Nortel Remote Office 9110 Release Note

Also see for 9110: Reference guide Reference guide Release note Quick start guide Installation and administration guide

Nortel Remote Office 9110 Release Note Manual pdf 25 page image

1.4.2 Release Notes for Remote Office and RLC 25December 2003Impact of delay on voice qualityThe impact of the different voice algorithms (G.729A, G.726, and G.711) is welldocumented. G.729A provides 8 to 1 compression and does not produce perfectvoice quality. Most users consider it quite acceptable, although some users claimthat they can hear the difference between it and G.711. The 8 to 1 compressionratio and the acceptable voice quality make it the codec of choice for Voice overIP (VoIP). Multiple instances of transcoding (that is, compressing anddecompressing) can have a significant impact on voice quality. G.729A is morelikely to be negatively affected by transcoding than G.711.Most users do not understand the impact of network/PSTN delay or the impactof voice compression algorithms on the perceived quality of voice. In order tocompensate for the variation in transmission time across the network (IP andPSTN), the Remote Office product uses a jitter buffer to allow voice packets topass through it in a constant stream. The purpose of the jitter buffer is to removethe variable delays from the voice packets sent across the network, thus avoidingawkward-sounding speech. The default value of this jitter buffer is 90milliseconds (ms).Note: Once you configure the jitter buffer, the jitter buffer can vary up to 30 msabove or below the configured target.To estimate the total delay the user experiences, add the following values:! jitter buffer delay! network delay! algorithmic encoding delay of the algorithm in useTo make the calculation simple, use 30 ms as the algorithmic delay. (It variesdepending on the voice algorithm, but 30 ms is a good estimate).