This was the Part from the SPA Admin guide that I was referring to regarding Faxing.
T.38 Fax is only supported on the SPA2102 and the SPA8000. The SPA2102 supports a single connection, while the SPA8000 supports one connection for each pair of ports (1/2, 3/4, 5/6, and 7/8) for a maximum of four connections.
To optimize fax completion rates, complete the following steps
Step 1 Upgrade the ATA firmware to the latest version
Step 2 Ensure that you have enough bandwidth for uplink and downlink.
• For G.711 fallback, it is recommend to have ~100Kbps.
• For T.38, allocate at least 50 kbps.
Step 3 To optimize G.711 fallback fax completion rates, use the following settings on the Line tab of the
Linksys ATA:
• Network Jitter Buffer: very high
• Jitter buffer adjustment: disable
• Call Waiting: no
• 3 Way Calling: no
• Echo Canceller: no
• Silence suppression: no
• Preferred Codec: G.711
• Use pref. codec only: yes
Step 4 If you are using a Cisco media gateway for PSTN termination, disable T.38 (fax relay) and enable fax
using modem passthrough.
Step 5 Enable T.38 fax on the SPA 2102 by configuring the following parameter on the Line tab for the FXS
port to which the FAX machine is connected:
FAX_Passthru_Method: ReINVITE
Note If a T.38 call cannot be set-up, then the call should automatically revert to G.711 fallback.
