Study Unit 4 computer systems and data communication



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Network Operating System


A network operating system is a supervisory software program that resides on the server. It controls how the network operates by defining who can use the network and how information and peripherals are shared among users. The most commonly used network operating systems in schools are from the Microsoft windows family, which include Windows NT, Windows 2000 Server. Novel Netware, UNIX, LYNX and others are not common in our schools.

Network Media


Network Cables

Cable is the medium through which information usually moves from one network device to another. There are several types of cables which are commonly used with LANs. In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types. The type of cable chosen for a network is related to the network's topology, protocol, and size. You need to understand the characteristics of different types of cables and how they relate to other aspects of a network in order for you to develop a successful network.


In this section we discuss the following types of cables used in networks:


  • Unshielded Twisted Pair (UTP) Cable

  • Shielded Twisted Pair (STP) Cable

  • Coaxial Cable

  • Fiber Optic Cable

  • Wireless LANs

The two most popular types of structured network cabling are twisted-pair (also known as 10BaseT) and thin coax (also known as 10Base2).


Unshielded Twisted Pair (UTP) Cable

Twisted pair cabling comes in two varieties: shielded and unshielded. Unshielded twisted pair (UTP) is the most popular and is generally the best option for school networks (See fig. 1). This cable looks like ordinary telephone wire, except that it has 8 wires inside instead of 4.


It consists of two insulated copper wires arranged in a regular spiral pattern to minimize the electromagnetic interference between adjacent pairs. It is a low frequency transmission medium.


This cable is the most popular and is generally the best option for school networks, because of its low cost and easy installation. It is also ideal for short distance, usually less than 100 meters.




Fig4d: Wall Mounted Cabinet




Categories of Unshielded Twisted Pair


Type

Use

Category 1

Voice Only (Telephone Wire)

Category 2

Data to 4 Mbps (LocalTalk)

Category 3

Data to 10 Mbps (Ethernet)

Category 4

Data to 20 Mbps (16 Mbps Token Ring)

Category 5

Data to 100 Mbps (Fast Ethernet)

10BaseT cabling is available in different grades or categories. Some grades, or "cats", are required for Fast Ethernet networks, while others are perfectly acceptable for standard 10Mbps networks--and less expensive, too. All new networks use a minimum of standard unshielded twisted-pair (UTP) Category 5e 10BaseT cabling because it offers a performance advantage over lower grades.


The standard connector for UPT cable is an RJ-45 connector, which looks like a large telephone modular connector







Coaxial (Coax) Cable

Thin coax looks like the copper coaxial cabling that's often used to connect a Video Recorder to a TV.



It has an inner conductor surrounded by a braided mesh. Both conductors share a common center axial, hence the term "co-axial". It can support a size of bandwidth of up to 400 Mhz and can be used for distances between 300 and 600 meters. Its major advantage is that it is highly resistant to signal interference. Its major disadvantage is that it is quite bulky and sometimes difficult to install.

The most common type of connector used with coaxial cables is the BNC (Bayone-Neill-Concelman) connector, which is shown in fig …. below.


There are two types of coaxial cable namely thin coaxial which is also referred to as thinnet and thick coaxial which is also referred to as thicknet

.

The 10Base2 is the IEEE standard for Ethernet running on thin coaxial cable. The 2 refers to the approximate maximum segment length being 200 meters. This is popular in school networks, especially linear bus networks.


The IEEE standard for Ethernet running on thick coaxial cable is 10Base5. The 5 refers to the approximate maximum segment length being 500 meters. Thicknet has an extra protective plastic cover that helps keep moisture away from the center conductor. Its major disadvantage is that it is difficult to bend and install.

Fibre Optic


Fibre optics consists of a center glass core surrounded by several layers of protective materials. Fibre optic’s major advantage is that it is immune to environmental interference and has a greater capacity (bandwidth of up to 2 Gbps)

It is used for distances up to 100 kilometers and carries information at vastly greater speeds. It is also very small and lighter in weight than other media.
Its major limitation is that it is very expensive. It is difficulty to install, hence requires highly skilled installers and modifiers. Even with highly skilled personal adding additional nodes is difficult.



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