Advance computer networks notes-1

This article covers the some of the basics of computer networks.It provides a great insight of ethernet technology.It shows the development of ethernet technology by explaining the various types of ethernet technologies,its features and functionalities.

Wide Area Networks

• Also called long haul networks.


• Covers large geographical area.
  
  eg:Continents.


• Speed ranges from 1.5 Mbps to 155 Mbps.


• Greater delay between connections.


• Network contains series of complex computers called packet switches.

Local Area Networks

• Covers small area.
  
  eg:office,buildings etc.


• Faster then WAN.Speed ranges from 10Mbps to 2Gbps.



• Small delay few tenth of a millisecond to 10ms.


• Each device connected to a LAN consists of NIC( network interface card ).

Network Hardware Addresses

• Every computer attached to a computer assigned a unique address.


• Each packet sent across a network contains a destination field address that contains the address of the receipient.



• The destination address occurs in same location in all packets.


• Each hardware technology specifies how address are assigned to computers.

Ethernet Technology

• Ethernet is the name given to the popular packet switched LAN technology invented at Xerox PARC at 1970s.



• Xerox Corporation,Intel Corporation and Digital Equipment Corporation standardised Ethernet in 1978;IEEE released a compatible version of standard using the standard number 802.3


• Formally known as 10base5


• It is the most popular and original wiring scheme not used but its variants are used now.But it provide the base for study.


• Original ethernet uses coaxial cable










• The coaxial cable is called the ether and hence the name ethernet.


• The connection between a computer and the ether requires hardware device called a transceiver.


• Transceiver cable enters the ether through a small hole which the technicians refer to as tap.



• Ethernet uses two major components:
  
  Transceiver which connects to the centre wire or braided shield of the cable sensing and sending signals to ether.
  
  A host interface card or host adapter plugs into the computer bus.
  
  
  Attachment Unit Interface(AUI) cable connects cable to an adapter board in a host computer informally called transceiver cable and it contains many wires which carries the electrical power to opearte the tranceiver and signals that control the transceiver.
















Disadvantages





• Transceiver is costly.


• Transceiver is present in cable so it is difficult to install.


• Coaxial cable used is difficult to bend


• AUI cable is also difficult to bend.

Thin-wire ethernet

• It overcomes all disadvantages of conventional ethernet.


• It is formally called 10base2


• Coaxial cable used is thinner,flexible and less expensive.



• It is also called thinnet.


• Here the transceivers are replaced by special high speed digital circuits and provide direct connection from a computer to the network.


• Thus a computer contains both the host interface and the circuitory that connects to the cable.


• It uses BNC connectors which does not require tools to attach computer to cable.






Disadvantages



• It does not provide protection against interference.


• It covers somewhat shorter distances so the network could include only fewer computers.


• If a user disconnects from network all other computers are affected.













Twisted pair ethernet





• The coaxial cable used in these ethernets does not require shielding.In this we use unshielded conventional copper wire.


• User disconnect problem not there.



• It is formally called 10baseT.


• A set of 8 wires(4 pairs) is used to conect computer to a hub.


• Hub is an electronic device that stimulates signals on ethernet cable.


• Physically hub consists of a small box that usually resides in a wiring closet.


• A connection between a hub and a computer must be less than 100m long.