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PSTN calls to IP phones drop intermittently with Cisco CallManager 5.0 and there is cross talk on the line

Core Issue

While the session initiation protocol (SIP) trunk is used with Cisco CallManager 5.0, calls to the public switched telephone network (PSTN) can drop if Media Termination Point Required is checked under the SIP trunk configuration.

In addition, callers experience mixed lines on some calls. For example, the receptionist is on one call and a second call comes into the receptionist. The receptionist and the first caller hear the ringing of the second call and any subsequent conversation.


In order to fix the problem, uncheck the Media Termination Point Required check box under the SIP Trunk configuration.

Refer to these documents for more information:

The issue related to the crosstalk is also documented in Cisco bug ID CSCsg47594 for these Cisco IOS software releases:

  • Cisco IOS Software Release 12.4(4)XC03

  • Cisco IOS Software Release 12.4(07b)

  • Cisco IOS Software Release 12.4(08a)

  • Cisco IOS Software Release 12.4(03f)

  • Cisco IOS Software Release 12.4(9)T01

  • Cisco IOS Software Release 12.4(6)T04

  • Cisco IOS Software Release 12.4(11)T

  • Cisco IOS Software Release 12.4(4)T05

  • Cisco IOS Software Release 12.4(10a)

This issue can be observed when the same 5510 digital signal processor (DSP) is used as a Transcoding and Voice Termination resource.

In order to workaround this issue, complete one of these:

  • Disable Transcoding


  • Make sure that the Transcoding and Voice Termination are on different DSPs. In order to do this, configure the maximum number of transcoding sessions to a value such that it requires a multiple of 240 DSP credits.

This issue is fixed in these Cisco IOS software releases:

  • Cisco IOS Software Release 12.4(9)T03

  • Cisco IOS Software Release 12.4(13)

  • Cisco IOS Software Release 12.4(15)T

This issue is resolved in 9.4(0)DSP.

Refer to Cisco bug ID CSCsg47594 for more information.

Problem Type

Call control software  (CallManager, CallManager Express, ICS7750, SRST, SS7 call agents)

Voice quality problems (Audio quality: Choppy voice, hissing, echo, etc.)

Call Control


Call Connection

Call presentation

CallManager Features

Call presentation

Voice Quality

Crosstalk (Listen to short or long crosstalk samples.)

Frequency and Scope of Symptom

Occurs only on some calls

End Where Problem is Heard or Device Type Involved

IP phone

Call Topology and Direction


Signaling Protocol


CallManager Versions

CallManager 5.0