The Super G3 to G3 Fallback feature enables the SBC to unconditionally use T.38 protocol between two Super G3 fax machines. The call is always negotiated as if it were a G3-to-G3 fax call. Available options: Enabled (T.38 protocol is always negotiated between two Super G3 fax machines), or Disabled (T.38 protocol may not be negotiated between two Super G3 fax machines. Under many conditions, the call may come up as a modem pass-through call). T.38 must be properly configured in the SBC according to the following guidelines: - T.38 must be added/selected in the Media Profiles List for both ends of the call. See Creating and Modifying Media Lists.
- The Super G3 to G3 Fallback option must be enabled (through Fax Codec Configuration) on the fax origination side, termination side, or both sides.
- If the Signaling Group (for which the SG3 to G3 Fax Fallback is activated) is dedicated to voice and fax calls only (i.e. modem calls are not expected and the Modem Passthrough parameter in the Media List is disabled), the TDM switch inside the SBC is used to manipulate the connection to the called fax machine to force fallback to T.38 mode. This method is very reliable but it will disrupt modem calls--that is why it is used only if modem calls are not expected over the signaling group.
- If all call types (voice, fax and modem) are allowed over the signaling group, then a DSP based method is used to squelch some signals to the called fax machine. This method will not disrupt modem calling, however, it may not work reliably if the IP network has excessive packet loss and/or jitter.
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