The clustering of servers, or a server farm, is important to maintaining near-100 percent availability. If one (or multiple) servers fail or are taken down for maintenance, it should be transparent to the remote office/end user. Server farms are scalable as long as they can share databases. No server should be an "information island."
QoS is a process whereby switches and routers set up resources to move data quickly and reliably. Often ISPs cannot support true QoS because they do not control the entire connection, including local access and backbone interconnects.
The IETF published a standard called Diff-Serv, which is intended to allow ISPs to deploy different QoS levels on the Internet's backbone. This is accomplished by allowing users to mark data packets so that routers can forward them appropriately.
Diff-Serv has all but replaced Resource Reservation Protocol (RSVP) in an effort to implement QoS. RSVP relied on a type of signaling mechanism between devices on the Internet—specifically routers. This signaling setup was done on a per-connection basis, and it required that all routers on the Internet agree to a specific level of service.
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