Information Technology Reference
In-Depth Information
On the other hand, the CUCM database relationship has a little more substance to it. It is
not any more difficult to manage than ICCS (it just works behind the scenes), but it does
have some key concepts you'll want to know. First off, the CUCM IBM Informix database
uses a one-way replication method where a server known as the Publisher holds the master
copy of the database. All changes to the database (with some minor exceptions) occur on
the Publisher server and replicate to the Subscribers. Figure 2-5 illustrates this relationship.
Key
To p i c
Publisher
Subscribers
CUCM Cluster
Figure 2-5
CUCM Database Relationship
Each CUCM cluster supports a single Publisher and up to eight Subscribers. Think of the
Subscribers as the “workhorses” of the IPT network. These servers are providing dial tone,
receiving digits, routing calls, and streaming music on hold. However, the Publisher typi-
cally performs only two primary functions: It maintains the database and serves TFTP re-
quests. Because the Publisher serves such a critical role in maintaining the only writable
copy of the CUCM database, it is usually kept from all the heavier work. The TFTP re-
quests come from the Cisco IP Phones during their boot process (covered in Chapter 3).
Tip:
In smaller environments (500 IP phones or less), it's perfectly fine to use the
Publisher for call processing and database management. However, once you exceed that
number, it's generally a best practice to pull the Publisher out of call processing and leave
that work to the Subscribers. Likewise, once you exceed 1,250 users, Cisco recommends
moving the TFTP server role to a dedicated server.
