Optimisation - Aastra 800 User Manual

Voice over IP (VoIP)
Packet Propagation Delay and Packet Loss
Value
Propagation delay
< 50 ms
Propagation delay
50-100 ms
Propagation delay
100-150 ms
Propagation delay
150-200 ms
Propagation delay
200-300 ms
Propagation delay
> 300 ms

7.2.4 Optimisation

If you detect a large fluctuation in the propagation delay during measurement,
this may also cause the voice quality to deteriorate. This may indicate a defective
or overloaded line caused by bit-error or collision correction resulting from
retransmission by the transmission procedure.
An existing star-topology ethernet-network may uses a Hub as the central dis-
tributor of ethernet packets. A Hub repeats all ethernet packets received on all
connected lines. This can cause substantial collisions and result in a high fluctu-
ation in the propagation delay.
If this is the case, use a modern switch component. Selective forwarding of eth-
ernet packets ("Layer 2 switching") avoids collisions. Modern switch components
also evaluate the TOS byte of IP packets, thereby providing the optimal prerequi-
sites for VoIP telephony.
Quality Level
Optimal
0.5 level
depreciation
1 level
depreciation
2 level
depreciation
3 level
depreciation
4 level
depreciation
Note: The Aastra 800 uses a TOS byte ("Type of Service")
value of 0xB8 for IP packets with VoIP data. This requests
"Minimise Delay" and "Maximise Throughput" for IP packets
marked with this value.
Value
Loss < 1 %
Loss 1-2 %
Loss 2-3 %
Loss 3-4 %
Loss 4-6 %
Loss > 6 %
Fundamentals
Quality Level
Optimal
0.5 level
depreciation
1 level
depreciation
2 level
depreciation
3 level
depreciation
4 level
depreciation
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