A LoadBalanced Switch with an Arbitrary Number of Linecards - PowerPoint PPT Presentation

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A LoadBalanced Switch with an Arbitrary Number of Linecards

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Load balanced BV switch cannot guarantee any rate of service to any flow ... Impossible to guarantee any flow any bandwidth without running scheduling algorithm again ... – PowerPoint PPT presentation

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Title: A LoadBalanced Switch with an Arbitrary Number of Linecards


1
A Load-Balanced Switch with an Arbitrary Number
of Linecards
  • Offense
  • Anwis Das

2
High Level Goal
  • Design Scalable, fault-tolerant router
  • Operate at 100 Tb/s, 40 times more than current
    standards
  • Clearly a challenge

3
Tradeoffs?
  • Architecture is based upon load-balanced
    Birkhoff-von Neumann switch
  • Essentially a load-balancer followed by input
    buffered switch
  • Types of switches
  • Input buffered switches
  • Output buffered switches
  • Combined input-output switches (CIOS)
  • But is throughput all that matters??

4
Quality of Service
  • Load balanced BV switch cannot guarantee any rate
    of service to any flow
  • Providing Guaranteed Rate Services in the Load
    Balanced Birkhoff-von Neumann switch. Chang et
    al. Infocom 2003.
  • Such guarantees are required if a router wishes
    to implement certain classes of QoS such as
    Expedited Forwarding in DiffServe

5
Flexibility
  • Original Frame based scheduling allowed for flow
    guarantees
  • In this architecture, everything is fixed
  • Impossible to guarantee any flow any bandwidth
    without running scheduling algorithm again

6
Average Delay and Delay Variability
  • frame based scheduling suffers from an important
    drawback it often results in large cell delays
    and large delay variability
  • Issac Keslassy in On Guaranteed Smooth
    Scheduling for Input-Queued Switches in Infocom
    2003
  • Failed to mention packet mis-sequencing problem
    already solved. Load Balanced Birkhoff-von
    Neumann Switches, part II one-stage buffering,
    Computer Communications 2002
  • Problem is even worse in this paper due to their
    solution to solve the packet-missequencing
    problem
  • Scheduling is not smooth
  • Average delay high, burstiness, low short-term
    fairness

7
Linecards and Delay
  • Delay is proportional to frame size and and frame
    size is proportional to number of linecards
  • Delay is proportional to number of linecards!!
  • Large groups of linecardsgt lots of linecardsgt
    large delay!!

8
Fault Tolerance
  • Authors claim that lack of centralized scheduler
    leads to greater fault tolerance Agree
  • Ironically, the paper discusses how to improve
    fault-tolerance
  • Linecards, or MEMS switches, or connectors more
    likely to fail than centralized scheduler
  • Proposed Solution
  • Run algorithm to figure out static MEMS
    configuration
  • Too slow!!! (50 seconds vs. 50 milliseconds)
  • Polynomial algorithm means nothing in practice
  • Authors partially failed in what they set out to
    do

9
Crux of Paper
  • Outline- Part 1
  • L-L, L-G, G-G (easily deduce)
  • Outline- Part 2
  • G-G (Interesting, but more about this later)
  • G-L, L-L (Uninteresting) and similar work already
    done. Load Balanced Birkhoff-von Neumann
    Switches, part I one-stage buffering, Computer
    Communications 2002.
  • Invoking Santas principle, not much original
    work
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