Fax support – Nortel Networks NN43001-563 User Manual

Page 78

System description

Fax support

The IP trunk card transfers T.30 protocol (G3 Fax) implementations over
the IP network. Near real-time operational mode is supported where two
T.30 facsimile terminals are able to engage in a document transmission in
which the T.30 protocol is preserved.

The trunk uses the T.38 protocol on the connection between a pair of IP
Trunk 3.01 (and later) nodes.

The call acts in the same way as a gateway-to-gateway H.323 call. The call
is set up using the normal voice call process (that is, the normal voice call
codec negotiation process occurs and the corresponding codec payload size
and jitter buffer values are used). When the call setup is complete, the two
G3 Fax terminals are linked. The DSP detects the fax call setup tones and
switches to handle the fax call. For the remainder of the call, the parameters
administered for the fax call are used (for example, payload size).

Some implications of the fax call setup process are as follows:

•

a voice codec must be configured, even if only fax calls will be made

•

both ends of the call must be able to negotiate to a common voice codec
for the calls to be successful

All T.30 session establishment and capabilities negotiation are carried out
between the telephones through the IP trunk cards over the IP Trunk 3.01
(and later) network using the T.38 protocol. In terms of the internet fax
service roles, the IP trunk card acts as both the fax on-ramp gateway and
the fax off-ramp gateway, depending on the call direction.

The on-ramp gateway demodulates the T.30 transmission received from the
originating G3 Fax terminal. The T.30 facsimile control and image data is
transferred in an octet stream structure, using a Real Time Protocol (RTP)
payload, over User Datagram Protocol (UDP) transport mechanism.

Signaling specified by H.323 V.2 protocol is used for IP Trunk 3.01 (and
later) to IP Trunk 3.01 (and later) call setup.

Modules supporting facsimile transmission are responsible for the following:

•

fax speed detection and adjustment

•

protocol conversion from G3 Fax to RTP payload for fax data transfer

•

T.30 fax protocol support

•

T.38 fax-over-IP protocol

•

V.21 channel 2 binary signaling modulation and demodulation

•

High-level Data Link Control (HDLC) framing

•

V.27 term (2400/4800 bps) high speed data modulation and
demodulation

Nortel Communication Server 1000

IP Trunk Fundamentals

NN43001-563

01.01

Standard

Release 5.0

30 May 2007