dwidth by switching trans- missions to appropriate connections as the connections are set up. In other words, the path is conceived at the outset, and after the path is determined, all the subse- quent information follows the same path to the destination. In a connection- oriented network, there can be some delay up front while the connection is being set up; but once the path is established (and the same path is always followed), the delay is fixed and predictable at intermediate nodes. Connection-oriented networks can actually operate in either switching mode: They can be either circuit switched or packet switched. Connection-oriented Establishing Connections: Networking Modes and Switching Modes circuit-switched networks include the PSTN (covered later in this chapter and in detail in Chapter 4, "The PSTN"), SDH/SONET (covered in more detail in Chapter 4), and DWDM (covered in detail in Chapter 11, "Optical Networking") networks. Connection-oriented packet-switched networks (covered later in this chapter and in detail in Chapter 7, "Wide Area Networking") include X.25, Frame Relay, and ATM networks. Connection-oriented networks can be operated in two modes: Provisioned-In provisioned networks, the connections can be set up ahead of time based on expected traffic. These connections are known as permanent virtual circuits (PVCs). Switched-In switched networks, the connections are set up on demand and released after the data exchange is complete. These connections are known as switched virtual circuits (SVCs). Connectionless Networking In a connectionless network, no explicit connection setup is performed before data is transmitted. Instead, each data packet is routed to its destination based on infor- mation contained in the header. In other words, there is no precomputed path. Rather, each packet of the overall traffic stream is individually addressed and indi- vidually routed. In a connectionless network, the delay in the overall transit time is increased because each packet has to be individually routed at ea