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The IEEE 1355 standard

The Esprit OMI/HICgif project has developed two bi-directional serial link technologies which form the basis of the IEEE 1355 standard :

The work reported here is based on the DS link technology. The bit-level encoding is shown in Figure 1. The data line carries the binary data values and the strobe line only changes state when a data bit has the same value as the previous one. This scheme allows for a full bit period of skew tolerance. It also means that 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 .

 
Figure 1: DS-Link bit level protocol  

The IEEE 1355 protocol stack defines another three protocol layers above the bit layer: the character, exchange and packet layers. Characters are a groups of consecutive bits which represent data or control information. The exchange layer controls the exchange of characters in order to ensure the proper functioning of a link. It includes functions such as link flow control and the link startup mechanism. 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 will be lost due to internal buffer overflow.

Information in a DS link network is transferred in packets. A packet consists of a header, which contains the routing information, a payload of zero or more data bytes and an end of packet marker. The protocol allows arbitrary length packets to be sent.



Stefan Haas
Thu May 22 14:48:25 MET DST 1997