for higher network layers, often resulting in very low throughputs and long delays for data delivery. It is important to consider optics as a network system rather than an isolated communication link. As described in the section above on Transport Layer Design, the Physical Layer and the network architecture must be codesigned. High-priority areas of research include the following:
Understand the interaction of network protocols with the optical link and quantify the performance shortcomings.
Jointly design the Physical Layer and higher network layers, making judicious use of spatial, temporal, frequency, and route diversity.
Internetworking with other modalities, including using them as backup for guaranteed message delivery.