EMCC and Directory Syncronization: Be careful what you sync

One attractive new feature of UCM 8.x is Extension Mobility Cross Cluster (EMCC)
Extension mobility is the term used by Cisco for the ability to use a device profile to log into a EM capable phone, therefore preserving you personal settings (speed dials, your number etc.) while being on a different desk. This feature is  often used for shared desks or guest offices.

One of the caveats of EM was that one could only log into devices on a single cluster, e.g. if the organization has multiple clusters, user device profiles could not be used between clusters.

This limitation has been resolved in UCM 8.x with EMCC. EMCC allows one cluster to dynamically query "linked/trusted" clusters for a device profile.
The CCM Features Guide has a very nice diagram showing the login process.

EMCC Login Flow

There is one point which needs to be emphasized: For this to work, userids have to be unique across cluster and must not be duplicated. So if I am User "balbler" and the cluster in SJ is my home cluster and i want to do a EMCC login on the AMS cluster, my userid MUST not exist on the AMS cluster.
The reason for this is quite simple: The EMCC process will only query the remote cluster if it can not find the user in the local CCM db.

This is quite easy to do if you have a local user db.
It get's slightly more complicated if you bring LDAP integration into the picture.
DirSync allows you to sync userIDs from a LDAP directory (e.g. Active Directory or OpenLDAP) into the UCM user DB.
Most customers will have a single, global LDAP directory for the whole organization
In that case for EMCC to work, you have to make sure that usernames are not duplicated because of the sync.
There are 2 options on fulfilling this requirement:

• If possible sync only part of the LDAP tree (a subtree)
• Filter based on a attribute: This can be done via GUI on UCM 8.x (and was possible via sql manipulation of the ldapconfig table in prior versions)

So when planning on using EMCC and are already using LDAP Synchronisation, one needs to make sure there is a way to properly filter the users so there is no userid duplication.

Be aware that this will also mean that the ccm generated corporate directory will only contain the users from the local cluster. For a complate directory the CorpDir XML service will have to be replaced.