Support
Fax was designed to meet the various challenges of the PSTN, but Fax over IP (FoIP) is a different beast, and must adapt to the transmission protocols that IP utilizes. No other solution available is designed to meet the challenges presented by FoIP like Smart FoIP, which is available on all New Rock HX4G and MX8G gateways, as well as the New Rock OM20G and OM50G PBXs. By eliminating the top-two problems with FoIP; the late T.38 re-invite and the G.711 clock-synchronization problem, Smart FoIP provides near-PSTN success rates.
In relay-to-relay T.38 operations, there are two analog PCM sample clocks: one at the remote transmitting fax and the other at the local re-modulating modem. These two clocks always have a different rate. Bits generated at the transmitting endpoint fax terminal must be re-transmitted by the off-ramp gateway’s local modem. If the remote fax is generating bits faster than the off-ramp gateway’s local modem can send them out to the fax terminal, off-ramp overflow eventually occurs. In the reverse case (off-ramp faster than transmitting fax terminal), the on-ramp modem will run dry since the off-ramp gateway is sending the bits out faster than it receives them, and T.38 relay will have to spoof some bits to keep the transmitter running (provided you have a well designed relay, of course). Underflow is not as much of a problem, since the relay can insert additional flags in V.21 data or padding bits at the end of a line of image data (Does your relay do that?). But overflow is a problem as valid data must be tossed (and modems just hate that).
Tel:021-61202700 / 52217917
Address:5/F Block B, Building 1, No.188 Pingfu Road, Xuhui District, Shanghai 200231, China
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