The Integrated Cluster Bus for the IBM S/390 Parallel Sysplex

IBM has developed a new S/390(R) Parallel Sysplex(R) coupling interface for the G5 sewer called the Integrated Cluster Bus (ICB), This interface impro ves the coupling efficiency by greatly reducing message-passing latency. Us ing the transport layer of the S/390 self-timed interface (STI) introduced in the G3 sewer, ICE adds channel function to the hub chip to allow a more direct interconnection between S/390 servers. This new channel has the same function as the present intersystem channel (ISC), but because it is integ rated into the hub chip and therefore requires no additional components, it s reliability is much better than that of the ISC. Since the ISC transmits data at a peak rate of 106 MB/s over distances exceeding ten kilometers and the ICE transmits data at a peak rate of 333 MB/s at distances of ten mete rs, the ISC is still required for the more geographically dispersed Paralle l Sysplexes, whereas the ICE is well suited to the machine room, where mult iple sewers can be interconnected by ten-meter cables, This paper describes the design approach for the ICE. It describes the fundamental message-pass ing requirements of the Parallel Sysplex and how they are implemented in ve ry complex yet compact hardware in the server's hub chip.