The T.38 fax relay standard was devised in 1998 as a way to permit faxes to be transported across IP networks between existing Group 3 (G3) fax terminals. T.4 and related fax standards were published by the ITU in 1980, before the rise of the internet. In the late 90s, VoIP, or Voice over IP, began to gain ground as an alternative to the conventional Public Switched Telephone Network. However, because most VoIP systems are optimized (through their use of aggressive lossy bandwidth-saving compression) for voice rather than data calls, conventional fax machines worked poorly or not at all on them due to the network impairments such as delay, jitter, packet loss, and so on. Thus, some way of transmitting fax over IP was needed
We offer a wholesale solution for T.38 fax termination. Because VoIP faxing is easily affected by Internet jitter and latency, we use dedicated Cisco gateways and TDM ISDN circuits to terminate your fax calls.
If you would like a T.38 prefix to be enabled on your account, simply send a request to our support team. They will assign a separate prefix for your fax calls. Unlike the bulk of our routes, which use Tier 1 VoIP carriers, this routing option has been configured to connect directly to a Cisco voice gateway and PRI TDM circuit located in our facility. We have found that this is the only way to provide reliable and consistent T.38 fax support. The T.38 gateway routes use our Premium rate table. To use it, you must send calls with a unique prefix that will be routed to the Cisco gateway.
In order to maximize the chances of success when sending T.38 faxes, set the fax terminal to use V.29 at 9600 bps. Faster baud rates (eg. V.17 14400 bps) will not work as well.
