Introduction To Computer Networks
Modern world scenario is ever changing. Data Communication and network have changed the way business and other daily affair works. Now, they highly rely on computer networks and internetwork.
A set of devices often mentioned as nodes connected by media link is called a Network.
A node can be a device which is capable of sending or receiving data generated by other nodes on the network like a computer, printer etc. These links connecting the devices are called Communication channels.
Computer network is a telecommunication channel using which we can share data with other coomputers or devices, connected to the same network. It is also called Data Network. The best example of computer network is Internet.
Computer network does not mean a system with one Control Unit connected to multiple other systems as its slave. That is Distributed system, not Computer Network.
A network must be able to meet certain criterias, these are mentioned below:
Computer Networks: Performance
It can be measured in the following ways:
- Transit time : It is the time taken to travel a message from one device to another.
- Response time : It is defined as the time elapsed between enquiry and response.
Other ways to measure performance are :
- Efficiency of software
- Number of users
- Capability of connected hardware
Computer Networks: Reliability
It decides the frequency at which network failure take place. More the failures are, less is the network’s reliability.
Computer Networks: Security
It refers to the protection of data from any un authorised user or access. While travelling through network, data passes many layers of network, and data can be traced if attempted. Hence security is also a very important characteristic for Networks.
Properties of a Good Network
- Interpersonal Communication: We can communicate with each other efficiently and easily. Example: emails, chat rooms, video conferencing etc, all of these are possible because of computer networks.
- Resources can be shared: We can share physical resources by making them available on a network such as printers, scanners etc.
- Sharing files, data: Authorised users are allowed to share the files on the network.
In the broadest terms, people often view the Internet as a cloud. You put your data in one place, and it comes out the place you want it to on the other side, with what happens inbetween obscured in the fog.
In reality the internet is tens of thousands kilometers of fiber optic cable, hundreds of thousands to millions of kilometers of copper wire, and hardware and software connecting them all together in a redundant, fast, and self-sufficient network. But not to worry, it’s not that bad: you only have to worry about a very small portion of the network, you can let someone else worry about the rest.
A Working Metaphor for the Internet
- House – (address vs. physical description)
- Local Streets / Neighborhood – LAN
- State, City/County – ISP, local division of ISP
- Country – Internet
- Major Roads (US routes / Bigger State Routes) – Internet Connectivity
- Highways – Internet Backbones
- Post Office – Router (GET Picture of 495/395/95)
- Intersection – Hub
- Highway Intersection (Mixing Bowl) – Switch
Dynamic IP Addresses
Dynamic IP addresses are IP addresses that are not necessarily tied down to one machine. They are usually applied to personal computers and other devices that can be taken on an off a network without worrying about disrupting anything other than being suddenly disconnected while trying to send an e-mail. You will usually find a dynamic IP address on your personal computer.
Static IP Addresses
You are more likely to find a static IP address on a server than on a personal machine. This is because if the IP address to a server changes it will disrupt the ability of users to access the site (or sites) hosted on that server.
Domain Name System
The Domain Name System (DNS) associates various information with domain names. It serves as the phone book for the Internet by translating human-readable computer hostnames (ex: www.openbookproject.net) into IP addresses (ex: 220.127.116.11) which networking equipment needs to deliver information. DNS also stores other information such as the list of mail servers. DNS is an essential component of the Internet we use.
- DNS makes it possible to assign Internet names to organizations independent of the physical routing hierarchy represented by the numerical IP address.
- DNS distributes the responsibility for assigning domain names and mapping them to IP networks by allowing an authoritative name server for each domain to keep track of its own changes, avoiding the need for a central register to be continually consulted and updated.
- Nanoscale network A nanoscale communication network has key components implemented at the nanoscale including message carriers and leverages physical principles that differ from macroscale communication mechanisms.
- Nanoscale communication extends communication to very small sensors and actuators such as those found in biological systems and also tends to operate in environments that would be too harsh for classical communication.
- Personal area network
A personal area network (PAN) is a computer network used for communication among computer and different information technological devices close to one person. Some examples of devices that are used in a PAN are personal computers, printers, fax machines, telephones, PDAs, scanners, and even video game consoles.
A PAN may include wired and wireless devices. The reach of a PAN typically extends to 10 meters. A wired PAN is usually constructed with USB and FireWire connections while technologies such as Bluetooth and infrared communication typically form a wireless PAN.
- Local area network
A local area network (LAN) is a network that connects computers and devices in a limited geographical area such as a home, school, office building, or closely positioned group of buildings. Each computer or device on the network is a node. Wired LANs are most likely based on Ethernet technology. Newer standards such as ITU-T G.hn also provide a way to create a wired LAN using existing wiring, such as coaxial cables, telephone lines, and power lines.The defining characteristics of a LAN, in contrast to a wide area network (WAN), include higher data transfer rates, limited geographic range, and lack of reliance on leased lines to provide connectivity. Current Ethernet or other IEEE 802.3 LAN technologies operate at data transfer rates up to 100 Gbit/s, standardized by IEEE in 2010 Currently, 400 Gbit/s Ethernet is being developed.