Specifications

Network Configuration Concepts
221
WAN traffic working example
In this example, assume the following configuration:
• 50 IP phones at the corporate centre.
• 10 IP phones over a T1 link at a remote site.
• Trunk traffic is 65% of all traffic.
• Traffic between remotely located IP phones stays local to the remote site (it does not
traverse the WAN link).
Figure 36: WAN traffic example
Therefore
• The total traffic handled is 60 CCS.
• 3.5 CCS is local traffic.
• WAN traffic is 56.5 CCS = 60–3.5.
A previous calculation showed that a T1 WAN link could handle six G.711 voice channels without
QoS enabled. From ErlangB tables with P.001 blocking, such a link can handle 41.1 CCS. There
is a mismatch between presented traffic and carrying capacity.
Table 65: CCS calculation example
Calculation Formula Result
Remote phones 10
Total CCS at the remote site Remote phones x 6 CCS 60 CCS
Percentage of trunk traffic Total CCS x 65% 39 CCS
Percentage of intercom traffic Total CCS x (100 – trunk traffic)% 21 CCS
Local intercom traffic Intercom traffic x Ratio of local phones / total
phones (21x10/60)
3.5 CCS
Total traffic over the WAN Total traffic – local traffic 56.5 CCS