Subject: Number of LocalConnectionOptions in CRCX

From: Gordon Cutts <[email-masked]>
Date: Thu, 2 Dec 1999 15:14:14 -0500

To whoever can help,

As I have yet to send a question concerning MGCP, I hope I have chosen the
correct area.  My apologies if I have made a mistake.

During some of our interop testing I came across an interesting "grey area"
in the RFC draft-huitema-mgcp-v0r1-05.txt.  Here is the scenario:  The Call
Agent (CA) has already performed an AUEP for LocalConnecitonOptions on our
gateway to which we reply with two "L" parameter lines since the CODEC
packetization property is unique to each.  For example:

200 3 OK
L: a:PCMU;PCMA, p:20, m:sendonly;recvonly;sendrecv;inactive;netwloop, nt:IN
L: a:G723, p:30, m:sendonly;recvonly;sendrecv;inactive;netwloop, nt:IN

Later in the call flow when the CA sends the initial CRCX to our gateway it
provides multiple "L" parameter lines as well, such as:

CRCX 20 here/[email-masked] MGCP 0.1
C: 2f
M: inactive
X: 16
R: hu,hf
L: a:pcmu,p:20
L: a:G723,p:30

The two "L" lines is what is causing the problem.  The reason they are
sending two lines is because they don't want to send a single line and run
into the problem of giving a range for the packetization period where one
gateway can have a different incremental value than the other, i.e.
packetization of 5, 10, 20 vs. 10, 20, 30.  From what I can found in the
spec (2.3.4.  CreateConnection, p.38)

        *    It may state exactly one value, which the gateway will then use
for
     the connection,

        *    It may provide a loose specification, such as a list of allowed
     encoding methods or a range of packetization periods,

        *    It may simply provide a bandwidth indication, leaving the
choice of
     encoding method and packetization period to the gateway.

it is my understanding that the CA only provides one "L" parameter line in
its CRCX (and MDCX).  Since the CA is the one who is supposed to have the
brains and the gateways are "dumb" I believe that the CA should either tell
us specifically what we should use, or give us a general idea of what to use
(based upon matching properties with the remote gateway) from which we can
make a decision based upon priority.

Any help in this area would be greatly appreciated, and promptness would be
REALLY appreciated as time is of great importance.

Thanks to all for your time and effort.

Sincerely,

Gordon Cutts