
Networking 95
IP Telephony Configuration Guide
The bandwidth made available by silence suppression on full-duplex links with continuous
transmission rate – average bandwidth requirement, is available for lower priority data applications
that can tolerate increased delay and jitter.
Table 12 Bandwidth Requirements per BCM Gateway port for Full-duplex links.
LAN Engineering Examples
Example 1: LAN engineering - voice calls
Consider a site with four Business Communications Manager IP telephony ports. Assume a
preferred codec of G.729, which uses a voice payload of 20 ms. Silence compression is enabled.
The Ethernet LAN is half-duplex. Ethernet LAN may also be full duplex.
Given the above, what is the peak traffic in kbit/s that IP telephony will put on the LAN?
From Table 11 on page 94, the peak transmission bandwidth for G.729 with silence suppression
enabled on a half-duplex link is 34.4 kbit/s per call or 137.6 kbit/s for all four calls.
Codec
Type
Payload
Size Ethernet B/W
2
PPP B/W FR B/W
No SP
Silence
Suppression
No SP
Silence
Suppression
No SP
Silence
Suppression
peak peak Avg peak peak Avg peak peak Avg
msec kbit/s kbit/s kbit/s kbit/s kbit/s kbit/s kbit/s kbit/s kbit/s
G.711
(
64 kb/s)
10 116.8 116.8 116.8
3
97.6 97.6 97.6
3
103.2 103.2 103.2
3
20 90.48 90.4 90.4
3
80.8 80.8 80.8
3
83.6 83.6 83.6
3
30 81.6 81.6 81.6
3
75.2 75.2 75.2
3
77.1 77.1 77.1
3
G.729
(8 kb/s)
10 60.8 60.8 30.4 41.6 41.6 20.8 47.2 47.2 23.6
20 34.2 34.4 17.2 24.8 24.8 12.4 27.6 27.6 13.8
30 25.6 25.6 12.8 19.2 19.2 9.6 21.1 21.1 10.6
G.723.1
(6.3 kb/s)
30 24.0 24.0 12.0 17.6 17.6 8.8 19.5 19.5 9.8
G.723.1
(5.3 kb/s)
30 22.9 22.9 11.5 16.5 16.5 8.3 18.4 18.4 9.2
Notes:
1) Gray background indicates payload sizes used by Business Communications Manager 2.5 for transmission. Other values
listed indicate payload sizes that Business Communications Manager can receive.
2) Ethernet bandwidth includes the 14 byte Ethernet frame overhead plus a 12 byte inter-frame gap.
3) G.711 does not support silence suppression. Therefore the average bandwidth is the same as the peak bandwidth.
4) Bandwidths stated per channel (Rx or Tx).
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