TD 92326GB
2009-03-10 / Ver. E
Installation and Operation Manual
VoIP Gateway
139
PPP protocol (in the WAN) remains the same per packet, whilst the voice data quantity,
and with it the data actually used, is reduced. The bandwidth actually required is therefore
considerably higher (depending on the packet size) than the pure voice data bandwidth as
specified in the table
Background noise (crackling) or greatly increased delays, tells you if voice data can no
longer be transmitted quickly enough, due to insufficient bandwidth or excessive network
transit times. In such a case, increase the packet size for the telephony interface concerned
to reduce the effect, or select a more efficient encoding scheme (for example G.723-53
instead of G.729). The following table shows the required bandwidths, depending on the
encoding and packet size.
Required bandwidths depending on the packet size
Encoding
scheme
Effective bandwidth used (in kbit/s) related to packet sizes of:
20 ms
30 ms
60 ms
90 ms
150 ms
possible connections per 64 kbit/s
G.711
83 kbit/s
77 kbit/s
70 kbit/s
68 kbit/s
67 kbit/s
G.723-53 24 kbit/s
18 kbit/s
12 kbit/s
9 kbit/s
8 kbit/s
2 3 5 6 8
G.723-63 25 kbit/s
19 kbit/s
13 kbit/s
10 kbit/s
9 kbit/s
2 3 5 6 7
G.729
27 kbit/s
21 kbit/s
14 kbit/s
12 kbit/s
11 kbit/s
2 3 4 5 6
G.726-16
19 kbit/s at 150 ms
3
G.726-24
27 kbit/s at 150 ms
2
G.726-32
35 kbit/s at 150 ms
1
G.726-40
43 kbit/s at 150 ms
1
T.38
14 kbit/s at 120 ms
a
a.Faxes are transmitted using the T.38 protocol at a fixed packet size of 150 ms. Strictly speaking,
the fax data is not compressed. There is merely no overhead which would otherwise be necessary
for analogue transmission.
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