Subject: Why replicate parameters in SDP and the MGCP LCO?

From: Rajesh Kumar <[email-masked]>
Date: Tue, 10 Oct 2000 17:31:58 -0700

Mahamood,

Sorry for the late response. I have returned from a trip.
 
>      Could you please clafiry a doubt regarding ATM extensions/ SDP for
>MGCP?
>
>1. We have ATM paramaters appearing in the SDP draft authored by you.
>2. We have ATM parameters appearing in the local connection options. The draft
is available at ISC

When you wrote this, an obsolete ATM packagew as there on the ISC site. The
only valid local connection option and ATM package is now there on the ISC
site. It is  lled draft-mgcp-atm-package-00.txt. It contains the Local
Connection options and the package (i.e. the events). 

>3. We have ATM extension packages for MGCP.

THis is not separate. The only valid one is draft-mgcp-atm-package-00.txt on
the ISC site. Any other MGCP ATM documents on the ISC site are obsolete. If you
will pinpoint them to me, I will have them removed.

>
>To my knowledge, each of these completely specify the ATM parameters that 
>may be
>required by the underlying transport layer. Could you tell me why we need
>the same parameters represented and repeated in all three places?

Yes, there is duplication in the MGCP-ATM extensions and the SDP-ATM
extensions. Reasons: 
    *  Often the same information needs to be repeated as when the call agent
    sends a local connection option and the gateway sends back the same or a
    subset. THis is true even in standard rfc2705 MGCP e.g. for the codec. 
    * Some applications might have the call agent dictating these
parameters via
    MGCP, while others might have the gateways negotiating them through SDP. 
    * In the h.248/Megaco case, there are no local connection options. The call
    agent sets these parameters through SDP, while the gateway responds through
    SDP. So for the Megaco case at least, you need to represent all the
    parameters in SDP. 
    * In the MGCP case, you cannot assume that the call agent will behave the
    same way as in the Megaco case and convey parameters through SDP. Quite a
    few call agents do not even look at the SDP, therefore you need to
    replicate these parameters as MGCP local connection options. 
I hope this is clear. In the final analysis, we have to replicate parameters in
the MGCP local connection options and SDP. This is one of the weak points of
MGCP which h.248/Megaco rectifies.

Rajesh
>Thanx & regards,
>Mahamood

- Rajesh Kumar
        
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