SONET/SDH Add Drop Multiplexers (ADMs) are usually used for transport,
often times over a Wave Division Multiplexing (WDM) infrastructure to provide scale
and transparency. (Of course, other equipment providing higher-level functions such as
switching, routing, so on, is often present as well.) More information on SONET/SDH
infrastructure for delivery of services is discussed in Part II of this book.
Ethernet in the MAN/WAN
In the decade following the 1990s, the trend of data traffic in Service Provider networks
took a markedly upward turn. The emergence of the Internet, coupled with a whole host
of other emerging data (multi-media) applications such as Napster and like resulted in
a huge surge in data traffic.40 In fact, it was factually estimated that (Internet) traffic
was doubling at least every year (see Figure 1.10), which was indeed a disruptive??”and
unprecedented??”phenomenon [13].
Around this time, regulatory constraints were also being eased with the Telecom Act of
1996 in the U.S. and similar competitive measures globally, and a new set of competitive
TABLE 1.4 Comparing Ethernet, Frame Relay, ATM, and TDM in the MAN/WAN
ATM Frame Relay TDM Ethernet
Technology Cell-based,
connection-oriented
Cell-based,
connectionless
Not-packet,
connection-oriented
Packet, connectionless
Bandwidth fl exibility Limited
155M or 622M
Step function
Limited
Steps: 1.
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