Subject: Usage of sendrecv, sendonly, recvonly for separate port numbers for sending and receving media

From: [email-masked]
Date: Fri, 14 Dec 2001 09:45:56 -0600

Previous bis drafts had a section on SDP usage. While this has been removed
from bis-05, lot of us still refer to that section to clear some issues.
Howver, there is one conflicting issue that I wanted the SIP/SDP gurus to
comment on.
Bis-03 states that no assumption should be made about the source address
and port number of RTP/RTCP sender. The parameters sendrecv, recvonly,
sendonly are not meant to indicate the source address and port. While the
SDP RFC 2327 states just the opposite.

My question is: "If I want to send media from a separate port and receive
media on a different port, but use the same codec, do I put my SDP
parameters as
1) "sendrecv" or
2) Two separate with different "sendonly" and "recvonly" parameters.

Excerpt from bis-03

Section B.2.1 : The IP address and port present in the offer indicate
nothing about the source IP address and source port of RTP and RTCP packets
that will
   be sent by the offerer.

Excerpt from SDP RFC 2327

Page 24: a=sendonly
       This specifies that the tools should be started in send-only
       mode.  An example may be where a different unicast address is to
       be used for a traffic destination than for a traffic source. In
       such a case, two media descriptions may be use, one sendonly and
       one recvonly.

Thanks for your help with clarification,

Anoop