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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)

Symptom:
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.

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