CVOICE- Role of the Call Agent In MGCP

Unanswered Question
Jul 23rd, 2007

There is a Question, which says there are two routers( Residential Gateways) connected to each other thru CALL AGENT across the IP Network so,...........

At what point does the MGCP call agent turn over to the residential gateways the setup of the call path?

A.) After the call agent has been notified that an event has occurred at the source residential gateway.

B.) After the call agent has been notified of an event and has instructed the source residential gateway to create a


C.) The call agent is never out of the call path setup.

D.) After the call agent has sent a connection requests to both the source and destination and has relayed a

modify-connection request to the source so that the source and destination can set up the call path.

E.) After the call agent has forwarded session description protocol information to the destination from the source

and has sent a modify connection to the destination and a create-connection request to the source.

In Testking Correct Answer is "C"

In Actual Test Correct Answer is "D"

If we say that role of the Call Agent is defined till it makes the two endpoints communicate to each other ( what is called as MDCX- modify Connection ).

But what when, at the Conclusion of Call, i.e. one of the endpoints recognizes an On-hook Transition, then in that case again Call Agent has to send the DLCX ( Delete Connection ) to the particular gateway for the termination of the isn't it that CallAgent is never out of the call path setup as per the above explanation.

So am bit confused,what could be the correct answer for this?If So,Why?

I have this problem too.
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wagnerm Mon, 07/30/2007 - 13:15

The call agent's role is to send signaling to the gateways for a call. Plus,

the call agent(CA) has nothing to do with the talk path(RTP stream), this

is the gateway's(GW) job.

For me, the words "turn over to GW the setup of the call path" is the key phrase.

You mentioned DLCX but that is when the call is being deleted and doesn't have

anything to do with the setup. I can also mention the RSIP but that also has

nothing to do with the setup of a call.

1) So the call agent(CA) sends the CRCX to the first gateway(GW) and that GW

answers with a session description.(IP, port, codec)

2) The CA sends a CRCX to the 2nd GW with the session information of the first GW.

3) The CA sends a MDCX back to the first GW. If there is a codec change this

info is sent, if the codec is good, then the MDCX opens up the talk patch

between the two GWs with the parameter M:sendrecv.

(M: = connection Mode)

The setup of the call path is completed and both GWs can talk to each other

via the RTP stream.

The CA has turned over the call path to the GWs but will monitor for any

change of state. You mentioned DLCX but this is after the call path setup.

The CA is never out of the call flow.

RFC 3435 has a complete description of MGCP 1.0


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