Page 230 - Optical Communications Essentials

Constructing the WDM Network Puzzle

220 Chapter Thirteen

employed, the broad frequency tolerances allow the use of devices that are not
temperature-controlled. However, other requirements unique to metro applica-
tions arise, such as the following:
■ A high degree of connectivity is required to support the meshed traffic in
which various wavelengths are put on and taken off the fiber at different
points along the path.
■ A modular and flexible transmission platform is needed since the wavelength
add/drop patterns and link capacities vary dynamically with traffic demands
from different nodes.
■ Since the add/drop functions can change dynamically from node to node, spe-
cial components such as variable optical attenuators (VOAs) are needed to
equalize the power of newly added wavelengths with those that already are on
the fiber.
■ Transmission loss in metro applications is fairly high because of interconnection
losses and cascaded optical passthrough in successive nodes. Metro-optimized
optical amplifiers thus are essential.
■ Metro WDM networks must support a wide variety of transmission formats,
protocols, and bit rates. As listed in Table 13.1, these include SONET/SDH traf-
fic ranging from OC-3/STM-1 to OC-192/STM-64, ESCON (Enterprise
Systems Connection from IBM), FICON (Fibre Channel connection from
IBM), Fast Ethernet, Gigabit Ethernet, 10GigE, Fibre Channel, and digital
video.

TABLE 13.1. Data Formats and Protocols That Need to Be Accommodated
by a Metro WDM Network

Format or protocol Data rate
OC-3/OC-3c and STM-1/STM-1c 155Mbps
OC-12/OC-12c and STM-3/STM-3c 622Mbps
OC-48/OC-48c and STM-16/STM-16c 2.488Gbps
OC-192/OC-192c and STM-64/STM-64c 9.953Gbps
Fast Ethernet 125Mbps
Gigabit Ethernet (GigE) 1.25Gbps
10-Gigabit Ethernet (10GigE) 10Gbps
ESCON 200Mbps
FICON 1 or 2Gbps
Fibre Channel 133Mbps to 1.06Gbps
Digital Video 270Mbps

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