Nortel VoIP Gateway, Configuration Manual

Page: 158 / 220

158 Network engineering
P0606298 02
LAN engineering examples
Example 1: LAN engineering - voice calls
Consider a site with four VoIP Gateway ports. Assume a preferred codec of G.729 and a 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 the table under “Bandwidth requirements on half duplex links” on page 155 , the following
figure shows 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.
Figure 44 LAN engineering peak transmission
Ethernet B/W 2
No SP
Silence
Suppression
peak
(kbit/s)
peak
(kbit/s)
Avg
(kbit/s)
G.729
(8 kb/s)
10
20 34.4 34.4
30