Data and Computer
Data and Computer
Communications
Communications
Chapter 1
Chapter 1
Introduction
Introduction
The main topics of this book:
The main topics of this book:
Exchange of data between
Exchange of data between
two directly
two directly
Connected devices
Connected devices
Transmission
Transmission
interfacing
interfacing
data link control
data link control
multiplexing
multiplexing
Net connection
Net connection


WAN
WAN



LAN
LAN
Protocol
Protocol


Protocol architecture
Protocol architecture
Data communication
Data communication
PLAN OF THE TEXT
PLAN OF THE TEXT
Overview
Overview


Introduction of the topics
Introduction of the topics


Discussion of protocols
Discussion of protocols
Data Communication
Data Communication


Exchange of data/transmission/interfacing/link control/multiplex
Exchange of data/transmission/interfacing/link control/multiplex
ing

ing
Wide Area Networks
Wide Area Networks


Switching technologies (packet switching/circuit switching/ATM)
Switching technologies (packet switching/circuit switching/ATM)


Congestion control
Congestion control
Local Area Networks
Local Area Networks


Transmission media
Transmission media


Topologies
Topologies


Medium access control protocols
Medium access control protocols


Specific standardized LAN systems
Specific standardized LAN systems
Networking Protocols

Networking Protocols


Protocol architecture
Protocol architecture
Chapter 1 introduction
Chapter 1 introduction
Computer science
Data communication
merge1970s ~ 1980s
Data communication
Voice communication
No fundamental
diferences
Data processing equipment
Data communication equipment
Video communication
Single-processor computer
Multi-processor computer
LAN、MAN、WAN
A Communications Model
A Communications Model
Source
Source


generates data to be transmitted
generates data to be transmitted
Transmitter
Transmitter



Converts data into transmittable signals
Converts data into transmittable signals
Transmission System
Transmission System


Carries data
Carries data
Receiver
Receiver


Converts received signal into data
Converts received signal into data
Destination
Destination


Takes incoming data & process
Takes incoming data & process
Simplified Communications
Simplified Communications
Model
Model
-
-
Diagram
Diagram

Key Communications Tasks
Key Communications Tasks
Transmission System Utilization
Transmission System Utilization
Interfacing
Interfacing
Signal Generation
Signal Generation
Synchronization
Synchronization
Exchange Management
Exchange Management
Error detection and correction
Error detection and correction
Addressing and routing
Addressing and routing
Recovery
Recovery
Message formatting
Message formatting
Security
Security
Network Management
Network Management
Simplified Data
Simplified Data
Communications Model
Communications Model
Networking
Networking

Point to point communication not usually
Point to point communication not usually
practical
practical


Devices are too far apart
Devices are too far apart


Large set of devices would need impractical
Large set of devices would need impractical
number of connections
number of connections
Solution is a communications network
Solution is a communications network
Simplified Network Model
Simplified Network Model
Wide Area Networks
Wide Area Networks
Large geographical area
Large geographical area
Crossing public rights of ways
Crossing public rights of ways
Rely in part on common carrier circuits
Rely in part on common carrier circuits
Alternative technologies
Alternative technologies



Circuit switching
Circuit switching


Packet switching
Packet switching


Frame relay
Frame relay


Asynchronous Transfer Mode (ATM)
Asynchronous Transfer Mode (ATM)


ISDN
ISDN
Circuit Switching
Circuit Switching
Dedicated communications path established
Dedicated communications path established
for the duration of the conversation
for the duration of the conversation
e.g. telephone network
e.g. telephone network
Reliability is good
Reliability is good
Time delay is short
Time delay is short

Packet Switching
Packet Switching
Data sent out of sequence
Data sent out of sequence
Small chunks (packets) of data at a time
Small chunks (packets) of data at a time
Packets passed from node to node between
Packets passed from node to node between
source and destination
source and destination
Used for terminal to computer and computer to
Used for terminal to computer and computer to
computer communications
computer communications
Unreliable communications
Unreliable communications
No fixed connection
No fixed connection
Time delay is long
Time delay is long
Frame Relay
Frame Relay
Packet switching systems have large
Packet switching systems have large
overheads to compensate for errors
overheads to compensate for errors
Modern systems are more reliable
Modern systems are more reliable
Errors can be caught in end system
Errors can be caught in end system

Most overhead for error control is stripped
Most overhead for error control is stripped
out
out
Asynchronous Transfer Mode
Asynchronous Transfer Mode
ATM
ATM
Evolution of frame relay
Evolution of frame relay
Little overhead for error control
Little overhead for error control
Fixed packet (called cell) length
Fixed packet (called cell) length
Anything from 10Mbps to
Anything from 10Mbps to
Gbps
Gbps
Constant data rate using packet switching
Constant data rate using packet switching
technique
technique
Integrated Services Digital
Integrated Services Digital
Network
Network
ISDN
ISDN
Designed to replace public telecom
Designed to replace public telecom

system
system
Wide variety of services
Wide variety of services
Entirely digital domain
Entirely digital domain
Local Area Networks
Local Area Networks
Smaller scope
Smaller scope


Building or small campus
Building or small campus
Usually owned by same organization as
Usually owned by same organization as
attached devices
attached devices
Data rates much higher
Data rates much higher
Usually broadcast systems
Usually broadcast systems
Now some switched systems and ATM are
Now some switched systems and ATM are
being introduced
being introduced
Protocols
Protocols
A set of rules governing the exchange of data
A set of rules governing the exchange of data

between two entities in different systems
between two entities in different systems
Must speak the same language
Must speak the same language
Entities
Entities


User applications
User applications


e
e
-
-
mail facilities
mail facilities


terminals
terminals
Systems
Systems


Computer
Computer



Terminal
Terminal


Remote sensor
Remote sensor
Entity and System Model
Entity and System Model
Network
system system
entity entity
Key Elements of a Protocol
Key Elements of a Protocol
Syntax
Syntax
（语法）
（语法）


Data formats
Data formats


Signal levels
Signal levels
Semantics
Semantics
（语义）
（语义）



Control information
Control information


Error handling
Error handling
Timing
Timing
（定时）
（定时）


Speed matching
Speed matching


Sequencing
Sequencing
Characteristics of protocols
Characteristics of protocols
Direct/Indirect
Direct/Indirect
Monolithic/Structured
Monolithic/Structured
Symmetric/asymmetric
Symmetric/asymmetric
Standard/nonstandard
Standard/nonstandard
Protocol Architecture

Protocol Architecture
Task of communication broken up into
Task of communication broken up into
modules
modules
For example file transfer could use three
For example file transfer could use three
modules
modules


File transfer application
File transfer application


Communication service module
Communication service module


Network access module
Network access module
Simplified File Transfer
Simplified File Transfer
Architecture
Architecture
A Three Layer Model
A Three Layer Model
Network Access Layer
Network Access Layer
Transport Layer

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