Wan Engineering; Figure 45 Peak Traffic, Wan Link - Nortel VoIP Gateway Configuration Manual

WAN engineering

Wide Area Network (WAN) links are typically full-duplex links - both talk and listen traffic use
separate channels. For example, a T1 link uses a number of 64 kbit/s (DS0) duplex channels
allowing *64 kbit/s for transmit path and n*64 kbit/s for the receive path.
(WAN links may also be half-duplex.)
Example 1: WAN engineering - voice calls
Consider a site with four IP telephony ports and a full-duplex WAN link using PPP. The preferred
codec is G.729, which uses a voice payload of 20 ms. Silence compression is enabled.
Given the above, what is the peak traffic in kbit/s that IP telephony will put on the WAN?
From the table under
figure shows the peak transmission rate for G.729 is 24.8 kbit/s per call or 99.2 kbit/s in each
direction for all four calls. In other words, in order to support four G.729 calls, the WAN link must
have at least 99.2 kbit/s of usable bandwidth (in each direction).
The average bandwidth for each call is 12.4 kbit/sec per channel or 49.4 kbit/s for all four calls for
each channel. Low priority data applications can make use of bandwidth made available by silence
suppression.

Figure 45 Peak traffic, WAN link

G.729 10
(8 kb/s)
20
30
"Bandwidth requirements on full duplex links" on page
PPP B/W
Silence
No SP Suppression
peak peak Avg
(kbit/s) (kbit/s) (kbit/s)
24.8 12.4
Network engineering
Norstar VoIP Gateway Configuration Guide
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