Data and Computer
Communications
Chapter 1 – Data Communications,
Data Networks, and the Internet
Ninth Edition
by William Stallings
Data Communications, Data
Networks, and the Internet
“The fundamental problem of
communication is that of reproducing at
one point either exactly or approximately a
message selected at another point”
- The Mathematical Theory of
Communication,
Claude Shannon
Message
Message
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.
1.3
Figure 1.1 Five components of data communication
1.4
Figure 1.2 Data flow (simplex, half-duplex, and full-duplex)
1.5
1-2 NETWORKS
A network is a set of devices (often referred to as nodes)
connected by communication links. A node can be a
computer, printer, or any other device capable of sending
and/or receiving data generated by other nodes on the
network.
1.6
Figure 1.3 Types of connections: point-to-point and multipoint
1.7
Technological Advancement
Driving Forces
Traffic
growth at
a high &
steady
rate
• Development of
new services
• Advances in
technology
Changes in Networking
Technology
* Emergence of high-speed LANs
* Corporate WAN needs
* Digital electronics
Convergence
 The
merger of previously distinct telephony
and information technologies and markets
 Layers:
• applications
• these are seen by the end users
• enterprise services
• services the information network supplies to support
applications
• infrastructure
• communication links available to the enterprise
Convergence Layers
Benefits
Convergence benefits include:
Efficiency
Effectiveness
Transformation
• better use of
existing
resources, and
implementation
of centralized
capacity
planning, asset
and policy
management
• the converged
environment
provides users
with flexibility,
rapid
standardized
service
deployment and
enhanced
remote
connectivity
and mobility
• enables the
enterprise-wide
adoption of
global
standards and
associated
service levels
Communications Model
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
Transmission Lines
Capacity
The basic building block of
any communications facility
is the transmission line.
The business manager is
concerned with a facility
providing the
required capacity,
with acceptable reliability,
at minimum cost.
Reliability
Cost
Transmission
Line
Two mediums currently driving
the evolution of data communications
transmission are:
and
Networking
Advances in technology have led to greatly
increased capacity and the concept of
integration, allowing equipment and
networks to work simultaneously.
Voice
Data
Image
Video
Network Hardware
Classifying networks based on their scale:
 Local
Area Networks
 Metropolitan Area Networks
 Wide Area Networks
 Wireless Networks
 Home Networks
 Internetworks
18
Network Hardware
19
LANs and WANs
There are two broad categories
of networks:
Local Area Networks (LAN)
Wide Area Networks (WAN)
Wide Area Networks (WANs)
 Span
a large geographical area
 Require
 Rely
the crossing of public right-of-ways
in part on common carrier circuits
 Typically
consist of a number of
interconnected switching nodes
Wide Area Networks
Alternative technologies used include:




Circuit switching
Packet switching
Frame relay
Asynchronous Transfer Mode (ATM)
Circuit Switching
 Uses
a dedicated communications path
 Connected sequence of physical links
between nodes
 Logical channel dedicated on each link
 Rapid transmission
 The most common example of circuit
switching is the telephone network
Network Hardware
Wide Area Networks
24
Packet Switching
 Data
are sent out in a sequence of small
chunks called packets
 Packets are passed from node to node
along a path leading from source to
destination
 Packet-switching networks are commonly
used for terminal-to-terminal computer and
computer-to-computer communications
Asynchronous Transfer Mode
(ATM)
 Referred
to as cell relay
 Culmination of circuit switching and packet
switching
 Uses fixed-length packets called cells
 Works in range of 10’s and 100’s of Mbps
and in the Gbps range
 Data rate on each channel dynamically set
on demand
Local Area Networks (LAN)
Metropolitan Area Networks
(MAN)
Network Hardware
Wireless Networks
Categories of wireless networks:
 System interconnection
 Wireless LANs
 Wireless WANs
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Network Hardware
Wireless Networks
 System

interconnection
Bluetooth a short-range wireless network. Allows
system components together, digital cameras,
headsets, scanners, and other devices to connect to a
computer by merely being brought within range.
 Wireless


LANs
Every computer has a radio modem and antenna with
which it can communicate with other systems.
Standard for wireless LANs: IEEE 802.11, which most
systems implement and which is becoming very
widespread.
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Network Hardware
Wireless Networks
Wireless


WANs (cont.)
Wireless LANs an operate at rates up
to about 50 Mbps over distances of
tens of meters. While cellular systems
(Wireless WANs) operate below 1
Mbps, but the distance between the
base station and the computer or
telephone is measured in kilometers
rather than in meters.
High-bandwidth wide area wireless
networks are also being developed
(IEEE 802.16).
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The Internet
 Internet
evolved from ARPANET
 Developed to solve the dilemma of
communicating across arbitrary, multiple,
packet-switched network
 TCP/IP provides the foundation
Internet Key Elements
Internet Architecture
Figure 1.11 WANs: a switched WAN and a point-to-point WAN
1.35
Figure 1.12 A heterogeneous network made of four WANs and two LANs
1.36
Figure 1.13 Hierarchical organization of the Internet
1.37