CS 3413 Data Communications, Fall 2004 Assignment 3 Comments

This assignment had 10 questions, each worth 10 points.

The maximum score on this assignment is 100 points.

Problem number 6 was not graded. Everyone got credit for this problem.

Problem number 6 asked which protocols use differential encoding.
Unfortunately, the book gives several different descriptions of what differential encoding is.

• On page 135 it says: "In differential encoding, the information to be transmitted is represented in terms of the changes between successive signal elements. If this is the definition, then the following use differential encoding: NRZI, Bipolar-AMI, Pseudoternary, Manchester, Differential Manchester, B8ZS and HDB3.
• The book then says that "If the current bit is binary 0, then the current bit is encoded with the same signal as the preceding bit; if the current bit is a binary 1, then the current bit is encoded with a different signal than the preceding bit. If this is the definition, then only NRZI uses differential encoding. Even Differential Manchester is not using differential encoding under this definition since a 0 that follows a 0 is not encoded the same as the previous 1.
• The glossary in the back of the book gives a definition similar to the first one given above.