T.38 between Media-Gateways

[RobertBreu]

Hi,

i was asking myself if the T.38-Relay between Media-Gateways work in this configuration:

- Media-Gateway on Remote-Site with a MIX 4/8/4-Board and 4 ISDN-Basic-Rate-Access
- Media-Gateway on Main-Site with a Faxserver connected via a BRA2 and QSIG to the PBX
- Customer wants to send faxes via the ISDN-Access of the Remote-Site to the Faxserver on the Main-Site

CS is on BICS (Rel 9.1), the Fax-Server is a GFI-Faxmaker and the Gateways are boths GD3 (Main-Site with ARMADA, Remote-Site without...)

I have checked the configuration as mentioned in the System-Doc and also traced a fax-connection on the GD (but i only see UDP-packets and no T.38-Traffic)

Thank You!

[OXE_4400]

What actually wrong? Why are You asking?

http://en.wikipedia.org/wiki/T.38

The T.38 recommendation defines the use of both TCP and UDP to transport T.38 packets. Implementations tend to use UDP, due to TCP's requirement for acknowledgement packets and resulting retransmission during packet loss, which introduces delays. When using UDP, T.38 copes with packet loss by using redundant data packets.

OXEDB_R91\html\Fax_Parameters.html
FAX PARAMETERS
All these parameters apply to Fax over IP on INTIP and are linked to the T38 protocol.

System_Option
V21 redundancy depth
Number of times action repeated when transmitting V21 frames over UDP.
(Default value: 2)

T4 redundancy depth
Number of times action repeated when transmitting fax data over UDP.
(Default value: 0)


For me its everything OK.

[RobertBreu]

Hi,

thanks for your reply!

You are right, OXE has implemented T.38 as UDP but normaly you should see some T38 traffic in a tcpdump (just have to open it with wireshark).

And in my case i only see UDP-Packets without T.38 as protocol.

I have attached two screenshots from wireshark to show what i mean.

If you want i can send you a complete trace-file.

Thank you