Guidelines for Multiple Clusters
Earlier in this chapter we discussed a couple of scenarios where it would be necessary
to use multiple clusters.These were for very large networks with over 10,000
registered devices, and for IP Telephony networks distributed over wide area links.
Remember that clustering is not supported over a WAN. Communications
between clusters require H.323 inter-cluster links.
There are three multicluster designs that may be tailored to fit your design
goals:
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Figure 4.5 Clustering over a MAN
Multipoint Controller Unit
Cisco CallManager
114 Chapter 4 • AVVID Clustering
Multiple clusters within a campus or Metropolitan Area Network (MAN)
Multiple clusters over a multisite WAN with distributed call processing
Multiple clusters over a multisite WAN with centralized call processing
When using multiple clusters on a MAN, the following should be considered:
Call admission control is not required over a MAN.
Cisco recommends a maximum of two inter-cluster peers per device.
Where a gatekeeper is used, Cisco recommends a single H.323 connection
per cluster. Implement redundancy by assigning a CallManager
redundancy group to the gatekeeper.
If an inter-cluster link is established across a WAN, this becomes a bottleneck
for communication between clusters, and the WAN link should be scaled to deal
with this extra traffic.
For a network with several large sites, call processing should be distributed
between the sites, with H.323 Cisco IOS gateways acting as a gatekeeper.The
gatekeeper provides both inbound and outbound access control and can control
the amount of bandwidth on the WAN link used by voice applications. Call processing
is performed within each site, with calls traversing the WAN as needed.
If you have a network with a single central site, and multiple small branch
offices or telecommuters, remote call processing might be a suitable option. All
call processing will take place at the central site, and each remote site is configured
as a Cisco CallManager location (see Figure 4.6). CallManager tracks both
available and used bandwidth for each location, and will permit or deny calls
based on this information.With Cisco CallManager 3.x, up to 2,500 remote
devices can be configured. A single CallManager cluster, containing a single
CallManager server must be configured at the local site, specifically to handle
these remote sites.