DTMF relay in H.323 using signalUpdate message

Unanswered Question
Jul 24th, 2007

Upon reception of a DTMF digit from the end user, the Cisco H.323 MGW configured in out of band signal mode sends a User Input Indication (UII) signal message, with a length of 4s:

h245Control: 1 item

Item 0

Item: 14 octets

H.245

PDU Type: indication (3)

indication: userInput (13)

userInput: signal (3)

signal

signalType: 1

duration: 4000

rtp

timestamp: 4001535283

logicalChannelNumber: 1

When the end user releases digit key, the MGW sends a UII signalUpdate message to update the DTMF duration to the actual duration (here 125 ms):

h245Control: 1 item

Item 0

Item: 9 octets

H.245

PDU Type: indication (3)

indication: userInput (13)

userInput: signalUpdate (4)

signalUpdate

duration: 125

rtp

logicalChannelNumber: 1

This behavior is not a fault technically, but it causes problems with some equipments that do not recognize well the UII signalUpdate message.

I'm using IOS 5300 Software (C5300-IK8S-M), Version 12.2(15)T14.

Is this behavior still the same is more recent versions, or is it possible to change this behavior as follows:

1?) Send the signal message with a fixed duration much lower than 4s (typically around 100 ms), or

2?) Send the signal message ony when the DTMF duration is known (hence avoiding the signalUpdate)?

I have this problem too.
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b.hsu Mon, 07/30/2007 - 06:07

Possible workaround may be to send an extra unneeded digit which seems to implicitly indicate the previous digit is ended.

fmouillaud Mon, 07/30/2007 - 06:59

Well, we don't have any control over this: the digits are dialed by the end user. There's no such thing as an unneeded digit either in telephony....

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