• Ethernet = 18 Bytes
• 802.1Q/P Ethernet = up to 32 bytes
• PPP = 9 Bytes
• Frame Relay = 6 Bytes
• Multilink Protocol = 6 Bytes
Bandwidth Calculation
( [ Layer 2 overhead + IP/UDP/RTP header + Voice Payload ] / Voice Payload ) * Default CODEC
speed = Total Bandwidth
Example of a G.711 call over Ethernet using a 20ms packet size and not using RTP header
compression
(.020 * 64000) / 8 = 160 Bytes for Voice Payload
([ 18 + 40 + 160] / 160) * 64000 = 87200bps
If VAD is not enabled each side of the conversation would be streaming 87.2kbps in one direction for a
total of 174.4kbps.
The following chart shows the supported CODECS for IP phones with different packet sizes over PPP
and Ethernet.
CODEC Packet Size PPP Ethernet
G.711 10 103.2 kbps 110.4 kbps
G.711 20 83.6 kbps 87.2 kbps
G.711 30 77.1 kbps 79.5 kbps
G.711 40 73.9 kbps 75.6 kbps
G.722 10 103.2 kbps 110.4 kbps
G.722 20 83.6 kbps 87.2 kbps
G.722 30 77.1 kbps 79.5 kbps
G.722 40 73.9 kbps 75.6 kbps
G.729 10 47.2 kbps 54.4 kbps
G.729 20 27.6 kbps 31.2 kbps
G.729 30 21.1 kbps 23.5 kbps
G.729 40 17.8 kbps 19.6 kbps
G.729 50 15.9 kbps 17.3 kbps
G.729 60 14.5 kbps 15.7 kbps
13.8 Some Network Considerations
When adding the SL2100 to a customers network there are many things to be aware of. Before
implementation a detailed network diagram of the existing network must be obtained from the
customer. This diagram may provide you with information about possible network conditions that can
prevent or hinder the VoIP equipment from functioning correctly.
SL2100
ISSUE 1.0
9-28
IP Multiline Station (SIP)
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