Optical MAN Service
As in the WAN, the most important
application is the interconnection of electronic switches with
full-bandwidth circuits. The issues here are very similar to the
issues discussed in the WAN: analog optical circuits (carrying
digital data) using WDM technology is the proven near-term solution;
digital circuits using OTDM is a more distant candidate. However,
better link quality supports more wavebands and more capacity per
waveband, which may make it more economical to trade bandwidth for
electronic switching. In addition, very-high-rate digital pulse
streams are easier to propagate, which may tip the balance toward
OTDM or OCDMA in the future for some applications.
Time sharing of
circuits is a viable option and could provide additional circuit
granularity and add/drop functionality, thereby increasing the
number of circuits that could be supported. By introducing these
functions at the optical layer, the SONET/SDH layer might be removed
without forcing the ATM/IP layer to switch excessive bandwidth. Both
analog and digital circuits can be time-shared, but analog WDM/TDM
systems are more mature and have been demonstrated across a MAN.
Time sharing can
also be used to statistically share wavebands using a MAC protocol.
Again, there are analog WDM and digital OTDM architectures
In the more
distant future, simple store-and-forward optical packet/cell
networks operating at super-electronic rates (per packet/cell
stream) will be feasible. Unlike above, these systems require
optical memory within the network and all-optical packet switching
nodes. This makes these architectures technically difficult.
that because of the high-quality links, analog transport services
are more practical than in a WAN. An important application of this
is video distribution for passive optical networks (PONs or their