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What is Fax over IP? How does it work?
Fax over IP refers to the process of transmitting and receiving electronic faxes over IP (internet protocol). Traditional fax transmissions are based on the T.30 protocol and occur over a circuit-switched network - analog lines, digital voice T1, PRI ISDN, etc. Fax over IP is based on the T.38 protocol. When a fax is sent/received over IP, the fax travels over a packet-switched network.
How does Fax Over IP work?
Understanding how faxes are sent over an IP network requires a basic understanding of the T.38 and T.30 protocols.
- T.38 is the protocol that describes the process for sending and receiving faxes in real-time over a packet-switched network.
- T.30 is the protocol that describes the communication process between two fax devices on a circuit-switched network.
For an Internet aware fax device, such as a fax board, to reliably send and receive faxes over IP, that device must support the T.38 protocol. T.38 is designed to preserve the traditional fax experience, and ensures that faxes are successfully sent and received. T.38 will make adjustments for jitter, latency, and packet loss, which are inherent in all IP networks. This is important as fax devices are sensitive to timing. Without T.38, fax devices cannot reliably send and receive faxes over an IP network.
Faxing over an IP network involves a piece of equipment, called a gateway. Shown in the diagram below, the gateway acts as an intelligent bi-directional bridge between circuit-switched and IP networks.
While the gateway sits between the two fax end-point devices, in this case the Imecom DM Fax Server and a fax machine, the faxing intelligence resides in the end point devices. As in traditional circuit switched fax technology, fax over IP devices are responsible for negotiating, synchronizing, and communicating with each other.
On the back end, the gateway sends and receives T.30 data wrapped in T.38 packets while in front it receives a traditional T.30 fax signal. The gateway recognizes the data as a fax and the repackages the data for consumption by both end points.
T.30, the same protocol used for faxing over traditional circuit-switched networks, remains at the heart of every IP fax connection with each end point requiring a high degree of T.30 interoperability. This is necessary since Internet aware fax devices must also be able to communicate with legacy fax devices.
Supported Fax Boards
DM Fax Server supports the use of Dialogic Brooktrout TR1034 and SR140 products, both of which also support real-time fax over IP. The TR1034 series fax boards support traditional T.30 for faxing over a circuit-switched network and T.38 for fax over IP. The SR140 is a host-based "boardless" virtual fax board product that supports only T.38 for fax over IP. More.
Go Boardless
DM Fax Server supports the Dialogic Brooktrout SR140 fax software which enables you to implement and deploy a Fax over IP that's completely software-based - no more fax board hardware. And SR140 offers the same great benefits as Brooktrout TR1034 products. More.
Supported IP Telephony Equipment
Fax over IP is not yet possible with all available IP telephony solutions. But progress is being made. Click here for a list of supported IP telephony products.
