There is a potential cost, footprint and power savings by eliminating
unnecessary opto-electronic conversions on a signal path in a
core optical mesh network. Current networks have seen the deployment
of wavelength division multiplexing (WDM) technology, followed
more recently by the deployment of an optical transport layer
where optical crossconnects (OXCs) are connected using WDM links
.both currently deployed WDM systems and OXCs use electronics
in the signal path, thereby creating an opaque network .it is
very compelling to imagine an optical transport layer where signals
remain in the optical domain from the time the time the enter
the network until they leave the network, thereby creating a transparent
network.
To carry
out the assessment of opaque and transparent networks, we make
the following basic assumptions on the requirements for core mesh
networks:
" Network operators require a lowest cost network, not just
lowest cost network elements. For example, even though optical
may be cheaper than electrical network elements, a network without
wavelength conversions and tunable wavelength access in the optical
domain could lead to higher network cost due to inefficient capacity
usage than a network with wavelength conversions in the electrical
domain.
" A network operator must not be constrained to buy the entire
network from a single vendor.
" In order to build a dynamic, scalable and manageable backbone
network it is essential that manual configuration be eliminated
as much as possible.
" An optical switching system must be easily scalable with
low cost and and a small footprint as the network grows to many
hundreds of wavelength channels per fiber and to a speed 40 Gb/s
NETWORK ARCHITECTURES
Increased
traffic volume due to the introduction of new broadband services
is driving carriers to deployment of an optical transport layer
based on WDM. The network infrastructure of existing core networks
is currently undergoing a transformation from rings using synchronous
optical networks (SONET) add/drop multiplexers (ADMs) to mesh
topologies using OXCs. Even though the applications driving large
scale deployment of transparent optical switches are not currently
in place, and the traffic demand does not currently justify the
the use of transparent switches that are cost effective at very
high bit rates, it is possible that at some point in the future
transparent switches may be deployed in the network.,
Transparent
network architecture
The transparent
network is as shown. Since a signal from a client network element(NE),such
as a router, connected via a specific wavelength must remain on
the same wavelength when there is no wavelength conversion , only
a small size switch fabric is needed to interconnect the WDMs
and NEs in a node. This architecture also implies end-to-end bit
rate and data format transparency. Another architecture of a transparent
switch in a transparent network may include a single large fabric
instead of multiple switch matrices of small port counts. If one
is to provide flexibility, such an architecture design would require
the use of tunable lasers at the clients and wavelength conversions.