9. Transportation networks based on physical carriers may be more efficient for transmitting large messages (especially messages with maps, charts, or pictures). Computing the channel capacity is one way of comparing two different information transmission methods.

For example, suppose we have a financial contract consisting of 5 pages (each page contains 300 words of 5 letters); consequently, together with the “space” used as a word separator, each page contains 1800 characters (letter or number symbols), and the entire document contains 9000 symbols. A 100-mile transmission by Chappe telegraph, at 1 symbol per minute, would require 9000 minutes (150 hours). If we use a messenger traveling 10 miles per hour, the message would be delivered in 10 hours — the channel capacity of the messenger here is 900 symbols per minute. Suppose that we store a large historical set of financial data for thousands of companies containing glossy corporate annual reports, SEC filings, and market data. Data are stored on 1000 DVD disks. Suppose a single DVD holds 10 gigabytes (= 10 billion characters) and our Internet connection is calibrated at 10 megabytes (= 10 million characters) per second. How long would it take to send the 1000 DVD disks from New York to Philadelphia via the Internet? Suppose we have an express courier that is available to drive to New York to Philadelphia: what is the channel capacity of this service?