22-Elec-B4 Information Technology Networks, Undated paper: worked solutions

Paper format. National Examinations, May 2019 — 16-Elec-B4 Information Technology Networks. Three hours, closed book (one approved Casio or Sharp calculator). Five questions of 25 marks; any four constitute a complete paper worth 100 marks. Marks are printed in the left margin. All five questions are solved below, because the set is a study resource rather than an exam script.

Reference texts.

A. Leon-Garcia and I. Widjaja, Communication Networks: Fundamental Concepts and Key Architectures, 2nd ed. — the syllabus reference for this code (layering ch. 2, MAC ch. 6, TCP ch. 8, routing ch. 7).
J. F. Kurose and K. W. Ross, Computer Networking: A Top-Down Approach, 7th ed. — TCP congestion control (§3.7), distance-vector routing (§5.2).
A. S. Tanenbaum and D. J. Wetherall, Computer Networks, 5th ed. — OSI model (§1.4), CSMA/CD and the Ethernet slot time (§4.2–4.3).
T. S. Rappaport, Wireless Communications: Principles and Practice, 2nd ed. — frequency reuse and cell capacity (ch. 3).
S. Sesia, I. Toufik and M. Baker, LTE — The UMTS Long Term Evolution, 2nd ed. — OFDMA, the resource grid and reference signals (ch. 6, 8).

Check: one edge of the Question 4 graph. The printed drawing carries a weight label “1” centred on the A–B chord, but the line itself is not drawn. Every other weight label sits on a drawn edge, and eleven labels are printed against ten surviving lines. The edge A–B = 1 is therefore taken as present. Reading A–B as absent instead would leave A a leaf reachable only through C, changing d(A) from 4 to 9 and leaving the printed “1” orphaned.

22-Elec-B4 Information Technology Networks: Undated paper