As optical Ethernet networks begin to deliver huge bandwidth to end users, network managers will begin to demand differentiated services. Various functions can be applied to the incoming traffic and to traffic flows to improve performance.
While building new optical Ethernet infrastructures is a logical step for startup carriers, the incumbent carriers will want to accommodate Ethernet without totally redesigning their local networks.
As more and more networks migrate to IP, interoperability between IP and other communications technologies will become a larger concern for carriers. Support will be available for all copper, cable, and optical fibre media types for carriers and corporates. All the major forms of networking infrastructures will soon be supported, including ATM, Packet over Sonet, dense wave division multiplexing (DWDM), Gigabit Ethernet, T1 and T3, and coaxial cable.
Carrier networks will be developed in a way that guarantees interoperability with the vast base of existing LANs and WANs. But carriers are unlikely to replace existing ATM switches with optical Ethernet equivalents just to please corporate customers, because the cost/benefit calculations are unlikely to justify such moves.
There are several options available for upgrading carriers' networks to optical Ethernet. One involves IP packets being transported directly over a full Sonet/SDH infrastructure using Point-to-Point Protocol (PPP) encapsulation or over an Ethernet segment built from Sonet/SDH links. Sonet/SDH would be preferred for long distances and could be also be used at the MAN level. The problem here is that full Sonet TDM capabilities, the Sonet physical layer, and the Sonet management functions would all be included, resulting in considerable bandwidth overhead.
Another option is packet over Ethernet over Sonet/SDH (PES). This is a method based on technologies that are well understood. Under this approach, Ethernet is scalable from 10Mbit/s up to 10Gbit/s, allowing the bandwidth offered to be more closely matched to the anticipated demand.
This configuration adds a switching capability that can reduce the number of point-to-point links, so a full mesh may not be required. Ethernet therefore allows LAN, MAN, and WAN networks to be combined to form end-to-end connections, thereby reducing the need for format and protocol conversions.
Packet over Ethernet over WDM (PEW) is a slight variation on PES and is used to transport Ethernet over a wave division multiplexed physical layer. A key advantage of PEW is that the bandwidth overheads of ATM and Sonet/SDH can be eliminated. Both 1Gbit/s Ethernet and 10Gbit/s Ethernet are more affordable, more practical, and simpler than ATM.
A problem that may hinder the adoption of optical Ethernet by carriers is that the technology may be more awkward for carrier network managers than for corporate network managers. This is because carriers have used ATM-based Sonet/SDH architecture, so they have no existing legacy of Ethernet skills. These carriers will not take their ATM switches out and install optical Ethernet switches instead, unless they are presented with sufficient financial incentives from customers to do so. Given the declining value of bandwidth, this seems unlikely.
