cabling

What is Network Cabling?

Cable is the medium through which information usually moves from one network device to another. There are several types of cable 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. Understanding the characteristics of different types of cable and how they relate to other aspects of a network is necessary for the development of a successful network.

The following sections discuss the types of cables used in networks and other related topics.

• Unshielded Twisted Pair (UTP) Cable
• Shielded Twisted Pair (STP) Cable
• Coaxial Cable
• Fiber Optic Cable
• Cable Installation Guides
• Wireless LANs
• 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 

                                        

                                            

                                                                                                              Unshielded twisted pair

The quality of UTP may vary from telephone-grade wire to extremely high-speed cable. The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices. The tighter the twisting, the higher the supported transmission rate and the greater the cost per foot. The EIA/TIA (Electronic Industry Association/Telecommunication Industry Association) has established standards of UTP and rated six categories of wire (additional categories are emerging).

Categories of Unshielded Twisted Pair

category	speed	Use
1	1 Mbps	Voice Only (Telephone Wire)
2	4 Mbps	LocalTalk & Telephone (Rarely used)
3	16 Mbps	10BaseT Ethernet
4	20 Mbps	Token Ring (Rarely used)
5	100 Mbps (2 pair) 1000 Mbps (4 pair)	100BaseT Ethernet
5e	1,000 Mbps	Gigabit Ethernet
6	10,000 Mbps	Gigabit Ethernet

Unshielded Twisted Pair Connector

The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connector (See fig. 2). A slot allows the RJ-45 to be inserted only one way. RJ stands for Registered Jack, implying that the connector follows a standard borrowed from the telephone industry. This standard designates which wire goes with each pin inside the connector.

  

     

            

Shielded Twisted Pair (STP) Cable

Although UTP cable is the least expensive cable, it may be susceptible to radio and electrical frequency interference (it should not be too close to electric motors, fluorescent lights, etc.). If you must place cable in environments with lots of potential interference, or if you must place cable in extremely sensitive environments that may be susceptible to the electrical current in the UTP, shielded twisted pair may be the solution. Shielded cables can also help to extend the maximum distance of the cables.

Shielded twisted pair cable is available in three different configurations:

1. Each pair of wires is individually shielded with foil.
2. There is a foil or braid shield inside the jacket covering all wires (as a group).
3. There is a shield around each individual pair, as well as around the entire group of wires (referred to as double shield twisted pair).

Coaxial Cable

Coaxial cabling has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield. The metal shield helps to block any outside interference from fluorescent lights, motors, and other computers.

         

Although coaxial cabling is difficult to install, it is highly resistant to signal interference. In addition, it can support greater cable lengths between network devices than twisted pair cable. The two types of coaxial cabling are thick coaxial and thin coaxial.

Thin coaxial cable is also referred to as thinnet. 10Base2 refers to the specifications for thin coaxial cable carrying Ethernet signals. The 2 refers to the approximate maximum segment length being 200 meters. In actual fact the maximum segment length is 185 meters. Thin coaxial cable has been popular in school networks, especially linear bus networks.

Thick coaxial cable is also referred to as thicknet. 10Base5 refers to the specifications for thick coaxial cable carrying Ethernet signals. The 5 refers to the maximum segment length being 500 meters. Thick coaxial cable has an extra protective plastic cover that helps keep moisture away from the center conductor. This makes thick coaxial a great choice when running longer lengths in a linear bus network. One disadvantage of thick coaxial is that it does not bend easily and is difficult to install.

 

Coaxial Cable Connectors

The most common type of connector used with coaxial cables is the Bayone-Neill-Concelman (BNC) connector (See fig. 4). Different types of adapters are available for BNC connectors, including a T-connector, barrel connector, and terminator. Connectors on the cable are the weakest points in any network. To help avoid problems with your network, always use the BNC connectors that crimp, rather screw, onto the cable.

     

 

Fiber Optic Cable

Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials (See fig. 5). It transmits light rather than electronic signals eliminating the problem of electrical interference. This makes it ideal for certain environments that contain a large amount of electrical interference. It has also made it the standard for connecting networks between buildings, due to its immunity to the effects of moisture and lighting.

Fiber optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair. It also has the capability to carry information at vastly greater speeds. This capacity broadens communication possibilities to include services such as video conferencing and interactive services. The cost of fiber optic cabling is comparable to copper cabling; however, it is more difficult to install and modify. 10BaseF refers to the specifications for fiber optic cable carrying Ethernet signals.

The center core of fiber cables is made from glass or plastic fibers (see fig 5). A plastic coating then cushions the fiber center, and kevlar fibers help to strengthen the cables and prevent breakage. The outer insulating jacket made of teflon or PVC.

    

There are two common types of fiber cables -- single mode and multimode. Multimode cable has a larger diameter; however, both cables provide high bandwidth at high speeds. Single mode can provide more distance, but it is more expensive.

Specification	Cable Type
10BaseT	Unshielded Twisted Pair
10Base2	Thin Coaxial
10Base5	Thick Coaxial
100BaseT	Unshielded Twisted Pair
100BaseFX	Fiber Optic
100BaseBX	Single mode Fiber
100BaseSX	Multimode Fiber
1000BaseT	Unshielded Twisted Pair
1000BaseFX	Fiber Optic
1000BaseBX	Single mode Fiber
1000BaseSX	Multimode Fiber

network topologies

What is network topologies
Network Topology refers to layout of a network and how different nodes in a network are connected to each other and how they communicate. This slideshow describes five of the most common network topologies.


  

1. Mesh Topology:
In a mesh network, devices are connected with many redundant interconnections between network nodes. In a true mesh topology every node has a connection to every other node in the network. There are two types of mesh topologies:
 Full mesh topology occurs when every node has a circuit connecting it to every other node in a network. Full mesh is very expensive to implement but yields the greatest amount of redundancy, so in the event that one of those nodes fails, network traffic can be directed to any of the other nodes. Full mesh is usually reserved for backbone networks.
 Partial mesh topology is less expensive to implement and yields less redundancy than full mesh topology. With partial mesh, some nodes are organized in a full mesh scheme but others are only connected to one or two in the network. Partial mesh topology is commonly found in peripheral networks connected to a full meshed backbone.

2. Star Topology:
In a star network devices are connected to a central computer, called a hub. Nodes communicate across the network by passing data through the hub.
Main Advantage:
In a star network, one malfunctioning node doesn't affect the rest of the network.
Main Disadvantage:
If the central computer fails, the entire network becomes unusable.

  


3. Bus Topology:
 In networking a bus is the central cable -- the main wire -- that connects all devices on a local-area network (LAN). It is also called the backbone. This is often used to describe the main network connections composing the Internet.  Bus networks are relatively inexpensive and easy to install for small networks. Ethernet systems use a bus topology.
Main Advantage:
 It’s easy to connect a computer or device and typically it requires less cable than a star topology.
Main Disadvantage:
The entire network shuts down if there is a break in the main wire and it can be difficult to identify the problem if the network shuts down.

                                      

4. Ring Topology:
 A local-area network (LAN) whose topology is a ring. That is, all of the nodes are connected in a closed loop. Messages travel around the ring, with each node reading those messages addressed to it. One main advantage to a ring network is that it can span larger distances than other types of networks, such as bus networks, because each node regenerates messages as they pass through it.

5. Tree Topology:
 This is a "hybrid" topology that combines characteristics of linear bus and star topologies. In a tree network, groups of star-configured networks are connected to a linear bus backbone cable.
Main Advantage:
A Tree topology is a good choice for large computer networks as the tree topology "divides" the whole network into parts that are more easily manageable.
Main Disadvantage:
The entire network depends on a central hub and a failure of the central hub can cripple the whole network.

            

Network Adapters & Interfaces, NIC
A network card (also called network adapter, network interface card, NIC, etc.) is a piece of computer hardware designed to provide for computer communication over a computer network.


Network cards used to be expansion cards to plug into a computer bus, most newer computers have a network interface built into the motherboard, so a separate network card is not required unless multiple interfaces are needed or some other type of network is used.


The card implements the electronic circuitry required to communicate using a specific physical layer and data link layer standard such as ethernet or token ring. This provides a base for a full network protocol stack, allowing communication among small groups of computers on the same LAN and large-scale network communications through routable protocols, such as IP.


A network card typically has a twisted pair, BNC, or AUI socket where the network cable is connected, and a few LEDs to inform the user of whether the network is active, and whether or not there is data being transmitted on it. The Network Cards are typically available in 10/100/1000 Mbit/s. This means they can support a transfer rate of 10 or 100 or 1000 Mbit/s




What Is a Computer Operating System?
Computers use low-level software called an operating system (O/S) to help people build and run their own programs. Operating system software runs not just on laptop computers but also on cell phones, network routers and other so-called embedded devices.


Concentrator
As generally used, a concentrator is a device that acts as an efficient forwarder of data transmission signals. A remote access hub is sometimes referred to as a concentrator. The term aggregator is also frequently used with approximately the same meaning. A typical concentrator or remote access hub is a device that handles incoming dial-up calls for an Internet (or other network) point-of-presence and performs other services. A concentrator or hub may be able to handle up to 100 dial-up modem calls, support a certain number of ISDN connections, and support leased line and frame relay traffic while also functioning as a router.


Repeater
Network repeaters regenerate incoming electrical, wireless or optical signals. With physical media like Ethernet or Wi-Fi, data transmissions can only span a limited distance before the quality of the signal degrades. Repeaters attempt to preserve signal integrity and extend the distance over which data can safely travel.
Actual network devices that serve as repeaters usually have some other name. Active hubs, for example, are repeaters. Active hubs are sometimes also called "multiport repeaters," but more commonly they are just "hubs." Other types of "passive hubs" are not repeaters. In Wi-Fi, access points function as repeaters only when operating in so-called "repeater mode."




What is Ethernet?
Basically, Ethernet is both the name for the cable that enables network devices to connect to one another, and the name for the communication protocol that these cables use. When you refer to an Ethernet port, for example, you're referring to the physical port to which the Ethernet cable connects, but you're also referring to the method of communication that the cable uses; it networks via Ethernet protocols. Most modern Ethernet networks consist of Ethernet cards that contain the Ethernet port, Ethernet cables to connect devices and Ethernet routers or hubs to help regulate traffic.

What is localTalk
The cabling scheme supported by the AppleTalk network protocol for Macintosh computers. Most local-area networks that use AppleTalk, such as TOPS, also conform to the LocalTalk cable system. Such networks are sometimes called LocalTalk networks .
Although LocalTalk networks are relatively slow, they are popular because they are easy and inexpensive to install and maintain. An alternative cabling scheme that is faster is Ethernet.


What is terminator
(1) A device attached to the end-points of a bus network or daisy-chain. The purpose of the terminator is to absorb signals so that they do not reflect back down the line. Ethernet networks require a terminator at both ends of the bus, and SCSI chains require a single terminator at the end of the chain.
(2) A character that indicates the end of a string. In the C programming language, the null character serves as a terminator.

Introduction of Networking

INTRODUCTION TO NETWORKING

      A network is a collection of connected intelligent computing devices. The connection is not necessarily a fancy one. A connection between two computers by direct cabling is qualified to be a network. By this definition, a workstation which is loaded with a computer, a scanner, and a printer, is not treated as a network.

          

     

COMPUTER NETWORKING

      A computer network is simply two or more computers connected together so

they can exchange information.  A small network can be as simple as two

computers linked together by a single cable.

             

 TYPE OF NETWORK

   

 

      A network is a medium that connects computers around the world. With the network, information or data can be sent quickly without the limitations of distance and time.

      Computer networks are divided into five types:

1)      Local Area Network (LAN) is a small-scale private network inside the building.LANs are often used for connecting personal computers and workstations in a corporate office or factories to use shared resources (eg printers) and exchange information.

2)      Metropolitan Area Network (MAN) basically a LAN version of the larger size and usually use the same technology to the LAN. MAN could include corporate offices are located adjacent or also a town and can be used for private purposes (private) or public. MAN is able to support data and voice, even may be associated with cable television network.

3)      Wide Area Network (WAN) its scope covers a wide geographical area, often covering a country or even continent. WAN consists of a collection of machines that aim to run the programs (applications) user.

4)      Internet, Actually there are many in this world networks, often using hardware and software that is different. People who connect to the network often wish to communicate with others who connect to other networks. These desires need relationships between networks that are often not kampatibel and different. Usually to do this required a machine called a gateway in order to have sex and perform the necessary translation, both hardware and software. A collection of interconnected networks is called the Internet.

5)      Wireless Networking is a solution to the communication can not be done by using a cable network. For example, people who want to get information or to communicate despite being on top of a car or plane, it is absolutely necessary because the cable network without a cable connection is not possible to be made in the car or plane.Currently, wireless networks have rapidly adopted the use of satellite services and can provide faster access speeds than the network cables.

NETWORK COMPONENT

      In order for a computer to operate on a network, there are a range of different components that are required.  As part of the OCR syllabus, you need to be able to describe various devices and explain their role within a network 

ROUTER

      A Router is a device that transfers data from one network to another in an intelligent way. It has the task of forwarding data packets to their destination by the most efficient route.

      In order to do this, the router has a micro computer inside it.  This holds a table in memory that contains a list of all the networks it is connected to, along with the latest information on how busy each path in the network is, at that moment. This is called the 'routing table'.

      Function of router is:

1)      Reads the data packet's destination address 

2)      Looks up all the paths it has available to get to that address.           

3)      Checks on how busy each path is at the moment      

4)      Sends the packet along the least congested (fastest) path

                                                                                                                                   

BRIDGE                                                                                                                                

      A Bridge does just what you would expect it to do - it joins two networks together so as far as data packets are concerned it looks like one large network.

PROTOCOL

      A 'protocol' is a rather technical word. But it simply means an agreed method of doing something.

      A 'NETWORK PROTOCOL' is the agreed method of communication to be used within the network.

      Elements of a network protocol:

Ø  The list below indicates some the things that  need to  be considered:-

1)      Speed of the network - for example 10Mbit /s

2)      Error checks of the data packets when they arrive- how is it done

3)      Error correction of the data packets - method to be used

4)      Data packets received correctly - what method/signal will be used to tell the other machine that the data has arrived correctly

5)      How does the receiving machine know that the sending machine has finished sending all of the data? - what is the code to indicate this

6)      Data compression - does the protocol allow this to take place and if so, what method does it use?

Ø  There are many protocols in use across various networks:

1)      TCP - the protocol that the internet uses

2)      Kermit - popular for use with modems

3)      X.25 - a packet switched protocol

      Anyone can invent a protocol. Indeed some large companies develop their own often hoping the rest of the world will use it as well.

      Most widely used network protocols have been agreed and developed by international standards organisations such as the ITU (International Telecommunication Union).

GATEWAY

      A gateway converts the data passing between dissimilar networks so that each side can communicate with each other.

      The gateway is a mixture of hardware components and software.

HUB

      The network 'Hub' allows computers to share data packets within a network.

      Each computer will be connected to a single 'port' on the hub. So if you purchase an '8 port hub', you will be able to connect up to eight computers together.

      You can also 'daisy chain' hubs to allow even more computers to join the network.

SWITCH

      A switch has a number of ports and it stores the addresses of all devices that are directly or indirectly connected to it on each port.

      As a data packet comes into the switch,  its destination address is examined and a direct connection is made between the two machines.