Data and Computer Data and Computer
Communications Communications
Chapter 1 –
Chapter 1 – Data Communications, Data Communications, Data Networks, and the Internet
Data Networks, and the Internet
Data Communications, Data Data Communications, Data
Networks, and the Internet Networks, and the Internet
The fundamental problem of The fundamental problem of
communication is that of reproducing at communication is that of reproducing at
one point either exactly or approximately a one point either exactly or approximately a
message selected at another point
message selected at another point - - The The Mathematical Theory of Communication Mathematical Theory of Communication , ,
Claude Shannon
Claude Shannon
Contemporary Data Comms Contemporary Data Comms
trends trends
traffic growth at a high & steady rate traffic growth at a high & steady rate
development of new services development of new services
advances in technology advances in technology
significant change in requirements significant change in requirements
emergence of high-speed LANs emergence of high-speed LANs
corporate WAN needs corporate WAN needs
digital electronics digital electronics
A Communications Model
A Communications Model
Communications Tasks Communications Tasks
Transmission system utilization Addressing
Interfacing Routing
Signal generation Recovery
Synchronization Message formatting Exchange management Security
Error detection and correction Network management
Flow control
Data Communications Model
Data Communications Model
Transmission Medium Transmission Medium
selection is a basic choice selection is a basic choice
internal use entirely up to business internal use entirely up to business
long-distance links made by carrier long-distance links made by carrier
rapid technology advances change mix rapid technology advances change mix
fiber optic fiber optic
wireless wireless
transmission costs still high transmission costs still high
hence interest in efficiency improvements hence interest in efficiency improvements
Networking Networking
growth of number & power of computers is growth of number & power of computers is driving need for interconnection
driving need for interconnection
also seeing rapid integration of voice, also seeing rapid integration of voice, data, image & video technologies
data, image & video technologies
two broad categories of communications two broad categories of communications networks:
networks:
Local Area Network (LAN) Local Area Network (LAN)
Wide Area Network (WAN) Wide Area Network (WAN)
Wide Area Networks Wide Area Networks
span a large geographical area span a large geographical area
cross public rights of way cross public rights of way
rely in part on common carrier circuits rely in part on common carrier circuits
alternative technologies used include: alternative technologies used include:
circuit switching circuit switching
packet switching packet switching
frame relay frame relay
Asynchronous Transfer Mode (ATM) Asynchronous Transfer Mode (ATM)
Circuit Switching Circuit Switching
uses a dedicated communications path uses a dedicated communications path established for duration of conversation established for duration of conversation
comprising a sequence of physical links comprising a sequence of physical links
with a dedicated logical channel with a dedicated logical channel
eg. telephone network eg. telephone network
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 packets passed from node to node between source and destination
between source and destination
used for terminal to computer and used for terminal to computer and
computer to computer communications
computer to computer communications
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
Frame Relay provides higher speeds Frame Relay provides higher speeds
with most error control overhead removed with most error control overhead removed
Asynchronous Transfer Mode Asynchronous Transfer Mode
ATM ATM
evolution of frame relay evolution of frame relay
fixed packet (called cell) length fixed packet (called cell) length
with little overhead for error control with little overhead for error control
anything from 10Mbps to Gbps anything from 10Mbps to Gbps
constant data rate using packet switching constant data rate using packet switching technique with multiple virtual circuits
technique with multiple virtual circuits
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
switched LANs, eg Ethernet switched LANs, eg Ethernet
wireless LANs wireless LANs
Metropolitan Area Networks Metropolitan Area Networks
MAN MAN
middle ground between LAN and WAN middle ground between LAN and WAN
private or public network private or public network
high speed high speed
large area large area
The Internet The Internet
Internet evolved from ARPANET Internet evolved from ARPANET
first operational packet network first operational packet network
applied to tactical radio & satellite nets also applied to tactical radio & satellite nets also
had a need for interoperability had a need for interoperability
