A structure for an optical packet for transmission over an optical network comprises
a packet header (30) and a packet payload (32). The header comprises
first and second sections (34, 36). The first section (34) comprises
a series of clock pulses (40) at the data rate of the second section of
the packet header, or a multiple or sub-multiple thereof. This header structure
enables the clock pulses in the first section (34) to be used to control
the timing instants when the header information in the second section (36)
is read. The header information can thus be read using the data in the header alone,
without needing to alter the structure of the packet payload. The clock pulses
can be delayed in order to enable them to be used to control the reading of data
in the second section of the packet header. The invention ca be used in optical
communications networks.
