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 |
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.
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