Hi sienz,
I'm assuming you are referring to Cisco ATA 187.
The Cisco ATA supports two modes of fax services, in which fax signals are transmitted using the G.711 codec:
• Fax pass-through mode: The mode enables receiver-side called-station-identification (CED) tone detection with automatic G.711A-law or G.711μ-law switching.
• T38 fax relay mode: The T.38 fax relay feature enables devices to use fax machines to send files over the IP network. In general, when a fax is received, it is converted to an image, sent to the T.38 fax device, and converted back to an analog fax signal. T.38 fax relays configured with voice gateways decode or demodulate the fax signals before they are transported over IP.
Note: Success of fax transmission depends on network conditions and the fax modem response to these conditions. The network must have reasonably low network jitter, network delay, and packet loss rate.
Here is a link for the data sheet of ATA 187:
http://www.cisco.com/en/US/prod/collateral/voicesw/ps6788/phones/ps514/ps11026/data_sheet_c78-608596.html
HTH.
Regards,
Harmit.
