Previously we have discussed that current transport systems are coming to their limits. New perspectives are focusing mainly on optical packet switching networks, which integrate high bandwidth availability and ability of switching in transport layer [52]. While proposed technology isn't mature yet, intermediate step between current networks and all-optical networks has been proposed. This step combines advantages of optical switching and electronic memories and will be discussed later. All-optical network should deploy WDM multiplex on physical layer (Figure below).
To reflect described drawbacks of the optical technology, special structure of optical switch has been proposed. The outgoing port of the switching matrix chooses which packets are sent to the optical fiber. Therefore, it receives packets from all delay lines and using filters, it chooses right packets. The number of packets is equal or inferior to the number of wavelengths. This choice is made by control unit, which see global state of the node. Proposed switching matrix is general and can be used in various ways. The next step is to parameterize it, mainly the delay lines.
The most important is the length of one delay line. This parameter can be different in synchronous and in asynchronous networks. A synchronous network requires this value to be set equal to the length of optical packet. On the contrary, an asynchronous network sets this constant to the inferior values so that it is possible to order packets one after another.
As it was said previously, two approaches exist in optical packet switching: synchronous and asynchronous switching. It is obvious that they are different in their approach to the switching in each node. Synchronous switching takes advantage from switching of constant length packets, which are synchronized in the nodes. An asynchronous network supports packets of different lengths and these are switched without synchronization. In the next subsections, both approaches are examined in details.