Two complementary high-speed serial link technologies have been developed
within the framework of the OMI/HIC
Esprit project. They have been subsequently standardised and form
the basis of the IEEE 1355 [3] standard :
The standard allows modular scalable interconnects to be constructed based on high-speed point-to-point links and switch chips. Using the lightweight protocols of IEEE 1355 these networks can provide a transparent transport layer for a range of higher level protocols.
The IEEE 1355 protocol stack defines four protocol layers: bit, character, exchange and packet layers. Characters are 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. A credit based flow control scheme is used which operates on a per link basis. This scheme ensures that no characters will be lost due to buffer overflow.
Information in IEEE 1355 networks 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. The destination address in the header can be zero (for a directly connected link) or more bytes.