Determining if a PC can capture audio packets sent from an IP phone

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Determining if a PC can capture audio packets sent from an IP phone

Problem Summary None.
Error Message None.
Possible Cause None.
Recommended Action

To determine if an agent PC is unable to capture packets sent from the IP phone, Cisco recommends you use a public domain packet sniffer called Wireshark. (This is because Wireshark uses WinPCap, which is the same packet capture technology that is used by CTI OS Silent Monitor.):

  1. Download Wireshark from and install it on the agent’s machine.
  2. Verify that WinPcap is installed on the agent’s machine via Start->Control Panel->Add remove programs. WinPcap should be on the list. If not, install WinPcap as described in the Installing WinPcap section of this document.
  3. Run Wireshark: Select Capture > Start > OK.
  4. Make a voice call from or to the agent’s phone (there is no need to be logged onto CTI OS right now) and ensure that UDP packets are captured at roughly 100 packets/second.
  5. If no packets are captured, click stop, then Capture -> Start again.

However, make sure that you select a different Adapter from the drop down list, go to Step 3., and repeat the test. If there are no adapters listed in the Interface drop down list and you are not an Administrator on the PC, there may be a WinPcap user permissions issue. To fix this issue, check the value of the Start setting at the following Windows registry key:


Change the value of the Start setting to 0x00000002, reboot the PC, and try to monitor the agent again. If you are unable to capture packets on any of the adapters listed in the drop down list, and your PC is on a VLAN, your PC's network interface card may not be able to capture packets from a different VLAN. Some interface cards require special configuration to capture packets off a different VLAN. Refer to the CTI OS System Manager's Guide for Cisco ICM/IPCC Enterprise & Hosted Editions for details on how to qualify your network interface card for silent monitor.

Release Release 7.5(x)
Associated CDETS # None.

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