Triple-Play Service Deployment

Chapter 8: Troubleshooting VoIP
Common Causes
• Network Congestion
• Buffer overruns in network components
• Priority queuing and traffic shaping problems
Packet Delay – end-to-end network latency
• Customer experience – over talk and echo, contributor to jitter buffer discarded packets
Common Causes
• Priority queuing and traffic shaping problems (CoS/QoS)
• Choice of CODEC selection (packetization, buffering, compression)
• Network congestion
Packet Jitter - variation of arrival time between packets.
• Customer Experience - Clicking/popping noise to the end user, garbled speech.
Common causes
• Variation in network traffic levels
• Priority queuing and traffic shaping problems in combined VoIP / data networks
• Best Test – direct measurement of Jitter
Isolating VoIP problems
The following steps detail some of the ways that service providers
might respond to a customer’s complaint that a phone does not
work. The first step is to determine if the problem is in the network,
a provisioning issue, CPE related issue, or a customer issue. To
accomplish this task, the technician must perform an IP phone
emulation test. The next step is to attempt registration of the test
device with the gatekeeper/proxy server. The test set conducts
signaling decodes and displays signaling error messages. It proves
connectivity to the gatekeeper/proxy server and verifies
provisioning of the customer’s unique alias.The technician also uses
the device to place test calls on and off the network.
Another set of tests verifies the IP phone’s connectivity. A ping test
suite can help determine if a registration problem exists. The test
pings the gatekeeper/proxy server IP address. If off-net calls fail,
gateway provisioning may be causing the trouble or there may be a
connectivity issue. The latter can be identified by pinging the
gateway device’s IP address. A trace route test suite is performed if
the ping test fails with the gateway or gatekeeper/proxy server. The
trace route helps isolate path/device connectivity problems.
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