Evaluate the statement: In heavily overloaded switching backplanes, crossbar switching provides better performance than cell-backplane switching.

Difficulty: Easy

Correct Answer: True

Explanation:


Introduction / Context:
Switch fabric design impacts how well a switch sustains throughput as offered load increases. Two common architectures are crossbar (non-blocking port-to-port paths) and shared or cell-based backplanes (where packets are segmented into fixed-size cells and traverse shared internal bandwidth).



Given Data / Assumptions:

  • We compare performance under heavy overload.
  • Crossbar implies multiple simultaneous, dedicated paths across the fabric.
  • Cell backplane implies segmentation and shared internal bandwidth arbitration.


Concept / Approach:
Crossbar fabrics allow many non-conflicting port pairs to communicate simultaneously, reducing head-of-line blocking and internal contention. Under overload, scheduling can still allocate paths efficiently for parallel conversations. Cell-based backplanes incur segmentation/reassembly overhead, potential internal contention at shared memory or buses, and can suffer more from head-of-line blocking when queues back up.



Step-by-Step Solution:

Model internal contention: crossbar creates point-to-point switch paths; cell-backplane shares internal resources.Under high loads, crossbar maintains more concurrent transfers.Account for overheads: cell segmentation adds latency and buffer pressure.Conclude crossbar is superior under heavy overload.


Verification / Alternative check:
Vendor whitepapers and queueing models show crossbar/Clos fabrics approaching non-blocking behavior, whereas shared-memory or bus-based designs saturate earlier.



Why Other Options Are Wrong:

  • 'False' ignores well-known scaling advantages of crossbar under contention.
  • Qualifiers about 'low utilization' or 'only unicast' miss the core architectural benefit.


Common Pitfalls:
Confusing front-panel line-rate claims with sustained internal switching capacity; internal architecture determines behavior under stress.



Final Answer:
True

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