IP softphones

Computers running real-time softphone voice applications should support these features:

• Softphones support the G.711, G.729, and G.723 codecs.
• Echo-cancellation with an echo cancellation tail of at least 64 msec. Softphones support half-duplex to the speaker/microphone, and full duplex to the headset.
• A dynamic jitter buffer should be provided. Softphones support both dynamic and static jitter buffers. Networks should have less than 50 ms of delay, 20 ms of jitter, and 1% or less packet loss.
• Multi-media readiness. The PC should have a full duplex sound card.
• Full-duplex Ethernet network interface cards. 10/100 is sufficient. Also a 28,800 of higher modem is acceptable. VPN client software is normally required for remote connectivity.
• Good quality speakers and microphone, or a good quality headset. Headsets are recommended.
• Audio signals are sent over UDP and control signals sent over both UDP and TCP.