NEC SL1100 Networking Manual page 176

Issue 6.0
9 - 42
(.020 * 64000) /8 = 160 Bytes
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Example of G.729 with a 30ms packet size
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(.030 * 8000) /8 = 30 Bytes
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Now that you have the voice payload in bytes you can calculate the overall
bandwidth including the layer 2 media. Below are some of the common layer
2 media types and their overhead.
Ethernet = 18 Bytes

802.1Q/P Ethernet = up to 32 bytes
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PPP = 9 Bytes
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Frame Relay = 6 Bytes
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Multilink Protocol = 6 Bytes
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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.
NEC SL1100
IP Multiline Station (SIP)