For anyone running servers, containers and cloud infrastructure, Computer Networks is the most directly useful subject in the degree. Every “connection refused”, “timeout” or “DNS failure” is explained here. This article revisits the five units of the JNTUK course and links each to day-to-day cloud and Kubernetes work.
Unit 1: Introduction, models and the physical layer
Types of network and topology
| Type | Scale | Example |
|---|---|---|
| PAN / LAN | A room to a building | Home Wi-Fi, office Ethernet |
| MAN | A city | Cable or metro fibre network |
| WAN | Countries and continents | The Internet, leased lines |
Topologies: bus, star, ring, mesh, tree. Modern LANs use a star of switches. Switching types: circuit switching (a dedicated path, as in old telephone calls) and packet switching (data split into packets that share links, as on the Internet).
The layered models
| OSI layer | Job | TCP/IP layer | Examples |
|---|---|---|---|
| 7 Application | User-facing services | Application | HTTP, DNS, SMTP, SSH |
| 6 Presentation | Formatting, encryption, compression | TLS, JSON | |
| 5 Session | Dialogue control | ||
| 4 Transport | Process-to-process delivery | Transport | TCP, UDP |
| 3 Network | Addressing and routing | Internet | IP, ICMP |
| 2 Data link | Node-to-node delivery in a network | Link | Ethernet, Wi-Fi |
| 1 Physical | Bits on a medium | Cable, fibre, radio |
Each layer encapsulates the data of the one above by adding a header. The TCP/IP model is what the Internet actually uses; OSI is the reference vocabulary.
Physical layer
- Transmission media: guided (twisted pair, coaxial, fibre optic) and unguided (radio, microwave, satellite).
- Bandwidth, throughput and latency are different things. Latency is delay, bandwidth the capacity, and the bandwidth-delay product is how much data is “in flight”.
- Multiplexing: FDM, TDM, WDM.
- Switching and performance: delay is transmission + propagation + queuing + processing.
Today: when someone says “the network is slow”, ask whether it is latency (distance, a hop) or bandwidth (saturation). Cloud regions, CDNs and edge locations exist because latency is limited by the speed of light in fibre.
Unit 2: The data link layer
Framing, errors and flow control
The data link layer sends frames between adjacent nodes.
| Function | Methods |
|---|---|
| Framing | Character count, flag bytes with stuffing, bit stuffing |
| Error detection | Parity, checksum, CRC |
| Error correction | Hamming code |
| Flow control | Stop-and-wait, sliding window (Go-Back-N, Selective Repeat) |
Medium access control (MAC)
When many nodes share a medium, a protocol decides who transmits.
| Protocol | Idea |
|---|---|
| ALOHA / slotted ALOHA | Transmit at will; collisions are retried; max efficiency 18% / 37% |
| CSMA/CD | Listen first, detect collisions (classic Ethernet) |
| CSMA/CA | Avoid collisions by waiting (Wi-Fi) |
| Token passing | A token grants the right to send |
Ethernet, Wi-Fi and switching
- Ethernet frames carry source and destination MAC addresses (48 bits, for example
00:1A:2B:3C:4D:5E). Modern full-duplex switched Ethernet has no collisions. - A switch learns which MAC is on which port and forwards frames only there; a hub repeats to all ports. VLANs split one physical switch into several logical networks. The Spanning Tree Protocol prevents loops.
- Wi-Fi (IEEE 802.11) uses CSMA/CA; ARP maps an IP address to a MAC address on the local network. PPP is the point-to-point link protocol.
Today:
arp -aand a switch’s MAC table are this layer. Cloud VPCs and Kubernetes pod networks use virtual switches, VLAN-like segmentation (VXLAN) and ARP-style discovery inside the platform.
Unit 3: The network layer
IP addressing
An IPv4 address is 32 bits, written as four decimal bytes (192.168.1.10). It has a network part and a host part.
| Concept | Detail |
|---|---|
| Classful (old) | A, B, C, D, E by first bits |
| CIDR | 192.168.1.0/24: the prefix length gives the network size; a /24 has 256 addresses (254 usable hosts) |
| Subnetting | Splitting a network into smaller ones by extending the prefix |
| Private ranges | 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 |
| NAT | Many private hosts share one public address by rewriting ports |
| IPv6 | 128-bit addresses, no NAT needed, simplified header |
Other protocols: ICMP (ping, traceroute), DHCP (automatic address assignment), and fragmentation when a packet exceeds the link’s MTU.
Routing
A router forwards packets by looking up the destination in a routing table (longest-prefix match).
| Type | Algorithm | Protocols |
|---|---|---|
| Distance vector | Share your distances with neighbours (Bellman-Ford); can suffer “count to infinity” | RIP |
| Link state | Flood the whole topology and run Dijkstra | OSPF, IS-IS |
| Path vector | Exchange full paths between organizations | BGP, the protocol of the Internet |
Interior protocols run inside one organization (an autonomous system); BGP connects autonomous systems and applies policy. Congestion control and quality of service also appear in this unit.
Today: every VPC has a CIDR block, subnets, route tables and NAT gateways, and a security group and route table fix most “can’t reach” problems. Kubernetes assigns each pod an IP and each cluster has pod and service CIDRs, and overlapping CIDRs are a classic design mistake. Cloud providers’ regions are linked by BGP.
Unit 4: The transport layer
The transport layer delivers data between processes, identified by port numbers. A connection is identified by source IP, source port, destination IP and destination port.
| Feature | UDP | TCP |
|---|---|---|
| Connection | None (connectionless) | Yes (handshake) |
| Reliability | None | Acknowledgements, retransmission, ordering |
| Speed and overhead | Light and fast | Heavier |
| Use | DNS, VoIP, video, games, QUIC | Web, email, SSH, databases |
TCP in depth
- Three-way handshake: SYN, SYN-ACK, ACK to open; four-way FIN exchange to close; a TIME_WAIT state follows.
- Reliability: sequence and acknowledgement numbers, timeouts, fast retransmit.
- Flow control: the receiver advertises a window so the sender does not overwhelm it.
- Congestion control: slow start, congestion avoidance, fast recovery; the window grows until loss, then shrinks.
Socket programming (socket, bind, listen, accept, connect) is the API for building servers and clients. QUIC (used by HTTP/3) provides reliable streams over UDP.
Today:
netstatandssshow TCP states, and many “connection reset” and “too many TIME_WAIT” problems are explained here. Load balancers work at Layer 4 (TCP/UDP) or Layer 7 (HTTP). A Kubernetes Service forwards to pods by port, and ports 80, 443 and 22 are well-known ports.
Unit 5: The application layer and network security
Key protocols
| Protocol | Port | Purpose |
|---|---|---|
| DNS | 53 | Maps names to IP addresses (hierarchy: root, TLD, authoritative; records A, AAAA, CNAME, MX, TXT, NS; caching with TTL) |
| HTTP / HTTPS | 80 / 443 | The web: methods (GET, POST), status codes, headers, cookies; HTTP/2 adds multiplexing, HTTP/3 uses QUIC |
| SMTP, IMAP, POP3 | 25, 143, 110 | Email send and receive |
| FTP / SFTP | 21 / 22 | File transfer |
| SSH | 22 | Secure remote login |
| DHCP | 67/68 | Address assignment |
| SNMP | 161 | Network management |
Network security
| Topic | Idea |
|---|---|
| Cryptography | Symmetric (AES, one shared key), asymmetric (RSA, ECC, a key pair), hash functions (SHA-256), digital signatures |
| TLS | The handshake agrees on keys; certificates from a certificate authority prove identity; used in HTTPS |
| Firewalls | Packet filters, stateful inspection, application gateways |
| VPN and IPsec | Encrypted tunnels across untrusted networks |
| Common attacks | Sniffing, spoofing, DoS and DDoS, man-in-the-middle, DNS poisoning |
Today: a failed deployment is often DNS (wrong record or stale TTL), TLS (expired or mismatched certificate) or a firewall rule. Tools such as
dig,curl -v,openssl s_client,tracerouteandtcpdumpmap directly to this subject. Ingress controllers terminate TLS, cert-manager renews certificates, and CDNs such as CloudFront cache HTTP content.
One-minute recap
| Unit | Key idea | You meet it in |
|---|---|---|
| 1. Models and physical layer | OSI vs TCP/IP, encapsulation, latency vs bandwidth | Cloud regions, CDNs, performance diagnosis |
| 2. Data link | Framing, CRC, MAC protocols, Ethernet, switches, ARP | Switch tables, VLANs, VXLAN |
| 3. Network layer | IP, CIDR, subnetting, NAT, OSPF, BGP | VPCs, route tables, pod CIDRs |
| 4. Transport | TCP handshake, windows, congestion control, UDP | ss, resets, load balancers, QUIC |
| 5. Application and security | DNS, HTTP, TLS, firewalls, VPN | dig, curl, certificates, ingress |
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Written by Claude, Anthropic’s AI assistant, as part of Engineering Revisited, a quick refresher of the B.Tech subjects one at a time.