SIP ALG Many routers, firewalls and even some modems come with a feature called SIP ALG that modifies SIP packets as they pass through the networking device. This feature should in theory make it easier for SIP calls to work through NAT but, especially for Fax over IP, it is often implemented incompletely. You ca...

The T.30 fax protocol was designed for use over analog phone lines. In order for fax to work reliably over the Internet the analog signal used by fax machines must be converted into digital packets in a way that provides real-time fax transmission with very little data loss and delay. Since Voice over IP (VoIP) is ...

ECM stands for Error Correction Mode. In this mode, fax pages are sent in blocks and for any block that fails the error check the receiver will ask the sender to send it again until all blocks have been received successfully. ECM automatically detects and corrects errors in the fax transmission process that are som...

No, your SIP account credentials are not the same as those for your Web Self-Care portal. Therefore, should you change your Web Self-Care password, it will not affect your SIP settings. You can access the Web Self-Care portal at: https://my.t38fax.com  

In order to dial out of our service, calls must be made in accordance with the North American Numbering Plan (NANP) system. For example, calls within the USA must use 10 or 11-digit dialing, which means an optional 1, plus the area code and the remaining seven digits. For example, dialing 12158258792 or 2158258792 ...

By default, our free trial accounts allow you to have two (2) simultaneous fax calls. This will allow you to send a fax even if you're currently receiving a fax or receive two faxes simultaneously or even send two faxes simultaneously. If your test scenario needs more than two channels, please contact support a...

Yes, DTMF is supported via RFC2833.

When troubleshooting has failed to provide a solution to your problem, it's time to contact our support team. We'll need the following information: Your public IP address at the time you were testing (when in doubt, google "what is my ip" to get this) One or more specific call records for us ...

No, T38Fax.com does not store your faxes. We provide a SIP/T.38 trunking service similar to how a phone company provides a phone line to your office or home. In order to send and receive faxes, you must have a fax machine or fax server available to handle the fax calls in the same manner that a phone would be requ...

Businesses migrating to Voice over IP (VoIP) often find it desirable to move their fax traffic onto the IP network as well. However, VoIP networks are, as the name implies, optimized for voice traffic, and businesses implementing a Fax over IP (FoIP) solution as part of their fax system can benefit from understandi...

Outbound Calls We allow outbound calls to all 50 US states, Canada, and Puerto Rico. Notably, this does not include any other countries/territories that follow the 1+10-digit dialing format, also known as the North American Numbering Plan (NANP). These calls may look like supported calls at first glance as they a...

Aside from fax machines, there are many other kinds of modem devices on the telephone network. Fire alarms Credit card terminals ATMs Dial-up modems Many more... Since the behavior of modems is extremely variable - sometimes proprietary - and the problems that modems face have been largely resolved by cellu...

Yes, you can. The T.38 protocol will only engage if a fax machine is detected on the call. This is especially useful to home or small business users who need both a voice and fax line but want to keep things simple. If you are a PBX admin planning to use another carrier for voice, we highly recommend testing your o...