Transcript IT305: Computer Networks

Lecture 0: Course Overview
Lecturer Details
 Dr. Walid Khedr
 Email: [email protected]
 Web: www.staff.zu.edu.eg/wkhedr
 Department of Information Technology
Course Info
 Course Name: Computer Networks
 Course Number: IT305
 Course Group:
www.facebook.com/groups/it300305
 Office Hours: 11 am – 12 pm, Thursday
 Tools: Cisco Packet Tracer 6 simulator, Wireshark 1.1
protocol analyzer
 Prerequisite: CS260 (Operating Systems)
 Course Materials:
 Text Book
 Lecture Notes
Grading Policy
 Your final grade will be calculated as follows:
 Term Work: Assignments / Homework / Quizzes /
Midterm exam (20 points)
 Lab Exams (20 points)
 Oral Exam, Attendance and Participation (20 points)

How to participate?
 Ask questions
 Answer questions
 Make comments
 Total is 150 points
Grading Rules
1. Final exam is cancelled if attendance < %75
2. If final exam grade is less than %30, your final grade
will be just your final exam grade.
What is Computer Network
 A computer network or data network is a
telecommunications network which allows computers
to exchange data.
 In computer networks, networked computing devices
exchange data with each other along network links
(data connections).
 The connections between nodes are established using
either cable media or wireless media.
 The best-known computer network is the Internet.
Why computer networks is important
 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.
Why computer networks is important
 Current data networks have evolved to carry voice,
video streams, text, and graphics between many
different types of devices
Communication
 Before beginning to communicate with each other, we
establish rules or agreements to govern the
conversation.
 An identified sender and receiver
 Agreed upon method of communicating (face-to-face,
telephone, letter)
 Common language and grammar
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.
The Elements of Digital
Communication
The Elements of Digital
Communication
The Elements of Digital
Communication
The Elements of Digital
Communication
The Elements of Digital
Communication
The Elements of Digital
Communication
The Elements of Digital
Communication
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
The Elements of a Network
 Network Hardware
 Network Software
Network Hardware
 Network edge:
 hosts: clients and servers
 servers often in data centers
 Network core:
 interconnected routers
 switches
Network Media
 Communication across a network is carried on a
medium
 3 types of Media:
 Metallic wires within cables
 Glass or plastic fibers (fiber optic cable)
 Wireless transmission
Network Hardware
Networks can be classified by their scale:
Scale
Type
Vicinity
PAN (Personal Area Network) »
Building
LAN (Local Area Network) »
City
MAN (Metropolitan Area Network) »
Country
WAN (Wide Area Network) »
Planet
The Internet (network of all networks)
Personal Area Network
Connect devices over the range of a person
Example of a Bluetooth (wireless) PAN:
Local Area Networks
 Connect devices in a home or office building
 Called enterprise network in a company
Wireless LAN
with 802.11
Wired LAN with
switched Ethernet
Metropolitan Area Networks
Connect devices over a metropolitan area
Example MAN based on cable TV:
Wide Area Networks (1)
 Connect devices over a country
 Example WAN connecting three branch offices:
Wide Area Networks (2)
 An ISP (Internet Service Provider) network is also a
WAN.
 Customers buy connectivity from the ISP to use it.
Network Software
 Protocol layers »
 Service primitives »
 Relationship of services to protocols »
Rules that Govern Communications (Protocols)
 Communication in networks is governed by pre-defined
rules called protocols.
 These protocols are implemented in software and hardware
that is loaded on each host and network device
 Networking protocols suites describe processes such as:
 The format or structure of the message
How and when error and system messages are passed
between devices
 The setup and termination of data transfer sessions
Protocol
Layers
(1)
Protocol layering is the main structuring method used to
divide up network functionality.
•
Each protocol instance
talks virtually to its peer
• Each layer communicates
only by using the one
below
• Lower layer services are
accessed by an interface
• At bottom, messages are
carried by the medium
Protocol Layers (2)
 Example: the philosopher-translator-secretary architecture
 Each protocol at different layers serves a different purpose
Protocol Layers (3)
 Each lower layer adds its own header (with control inform-
ation) to the message to transmit and removes it on receive
Why Using Layer Models
 To visualize the interaction between various protocols,
it is common to use a layered model.
 Benefits of doing so:
Helps break down network function.
Create standard for equipment manufacturing.
Allows vendors to focus in specialized areas of the network
Service Primitives (1)
 A service is provided to the layer above as primitives
 Hypothetical example of service primitives that may
provide a reliable byte stream (connection-oriented)
service:
Service Primitives (2)
 Hypothetical example of how these primitives may be
used for a client-server interaction
Server
Client
LISTEN (0)
CONNECT (1)
Connect request
Accept response
SEND (3)
RECEIVE
ACCEPT (2)
RECEIVE
Request for data
SEND (4)
Reply
DISCONNECT (5)
Disconnect
DISCONNECT (6)
Disconnect
Relationship of Services to Protocols
Recap:
 A layer provides a service to the one above
[vertical]
 A layer talks to its peer using a protocol [horizontal]
Reference Models
Reference models describe the layers in a network
architecture
 OSI reference model »
 TCP/IP reference model »
 Model used for this text »
OSI Reference Model
 A principled, international standard, seven layer
model to connect different systems
– Provides functions needed by users
– Converts different representations
– Manages task dialogs
– Provides end-to-end delivery
– Sends packets over multiple links
– Sends frames of information
– Sends bits as signals
TCP/IP Reference Model
 A four layer model derived from experimentation;
omits some OSI layers and uses the IP as the network
layer.
IP is the
“narrow waist”
of the Internet
Protocols are shown in their respective layers
Model Used in this Book
It is based on the TCP/IP model but we call out
the physical layer and look beyond Internet
protocols.
Protocol Data Units (PDU) and Encapsulation
Protocol Data Units (PDU) and Encapsulation
The Process of Sending and Receiving (F2.4.6.1)
Example Networks
 The Internet »
 3G mobile phone networks »
 Wireless LANs »
 RFID and sensor networks »
Contents
1. Introduction
 presents the basics of communication and how
networks have changed our lives.
2. Application Layer Functionality and Protocols
 introduces you to the top network model layer, the
Application layer.
3. Transport Layer
 introduces you to the Transport Layer
4. Network Layer
 introduces the OSI Network layer.
CCNA1 : Network Fundamentals Contents
6. Data Link Layer
 discusses the services provided by Data Link layer
7. Physical Layer

introduces the Physical layer
Offline Course Materials
Packet Tracer Simulation Tool
 A powerful network simulation program developed by
Cisco that allows students to experiment with network
behavior.
Wireshark 1.10
 Wireshark is the world's foremost network protocol analyzer, and is the
standard across many industries and educational institutions.
 http://www.wireshark.org/
Reading
 Chapter 1
 Download and study Packet Tracer 5.3
Next Lecture
 Chapter 1