Optical MAN Service Options

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.

Finally, note 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 derivatives SuperPONs).