timedia transport, computer- aided design, medical file transport, data center access, and local loop access. Therefore, the most likely environments for 10GigE are carriers, university cam- puses, research and development labs, and some government agencies. But, at the moment, 10GigE is not a common enterprise solution, although it may become in the near term as companies seek more bandwidth to accommodate advanced applications while wishing to use a technology with which they have well-founded knowledge and experience. The Optical Core: Overlay Versus Peer-to-Peer Networking Models The IEEE is setting two separate physical-layer standards for 10GigE. The first is for LANs; it offers a capacity of exactly 10Gbps and is really just a faster version of GigE. The second is targeted at WANs. Strictly speaking, it is not Ethernet, and it does not run at 10Gbps; instead, it transports Ethernet frames over an SDH or SONET link at 9.29Gbps, which makes is compatible with existing carrier net- works but limits the number of GigE links that can be aggregated to nine. There are two categories of WAN physical interfaces for 10GigE: electrical and optical. Electrical interfaces are less costly to build than optical interfaces, and the reality is that today most commercial buildings do not have fiber access. There are two electrical interfaces. 10Gbps on coax, known as 10GBASE-CX4, has about a 50-foot (15-m) range. It would most likely be used to connect devices within the same room. The other interface is 10Gbps on wire pair, using unshielded twisted- pair. Real solutions are expected sometime in 2006, with the initial definitions including 10GBASE-T over Category 7 wiring (up to 330-foot [100-m] range), screened or enhanced Category 6 wiring (up to 330-foot [100-m] range), or stan- dard Category 6 (less than or equal to 180 feet [55 m]). In terms of fiber options, a LAN physical interface can operate at the full 10Gbps rate up to a range of 1,000 feet (300 m). This would be suitable for local applications and could be confi