Transcript - LearnGroup

Chapter 1
Introduction
1.1
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Course Information










1.2
Code
Name
Instructor
E-mail
Time
TA
Office Hours
Text 1
:
:
:
:
:
:
:
:
IT251
Data Communications
Ahmed Abo-Bakr, Ph.D.
[email protected]
Mondays 8 am – 11 am
TBA
BAO
Data Communications and Networking, 4/e
Behrouz A. Forouzan
Text 2
: Data and Computer Communications, 8/e
William Stallings Prentice Hall, 2007
Course Group:
[email protected]
Course Description





1.3
Brief introduction of networking; layers and protocols,
principles of data communications, the fundamentals of
signaling, basic transmission concepts, transmission media,
line sharing techniques, physical and data link layer protocols,
error detection and correction,
data compression, network security techniques, common
carrier services and data networks, and the mathematical
techniques used for network design and performance
analysis,
Potential topics include analog and digital signaling; data
encoding and modulation; Shannon channel capacity; FDM,
TDM, and STDM multiplexing techniques; inverse
multiplexing; analog and digital transmission; PCM encoding
and T1 transmission circuits;
Important Dates

Week (1), October 13th


Week (9), December 8th


Mid-Term Exam
Week (11), December 22nd

1.4
Warming Up, Introduction
Last Lecture
Assignments




1.5
Several homework sheets will be distributed
throughout the term via course group e-mail.
Late homework will be accepted if delivered no
more than one week of its due date. However,
late homework will be graded from 80%.
For example, if a late assignment is graded out of
10 pts and received 7/10, the grade will be
recorded as (0.8 × 7 ≈ 5.5 / 10)
Homework delivered after the “one-week”
allowance will NOT be accepted and will be
recorded as ZERO.
Contacts


1.6
Preferred way of getting in touch is
through educational e-mails ONLY which
will be answered promptly.
Educational e-mails are those e-mails
hosted at aun.edu.eg or compit.au.edu.eg
or fci.au.edu.eg
Grading




1.7
Students’ level will be evaluated according
to the work done throughout the term and
their grades will be distributed as follows:
Assignments
: 25
Mid-Term Exam(s): 25
Final Exam
: 50
How to activate your .edu e-mail?

1.8
http://195.246.49.215/mis/E_Mails.aspx
How to join educational groups?




1.9
www.mail.office365.com
Gear menu → Options
Groups → Join
Choose your group and
click on Join
DATA COMMUNICATIONS
1.10

1.11
Knowledge of data communications and
networking is crucial to today's IT
professional. Virtually all computers are
connected to some sort of network and
exchange information with each other.
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.
Topics discussed in this section:
 Components of a data communications system
 Data Flow
1.12


1.13
The purpose of Data Communications is to provide the rules and
regulations that allow computers with different operating
systems, languages, cabling and locations to share resources.
The rules and regulations are called protocols and standards in
Data Communications.
For data communications to occur, the communicating devices
must be part of a communication system made up of a
combination of hardware (physical equipment) and software
(programs). The effectiveness of a data communications system
depends on four fundamental characteristics: delivery, accuracy,
timeliness, and jitter.




1.14
Delivery. The system must deliver data to the correct destination. Data
must be received by the intended device or user and only by that
device or user.
Accuracy. The system must deliver the data accurately. Data that have
been altered in transmission and left uncorrected are unusable.
Timeliness. The system must deliver data in a timely manner. Data
delivered late are useless. In the case of video and audio, timely
delivery means delivering data as they are produced, in the same order
that they are produced, and without significant delay. This kind of
delivery is called real-time transmission.
Jitter. Jitter refers to the variation in the packet arrival time. It is the
uneven delay in the delivery of audio or video packets. For example, let
us assume that video packets are sent every 3D ms. If some of the
packets arrive with 3D-ms delay and others with 4D-ms delay, an
uneven quality in the video is the result.
Figure 1.1 Components of a data communication system
1.15
Figure 1.2 Data flow (simplex, half-duplex, and full-duplex)
1.16
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. A link can be a cable, air, optical fiber, or any
medium which can transport a signal carrying
information.
Topics discussed in this section:
 Network Criteria
 Physical Structures
 Categories of Networks
1.17
Network Criteria
A network must be able to meet a certain number of
criteria. The most important of these are performance,
reliability, and security

Performance



Reliability



Depends on Network Elements
Measured in terms of Delay and Throughput
Failure rate of network components
Measured in terms of availability/robustness
Security

Data protection against corruption/loss of data due to:


1.18
Errors
Malicious users
Physical Structures

Type of Connection



Physical Topology


1.19
Point to Point - single transmitter and receiver
Multipoint - multiple recipients of single transmission
Connection of devices
Type of transmission - unicast, mulitcast, broadcast
Figure 1.3 Types of connections: point-to-point and multipoint
1.20
Figure 1.4 Categories of topology
1.21
Figure 1.5 A fully connected mesh topology (five devices)
Number of links?!
Throughput
Robust
Secure
Installation
Wiring
Expensive
Each node is exactly connected to (n-1) nodes
1.22
n(n-1)/2
Figure 1.6 A star topology connecting four stations
Number of links?!
Robust
Installation
Less expensive
n links
CPF
(Central Point of Failure)
Each node requires a single link to the Hub
1.23
Figure 1.7 A bus topology connecting three stations
Installation
Less expensive
Fault isolation
Robustness
Degradation
Reconfiguration
Taps limitations
Single line and n (Taps + Drop line)
1.24
Figure 1.8 A ring topology connecting six stations
Installation
Less expensive
Fault tolerance
Device Limitations
Signals are unidirectional, repeaters regenerate bits until
received by the receiver
1.25
Figure 1.9 A hybrid topology: a star backbone with three bus networks
1.26
Categories of Networks

Local Area Networks (LANs)



Wide Area Networks (WANs)



Long distances (can be world-wide)
Provide connectivity over large areas
Metropolitan Area Networks (MANs)

1.27
Short distances (normally less than 2 mi)
Designed to provide local interconnectivity
Provide connectivity over areas such as a city, a campus
Figure 1.10 An isolated LAN connecting 12 computers to a hub in a closet
1.28
Figure 1.11 WANs: a switched WAN and a point-to-point WAN
1.29
Figure 1.12 A heterogeneous network made of four WANs and two LANs
1.30
1-3 THE INTERNET
The Internet has revolutionized many aspects of our daily
lives. It has affected the way we do business as well as the
way we spend our leisure time. The Internet is a
communication system that has brought a wealth of
information to our fingertips and organized it for our use.
Topics discussed in this section:
Organization of the Internet
Internet Service Providers (ISPs)
1.31
Figure 1.13 Hierarchical organization of the Internet
1.32
1-4 PROTOCOLS
A protocol is synonymous with rule. It consists of a set of
rules that govern data communications. It determines
what is communicated, how it is communicated and when
it is communicated. The key elements of a protocol are
syntax, semantics and timing
Topics discussed in this section:
 Syntax
 Semantics
 Timing
1.33
Elements of a Protocol

Syntax



Semantics



Interprets the meaning of the bits
Knows which fields define what action
Timing


1.34
Structure or format of the data
Indicates how to read the bits - field delineation
When data should be sent and what
Speed at which data should be sent or speed at which it is being
received.
Network Protocols
Hello
Hello
TCP connection request
TCP connection reply
What’s the time?
Request web page
2:00
1.35
Send the file
Protocol “Layers”
Networks are complex!
Question:
 many “pieces”:
Is there any hope of
 hosts
organizing structure
 routers
of network?
 links of various media
 applications
 protocols
 hardware, software
1.36
Organization of air travel
ticket (purchase)
ticket (complain)
baggage (check)
baggage (claim)
gates (load)
gates (unload)
runway takeoff
runway landing
airplane routing
airplane routing
airplane routing

1.37
a series of steps
Layering of airline functionality
ticket (purchase)
ticket (complain)
baggage (check)
baggage (claim
baggage
gates (load)
gates (unload)
gate
runway (takeoff)
runway (land)
takeoff/landing
airplane routing
airplane routing
airplane routing
departure
airport
airplane routing
airplane routing
intermediate air-traffic
control centers
arrival
airport
Layers: each layer implements a service
 via its own internal-layer actions
 relying on services provided by layer
below
1.38
ticket
Why layering?
Dealing with complex systems:



1.39
Explicit structure allows identification, relationship of
complex system’s pieces
 layered reference model for discussion
Modularization eases maintenance, updating of system
 change of implementation of layer’s service
transparent to rest of system
 e.g., change in gate procedure doesn’t affect rest of
system
Layering considered harmful?
Internet protocol stack

application: supporting network
applications


transport: host-host data transfer


1.40
IP, routing protocols
link: data transfer between
neighboring network elements


TCP, UDP
network: routing of datagrams
from source to destination


FTP, SMTP, HTTP
PPP, Ethernet
physical: bits “on the wire”
application
transport
network
link
physical
source
message
segment H
M
t
datagram H H
n t
frame H H H
l n t
M
M
Encapsulation
application
transport
network
M
link
physical
M
l n t
H H H
link
physical
l n t
H H H
M
switch
destination
M
t
H H
n t
H H H
l n t
H
1.41
M
M
M
application
transport
network
link
physical
n t
H H H
l n t
H H
M
M
network
link
physical
n t
H H H
l n t
H H
M
M
router
Network Layers
Application Layer
Transport Layer
Network Layer
Data Link Layer
Physical Layer
1.42
What is the Internet?



Millions of connected computing devices:
hosts = end systems
Running network apps
Communication links



1.43
fiber, copper, radio, satellite
transmission rate = bandwidth
Routers: forward packets (chunks of data)
HOW BIG IS THE INTERNET?
1.44
http://news.sciencemag.org/2011/05/scienceshotyou-are-here
BOSTON—Astronomers have produced the most
complete 3D map of the nearby universe to date.
Using telescopes in both hemispheres, they
measured distances to a whopping 45,000 galaxies
out to a distance of 380 million light-years—for the
astronomy buffs, a red shift of .07.
1.45
Outer Space
1.46
http://www.opte.org/
1.47
1.48
http://internet-map.net/
1.49