Network Media Primer
an extensive glossary of networking terms and toolsA communication between two computers is not possible without a transmission medium. There are different types of media, which have different properties, and the selection of media depends entirely on the needs, size, and environment of the network. The most commonly used transmission medium is copper and fiber optic wires, air, and radio waves. This section deals with different types of cables used to connect the computers in a network.
The most widely used network medium is copper wire. Since it is a good conductor of electricity, the digital signals generated by the computer are converted into electrical signals so that they can be sent over the network. The disadvantage of copper wire is that there is too much energy loss if the message is sent over long distances. The different types of copper wires are described as follows:
UTP (Unshielded Twisted Pair)
Unshielded twisted pair cable is the most popular cable type used in today's networks. It consists of various pairs of unshielded twisted copper wires. It is extensively used in telephone systems and computer networking due to it low cost, easy installation and maintenance. UTP cables provide transmission speeds 4 Mbps to 100 Mbps, depending on the type and category of the cable used. The disadvantage of this cable is that it cannot be used for networks spread over long distances, as its runs are limited to 100 meters or less. As it is not shielded, it is more sensitive to electro magnetic interference. UTP cables are used in various Ethernet networks, which implement star topology. The commonly used categories of UTP cables used in computer networking are the following:
- Category 3: These types of UTP cables use four pairs of twisted cable and provide transmission speed of up to 16 Mbps. They are commonly used in Ethernet networks that operate at the speed of 10 Mbps. A higher speed is also possible by these cables implementing the Fast Ethernet (100Base-T4) specifications. This cable is used mainly for telephone systems.
- Category 5: This category of UTP cable is the most commonly used cable in present day networks. It consists of four twisted pairs and is used in those Ethernet networks that run at the speed of 100 Mbps. Category 5 cable can also provide a higher speed of up to 1000 Mbps.
- Category 5e: It is also known as Category 5 Enhanced cable. Its specification is the same as category 5, but it has some enhanced features and is used in Ethernets that run at the speed of 1000 Mbps.
- Category 6: This is the category 5e cable, but it has been designed to support high-speed networks that run at the speed of 1000 Mbps. It consists of four pairs of wire and uses all of them for data transmission. Category 6 provides more than twice the speed of Category 5e, but is also more expensive.
STP (Shielded Twisted Pair)
Shielded twisted pair cable consists of one or more pairs of twisted wires that are insulated with a metal foil to minimize electromagnetic interference. The metal shield is connected to the ground to prevent external signals from getting into and internal signals from getting out of the cable Different types of STP cables with different characteristics are available. It is extensively used in IBM networks implementing Token ring network specifications. These cables provide transmission speeds of up to 16 Mbps in Token rings and an overall speed of up to 155 Mbps. The maximum segment it provides is commonly 100 meters, although a few hundred meters is also possible. The advantage of using the STP cable is that its ability to reduce the EMI is better than the UTP cable. Its disadvantages are that it is costly and provides less speed than the UTP cable.
Coaxial cables were the first cables used in Ethernet networks. This cable consists of an insulator that separates the braided inner conductor and the outer conductor, which is a woven copper braid. These cables are commonly used for cable TV connections at homes. It is also used by 10 Base5 and 10 Base2 Ethernet networks. Coaxial cable is of two types, namely the Thinnet and the Thicknet, depending on the thickness of the cable. Thinnet supports a maximum segment length of 185 meters, and Thicknet can send signals up to 500 meters. The cost of the cable depends on which type of cable is used. Thinnet is less costly and easier to install, whereas Thicknet is costlier and demands more efforts in installation. The transmission speed these cables provide is between 2.5 Mbps and 10 Mbps. Coaxial cables are more resistant to EMI than the UTP cable, as they use insulators to minimize the external interference.
Fiber Optic Cable
Fiber optic cables are made up of glass, and they transmit data in the form of light, unlike the copper wire that uses electrical signals. A reflective coating that allows light beams to travel without outer interference covers the glass cable. The advantages of Fiber optic cables are that signals can be sent at a much higher speed and to very long distances without the risk of outer interference. Fiber optic cables can be categorized as Single Mode Fiber (SMF) and Multi Mode Fiber (MMF), which are explained as follows:
SMF (Single Mode Fiber) optic cable - The Single Mode Fiber optic cable supports high-speed local area networks (LAN) covering long distances and also wide area networks (WAN) that spread over different buildings or cities. It is used in 10GBase-LR Ethernet specification, which runs at the speed of 10Gbps. The SMF cable is so named because it allows only one mode of light to transmit.
MMF (Multi Mode Fiber) optic cable - The Multi Mode Fiber optic cable is also used for high-speed networks that are spread over short distances. It is used for 10GBasse-SR Ethernet standard that supports the transmission speed of 10 Gbps, Unlike the SMF cable, the MMF Cable allows the light signals to travel in more than one path. It is used extensively for short distance networking, as it is less costly than the SMF cable.
Media Connectors are used to connect the cables to the computers or other devices in a network. The type of connector used in a particular network depends upon the type of cable used, as different types of cables have their own specific types of connectors. Some commonly used media connectors are listed below:
- RJ-11: The RJ-11 connector is used to connect the telephone cable to the telephone jack. It is a rectangular connector, which has only four pins or conductors. The type of cable used with this connector is Category 3 UTP cable.
- RJ-45: RJ-45 is a type of connector similar to an RJ-11 telephone connector, but it is larger in size because it has eight conductors. An unshielded twisted-pair (UTP) connection uses an RJ-45 connector. It is used in Ethernet networks.
- F-Type: This type of connector is used with RG 6 or RG 11 coaxial cables for connecting televisions and VCRs. It consists of a single pin in the middle, which is also the central conductor. These connectors are of two types, namely 'twist-on' or 'crimp-type', in which the latter is more commonly used. F-Type connectors can be categorized according to the type of cable used and the common types are F-59, F-6, F-11, F-61 and F-71.
- ST: ST stands for the "straight tip" fiber optic connector developed by AT & T. It is a popular connector used with fiber optic cables. It is used in gigabit Ethernets.
- SC (Subscriber Connecter or Standard Connector): It is also a type of low cost connector used in 100 Base-FX fiber optic networks. It can be pushed into the device and can be removed by pulling out.
- IEEE 1394 (Fire Wire): Institute of Electrical and Electronics Engineers (IEEE) 1394 is a standard for high-speed serial bus that provides enhanced PC connectivity for a wide range of devices. The IEEE 1394 connector is used to connect devices including consumer audiovisual components, traditional PC storage devices, and handheld devices. IEEE 1394 is also known as Fire wire.
- Fiber LC (Local Connector): It is a small sized fiber optic connector, which looks like the SC connector but is half the size. It is used in gigabit Ethernets.
- MT-RJ (Mechanical Transfer Registered Jack): It is also a fiber optic connector used in gigabit Ethernets.
Besides cables and connectors, various other types of network devices are used for the proper functioning of a network. Some of the commonly used network components are described as follows:
- Hub: A hub is a device used to link computers in a network. It connects the computers that have a common architecture, such as Ethernet, ARCnet, FDDI, or Token Ring. All hub-computer connections for a particular network use the same type of cable, which can be twisted-pair, coaxial, or fiber-optic. Hubs are generally used in star topology networks. Token Ring hubs are also known as Multistation Access Units (MSAUs). A hub works on the physical layer of the OSI model. The following two types of hubs are available:
- Active hub is a central device used to connect computers in a star network. It regenerates and retransmits deteriorated signals on the network.
- Passive hub is a central device used to connect computers in a star network. It receives information through one of its ports and sends it to the computers connected to every other port. Therefore, although the information is broadcast to the network, only the destination computer reads it. A passive hub does not regenerate signals
Media Access Control
(MAC) address is a numerical identifier that is unique for each network interface card (NIC). MAC addresses are 48-bit values expressed as twelve hexadecimal digits, usually divided into hyphen-separated pairs, for example, FF-00-F8-32-13-19. MAC addresses are also referred to as hardware addresses, Ethernet addresses, and universally administered addresses (UAAs).
ISDN (Integrated Services Digital Network) adapter: Integrated Services Digital Network (ISDN) is a digital telephone/telecommunication network that carries voice, data, and video over an existing telephone network infrastructure. It requires an ISDN modem at the both ends of a transmission. ISDN adapter is designed to provide a single interface for hooking up a telephone, fax machine, computer, etc.
WAP (Wireless Access Point): - A WAP is a communication device capable of both transmitting and receiving signals in a wireless LAN. This unit is connected to servers or directly to the network and other devices using a standard cabled network protocol.
Modem: Modem stands for Modulator-Demodulator. It is a device that enables a computer to transmit information over standard telephone lines. Since a computer stores information digitally and a telephone line is analog, a modem converts digital signals to analog and vice versa. The conversion of a digital signal to analog is known as modulation and that of an analog signal to digital is known as demodulation.
Transceiver (Media Converter): - It is a communication device that can both transmit and receive signals over a medium. It is used to convert one type of media topology to another. The benefit of using transceivers is that it maintains the signal integrity.
A firewall is a combination of software and hardware that prevents data packets from coming in or going out to a specified network or computer. It is used to separate an internal network from the Internet. It analyzes all the traffic between a network and the Internet, and provides centralized access control on how users use the network. A firewall can also perform the following functions:
- Block unwanted traffic.
- Direct the incoming traffic to more trustworthy internal computers.
- Hide vulnerable computers that are exposed to the Internet.
- Log traffic to and from the private network.
Hide information, such as computer names, network topology, network device types, and internal user IDs from external users.
About the Author:
uCertify was formed in 1996 with an aim to offer high quality educational training software and services in the field of information technology to its customers. uCertify provides exam preparation solutions for the certification exams of Microsoft, CIW, CompTIA, Oracle, Sun and other leading IT vendors. To know more about uCertify, please visit http://www.ucertify.com/
* title = Network Media
* author = Roger Stuart, Team uCertify
* url = http://www.ucertify.com
* dept = EDU Adult: learning, how-to, resources, tools
* audience = Computer programmer or network administrator
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