A, B, C and D
All four of these are valid Cisco CallManager designs. E is incorrect because you need at least one call-processing agent in each cluster.
A 1:1 redundancy design offers maximum redundancy because each Cisco CallManager involved in call processing has a dedicated backup server. This model is often very cost prohibitive to most companies.
C and D
Although using a single cluster over WAN connections has very strict delay and bandwidth requirements, there are plenty of benefits. A common dial plan across all sites allows the network administrator to create a single dial plan, which replicates to all remote sites. In addition, if a Cisco CallManager fails, the IP Phones can failover to a Cisco CallManager server at another site, maintaining their full feature set.
B and C
Every Cisco CallManager cluster should have at least two servers, which allows call processing to continue should a single server fail. The data of the voice network is made redundant through the SQL database replication that occurs between servers in the cluster.
There can only be a single publisher server for the entire Cisco CallManager cluster. This is a SQL 2000 database restriction as the SQL publisher maintains the only writable copy of the database.
A Cisco CallManager cluster supports a single SQL publisher and up to eight SQL subscriber servers.
Survivable Remote Site Telephony (SRST) is absolutely necessary in a centralized Cisco CallManager design. SRST supports the remote IP Phones, providing PSTN calling access if the WAN connection fails.
If the Cisco CallManager server at a location fails, the IP Phones can failover to another Cisco CallManager server at a remote site.
A and C
The H.323 gatekeeper and SIP proxy server have the ability to be the centralized point of dial plan information. This keeps the network administrator from having to re-create the network dial plan at each of the sites.
Cisco will support a maximum cluster size of 30,000 IP Phones in Cisco CallManager 4.0. This large cluster size was introduced in Cisco CallManager version 3.3 and was a tremendous increase from earlier Cisco CallManager versions.
Part I: Cisco CallManager Fundamentals
Introduction to Cisco Unified Communications and Cisco Unified CallManager
Cisco Unified CallManager Clustering and Deployment Options
Cisco Unified CallManager Installation and Upgrades
Part II: IPT Devices and Users
Cisco IP Phones and Other User Devices
Configuring Cisco Unified CallManager to Support IP Phones
Cisco IP Telephony Users
Cisco Bulk Administration Tool
Part III: IPT Network Integration and Route Plan
Cisco Catalyst Switches
Configuring Cisco Gateways and Trunks
Cisco Unified CallManager Route Plan Basics
Cisco Unified CallManager Advanced Route Plans
Configuring Hunt Groups and Call Coverage
Implementing Telephony Call Restrictions and Control
Implementing Multiple-Site Deployments
Part IV: VoIP Features
Configuring User Features, Part 1
Configuring User Features, Part 2
Configuring Cisco Unified CallManager Attendant Console
Configuring Cisco IP Manager Assistant
Part V: IPT Security
Securing the Windows Operating System
Securing Cisco Unified CallManager Administration
Preventing Toll Fraud
Hardening the IP Phone
Understanding Cryptographic Fundamentals
Understanding the Public Key Infrastructure
Understanding Cisco IP Telephony Authentication and Encryption Fundamentals
Configuring Cisco IP Telephony Authentication and Encryption
Part VI: IP Video
Introducing IP Video Telephony
Configuring Cisco VT Advantage
Part VII: IPT Management
Introducing Database Tools and Cisco Unified CallManager Serviceability
Configuring Alarms and Traces
Using Additional Management and Monitoring Tools
Part VIII: Appendix
Appendix A. Answers to Review Questions