Protocol Criteria For Foip; Fax Flow; Foip Configuration - 3Com MSR 50 Series Configuration Manual

2344 C 135: F
HAPTER AX OVER

Protocol Criteria for FoIP

Fax Flow

FoIP Configuration

IP C
ONFIGURATION
IP real-time fax complies with the ITU-T T.30 and T.4 protocols on the PSTN side
and the H.323 and T.38 protocols on the IP network side.
T.30 protocol is about file and fax transmission over PSTN. It describes and
■
regulates the communication flow of G3 fax machines over common
telephone networks, signal format, control signaling, and error correction to
the full extent.
T.4 protocol is a standard protocol involving the G3 fax terminals for file
■
transmission. It provides a standard regulation for the G3 fax terminals on
image encoding/decoding scheme, signal modulation and speed, transmission
duration, error correction, and file transmission mode.
T.38 protocol is about the real-time G3 fax over IP networks. It describes and
■
regulates the communication mode, packet format, error correction and
partially the communication flow of real-time G3 fax over IP networks.
In FoIP, the call setup, handshake, rate training, packet transfer, and call release are
always realtime. From the perspective of users, there is no difference from faxing
over PSTN.
Signals that a G3 fax machine receives and sends are modulated analog signals.
Therefore the router processes fax signals in a different way it processes telephone
signals. The router needs to perform modulation and demodulation for fax signals
(that is, the router demodulates analog signals from PSTN into digital signals, or
modulates digital signals from the IP network into analog signals), but does not
need to compress fax signals.
A real-time fax process consists of five phases:
1 Fax call setup phase. This phase is similar to the process of a telephone call setup.
The difference is that the fax individual tone identifying the sending/receiving
terminal is included.
2 Prior-messaging phase. During this phase, fax capability is negotiated and rate
training is performed.
3 Messaging phase. During this phase, fax packets are transmitted in accordance
with the T.4 procedure, and packet transmission is controlled (including packets
synchronization, error detection and correction, and line monitoring).
4 Post-messaging phase. During this phase, control operations such as packet
authentication, messaging completion, and multi-page continuous transmission.
5 Fax call release phase. During this phase, the fax call is completed.
Before configuring FoIP, you should configure POTS and VoIP voice entities. For the
specific configuration procedure, refer to
2266 and "Configuring VoIP Entity" on page
After the VoIP configuration, you can make IP phone calls. Usually, the default FoIP
configuration can be used to send and receive faxes so long as a fax machine is
connected in this case. FoIP configuration is mainly to set the specific FoIP
parameters, or used for some particular situations where the fax cannot be made
by using the default transmit energy level of a gateway carrier.
"Configuring POTS Entity" on page
2271.