Voice over IP (VoIP)

 

 

Fundamentals

 

 

 

 

 

Packet Propagation Delay and Packet Loss

 

 

 

 

 

 

 

Value

Quality Level

Value

Quality Level

 

 

 

 

 

 

Propagation delay

Optimal

Loss < 1 %

Optimal

 

< 50 ms

 

 

 

 

 

 

 

 

 

Propagation delay

0.5 level

Loss 1-2 %

0.5 level

 

50-100 ms

depreciation

 

depreciation

 

 

 

 

 

 

Propagation delay

1 level

Loss 2-3 %

1 level

 

100-150 ms

depreciation

 

depreciation

 

 

 

 

 

 

Propagation delay

2 level

Loss 3-4 %

2 level

 

150-200 ms

depreciation

 

depreciation

 

 

 

 

 

 

Propagation delay

3 level

Loss 4-6 %

3 level

 

200-300 ms

depreciation

 

depreciation

 

 

 

 

 

 

Propagation delay

4 level

Loss > 6 %

4 level

 

> 300 ms

depreciation

 

depreciation

 

 

 

 

 

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.

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.

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Aastra Telecom 800 manual Optimisation, Packet Propagation Delay and Packet Loss Value Quality Level