Aastra OpenCom 130 User Guide - Page 113

Voice over IP (VoIP) Fundamentals Packet Propagation Delay and Packet Loss Value Quality Level Value Propagation delay Optimal < 50 ms Loss < 1 % Propagation delay 0.5 level deprecia- Loss 1-2 % 50-100 ms tion Propagation delay 1 level deprecia- Loss 2-3 % 100-150 ms tion Propagation delay 2 level deprecia- Loss 3-4 % 150-200 ms tion Propagation delay 3 level deprecia- Loss 4-6 % 200-300 ms tion Propagation delay 4 level deprecia- Loss > 6 % > 300 ms tion Quality Level Optimal 0.5 level depreciation 1 level depreciation 2 level depreciation 3 level depreciation 4 level depreciation 9.2.4 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 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. Note: The OpenCom 100 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. 111