Compaq W25 - Manual (Page 8)

3 Ericsson W25
The Ericsson W25 will work as a gateway, using T.38 protocol. The fax
terminal shall be connected to the dedicated fax port on the Ericsson W25.
Associated to this fax port is a SIP User Agent, which manages and
controls the media streams by using the SIP protocol (RFC 3261) towards
the SIP server and the PSTN Gateway.
Depending on configuration, Fax calls between two FWT on the same radio
networks can be sent directly between the FWT’s not using the PSTN.
3.1 Signaling
The Ericsson W25 conforms to the SIP protocol according to RFC3261.
3.1.1 Details over the SIP Implementation
The Ericsson W25 supports:
• SDP according to RFC 2327.
• SDP usage according to RFC 3264.
• Media “hold” by using destination address 0.0.0.0
• Configuration of SIP message timers T1, T2 and B as defined in
RFC 3261.
• URI for fax calls, RFC 3966.
• PRACK method according to RFC 3262.
• Session timer, RFC 4028.
3.2 Security
The Ericsson W25 authenticates towards the VoIP system using the HTTP
Digest Authentication mechanism.
3.3 Media Stream
Due to the procedure of setting up a fax call both G.711 and T.38 is
supported by the Ericsson W25. The W25 requires that the call is first setup
as a normal voice connection (using G.711) before a switchover from voice
to T.38 fax is done with SIP Re-INVITE practices.
3.3.1 Jitter Buffer
One important function in the Ericsson W25 is the jitter buffer, which is
necessary to have due to the latency and jitter in the IP network. The
access network contributes with most of the latency and jitter, so to reduce
this a HSPA connection is recommended.
8 2/221 02-FGB 101 327 Uen B – November 2007