![](bg2.png)
have been proposed to provide fast, efficient and
reliable communications at a reasonable cost (cf.
Chao, 2007). However, no single solution network is
generally preferred because the cost-effectiveness of
a particular design varies with such factors as its
application, the required speed of data transfer, the
actual hardware implementation of the switching
network, the number of input/output ports, and the
construction cost.
As far as MINs are concerned, they can be built
using a variety of structures. Two significant
examples of topological structures based on the
single plane design are switching networks based on
the cube
i
and PM2I interconnection functions (Lien,
2010). Therefore, there is an open question about
the performance vs.-reliability trade-off that
a multiple-path structure of the PM2I network
might
offer, for various distributed control algorithms and
decision rules, when compared to a cube-type
network.
3 THE SWITCH MODEL
To evaluate the properties of a fabric based on the
given switching network (MIN), the following
assumptions are made about the operation and the
environment of the interconnection network: the
single plane design of switching fabric is taken into
account; because, in this contribution, we are
focused primarily on the performance, the slotted
traffic source model is used with a uniform random
distribution of packet destinations; the switching
network is operated synchronously, meaning that the
packets are transmitted only at the beginning of
a time slot given by the packet clock and each input
link is offered the same traffic load; the buffering is
external to the switch fabric, i.e. non-buffered switch
fabrics formed from non-buffered SEs are under
consideration. Therefore, the queuing effects are
unaccounted in this model. All output ports perform
the function of a perfect sync and a conflict is said to
occur if more than one packet arrives at the same
output link at the same time.
Two classes of packet switched MINs, one with
redundant interconnection paths and one without are
under consideration (i.e. the cube-type class of MINs
known as unique-path networks and the PM2I class
of MINs which have multiple paths between a given
network input-output pair). It is clear that faults in
the switching network often result in degraded
performance of a fabric. Because failures occur at
random and the combinations of the type, number
and location of faults can also vary, the influence of
failures on the performance of switching fabric is
usually examined by simulation. These aspects have
been already investigated (Hulicki, 2013) and hence
they are not included in the model of switching
fabric used in this contribution.
4 PERFORMANCE EVALUATION
Although recently a new (analytic) method for the
performance analysis of multistage switching fabrics
has been proposed (Hulicki, 2013a), in this paper,
the performance of switching fabric, based on both
of the aforementioned classes of packet switched
MINs, has been studied using simulated
experiments. A discrete time event-driven simulator
has been designed to carry out simulations. Such
a tool enables one to simulate the real operation of
switch fabric as well as to estimate its performance
measures. The simulator uses the switch model and
the most commonly used performance measures. It
enables performance evaluation of the fabric under
different traffic and/or interconnection patterns,
including both uniform and non-uniform traffic
patterns. Moreover, in order to stop packets from
entering the switching fabric once its resources are
exhausted, the switching network of a router often
employs a backpressure mechanism (Lien, 2010).
Therefore, except for non-buffered MINs, the
simulator also allows for a modification to the
switching fabric, i.e. an implementation of buffering
(introduced at the input/output of the switching
network or to the SEs) or using different types of
SEs (that allow for diverse switching functions), as
well as an evaluation of the fabric’s dependability
under diverse fault models, including combinations
of the type, number and location of faults.
As it has been already mentioned, this
contribution presents only selected results from the
simulation experiments because the results point to
a similar trend and the utilization of fabric,
efficiency of switching and packet loss (or packet
drop rate) can serve as good indicators for the
performance of switching fabric. The simulation
results have been shown and compared in a few
figures (Figs. 2, 3, 4, 5, 6 and 7). Each data value
given in these figures is the result after n
r
= 100,000
clock cycles in the simulation (cf. Fig.1), where this
number of cycles is found to yield steady-state
outcomes (95% conf. lev.). If the number of cycles
is less than 10,000 , the steady-state is not reached,
so the simulation results cannot be valid (cf. lowest
curve in Fig.1).
SIMULTECH2014-4thInternationalConferenceonSimulationandModelingMethodologies,Technologiesand
Applications
568