This document provides an overview of computer networks. It defines a computer network as a system of interconnected computers and devices that communicate using common protocols over digital connections. These connections can be wired, wireless, or optical. The document then describes different types of networks based on size and coverage area, including personal area networks, local area networks, metropolitan area networks, and wide area networks. It also covers network architectures, topologies, switching methods, the OSI model, and examples of protocols used at each layer of the OSI model.

1. Computer Networks
-Deepthi B

2. What is Computer Network?
A computer network is a system of interconnected computers and peripheral devices.
Computers use common communication protocols over digital interconnections to
communicate with each other. These interconnections are made up
of telecommunication network technologies based on physically wired, optical, and
wireless radio-frequency methods that may be arranged in a variety of network
topologies.

3. Types of Networks
Based on the size and the coverage area, networks are categorized into the following
types:
• Personal Area Networks (PAN)
• Local Area Networks (LAN)
• Metropolitan Area Networks (MAN)
• Wide Area Networks

4. Classification of Network Architecture
1. Client Server Architecture
2. Peer-to-Peer Architecture

5. Types of Network Topology
Pattern of
interconnection of
nodes in a network is
called topology.

6. Packet Switching vs Circuit Switching

7. OSI Model
Application layer : Protocols includes HTTP,SMTP,FTP,
DNS. The unit of communication is message.
Transport layer: Protocols include TCP and UDP. The unit
of communication is segment
Network Layer: Protocols include IP, ICMP, ARP. The unit
of communication is Packet.
Data Link Layer: Protocols include Ethernet, ATM. The unit
of communication is Frames.
Physical Layer: Protocols include Ethernet, Fibre,
Wireless. The unit of communication is bits

8. Application Layer
Persistent vs Non Persistent HTTP
HTTPS: HTTP +SSL
DNS

9. Transport Layer
Connectionless: UDP
Connection-oriented: TCP-
rdt, flow control- stop and wait
protocol, go back N, selective repeat
protocol, sliding window protocol
Congestion control

10. Network Layer
Router- Networking device that connects
two local networks
Fragmentation: process of diving a datagram
into fragments during transmission by
intermediary devices like routers
IPv4, IPv6
DHCP-(Dynamic Host Configuration Protocol)
provides automatic central management for the
distribution of IP addresses within a network.
NAT: (Network Address Translation) all devices in local
network share just one IPv4 address as far as outside
world is concerned
Classless and Classful addressing
Routing Algorithms
IP
Addressing

11. Link Layer and Physical Layer
Link layer
Switches (A networking device that is used to connect many devices together in a computer network)
and bridges in LL
Error correction done by single, 2-d bit parity checking and crc.
Multiple Access Protocols
MAC address:48-bit address used “locally” to get
frame from one interface to another physically-connected interface
ARP table to map IP add; MAC add;TTL
Ethernet: widest used technology for LAN
Hub and repeater in physical layer

12. A day in life of a web request
Arriving mobile client attaches to network
Requests web page: www.google.com
Connecting laptop needs to get its own IP address, addr of first-hop router, addr of DNS server: use DHCP
DHCP server formulates DHCP ACK containing client’s IP address, IP address of first-hop router for client,
name & IP address of DNS server
DHCP client receives DHCP ACK reply
Before sending HTTP request, need IP address of www.google.com: DNS
DNS query created, encapsulated in UDP, encapsulated in IP, encapsulated in Eth. To send frame to router,
need MAC address of router interface: ARP

13. A day in life of a web request
ARP query broadcast, received by router, which replies with ARP reply giving MAC address of router
interface
IP datagram containing DNS query forwarded via LAN switch from client to 1st hop router
IP datagram forwarded from campus network into ISP network, routed (tables created by RIP, OSPF, IS-IS
and/or BGP routing protocols) to DNS server.
Demuxed to DNS
DNS replies to client with IP address of www.google.com

14. Thankyou