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221 02-FGB 101 327 Uen C – December 2006 23
5 Fax Support (W25 only)
To enable Fax support the Ericsson W25 uses the Voice over IP (VoIP)
protocol called SIP.
The Ericsson W25 works as a fax gateway between the POTS interface
and the IP network using the T.38 protocol. The fax machine is connected
to one of the two POTS interfaces on the Ericsson W25, which is dedicated
for a fax machine.
Connected to this fax port is a SIP user agent, which manages and controls
the media streams by using the SIP protocol towards the SIP server and
media Gateway.
5.1 Signaling
The Ericsson W25 conforms to the SIP protocol (RFC 3261).
5.2 Security
The Ericsson W25 authenticates towards the VoIP system using the HTTP
Digest Authentication mechanism.
5.3 Media Stream
To transfer the fax call the T.38 protocol is used.
5.3.1 Jitter Buffer
To handle latency and jitter the W25 has a jitter buffer.
5.3.2 Echo Canceller
To improve the fax transfer, the Ericsson W25 has an echo canceller in
accordance with G.168.
5.3.3 QoS
The outgoing VoIP related traffic will be prioritized before other traffic from
the Ericsson W25 to reduce the uplink delay and jitter.