The popularity of the Internet and internet protocol- (IP-) based internet services is promising enormous growth in data traffic originating from hosts that are IP endpoints. This growth is being fueled by various applications such as those driven by the World Wide Web (WWW) and by the indirect impact of increased computing power and storage capacity at the end systems. The advent of new services with increasing intelligence and the corresponding bandwidth demands are further adding to the traffic growth. New access technologies such as asymmetric digital subscriber line (ADSL), high-bit-rate digital subscriber line (HDSL), and fiber to the home (FTTH) would remove the access bottlenecks and enforce an even faster growth of demand on the backbone network. As noted earlier, these changing trends have led to a fundamental shift in traffic patterns and the traffic is mostly due to data communications.

In the past, the amount of data traffic on carrier networks was small compared with voice-centric traffic. Therefore, the carrier networks were designed to primarily support voice traffic, and the data traffic was transmitted using the voice channels. Now, the core networks are being designed primarily for data traffic with voice support at the edges. Voice traffic can be carried in the core networks using “voice-over- IP” or similar paradigms. To meet these growing demands, the use of WDM will continue to increase in backbone networks. Architectures will be required to satisfy the need for better quality of service (QoS), protection, and availability guarantees in IP networks.