
102 Efficient Networking
P0937663 03.1
With no silence suppression, both the transmit path and the receive path continuously transmit
voice packets. Therefore, the peak bandwidth requirement per call on half-duplex links is:
(Half Duplex links, No Silence Suppression)
On half-duplex links with silence suppression enabled, the half-duplex nature of normal voice
calls allows the sender and receiver to share the same bandwidth on the common channel. While
the sender is talking, the receiver is quiet. Since only one party is transmitting at a time, silence
suppression reduces the peak bandwidth requirement per call on a half-duplex link to:
(Half Duplex links, With Silence Suppression)
Bandwidth requirements on full duplex links
Table 14 provides bandwidth requirements for normal two-way voice calls on a full-duplex link
for a variety of link protocols, codec types and payload sizes. Bandwidths for full-duplex links are
stated in terms of the individual transmit and receive channels. For instance a 64 kbits full duplex
link (e.g. a DS0 on T1 link) has 64 kbits in the transmit direction and 64 kbits in the receive
direction.
Notes:
1) Gray background indicates payload sizes used by Business Communications Manager 2.5 for transmission. Other values
listed indicate payload sizes that BCM 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.
Table 14 Bandwidth Requirements per Gateway port for Full-duplex links
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
ms peak
(kbit/s)
peak
(kbit/s)
Avg
(kbit/s)
peak
(kbit/s)
peak
(kbit/s)
Avg
(kbit/s)
peak
(kbit/s)
peak
(kbit/s)
Avg
(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
Peak Bandwidth per call 2 Continuous Transmission Rate()=
Peak Bandwidth per call 1 Continuous Transmission Rate()=
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