MATLAB SIMEVENTS RELEASE NOTES Betriebsanweisung PDF herunterladen (Seite 111)

Model a Packet Switch

5-21

• The priorities of the entity generation events. In this example, all Time-Based

Entity Generator blocks share the same Generation event priority parameter

value.

• The Execution order parameter in the model's Configuration Parameters dialog

box. In this example, the parameter is set to Randomized.

As a result, when two packets are generated simultaneously, the sequence of

generation events in this example is random.

• End of blockage: Multiple packets with the same intended destination are at the

head of their respective queues precisely when the Path Combiner block's entity

output port changes from blocked to unblocked.

For example, suppose all of the queues have leading packets destined for the first

server, which is busy serving an earlier packet. The Path Combiner block's entity

output port is blocked. When the server completes service on the earlier packet,

the Path Combiner block's entity output port becomes unblocked. At that moment,

the Path Combiner block notifies its entity input ports of the status change, in a

sequence determined by the Input port precedence parameter. In this example,

the parameter is set to Equiprobable. As a result, when packets waiting at the head

of their queues have the same intended destination that changes from unavailable

to available, the sequence in which these packets are selected for advancement is

random.

Model the Channels

The packet switch example does not model the channel in detail. The channel's key

purpose is to process one packet at a time, for a duration that depends on the length of

the packet. During processing, other packets bound for the same destination must wait,

which introduces resource contention into the simulation.

Each channel is modeled as a Single Server block that delays each entity by an amount

of time stored in the entity's Length attribute. Each destination is modeled as an Entity

Sink block.

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MATLAB SIMEVENTS RELEASE NOTES Betriebsanweisung Seite 111