
 I want to know whether "c=IN IP4 10.10.136.128" is correct , why sipc 
doesn't use  the multicast address ,i.e "c=IN IP4 239.255.233.245/15" .

Thanks for your help.