Study Unit 4 computer systems and data communication


Advantages of a Wireless LAN



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Advantages of a Wireless LAN


Wireless LANs have advantages and disadvantages when compared with wired LANs. A wireless LAN will make it simple to add or move workstations, and to install access points to provide connectivity in areas where it is difficult to lay cable. Temporary or semi-permanent buildings that are in range of an access point can be wirelessly connected to a LAN to give these buildings connectivity. Where computer labs are used in schools, the computers (laptops) could be put on a mobile cart and wheeled from classroom to classroom, providing they are in range of access points. Wired network points would be needed for each of the access points.
The installation of cables is time consuming and expensive. The advantages of not doing so are apparent:

  • the amount of work required and the time taken to complete it are significantly reduced

  • the network is accessible in places where wiring would have been difficult or impossible

  • with no cables linking computers together, cable-related faults and network downtime are minimised

  • Where a wireless network is in place, teachers or students can have continuous access to the network, even as they move with their equipment from class to class.

  • The space over which a wireless network operates is not planar but spherical. Therefore, in a multi-level site, network access is available in rooms above or below the access point, without the need for additional infrastructure.

  • In a location within a school where network access is required occasionally, desktop computers fitted with wireless network cards can be placed on trolleys and moved from location to location. They can also be located in areas where group work is taking place. As they are connected to the network, documents and files can be shared, and access to the Internet is available, enhancing group project work. 

  • As the range of the wireless network extends outside the building, students and teachers can use wireless devices to gather and record data outside, e.g., as part of a science experiment or individual performance data as part of a PE class.



Below are some specific advantages of a WLAN:

  • It is easier to add or move workstations

  • It is easier to provide connectivity in areas where it is difficult to lay cable

  • Installation can be fast and easy and can eliminate the need to pull cable through walls and ceilings

  • Access to the network can be from anywhere in the school within range of an access point

  • Portable or semi-permanent buildings can be connected using a wireless LAN

  • Where laptops are used, the ‘computer suite’ can be moved from classroom to classroom on mobile carts

  • While the initial investment required for wireless LAN hardware can be similar to the cost of wired LAN hardware, installation expenses can be significantly lower

  • Where a school is located on more than one site (such as on two sides of a road), it is possible with directional antennae, to avoid digging trenches under roads to connect the sites

  • In historic buildings where traditional cabling would compromise the façade, a wireless LAN can avoid drilling holes in walls

  • Long-term cost benefits can be found in dynamic environments requiring frequent moves and changes

  • They allows the possibility of individual pupil allocation of wireless devices that move around the school with the pupil.






Disadvantages of a WLAN

  • As the number of computers using the network increases, the data transfer rate to each computer will decrease accordingly

  • As standards change, it may be necessary to replace wireless cards and/or access points

  • Lower wireless bandwidth means some applications such as video streaming will be more effective on a wired LAN

  • Security is more difficult to guarantee, and requires configuration

  • Devices will only operate at a limited distance from an access point, with the distance determined by the standard used and buildings and other obstacles between the access point and the user

  • A wired LAN is most likely to be required to provide a backbone to the wireless LAN; a wireless LAN should be a supplement to a wired LAN and not a complete solution

  • Long-term cost benefits are harder to achieve in static environments that require few moves and changes

  • It is easier to make a wired network ‘future proof’ for high data transfer.








Network Topologies


Networks have a physical and a logical topology. In this section the physical topology of a network is discussed. The physical topology of a network refers to the configuration of cables, computers, and other peripherals. Physical topology should not be confused with logical topology which is the method used to pass information between workstations.


Main Types of Physical Topologies


The physical topologies that are commonly found in computer networks are:

Linear Bus (Trunkline)

A linear bus topology consists of a main run of cable with a terminator at each end (See fig. 4.1). All nodes (file server, workstations, and peripherals) are connected to the linear cable.



It is easy to connect a node to a linear bus and less expensive since network structure requires less cable. Its major disadvantage is that the entire network shuts down if there is a break in the main cable and it is difficult to identify the problem if the entire network shuts down.



Advantages of a Linear Bus Topology


  • Easy to connect a computer or peripheral to a linear bus.

  • Requires less cable length than a star topology.


Disadvantages of a Linear Bus Topology


  • Entire network shuts down if there is a break in the main cable.

  • Terminators are required at both ends of the backbone cable.

  • Difficult to identify the problem if the entire network shuts down.

  • Not meant to be used as a stand-alone solution in a large building.
















Star


A star topology is designed with each node (file server, workstations, and peripherals) connected directly to a central network hub or concentrator (See fig. 5.2). A separate cable connects to each computer, and if one cable breaks, only a single computer should be affected. The hub or concentrator manages and controls all functions of the network. It also acts as a repeater for the data flow.


Data on a star network passes through the hub or concentrator before continuing to its destination. The hub or concentrator manages and controls all functions of the network. It also acts as a repeater for the data flow. This configuration is common with twisted pair cable; however, it can also be used with coaxial cable or fiber optic cable.

Advantages of a Star Topology


  • Easy to install and wire.

  • No disruptions to the network then connecting or removing devices.

  • Easy to detect faults and to remove parts.

Disadvantages of a Star Topology


  • Requires more cable length than a linear topology.

  • If the hub or concentrator fails, nodes attached are disabled.

  • More expensive than linear bus topologies because of the cost of the concentrators.





Star Wired Ring (Token Ring)

Star wired ring (Token ring) network was developed by IBM for IBM-compatible computers. It employs a special coded message called a token that the operating software passes in sequence to each computer on the network. It has a bandwidth capacity of 4 or 16 Mbps using twisted pair cables.



Daisy-Chain



The Daisy-Chain network is similar to a bus, except the electrical signal is routed through each computer as it moves along the line. Thus it is not practical in multi-room network installations. It is mainly used on the Macintosh network. Its major advantage is that it is easy to install. The entire network shuts down if there is a problem on a node. The Daisy-Chain network is very slow.





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