Methods and apparatus for providing data communication between modems coupled over digital channels are provided. In one aspect, the present invention features an apparatus used in a system for providing communication over a digital channel to couple a first modem on a first network to a second modem on a second network. The apparatus includes a modem module that couples to the first modem at a data rate determined in part by a modulation rate of the modem module. The apparatus further includes a digital channel interface module coupled to the modem module, the digital channel interface module including a buffer that receives data from the digital channel and provides data to the modem module. The apparatus also includes a control circuit that detects a level of data in the buffer and modifies the modulation rate of the modem module based on the level of data detected.