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- DC = "Data Center"
- TOR = "Top of Rack"
- TOR switches connect all machines within a rack and provide uplinks to higher network levels in the topology
- TOR switches may use 1 or more ports to uplink. The ports may be of the same bandwidth as the hosts (e.g. gigabit) or higher (e.g. 10GigE)
- DCs organize machines (~20-40) into racks, which all connect to a TOR switch, which in turn connects to some aggregation switch
- TOR switches connect all machines within a rack and provide uplinks to higher network levels in the topology
- EOR = "End of Row"
- switch connecting a row of racks
- appears to describe both one big switch handling all hosts for several racks, or an aggregation switch connecting to TORs of several racks.
- hierarchical vs. fat-tree topologies:
- hierarchical => different switches and bandwidths at the core than toward leaves
- fat-tree => same switches everywhere, all at same bandwidth
- Oversubscription - networks can be oversubscribed at various points.
- Switches generally have enough backplane bandwidth to saturate all internal ports
- But uplinks to other switches may be a fraction of this, reducing total bandwidth between hosts on different switches
- using multiple ports and/or higher speed uplinks can mitigate this
- Oversubscription often described as a ration (n:m), e.g. for every n megabits of bandwidth at a host port, only m megabits of bandwidth exist between it and the most distant machine in the network
- cut-through vs. store-and-forward
- switches can either buffer entire frames and retransmit out a port (store-and-forward) or stream them without fully buffering in-between (cut-through)
- cut-through can provide better latency
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