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

	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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