Subject: some discrepancies.........

From: "rahul pande" <[email-masked]>
Date: Wed, 27 Sep 2000 18:54:22 IST

hello Sir,

In MGCP ::
  under the heading "Encoding of the session description" its stated :

   "The session description is encoded in conformance with the session
    description protocol, SDP. MGCP implementations are expected to be
    fully capable of parsing any conformant SDP message, and should send
    session descriptions that strictly conform to the SDP standard."

Sir, In MGCP under the topic "Usage of SDP in a network access service"
a new <media> attribute is defined i.e. "nas/XXXX" where as in SDP the 
syntax for <media> is ::

   IN SDP----> <media> = 1*(alpha-numeric)
                        ;typically "audio", "video", "application"
                        ;or "data"
  It won't accept the char '/'.

In an example in MGCP ::
                        v=0
                        m=nas/radius *****pay a note here*******
                        c=IN IP4 radius.example.net
                        a=bearer:v.34
                        a=framing:ppp-asynch
                        a=dialed:18001234567
                        a=called:12345678901
                        a=dialing:12340567890

In SDP the "m=" attribute syntax is as follows ::
"m=" media space port ["/" integer] space proto 1*(space fmt) CRLF

Here all the fields are mandatory and so port and other things cannot be 
left out.

These are few of the discrepancies i found in MGCP b'cause of which old sdp 
implementations won't work with MGCP. Its easy to add new attributes but 
would be difficult to change the grammar that is already existing.

In "Megaco" also is saying that you can skip "s=", "t=", "o=" lines in sdp 
message but an RFC2327 conformant SDP would definitely issue an error and 
would reject the message.

Please comment on the above and let me know how old sdps can handle the new 
definitions.
    Thanking you,
      rahul

"When text encoding the protocol, the descriptors consist of session
   descriptions as defined in SDP (RFC2327).  In session descriptions
   sent from the MGC to the MG, the following exceptions to the syntax
   of RFC 2327 are allowed:

    * the "s=", "t=" and "o=" lines are optional"

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---

From: Flemming Andreasen <[email-masked]>
Date: Wed, 27 Sep 2000 19:07:05 -0400

The MGCP part should probably rather be posted to [email-masked]

With that being said, let's just say that NAS was not the best specified part
of RFC 2705.  We are currently working on an updated version of 2705 (and yes,
all usage of SDP in MGCP must be RFC 2327 compliant).

-- Flemming

--
Flemming Andreasen
Cisco Systems