Two methods of mapping Ethernet into SONET emerged in the mid-1990s. Ethernet
over asynchronous transfer mode (ATM) proved a natural choice, since ATM??™s future
looked bright at that time, and standards, including the ATM Forum??™s user network
interface (UNI) 3.1 specification [4], already included a mapping of ATM cells into
SONET payloads. If Ethernet frames could be mapped into ATM cells, then they could
be carried over SONET. The Internet Engineering Task Force (IETF) defined the mapping
of Ethernet into ATM in the well-known Request for Comments (RFC) specification, ???RFC
1483??? (now superseded by RFC 2684 [5]). Fujitsu??™s FASTLANE product, first introduced
in 1997, featured one of the industry??™s first ATM-based EoS implementations. FASTLANE
comprised a set of plug-in cards for Fujitsu??™s popular FLM 150 ADM system. Figure 11.3a
illustrates the FLM 150 ADM.
Meanwhile, several router vendors were developing SONET-based router interfaces
using the point-to-point protocol (PPP) and high-level data-link control (HDLC) protocol
to map IP packets into the SONET payload [6, 7]. Some SONET ADM vendors adopted
a variant of this method to map Ethernet frames into SONET.
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