Detail Explanation of Soft Real Time System with example | Real Time System

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soft real time systemSoft real time system with examples,
Real Time System Notes | Sixth Semester,
BSc.CSIT | Tribhuvan University (TU)

Soft Real Time System
A real time system in which timing constraint is soft and few misses of deadlines do no serious harm. Only the system’s overall performance becomes poorer and poorer when more and more jobs with soft deadlines complete late.

The usefulness of a result produced by soft real time job decreases gradually as the tardiness of the job increases. If the user demands the best quality of service the system can provide but allows the system to deliver qualities below what it is defined by the timing constraints, then the timing constraints are soft. The less rigorous validation required of the system and often, more relaxed time constraint allow the developer to consider other performance metric equally seriously. It may be important for such a system to have as small average response time and high throughput.

Timing requirement of soft real time system are often specified in probabilistic terms. Example: Take a telephone network. In response to our dialing a telephone number, a sequence of jobs execute in turn, each routes the control signal from one switch to another in order to set up a connection. We expect our call will be put through in a short time.

To ensure that the expectation is met, most of the time, a timing constraint may be imposed (eg: sequence must complete in no more than 10 sec, 95% of the time). A system may have critical timing requirement but is nevertheless considered to be a soft real time system.

Example: Stock price quotation system. It should update the price of stock each time the price changes. Here, a late update is highly undesirable. However in a volatile market when prices fluctuate at unusually high rates, we expect that the system can’t keep up with every price change but does its best according to some criteria. Occasional late or missed update are tolerated as a trade off for other factors.

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