, enabling the convergence of voice, data, and video on one net- work, with one control plane. (The term control plane refers to infrastructure and distributed intelligence that sets up and releases connections and may restore connection in case of a failure. It also includes protocols and mechanisms required to disseminate this information, as well as algorithms for engineering optimal paths between endpoints.) IP and ATM As discussed earlier in this section, ATM is used to support a great deal of Internet backbones. IP is also used in next-generation networks. (IP is discussed in detail in Chapter 8.) Approximately 85% of all IP backbones currently use ATM in the core, although MPLS is gradually being introduced in place of ATM. Features of IP IP was designed to work in the LAN world. It is a connectionless environment, which means it provides the capability of having information moved between net- work elements without a preconceived path between the source and destination. In a LAN environment, bandwidth is relatively inexpensive, and the deployment, by Packet-Switched Networks definition, is over a small geographic area. Because of the small coverage area, tran- sit delay is typically not an issue in a LAN. In the event of congestion, IP discards packets. TCP retransmits the lost pack- ets quickly and transparently to the users, and because of the short transit delay, discarded packets are quickly detected, so users don't perceive delays in down- loads. But WANs, by definition, are typically deployed over longer distances than LANs, and in WANs, transit delays become a major issue in two ways: in control- ling the QoS and in identifying the loss of packets that may have occurred because of congestion. Also, bandwidth is more expensive in a WAN than in a LAN; you pay for every bit sent over a WAN link, so packet discards that create retransmis- sions can make the expense of retransmission alone significant. Problems with IP Networks Traditional IP routers were not intended to handle the large-scale type of ne