n control to properly ensure the service quality needed to transport voice and other real-time traffic. The IEEE has defined a new format called 802.1 pq, which adds an additional four-octet header field that includes a three-bit priority indicator in the LAN header, allowing eight levels of priority. LAN switches can act on 802.1 pq to define high-, medium-, and low-priority data traffic. Because of its problems with QoS, Ethernet cannot be used in the public network without the deployment of IP with MPLS or GMPLS in order to carry voice or deliver bandwidth of different sizes. The Optical Core: Overlay Versus Peer-to-Peer Networking Models The Peer-to-Peer Model The peer-to-peer model, promoted by the data community and the IETF and IEEE standards organizations, relies on the GigE and 10GigE standards. It is character- ized by full visibility of the entire network for all devices, the edge devices needing to know only about the closest optical switches, and the routers and optical switches being peers. Ethernet has a long and rich history and, it would appear, future. The concept of Ethernet is based on the notion that peers in a network send messages to each other over a radio system contained within a common wire or channel-which is referred to as the ether. Each user, or peer, has an individual and distinct 48-bit key known as the Media Access Control (MAC) address. Today, because of the perva- siveness of Ethernet and the low cost of hardware required to support it, most com- puters come equipped with the functionality of an Ethernet card. One of the great benefits associated with Ethernet is the fact that, despite its many different generations, variations, and wiring plans, it is all the same, making it easy to interconnect all types of Ethernet by using highly available and inexpen- sive hardware. Ethernet, which is mostly standardized under IEEE 802.3, is the most widely used LAN technology, replacing other LAN standards such as IBM's Token Ring or FDDI. The four major categories of Ethernet standards a