The last four digits are used at the access layer to identify a particular telephone. The next three numbers are used at the distribution layer to identify an exchange that services several phone numbers. The area code is used at the core level for routing between different regions.
This is a speed drill. Using only your head, convert the following binary numbers to decimals.
11100000
11111100
10000000
11110000
00111111
224, 252, 128, 240, and 63 (64 – 1)
