Computer Basics

Computer Networks

Computer Network:

A computer network is two or more computing devices connected sharing resources among them. The various kinds of nodes (hosts) in the computer network can be router, hub, modem, servers, computers, mobile phones, printers etc. The network can be wired or wireless

Advantages of computer network:
• Reduction of costs due to sharing of resources
• Scalability can be achieved
• A network is more reliable than depending on a single source
• Information is easily accessible

Types of networks based on area:
• Personal area network (PAN) connects personal use devices within a range of about 30 feet. It can be wired or wireless. Example is mobile phone connected to television.
• Local area network (LAN) connects devices within a range of about 1 km. The connections are wireless or wired by cables, fibre optics etc. Data transfer rate is fast. It is secure.
• Metropolitan area network (MAN) connects devices within a range of about 40 km. Multiple LANs can also be connected to form a MAN. Data transfer rate is fast but is slower than LAN.
• Wide area network (WAN) connects devices across countries or continents. Many LANs and MANs can be connected to form a WAN. Internet is an example of WAN.

Network topology:
• It is the way the components are arranged in the network
Types of topologies:
• Bus topology
• Ring topology
• Star topology
• Mesh topology
• Tree topology

Bus topology:

All the devices are connected to a single communication line
Any of the nodes can receive data
It is cheaper and easy to maintain

Ring topology:


Each node is connected to two other nodes forming ring shape
Data will travel through all the nodes between source and destination
Data can be transmitted in one direction
If one node fails, the whole ring fails

Star topology:


All hosts are connected to a central node. If the central node fails, whole network fails
The central node can broadcast to all the nodes or to a single node

Full mesh topology:


In full mesh topology each node is connected to every other node

Partial mesh topology:


In partial mesh topology, not all nodes are interconnected

Tree topology:


In tree topology all nodes are connected to a root node forming a tree structure or a hierarchy
It is also called a star-bus topology
Easy to maintain and find errors

Routers:
• Routers transmit data to different networks
• They have the information of which networks are connected to them
• The router analyses the data packet received and transmits it to the destination
• The routing table helps in providing the route from source to destination
• Router can be wired or wireless
Modems (Modulator demodulator):
• The modem that is sending data converts the digital data to analog signals and it is called modulator
• The modem that is receiving data converts the analog signals to digital data and it is called the demodulator

Repeater:
• Repeater regenerates the signal received and reduces noise
• Repeater helps the signal to cover longer distances
Hub:
• Hub connects multiple network devices
• Sends data packets to all devices
• Collision happens when two devices send a packet at the same time
• It can be used with digital and analog data if configured
Gateway:
• It is used to communicate between different networks which may even have different protocols
• It maintains the paths of networks which helps in routing the traffic
• It works at any layer in OSI

Bridge:
• Bridge connects multiple network segments e.g., connecting LANs
• It is at the data link layer in OSI
• It has single input and single output
• It looks at MAC addresses of source and destination and sends data accordingly
Switch:
• It connects multiple hosts.
• It uses MAC addresses and sends data to the port connected to the device
• It can send multiple packets at the same time
• It does not send noisy or corrupted signals

Ethernet card (Network interface card):
• It is a network adapter that is on mother board of computer.
• The computer is connected to the network through network interface card with the help of an ethernet cable
• The MAC address of network interface card helps in identifying computer on network
RJ45 (Registered Jack 45):
• It is a network interface which is at the end of all network cables
• It has eight pins
• Used mostly in ethernet cables

History of networking:
• Late 1960s – The first connected computer network Advanced Research Projects Agency Network (ARPANET) came into existence
• 1969 – First message exchanged between University of California at Los Angeles (UCLA) and Stanford Research Institute (SRI)
• 1971- First email sent by Ray Tomlinson
• 1973 – Ethernet developed by Robert Metcalfe. Also the first international network connection SATNET deployed by ARPA (Advanced Research Projects Agency)
• 1974 – Telnet initiated and also “Internet” name evolved
• 1976 – First true IP router developed by Ginny Strazisar
• 1978 – TCP/IP invented by Bob Khan
• 1981 – Internet protocol IPV4 was defined
• 1983 – TCP/IP started, and Domain Name System (DNS) started
• 1986 – NSFNET (National science foundation network) started, and BITNET II started to address bandwidth issues
• 1990 – First network switch introduced
• 1996 – Internet protocol IPV6 introduced
• 1997 – 802.11 standard for Wi-fi introduced
• 1999 – WEP encryption protocol for wi-fi introduced
• 2003 – WPA and WPA2 encryption protocol was introduced
• 2018 – WPA3 encryption introduced

MAC (Media Access Control) Address:
• It is a unique address assigned to network interface controller (NIC)
• Assigned by manufacturer and therefore is permanent address
• It is a 48-bit hexadecimal address. e.g. 00:F6:F7:00:AE:5C
• The first 3 bytes are called Organizationally Unique Identifier (OUI)
IP (Internet protocol) Address:
• Identifies a device on the network
• IP addresses are dynamic as nodes may get removed or added to the network
• IPV6 address is 128-bit represented by 8 groups of hexadecimal numbers separated by colons
• IPv4 address is 32-bit represented by 4 groups of decimal numbers separated by colons

Domain Name System:
• It is a hierarchical naming system for resources (computers etc.) on internet
• It is the system that identifies the resources on internet or internet protocol networks. The domain name can be mapped to the IP address of the resource
• It has Domain Name Server which converts the domain name to its corresponding IP address
• The Domain Name Server has a database of domain names and the corresponding IP addresses

Computer network models:
• OSI (Open System interconnection) model
 Application layer is the top layer and is the interface to the user. It has protocols like http, ftp etc. for passing information. Example of application is browser
 Presentation layer transforms the data received from application layer to the required format to send over network. For example it may encrypt data, compress data or convert from ASCII to EBCDIC
 Session layer creates sessions alias communication channels between hosts. It opens the session to transfer data and closes session after completion
 Transport layer deals with end to end issues between hosts. It is responsible for transporting the data between hosts. It may break the data packets to smaller packets if required
 Network layer performs routing of packets across the network in the best possible route. The IP addresses of sender and receiver are placed in header
 Data link layer makes sure the communication between nodes is reliable by making transmission free of errors
 Physical layer is responsible for physical connection between nodes. It transmits bits (0s and 1s). It is the lowest layer of OSI model
 Application layer is the topmost layer that is responsible for handling protocols like http, ftp etc.
 Transport layer is responsible for end-to-end delivery of data. This layer defines the flow of data. Transmission control protocol (TCP) and User Datagram protocol (UDP) are used
 Internet layer defines routing and addressing. IP, ARP and ICMP protocols are used
 Network Access layer is the lowest layer. It deals with hardware and protocols to send data physically across the network