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| 10.3 |  | Examining Fiber Optic Transports |
| 10.3.7 |  | 10-Gigabit Ethernet standards |

Positioned as a high-speed technology for networking applications in LANs, MANs, and WANs, 10 Gigabit Ethernet (10 GbE) will provide very high bandwidth with simplicity and relatively low cost. In LAN applications, 10 Gigabit Ethernet will enable network managers to scale their packet-based networks from 10 Mbps to 10,000 Mbps and thereby leverage their investments in Ethernet as they increase the performance of their networks. In MAN and WAN applications, 10 Gigabit Ethernet will enable Internet service providers (ISPs) and network service providers (NSPs) to create very high-speed links at very low cost between colocated carrier-class switches and routers.

In the OSI model, Ethernet is fundamentally a Layer 2 protocol. 10 Gigabit Ethernet uses the IEEE 802.3 Ethernet Media Access Control (MAC) protocol, the IEEE 802.3 Ethernet frame format, and the minimum and maximum IEEE 802.3 frame size. Just as 1000BASE-X and 1000BASE-T (Gigabit Ethernet) remained true to the Ethernet model, 10 Gigabit Ethernet continues the natural evolution of Ethernet in speed and distance. Since it is a full-duplex only and fiber only technology, it does not need the carrier sense multiple access collision detect (CSMA/CD) access method that defines slower, half-duplex Ethernet technologies. In every other respect, 10 Gigabit Ethernet remains true to the original Ethernet model. An Ethernet physical layer device, which corresponds to Layer 1 of the OSI model, connects the media, optical or copper, to the MAC layer, which corresponds to OSI Layer 2. Ethernet architecture further divides Layer 1 into a physical media dependent (PMD) and a physical coding sublayer (PCS). Optical transceivers, for example, are PMDs. The PCS is made up of coding algorithms and a serializer. It often implements multiplexing functions.

The 802.3ae specification defines two physical layer types, such as the LAN and WAN PHYs. The WAN PHY has an extended feature set added onto the functions of a LAN PHY. These PHYs are solely distinguished by the PCS.

The WAN PHY differs from the LAN PHY by the inclusion of a simplified SONET framer. Since SONET OC-192 is within a few percent of 10 Gbps, it is simple to implement a MAC to be able to operate with a LAN PHY at 10 Gbps or a WAN PHY at the SONET OC-192 payload rate. To enable low-cost WAN PHY implementations, the IEEE 802.3ae committee specifically rejected conformance to SONET jitter, stratum clock, and other SONET optical specifications. Therefore, the WAN interface sublayer (WIS) does not render a 10 Gigabit Ethernet WAN PHY compliant with either SONET or SDH at any rate or format.

The LAN PHY is the most cost-effective solution to support the existing 10 Gigabit Ethernet applications across LAN and MAN distances on dark fiber and dark wavelengths. However, it lacks the ability to speak the same language as the synchronous TDM gear, most prevalent in the WAN environment. The WAN PHY can be used to connect Ethernet-based networks to the existing SONET/SDH TDM and DWDM infrastructure and support lit wavelengths and lit fiber over WAN distances.

It is expected that the LAN PHY will also be used in pure optical switching environments extending over long haul distances. This is possible because, by using optical equipment that incorporates the capability to transparently carry any higher-level technologies, such as 10 GbE, ATM, SONET, SDH, and so on. LAN and TDM services will seamlessly converge into a single optical infrastructure. This infrastructure will provide a Layer 1 transport across MAN/WAN distances and will offer carrier-grade reliability, being at the same time totally technology agnostic. Therefore, the importance of the WAN PHY for long haul applications will also diminish.