Living in a Network
Centric World
IT305: Computer Networks – Chapter 1
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
1
Course Info
 Dr. Walid Khedr, Ph.D.
–Email: khedrw@yahoo.com
–Web: www.staff.zu.edu.eg/wkhedr
–Department of Information Technology
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Contents
1. Living in a Network-Centric World
2. Communicating over the Network
3. Application Layer Functionality and Protocols
4. OSI Transport Layer
5. OSI Network Layer
6. Addressing the Network IPv4
7. Data Link Layer
8. OSI Physical Layer
9. Ethernet
10. Planning and Cabling Networks
11. Configuring and Testing Your Network
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Introduction
 Among all of the essentials for human existence is the
need to interact with others.
 Communication is almost as important to us as our
reliance on air, water, food.
 The creation and interconnection of robust Data
Networks is having a profound effect.
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Data Networks
 Current data networks have evolved to carry voice, video streams, text,
and graphics between many different types of devices
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Communication
 It can be in many forms and occurs in many
environments
 Before beginning to communicate with each other, we
establish rules or agreements to govern the
conversation. (Protocols)
 Among the protocols that govern successful human
communication are:
– An identified sender and receiver
– Agreed upon method of communicating (face-to-face,
telephone, letter, photograph)
– Common language and grammar
– Speed and timing of delivery
– Confirmation or acknowledgement requirements
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The Elements of Digital Communication
 Message sources devices that need to send a message to
devices.
 A channel, consists of the media that provides the pathway over
which the message can travel from source to destination.
 Messages can be sent across a network by first converting them
into binary digits, or bits. These bits are then encoded into a signal
that can be transmitted over the appropriate medium.
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A Closer Look at Network Structure
Network
Structure
Hardware
Software
Devices
Network Edge
(intermediary devices)
Media
Network Core
(End Devices
Wired
Wireless
Service
Proccess
Protocols
Applications
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Network Edge (End Devices)
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The Network Core and Intermediary Devices
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Network Core
 Mesh of interconnected routers that
connect the Internet’s end systems.
 The fundamental question: how is
data transferred through net?
–Circuit Switching: dedicated
circuit per call: telephone net
–Packet-Switching: data sent thru
net in discrete “chunks”
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Network Core: Circuit Switching
 A circuit-switched network is one that establishes a
dedicated circuit (or channel) between nodes and
terminals before the users may communicate.
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Network Core: Circuit Switching
 The four circuit switches are interconnected by four links.
 Each of these links consists of n circuits, so that each link can
support n simultaneous connections.
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Multiplexing Circuit Switching
 Frequency Spectrum: the difference between the highest and
lowest frequencies available for network signals.
 Frequency Division Multiplexing (FDM): The frequency spectrum of
a link is shared among the connections established across the link.
–The link dedicates a frequency band to each connection for the
duration of the connection.
 Time Division Multiplexing (TDM): Time is divided into frames of
fixed duration and each frame is divided into a fixed number of
time slots.
–When the network establish a connection across a link, the network
dedicates one time slot in every frame to the connection.
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Multiplexing Circuit Switching
Example:
FDM
4 users
frequency
time
TDM
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
frequency
Frame
time
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Network Core: Packet Switching
 Packet switching splits traffic data into packets that are routed over a
shared network.
 Packet-switching networks do not require a circuit to be established, and
they allow many pairs of nodes to communicate over the same channel.
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Multiplexing Packet Switching
 STDM method analyzes statistics related to the typical workload of
each input device (printer, fax, computer) and determines on-thefly how much time each device should be allocated for data
transmission on the cable or line.
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Four sources of packet delay
transmission
A
propagation
B
nodal
processing
queueing
dnodal = dproc + dqueue + dtrans + dprop
dtrans: transmission delay:
 L: packet length (bits)
 R: link bandwidth (bps)
 dtrans = L/R
dtrans and dprop
very different
dprop: propagation delay:
 d: length of physical link
 s: propagation speed in medium
(~2x108 m/sec)
 dprop = d/s
* Check out the Java applet for an interactive animation on trans vs. prop delay
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Communicating Over Networks
 All networks have four basic elements in common:
– Rules or agreements to govern how the messages are sent,
directed, received and interpreted
– The messages or units of information that travel from one
device to another
– A means of interconnecting these devices - a medium that
can transport the messages from one device to another
– Devices on the network that exchange messages with each
other
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The Elements of a Network
 Devices
– These are used to
communicate with one
another
 Medium
– This is how the devices
are connected together
 Messages
– Information that travels
over the medium
 Rules
– Governs how messages
flow across network
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The Elements of a Network
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The Elements of a Network
 Network connections can be wired or wireless
 Cable: UTP, Coaxial, Optic Fibers etc
 Wireless: Bluetooth, laser, microwave etc
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The Elements of a Network
 Protocols are the rules that the networked devices use
to communicate with each other. The industry standard
in networking today is a set of protocols called TCP/IP
(Transmission Control Protocol/Internet Protocol).
 On the top of TCP/IP:
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The Elements of a Network
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The Elements of a Network
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The Elements of a Network
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The Elements of a Network
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The Elements of a Network
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The Elements of a Network
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The Elements of a Network
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Converged Networks
 Traditional telephone, radio, television, and computer
data networks each have their own individual versions
of the four basic network elements.
 In the past, every one of these services required a
different technology to carry its particular
communication signal.
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Converged Networks
 Technology advances are enabling us to consolidate
these disparate networks onto one platform - a platform
defined as a converged network.
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Network Architecture Characteristics
 There are 4 basic characteristics for networks in
general to meet user expectations
– Fault tolerance
– Scalability
– Quality of service (QoS)
– Security
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A Fault Tolerant Network Architecture
 Fault tolerance is the ability for a network to recover
from an error, such as the failure of a device or a link (a
connection between two devices).
 Fault tolerance is often achieved by having redundant
devices or links, so that if one fails, messages can be
re-routed around the failure through other devices or
links.
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A Fault Tolerant Network Architecture
 Early network type: Circuit switched connectionoriented network
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A Fault Tolerant Network Architecture
 Packet switched networks, the data are broken up into many small
packets that are sent independently through the network, each
finding its own best route through the network.
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A Scalable Network Architecture
 Scalability means the ability to expand to meet new demands.
 Most networks are designed in a hierarchical, layered approach so
new devices and links can be added without interfering with
existing networks.
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Providing Quality of Service (QoS)
 Quality of Service is a control mechanism that can
provide different priority to different users or data flow
or guarantee a certain level of performance to a data
flow in accordance with request from the application
program.
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Providing Quality of Service (QoS)
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Providing Quality of Service (QoS)
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Providing Network Security
 Unauthorized use of communication data might have
serious consequences
 2 types of network security concerns that must be
addressed to prevent serious consequences:
– Network Infrastructure Security - physical securing of devices
that provide network connectivity and preventing unauthorized
access to the management software that resides on them
– Content Security - protecting the information contained within
the packets being transmitted over the network and the
information stored on network attached devices
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Providing Network Security
 Security measures taken in a network should:
– Prevent unauthorized disclosure or theft of information
– Prevent unauthorized modification of information
– Prevent Denial of Service
 Means to achieve these goals include:
– Ensuring confidentiality
– Maintaining communication integrity
– Ensuring availability
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Summary
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Reading
 Chapter 1 - Living in a Network-Centric World
 Packet Tracer Skills Integration Activity 1.7.1.3
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Next Lecture
 Chapter 2: Communicating over the Network
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Questions
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