1. Chapter 1 Introduction 1.#
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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2. Topics discussed in this section:
1-1 DATA COMMUNICATIONS
The term telecommunication means communication at a distance. The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data. Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable.
Topics discussed in this section:
Components
Data Representation Data Flow
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3. Data Communication Data Data Communication
Information presented in whatever form is agreed upon by the parties creating and using the data
Binary information units (0s and 1s)
Data Communication
Exchange of data between two devices via transmission medium
Fundamental Characteristics
Delivery: deliver data to correct destination
Accuracy: deliver data accurately
Timeliness:
Deliver data in a timely manner
Delivering data as they are produced, in the same order that they are produced, and without significant delay
Real-time transmission

4. Data Communication System Component

5. Data Communication System Components (cont.)
Message
Information (data) to be communicated
Sender
Device sending data message
Receiver
Device receiving message
Medium
Physical path by which a message travels
Protocol
Set of rules governing data communication
Agreement between communicating devices

6. Direction of Data Flow Simplex Unidirectional communication
Keyboard, monitor

7. Direction of Data Flow (cont.)
Half-duplex
Both transmit and receive, but not at the same time
Walkie-talkie

8. Direction of Data Flow (cont.)
Full-duplex
Transmit and receive simultaneously
Telephone network

9. Network
Network
A set of devices (nodes) connected by communication links

10. Network Criteria Performance Reliability Security
Throughput, delay, jitter, loss…
Factors including number of users, type of transmission medium, hardware, software
Reliability
Frequency of failure, recovery time of a network after a failure, network’s robustness in a catastrophe
Security
Protecting data from unauthorized access

11. Physical Structure Type of Connection Point-to-Point
Provide a dedicated link between two devices
Reserve entire capacity of the channel for transmission between two devices

12. Physical Structure (cont.)
Type of Connection (cont.)
Multipoint (or Multidrop)
More than two devices share a single link
Spatially shared: several devices use link simultaneously
Timeshare:users must take turns

13. Physical Structure (cont.)
Physical Topology
The way in which a network is laid out physically

14. Physical Structure (cont.)
Physical Topology (cont.)
Mesh
Every device has a dedicated p-to-p link to every other device
Guarantee data load between two devices
Robust, meaning one link failure does not halt entire system
Privacy or security
Easy fault identification and fault isolation
Amount of cabling and number of I/O ports required (n(n-1)/2)

15. Physical Structure (cont.)
Physical Topology (cont.)
Star
Dedicated p-to-p link to central controller (hub)
Less expensive than mesh
Easy to install and reconfigure due to only one link and one I/O port
Robustness due to easy fault identification and fault isolation
More cabling than other topologies (tree, ring, bus)
Single failure problem

16. Physical Structure (cont.)
Physical Topology (cont.)
Bus
Multipoint configuration
Ease of installation
Limited number of taps a bus can support and distance
Difficult reconfiguration and isolation

17. A hybrid topology: a star backbone with three bus networks
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18. Figure 1.10 An isolated LAN connecting 12 computers to a hub in a closet
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19. Physical Structure (cont.)
Physical Topology (cont.)
Ring
Dedicated p-to-p configuration with two devices on either side
Easy to install and reconfigure
Simplified fault isolation
Unidirectional traffic
A break in the ring can disable entire network

20. Categories of Networks
Classification of interconnected processors by scale

21. Categories of Networks (cont.)
Local Area Network (LAN)
Privately owned and limited size to a few kilometers
Allow resources to be shared between PCs or workstations
Bus, ring or star

22. Categories of Networks (cont.)
Metropolitan Area Network (MAN)
Extend over an entire city
Single network or a means of connecting LANS into a larger network
(ex) Telco.s provide a popular MAN service called SMDS (Switched Multi-megabit Data Services)

23. Categories of Networks (cont.)
Wide Area Network (WAN)
Provide long-distance transmission of data over large geographical areas (country or continent)
Utilize public, leased, or private communication equipment
Enterprise Network
WAN that is wholly owned and used by a single company

24. Figure 1.11 WANs: a switched WAN and a point-to-point WAN
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25. Categories of Networks (cont.)
Internetworks
internetworks or internet
Collection of interconnected networks

26. Brief History of Internet
ARPANET
Advanced Research Projects Agency (ARPA) in the DOD : presented ideas of ARPANET, 1967
Reality : 1969 (UCLA, UCSB, SRI, U of Utah)
Birth of the Internet
Vint Cerf and Bob Kahn devised to interconnect networks, in 1972
Presented TCP concepts in 1973; later, TCP  splitting into TCP and IP
In 1983, TCP/IP became to official protocol for the ARPANET

27. Internet Today

28. Internet
Specific
worldwide
internet

29. Protocols Set of rules (conventions) governing data communications
Key Element
Syntax
Structure or format of data, meaning the order in which they are presented
Semantics
Meaning of each section of bits
Timing
Two characteristics: when data should be sent and how fast they can be sent
Entity
Anything capable of sending or receiving information

30. Standards Standard Categories De Jure standards De Facto Standards
Essential in creating and maintaining an open and competitive market and in guaranteeing national and international interoperability
Categories
De Jure standards
Legislated by an officially recognized body
De Facto Standards
Have not been approved by an organized body but have been adopted as standards through widespread use

31. Standard Organizations
Standards Creation Committees
International Standards Organization (ISO)
International Telecommunications Union-Telecommunication Standards Sector (ITU-T, formerly CCITT)
American National Standards Institute (ANSI)
Institute of Electrical and Electronics Engineers (IEEE)
Electronic Industries Association (EIA)

32. Standard Organizations (cont.)
Forum
Developed by special-interest groups to accommodate the need for working models and agreements and to facilitate the standardization process
Speed acceptance and use of technologies in telecommunications community
Frame relay forum, ATM forum and ATM consortium
Internet Society (ISOC) and Internet Engineering Task Force (IETF)
Regulatory Agencies
Government agencies regulating all communications technology
FCC

33. Internet Standards Internet Standard
A thoroughly tested specification that is useful to and adhered by those who work with the Internet
A specification begins as an Internet draft
Working document with no official status and six-month life-time
RFC (Request for Comment)
Recommendation from Internet authorities

34. Chapter 2 Network Models
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

35. Layered Task: Sending a Letter

36. Topics discussed in this section:
2-2 THE OSI MODEL
Established in 1947, the International Standards Organization (ISO) is a multinational body dedicated to worldwide agreement on international standards. An ISO standard that covers all aspects of network communications is the Open Systems Interconnection (OSI) model. It was first introduced in the late 1970s.
Topics discussed in this section:
Layered Architecture Peer-to-Peer Processes
Encapsulation

37. ISO is the organization. OSI is the model.
Note
ISO is the organization. OSI is the model.

38. Figure 2.2 Seven layers of the OSI model

39. The Physical Layer Responsibility: Issues:
transmission of raw bits over a communication channel.
Issues:
mechanical and electrical interfaces
time per bit
distances

40. The Data Link Layer - Data Link Control
Responsibility:
provide an error-free communication link
Issues:
framing (dividing data into chunks)
header & trailer bits
addressing

41. The Data Link Layer - The MAC sublayer
Medium Access Control
needed by muti-access communications.
MAC provides ‘virtual wires’ on multi-access networks.
Multi-access
Point-to-point

42. The Network Layer Responsibilities: Issues:
path selection between end-systems (routing/address).
subnet flow control.
translation between different network types.
Issues:
packet headers (address)
virtual circuits (routing)

43. Hop-by-Hop
Process A
Process B

44. End-to-End
Process A
Process B

45. The Transport Layer Responsibities: Issues:
provides virtual end-to-end links between peer processes.
fragmentation & reassembly
end-to-end flow control
Issues:
headers
error detection
reliable communication

46. The Session Layer Responsibilities:
establishes, manages, and terminates sessions between applications.
service location lookup
Many protocol suites do not include a session layer.

47. The Presentation Layer
Responsibilities:
data encryption
data compression
data conversion
Many protocol suites do not include a Presentation Layer.

48. The Application Layer Responsibities: Issues:
anything not provided by any of the other layers
Issues:
application level protocols
appropriate selection of type of service

49. Layering & Headers
Each layer needs to add some control information to the data in order to do its job.
This information is typically prepended to the data before being given to lower layers.
Once the lower layers deliver the the data and control information - the peer layer uses the control information.

50. Headers Process DATA Process Transport H DATA Transport Network H H
Data Link H H H
DATA
Data Link

51. What are the headers? Physical: no header - just a bunch of bits.
Data Link:
address of the receiving endpoints
address of the sending endpoint
length of the data
checksum.

52. Network layer header (IP header)
IP protocol version
type of service
length of the data
packet identifier
fragment number
time to live
protocol
header checksum
source network address
destination network address

53. Inter-Network Net B Net A
Connection of two or more distinct (possibly dissimilar) networks.
Requires some kind of network device to facilitate the connection.
Net B
Net A

54. Network Interface Card(NIC)

55. Thick Ethernet Wiring

56. Thin Ethernet Wiring

57. Twisted Pair Ethernet

58. Connecting Networks Repeater: physical layer Bridge: data link layer
Router: network layer
Gateway: network layer and above.

59. Internet Model (TCP/IP)
Sometimes called the TCP/IP protocol suite
Composed of five layers
Physical (1), Data link, Network, Transport, Application (5)
Layer
A collection of networking functions which have related uses
Define a family of functions distinct from those of other layers
Call upon services of the layer just below it
Provide a more comprehensive and flexible architecture

60. Internet Layer

61. Peer-to-Peer Processes
Processes on each machine that communicate at a given layer
Interface
Define what information and services a layer must provide for the layer above it

62. Peer-to-Peer Processes (cont.)

63. An Exchange using Internet Model

64. Physical Layer
Responsible for transmitting individual bits from one node to the next
Function required to transmit a bit stream over a physical medium
Mechanical, electrical, functional and procedural interface, and physical transmission medium

65. Data Link Layer
Responsible for transmitting frames from one node to the next
Transform physical layer, a raw transmission facility, to a reliable link
Make physical layer appear error-free to upper layer
Framing, physical addressing, flow control, error control, access control

66. Hop-to-Hop (Node-to-Node) Delivery

67. Example of Data Link Layer Communication

68. Network Layer
Responsible for delivery of packets from the original source to the final destination
Source-to-destination delivery of a packet possibly across multiple networks
Logical addressing, Routing

69. Source-to-Destination Delivery

70. Example of Network Layer Communication

71. Transport Layer
Responsible for delivery of a message from one process within source to another process within destination
Responsible for process-to-process delivery of the entire message
Port addressing, segmentation and reassembly, connection control, flow control, error control

72. Reliable Process-to-Process Delivery of Message

73. Example of Transport Layer Communication

74. Application Layer Responsible for providing services to the users
Enable user, whether human or software, to access the network
Mail services, File transfer and access, Remote log-in, Accessing the World Wide Web (WWW),…

75. Summary of Layers

76. OSI (Open Systems Interconnection) Model
Based on the proposal developed by ISO
7 layers

77. Session layer Network dialog controller Dialog control Synchronization
To establish, maintain, and synchronize interaction between communicating systems
Dialog control
Synchronization

78. Presentation layer
Syntax and semantics of information exchanged between two systems
Translation
Interoperability between different encoding methods
Encryption
Compression

79. TCP/IP and OSI Model