Aastra XS - 5.4.8 Fax and Modem transmission over IP

Product Guide - A5000 R5.4 – Aastra X series
BPS0121AENAA01 Page 60/74
5.4.8 Fax and Modem transmission over IP
Concerning fax or modem transmission over IP, several configurations exist:
• An iPbx has an external access on each site. Therefore, fax machines and modems can
transmit directly over the ISDN.
• Interconnected IP sites exchange faxes or a satellite site does not have access to the carrier
network.
Aastra X Series have specific encoding entitled G.711 FAX on their IP access points to transmit faxes
over IP. The IP access point detects the 2100-Hz carrier wave transmitted by the fax machine and
then transforms the call's encoding type into G 711 FAX encoding to allow this transmission to take
place. Considering this type of encoding, fax transmission over the WAN is possible if the throughput
of this link is strictly greater than 128kbits/s. A 256-kbit/s bandwidth is required.
The modems that operate according to this mechanism described previously for faxes interoperate.
Group 4 type fax devices must send and receive their calls directly on the ISDN, just like the
videoconference ISDN flows or point-to-point data transmissions on the ISDN.
FoIP: Fax T38
T38 is a FoIP (Fax over IP) standard which defines fax emission and reception via a VoIP network.
T38 is described in RFC 3362 and defines the way a fax device has to transmit/receive fax data.
The gateways of the Aastra X Series implement this standard (protocol and encoding law policy) -
from R5.1B – in the EIP daughter boards.
T38 fax is working on following scenarios (mandatory architecture) shown below:
Analogue faxes are always linked to the Aastra X Series or positioned behind the SIP ATA gateways
(Analogue Telephony Adaptor). T38 faxes are linked directly to LAN/WAN in RJ45. The data
transmitted between these types of fax are routed via the EIP cards of the AX Series.
Aastra X Series are compatible with analogue faxes of G3 and super G3 types. For Super G3, even if
the T.38 mode is configured, sometimes the fax may be transmitted in G.711.