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Figure 75: Case Study I: Configuration of the Three Sites
Atlanta
S8700
G650
G650
PSTN
Site 1: Headquarters
End Users: 1,755
IPSIs: 1
MedPros: 3
C-LANs: 5
The single WAN link is the weakest link in this configuration. Because WAN facilities are usually
leased, because they are not under an enterprise's direct control, and because of the expense
involved in procuring WAN circuits, WAN availability has historically been in the range of 99% to
99.5%, although some service providers do offer SLAs guaranteeing 99.9% availability per
WAN circuit. Call control signaling traffic traverses the WAN link to give service to the phones in
Boston and Cleveland. As a result the availability of these two sites is no greater than the WAN
link.
Boston
WAN Edge
Routers
WAN
Cleveland
Design for High Availability
Site 2: Branch Office
End Users: 648
IPSIs: 1
MedPros: 2
C-LANs: 2
G650
PSTN
Site 3: Branch Office
End Users: 270
PSTN
2 G700 Media Gateways
cydfcas1.pdf KLC 121103
Issue 3.4.1 June 2005
263
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