The midterm covers the following subjects (from the Forouzan book + class lecture material) :

Whatever is not mentioned explicitly, is included in the exam material.

Chapter 1: Introduction

Know only implicitly. No explicit questions about Chapter 1.

Chapter 2: Basic Concepts

All.

Chapter 3: The OSI model

All, with the exception of 3.3 (TCP/IP protocol suite).

Chapter 4: Signals

Know only implicitly. No explicit questions about Chapter 4.

Chapter 5: Encoding and Modulating

All, but no details such as Figure 5.37.

Chapter 6: Transmission of Digital Data: Interfaces and Modems

Chapter 7: Transmission Media

Chapter 8: Multiplexing

Chapter 9: Error Detection and Correction

All, including the much more detailed class presentations.

Chapter 10: Data Link Control