Question

Suppose that you are measuring the time to receive a segment. When an interrupt occurs, you read out the system clock in milliseconds. When the segment is fully processed, you read out the clock again. You measure 0 msec 270,000 times and 1 msec 730,000 times. How long does it take to receive a segment?

Short answer

It takes 0.73 milliseconds to receive a segment on average.

Step-by-step solution

Understand the Measurements

The measurements show how many times each time frame was recorded. You measure 0 milliseconds 270,000 times and 1 millisecond 730,000 times.

Calculate Total Time for Each Measurement

Multiply the number of times each measurement occurs by the time duration it represents. For 0 milliseconds: \(270,000 \times 0 = 0\) milliseconds. For 1 millisecond: \(730,000 \times 1 = 730,000\) milliseconds.

Find the Total Number of Segments

Add up all the segments processed: \(270,000 + 730,000 = 1,000,000\).

Calculate the Average Time per Segment

To find how long it takes on average to receive a segment, divide the total time accumulated by the total number of segments. Since total time is 730,000 milliseconds and total segments are 1,000,000, it results in \( \frac{730,000}{1,000,000} = 0.73 \) milliseconds per segment.

Key concepts

Latency Measurement

Latency measurement is a crucial aspect of evaluating network performance. It refers to the delay between a request being sent and a response being received. In the context of network operations, knowing how long it takes to process a segment can help identify bottlenecks or performance issues.

When measuring latency, it's essential to record time accurately. To do this, we use a system clock that records the time instantaneously in milliseconds whenever certain events occur.

• **Interrupt**: Marks the start time of the event.
• **Processing Completion**: Marks the end time of the event.

Each measurement helps build a pattern of typical response times.

For instance, in our exercise, you recorded measurements for segments that took 0 milliseconds and segments that took 1 millisecond. Although it might seem like there's no delay when a segment takes 0 milliseconds, this is still vital information. It indicates rapid processing capability under specific conditions.

Time Calculation

Time calculation involves determining the precise duration taken by network processes. For the task of receiving a network segment, the system records the times when each segment started and finished processing. To calculate the actual time taken for each segment, we subtract the start time from the end time.

In cases where multiple readings are given, as seen in the problem where 0 milliseconds were recorded 270,000 times and 1 millisecond was recorded 730,000 times, calculating the exact cumulative time is crucial.

• **Step 1**: Look at each measurement and multiply it by the number of occurrences, which allows for an aggregate sum over the entire dataset.
• **Step 2**: Accumulate these values to get the total time taken across all segments. Here, the total time calculation is simple since it's a multiplication process, yielding 730,000 milliseconds overall.

This total helps us understand the network's overall processing time and efficiency.

Average Time per Segment

Average time per segment is a useful metric for understanding the typical delay experienced per segment in the network. This average is calculated by dividing the total time by the number of segments processed. It is a straightforward concept but tremendously helpful in evaluating and optimizing network performance.

In this exercise, you first calculated the total processing time for all segments, which amounted to 730,000 milliseconds. With 1,000,000 segments processed, the average time per segment is found by the formula:

\(\text{Average Time} = \frac{\text{Total Time}}{\text{Total Segments}} = \frac{730,000 \text{ ms}}{1,000,000} = 0.73 \text{ ms per segment}.\)

This means that on average, each segment experiences a delay of 0.73 milliseconds. Lowering this average could lead to noticeable improvements in network performance. Focusing on reducing interruptions and optimizing processing can help achieve a better average time per segment.