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Collaboration, Voice & AV · Intermediate

Digital Signal Processor (DSP)

A specialized processor on voice gateways and routers that performs codec conversion, conferencing, transcoding and echo cancellation.

Definition

DSPs handle real-time media tasks that general-purpose CPUs do inefficiently, such as converting TDM to RTP, transcoding between codecs, mixing conference audio and running echo cancellers. On Cisco ISR routers DSPs reside on PVDM modules, and the number of DSP resources determines how many TDM calls, transcoding sessions or conference participants are supported. DSP capacity varies with codec complexity, with high-complexity codecs such as G.729 consuming more.

Example

A PVDM4-64 in an ISR 4451 provides DSP resources for a PRI plus a hardware conference bridge registered to CUCM.

Exam tip

Use the Cisco DSP Calculator logic: high-complexity codecs reduce the number of channels per DSP, and transcoding and conferencing both consume DSPs.

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