1. COMMUNICATION MEDIA AND DEVICES
TTS2233- CHAPTER 6
COMMUNICATION MEDIA AND DEVICES

2. Communications channel
Computer communications describes a process in which two or more computers or devices transfer data, instructions, and information
Sending device
Communications channel
Receiving device
Discovering Computers 2010: Living in a Digital World Chapter 9

3. Communications What is needed for successful communications?
Sending device — initiates instruction to transmit data, instructions, or information
Communications device — connects the sending device to the communications channel
Communications channel — media on which data, instructions, or information travel
Communications device — connects the communications channel to the receiving device
Receiving device — accepts transmission of data, instructions, or information

4. DATA COMMUNICATIONS
Mail, telephone, TV, radio, books, newspapers are traditional method for users to send and receive information.
Data communication systems have been evolving since mid-1960s
Data communication system is the computers systems that transmit data over communication lines such as telephone and cables.
Network is a computer system that uses communication equipment to connect two or more computers and their resources.

5. PUTTING TOGETHER A NETWORK: A FIRST LOOK
The basic components of a data communications system are:

6. Communication Systems
Electronic systems that transmit data from one location to another
Communication systems can be wired or wireless
Basic elements
Sending and receiving devices – computer or a specialized communication device
Communication channel – carries the message
Connection devices – act as an interface between sending and receiving devices; convert outgoing messages into packets (key term) that can travel across the communication channel
Data transmission specifications – rules and procedures that coordinate the sending and receiving devices

7. Communication Systems
9-7
Four basic elements
Sending and receiving devices
Communication channel
Connection devices
Data transmission specifications
Electronic systems that transmit data from one location to another
Communication systems can be wired or wireless
Basic elements
Sending and receiving devices – computer or a specialized communication device
Communication channel – carries the message
Connection devices – act as an interface between sending and receiving devices; convert outgoing messages into packets (key term) that can travel across the communication channel
Data transmission specifications – rules and procedures that coordinate the sending and receiving devices

8. Network design consideration
The task of network design is complex one.
Here is a list of questions that might occur to a customer who was considering installing a network.
Modems speed.
Communication media
Geographical area
Network topology

9. DATA TRANSMISSION A terminal or computer produces digital signals.
Some combination lines accept digital transmission
However, most telephones lines built for voice transmission that requires analog signals.

10. Digital and Analog transmission
Types of signals
Analog
Digital

11. Digital and Analog transmission
Digital transmission sends data as distinct pulses, either on or off.
Some communication media are not digital such as telephone lines, coaxial cables and microwave circuits are already in place for voice (analog) transmission.
Therefore, the most communications devices all use analog transmissions, a continuous electrical signal in the form of a wave.
To be sent over analog lines, a digital signal must be converted to an analog form.
Modulation – conversion from digital to analog signals
Demodulation- conversion from analog to digital signals.

12. COMMUNICATIONS MEDIA Twisted-pair cable Fiber-optic cable
Coaxial cable

13. Types of communication media
Wire pairs/ twisted pair
The most communication media.
Wire pairs are inexpensive.
Consist of two separate insulated copper wires that twisted together.
They are often use because they have already been installed in a building (network cabling) and telephone systems.
slowest; being phased out by more advanced and reliable media

14. Types of communication media
Coaxial cables
Known for sending a strong signal.
Coaxial cables has much higher bandwidth
The cable that connects your TV to the cable TV system is the most common type of coaxial cable.
single solid copper core; 80 times transmission of twisted pair; television and computer networks
Consist of a single copper wire surrounded by at least three years: (1) an insulating material, (2) a woven or braided metal, and (3) a plastic outer coating.

15. Types of communication media
Fiber Optics
Fiber optics use light and the cables are made of glass or plastic fibers, each thinner than a human hair.
Fiber optics cable has much higher bandwidth than coaxial cable.
It uses light rather than electricity.
26,000 times capacity of twisted pair cable; more secure and reliable; best over limited distances; lighter, more reliable, and more expensive than coaxial cable

16. Types of communication media
Microwave transmission
Use as line-of-sight transmission of data signals via atmosphere.
Often antennas in high places, such as the tops of mountains and buildings- are positioned at points approximately 30 miles apart to continue the transmission.
Microwave transmission offers high speed, cost-effectiveness and ease implementation.
One problem is susceptibility to interference by whether conditions.

17. Wireless Transmission Media
Microwaves are radio waves that provide a high-speed signal transmission
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Figure 9-41
Discovering Computers 2010: Living in a Digital World Chapter 9

18. Types of communication media
Satellite transmission
Satellite transmission is a form of microwave transmission in which a satellite acts as the relay station.
Its basic components are earth stations, which send and receive signals.
Transponder is the satellite components that receive the transmission from an earth.
This entire process takes only a fraction of a second.

19. Wireless Transmission Media
A communications satellite is a space station that receives microwave signals from an earth-based station, amplifies it, and broadcasts the signal over a wide area
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Figure 9-42
Discovering Computers 2010: Living in a Digital World Chapter 9

20. Types of communication media
Wireless transmission
Wireless transmission is a group of technologies has recently emerged that transmit data over relatively short distances.
IrDA uses infrared to transmit data a few feet between devices, such a PDA and a desktop or a computer and a printer.
Similar to TV remote, IrDA requires a direct line-of-sight.
Bluetooth is another short distance technique (30 feet or less) that uses radio waves to connect mobile devices such as handhelds, notebooks and cell phones.
Wi-Fi (Wireless Fidelity) is a standard uses for distances up to about 150 feet.
Wi-Fi capability is built into some notebook model, allowing them to easily join wireless LANs.
802.11a and g are the newest members of this family and allow transmission at speeds up to 54 Mbps.

21. Communication Media Summary

22. Facilitating communications Sharing data and information
NETWORK
Network is a collection of computers and devices connected via communications devices and transmission media
Advantages of a network include:
Facilitating communications
Sharing hardware
Sharing data and information
Sharing software
Transferring funds

23. Networks
The design of computers, devices, and media on a network is sometimes called the network architecture
Client/server network
Peer-to-peer network

24. Networks

25. Networks
A local area network (LAN) is a network that connects computers and devices in a limited geographical area
A wireless LAN (WLAN) is a LAN that uses no physical wires

26. Networks
A metropolitan area network (MAN) connects LANs in a metropolitan area
A wide area network (WAN) is a network that covers a large geographical area

27. NETWORK TOPOLOGIES A topology is the physical layout of a network.
There are three commons topologies: star, ring and bus networks.
In a network topology a component is called a node, which is usually a computer on a network.
The term node is connected to a network including server, computers and peripheral devices such as printers.

28. Networks
Star network
Bus network
Ring network

29. A star network
Has a central (hub) computer that is responsible for managing the network.
All messages are routed via the hub computer.
Any connection failure between a node and the hub will not affect the overall system.
However, if the hub computer fails, the network fails.

30. A Ring network Links all nodes together in a circular chain.
Data messages travel on only one direction around the ring.
Each node examines any data that that passes by to see whether that node is the addressee; if not, the data is passed on to the next node in the ring.
If one node fails, the ring is broken, and the entire network fails.

31. A bus network
A bus network has a single line (the bus) to which all the network nodes are attached.
Computers transmit data in the hope no collision, if the collision occurs, the sending node simply tries again.
Nodes can be attached and detached without affecting the network.
Furthermore, if one node fails, it does not affect the rest of the networks.

32. Communication Devices
Modem
A modem is a device that converts a digital signal to analog signal and vice versa.
Modem is short for modulator and demodulator.
Most modems are directly connected to phone system by a cable.
LANs do not use the telephone network. Networks that are LANs are made up of a standard set of components:
Types of modem:
External modem – is separate from computer.
Advantage – it can be used with a variety of computers
Internal modem – board can be inserted into the computer
Most personal computer use internal modem as standard equipment.

33. Communication Devices
Network cable
All networks need some system for interconnection. In some LANs the nodes are connected by a shared network cable.
Low cost LANs are connected with twisted pairs, but many LANs use coaxial cables or fiber-optic cable, which may be more expensive but are faster.
Some local area networks, are wireless which easy to set up and reconfigure, but they have slower transmission rates.

34. Communication Devices
A network Interface card (NIC)
NIC connects each computer to the wiring in the network.
On a desktop computer, a NIC is a circuit board that fits in one of the computer’s internal expansion slots.
A notebook computer may use NIC in a PC card.

35. Communication Devices
Bridge  
A hardware/software combination that recognizes the messages on a network and passes on messages addressed to nodes in other networks.
Router
Is a special computer that directs communications traffic when several networks are connected.
Gateway
Is a collection of hardware and software resources that lets a node communicate with a computer on another dissimilar (different) network.

36. Communications Devices
A communications device is any type of hardware capable of transmitting data, instructions, and information between a sending device and a receiving device
A dial-up modem converts signals between analog and digital

37. Communications Devices
A digital modem sends and receives data and information to and from a digital line
DSL modem
Cable modem

38. Communications Devices

39. Communications Devices
A wireless modem uses the cell phone network to connect to the Internet wirelessly from a notebook computer, a smart phone, or other mobile device

40. Communications Devices
A network card enables a computer or device to access a network
Available in a variety of styles
Wireless network cards often have an antenna

41. Communications Devices
A wireless access point is a central communications device that allows computers and devices to transfer data wirelessly among themselves or to a wired network

42. Communications Devices
A router connects multiple computers or other routers together and transmits data to its correct destination on a network
Many are protected by a hardware firewall

43. Communications Devices
A hub or switch connects several devices in a network together

44. EXERCISE
Define network topology, and discuss three types of topologies. Draw each network topology diagram.
Describe the differences between the three major physical connection mediums: twisted-pair cable, coaxial cable, and fiber-optic cable. 
Explain the difference between analog and digital signals.