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2 System Overview
The system utilizes IP technology over fixed broadband networks and uses
SIP for control signaling and RTP for media transportation together with
POTS interface.
PSTN
IP
Access
network
Fax
Gateway
SIP
Server
Edge
Router
Fax over IP
Analog lineAnalog line
W25
VoIP System
T.38
T.30T.30
Figure 1 - Typical network for VoIP running Fax (T.38)
The fax machines will still use the analog POTS interface. In the picture
above one fax is connected to the dedicated POTS port on the Ericsson
W25 and the other to the PSTN.
The Ericsson W25 is a SIP user agent, which is registered in the SIP
server. The user agent originates and terminates the FoIP (Fax over IP)
calls and use the SIP protocol to manage and control the media streams
(RTP). In order to handle calls to and from a Fax machine the Ericsson
W25 also needs to support the fax relay codec T.38, which enables real-
time Group 3 facsimile communication between two fax terminals over an
IP network.
The Ericsson W25 will be interoperable with Ericsson’s IMT (IMS
Multimedia Telephone). Other SIP servers and Fax gateways should also
work as long as they support SIP v2 (RFC 3261) and T.38, but
interoperability testing needs to be done to verify this.
