Advantages
Easy to implement
Low Cost
Disadvantages
Difficult to isolate network faults
A cable fault affects all workstations
As the number of workstations increase, the speed of the network slows down
Saturday, February 9, 2008
Bus Network Topology Summary
Difficult to isolate network faults
A cable fault affects all workstations
As the number of workstations increase, the speed of the network slows down
Bus Topology
all workstations connect to the same cable segment
commonly used for implementing Ethernet at 10mbps
the cable is terminated at each end
wiring is normally done point to point
a faulty cable or workstation will take the entire LAN down
two wire, generally implemented using coaxial cable during the 1980's
The bus cable carries the transmitted message along the cable. As the message arrives at each workstation, the workstation computer checks the destination address contained in the message to see if it matches it's own. If the address does not match, the workstation does nothing more.
If the workstation addresses matches that contained in the message, the workstation processes the message. The message is transmitted along the cable and is visible to all computers connected to that cable.
There are THREE common wiring implementations for bus networks
10Base2 -(thin-net, Cheaper Net) 50-ohm cable using BNC T connectors, cards provide transceiver
10Base5-(Thick Net) 50-ohm cable using 15-pin AUI D-type connectors and external transceivers
10BaseT- (UTP) UTP cable using RJ45 connectors and a wiring centre
The above diagram shows a number of computers connected to a Bus cable, in this case, implemented as Thin Ethernet. Each computer has a network card installed, which directly attaches to the network bus cable via a T-Connector.
It is becoming common to use 10BaseT (UTP) for implementing Ethernet LANS. Each workstation is wired in star fashion back to a concentrator wiring centre (hub). The hub is a multi-port device supporting up to about 32 ports. One of these ports is connected to a server, or the output of the hub can be connected to other hubs.
NETWORK TOPOLOGY
Topology refers to the way in which the network of computers is connected. Each topology is suited to specific tasks and has its own advantages and disadvantages.
The choice of topology is dependent upon
type and number of equipment being used
planned applications and rate of data transfers
required response times
cost
There are FOUR major competing topologies
Bus
Ring
Star
FDDI Most networking software support all topologies.
The choice of topology is dependent upon
type and number of equipment being used
planned applications and rate of data transfers
required response times
cost
There are FOUR major competing topologies
Bus
Ring
Star
FDDI Most networking software support all topologies.
History of the World Wide Web
Before the World Wide Web the Internet really only provided screens full of text (and usually only in one font and font size). So although it was pretty good for exchanging information, and indeed for accessing information such as the Catalogue of the US Library of Congress, it was visually very boring.In an attempt to make this more aesthetic, companies like Compuserve and AOL began developing what used to be called GUIs (or graphical user interfaces). GUIs added a bit of colour and a bit of layout, but were still pretty boring. Indeed IBM personal computers were only beginning to adopt Windows interfaces - before that with MSDOS interfaces they were pretty primitive. So the Internet might have been useful, but it wasn't good looking.Probably the World Wide Web saved the net. Not only did it change its appearance, it made it possible for pictures and sound to be displayed and exchanged.The web had some important predecessors, perhaps the most significant of these being Ted Nelson's Xanadu project, which worked on the concept of Hypertext - where you could click on a word and it would take you somewhere else. Ted Nelson envisaged with Xanadu a huge library of all the worlds' information. In order to click on hyperlinks, as they were called, Douglas Engelbart invented the mouse, which was to later become a very important part of personal computers. So the idea of clicking on a word or a picture to take you somewhere else was a basic foundation of the web.Another important building block was the URL or Uniform Resource Locator. This allowed you a further option to find your way around by naming a site. Every site on the worldwide web has a unique URL (such as www.nethistory.info).The other feature was Hypertext Markup Language (html), the language that allowed pages to display different fonts and sizes, pictures, colours etc. Before HTML, there was no such standard, and the "GUIs we talked about before only belonged to different computers or different computer software. They could not be networked.It was Tim Berners Lee who brought this all together and created the World Wide Web. The first trials of the World Wide Web were at the CERN laboratories (one of Europe's largest research laboratories) in Switzerland in December 1990. By 1991 browser and web server software was available, and by 1992 a few preliminary sites existed in places like University of Illinois, where Mark Andreesen became involved. By the end of 1992, there were about 26 sites.The first browser which became popularly available to take advantage of this was Mosaic, in 1993. Mosaic was as slow as a wet week, and really didn't handle downloading pictures well at all - so the early world wide web experience with Mosaic, and with domestic modems that operated at one sixths of current modem speeds at best, were pretty lousy and really didn't give much indication of the potential of this medium. On April 30, 1993 CERN's directors made a statement that was a true milestone in Internet history. On this day, they declared that WWW technology would be freely usable by anyone, with no fees being payable to CERN. This decision - much in line with the decisions of the earlier Internet pioneers to make their products freely available - was a visionary and important one. The browser really did begin to change everything. By the end of 1994 there were a million browser copies in use - rapid growth indeed!! In the same year Marc Andreesen founded Netscape Corporation, and the World Wide Web Consortium, which administers development of Word Wide Web standards, was formed by Tim Berners Lee.Then we really started to see growth. Every year from 1994 to 2000, the Internet saw massive growth, the like of which had not been seen with any preceding technology. The Internet era had begun.The first search engines began to appear in the mid 1990s, and it didn't take long for Google to come on the scene, and establish a dominant market position.In the early days, the web was mainly used for displaying information. On line shopping, and on line purchase of goods, came a little bit later. The first large commercial site was Amazon, a company which in its initial days concentrated solely on book markets. The Amazon concept was developed in 1994, a year in which some people claim the world wide web grew by an astonishing 2300 percent! Amazon saw that on line shopping was the way of the future, and chose the book market as a field where much could be achieved.By 1998 there were 750,000 commercial sites on the world wide web, and we were beginning to see how the Internet would bring about significant changes to existing industries. In travel for instance, we were able to compare different airlines and hotels and get the cheapest fares and accommodation - something pretty difficult for individuals to do before the world wide web. Hotels began offering last minute rates through specially constructed websites, thus furthering the power of the web as a sales medium. And things went even further - in some fields of travel, individuals would outline where they wanted to travel to and from, and travel companies would then bid for the business. All these developments rapidly changed the way traditional markets worked. In some industries, the world would never be the same again.
Written by Ian Peter
Written by Ian Peter
The beginnings of the Internet
It will help in discussing the beginnings of the Internet to define what the Internet is. Now you can get as many different definitions of what the Internet is as you can dictionaries. But for must of us, the simple description, a "worldwide system of interconnected networks and computers" is pretty good and adequate. But when people get more technical, they tend to add to the definition terms such as "a network that uses the Transmission Control Protocol - Internet protocol" (or TCP/IP).Many people have heard that the Internet began with some military computers in the Pentagon called Arpanet in 1969. The theory goes on to suggest that the network was designed to survive a nuclear attack. However, whichever definition of what the Internet is we use, neither the Pentagon nor 1969 hold up as the time and place the Internet was invented. A project which began in the Pentagon that year, called Arpanet, gave birth to the Internet protocols sometime later (during the 1970's), but 1969 was not the Internet's beginnings. Surviving a nuclear attack was not Arpanet's motivation, nor was building a global communications network. Bob Taylor, the Pentagon official who was in charge of the Pentagon's Advanced Research Projects Agency Network (or Arpanet) program, insists that the purpose was not military, but scientific. The nuclear attack theory was never part of the design. Nor was an Internet in the sense we know it part of the Pentagon's 1969 thinking. Larry Roberts, who was employed by Bob Taylor to build the Arpanet network, states that Arpanet was never intended to link people or be a communications and information facility. Arpanet was about time-sharing. Time sharing tried to make it possible for research institutions to use the processing power of other institutions computers when they had large calculations to do that required more power, or when someone else's facility might do the job better.What Arpanet did in 1969 that was important was to develop a variation of a technique called packet switching. In 1965, before Arpanet came into existence, an Englishman called Donald Davies had proposed a similar facility to Arpanet in the United Kingdom, the NPL Data Communications Network. It never got funded; but Donald Davies did develop the concept of packet switching, a means by which messages can travel from point to point across a network. Although others in the USA were working on packet switching techniques at the same time (notably Leonard Kleinrock and Paul Baran), it was the UK version that Arpanet first adopted.However, although Arpanet developed packet switching, Larry Roberts makes it clear that sending messages between people was "not an important motivation for a network of scientific computers". Its purpose was to allow people in diverse locations to utilise time on other computers. It never really worked as an idea - for a start, all the computers had different operating systems and versions and programs, and using someone else's machine was very difficult: but as well, by the time some of these problems were being overcome, mini-computers had appeared on the scene and the economics of time sharing had changed dramatically.So it's reasonable to say that ARPANET failed in its purpose, but in the process it made some significant discoveries that were to result in the creation of the first Internet. These included email developments, packet switching implementations, and development of the (Transport Control Protocol - Internet Protocol) or TCP/IP.TCP/IP is the backbone protocol which technical people claim is the basis for determining what the Internet is. It was developed in the 1970s in California by Vinton Cerf, Bob Kahn, Bob Braden, Jon Postel and other members of the Networking Group headed by Steve Crocker. TCP/IP was developed to solve problems with earlier attempts at communication between computers undertaken by ARPANET.Vinton Cerf had worked on the earlier Arpanet protocols while at the University of California in Los Angeles from 1968-1972. He moved to Stanford University in late 1972. At the same time Bob Kahn, who had been the chief architect of the Arpanet while working for contracting form Bolt Beranek and Newman, left that firm and joined ARPANET.In October 1972 ARPANET publicly demonstrated their system for the first time at the International Computer Communications Conference in Washington DC. Following that meeting, an International Networking Group chaired by Vinton Cerf was established. Bob Kahn visited Stanford in the spring of 1973 and he and Vint Cerf discussed the problem of interconnecting multiple packet networks that were NOT identical. They developed the basic concepts of TCP at that time, and presented it to the newly established International Networking Group. This meeting and this development really rates as the beginning of the Internet. Nobody knows who first used the word Internet - it just became a shortcut around this time for "internetworking". The earliest written use of the word appears to be by Vint Cerf in 1974.By 1975 the first prototype was being tested. A few more years were spent on technical development, and in 1978 TCP/IPv4 was released.It would be some time before it became available to the rest of us. In fact, TCP/IP was not even added to Arpanet officially until 1983.So we can see that the Internet began as an unanticipated result of an unsuccessful military and academic research program component, and was more a product of the US west coast culture of the 1980s than a product of the post-war Pentagon era.
Written by Ian Peter
Written by Ian Peter
History of PC networking
At the same time as the academic and research communities were creating a network for scientific purposes, a lot of parallel activity was going on elsewhere building computer networks as well.
A lot of the West Coast hackers belonged to the Homebrew Computer Club, founded by Lee Felsenstein. Lee had actually begun networking computers before the development of the PC, with his Community Memory project in the late 1970s. This system had dumb terminals (like computer screens with keyboards connected to one large computer that did the processing). These were placed in laundromats, the Whole Earth Access store, and community centres in San Francisco. This network used permanent links over a small geographical area rather than telephone lines and modems.
The first public bulletin board using personal computers and modems was written by Ward Christensen and Randy Seuss in Chicago in 1978 for the early amateur computers. It was about 1984 that the first bulletin boards using the IBM (Bill Gates/Microsoft) operating system and Apple operating systems began to be used. The most popular of these was FidoNet.
At that time the Internet technologies were only available on the UNIX computer operating system, which wasn't available on PCs. A piece of software called ufgate, developed by Tim Pozar, was one of the first bridges to connect the Fidonet world to the Internet world. An alternative approach undertaken by Scott Weikart and Steve Fram for the Association for Progressive Communications saw UNIX being made available on special low cost PCs in a distributed network.
In the community networking field early systems included PEN (Public Electronic Network) in Santa Monica, the WELL (Whole Earth 'Lectronic Link) in the Bay area of San Francisco, Big Sky Telegraph, and a host of small businesses with online universities, community bulletin boards, artists networks, seniors clubs, womens networks etc. ..
Gradually, as the 1980s came to a close, these networks also began joining the Internet for connectivity and adopted the TCP/IP standard. Now the PC networks and the academic networks were joined, and a platform was available for rapid global development.
By 1989 many of the new community networks had joined the Electronic Networkers Association, which preceded the Internet Society as the association for network builders. When they met in San Francisco in 1989, there was a lot of activity, plus some key words emerging - connectivity and interoperability. Not surprisingly in the California hippy culture f the time, the visions for these new networks included peace, love, joy, Marshall McLuhan's global village, the paperless office, electronic democracy, and probably Timothy Leary's Home Page. However, new large players such as America on Line (AOL) were also starting to make their presence felt, and a more commercial future was becoming obvious. Flower power gave way to communications protocols, and Silicon Valley just grew and grew.
PEN (The Public Electronic Network) in Santa Monica, may be able to claim the mantle of being the first local government based network of any size. Run by the local council, and conceived as a means for citizens to keep in touch with local government, its services included forms, access to the library catalogue, city and council information, and free email.
PEN started in February 1989, and by July 1991 had 3,500 users. One of the stories PEN told about the advantages of its system was the consultations they had with the homeless people of Santa Monica. The local council decided that it would be good to consult the homeless to find out what the city government could do for them. The homeless came back via email with simple needs - showers, washing facilities, and lockers. Santa Monica, a city of 96000 people at the time, was able to take this on board and provide some basic dignity for the homeless -and at a pretty low cost. This is probably the first example of electronic democracy in action.
Meanwhile, back in the academic and research world, there were many others who wanted to use the growing network but could not because of military control of Arpanet. Computer scientists at universities without defence contracts obtained funding from the National Science Foundation to form CSNet (Computer Science Network). Other academics who weren't computer scientists also began to show interest, so soon this started to become known as the "Computer and Science Network". In the early days, however, only a few academics used the Internet at most universities. It was not until the1990s that the penetration of Internet in academic circles became at all significant.
Because of fears of hackers, the Dept of Defence created a new separate network, MILNet, in 1982. By the mid-1980s, ARPANET was phased out. The role of connecting university and research networks was taken over by CSNet, later to become the NSF (or national science foundation) Network.
The NSFnet was to become the U.S. backbone for the global network known as the Internet, and a driving force in its early establishment. By 1989 ARPANet had disappeared, but the Information Superhighway was just around the corner.
Written by Ian Peter
A lot of the West Coast hackers belonged to the Homebrew Computer Club, founded by Lee Felsenstein. Lee had actually begun networking computers before the development of the PC, with his Community Memory project in the late 1970s. This system had dumb terminals (like computer screens with keyboards connected to one large computer that did the processing). These were placed in laundromats, the Whole Earth Access store, and community centres in San Francisco. This network used permanent links over a small geographical area rather than telephone lines and modems.
The first public bulletin board using personal computers and modems was written by Ward Christensen and Randy Seuss in Chicago in 1978 for the early amateur computers. It was about 1984 that the first bulletin boards using the IBM (Bill Gates/Microsoft) operating system and Apple operating systems began to be used. The most popular of these was FidoNet.
At that time the Internet technologies were only available on the UNIX computer operating system, which wasn't available on PCs. A piece of software called ufgate, developed by Tim Pozar, was one of the first bridges to connect the Fidonet world to the Internet world. An alternative approach undertaken by Scott Weikart and Steve Fram for the Association for Progressive Communications saw UNIX being made available on special low cost PCs in a distributed network.
In the community networking field early systems included PEN (Public Electronic Network) in Santa Monica, the WELL (Whole Earth 'Lectronic Link) in the Bay area of San Francisco, Big Sky Telegraph, and a host of small businesses with online universities, community bulletin boards, artists networks, seniors clubs, womens networks etc. ..
Gradually, as the 1980s came to a close, these networks also began joining the Internet for connectivity and adopted the TCP/IP standard. Now the PC networks and the academic networks were joined, and a platform was available for rapid global development.
By 1989 many of the new community networks had joined the Electronic Networkers Association, which preceded the Internet Society as the association for network builders. When they met in San Francisco in 1989, there was a lot of activity, plus some key words emerging - connectivity and interoperability. Not surprisingly in the California hippy culture f the time, the visions for these new networks included peace, love, joy, Marshall McLuhan's global village, the paperless office, electronic democracy, and probably Timothy Leary's Home Page. However, new large players such as America on Line (AOL) were also starting to make their presence felt, and a more commercial future was becoming obvious. Flower power gave way to communications protocols, and Silicon Valley just grew and grew.
PEN (The Public Electronic Network) in Santa Monica, may be able to claim the mantle of being the first local government based network of any size. Run by the local council, and conceived as a means for citizens to keep in touch with local government, its services included forms, access to the library catalogue, city and council information, and free email.
PEN started in February 1989, and by July 1991 had 3,500 users. One of the stories PEN told about the advantages of its system was the consultations they had with the homeless people of Santa Monica. The local council decided that it would be good to consult the homeless to find out what the city government could do for them. The homeless came back via email with simple needs - showers, washing facilities, and lockers. Santa Monica, a city of 96000 people at the time, was able to take this on board and provide some basic dignity for the homeless -and at a pretty low cost. This is probably the first example of electronic democracy in action.
Meanwhile, back in the academic and research world, there were many others who wanted to use the growing network but could not because of military control of Arpanet. Computer scientists at universities without defence contracts obtained funding from the National Science Foundation to form CSNet (Computer Science Network). Other academics who weren't computer scientists also began to show interest, so soon this started to become known as the "Computer and Science Network". In the early days, however, only a few academics used the Internet at most universities. It was not until the1990s that the penetration of Internet in academic circles became at all significant.
Because of fears of hackers, the Dept of Defence created a new separate network, MILNet, in 1982. By the mid-1980s, ARPANET was phased out. The role of connecting university and research networks was taken over by CSNet, later to become the NSF (or national science foundation) Network.
The NSFnet was to become the U.S. backbone for the global network known as the Internet, and a driving force in its early establishment. By 1989 ARPANet had disappeared, but the Information Superhighway was just around the corner.
Written by Ian Peter
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