Friday 1 November 2013

CUCM Clustering and Database Replication

What is a CUCM Cluster?
- A CUCM Cluster is a group of CUCM servers running the same version of CUCM working together as a single system to provide high availability of services for clients, transparent sharing of resources, features and enables system scalability.
- When a failure occurs on one server in a cluster, resources are redirected and the workload is redistributed to another server.
- The clustering feature of CUCM also provides a mechanism for distributing call processing and database replication among multiple CUCM servers. - The CUCM can support these two types:

Cluster : 
  • Supports upto 30000 IP phones
  • Can be scaled to a maximum of 20 Servers in which there can be a maximum of : 1 Publisher, 8 Call Processing Subscribers, 2 TFTP servers, 9 Other Servers.
Supercluster (Mega Cluster) :
  • Requires Cisco BU approval via Cisco Accounts Team
  • Supports upto 60000 IP phones
  • Can be scaled to a maximum of 21 Servers in which there can be a maximum of  : 1 Publisher, 16 Call Processing Subscribers, 2 TFTP Servers, 2 Other servers
There are two types of data communication between CUCM servers :
1) Database Replication :
Replication is the process of copying and maintaining database objects in multiple databases that make up a distributed database system. Replication can improve the performance and protect the availability of applications because alternate data access options exist.
- Read/write copy of the database is with the Publisher.
- This database is located in the IBM-IDS server. (Informix Dynamic Server manufactured by IBM Corp.)
- This is replicated to all Subscribers in a Hub (Publisher) and Spoke (Subscriber) topology i.e in a single direction from the Publisher to all subscribers (as shown in above figure).
- The Database replication is secured using embedded Red Hat Linux, iptables dynamic firewall (within the CUCM) and database security password (given during installation)

2) Cluster Communication :
ICCS Signaling :
- Used to replicate run-time data such as : Registration of devices, Locations bandwidth, Shared Media Resources.
- This signaling runs only between the servers that have the "ccm.exe" service i.e the Call manager service running (Call Processing agents).
- Uses TCP ports 8002-8004.
CDR & CAR :
- Call Detail Records are logged by the Call Processing Engine taking the call.
- These are periodically pushed to the Publisher server.
- The Cisco CAR or any third party billing application server always points to and collects data from the Publisher.

User Facing Features :
These features are two way replicated between Publisher and Subscriber.
These features work even if the publisher is down (from 8.x) :
  • Call Forward All (CFA)
  • MWI
  • Privacy Enabled/Disabled
  • DND
  • Extension Mobility Login
  • Hunt group login
  • Device Mobility
  • CTI CAPF Status
  • Credential Authentication
- Abhinay Mylavarapu.

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