Photonic Network Communications, 2:4, 361±367, 2000
# 2000 Kluwer Academic Publishers. Manufactured in The Netherlands.
Economic Optical Networking in the Metropolitan Area
Hubert A. Ja
rn Kracker,* Lutz Rapp
Siemens AG, Information and Communication Networks, Hofmannstr. 51, D-81379 Mu
Accepted July 19, 2000
Abstract. The rapid introduction of wavelength division multiplexing (WDM) technology in long distance ®ber optic communication networks
which has been observed in the recent years has been driven by line economy. Not merely the ability to overcome ®ber scarcity, but also the
savings associated with the replacement of many electronic regenerators by fewer optical ampli®ers, have motivated the carriers to employ
WDM. These arguments do not often apply to optical networking in metropolitan areas because transmission distances are short. For this reason,
metro-WDM has been deployed in a few rare cases only, though it has been widely discussed by a broad scienti®c and industrial community. In
this paper, an advanced operational concept for all optical transport networks in the metropolitan area is introduced. It focuses on node economy,
i.e., the technical concepts to provide gigabit services access to the transport network at minimum cost, characterized by the following basic
features: protocol independence, monitoring, protection and fast bandwidth provisioning.
Keywords: wavelength division multiplexing, optical transport networking, communication networks operations, managed ®ber, optical
crossconnecting, customer premises equipment
Information and telecommunication technology has
been accelerating for several decades and no clear
limits potentially saturating the growing need for
transmission capacity have been identi®ed . The
transport of kb/s and Mb/s data streams has been
managed by time division multiplexing employing the
plesiochronous and the synchronous digital hierarchy.
Moreover, packet switching systems have been used
for statistical multiplexing of connectionless and
virtually circuit switched traf®c. The accumulation
of many and various types of services has demanded
interfaces at concentrators and even at primary source
equipment, operating at bit rates of several Gb/s.
Optical path layered networks are considered to be
the most competitive technology for the transport of
these gigabit services . The use of simple passive
waveguide and multiplexing devices to implement
optical bypassing leads to a substantial cost reduction
of the overall transport infrastructure .
Furthermore, due to the transparency  of optical
path layered networks, this investment is save in spite
of the obvious uncertainty of which transmission
format will dominate, or whether there will be any
In long distance networks the latter advantage has
not yet been exploited as the focus of deploying
wavelength division multiplexing (WDM) systems
has been to maximum utilization of the ®ber resources
and to optimize con®guration of line equipment.
There is a mismatch between the general concept and
the practical application which seems to be an open
issue in optical transport networking.
For an optical multiplex section (OMS), each
optical channel (OCh) link is usually speci®ed in
terms of a maximum bit rate and a bit error
probability. In particular, the optical power and
chromatic dispersion budget of the OMS as well as
the consequences of detrimental effects like crosstalk
, nonlinearities  or polarization mode dispersion
 have been considered to guarantee the perfor-
mance at the speci®ed maximum bit rate. When
approaching the physical limits of a WDM system in
terms of number of wavelengths and span lengths
between the repeaters and regenerators, loading one,
*During the preparation of this work the author was with the ``Technische Fachhochschule'' Berlin, Communications Laboratory.