The Esprit OMI/HIC
project has developed two bi-directional link protocols which form
the basis of the IEEE 1355 standard, these are:
The work reported here is based on the the DS link protocol as shown
in Figure 1. The data line carries the binary data values and the
strobe line only changes state when the next data bit has the same
value as the previous one. The links are asynchronous, as the data/strobe
signal pair carries an encoded clock. Studies on the reliability of
DS links [6], up to distances of 20 meters, have measured a bit
error rate of better than 
.
On top of the bit level there are a further three levels of protocol: the character, exchange and packet levels. Characters are a group of consecutive bits used to represent data or control information. The exchange layer describes the exchange of characters to ensure the proper function of a link. DS links use a credit based flow control scheme which operates on a per link basis. This ensures that the switching fabric is lossless: no characters are lost internally due to buffer overflow.
Information is transferred in the form of packets. A packet consists of a header, which contains routing information, a payload containing zero or more data bytes and an end of packet marker. The protocol allows arbitrary length packets to be exchanged.
