Special Report: Next Generation Internet Applications
Instead, Ethernet relies on collision detection and other contention based techniques to share resources. Ethernet does not provide any QoS mechanisms. As such, Ethernet is not well suited for carrying traffic along high-density traffic routes where many different types of traffic must contend in a predictable fashion for a common resource. Ethernet lacks recognized standards for network protection and restoration, making it vulnerable to cable cuts and equipment outages. Therefore, Gigabit and Ten-Gigabit Ethernet are unlikely technologies for high capacity photonic networks used in the core of the national infrastructure.
Instead, carriers will make Ethernet one of the network access options along the periphery of a high- speed ATM-over-DWDM, an IP-over-DWDM, or, eventually, an alloptical photonic switching network. Ethernet access speeds will increase to 1 Gbps as Gigabit Ethernet becomes prevalent within the enterprise networks. Provisioning Gigabit Ethernet access will become more attractive to the carriers as their core networks migrate to 10 Tbps DWDM and 10 Gbps OEO electronics.
3.2 DWDM Inroads Within High Capacity Core Networks Current wide area networks consist mainly of electronic switching systems interconnected by point-to- point optical transmission channels. Figure 22 is a logical representation of an example wide area network that uses only optical cables as transmission links between switches or routers. SONET interfaces embedded within ATM switches and IP routers encapsulate data packets inside SONET frames for transmission across the fiber optic cable. The figure represents a straightforward, logical network design. However, the design does not fully utilize the optical capacity, and thus, it is costly if applied to wide area networks. The addition of SONET multiplexers in Figure 23 consolidates the traffic onto fewer optical fibers and reduces the infrastructure cost. However, even the addition of SONET multiplexers does not fully utilize the vast capacity of a single fiber optic strand.
Note that the SONET multiplexer in Figure 24 combines ATM and IP transmissions at speeds lower than OC-192 into a combined transmission that makes economical use of the fiber optic capacity. Network designers frequently employ SONET multiplexers to combine lower speed traffic originating along the periphery of high capacity networks. The multiplexer's OEO electronics limit the multiplexer's ability to combine traffic onto high capacity fiber optic channels. In the figure, the multiplexer can combine traffic into fiber optic channels of 10 Gbps (OC-192) or less. Current fiber optic technology provides capacities of at least 10 Tbps over a single fiber optic strand. Practical electronics for OEO conversion have capacity limitation of 10 Gbps (OC-192) today. It is anticipated that advances in OEO electronics will increase the OEO electronic speeds to 40 Gbps (OC- 768) within the next four years.
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