
Networking 93
IP Telephony Configuration Guide
Table 10 Voice over IP Transmission Characteristics for unidirectional continuous media stream
Bandwidth Requirements on Half Duplex Links
Table 11 on page 94 provides bandwidth requirements for normal two-way voice calls on a
half-duplex link for a variety of link protocols, codec types and payload sizes.
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::
peak Band Width per call = 1 * Continuous Transmission Rate
(Half Duplex links, With Silence Suppression)
Codec
Type Payload Size
IP
Packet Ethernet B/W
2
PPP B/W FR B/W
ms Bytes Bytes kbit/s kbit/s kbit/s
G.711
(64 kb/s)
10 80 120 116.8 97.6 103.2
20 160 200 90.4 80.8 83.6
30 240 280 81.6 75.2 77.1
G.729
(8 kb/s)
10 10 50 60.8 41.6 47.2
20 20 60 34.4 24.8 27.6
30 30 70 25.6 19.2 21.1
G.723.1
(6.3 kb/s)
30 24 64 24.0 17.6 19.5
G.723.1
(5.3 kb/s)
30 20 60 22.9 16.5 18.4
Notes:
1) Gray Background indicated payload sizes used by Business Communications Manager 2.5 for transmission. Other
values listed indicate payload sizes that the Business Communications Manager 2.5 can receive.
2) Ethernet bandwidth includes the 14 byte Ethernet frame overhead plus a 12 byte inter-frame gap.
Peak Bandwidth per call 2 Continuous Transmission Rate()=
Peak Bandwidth per call 1 Continuous Transmission Rate()=
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