5.5.4 DSP Resource UsageDescriptionTo digitally process audio signals, such as a telephone call, the PBX must use a certain number of DSP (DigitalSignal Processing) resources. DSP resources are provided by the DSP card installed in the PBX. Since thereare a limited number of DSP resources, no further operations (e.g., telephone calls, playing an OGM) can beperformed if all resources are being used.The following list shows some of the basic operations that require DSP resources.• IP extension call• IP trunk call• Conference• Accessing the Unified Messaging system (including recording calls)• OGM playback• Echo cancellerFor IP extension and trunk calls, the number of required resources differs depending on the codec (G.711 orG.729) used.NoteThe examples in this section are intended to illustrate the concept of DSP resource usage. More complexsituations may necessitate additional resources, and in some cases fewer resources may be necessary.Examples of DSP resource usageFundamentally, the number of resources required for a given situation is the sum of the resources required foreach individual operation. The following examples illustrate DSP resource usage in various situations.[IP trunk to IP extension]IP TrunkIP-PTX YPBXG.729A G.711If an IP trunk call using the G.729 codec requires X number of resources, and an IP extension call using theG.711 codec requires Y number of resources, then the number of resources required for a call from an IPextension to an IP trunk requires X + Y number of resources.[Unified Messaging access]IP-PTYXPBXG.711UMPlaying back messages from or recording messages to the Unified Messaging (UM in the figure above) systemrequires DSP resources, X in this example, in addition to the resources required for the G.711 codec (Y). Thetotal cost is X + Y.Feature Guide 5315.5.4 DSP Resource Usage
