Data Communications and Networking, 5th Edition, Behrouz A. Forouzan, McGraw Hill, 2012

1. PART I: OVERVIEW
INTRODUCTION
Subject: Computer Networks
Tutor: Bilal Munir Mughal
1
Ch-1

2. Content Outline
 DATA COMMUNICATIONS
 Components
 Data Representation
 Data Flow
 NETWORKS
 Network Criteria
 Physical Structures
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3. Content Outline
 NETWORK TYPES
 Local Area Network
 Wide Area Network
 Switching
 The Internet
 Accessing the Internet
 STANDARDS AND ADMINISTRATION
 Internet Standards
 Internet Administration
 INTERNET HISTORY
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4. Data Communications: Definition
 Data Communications:
 For data communications to occur, the communicating
devices must be part of a communication system
made up of a combination of hardware (physical
equipment) and software (programs).
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Transfer of data from one device to another via
some form of transmission medium.

5. Data Communications: Motivations
 Efficient way to share resources
 Cost – less expensive
 Accessibility – easier
 Efficient way to exchange information
 Time – faster
 Size – bigger
 Correctness – more accurate
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6. Data Communications: Effectiveness
The effectiveness of a data communications system
depends on four fundamental characteristics:
1. Delivery. The system must deliver data to the correct destination. Data must be
received by the intended device or user and only by that device or user.
2. Accuracy. The system must deliver the data accurately. Data that have been
altered in transmission and left uncorrected are unusable.
3. Timeliness. The system must deliver data in a timely manner. Data delivered late
are useless. In the case of video and audio, timely delivery means delivering data
as they are produced, in the same order that they are produced, and without
significant delay (called real-time transmission).
4. Jitter. Jitter refers to the variation in the packet arrival time. It is the uneven delay
in the delivery of audio or video packets. For example, let us assume that video
packets are sent every 30 ms. If some of the packets arrive with 30-ms delay and
others with 40-ms delay, an uneven quality in the video is the result.
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7. Data Communications
7
Hi, how are you?
01010001
Hi, how are you?
User
Computer
you?
how
are
Hi,
you?
how
are
Hi,
01010001

8. Data Communications: Components
8
Hi, how are you?
5 Protocol
4 Medium
3 Receiver
2 Sender
1 Message

9. Data Representation
 Numbers
 8/16/32 bit integers
 floating point
 Text
 ASCII, Unicode
 Images
 Bit patterns, Graphics formats JPG/GIF/etc
 Audio  Samples of continuous signal
 Video  Sequence of bitmap images
9
150
2
255

10. Direction of Data Flow
 Simplex: One direction only
10
Server Monitor
data flow
Keyboard
data flow

11. Direction of Data Flow
 Half Duplex: Both directions, one at a time
 E.g., walkie-talkies
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data flow at time 1
data flow at time 2

12. Direction of Data Flow
 Full Duplex: Both directions simultaneously
 E.g., telephone
 Can be emulated on a single communication link using
various methods
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data flow
data flow

13. Networks
 Network: a set of devices connected by media links
13
Media Links
Printer
Workstation
Laptop
Scanner
Server
SD
iMac

14. Networks: Criteria
 A network must be able to meet a certain number
of criteria. The most important of these are
 Performance
 Reliability
 Security
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15. Networks: Criteria
 Performance can be measured in many ways,
including transit time and response time.
 Transit time is the amount of time required for a
message to travel from one device to another.
 Response time is the elapsed time between an inquiry
and a response.
 The performance of a network depends on the
 number of users
 type of transmission medium
 capabilities/efficiency of hardware, software
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16. Networks: Criteria
 Performance is often evaluated by two networking
metrics: throughput and delay.
 We often need more throughput and less delay.
 However, these two criteria are often contradictory.
If we try to send more data to the network, we may
increase throughput but we increase the delay
because of traffic congestion in the network.
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17. Networks: Criteria
 Reliability
 In addition to accuracy of delivery, network reliability
is measured by the frequency of failure, the time it
takes a link to recover from a failure, and the network’s
robustness in a catastrophe.
 Security
 Network security issues include protecting data from
unauthorized access, protecting data from damage,
and implementing policies and procedures for
recovery from breaches and data losses.
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18. Physical Structures: Types of
Connections
 Point-to-point
 Multipoint (multidrop)
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19. Point-To-Point Connection
19
A point-to-point connection provides a dedicated link between two devices.

20. Multipoint Connection
20
Wireless
A multipoint (also called multidrop) connection is one in which more than two specific
devices share a single link.

21. Topology
 Topology: physical or logical arrangement of
devices
 Mesh
 Star
 Bus
 Ring
 Hybrid
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22. Fully Connected Mesh Topology
22
A
C
B
D

23. Fully Connected Mesh Topology
 Pros:
 Dedicated links
 Robustness
 Privacy
 Easy to identify fault
 Cons:
 A lot of cabling
 A lot of I/O ports
 Difficult to move
23
Number of physical links n (n – 1) / 2 in duplex-mode
A
C
B
D

24. Star Topology
24
Hub
A D
B C
Drop
Drop

25. Star Topology
25
Switch
A D
B C

26. Star Topology
26
Hub
A D
B C

27. Star Topology
 Pros:
 One I/O port per device
 Little cabling
 Easy to install
 Robustness
 Easy to identify fault
 Cons:
 Single point of failure
 More cabling still required
27
Hub
Number of physical links n
where n = number of nodes

28. Bus Topology
28
Drop
line
Tap
Terminator

29. Bus Topology
29
A B C D

30. Bus Topology
30

31. Bus Topology
 Pros:
 Little cabling
 Easy to install
 Cons:
 Difficult to modify
 Difficult to isolate fault
 Break in the bus cable
stops all transmission
31
Number of physical links n + 1(backbone)
where n = number of nodes

32. Ring Topology
32
A
B
C
D

33. Ring Topology
33

34. Ring Topology
 Pros:
 Easy to install
 Easy to identify fault
 Cons:
 Delay in large ring
 Break in the ring stops
all transmission
34
Number of physical links n
where n = number of nodes

35. Hybrid Topologies
35
ACT
ACT
10M100M
1 2 3 4
13 14 15 16
5 6 7 8
17 18 19 20
9 10 11 12
21 22 23 24
UPLINK
1 2 3 4 5 6 7 8 9 101112
131415161718192021222324
COL
COL
PWR
SWITCH
ACT
ACT
10M100M
1 2 3 4
13 14 15 16
5 6 7 8
17 18 19 20
9 10 11 12
21 22 23 24
UPLINK
1 2 3 4 5 6 7 8 9101112
131415161718192021222324
COL
COL
PWR
SWITCH

36. Network Types
 Local Area Network (LAN)
 Wide Area Network (WAN)
36

37. Local Area Networks
 Network in a small area e.g. single office, building,
or campus
37

38. Wide Area Networks
 Network providing long-distance communication over
a country, a continent, the whole world or beyond
38

39. Wide Area Networks
 Distinct examples of WANs today: point-to-point
WANs and switched WANs.
 Point-to-Point WAN
 Switched WAN
39

40. Switching
41

41. Network of Networks
42
Company A
Company D
Network Interface Card (NIC)
Company B
Company C

42. Internetworking
 How to allow devices from different standards to
communicate
 Gateways/routers – devices capable of
communicating in several standards
 These become "network of networks"
43

43. Internetworks
 Two or more connected networks become an
internetwork, or internet
 Example: The Internet
44
Network1 Network2
Gateway
Network3

44. The Internet
 The largest internetwork (network of networks) in the
world
 Devices communicating with TCP/IP protocol suite
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45. Accessing The Internet
 Using Telephone Networks
 Dial-up service
 DSL Service
 Using Cable Networks
 Using Wireless Networks
 Direct Connection to the Internet
46

46. Internet Standards
 An Internet standard is a thoroughly tested
specification that is useful to and adhered to by
those who work with the Internet.
 It is a formalized regulation that must be followed.
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47. Internet Standards
 There is a strict procedure by which a specification
attains Internet standard status. A specification
begins as an Internet draft.
 An Internet draft is a working document (a work in
progress) with no official status and a six-month lifetime.
 Upon recommendation from the Internet authorities, a
draft may be published as a Request for Comments
(RFC).
 Each RFC is edited, assigned a number, and made available
to all interested parties.
 RFCs go through maturity levels and are categorized
according to their requirement level.
48

48. Internet Standards: RFC Maturity
Levels
 Maturity Levels
 An RFC, during its lifetime, falls into one of six maturity
levels:
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49. Internet Standards: RFC Maturity
Levels
 Proposed Standard.
 A proposed standard is a specification that is stable, well
understood, and of sufficient interest to the Internet community.
 At this level, the specification is usually tested and implemented
by several different groups.
 Draft Standard.
 A proposed standard is elevated to draft standard status after
at least two successful independent and interoperable
implementations.
 Barring difficulties, a draft standard, with modifications if specific
problems are encountered, normally becomes an Internet
standard.
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50. Internet Standards: RFC Maturity
Levels
 Internet Standard.
 A draft standard reaches Internet standard status after
demonstrations of successful implementation.
 Historic.
 The historic RFCs are significant from a historical
perspective.
 They either have been superseded by later specifications or
have never passed the necessary maturity levels to become
an Internet standard.
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51. Internet Standards: RFC Maturity
Levels
 Experimental.
 An RFC classified as experimental describes work related to
an experimental situation that does not affect the operation
of the Internet.
 Such an RFC should not be implemented in any functional
Internet service.
 Informational.
 An RFC classified as informational contains general,
historical, or tutorial information related to the Internet.
 It is usually written by someone in a non-Internet
organization, such as a vendor.
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52. Internet Standards: RFC
Requirement Levels
RFCs are classified into five requirement levels
 Required.
 An RFC is labeled required if it must be implemented by all
Internet systems to achieve minimum conformance.
 For example, IP and ICMP (Chapter 19) are required
protocols.
 Recommended.
 An RFC labeled recommended is not required for minimum
conformance; it is recommended because of its usefulness.
 For example, FTP (Chapter 26) and TELNET (Chapter 26)
are recommended protocols.
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53. Internet Standards: RFC
Requirement Levels
 Elective.
 An RFC labeled elective is not required and not
recommended. However, a system can use it for its own
benefit.
 Limited Use.
 An RFC labeled limited use should be used only in limited
situations. Most of the experimental RFCs fall under this
category.
 Not Recommended.
 An RFC labeled not recommended is inappropriate for
general use. Normally a historic (deprecated) RFC may fall
under this category.
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54. Internet Administration
 Appendix G gives the addresses, e-mail addresses,
and telephone numbers for some of groups involved
in growth and development of the internet.
55
Figure 1.17 shows general organization of Internet
administration.

55. Internet Administration
 The Internet Society (ISOC) is an international,
nonprofit organization formed in 1992 to provide
support for the Internet standards process.
 ISOC accomplishes this through maintaining and
supporting other Internet administrative bodies such as
IAB, IETF, IRTF, and IANA.
 ISOC also promotes research and other scholarly
activities relating to the Internet
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56. Internet Administration
 The Internet Architecture Board (IAB) is the technical
advisor to the ISOC.
 The main purposes of the IAB are to oversee the continuing
development of the TCP/IP Protocol Suite and to serve in a
technical advisory capacity to research members of the Internet
community.
 IAB accomplishes this through its two primary components, the
Internet Engineering Task Force (IETF) and the Internet Research
Task Force (IRTF).
 Another responsibility of the IAB is the editorial management of
the RFCs, described earlier.
 IAB is also the external liaison between the Internet and other
standards organizations and forums.
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57. Internet Administration
 The Internet Engineering Task Force (IETF) is a forum
of working groups managed by the Internet
Engineering Steering Group (IESG).
 IETF is responsible for identifying operational problems
and proposing solutions to these problems.
 IETF also develops and reviews specifications intended as
Internet standards.
 The working groups are collected into areas, and each
area concentrates on a specific topic.
 Currently nine areas have been defined. The areas include
applications, protocols, routing, network management, IP next
generation (IPng), and security.
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58. Internet Administration
 The Internet Research Task Force (IRTF) is a forum
of working groups managed by the Internet
Research Steering Group (IRSG).
 IRTF focuses on long-term research topics related to
Internet protocols, applications, architecture, and
technology.
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59. INTERNET HISTORY
 Check your textbook for reference.
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60. 61
Questions?