Connectivity allows applications to transparently communicate with other programs or processes, regardless of their location. The key element of connectivity is the network operating system (NOS). NOS provides services such as routing, distribution, messaging, file and print, and network management services. NOS rely on communication protocols to provide specific services. The protocols are divided into three groups: media, transport and client-server protocols. Media protocols determine the type of physical connections used on a network (some examples of media protocols are Ethernet, Token Ring, Fiber Distributed Data Interface (FDDI), coaxial and twisted-pair). A transport protocol provides the mechanism to move packets of data from client to server (some examples of transport protocols are Novell's IPX/SPX, Apple's AppleTalk, Transmission Control Protocol/ Internet Protocol (TCP/IP), Open Systems Interconnection (OSI) and Government Open Systems Interconnection Profile(GOSIP)). Once the physical connection has been established and transport protocols chosen, a client-server protocol is required before the user can access the network services. A client-server protocol dictates the manner in which clients request information and services from a server and also how the server replies to that request (some examples of client- server protocols are NetBIOS, RPC, Advanced Program-to-Program Communication (APPC), Named Pipes, Sockets, Transport Level Interface (TLI) and Sequenced Packet Exchange (SPX)).   _{Your Comment}