For Hosted Messaging and Collaboration version 4.5, the sheer volume of OABs expected in a hosted environment leads to the introduction of a pool consisting of group of CAS servers for configuring redundant OAB distribution points. This also provides easy solution for high availability and provisioning.

CAS Web distribution pool is a piece of new concept introduced by Hosted Messaging and Collaboration version 4.5.  A CAS web distribution pool is a logical artifact that includes one or more CAS servers, each configured with a web distribution point.  Although the configurations may not be identical across the pool of CAS servers, the set of OABs replicated to the CAS servers within the pool are identical, if time variances are taken into consideration (for example, the OABs may be replicated at different time).

To use Web-based OAB distribution, the process is the following:

  1. Provision a set of CAS Web Distribution Pools, one of the pool can be designated as the default pool.
  2. Subscribe a MAPI enabled organization to a hosted email plan with feature <outlookClient> = Outlook 2007.  This assumes that users within the organization all use outlook 2007 as their client, as web-based OAB distribution is only supported on Outlook 2007.  The organization’s Offline Address Book will be provisioned against the default CAS Web Distribution Pool, which means that the users can download their OABs from any of the CAS servers in the pool.

CAS web distribution pool is designed to provide fault tolerance while also serves as a scale out unit.  In the event that a CAS server reaches beyond its capacity --for example, extended replication latency due to increased number of OABs, one can simply define a new CAS pool, and direct new organization provisioning to use the new pool instead.  In this way, each OAB CAS Pool will hold a subset of the total number of OABs.  To support increased number of concurrent user downloads, simply add new CAS servers to the pool used for OAB web distribution.

Reference architecture will detail the deployment of a CAS server pool for OAB distribution.