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Troubleshooting Network-Related Voice Quality Issues

Communications Server 2007 R2

Topic Last Modified: 2009-07-20

You can troubleshoot voice quality issues that are related to the network as follows:

  1. Check for packet loss on calls as follows:
    • Use Monitoring Server to identify any trend in packet loss over time. To investigate a particular call or conference from a user, use the call list report.
    • Use Monitoring Server to examine the IP addresses of the user who is reporting audio quality issues. IP addresses, together with the subnet mask provided in each report, can reveal the subnet that the user was using and, in some cases, whether the user was using Wi-Fi or was connected by using a virtual private network (VPN).
    • Use Monitoring Server to compare packet loss among different subnets.
    • Ping the client computer that you are troubleshooting from another computer in the network. Use the -n 100 parameter to get a better statistical value.
    • For wireless networks, ping the default gateway to measure the loss on the wireless link.
    • If you suspect that packets are being lost between one of the computers and the Mediation Server, ping the Mediation Server from that computer.
    • Use Network Monitor to capture a few minutes of conversation, and then examine the data to detect packet loss. The RTP headers are not encrypted, and you can examine the SEQ (that is, sequence number) field for continuity. Gaps in the sequence number correspond to packet losses of the same quantity. Gaps of several missing packets (that is, burst loss) are a stronger indicator of audio quality issues than random losses of single packets.
      Dd572545.note(en-us,office.13).gifNote:
      Microsoft Network Monitor 3.3 is a free, licensed component that is not provided with Windows operating systems on client computers, so use of the tool is limited to computers on which it is installed.
    • If Office Communications Server is deployed in a network that uses IPSec, use Network Monitor 3.3 to look for the existence of IPSec negotiation on the RTP streams. For enterprise networks where IPSec has been deployed, IPSec must be disabled over the range of ports that are used for the delivery of audio, video, and panorama video. IPSec negotiation can result in delays in the allocation of media ports. For details, see IPsec Exceptions in the Planning and Architecture documentation.
    • Install the Pre Call Diagnostic Tool on the client computer. Using the expanded user interface, look for packets that are being lost. This will indicate packet loss along the last leg of the network only.
    Dd572545.note(en-us,office.13).gifNote:
    Some of these network troubleshooting techniques need to be performed directly from the client computer of the user who is experiencing the issue. Also, some of the techniques can be used only for clients that are in the internal network because technical restrictions (such as tool availability to clients) limit the applicability of these techniques for external users.
  2. Check the network latency between two computers as follows:
    • Use Monitoring Server to compare round-trip times between corresponding subnets.
    • To investigate a particular call or conference from a user, use the call list report in Monitoring Server.
    • Ping the client computer that you are troubleshooting from another computer in the network. Use the -n 100 parameter to get a better statistical value.
    • Use abnormal latencies between two computers to locate routing paths that are too long.
  3. Check the jitter of network packets between two computers as follows:
    • To investigate a particular call or conference from a user, use the call list report in Monitoring Server.
    • Ping the client computer that you are troubleshooting from another computer in the network. Use the -n 100 parameter to get a better statistical value. Large variations in the round-trip time (RTT) from one ping response to the next can also be a sign of network congestion.
    • Use Network Monitor 3.3 to capture a few minutes of audio conversation. Examine the variation in packet arrival times between subsequent packets. Large jumps in interval times can cause audio loss or distorted audio.
    • Use the Pre Call Diagnostic Tool to measure the network jitter along the last leg of the network. This can be viewed in the expanded Pre Call Diagnostic Tool interface.
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