Hi Fran,
There is no way to have two actual Publishers or to promote a Sub to Pub at this time. But in the newer CUCM versions there is an extra measure of redundancy. Here is the background (there is no way to do this on any CCM version until 6.x)
The configuration database is stored on a publisher server, and a read-only copy is replicated to the subscriber members of the cluster. Changes made on the publisher are communicated to the subscriber databases, ensuring that the configuration is consistent across the members of the cluster, as well as facilitating spatial redundancy of the database.
The publisher server is the only server that has read and write access to the configuration database. When configuration changes are made, other members of the cluster have a read-only copy of the database.
From this CCM SRND;
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/4x/42clproc.html
This changes with the release of CCM 6.x;
In prior versions of Cisco Unified Communications Manager, subscriber servers in the cluster use the publisher database for READ/WRITE access, and only use the local database for READ access when the publisher database cannot be reached. With Cisco Unified Communications Manager Release 6.0, subscriber servers in the cluster READ the local database. DB WRITES happens in both the local database as well as the publisher database, depending on the type of data. DBMS (IDS) replication is used to synchronize the databases on the nodes of the cluster. When recovering from a failover conditions such as loss of WAN connectivity for extended period of time, the Cisco Unified Communications Manager databases need to be synchronized with any changes that may have been made during the outage. This process happens automatically when database connectivity gets restored. This process may take longer over low bandwidth and/or higher delay links.
Database modifications for CallProcessing
User Facing features can be made on subscribers. These include updates for:
Call Forward All (CFA)
Message Waiting Indication (MWI)
Privacy Enable/Disable
Do Not Disturb Enable/Disable (DND)
Extension Mobility Login (EM)
Monitor (for future use, currently no updates at the user level)
Hunt Group Logout
Device Mobility
CTI CAPF status for end users and application users
Credential hacking and authentication
From this 6.x SRND;
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/6x/callpros.pdf
Redundant TFTP Servers are supported and recommended :)
From this CCM SRND;
The TFTP service can be enabled on any server in the cluster. However, in a cluster with more than1250 users, other services might be impacted by configuration changes that can cause the TFTP service to regenerate configuration files. Therefore, Cisco recommends that you dedicate a specific server to the TFTP service in a cluster with more than 1250 users, with Extension Mobility, or with other features that cause configuration changes.
The TFTP server is used by phones and MGCP gateways to obtain configuration information. There is no restriction on the number of servers that can have TFTP service enabled, however Cisco recommends deploying 2 TFTP servers for a large cluster, thus providing redundancy for TFTP service.
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/4x/42clproc.html#wp1051169
Hope this helps!
Rob
