reliable link-level packet delivery in hardware,
multiple virtual channels for both deadlock avoidance and performance isolation, and
age-based arbitration to provide fair access to network resources.
There are two types of nodes in the Cray XT system. Endpoints (nodes) in the system are
either compute or system and IO (SIO) nodes. SIO nodes are where user's login to the system and
Figure 8.5: High level block diagram of the Seastar interconnect chip.
8.2.1 3-D TORUS
The Cray XT interconnect can be configured as either a k -ary n -mesh or k -ary n -cube (torus)
topology. As a torus, the system is implemented as a folded torus to reduce the cable length of the
wrap around link. The 7-ported Seastar router provides a processor port, and six network ports
corresponding to +x, -x, +y, -y, +z, and -z directions. The port assignment for network links is not