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Specifies whether or not the T.38 will fall back to Fax Passthrough if not supported by peer.

If fallback is disabled, and Sonus SBC 1000/2000 the

If fallback is enabled, under the same circumstances as above, then when T.38 switch-over fails, the Sonus SBC 1000/2000 will attempt to switch-over to G.711 codec (if the peer supports it).

Specifies the maximum FAX connection bit rate (bits/second).

This is the maximum rate at which a fax call will be negotiated between the Sonus SBC 1000/2000 and the fax machine. It takes longer to transfer a page at lower rate, however, lower rate may make the fax call more reliable.

Specifies the number of redundant packets sent for each T.30 (signaling) message.

In a T.38 fax call, there are two types of packets exchanged between the two gateways: signaling packets carrying fax call control information and payload packets carrying page data. The Signaling Packet Redundancy parameter controls the number of redundant packets sent by Sonus SBC 1000/2000 for each T.38 signaling packet. Use a low value for this parameter if the data network is of good quality with no or little packet loss.

Specifies the error correction mode (ECM) for fax calls.

ECM is used to make the fax call reliable (using retransmissions between fax machines). When disabled in the Sonus SBC 1000/2000 configuration, ECM will not be used, even if both fax machines support it.

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.