Nortel RLC Installation And Administration Manual page 91

June 2005
The following table indicates one-way delay in ms for the common
configurations. It can seem unusual that the ISDN delay is larger than the IP
delay. However, this is due to the serialization delay of sending the packets
across the relatively low-speed (64K) channels provided by ISDN. (The IP
Network delay assumes high-speed Internet access as part of the intranet.)
Minimum recommended
jitter buffer setting
Algorithmic delay
Reasonable network delay 10
Total One Way Delay
Excessive delay results in users talking over each other (that is, both users
speaking at the same time). Studies vary as to when this becomes a voice quality
problem, but most of them suggest that this occurs between 120 and 180 ms.
Real-time data transmission produces two types of packet loss:
network-related packet loss (that is, packets lost due to either errors or
delays in transmission)
jitter buffer-related packet loss (that is, packets lost due to their being
thrown away when the jitter buffer is full)
In effect, there is a trade-off between jitter buffer delay (jitter buffer size) and
packet loss delay at the Remote Gateway 9100 Series unit. The relationship
between jitter buffer size and packet loss has a direct impact on the user's
perception of voice quality.
Customer feedback and experience indicate that configuring the jitter buffer to
reduce delay produces better results. Delay, as introduced by the size of the jitter
buffer, is inversely proportional to lost packets. A jitter buffer configuration of
30 ms results in less delay, but a greater likelihood of lost (thrown away)
packets. Most customers find packet loss of 1% far more acceptable than an
increase in one-way delay beyond 180 ms.
RLC Installation and Administration Guide
G.729A
IP Network Over
Delay PSTN
30 30
30 30
20
70 80
Planning for RLC installation
G.726 G.711
Over Over
PSTN PSTN
60 90
30 30
20 20
110 140
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