cit notes

CIT Notes

Prof. Rakhi Tripathi&

Prof. Rajneesh Chauhan

Three Faces of Networking

• Fundamental concepts of networking– How data moves from one computer to another over a network– Theories of how network operate

• Technologies in use today– How theories are implemented, specific products– How do they work, their use, applications

• Management of networking technologies– Security– Network Design– Managing the network

Copyright 2005 John Wiley & Sons, Inc 1 - 2

Network Types (based on Scale) • Local Area Networks (LANs) - room, building

– a group of PCs that share a circuit.

• Backbone Networks - less than few kms– a high speed backbone linking the LANs at various locations.

• Metropolitan Area Networks (MAN) - (< few 10 kms)– connects LANs and BNs at different locations – leased lines or other services used to transmit data.

• Wide Area Networks (WANs) - (> few 10 kms)– Same as MAN except wider scale


Intranet vs. Extranet

• Intranet– A LAN that uses the Internet technologies– Open only those inside the organization– Example: insurance related information provided to employees over

an intranet

• Extranet– A LAN that uses the Internet technologies– Open only those invited users outside the organization– Accessible through the Internet– Example: Suppliers and customers accessing inventory information in a

company over an extranet


7-Layer Model of OSI

• Application Layer– set of utilities used by application programs

• Presentation Layer– formats data for presentation to the user– provides data interfaces, data compression and translation between

different data formats

• Session Layer– initiates, maintains and terminates each logical session between

sender and receiver


Please Do Not Touch Steve’s Pet Alligator

Physical DataLink Network Transport Session Presentation Application

Integration of Voice, Video & Data• Also called “Convergence”

– Networks that were previously transmitted using separate networks will merge into a single, high speed, multimedia network in the near future

• First step (already underway)– Integration of voice and data

• Next Step – Video merging with voice and data – Will take longer partly due to the high data rates

required for video


World Wide Web

• Web began with two innovative ideas:– Hypertext

• A document containing links to other documents– Uniform Resource Locators (URLs)

• A formal way of identifying links to other documents

• Invention of WWW (1989)– By Tim Berners-Lee at CERN in Switzerland

• First graphical browser, Mosaic, (1993)– By Marc Andressen at NCSA in USA; later founded Netscape


CERN - Conseil Européen pour la Rechèrche Nucléaire (Berners-Lee, T. (2000) Weaving the Web. New York: HarperCollins. P. 4)

NCSA - National Center for Supercomputing Applications

How the Web Works


HTTP Response

HTTP Request

Client Computer

Server ComputerMain Web communications protocol: HTTP: Hypertext Transfer Protocol

Clicking on a hyperlink or typing a URL into a browser starts a request-response cycle

A request-response cycle: includes multiple steps since web pages often contain embedded files, such as graphics, each requiring a separate response.

HTML - Hypertext Markup Language

• A language used to create Web pages • Also developed at CERN (initially for text files)• Tags are embedded in HTML documents

– include information on how to format the file• XML - Extensible Markup Language

– A new markup language becoming popular


HTML vs. XML

• XML was designed to describe data and to focus on what data is. HTML was designed to display data and to focus on how data looks .

• HTML is about displaying information, while XML is about describing information.


Electronic Mail• Heavily used Internet application

– Much, much faster than snail mail (regular mail)

– Extremely inexpensive (compared to $3-$10 per paper mail cost)

• Includes preparation, paper, postage, etc, – Can substitute for other forms of communication, such as telephone calls

• Eliminates “telephone tag”– E-mail users can answer at his/her convenience, instead of time

of call


E-mail Standards• SMTP - Simple Mail Transfer Protocol

– Main e-mail standard for• Originating user agent and the mail transfer agent • Between mail transfer agents

– Originally written to handle only text files– Usually used in two-tier client-server architectures

• Post Office Protocol (POP) and Internet Mail Access Protocol (IMAP)– Main protocols used between the receiver user agent and mail

transfer agent– Main difference: with IMAP, messages can be left at the server

after downloading them to the client• Other competing standards

– Common Messaging Calls (CMC), X.400


Web-based e-mail


LAN

LAN

SMTP packet

SMTP packet

SMTP packet

Internet

Client computer with


Server computer with




Web server software

Web server software

email server software

e-mail server software

IMAP orPOP packet

IMAP packet

HTTP request

HTTP request

HTTP response

HTTP response

Web browser

Web browser

Sample SMTP Message


Note that this SMTP message has no attachments.

File Transfer Protocol (FTP)• Enables sending and receiving files over the Internet• Requires an application program on the client computer and

a FTP server program on a server • Commonly used today for uploading web pages• Many packages available using FTP

– WS-FTP (a graphical FTP software)• FTP sites

– Closed sites• Requires account name and password

– Anonymous sites• Account name: anonymous; password: email address


Instant Messaging (IM)

• A client-server program that allows real-time typed messages to be exchanged– Client needs an IM client software– Server needs an IM server package

• Some types allow voice and video packets to be sent– Like a telephone

• Examples include AOL and ICQ• Two step process:

– Telling IM server that you are online– Chatting


How Instant Messaging Works


LAN

LAN

LAN

IM packet

IM packet

IM packet

IM packet

Internet


IM client software

e-mail client software



with IM server software

Sender sends a request to the IM server telling it that sender is online. If a friend connects, the IM server sends a packet to sender’s IM client and vice versa.

If a chat session has more than two clients, multiple packets are sent by the IM server. IM servers can also relay information to other IM servers.

When the sender types in text, the IM client sends the text in a packet to the IM server which relays it to the receiver.

Voice over IP

• Phone service over the Internet

• Phone service via VoIP costs less than equivalent service from traditional sources due to using a single network to carry voice and data


Existing System

Copyright 2010 John Wiley & Sons, Inc

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PBX

IIT, Delhi

PBX

MTNL

Other six organizations

: All the existing internal phones configured with their old PBX

Six organizations: IIT-Bombay, IIT- Madras, IIT-Kharagpur, IISc Bangalore, CDAC and ERNet

VoIP System


2 Mbps link

: IP soft/hard phones configured with VoIP server

PBX

VoIP Server

IIT,Delhi

PBX

VoIP Server

Other six organizations

Cost

• Startup cost: hardware, software, trainees and permanent employees

• Recurring cost: maintenance


User Benefits• Cost benefit

• Ease of placing an STD call

• QoS provided

• Transferring data + video conferencing

Requirements


Features Open Source Cisco CallManager

Price Free Rs. 5.4 lakh

Documentation Not yet complete Well maintained

Support No support Good Support

Reliability Good Excellent

Scalability Average Very Good

QoS Provided Good Good

Handling Calls 10,000 10,000+

Extended Mobility* Not Yet Yes

Compatibility With all protocols Only with standard

protocols

Interoperability Yes. With most of the

standard systems

Yes. With most of the

standard systems

Hard Vs. Soft Phones


Videoconferencing• Provides real time transmission of video and audio signals

between two or more locations– Allows people to meet at the same time in different locations– Saves money and time by not having to move people around – Typically involves matched special purpose rooms with cameras and

displays

• Desktop videoconferencing– Low cost application linking small video cameras and microphones

together over the Internet– No need for special rooms– Example: Net Meeting software on clients communicating through a

common videoconference server


Cisco Videoconferencing


Videoconferencing Standards

• Proprietary early systems • Common standards in use today

– H.320• Designed for room-to-room videoconferencing over high-speed

phone lines– H.323

• Family of standards designed for desktop videoconferencing and just simple audio conferencing over Internet

– MPEG-2• Designed for faster connections such as LAN or privately owned

WANs


Virtual LANs (VLANs)

• A new type of LAN-BN architecture– Made possible by high-speed intelligent switches– Computers assigned to LAN segments by software

• Often faster and provide more flexible network management– Much easier to assign computers to different segments

• More complex and so far usually used for larger networks• Basic VLAN designs:

– Single switch VLANs – Multi-switch VLANs


Virtual Private Networks• Provides equivalent of a private packet switched network over

public Internet– Use Permanent Virtual Circuits (tunnels) that run over the public

Internet, yet appear to the user as private networks – Encapsulate the packets sent over these tunnels using special

protocols that also encrypt the IP packets • Provides low cost and flexibility

– Uses Internet; Can be setup quickly• Disadvantages of VPNs:

– Unpredictability of Internet traffic – Lack of standards for Internet-based VPNs, so that not all vendor

equipment and services are compatible


VPN Architecture

Wireless LANs (WLANs)

• Use radio or infrared frequencies to transmit signals through the air (instead of cables)

• Basic Categories– Use of Radio frequencies (FOCUS of this chapter)

• 802.1x family of standards (aka, Wi-Fi)– Use of Infrared frequencies (Optical transmission)

• Wi-Fi grown in popularity – Eliminates cabling – Facilitates network access from a variety of locations– Facilitates for mobile workers (as in a hospital)– Used in 90 percent of companies


Principal WLANs Technologies

• WI-FI– IEEE 802.11b

• Standardization started after .11a, but finished before, more commonly used than .11a

– IEEE 802.11a• First attempt to standardization of WLANs; more complicated than

.11b– IEEE 802.11g

• WIMAX• Bluetooth

– Also an IEEE standard 802.15


Components of WLANs

• Network Interface Cards– Many laptops come with WLAN cards built in– Also available as USB cards– About 100-300 feet max transmission range

• Access Points (APs)– Used instead of hubs; act as a repeater

• Must hear all computers in WLAN


WIMAX

• Commercial name for family of IEEE 802.16 standards

• Two primary types: Fixed and mobile• Logical and physical topology same as 802.11

and shared Ethernet• Uses controlled access with a version of 802.11

point coordination function• Two types:

– 802.16d– 802.16e


Computer Security Incidents• Computer security increasingly important

– More sophisticated tools for breaking in– Viruses, worms, credit card theft, identity theft leave firms with

liabilities to customers• Incidents are escalating at increasing rate• Computer Emergency Response Team (CERT) was formed at

Carnegie Mellon University with US DoD support– responds and raises awareness of computer security issues,

www.cert.org• Worldwide annual information security losses may be $2

trillion


Types of Security Threats• Business continuity planning related threats

– Disruptions• Loss or reduction in network service• Could be minor or temporary (a circuit failure)

– Destructions of data• Viruses destroying files, crash of hard disk

– Disasters (Natural or manmade disasters )• May destroy host computers or sections of network

• Intrusion– Hackers gaining access to data files and resources– Most unauthorized access incidents involve employees– Results: Industrial spying; fraud by changing data, etc.


Network Assets• Identify the assets on the network

– Organization’s data files most important– Mission-critical applications also very important

• Programs critical to survival of business– Hardware, software components

• Important, but easily replaceable• Evaluate assets based on their importance• Prioritizing assets is a business decision, not a technology

decision• Value of an asset is a function of:

– Its replacement cost– Personnel time to replace the asset– Lost revenue due to the absence of the asset


Types of Assets


Hardware • Servers, such as mail servers, web servers, DNS servers, DHCP servers, and LAN file servers

• Client computers• Devices such as hubs, switches, and routers

Circuits • Locally operated circuits such LANs and backbones• Contracted circuits such as MAN and WAN circuits• Internet access circuits

Network Software

• Server operating systems and system settings• Applications software such as mail server and web server software

Client Software

• Operating systems and system settings• Application software such as word processors

Organizational Data

• Databases with organizational records

Mission critical applications

• For example, for an Internet bank, the Web site is mission critical

Security Threats• Identify threats

– Any potentially adverse occurrence that can• Harm or interrupt the systems using the network, or • Cause a monetary loss to an organization

• Rank threats according to – Their probability of occurrence– Likely cost if the threat occurs

• Take the nature of business into account– Example: Internet banking vs. a restaurant

• Bank’s web site: has a higher probability of attack and much bigger loss if happens

• Restaurant web site: much less likely and small loss


Inadequacy of Traditional Design• Three forces make the traditional design approach less

appropriate for many of today’s networks:1. Rapidly changing technology of computers, networking devices and

the circuits• More powerful devices, much faster circuits

2. Rapidly growing network traffic• Difficulty of estimating demand and growth requires shorter

planning periods of 3 years or so3. Dramatic change in the balance of costs

• Before: Equipment was costly; now: staff• Design goal: Minimize the staff management time to operate

rather than the hardware costs, such as using standardized equipment


Building Block Network Design• Building block design is simpler than traditional• Key concept is to use a few standard components to reduce

long run costs by simplification• Start with a few standard components with ample capacity

without extensive traffic analysis– Use few types of devices, over and over, narrow product choice but

deep throughout organization– Simpler design process yields easily managed network

• Phases of design– Needs analysis, technology design, and cost assessment– Cycles through, refining the outcome of each phase


Phases of Building Block Design• Needs analysis

– Understand current and future needs• Classify users and applications as typical or high volume • Identify specific technology needs

• Technology design – Examine available, off-the-shelf technologies and assess which ones

meet the needs of user needs– In case of difficulty in determining traffic needs, provide more

capacity to keep ahead of growth• Cost assessment

– Consider the relative cost of technology


Building Block Network Design


Cycles through all three phases, refining the

outcome of each phase

Reaching a Final Network Design


Process of cycling through all three design phases is cyclical and repeated over time.

Needs Analysis• Goal is to understand why the network is being built and what

users and applications it will support– improve poor performance?– enable new applications?– upgrade, replace old equipment?– standardize equipment based on vendor or protocol?

• Goals differ depending on the network– LAN and BN typically are built with organizational ownership, best to

design in over-capacity– MAN/WAN rely more on leased equipment and circuits, best to design

at capacity, and then lease additional circuits as required


cit notes

Documents

john wiley sons

data compression

high data rates

userprovides data interfaces

backbone networks

separate networks

metropolitan area networks

wide area networks wans