Subject: [Megaco] Responding to COT (ct/rsp)

From: "Ron Gilaad" <[email-masked]>
Date: Sun, 3 Jun 2007 14:41:03 +0300

Hi all,

According to H.248: Upon reception of a command with the rsp Signal, the
MG either applies a loopback or (for 2-wire circuits) awaits reception
of a continuity
test tone.
According to Megaco/H.248 Call flow examples draft (page 122):
http://tools.ietf.org/html/draft-ietf-megaco-callflows-04, There can be
two possible cases for responding to the continuity test originated from
the PSTN network. In the first case the Trunking Gateway generates a
signal whose frequency is different from the frequency of the received
signal and in the second case it loops back the received signal to the
switch that originated it. In this example we assume the case of
Loopback. The mode of the termination is also set to loopback to
facilitate this. Here is the example from the draft:
MGC to TGW: MEGACO/1 [216.33.33.61 <> ]: 27000 Transaction = 1234 {
Context = '-' { Modify = Trunk1/line1 {Media { TerminationState
{ServiceState = test} LocalControl { mode = loopback} } Signals = {
ct/rsp } } } } 
My questions is: How shall the MG react when receiving the ct/rsp
signal? H.248 assumes that for 4 wires circuits the MG shall apply a
loopback and there are no other choices. The draft, on the other hand,
claims that the loopback indication is set using the LocalControl { mode
= loopback}. Since LocalControl is part of the media stream, when
receiving such a command from the MGC, our MG tries to create a new
stream and fails because the termination is under test).
Thanks in advance,

Ron 

Ron Gilaad
RAD Data Communications.
24 Raoul Wallenberg St.
Tel Aviv 69719
Tel: 972-3-6455411 
mailto:[email-masked]

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