© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 1

Living in a Network Centric World

IT305: Computer Networks – Chapter 1

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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

H a rdwa re S o f twa re

Ne two rkS tru ctu re

D e v ice s M e dia S e rv ice Pro cce s s

N e twor k Edg e(in te r m e diar y de vic e s )

Ne two rk C o re(En d D e v ice s

Pro to co ls A pplica t io n sW ire d W ire le s s

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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

FDM

frequency

time

TDM

frequency

time

4 users

Example:

1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4

Frame

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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-the-fly how much time each device should be allocated for data transmission on the cable or line.

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dtrans: transmission delay:

L: packet length (bits) R: link bandwidth (bps)

dtrans = L/R

dprop: propagation delay: d: length of physical link s: propagation speed in

medium (~2x108 m/sec) dprop = d/sdtrans and dprop

very different

Four sources of packet delay

propagation

nodalprocessing queueing

dnodal = dproc + dqueue + dtrans + dprop

A

B

transmission

* 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 connection-

oriented 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