From: http://www.cisco.com/en/US/tech/tk652/tk698/technologies_white_paper09186a00801545e4.shtml

  Introduction
  High Level Troubleshooting Procedure
  Categorize and Define the Symptoms
  Sample Sound Recordings
  Noise
  Voice Distortion
     Echoed Voice
     Garbled Voice
     Volume Distortion
  Common Problems Hearing Sound Files
  Cisco Support Community - Featured Conversations
  Related Information 

From: http://www.cisco.com/en/US/docs/telepresence/infrastructure/articles/cisco_telepresence_packet_loss_poor_quality_audio_visual_one_direction_kb_82.shtml

• If you are seeing a lot of packet loss in one direction, this could be caused by a duplex mismatch somewhere in your network.
• If you are new to video conferencing over IP, you may have had a duplex mismatch in your network for some time: TCP traffic will be slowed down by it - and this may pass unnoticed - but UDP traffic will be lost.

From: http://msdn.microsoft.com/en-us/library/aa259670(v=sql.80).aspx

• In Control Panel, open Administrative Tools, and then open Performance.
• In the Windows Performance tool, expand Performance Logs and Alerts, right-click Counter Logs, and then click New Log Settings

From: http://social.technet.microsoft.com/Forums/en-US/winserverPN/thread/35f79821-7ab5-4335-89d5-cec58fa31d33/

If you want to monitor the amount of UDP packet loss you are experiencing I would use the performance logs and alerts utility.  The counter I
believe you would be interested in is under the UDP performance object, counter being "Datagrams Received Errors".  Also, you can query any
of these counters via WMI.

From: http://www.loadtest.com.au/types_of_tests/soak_tests.htm

Network testing

  Soak testing is running a system at high levels of load for prolonged periods of time. 
  A soak test would normally execute several times more transactions in an entire day (or night)
  than would be expected in a busy day, to identify any performance problems that appear after a
  large number of transactions have been executed.

From: http://packetloss.sourceforge.net/

  Packetloss is a set of programs to detect packet losses in UDP and TCP between two hosts. It does
  this by sending a continuous stream of packets, and detects any delay or loss in the streams. It is useful to measure the impact of failover tests

From: http://www.onsip.com/blog/2007/10/25/detecting-ip-packet-loss-ubernerds

 Now you might think someone would have a hard time hearing a 1/50 second gap in a 3 minute conversation.
 And you would be right. But if there is an IP network in the middle of the conversation, it turns out that
 drop detection depends greatly on the the piece of IP phone hardware/software one is talking on. In this case,
 the Polycom IP phone on my desk was useless as an empirical tool in helping me track down the 0.05% packet loss
 in question - I simply could not hear it. However, the Grandstream GXP-2000 (version 1.1.0.14) we have in our 
 test bed turned out to be an invaluable tool since it has the uncanny ability to turn the 1/50 second gap caused
 by a single lost packet into a multi-second garbled mess. So, if like me, you enjoy testing for dropped packets,
 I highly recommend adding the Grandstream to your toolbox - it is a great tool and worth far more than the retail price.