We propose a communication protocol, called the virtual circuit deflection
(VCD) protocol, which combines some of the individual characteristics of vi
rtual circuit switching and deflection routing. An advantage of the VCD pro
tocol over previous (datagram) deflection schemes is that deflections in th
e former occur on a per session basis (or a per subsession basis, if sessio
ns need to be split to find adequate capacity on the outgoing links), while
in the latter, they occur on a per packet basis. This makes packet reseque
ncing at the destination considerably easier to accomplish in the VCD proto
col than in datagram deflection schemes. The VCD protocol exploits the stor
age arising from the high bandwidth-delay product of optical fibers to prov
ide lossless communication with little buffering at the switches and withou
t the need for advance reservations. This makes it particularly suitable fo
r networks that use optical switching, where buffers are expensive to imple
ment with current optical technology. We present a simple implementation of
the VCD protocol for such networks, which requires only limited buffering,
accomplished through the use of a minimal number of optical delay lines. W
e also analyze the performance of the protocol for the Manhattan Street net
work topology by using new analytical models, In particular, we examine the
effect of the traffic load and the network size on the throughput and the
length of the paths followed by the sessions, and compare the analytical re
sults obtained with corresponding simulation results, Our results indicate
that the VCD protocol is efficient under both light and heavy traffic condi
tions, especially when the link capacities are large compared to the basic
rate of individual sessions, as is expected to be the case in future multig
igabit networks.