The VG224 supports fax machines and modems. When using fax machines, the VG224 supports Cisco fax relay, T.38 fax relay, and fax pass-through. Cisco or T.38 fax relay technologies allow the transfer of faxes across the network with high reliability using less bandwidth than a voice call. All modems can be connected to the VG224 and are transferred over the network using modem pass-through.
The configuration of Media Gateway Control Protocol (MGCP) fax pass-through on Cisco voice gateways is similar to the configuration of MGCP VoIP calls. The configuration is done by means of several commands in addition to a standard VoIP configuration. The same configuration must be present on the originating and terminating gateways.