VoIP Voice and Fax Signal Processing

10.9 FIXED JITTER BUFFER IMPLEMENTATION GUIDELINES

FJB has to work very similarly to AJB with the main difference of lack of provision to track network conditions. In actual implementation, AJB is made to work like FJB with disabling of adapting tracking of playout time.

• Jitter buffer to remove duplicate packets with minimal processing.
• The jitter buffer lower threshold is usually from 20 to 70 ms, and the upper limit is 400 ms for voice calls. The upper threshold has to be greater than or equal to the expected spike.
• The jitter buffer lower threshold may be increased for fax and modem pass-through calls.
• Jitter buffer has to maintain a stationary pattern for packet drops and VAD silences.
• Jitter buffer should be prevented from complete under-run. Before under-run occurs, possible silence zones need to be created at a rate of 1 in 10,000 packets (meaning one 10-ms packet for every 100 seconds). Here also preference has to be given based on talk-spurt detection.
• Jitter buffer should be prevented from over-run. Before reaching the over-run, old packet removal needs to be created at a rate of 1 in 10,000 packets (meaning one 10-ms packet for every 100 seconds). Here also preference has to be given to talk-spurt detection.

VoIP Voice and Fax Signal Processing, by Sivannarayana NagireddiCopyright © 2008 by John Wiley & Sons, Inc.