Networking Reference
In-Depth Information
input network
output network
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(a)
(b)
Figure 4.6: (a) High-Radix Clos topology and (b) corresponding folded-Clos topology. The channels in
the folded-Clos represent bidirectional channels. The routers in the right-most column of (b) are radix-4
while the others in (b) are radix-8. If the same radix-8 routers need to be used in the folded-Clos network,
two radix-4 routers can be combined into a single radix-8 router.
many paths - one for each middle-stage switch in the Clos - between each pair of nodes. This path
diversity enables the Clos to route arbitrary traffic patterns with no loss of throughput.
Like a butterfly ( k -ary n -fly) network, a folded-Clos is also an indirect network. The router
nodes are distinct from the endpoints. The first tier of the network connects k/ 2 hosts (endpoints) to
the switch, and k/ 2 uplinks to other switches in the next tier. If the injection bandwidth is balanced
with the uplink bandwidth, we refer to the network as fully provisioned ; however, if there is more
injection bandwidth than uplink bandwidth, then it is oversubscribed . Oversubscription is common
in datacenter applications since it reduces cost and improves utilization. The input and output stages
 
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