CSCI-235
Micro-Computer in Science
The Network
Communications

Communication is the process
of sending and receiving
messages

Communication channels are
the paths through which
messages are passed

Communication devices
transform electronic signals
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Five components of data communication
1.3
Data flow (simplex, half-duplex, and full-duplex)
1.4
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.
Types of connections: point-to-point and multipoint
1.6
Categories of topology
1.7
A fully connected mesh topology (five devices)
1.8
Figure 1.6 A star topology connecting four stations
1.9
A bus topology connecting three stations
1.10
A ring topology connecting six stations
1.11
A hybrid topology: a star backbone with three bus networks
1.12
An isolated LAN connecting 12 computers to a hub in a closet
1.13
A heterogeneous network made of four WANs and two LANs
1.14
Data Rate and Bandwidth
 Any
transmission system has a limited
band of frequencies
 This limits the data rate that can be carried
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Bandwidth
 Bandwidth
is usually used to refer to the
data rate (i.e., the amount of data that can
be transmitted through a communications
channel)
 Digital bandwidth is measured in bits per
second (bps), kilobits per second (Kbps),
megabits per second (Mbps), or gigabits
per second (Gbps)
 Low bandwidth is 56 Kbps and high
bandwidth is 622 Mbps
Protocol
 Protocols
are fixed, formalized standards that
specify how computers can communicate over
a network
 Set of conventions between two entities
involved in a communication
 Elements



syntax : data format and signal levels
concerns the format of the data blocks
semantics : include control information for
coordination and error handling
timing : speed matching and sequencing
Protocol Architecture
 Software
structure that implements the
communication function
 Consists of a layered set of protocols
 Separate layers or protocols implemented
in separate modules
 Different applications have different
requirements at each layer
Tasks involved in sending a letter
2.19
Seven layers of the OSI model
2.20
The interaction between layers in the OSI model
2.21
An exchange using the OSI model
2.22
Physical layer
2.23
Modems: From Digital to Analog
and Back
Modulation
Analog
Digital
Demodulation
Analog

Digital
Modems are devices that transform signals when
sending and receiving transmissions

Modulation – Transforming digital signals to analog

Demodulation – Transforming analog signals to digital
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Switching and Routing Techniques
Circuit switching
 Networks create an endto-end circuit between the
sending and receiving
computers
 Electronic switches
establish and maintain
the connection
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


Packet switching
Outgoing messages are
divided into fixed-size
data units called packets
Packets are numbered
and addressed to the
receiving computer
Routers examine the
packets and send them to
their destination
CIRCUIT SWITCHING
Telephone Node
OUT
Telephone Node
IN
OUT
IN
Advantages and Disadvantages
of Circuit and Packet Switching
Advantages
Disadvantages
Costly
Voice and real-time A direct electrical
Circuit switching transmission
connection between
No delivery delays the computers is
required
Efficient, less
expensive, and
reliable
Packet switching
Will function if part
of the network is
down
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Delays in receiving
packets
Not ideal for realtime voice
communication
Data link layer
2.28
Hop-to-hop delivery
2.29
Network layer
2.30
Source-to-destination delivery
2.31
Transport layer
2.32
Reliable process-to-process delivery of a message
2.33
Session layer
2.34
Presentation layer
2.35
Application layer
2.36
Summary of layers
2.37
TCP/IP and OSI model
2.38
Types of Computer Networks
Local Area Network
(LAN)
 Links computers within a
Wide Area Network
(WAN)

Links computers separated
by a few miles or
thousands of miles

Uses long-distance
transmission media
building or group of
buildings
 Uses direct cables, radio,
or infrared signals
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Local Area Networks (LANs)
 Network
access is controlled by a network
administrator
 Users
can access software, data, and
peripherals

LANs require special hardware and software
 Computers
connected to a LAN are called
workstations or nodes
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LAN Hardware and Software
Networking Hardware
Networking Software
 Network interface card (NIC)  Operating system that
– Provides the connection
between the computer and
the network
 Inserted into a computer’s
expansion slot
NIC
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supports networking (Unix,
Linux, Windows, Mac OS)
 Additional system
software
Client-Server Networks
 Typical corporate networks are client-server
 Clients send requests to servers for programs
and data, and to access peripherals
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Peer-to-Peer Networks
 All computers on the network are treated as
equal
 Users decide which files and peripherals to
share
 Peer-to peer is not suited for networks with
many computers
 Peer-to-peer is easy to set up. Example: home
networks
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Wide Area Networks (WANs)

WANs are similar to long-distance
telephone systems
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WAN Applications
LAN-to-LAN
 WANs are used to connect LANs at two or
more geographic locations
 Companies
use WANs to connect their
branches to one network system
 The
largest WAN is the Internet
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