 packets will arrive. Connection-Oriented Packet-Switched Networks The connection-oriented packet- switched environment is something like a telephone network, in which a call setup is performed end to end. X.25, Frame Relay, ATM, and MPLS are all connection- oriented techniques. In a connection-oriented packet-switched network, only one call request packet contains the source and destination address (see Figure 3.7). Therefore, the subsequent packets don't have to contain the address information, which reduces the overall overhead. The call request packet establishes the virtual circuit. Each individual switch along each path, then, forwards traffic to the appro- priate next switch until packets all arrive at the destination. With connection- oriented networks, each individual packet does not need to be routed. Instead, each packet is marked as belonging to some specific flow that identifies which vir- tual circuit it belongs to. Thus, the switch needs only to look at the mark and for- ward the packet to the correct interface because the flow is already set up in the switch's table. No repeated per-packet computation is required; consequently, connection-oriented networks reduce latencies, or delays. In the connection-oriented environment, the entry node contains the routing table, where the path is calculated and determined, and all packets follow that same path to the destination node, thereby offering a better guarantee of service. Network backbone Initial call request packet establishes a virtual circuit (X.25, Frame Relay, ATM, MPLS) Packet switch (X.25, Frame Relay, ATM, or MPLS label edge router or terabits per second switch router) Routing table Packet Figure 3.7 A connection-oriented network Chapter 3 Establishing Communications Channels Advantages and Disadvantages of Packet Switching Packet-switching tech- niques have a number of limitations, including the following: Latencies occur because connection-oriented packet switching is a store- and-forward mechanism. Jitter occurs. Jitter refers to variable 