1. Computer Communication Networks
Data Transmission, Media
Signal Encoding Techniques
Data Communication Techniques
Data Link Control, ATM
Multiplexing, Switching, Routing
Spread Spectrum, Wireless Networks
Local and Wide Area Networks
Introductory Lecture

2. Course Overview Data Communication Networks and Open System Standards
Data Transmission
Data Link Controls
Technologies of Local Area Networks and Wide Area Networks
Communication Architecture and Protocols

3. Course Objectives
The aim of this course is to provide a unified overview in the basic principles of data communications and computer networks.
The lectures emphasize basic principles and topics of fundamental importance concerning the technology and architecture of this field, as well as providing the state of the art topics.

4. Course Objectives Followings are the basic objectives :
To provide a conceptual foundation for the study of data communications using the Open Systems Interconnect (OSI) model for layered architecture
To develop an understanding in basic hardware and software environments for data communications and computer networks

5. Text Books
Data and Computer Communications, 7th Edition, Prentice Hall, 2004
by William Stallings
Data Communication and Networking, 3rd Edition, McGraw- Hill, 2004
by Behrouz A. Forouzan

6. Course Website

7. Class Schedule [Tuesdays 4~6 / 6~9]
No.
Lecture Topics
Text's slides 1
Course Orientation, Overview
chapter 1, chapter 2 2
Data Transmission, Media
chapter 3, chapter 4 3
Signal Encoding Techniques
chapter 5 4
Data Communication Techniques
chapter 6 5
Data Link Control
chapter 7 6
Multiplexing
chapter 8 7
Spread Spectrum
chapter 9 8
Circuit and Packet Switching, ATM
chapter 10 9
Routing/Congestion Control in Switched Networks
chapter 12, chapter 13 10
Cellular Wireless Networks
chapter 14 11
LANs
chapter 15 12
High Speed LANs
chapter 16 13
Class Summary

8. Overview

9. Simplified Communications Model
Source
Generates data to be transmitted
Transmitter
Converts data into transmittable signals
Transmission System
Carries data
Receiver
Converts received signal into data
Destination
Takes incoming data

10. Simplified Communications Model - Diagram

11. Simplified Data Communications Model

12. Networking Point to point communication not usually practicalB
Point to point communication not usually practical
Devices are too far apart
Large set of devices would need impractical number of connections
Solution is a communications network
Wide Area Network (WAN)
Local Area Network (LAN)

13. Connecting N users: Directly ...
Bus: broadcast, collisions, media access control
Full mesh: Cost vs simplicity
. . .
Bus
Full mesh
Address concept needed if we want the receiver alone to consume the packet!

14. Connecting N users: Indirectly
Star: One-hop path to any node, reliability, forwarding function
“Switch” S can filter and forward!
Switch may forward multiple packets in parallel for additional efficiency!
Star S

15. Connecting N users: Indirectly …
Ring: Reliability to link failure, near-minimal links
All nodes do “forwarding” and “filtering”
Ring

16. Topologies: Indirect Connectivity
Ring
Star
Tree

17. Inter-Networks: Networks of Networks… …
Internet = … …
Our goal is to design this black box on the right

18. Wide Area Networks Large geographical area
Crossing public rights of way
Rely in part on common carrier circuits
Alternative technologies
Circuit switching
Packet switching
Frame relay
Asynchronous Transfer Mode (ATM)

19. Circuit Switching
Dedicated communications path established for the duration of the conversation
e.g. telephone network

20. Packet Switching Data sent out of sequence
Small chunks (packets) of data at a time
Packets passed from node to node between source and destination
Used for terminal to computer and computer to computer communications

21. Frame Relay
Packet switching systems have large overheads to compensate for errors
Modern systems are more reliable
Errors can be caught in end system
Most overhead for error control is stripped out

22. Asynchronous Transfer Mode
ATM
Evolution of frame relay
Little overhead for error control
Fixed packet (called cell) length
Anything from 10Mbps to many Gbps
Constant data rate using packet switching technique

23. Local Area Networks Smaller scope Building or small campus
Usually owned by same organization as attached devices
Data rates much higher
Usually broadcast systems
Now some switched systems and ATM are being introduced

24. LAN Configurations Switched Switched Ethernet
May be single or multiple switches
ATM LAN
Fibre Channel
Wireless
Mobility
Ease of installation

25. Metropolitan Area Networks
MAN
Middle ground between LAN and WAN
Private or public network
High speed
Large area

26. Networking Configuration

27. Further Reading
Stallings, W. [2003] Data and Computer Communications (7th edition), Prentice Hall, Upper Saddle River NJ, Chapter 1
Web site for Stallings book

28. Protocols and Architecture

29. Need For Protocol Architecture
E.g. File transfer
Source must initiate communications. Find Path or inform network of destination
Source must check destination is prepared to receive
File transfer application on source must check destination file management system will accept and store file for his user
May need file format translation
Task broken into subtasks
Implemented separately in layers in stack
Functions needed in both systems
Peer layers communicate

30. Key Elements of a Protocol
Syntax
Data formats
Signal levels
Semantics
Control information
Error handling
Timing
Speed matching
Sequencing

31. Protocol Architecture
Task of communication broken up into modules
For example file transfer could use three modules
File transfer application
Communication service module
Network access module

32. Simplified File Transfer Architecture

33. A Three Layer Model Network Access Layer Transport Layer
Application Layer

34. Network Access Layer
Exchange of data between the computer and the network
Sending computer provides address of destination
May invoke levels of service
Dependent on type of network used (LAN, packet switched etc.)

35. Transport Layer Reliable data exchange
Independent of network being used
Independent of application

36. Application Layer Support for different user applications
e.g. , file transfer

37. Protocol Architectures and Networks

38. Addressing Requirements
Two levels of addressing required
Each computer needs unique network address
Each application on a (multi-tasking) computer needs a unique address within the computer
The service access point or SAP
The port on TCP/IP stacks

39. Protocols in Simplified Architecture

40. Protocol Data Units (PDU)
At each layer, protocols are used to communicate
Control information is added to user data at each layer
Transport layer may fragment user data
Each fragment has a transport header added
Destination SAP
Sequence number
Error detection code
This gives a transport protocol data unit

41. Protocol Data Units

42. Network PDU Adds network header
network address for destination computer
Facilities requests

43. Operation of a Protocol Architecture

44. Standardized Protocol Architectures
Required for devices to communicate
Vendors have more marketable products
Customers can insist on standards based equipment
Two standards:
OSI Reference model
Never lived up to early promises
TCP/IP protocol suite
Most widely used
Also: IBM Systems Network Architecture (SNA)

45. OSI Open Systems Interconnection
Developed by the International Organization for Standardization (ISO)
Seven layers
A theoretical system delivered too late!
TCP/IP is the de facto standard

46. OSI - The Model A layer model
Each layer performs a subset of the required communication functions
Each layer relies on the next lower layer to perform more primitive functions
Each layer provides services to the next higher layer
Changes in one layer should not require changes in other layers

47. OSI Layers

48. The OSI Environment

49. OSI as Framework for Standardization

50. Layer Specific Standards

51. Elements of Standardization
Protocol specification
Operates between the same layer on two systems
May involve different operating system
Protocol specification must be precise
Format of data units
Semantics of all fields
allowable sequence of PDUs
Service definition
Functional description of what is provided
Addressing
Referenced by SAPs

52. Service Primitives and Parameters
Services between adjacent layers expressed in terms of primitives and parameters
Primitives specify function to be performed
Parameters pass data and control info

53. Primitive Types REQUEST
A primitive issued by a service user to invoke some service and to pass the parameters needed to specify fully the requested service
INDICATION
A primitive issued by a service provider either to:
indicate that a procedure has been invoked by the peer service user on the connection and to provide the associated parameters, or
notify the service user of a provider-initiated action
RESPONSE
A primitive issued by a service user to acknowledge or complete some procedure previously invoked by an indication to that user
CONFIRM
A primitive issued by a service provider to acknowledge or complete some procedure previously invoked by a request by the service user

54. Timing Sequence for Service Primitives

55. OSI Layers (1) Physical Physical interface between devices Mechanical
Electrical
Functional
Procedural
Data Link
Means of activating, maintaining and deactivating a reliable link
Error detection and control
Higher layers may assume error free transmission

56. OSI Layers (2) Network Transport of information
Higher layers do not need to know about underlying technology
Not needed on direct links
Transport
Exchange of data between end systems
Error free
In sequence
No losses
No duplicates
Quality of service

57. OSI Layers (3) Session Control of dialogues between applications
Dialogue discipline
Grouping
Recovery
Presentation
Data formats and coding
Data compression
Encryption
Application
Means for applications to access OSI environment

58. Use of a Relay

59. TCP/IP Protocol Architecture
Developed by the US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET)
Used by the global Internet
No official model but a working one.
Application layer
Host to host or transport layer
Internet layer
Network access layer
Physical layer

60. Physical Layer
Physical interface between data transmission device (e.g. computer) and transmission medium or network
Characteristics of transmission medium
Signal levels
Data rates
etc.

61. Network Access Layer Exchange of data between end system and network
Destination address provision
Invoking services like priority

62. Internet Layer (IP) Systems may be attached to different networks
Routing functions across multiple networks
Implemented in end systems and routers

63. Transport Layer (TCP)
Reliable delivery of data
Ordering of delivery

64. Application Layer
Support for user applications
e.g. http, SMTP

65. OSI v TCP/IP

66. TCP Usual transport layer is Transmission Control Protocol
Reliable connection
Connection
Temporary logical association between entities in different systems
TCP PDU
Called TCP segment
Includes source and destination port (c.f. SAP)
Identify respective users (applications)
Connection refers to pair of ports
TCP tracks segments between entities on each connection

67. UDP Alternative to TCP is User Datagram Protocol
Not guaranteed delivery
No preservation of sequence
No protection against duplication
Minimum overhead
Adds port addressing to IP

68. TCP/IP Concepts

69. Addressing level Level in architecture at which entity is named
Unique address for each end system (computer) and router
Network level address
IP or internet address (TCP/IP)
Network service access point or NSAP (OSI)
Process within the system
Port number (TCP/IP)
Service access point or SAP (OSI)

70. Trace of Simple Operation
Process associated with port 1 in host A sends message to port 2 in host B
Process at A hands down message to TCP to send to port 2
TCP hands down to IP to send to host B
IP hands down to network layer (e.g. Ethernet) to send to router J
Generates a set of encapsulated PDUs

71. PDUs in TCP/IP

72. Example Header Information
Destination port
Sequence number
Checksum

73. Some Protocols in TCP/IP Suite

74. Required Reading
Stallings, W. [2003] Data and Computer Communications (7th edition), Prentice Hall, Upper Saddle River NJ, Chapter 2
Web site for Stallings book
RFCs from Internet

75. Q&A ?