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Introduction
Four such 64-node networks and an additional stage of switches can be used to construct
a 256-way network. Alternatively, the unused uplinks can be used to double the number
of nodes a switch can connect. This avoids the need to add an additional switch stage but
the resulting network cannot be expanded further. This technique is used in the
128-node network, shown in Figure A.3.
Figure A.3: A 3-Stage, 128-Node, Switch Network
There are switch network modules that connect up to 16 or 128 nodes. The 16-node
network is a rack-mountable module containing a single network board. The 128-node
network is a rack-mountable chassis containing up to 24 network boards: 8 at the front
connecting the nodes to the lower stages; and 16 at the rear providing the upper stages
of the network. A central backplane joins the stages. These switch modules may be
partially populated for networks containing fewer than 128 nodes.
The number of nodes and switches in these networks is shown in Table A.1. The number
of switches refers to the total number of Elite ASICs required to construct the network.
The number of hops refers to the maximum number of links traversed for nodes that
have to communicate through a top switch. The bidirectional nature of the links means
that traffic can be localized to a subtree large enough to span both nodes.
Table A.1: Switch Network Parameters
Name Levels Nodes Switches Hops
QM-S16 2 16 8 4
QM-S128 3 128 80 6
The Elan performs automatic routing and broadcast communications. Using the switch
Compaq AlphaServer SC Interconnect Terms A-3