/mcpDescription IM and Presence Deployment The IM and Presence Service and Unified Communications Manager cluster nodes are part of the same cluster. The IM and Presence cluster shares a platform and many of the same services as the telephony cluster. Each cluster will have nodes of both. This option requires a 1x1 mapping of Unified CM telephony clusters to IM and Presence clusters. Basic installations order followed is same as mentioned in the Attended Install method. For more information, see the "Installation Methods". For touchless installations, you can install all Unified Communications Manager and IM and Presence Service cluster nodes concurrently in a single process. Standard Deployment (de-centralized/distributed) ) A single IM and Presence Service central cluster is installed separately from your Unified Communications Manager telephony cluster(s) and may be located on different hardware servers. The single IM and Presence Service cluster maps to all Unified Communications Manager telephony clusters. This allows you to scale your telephony deployment and IM and Presence deployment separately. For basic installations: 1. Install a local Unified Communications Manager publisher node in the central IM and Presence Service cluster. This node is not a part of your telephony deployment. The node handles functions like database and user provisioning for the central cluster. 2. Install the IM and Presence Service database publisher node. 3. Install any IM and Presence subscriber nodes. For touchless installations, you can install your local Unified Communications Manager publisher node and your IM and Presence Service central cluster in a single process. However, your telephony cluster must be installed separately. For more information, see the "Configure Centralized Deployment" chapter at Configuration and Administration of the IM and Presence Service Guide. IM and Presence Centralized Cluster Deployment Run the Collab Sizing Tool to get the required virtual machine count and specs of each virtual machine. If you don't want to run the Collab Sizing Tool, follow the guidance in the OVA readme and the OVA wizard to select a predefined starting point, which can be changed later if needed. For more information, see the Cisco Virtualization Guide for Cisco On-premises Calling Applications<url TBD>. Cluster Size Unified Communications Manager supports a megacluster that can support up to 8 primary call processing nodes and 8 secondary/standby call processing nodes.The total number of servers in a cluster, including the Unified Communications Manager publisher node, TFTP server, and media servers, cannot exceed 21. The maximum number of IM and Presence Service nodes in a Standard cluster is 6. Installation Guide for Cisco Unified Communications Manager and the IM and Presence Service, Release 15 and SUs 4 Planning the Installation Topology Options