1. INTRODUCTION TO COMPUTER NETWORKS
Chapter 2
INTRODUCTION TO COMPUTER NETWORKS

2. Learning outcomes The difference between networks and internets
The difference between logical and physical addresses
What is a protocol in the context of computer networking
How protocols are used on remote computers to communicate easily
Explain the concept of layering
OSI ,
TCP/IP and
hybrid models

3. Reading Joe Casad, Teach Yourself TCP/IP, Chs 1-2
William Buchana, Mastering the Internet, Ch. 3
Neil Briscoe, Understanding the 7-layer OSI model, July 2000.
Julian Moss, Understanding TCP/IP (first part September 1997)

4. What is a network? A network consists of two or more computers
connected by network media
.i.e cables, telephone lines, radio waves
share the same resources such as database, printer
Exchange files
Exchange electronic message between each others

5. Example of a simple network

6. How are they linked? Computers on a network may be linked through:
cables,
telephone lines,
radio waves, satellites or
wireless technologies

7. An example of a network
Router
Hub
Bridge
Segment
Node
Hub
Internet

8. Applications of Networks
Introduction to Computer Networks
Applications of Networks
Resource Sharing
Hardware (computing resources, disks, printers)
Software (application software)
Information Sharing
Easy accessibility from anywhere (files, databases)
Search Capability (WWW)
Communication
Message broadcast
Remote computing
Distributed processing (GRID Computing)

9. Categories of networks

10. Local Area Network
A LAN is a network that is used for communicating among computer devices, usually within an office building or home
LAN’s enable the sharing of resources such as files or hardware devices that may be needed by multiple users
Is limited in size, typically spanning a few hundred meters, and no more than a mile
Is very fast, with speeds from 10 Mbps to 10 Gbps
Requires very little wiring, typically a single cable connecting to each device
Has lower cost compared to MAN’s or WAN’s

11. LAN

12. LAN (Continued)

13. Metropolitan-Area Networks (MAN)
MAN is designed extended over an entire city.
May be wholly owned and operated by a private company, or it may be a service provided by a public company, such as a local telephone company.

14. Wide-Area Networks (WAN)
Provides long-distance transmission of data, voice, image, and video information over large geographic areas

15. WAN (Continued)
WANs connect larger areas, such as whole states, or even the world.
Transoceanic cables and satellites are used to connect WANs

16. Topology
The physical topology of a network refers to the configuration of cables, computers and other peripherals.
The main types of network topologies are:
Linear Bus
Star
Ring
Tree or Hybrid

17. Linear Bus topology
A linear bus topology consists of a main run of cable with a terminator at each end. All servers workstations and peripherals are connected to the linear cable

18. Star topology
A star network is designed with each node (file server, workstation, peripheral) connected directly to a central network hub or server

19. Ring topology
A ring network is one where all workstations and other devices are connected in a continuous loop. There is no central server

20. Tree or hybrid topology
A tree or hybrid topology combines characteristics of linear bus and star and/or ring topologies.
It consists of groups of star-configured workstations connected to a linear bus backbone cable

22. Network Operating Software
Network operating systems co-ordinate the activities of multiple computers across a network
The two major types of network OS are:
Peer-to-peer
Client/server

23. Peer to peer network OS
In peer to peer network OS, there is no file server or central management source; all computers are considered equal
Peer to peer networks are design primarily for small to medium LANS
AppleShare and Windows for Workgroups are examples of programs that can function as peer to peer

24. Client/Server network OS
Client/server network OS centralise functions and applications in one or more dedicated file servers.
The file server provides access to resources and provides security
Novel Netware and Windows NT Server are examples of client/server network operating systems

25. Network Hardware and Physical Media
Network hardware includes:
Computers
Peripherals
Interface cards and
Other equipment needed to perform data processing and communications within the network

26. File servers
A very fast computer with a large amount of RAM and storage space along with a fast network interface card
The network operating system software resides on this computer

27. Workstations
All computers connected to the file server on a network are called workstations

28. Network interface cards
The network interface card (NIC) provides the physical connection between the network and the computer workstation.
Most NICs are internal with the card fitting into an expansion slot in the computer.
Three common network interface connections are Ethernet cards, Local Talk connectors and Token Ring cards

29. Ethernet cards
The most common Network Interface Cards are Ethernet cards
They contain connections for either coaxial or twisted pair cables, or both
Co-axial cable
Twisted pair cable

30. Concentrators / Hubs
A concentrator is a device that provides a central connection point for cables from workstations, servers and peripherals
Hubs are multi-slot concentrators

31. Switches
hubs provide an easy way to scale up and shorten the distance that the packets must travel to get from one node to another
they do not break up the actual network into discrete segments. That is where switches come in.

32. Switches (continued) A vital difference between a hub and a switch is
all the nodes connected to a hub share the bandwidth among themselves.
while a device connected to a switch port has the full bandwidth all to itself.
Think of a switch as a ‘clever’ hub

33. Repeaters
A signal loses strength as it passes along a cable, so it is often necessary to boost the signal with a device called a repeater
A repeater might be a separate device, or might be part of a concentrator

34. Bridges
A bridge is a device that allows you to segment a large network into two smaller, more efficient networks

35. An example of a network with a bridge
Router
Hub
Bridge
Segment
Node
Hub
Internet

36. Routers A router translates information from one network to another
The router directs traffic to prevent “head-on” collisions
If you have a LAN that you want to connect to the Internet, you will need a router to serve as the translator between information on your LAN and the Internet

37. Routers (continued)

38. Physical Media
Physical media provide the connections between network devices that make networking possible
There are four main types of physical media in widespread use today:
Coaxial Cable
Twisted Pair
Fiber Optic Cable
Wireless Media

39. Ethernet Physical Media :- Maximum Segment Length LAN Technologies
10 Base Thick Co-axial Cable with Bus Topology
10 Base Thin Co-axial Cable with Bus Topology
10 BaseT UTP Cat 3/5 with Tree Topology
10 BaseFL Multimode/Singlemode Fiber with Tree
Topology
Maximum Segment Length
10 Base m with at most 4 repeaters (Use Bridge to extend the network)
10 Base m with at most 4 repeaters (Use Bridge to extend the network)
10 BaseT m with at most 4 hubs (Use Switch to extend the network)

40. Thick Coaxial Cable Used in the first Ethernet networks
Type RG-11 / 10Base5
Usually orange/black
Thickness of a small garden hose
Very expensive and heavy cable
Two strands along the axis
Conductor down the center
Insulator surrounds conductor
Shielded mesh serves as outside
Thick Ethernet cable:
is a specially manufactured cable to be used only in certain Ethernet environments
provides many layers of shielding.

41. Thin Coaxial Cable Alternative to Thick Ethernet Cable
Type RG-58 / 10Base2 / “Cheapnet”
Usually black
Thickness of a pencil
More flexible than thick Ethernet
Reduced the cost of the cabling
Flexible
Thin Ethernet cable:
was designed in 1984 as an alternative to thick Ethernet cable.
provides a simplification of the Ethernet cabling scheme.
uses a commonly manufactured cable type.
reduces installation time from about 5 minutes to around 1minute.
eliminated or moved certain thick coaxial components which
introduced new connectors

42. Coaxial cable connectors
The most common type of connector used with coaxial cables is the BNC connector

43. Twisted Pair Cable Phone Systems
Twisted Pair Cable consists of two copper wires, usually twisted around each other to cancel out any noise in the circuit
Two main type of Twisted Pair Cabling
Shielded Twisted Pair (STP)
Unshielded Twisted Pair (UTP)

44. Shielded Twisted Pair (STP)
STP is the original media used for token ring networks
STP can be used for high-speed networks, such as FDDI or ATM, where shielding is important.
RJ-45

45. Unshielded Twisted Pair (UTP)
UTP 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

46. UTP (Continued) Most commonly used twisted pair cable
Uses common telephone wire
UTP was standardized by the IEEE committee in October of 1990
UTP for LANs is now classified as:
Category 3 - used for LANs up to 10 Mbps
Category 4 - used for LANs up to 16 Mbps
Category 5 - used for LANs up to 100 Mbps
Unshielded Twisted Pair (UTP) cable:
provides an alternative, easy to use, less expensive cable type for Ethernet networks. .
implements the star topology on Ethernet which allows for better network management
introduced a new component called the concentrator which allows for network cabling to be collapsed into one entity.

47. Fiber Optic Cable
Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials
It transmits light rather than electronic signals
It is the standard for connecting networks between buildings, due to its immunity to the effects of moisture and light

48. Fiber Optic (continued)
Fiber optic cable has the ability to transmit signals over much longer distances than coaxial or twisted pair
It can also carry information at vastly greater speeds
Fiber optic cable is more difficult to install than other cabling

49. Wireless LANS
Wireless networks use high frequency radio signals to communicate between the workstations and the fileserver or hubs.
Disadvantages of wireless networks are:
they are expensive (relatively),
provide poor security,
are susceptible to interference and
are slower than cabled networks

50. Introduction network Protocol
A protocol is a set of rules that governs the communications between computers on a network
These rules include guidelines that regulate:
the method of access,
types of cabling and
speed of size data transfer
PROTOCOL =
SET OF RULES ABOUT COMMUNICATIONS BETWEEN NETWORKS!

51. The most common protocols are:
Ethernet
Local Talk
Token Ring
FDDI
ATM
Protocol = a formal description of a set of rules and conventions that govern how devices on a network exchange information
Did you ever wonder what HTTP in web addresses was about? It stands for HyperText Transfer Protocol

52. Ethernet Most widely used
Uses an access method called CSMA/CD (Carrier Sense Multiple Access/Collision Detection

53. A bit like waiting for some one to get
What does that mean?
Each computer in the network ‘listens’ to the cable before sending anything through the network. If the network is clear, the computer will transmit.
If another computer is already transmitting on the cable, the computer will wait and try again when the line is clear
A bit like waiting for some one to get
off the telephone

54. CSMA/CD =Carrier Sense Multiple Access /Collision Detection
Ethernet (continued)
A collision happens if two computers attempt to transmit at the same time.
Each computer then backs off and waits a random amount of time before attempting to retransmit
.It is normal to have collisions using this method,
but the delays caused by collisions and transmissions is small, and does not effect speed of transmission on the network
CSMA/CD =Carrier Sense Multiple Access /Collision Detection

55. Ethernet (continued)
Ethernet protocol allows for data to be transmitted over twisted pair, coaxial or fiber optic cable at a speed of 10 Mbps
(more on that later)

56. Fast Ethernet
To allow for faster transmission, the Ethernet protocol has developed a new standard that supports 100 Mbps
Fast Ethernet requires the use of more expensive equipment and network cards

57. One gigabit per second = one thousand megabits per second
Gigabit Ethernet
The Ethernet protocol has also developed a new standard that allows transmission of 1 Gbps (gigabit per second)
One gigabit per second = one thousand megabits per second

58. Local Talk
Local Talk is a network protocol that was developed by Apple for Macintosh computers
Local Talk uses the CSMA/CA
Carrier Sense Multiple Access with Collision Avoidance
It works in a similar way to CSMA/CD
It is a lot slower than Ethernet (only 230 Kbps)

59. Token Ring Token ring protocol involves ‘token-passing’.
It is not as popular as Ethernet protocol
A single electronic ‘token’ moves around the ring from one computer to the next. If a computer wishes to transit and receives an empty token, it attaches data to the token which then proceeds around the ring until it comes to the computer the data is meant for.

60. FDDI Stands for Fiber Distributed Data Interface
Is used mainly to connect two or more LANs, often over large distances
Can operate over fiber optic cable at 100 Mbps

61. ATM- Asynchronous Transfer Mode
Transmit data at a speed of 155 Mbps and higher
Works by transmitting all data in small packets of fixed size (other protocols transfer variable size packets)
Like FDDI , is most often used to connect two or more LANs

62. Where does TCP/IP fit into all this?
TCP/IP is the protocol that is used for the transmission of information over the Internet
IP (Internet Protocol) - the main delivery system for information over the Internet
TCP (Transport Control Protocol) - used to break apart and rebuild information that travels over the Internet
In Chapter 3 We will look into this protocol in details.