Chapter 10

04/13/23 1

CLOS-NETWORK SWITCHES

H. Jonathan ChaoH. Jonathan Chao04/13/23

A Growable Switch Configuration

i j


Routing Constraint in Clos-Network Switch


Routing In A Clos Network


A TST Switch Representation After the Space-to-Time Transformation


Matching of Ai versus Bj (X=busy, blank=open)


Parallel Assignments In a Cyclic Manner from Minislot to Minislot


CRRD Switch with Virtual Output Queues (VOQs) In the Input Modules

LI(i,r) LC(r,j)


Terminology


Schematic Configuration of a 40X40 Multistage ATLANTA Switch


Three Main Principles in ATLANTA Switch


Random Dispatching Scheme


Random Dispatching Scheme (Cont’d)

In Phase 2, a VOQ’s request from IM may lose contention in CM because of contention in the CM or backpressure from the corresponding output queue.

If this request loses contention due to backpressure, IM will choose another VOQ as candidate at the next time slot. Otherwise, this VOQ will be chosen as candidate at the next time slot again.


Example of A Multicast Connection In a 40x40 ATLANTA Switch with Multistage Fabric. The Minimum Multicast Tree for Cells of that Multicast Connection is Highlighted


Random Dispatching Schemes ATLANTA Switch (need internal expansion) Washington University Gigabit Switch (cause

the out-of-sequence)


Example of Random Dispatching Scheme(n=m=k=2)

VOQ(0,0,0) can send through CM(0) is

The total link utilization of OP(0,0) is

Throughput_Max:


One question arises:

Is it possible to achieve a high throughput by using a practical dispatching scheme, without allocating any buffers in the second stage to avoid the out-of-sequence problem and without expanding the internal bandwidth?


Concurrent Round-Robin Dispatching (CRRD) Scheme

The basic idea of CRRD is to use desynchronization effect.


Example of desynchronization effect of CRRD (n=m=k=2)


Concurrent Master-Slave Round-Robin Dispatching (CMSD) Scheme

CMSD uses hierarchy round-robin arbiters, it provides more features of scalability in terms of reduction of dispatching scheduling time and interconnection crosspoints, while preserving CRRD’s advantage.

m

n

k

111


Concurrent Master-Slave Round-Robin Dispatching (CMSD) Scheme (Cont’d)

Note that, G(i,j) is denoted as a VOQ group that consists of n VOQs, each of which is denoted as VOQ(i,j,h).


Example of Desynchronization Effect of CMSD (n=m=k=2)


Delay Performance of CRRD and RD Schemes (n=m=k=8)

Bernoulli Traffic

CRRD achieves100% throughput under uniform traffic, which is independent of number of iterations in the IM.


Delay Performance of CMSD in Bursty Traffic Compared with CRRD (n=m=k=8)

CMSD also achieves100% throughput under uniform traffic, which is independent of number of iterations in the IM.


Relationship between Switch Throughput and Expansion Factor (n=k=8)

RD needs the expansion ratio of more than 1.5 to achieve 100% throughput, which CRRD and CMSD do not need expansion by using simple round robin arbiters.


Switch Throughput Under Non-Uniform Traffic (n=m=k=8)

The throughput of CRRD and CMSD is higher than that of RD, when the traffic is slightly unbalanced.


Analogy among scheduling schemes


The Correspondence Between the Middle-Stage Route Scheduling In a Clos Network and the Edge-Coloring of the Regular Bipartite Multigraph


Illustration of Time-Space Interleaving Principle


Latin-Square Assignment


Route Assignment By Latin Square for Uniform Traffic


Route Scheduling In the Middle-Stage for Uniform Traffic


Route Scheduling In Central Modules for the Second Example of Uniform Traffic


Procedure of Capacity and Route Assignment


Route Scheduling Example (Heterogeneous Traffic)

Chapter 10

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