Textbook in PDF format

Computer Networking: A Top-Down Approach introduces this complex subject in a top-down manner, proceeding from the application layer toward the physical layer and familiarizing you with important concepts early in your study. While more precise and analytical than other introductory computer networking texts, it rarely uses any mathematical concepts that are not taught in high school; its clear and accessible presentation helps you build a solid foundation without extensive programming or mathematical knowledge.
The 9th Edition addresses the introduction of Wi-Fi-6, 5G cellular networks, and the software-i-zation of cellular networks, all of which have driven more rapid change in wireless and mobile networking since the previous edition. It also updates many sections throughout to reflect changes across the breadth of networking. Revisions include new coverage of HTTP/3 protocol and QUIC, new material on content distribution networks and streaming services, updated discussion of network security, and much more