On a voice gateway with the C5510 Digital Signal Processors (DSPs) that is configured for E1 Channel Associated Signaling (CAS) voice and runs Cisco IOS Software Release 12.4(7b) with DSPware 4.4.20, the DSP crashes intermittently and all the active calls drop.
After the crash, the syslog debugs of the router show this error message:
ocal1Alert2931: *Oct 2 18:32:32.577: %C5510-1-NO_RING_DESCRIPTORS: No more ring descriptors available on slot 0 dsp 4
Other DSP and gateway combinations can also experience the same issue.
This issue is documented in Cisco bug ID CSCsf96641, which is a duplicate of Cisco bug ID CSCse98109. Currently, there are no workarounds available.
In order to resolve this issue, upgrade to Cisco IOS Software Release 12.3(11)T11 and DSPware 4.4.21. This combination is more stable.
This issue is fixed in DSPware 8.4(2) and in these Cisco IOS software releases: