The client apps run on real-world networks and user owned hardware. The QoS on real-world networks are unpredictable, based several factors such as location, ISP, Wireless provider, peak times, load on the network etc. On the other hand, server applications are hosted within a datacenter, where hardware, capacity, network are under control of the application owner.
MMS bridges client apps with the server apps.
Client Apps can be,
Server Apps can be,
Client Apps connect to /client
end point.
Server Apps connect to /server
end point.