Computer Networking

Semester V · BCA 301 · 3 credits

7 units · 46 teaching hours · about 5 h of reading

0 / 7 chapters done

Introduction to Computer Networks 4 hrs · 33 min read · 10 figures
The syllabus asks for
- What a network is
- Types of networks
- Topologies
- Network devices
- Layered architecture and protocol stacks
- The OSI reference model
- The TCP/IP model
- Performance: bandwidth, delay and throughput
- Standards and organisations
- Seeing the ideas: networks, topologies, layers and delay
Key points
- A network moves data between hosts using agreed protocols, addresses and media. LAN, MAN and WAN differ by span; the Internet is a network of networks.
- Topology affects cost and reliability; today's LANs are physical stars built around switches.
- Layering divides the work: each layer serves the one above and talks to its peer. OSI has seven layers, TCP/IP four.
- Data is encapsulated on the way down and decapsulated on the way up; headers are overhead.
- Latency = transmission + propagation + queuing + processing; BDP tells how much data fills the pipe.
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The Physical Layer 7 hrs · 41 min read · 15 figures
The syllabus asks for
- Functions of the physical layer
- Data and signals
- Data rate limits
- Line coding and digital signalling
- Transmission media
- Multiplexing
- Switching
- Telephone, cable and mobile data networks
- Seeing the ideas: signals, media, multiplexing and switching
Key points
- The physical layer moves raw bits as signals. Impairments are attenuation, distortion and noise.
- Nyquist limits a noiseless channel by bandwidth and levels; Shannon limits a noisy one by bandwidth and SNR.
- Line codes trade bandwidth against clock recovery: Manchester is self-clocking, NRZI and AMI are simpler.
- Fibre outperforms copper in bandwidth, distance and noise immunity; UTP dominates the last 100 m.
- Multiplexing shares a link by frequency, time or wavelength; switching shares a network by circuits or packets, and bursty data favours packets.
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The Data Link Layer and LANs 12 hrs · 50 min read · 15 figures
The syllabus asks for
- Services of the data link layer
- Framing
- Error detection
- Error correction: Hamming codes
- Flow control and error control
- HDLC and PPP
- Multiple access protocols
- Ethernet
- Wireless LAN (IEEE 802.11)
- Seeing the ideas: frames, checks, windows and shared media
Key points
- The data link layer frames the bit stream, detects (and may correct) errors, controls flow and arbitrates access to shared media.
- Bit stuffing (HDLC) and byte stuffing (PPP) keep flags out of data. Parity is weak, the Internet checksum is cheap, CRC is strong against bursts.
- Hamming codes place parity bits at powers of two; the syndrome points at the faulty bit.
- Sliding-window protocols keep the pipe full; Go-Back-N is simple, Selective Repeat is efficient.
- Random access (ALOHA, CSMA/CD, CSMA/CA) trades collisions for simplicity; switched Ethernet has replaced shared Ethernet, and Wi-Fi uses collision avoidance.
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The Network Layer: Addressing and Routing 10 hrs · 49 min read · 16 figures
The syllabus asks for
- Network layer services
- The IPv4 datagram
- IPv4 addressing
- Subnetting, VLSM and supernetting
- Supporting protocols
- IPv6
- Routing: concepts
- Seeing the ideas: addresses, routes and the boxes that follow them
Key points
- IP is a best-effort, connectionless service; routers forward by longest-prefix match on the destination address and split oversize datagrams into fragments.
- CIDR, subnetting, VLSM and aggregation allow addresses to be allocated and summarised flexibly; ARP, ICMP, DHCP and NAT make IPv4 usable; IPv6 restores the address space.
- Link-state routing (Dijkstra) gives every router the same map; distance-vector routing (Bellman–Ford) shares tables with neighbours and risks count-to-infinity.
- OSPF and RIP route inside an AS, BGP between ASes.
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The Transport Layer 6 hrs · 38 min read · 11 figures
The syllabus asks for
- Functions of the transport layer
- UDP
- Principles of reliable data transfer
- TCP services and the segment
- Flow control
- Error control and timers
- Congestion control
- Elements of transport protocols
- Sockets in practice
- Seeing the ideas: ports, segments, windows and congestion
Key points
- The transport layer gives process-to-process delivery with ports. UDP is a thin, fast, unreliable service; TCP is a reliable byte stream.
- TCP sets up with a three-way handshake, numbers bytes, acknowledges cumulatively, retransmits on timeout or three duplicate ACKs and tears down with FINs.
- Flow control uses the receiver's window; congestion control uses cwnd with slow start, additive increase and multiplicative decrease.
- Throughput is bounded by window / RTT, which is why high-speed long-delay paths need window scaling.
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The Application Layer 4 hrs · 43 min read · 15 figures
The syllabus asks for
- Functions and architectures
- The Domain Name System
- DHCP and the bootstrap sequence
- The World Wide Web and HTTP
- Remote login and file transfer
- Electronic mail
- Network management and analysis tools
- Peer-to-peer and content delivery
- Seeing the ideas: names, pages, mail, transfers and monitors
Key points
- Application protocols are agreements over sockets: client–server or peer-to-peer, over TCP or UDP.
- DNS maps names to addresses with a distributed hierarchy of servers, caching by TTL and typed records.
- HTTP is a stateless text protocol; cookies add state, caching and persistent connections reduce load time; HTTPS adds TLS.
- FTP separates control and data connections; SMTP pushes mail, POP3 and IMAP pull it; MIME carries binary content as Base64.
- SNMP, MRTG, PRTG, Packet Tracer and Wireshark are the tools to monitor, simulate and analyse.
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Network Security 3 hrs · 41 min read · 16 figures
The syllabus asks for
- Security goals and threats
- Cryptography basics
- Secure protocols
- Firewalls and intrusion detection
- Good practice
- Seeing the ideas: ciphers, keys, hashes, handshakes and firewalls
Key points
- Security aims at confidentiality, integrity, availability, authentication and non-repudiation; attacks are passive or active.
- Symmetric ciphers (AES) are fast but need key distribution; public-key systems (RSA, Diffie–Hellman) solve distribution and give signatures; hashes provide integrity.
- Certificates bind keys to names through CAs; TLS combines all of them to secure the web; IPsec and WPA2 do it at the IP and Wi-Fi layers.
- Firewalls filter by policy, IDS/IPS detect and block attacks, and good practice (patching, least privilege, segmentation, MFA) matters more than any single device.
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