Let us jump straight into the key Skype related services of the Central Management Store better known as the CMS.
-- Master Replicator Agent
-- File Transfer Agent
-- Replica Replicator Agent
Master Replicator Agent
This service belongs to the Skype front-end pool that contains the master CMS. Only a single front-end pool in the topology can contains the master CMS; this is generally the front-end pool where you installed Skype for Business server first during the initial deployment. By definition, it is the location of the backend SQL server database that contains the (XDS) database. Keep in mind you could move the (XDS) database to another SQL backend server through move cmdlet in the Skype management shell.
Note: The location of the master CMS is stored in an Active directory object called “msRTCSIP-GlobalTopologySetting” which under its properties you find an attribute named “msRTCSIP-BackEndServer”.
Another method to find the location of the master CMS is by locating the “Service Connection Point” SCP that is created by the topology builder the first time you published the topology and can be checked by using the Get-CsManagementConnection.
Figure1: Cmdlet result of Get-CsManagementConnection to find the location of the back-end CMS
It does not matter if that pool contains 3 or 8 front-end servers, each front-end server in the pool that contains the master CMS will have a service running called "Master Replicator Agent". The Master Replicator Agent service generates a data package containing new changes to CMS and stores a copy in each to-replica directory for every Skype Server replica; the data package must be copied to all replicas.
File Transfer Agent
The File Transfer Agent service runs on the master CMS pool front-end servers and copies information and data from the topology to all other Skype for Business servers as replicas via Server Message Block (SMB). The good thing is that the data packages are usually small in nature, generally less than 100 kb in size of the deltas of changes in the topology. Being that the deltas are small provides for ease of replication of Skype related topology changes across the network.
Replica Replicator Agent
Every Skype server in the topology has a Replica Replicator agent that is running, when a Skype server starts, the Replica Replicator Agent service generates a status.zip package to report the current replication status to the CMS store.
Note: All the management store services of the CMS run on the master CMS pool, however the “Replica Replicator agent will run on all the servers in the Skype server in the topology; hence servers that are part of the master CMS pool have all the services related below.
Central Management Store Services
The collection of CMS services together provide a functional cohesive service to the Skype environment. Knowing what they do and when is also a key part to understanding how replication works, failover of pools, and how data is sent from the master CMS to the other Skype for Business servers also. You can almost look at these services as the Three Musketeers. Then I know some literature people would say there where actually Four Musketeers; but keep in mind the author was telling his story of how he became one.