ere is a growing commonality between LANs and WANs. The ongoing evolution and introduction of advanced applications requires high bandwidth and has driven the LAN standards to evolve to high-speed specifications. At the same time, with the introduction of very high-speed Ethernet, the applications for what was a LAN technology have pro- gressed beyond building and campus networks to include use in the local loop as a first- mile technology, in MANs as high-speed citywide networks, and even in WAN backbones. Chapter 6 Local Area Networking One major advantage of using Ethernet across the various network domains is that it bridges the gap between LANs and WANs, and it provides the opportunity to use one common architecture and protocol on an end-to-end basis. Ethernet has long been the number-one choice for LANs, and as it is improving in performance over longer dis- tances, it has become a viable solution in the MAN space, with metro-Ethernet; there are even some who see it as an alternative in the WAN environment. (These perspectives are discussed in Chapter 11.) Meanwhile, it is important to note that the service provider hosting sites are looking a great deal like enterprise data centers. Service providers and large enterprises alike are taking advantage of many developments in the optical realm, including dark fiber, wave- length services, and Coarse Wavelength Division Multiplexing (CWDM). There is a com- mon emphasis on user service-level management, accounting, and rapid deployment. Finally, IP and Ethernet are becoming more pervasive in both the LAN and WAN worlds. Chapter 7, "Wide Area Networking," discusses WANs in detail. Chapter Wide Area Networking A wide area network (WAN) is a group of computer networks connected over long distances by telecommunications links, which can be either wireline or wireless. A number of WAN links can be used, each of which was developed to address spe- cific requirements in data communications. To meet specific network and applica- tion needs, a number of WAN techniques (