T-Home Comfort Pro S, Руководство по установке

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Voice over IP (VoIP) Fundamentals
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 cor-
rection resulting from retransmission by the transmission procedure.
An existing star-topology ethernet-network may uses a Hub as the central distributor of ethernet packets. A
Hub repeats all ethernet packets received on all connected lines. This can cause substantial collisions and
result in a high fluctuation in the propagation delay.
If this is the case, use a modern switch component. Selective forwarding of ethernet packets (“Layer 2
switching”) avoids collisions. Modern switch components also evaluate the TOS byte of IP packets, thereby
providing the optimal prerequisites for VoIP telephony.
N
Note: The Comfort Pro S uses a TOS byte (“Type of Service”) value of 0xB8 for IP pack-
ets with VoIP data. This requests “Minimise Delay” and “Maximise Throughput” for IP
packets marked with this value.
Propagation delay 150-
200 ms
2 level depreciation Loss 3-4 % 2 level depreciation
Propagation delay 200-
300 ms
3 level depreciation Loss 4-6 % 3 level depreciation
Propagation delay
> 300 ms
4 level depreciation Loss > 6 % 4 level depreciation
Packet Propagation Delay and Packet Loss
Value Quality Level Value Quality Level