Nortel VoIP Gateway, Configuration Manual, Page: 157 / 220

Network engineering 157
Norstar VoIP Gateway Configuration Guide
Bandwidth requirements on full duplex links
The following table 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.
With no silence suppression, both the transmit path and the receive path continuously transmit
voice packets. Enabling silence suppression on full-duplex links reduces the average bandwidth.
However, since transmit and receive paths use separate channels, the peak bandwidth per call per
channel does not change. Therefore, peak bandwidth requirements per channel (Rx or Tx) per call
on a full-duplex link is:
Peak Bandwidth per channel per call = 2(Continuous Transmission Rate)
(Full Duplex links, With or Without Silence Suppression)
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 28 Bandwidth Requirements per Gateway port for Full-duplex links
Codec
Type
Payload
Size
Ethernet B/W 1 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
2
97.6 97.6 97.6
2
103.2 103.2 103.2
2
20 90.48 90.4 90.4
2
80.8 80.8 80.8
2
83.6 83.6 83.6
2
30 81.6 81.6 81.6
2
75.2 75.2 75.2
2
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) Ethernet bandwidth includes the 14 byte Ethernet frame overhead plus a 12 byte inter-frame gap.
2) G.711 does not support silence suppression. Therefore the average bandwidth is the same as the peak bandwidth.
Bandwidths stated per channel (Rx or Tx).