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「Network」

A collection of computers and devices connected together via communication device and transmission media to share resources.

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「Communication」

• The process in which two or more computers or devices transfer data, instruction and information.

• Some communication involve cables and wires ; others are sent wirelessly through the air.

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「Communication System」

• Sending devices

— initiates an instruction to transmit data, instructions, or information.

• Receiving devices

— accepts the transmission of data, instructions, or information.

• Communication device

— is any type of hardware capable of transmitting data, instructions, and information that connect the sending device and a receiving device to transmission media.

— example : modem, hub, switch, router, wireless access point, network card.

• Transmission Media / communication channel

— consist of materials or substances on which the data, instructions, or information travel.

⇨ Wired / Physical

— use wire, cable and other tangible materials to send communications signals.

— example : twisted pair cable, coaxial cable, fiber optic cable.

⇨ Wireless

— send communications signals through the air or space.

— sender and receiver are not connected by any electrical or optical wires/cables.

— example : infrared, broadcast radio, cellular radio, microwaves, communication satellite

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「Communication Device」

• Digital Modems
— A broadband modem / digital modem is a communication device that sends and receives data and information to and from a digital line.

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⇨ Cable Modems
— Sends and receive digital data over the CATV network.

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⇨ DSL Modems
— Sends digital data and information from a computer to a DSL line.
— Receives digital data and information from a DSL line.

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⇨ ISDN Modems
— Sends digital data and information from a computer to an ISDN line.
— Receives digital data and information from an ISDN line.

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• Wireless Modems
— Some mobile users have a wireless modem that uses a mobile service provider’s network to connect to the Internet wirelessly from a computer or mobile device.
— Wireless modems, which have an external or built-in antenna, are available as USB adapters and other devices.
— Some smartphones also can function as a wireless modem, called a mobile hot spot, when tethered to a personal computer or mobile device.

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• Wireless Access Point
— Is a central communications device that allows computers to transfer data wirelessly among themselves or to transfer data wirelessly to a wired network.
— Wireless access points have high-quality internal or external antennas for optimal signals.
— For the best signal, some manufacturers suggest positioning the wireless access point at the highest possible location and using a device to strengthen your wireless signal.

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• Routers
— Is a communication device that connects multiple computers or other routers together and transmit data to its correct destination on a network.

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• Network Cards / Network Interface Card (NIC)
— Is a communication device that enables a computer or device that does not have built-in networking capability to access a network.
— The network card coordinates the transmission and receipt of data, instructions, and information to and from the computer or device containing the network card.

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• Hub and Switch
— Is a device that provides a central point for cables in a network.
— Larger networks typically use a hub, while smaller networks use a switch.
— Some hubs and/of switches include routers. That is, the hub or switch receives data from many directions and then forwards it to one or more destinations.

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「Transmission Media」

• Transmission media consists of materials or substances capable of carrying one or more signals.

• A communications channel, or transmission media on which the data, instructions, or information travel.

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「Transmission Media」

⇨ Wired / Physical Transmission Media
• Twisted Pair Cable
- consists of one or more twisted-pair wires bundled together.
- each twisted-pair wire consists of two separate insulated copper wires that are twisted together.

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• Coaxial cable
- consists of a single copper wire surrounded by at least three layers :-
> an insulating material
> a woven or braided material
> a plastic outer coating
> connected computer to modem

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• Fiber optic cable
- consists of dozens or hundreds of thin strands of glass or plastic that use light to transmit signals.
- each strand, called an optical fiber, is as thin as human hair.
- inside the fiber-optic cable, an insulating glass cladding and a protective coating surround each optical fiber.
- longer distance to carry data as pulse of light.

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⇨ Wireless
• Broadcast Radio
- Is a wireless transmission medium that distributes radio signals through the air over long distances, such as between cities, regions, and countries, and short distances, such as within an office or home .
- Bluetooth, Wi-Fi use broadcast radio signals.
- Cellular radio is a form of broadcast radio that is in wide use for mobile communications, specifically wireless modems and mobile phones.

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• Microwaves
- Are radio waves that provide a high-speed signal transmission.
- Microwave transmission, often called fixed wireless involves sending signals from one microwave station to another.

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• Communications Satellite
- Is a space station that receives microwave signals from an earth-based station, amplifies (strengthens) the signals, and broadcasts the signals back over a wide are to any number of earth-based stations.

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「Advantages of a Network」

• Facilitating communications
- people communicate efficiently and easily via email, Internet messaging, chat rooms, blogs, wikis, online social networks, video calls, online meetings, video conferencing, VoIP, text messaging and more.

• Easy in sharing hardware
- each computer or device on a network can be provided access to hardware on the network.

• Easy in sharing data and information
- Any authorised user can access data and information stored on a network.

• Easy in sharing software
- Users connected to a network can access to the software on the network.

• Easy in transferring funds
- Electronic finds transfer (EFT), allows users connected to a network to exchange money from one account to another via transmission media.

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「Disadvantages of a Network」

• Attack by viruses
- When computers are connected by a network, the virus can spread itself electronically, at computer speeds.

• Network failure
- If the file server fails then no-one on the network can access any files or folders. This means that nobody can do any work. For an organisation, this would be extremely costly and disruptive.

• Slow service
- As more users log onto the network and request files, send things to be printed and open more software applications, the network can start to slow down.

• High cost
- Every workstation needs a network interface card to enable it to be connected to the network. Other hardware such as hubs, switches and routers are often needed.

• Expert support required
- Networks need constant monitoring to ensure that the performance is maintained and that all of the components are working properly.

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「Network Architecture」

• The configuration of computers, devices, and media on a network.

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「Types of network architecture」

• peer-to-peer
- each computer or mobile device, called a peer have equal responsibilities and capabilities, sharing hardware, data or information with other computers and mobile devices on the peer-to-peer network.
- suitable for small network. connects fewer than 10 computers.

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• Client/Server
- one or more computers act as a server, and the other computers on the network request services from the server.
- Clients are other computers and mobile devices on the network that really on the server for its resources.
- Server controls access to the hardware, software, and other resources on the network and provides a centralised storage area for programs, data, and information.

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「Differences Peer-to-peer and Client/Server」

• Peer-to-peer

— Advantage :
- Easy and inexpensive to set up the network.
- More reliable because failure of one peer will not affect other peers.
- All the peers can share their resources to others.

— Disadvantage :
- Lack of security control or other management functions.
- Data recovery or backup is very difficult. Each computer has to maintain its own backup system.

• Client/Server

— Advantage :
- Centralised control by the server promotes better security and management of the network.
- Data backup and recovery is easier since all data is stored in the server.

— Disadvantage :
- High cost to set up and maintain the network.
- Less reliable because too dependent on the server, failure of server will affect the operations of the whole network.
- Network congestion may occur if too many clients request services from server at the same time.

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「Types of Peer-to-Peer (P2P)」

• Home Peer-to-Peer
- accessibility of resources is limited (within home, school)
- sharing network printer

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• Internet Peer-to-Peer
- scope of accessibility is world wide
- download movie from P2P network

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「Classification of Network」

• Network usually are classified as a local area network (LAN) and wide are network (WAN).

• The main difference among these classifications is their area of coverage.

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〚 LAN 〛

• Area of coverage
- A network that connects computers and devices in a limited geographical area such as home, school, office building or closely positioned group of buildings.
- A wireless LAN (WLAN) is a LAN that uses no physical wires.

• Connectivity

- Computers are located within the same building, usually connected through wires.

• Ownership

- Owned and controlled by a single person or organisation.

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〚 WAN 〛

• Area of coverage
- a network that covers a large geographic area (such as a city, country, or the world) using a variety of wired and wireless transmission media.
- a WAN can be one large network or can consist of multiple LANs connected together.
- the Internet is the world’s largest WAN.

• Connectivity
- Computers connected via satellite or Internet.

• Ownership
- Exist under collective ownership and management over long distance / no ownership / public.