Figure 9-22 ATM trunking interworking function.
Figure 9-23 ATM desktop IWF interface requirements.
Copyr ight © CRC Pr ess LLC
by Abhijit S. Pandya; Ercan Sen CRC Press, CRC Press LLC
ISBN: 0849331390 Pub Date: 110198
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Chapter 10 ATM Traffic Simulation
The ATM traffic simulation environment described in this chapter consists of three simulators running in tandem as depicted in Figure 10-1. Their operations are synchronized via a common scheduler.
Figure 10-1 Simulation Model
In a typical event-driven traffic simulator environment events are generated using a random number generation function which reflects the desired traffic characteristics under consideration. The simulation
clock is advanced by the simulator scheduler to the earliest event rather than ticking the clock at unit intervals. This approach saves a considerable amount of simulation time over a time-driven simulation in
which the system clock is advanced at unit intervals.
The simulation environment described in this chapter has the characteristic of a consumer-producer interaction. The ATM traffic generator assumes the role of a producer. The buffer allocation and routing
simulators assume the role of a consumer. ATM cells are generated by the ATM traffic generator and fed into the buffer allocation simulator. Due to limited buffer capacity, arriving ATM cells at a full input
buffer are discarded. This action contributes to performance degradation of the system and it is measured as one of the performance criteria. Cells buffered in the input queues are serviced by the
routing simulator in each time slot. The ATM traffic simulator and the buffer allocation simulator run synchronously. A cell generated by the ATM traffic simulator is processed by the buffer allocation
Figure 10-2 The block diagram of time-driven ATM traffic simulator.
The modular structure of the simulation environment provides plug-in capability to evaluate various models for buffer allocation or routing control under the same traffic conditions. For example, in this
chapter, we demonstrate the evaluation of an input queuing scheme for buffer allocation and a crossbar switch for the routing control for overall ATM switch performance.
The quality of the simulation results is heavily influenced by the quality of the random number generator used in the ATM traffic simulator for generating ATM cell events. Periodicity and uniform distribution
are the two critical aspects of the random number generator used for the simulation. The periodicity should be much greater than the size of the simulation number of iterations. For an ATM traffic study,
a very large simulation size is required when the simulation is running at the cell traffic level. Therefore, a random number generator with large periodicity is essential for an ATM cell traffic simulator.
Additionally, the uniform distribution of the random numbers generated by the random number generator is also essential for unbiased simulation results.
The ATM traffic simulator described in this chapter was developed on an IBM-PC platform with Windows95 operating system. The simulator was written in Microsoft Visual-C version 1.0. The
Microsoft Visual-C compiler is a 16-bit compiler rather than a 32-bit compiler. Therefore, the random number generator function RAND48 48-bit random number generator from a SUN Sparc 4
workstation environment a UNIX platform was transformed to a 16-bit version for the Microsoft Visual-C compiler. The simulator was compiled and run on both IBM-PC and Sun workstations. The
results from both environments were compared for consistency. The simulator with a 16-bit version of RAND48 on IBM-PC produced the same results as with the Sun workstation version.
The RAND48 is a mixed Linear-Congruential Generator based on the following formula:
The following performance measurements were used for the performance analysis: cell routing delay, throughput, and cell loss probability.
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