Allocating DSPs on SDP Offer or Answer
By default, the device allocates DSP resources for a call at the SDP Offer stage. If DSP resources are available at this stage, the device reserves DSPs for the call just in case call setup succeeds with the SDP Answer and DSPs are required (e.g., for transcoding). If there are no free DSP resources at the SDP Offer stage, no DSP resources are allocated for the call, at any stage of the SDP Offer-Answer exchange, and if DSPs are required (based on the SDP Answer), the device rejects the call.
However, this default behavior may cause call failure for a call requiring DSPs even when the device has sufficient DSP resources. For example, assume the device is licensed for 10 concurrent transcoding calls and is currently handling the establishment of 10 calls where only half require transcoding (DSPs). For all these calls, the device allocates DSPs during the SDP Offer stage (even if some of these calls may not require DSPs, based on the SDP Answer). If during this time the device starts processing an 11th call that requires transcoding (DSPs), since it has already allocated all of its DSP resources, it doesn't allocate any DSPs to this call and as a result, the device rejects the call.
To avoid such scenarios, you can configure the device to allocate DSPs only at the SDP Answer stage (SIP 200 OK or 180), when it can determine if DSPs are required or not for the call. If DSPs are required and DSP resources are available, the device allocates DSPs. If DSPs are required but there are no available DSPs, the device rejects the call.
| ➢ | To disable reserving DSPs on SDP Offer: |
| 1. | Open the Media Settings page (Setup menu > Signaling & Media tab > Media folder > Media Settings). |
| 2. | From the 'Reserve DSP on SDP Offer' drop-down list, select Disable. |
| 3. | Click Apply. |