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Cisco Bug: CSCvt78489 - MTP session leak on HW MTP in specific call recording scenario with TRP and codec change

Last Modified

Oct 13, 2020

Products (1)

  • Cisco Unified Communications Manager (CallManager)

Known Affected Releases

11.5(1) 12.0(1) 12.5(1)

Description (partial)

MTP session leak on HW MTP in specific call recording scenario with TRP enabled and Xcoder allocation due to codec mismatch.

Scenario leading to the issue:

IP Phone A is connected to external HiEnd audio system and wideband G.722 codec is used to provide better audio quality.
Call Recording is enabled for IP Phone A and recorder is locked to G.722 codec
IP Phone A is located in isolated network segment and TRP is required to traverse Voice VLAN
IOS SW MTP is used as TRP with codec pass-through
PSTN provider supports only G.711 and G.729 codecs
HW MTP is pre-allocated to serve as TRP
Xcoder is engaged and call is connected via XCoder w/o TRP engagement
After call is completed pre-allocated MTP session will be stuck on HW MTP

On IOS MTP you will see growing number of inactive connections when such calls are traversing CUCM and pre-allocating this MTP:

IOS_HW_MTP#show sccp connections | include inac
43927109   33604999     mtp   inactive UNKNOWN 25330 0     UNKNOWN           
43927132   33605236     mtp   inactive UNKNOWN 25410 0     UNKNOWN           
43927237   33606036     mtp   inactive UNKNOWN 25558 0     UNKNOWN           
43927246   33606090     mtp   inactive UNKNOWN 25620 0     UNKNOWN           
43927094   33604923     mtp   inactive UNKNOWN 25332 0     UNKNOWN           
43927095   33604924     mtp   inactive UNKNOWN 25336 0     UNKNOWN           
104157298  33605237     mtp   inactive UNKNOWN 25262 0     UNKNOWN           
104157311  33605390     mtp   inactive UNKNOWN 25486 0     UNKNOWN           
104157363  33606037     mtp   inactive UNKNOWN 25592 0     UNKNOWN

These connections can't be cleared unless un-register MTP profile or reboot GW.

- Call recording enabled
- TRP enabled
- codec mismatch b/w PSTN call leg and TRP codec
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