ed by 100.2 Hence, a corporate site with aggregate LAN traffic of 1 Gbps (for example, 100 users on 10-Mbps LAN seg- ments) will need 10 Mbps of sustained WAN throughput. In a few years, when these 100 users are on 100-Mbps segments, the corresponding WAN requirement from such a site will be 100 Mbps. Network survivability, high availability, security, and fast restoration are also key desiderata of end users regardless of their bandwidth needs. Some people see wavelength leasing and wavelength on demand as evolving user requirements as well. These services, however, fall more in the circuit-switched mode of operation when contrasted with the newly introduced packet-mode services based on Ethernet and Eth- ernet-like technologies that are receiving considerable industry attention. Users hope to be the beneficiaries of the bandwidth glut that was being reported in the press in the 2001-2002 time period. The need for reliable broadband services is obvious. At least two parochial uses of the term "broadband" have evolved in the recent past. Some people have applied broadband to mean xDSL Internet access at what turned out to be 384, 768, or at most 1,544 Kbps. This is far from being broadband in any sense of the word. Others have applied broadband to mean cable-TV-based res- idential services on digital cable. The proper use of the word "broadband" (according to the International Telecommunications Union [ITU]) is for a service that has a speed greater than a T1 (1.544 Mbps); hence, to qualify as broadband, a service needs at least 3.088 Mbps (T1C), 6.312 Mbps (T2), 10 Mbps, or more. In fact, today many people consider 100 Mbps, 1 Gbps, or 10 Gbps to be the reference speeds for broadband. Current technology even supports speeds of 40 to 320 Gbps; these, however, are more back- bone network speeds than user-level speeds. The purpose of this book is to survey the architectures and technologies needed to deliver reliable, cost-effective, sustainable, secure, and carrier- grade broadband services to commercial customers