e., WAN PHY, which is based on a simplified concatenated SONET STS-192c/
SDH-4-64c frame with a 9.58464 Gbps data rate (10G-Base-SW/LW/EW) [6]. This facilitates
seamless interconnection across extensive SONET/SDH infrastructures such
as add-drop multiplexer (ADM) rings, DCS meshes, DWDM networks, regenerators, and
so on. In order to reduce cost, however, full SONET functionality is not supported in
Fiber and WDM 211
the WAN PHY. Specifically, only minimal path/section/line overhead processing is done
(enough to isolate faults), and stratum clock timing is eliminated along with stringent
laser source requirements. As a result, 10 Gigabit Ethernet ports are significantly cheaper
than comparable packet-over-SONET (PoS) interfaces (RFC 1619) [6]. In addition, the
WAN PHY also supports additional 64b/66b encoding to handle faster 10 Gbps rates. Note
that the actual distance reach of the 10 Gbps DWDM interfaces (e.g., 10G Base-ER/EW)
are not of direct consequence since carrier DWDM networks usually provide amplification
and/or regeneration to traverse hundreds or thousands of kilometers.
There has also been an ongoing miniaturization of optical transceiver modules and the
move toward end-user pluggables.
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