A telephone exchange has 9000 subscribers. If the number of calls originated during the busy hour is 10,000 in one hour, what is the average calling rate per subscriber?

Introduction / Context:
Traffic engineering in telephony requires understanding the offered traffic load, measured in Erlangs or as an average call rate. Busy-hour call attempts per subscriber are key for designing capacity of switches and trunks.

Given Data / Assumptions:

• Total subscribers = 9000.
• Total calls in peak hour = 10,000.

Concept / Approach:

Calling rate per subscriber = total calls / number of subscribers. This provides the average number of originated calls per subscriber during the busy hour.

Step-by-Step Solution:

Verification / Alternative check:

Divide precisely: 10,000 ÷ 9000 = 1.111. Thus 10/9 is the exact expression.

Why Other Options Are Wrong:

• 0.9 or 0.81 or 0.1: numerical errors, not the correct ratio.
• 1 call: underestimates slightly; true ratio is greater than 1.

Common Pitfalls:

Misinterpreting the calling rate as calls per second instead of per subscriber per hour; forgetting to normalize by subscriber count.

Final Answer:

10/9 calls per subscriber