An improved packet handler for VoIP cable modems and other high-speed digital devices includes a direct communication link via hardware among internal processing components. Incoming and outgoing digital information packets are filtered into MAC packets, voice PDU packets, and non-voice PDU packets, such that priority can be given to relaying voice packets and minimizing potential voice delay within the cable network. Hardware components, including specialized logic circuitry, modify voice packets to an appropriate signal form for subsequent signal processing or signal transmission. Proprietary bus communication protocols can also be provided to facilitate relay of packets between a central processing unit (CPU) and a digital signal processor (DSP) within a VoIP cable modem. Line cards including subscriber line interface circuit (SLIC) and subscriber line audio processing circuit (SLAC) components provide analog-to-digital (A/D) and digital-to-analog (D/A) conversion functionality.