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Traffic engineering
222 Avaya Application Solutions IP Telephony Deployment Guide
table of WAN bandwidths, Table 44: IP WAN bandwidth requirements for media streams on
page 222, which assumes the use of cRTP:
This table can be used in the WAN bandwidth calculation for the system in Example 6: IP
bandwidth considerations.
Example 8: WAN bandwidth
In Example 6: IP bandwidth considerations, the total IP WAN bandwidth usage between each
pair of sites was calculated, and expressed in Erlangs at the bottom of Table 40
. Specifically, the
total WAN bandwidth usage between Sites 1 and 2 is 24.0 Erlangs, between Sites 1 and 3 is
10.0 Erlangs, and between Sites 2 and 3 is 4.0 Erlangs. This implies that the average number of
media streams simultaneously in use at any given time between Sites 1 and 2 is 24. Analogous
statements can also be made regarding WAN traffic between each of the other two pairs of
sites.
Every media stream across the IP WAN, between any pair of sites, is assumed to use the
compressed G.729 codec, since bandwidth is relatively inexpensive within a private LAN, as
opposed to a public WAN. Assume, for the sake of this example, a standard IP packet size of 20
ms. For the G.729 codec, Table 44
indicates that each (unidirectional) media stream consumes
12.4 kbps of IP WAN bandwidth. Similar to the case in Example 7: LAN bandwidth
, 24 is the
average number of simultaneous bidirectional media streams. As in Example 7: LAN bandwidth
,
the bandwidth is sized to a “GOS” of P001 (“GOS” in this context is actually a pseudo-GOS; true
GOS is associated with a fixed number of channels, as is typical of circuit-switched systems).
The standard infinite-server queueing model implies that less than 0.1% of the time there is at
least 40 simultaneous media streams between Sites 1 and 2. So, it is sufficient to engineer the
WAN bandwidth between those two sites to support 39 simultaneous media streams. Therefore,
the WAN between Sites 1 and 2 requires at least (39 simultaneous media streams) x (12.4 kbps
per media stream) = 484 kbps of bandwidth. This result, along with the analogous results for the
WAN traffic between the other two pairs of sites, are provided in Table 45:
IP WAN bandwidth
requirements in each direction, for Example 8: WAN bandwidth on page 223.
Table 44: IP WAN bandwidth requirements for media streams
Packet “size”
(ms)
G.711 (kbps) G.729 (kbps)
10 72.8 16.8
20 68.4 12.4
30 66.9 10.9
60 65.5 9.5