me manner over the same link. The types of links that connect the Frame Relay switching points operate at high speeds-they run the full range of the wide band of the PDH hierarchy. Where a Frame Relay network is running over a T-carrier infrastructure, the links can operate at 1.5Mbps to 45Mbps; for networks being served by E-carrier platforms, the links can operate at 2Mbps to 34Mbps. The standards for Frame Relay come from the ITU-T, which defines Frame Relay as "a conversational communication service provided by a subnetwork for high-speed bursty data." This definition implies that Frame Relay has two-way capability (it is "conversational") and that it is not an end-to-end solution (it is a "subnetwork"). So we don't look for a Frame Relay device such as a Frame Relay telephone; instead, we look at Frame Relay to serve as the cloud-that is, the WAN solution that links computer networks distributed across a country or across the Chapter 7 Wide Area Networking world. And "high-speed bursty data" suggests that Frame Relay's preliminary appli- cation is in support of data and, specifically, LAN-to-LAN internetworking. Frame Relay Applications One environment that might be a candidate for Frame Relay is a hub-and-spoke network, in which traffic from remote locations travels through a central site. This is similar to the airline system, in which key airports serve as main hubs; the larg- est of the 777s travel between the main hubs, and to get to a smaller city, you go through a hub to get on a smaller aircraft that then takes you to your destination. Frame Relay is also used to replace the use of expensive leased lines. Depending on the network topology, Frame Relay could potentially reduce costs up to 50% com- pared to using leased lines. Frame Relay is also used to give a network some bandwidth flexibility-that is, bandwidth-on-demand. Because the main application of Frame Relay is LAN internetworking, and because LANs produce highly unpredictable traffic flows, paying for a subscribed set of bandwidth whether or