Subtopic 2

 COMMUNICATION DEVICES : HARDWARE REQUIREMENTS

Communication devices are hardware components that enable a computer to send or receive data, instructions and information to and from one or more computers.

Examples of communication devices are:

1.  Network Interface Card (NIC)

2.  Wireless Network Interface Card

3.  (WNIC)

4.  Internal and external modem

5.  Hub or switch

6.  Router

7.  Wireless access point

NETWORK INTERFACE CARD

A network card, sometimes pronounced as NICK, is an adapter card or PC card that enables the computer to access the network.

WIRELESS NETWORK INTERFACE CARD

Wireless Network Interface Card is a network card that provides wireless data transmission.

                                                            Wireless Network Interface Card

NETWORK COMMUNICATION CHANNELS

There are two types of modem, internal modem and external modem. An

internal modem only works in stand-alone computers. It is built into the

computer.

An external modem is separated from the computer and is also mobile.

                                               

HUB/SWITCH

Hub or switch is a common connection point for devices in a network. Hubs are commonly used to connect segments of a LAN.

             

ROUTER

A router is a communications device that connects multiple computers or

other routers together and transmits data to the correct destination.

 WIRELESS ACCESS POINT

A wireless access point is a central communications device that allow

computers to transfer data. This device can help information to be

transferred wireless to other wireless devices or to a wired network.

Wireless access point has high quality antennas for optimal signals.

FUNCTIONS OF COMMUNICATION DEVICES

NETWORK INTERFACE CARD

A Network Interface Card is a piece of computer hardware designed to allow computers to communicate over a computer network. 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.

WIRELESS NETWORK INTERFACE CARD

A Wireless Network Interface Card or WNIC is a network card which connects to a radio-based computer network.

WNIC is an essential component for wireless desktop computer. This card uses an antenna to communicate through microwaves.

 WNICs are designed around the IEEE 802.11 standard which sets out low-level specifications on how all wireless networks operate and can operate in two modes known as infrastructure mode and ad hoc mode.

INFRASTRUCTURE MODE

In an infrastructure mode network the WNIC needs an access point: all data is transferred using the access point as the central hub. All wireless nodes in an infrastructure mode network connect to an access point. All nodes connecting to the access point must have the same service set identifier as the access point.

AD HOC MODE

In an ad hoc mode network the WNIC does not require an access point, but can directly interface with all other wireless nodes directly.

All the peer nodes in an ad hoc network must have the same channel and service set identifier.

MODEM

A modem is a device that enables a computer to transmit data over telephone or cable lines.

Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves. A modem converts between these two forms.

HUB / SWITCH

Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports.

When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all the packets. 

 A hub connects all the devices on its ports together. A switch understands when two devices want to talk to each other, and gives them a switched connection.

ROUTER

A router is a computer networking device that forwards data packets across a network toward their destinations, through a process known as routing.

A router acts as a junction between two or more networks to transfer data packets among them. In order to route packets, a router communicates with other routers using routing protocols.

WIRELESS ACCESS POINT

A wireless access point is a device that connects wireless communication devices together to form a wireless network.

Wireless access point (or Wireless AP) usually connects to a wired network and can relay data between wireless devices and wired devices.

Several Wireless APs can link together to form a larger network that allows "roaming". Wireless access points have IP addresses for configuration.

TRANSMISSION MEDIUM

In communications, transmission is the sending of electrical messages in the form of wave or energy. Transmission medium means any material substance which can propagate waves or energy.

Computers and other telecommunication devices use signals in a form of wave or energy to represent data which are sent through a transmission media.

TYPES OF TRANSMISSION MEDIA

Transmission media can be divided into two broad categories. The physical transmission media, or guided medium and the wireless transmission media. 








The twisted-pair cable, coaxial cable and fibre optic cable are examples of physical transmission media.

 

 Wireless transmission medium or unguided medium is through air. 

PHYSICAL TRANSMISSION MEDIUM

In physical transmission medium, waves are guided along  a solid transmission medium.

Wireless transmission medium waves are unguided and the transmission and reception are by means of antennas.

In our daily activities we probably use both media consciously or unconsciously.

For example, we use physical transmission medium when we:

• connect a PC to a printer using parallel port or USB port
• connect a PC to the same phone line for Internet communication such as TMNET Streamyx.
• PCs are connected using twisted-pair cables to wall sockets in the office

We use wireless transmission medium when we:

• listen to the radio
• talk over the telephone
• use hotspots that have wireless Internet access with WiFi technology at restaurants and airports.

WIRELESS TRANSMISSION MEDIA

Wireless data transmission means data communication between network devices without using cables or cords, but by using radio frequency or infrared waves. Wireless data transmission is categorised into short, medium and long range data transmission.

An example for short range is Bluetooth or Infrared. Medium range data transmission is WiFi or wireless LAN and for long range it is 3G. 

3G is a so-called "third-generation” broadband packet-based transmission of text, digitised voice, video, and multimedia at data rates up to and possibly higher than 2 megabits per second (Mbps), offering a consistent set of services to mobile computer and phone users no matter where they are located in the world. 3G works over wireless air interfaces.

TRANSMISSION ENVIRONMENT

In our daily activities, such as talking over the phone, sending short messages, sending email or uploading files to remote users, will likely involve a combination of transmission mediums along the way.

The sender and the receiver will also involve many communication devices especially switches and routers. These devices are interconnected by transmission mediums that can be from any of the physical or wireless transmission mediums stated earlier.

In network communications, it is common to represent the interconnection between devices as network clouds.

PHYSICAL TRANSMISSION MEDIA

Physical transmission media refers to material substances that can propagate  waves or energy. It is used to guide electrical messages from one end to the other.

Ethernet and token ring LANs often use physical transmission media.

CABLES AS A PHYSICAL TRANSMISSION MEDIUM

Cables are used as a physical transmission medium. There are three types of cables used in transmitting electrical messages. They are:

•  Twisted-Pair Cable - Two insulated copper wires that are twisted around each other. Each connection on twisted-pair requires both wires.
•  Coaxial Cable - A cable consisting of a conducting outer metal tube that encloses and is insulated from a central conducting core, used primarily for the transmission of high-frequency signals.
•  Fibre Optic Cable - Glass fibre used for laser transmission of video, audio and/or data.

TWISTED-PAIR CABLE

The twisted-pair cable is generally a common form of transmission 
medium. It consists of two wires or conductors twisted together, 
each with its own plastic insulation.
 The twisted wires cancel out electromagnetic
 interference that can cause crosstalk, the noise generated by adjacent pairs.

The most common connector used for twisted-pair cable is RJ-45.

Electromagnetic

A wave produced by the interaction of time-varying electric and magnetic fields.

Crosstalk

Undesired coupling of a signal from one circuit, part of a circuit, or channel, to another.

RJ-45

Registered Jack-45 (RJ-45) is an eight-wire connector used commonly to connect computers onto Local Area Networks (LAN), especially Ethernets.

TYPES OF TWISTED PAIR CABLE

The Unshielded Twisted-Pair or UTP is the most common twisted-pair cable used in communications.

It has four pairs of colour-coded twisted-pair cables that are covered with a plastic outer jacket.

UTP Cable

Cables that consist of pairs of unshielded wire twisted together. It is the most common kind of copper telephone wiring.

The Shielded Twisted-Pair or STP is another form of twisted-pair cable.

Its four pairs of colour-coded wires are each wrapped in metallic foil, and all four are then collectively wrapped in a layer of metallic braid or foil. Finally, this layer is wrapped with a plastic outer jacket.

STP Cable

Twisted-pair cable wires that consist of an outer covering or shield.

COAXIAL CABLE

The coaxial cable, often referred to as ‘coax’, consists of a single copper wire surrounded by at least three layers. They are an insulating material, a woven or braided metal and a plastic outer coating.

This cable is often used as cable television (CATV) network wiring because it can be cabled over longer distances in comparison to the twisted-pair cable.

PART OF COAXIAL CABLE

The coaxial cable consists of a centre inner conductor of solid or stranded wire enclosed in an insulating sheath.

The sheath is enclosed in an outer conductor of metal foil or a woven copper braid.

This outer conductor is also enclosed in another insulating sheath, and the whole cable is protected by a plastic cover. The outer conductor acts as the second wire in the cable. It also acts as a shield for the inner conductor and helps reduce outside interference.

CONNECTORS FOR THE COAXIAL CABLE

The connector most commonly used in connecting a coaxial cable to a device is the BNC connector. BNC is short for British Naval Connector or Bayonet-Neill-Concelman.

There are three popular BNC connectors. They are:

• BNC connector: used to connect devices such as the TV set
• BNC T connector: used in Ethernet networks
• BNC terminator: connected at the end of a cable to prevent the reflection of signals

FIBER OPTIC CABLE

The fibre optic cable is a networking medium that uses light for data transmission.

The intensity of light is increased and decreased to represent binary one and zero. Its core consists of dozens or hundreds of thin strands of glass or plastic which uses light to transmit signals.

Each strand, called an optical fibre, is as thin as a human hair.

Transmission

The act of sending electrical messages (and also radiant energy that passes through media.)

Binary

The binary system is a way of counting using just the two numbers 0 and 1.

Optical Fibre

A flexible optically transparent fibre usually made of glass or plastic, through which light can be transmitted by successive internal reflections.

PARTS OF A FIBER OPTIC CABLE

Inside a fibre optic cable, each optical fibre is clad with an insulating glass and a protective coating.

Typically, a fibre optic cable has five parts.

•  The core is the light transmission element. It is typically made of glass or plastic.
•  Cladding surrounds the core. It is also made of glass or plastic but is less dense than the core.
•  Buffer surrounds cladding. It is usually made of plastic and helps shields the core and cladding from being damaged.
•  A strengthening material surrounds the buffer to prevent the fibre cable from being stretched when installers pull it.
•  Outer jacket surrounds the cable to protect the fibre against abrasion, solvents and other contaminants.

CONNECTORS OF A FIBER OPTIC CABLE

The most commonly used fibre optic connectors are SC, ST, FC and MT-RJ connectors.

SC

A fibre optic cable connector that uses a push-pull latching mechanism similar to common audio and video cables.

        ST

A fibre optic cable connector that uses a bayonet plug and socket.

 
FC

A fibre optic cable connector that uses a threaded plug and socket.

 
MT-RJ

Mechanical Transfer Registered Jack (MT-RJ), a fibre optics connector popular for small form factor devices due to its small size.

WIRELESS TRANSMISSION MEDIA

WIRELESS COMMUNICATION

Wireless is a method of communication that uses electromagnetic waves rather than wire conductors to transmit data between devices. Wireless networks are telephone or computer networks that use radio frequencies and infrared waves as their carrier.

The mediums used in wireless communications are air, vacuum and even water. Air is the most commonly used medium. Signals are normally broadcasted through air and are available to anyone who has a device capable of receiving them.

WIRELESS TECHNOLOGY

The use of wireless technology as a method of data transport appears very similar to a wired technology. 
In a wireless media however, signal transmission is unguided and the device communicates without using wires between nodes, usually by relying on radio frequencies instead.

WIRELESS TRANSMISSION

Wireless transmission can be categorised into three broad groups:

•  Radio Waves
•  Microwaves
•  Infrared