12-21-2007 08:17 AM
Hi,
we use more than one CISCO 5400 as
VoIP terminations, since we are VoIP
Providers.
We experience some trasmitting fax problem with T.38 FAX Relay.
It seems that many customer's CPE,
after CISCO 5400 Re-Invite, wait for
a T.38 packet before sending/receiving
T.38 packets.
But CISCO too wait a T.38 packet!!!
So communication hangs a while
then call is dropped.
We have seen that all CPEs that provide
a "T.38 No Signal" packet to CISCO
gateway after Re-Invite
succeed on fax trasmitting.
We use Cisco IOS Software (C5400-IS-M).
Is there any way to let CISCO sending
"T.38 No Signal" packets after Re-Invite?
Any help will be apreciated.
Christian
12-28-2007 08:01 AM
The issue can arise if the tcp session mtu size is set too small.Try setting the mtu size using the command ip tcp path-mtu-discovery.
01-07-2008 03:18 AM
Thank you. we will test.
Do you think your command works for UDP too? (T.38 packets are like RTP packets, then UDP)
Do you think using it we should experience
gateway start sending T.38 packets?
Thank you so far.
Christian
05-20-2008 07:46 AM
Have it work? I got the same problem like you
05-20-2008 07:55 AM
No but we have discovered a problem on T.30
due to third party ATA/IAD.
Basically after the T.38 re-invite, calling device doesn't send a CNG.
That's a required message to start T.30 negotiation of speed and so on.
Generally specking CISCO TAC suggest a 12.4T
IOS to have the best behavior for FAX.
05-20-2008 08:25 AM
I have already use 12.4(15)XY2. Is it related to 3rd party ATA? The CNG doesn't sent from where?
And how do you resolve? Are using another ATA?
05-20-2008 11:40 PM
We are now working with third party ATA firmware
developpers.
Re-Invite in T.38 can be done by calling or called party but a T.38 packet containing CNG
must be sent by calling party in order to start
speed handshake and fax trasmission.
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