Optical Ethernet for metropolitan nets

Ethernet has taken over sector after sector of the networking world, from workgroups to enterprise backbones.

Now, a technology called Optical Ethernet is beginning to revolutionize metropolitan-area networks by delivering very high bandwidths — 100M bit/sec, 1G bit/sec or even higher — across cities and regions, at prices similar to today's 1.5M bit/sec T-1s.

Current MANs are built using SONET technology. Designed originally for low-speed, circuit-switched traffic, SONET running at 10G bit/sec is proving too costly and inflexible to carry the vast amount of IP traffic required by the Internet economy. Enter Optical Ethernet — a technology based on the proven Ethernet standard, but which adds the traffic engineering and management capabilities carriers need, and integrates these with optical networking to deliver the distances and speeds required to traverse metropolitan areas.

Based fundamentally on Ethernet, Optical Ethernet MANs let carriers deliver standard, well-known 10/100M bit/sec or 1G bit/sec Ethernet interfaces – the same as those used to easily connect office networks today. And instead of a SONET ring, the metropolitan backbone for Optical Ethernet networks will be based on the 10G bit/sec Ethernet standard now being completed in the IEEE working group 802.3ae.

The advantages:

* Ethernet is 10 times less expensive than the SONET technology being used today.

* Ethernet is a simple and widely understood technology.

Ethernet is the best technology for carrying IP traffic – Ethernet and IP have grown up together.

Optical technologies enable Ethernet networks to extend over much greater distances than campus Ethernet nets. Running over single-mode fiber, Optical Ethernet lets links in the network range from 3 to more than 6 miles in the case of 1310-nm wavelength technology, and up to 43.4 miles for 1550-nm wavelength technology.

Key components of Optical Ethernet are the abilities to segregate traffic of different users and to deliver the particular service level each user purchases.

Traffic segregation is accomplished by using the IEEE 802.1pQ virtual LAN (VLAN) standard. This standard lets Optical Ethernet networks mark each user's traffic with a VLAN tag as it enters the network and then use this tag to keep each user's traffic separate as it crosses the network. Of course, 802.1pQ was designed for enterprise networks and the number of possible VLAN tags is too low. Work is under way in IEEE to extend this number from 4,096 to approximately 16 million.

Optical Ethernet can also deliver guaranteed levels of latency, jitter and bandwidth. Optical Ethernet networks deliver user-specified levels of delay and jitter by using the techniques developed in the Internet Engineering Task Force Differentiated Services (Diff-Serv) project. As eaach packet enters the network, information from the packet is used to assign it to a particular class of service. User contracts also specify bandwidths, which network operators guarantee by limiting the aggregate of guarantees to network capacity. Then the rate of incoming traffic is compared with the contract. Traffic above contract is carried — but only as long as it does not congest resources required to carry guaranteed traffic.

Using these techniques, Optical Ethernet networks can easily handle the needs of both data and circuit-switched or voice applications. Circuit traffic requires only modest bandwidth, but quite demanding levels of latency and jitter. Optical Ethernet easily achieves voice-quality levels of delay and jitter by combining the sheer speed of the 10G bit/sec backbone network with Diff-Serv's quality of service.

Carriers deploying Ethernet into metropolitan networks have been pushing the edges of the available Ethernet technology. Enterprise technology does not easily scale to carrier applications. Ethernet's move from workgroup to enterprise backbone was not made by deploying more workgroup switches, but by purchasing enterprise-class switches. Similarly, to scale Ethernet across MANs, carriers will need solutions that can satisfy the unique requirements of the carrier environment.

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