https://www.tutorialspoint.com/data_communication_computer_network/index.htm
CSS Computer Science (Optional) — Paper-II, Section-A, Topic II.
Organised by OSI layer, bottom-up (Physical → Data Link/WAN → Network → Transport → Application), with cross-layer Devices and Security groups kept separate — so topics that get compared against each other in the exam (e.g. hub vs switch vs router, or TCP vs UDP) now sit together instead of being scattered across a flat book-order list. Each subpage still follows the same internal structure: Definition → Key Points → CSS Exam Angle → Example → Likely Question. Years in brackets mark topics that have appeared in past CSS papers.
| Layer | Topics |
|---|---|
| Foundations & Models | Overview of Networking, Classification of Network, OSI Model |
| Physical (L1) | Physical Layer Functionalities, Transmission Media, Network Topologies |
| Data Link (L2) & WAN Switching | Switching, Error Detection & Control, ARQ, Multiple Access Protocols, LAN Technologies, X.25, Frame Relay, ATM, MPLS |
| Network (L3) | Network Layer, ARP, IPv6, ICMP, NAT, Internet Routing Protocols |
| Cross-Layer (L1–L3) | Network Devices |
| Transport (L4) | Transport Layer, Multiplexing, UDP, Reliable Data Transfer/TCP, Congestion Avoidance |
| Application (L5–L7) | Network Application Architectures, Servers, HTTP, FTP, Email (SMTP/POP3/IMAP), DNS, CDN, P2P, DHT, SIP |
| Security & Overlay (Cross-Layer) | Security Overlay Networks, Network Attacks, Top 7 Attack Types, Protecting IP Rights in Domain |
Prerequisite concepts and the reference model everything else below builds on.
Raw bits, transmission media, physical/signal-level topics.
Physical Layer Functionalities
Framing, error/flow control on one hop, and the switching/WAN technologies built on top of it.