cilities between the switches directly affects the performance of packet-switched networks; this is why many new-generation packet switches-IP routers and ATM switches, for instance-now come with high-speed interfaces, such as OC-48 (i.e., 2.5Gbps) interfaces. OC-48 interfaces on a switch could potentially eliminate the need for an entire layer of aggregation that we currently do according to the traditional model of 64Kbps channels. By eliminating that layer of aggregation, we can actually allow direct connection to an optical network by using DWDM at the full rate of the service and interface. (See Chapter 1, "Telecommunications Technology Fundamentals," and Chapter 11, "Optical Networking," for information on DWDM.) With data traffic growing all Input Ports A AAAA AAA Shared Communications Channel Packet Switch AAECCEEACAA CC CCC CC Output Ports EE EE E Virtual Circuit Routing Table Buffer Figure 7.12 Packet switching Chapter 7 Wide Area Networking the time, transport networks will increasingly rely on data switches to manage and aggregate the traffic, and the transport network will be providing low-cost and reli- able connections between these switches. Remember from Chapter 3 that there are two main types of packet-switched networks: connection-oriented and connectionless networks. In a connection- oriented environment (such as X.25, Frame Relay, ATM, and VPNs that are based on Frame Relay or ATM networks), a call is set up end to end at the onset of the communication. Only one call request process that contains the source and desti- nation address is necessary. That initial call request packet establishes a virtual cir- cuit to the destination so that subsequent packets need only be read for the marking information that defines the virtual circuit to be taken. The intermediate nodes do not need to look at the addressing information in order to calculate a path for each packet independently. This reduces delay because routing decisions do not have to be made at the intermediate nodes. Where the error control