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Not applicable to SBC Software Edition.


Most compressed codecs are unsuitable for fax transmission; the result ranges from poor to unusable based on specific endpoints and network topology. ITU has defined the T.38 protocol for Fax transmittal over IP networks. The SBC supports detecting Fax tones and re-negotiating to T.38, or receiving a re-negotiation to T.38. T.38 is also used with uncompressed codecs such as G.711.

The SBC is configurable to use predefined T.38 maxBitRate values using Packet Service Profile (see Packet Service Profile (CLI) for command details).

CLI Syntax:
% set profiles media packetServiceProfile <unique_profile_name> t38 maxBitRate <2.4Kbits_s | 4.8Kbits_s | 9.6Kbits_s | 14.4Kbits_s>

When G711 is selected as the audio codec and fax toneTreatment is set to faxRelayOrFallbackToG711, the SBC does not transition to T.38 when fax tone is detected, but responds to T.38 transitions offered by the peer. However, when toneTreatment is set to faxRelay, the SBC initiates a transition to T.38 when fax tone is detected even if audio codec is G711. For a complete listing of fax tone behavior see fax parameter in Table 1 of Codec Entry (CLI) page.

 

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