24/12/13

24/12/13

24/12/13

24/12/13

24/12/13

OSI Layers Protocol Functions

Presented by K.GAYATHRI

OSI Model

Introduction

The Open Systems Interconnection (OSI) model is a reference tool for understanding data communications between any two networked systems.

Some Benefits of OSI Model

1.Less complex,More quality

2.Easier to learn and Develop

3.Multivendor interoperability

4.Standard interface

5.Troubleshooting.

OSI Model 7 Layers With Protocols

Physical Layer

Purpose

Deals with the transmission of 0s and 1s over the physical mediaTranslation of bits into signals(Electrical,Mechanical)The Physical layer provides specifications for a variety of hardware: Cabling Connectors Network interface cards (NICs) Wireless radios Hubs

Ethernet

Ethernet is a family of technologies that provides data-link and physical specifications for controlling access to a shared network medium.

Ethernet has several benefits over other LAN technologies:

Simple to install and manage

Inexpensive

Flexible and scalable

Easy to interoperate between vendors

Cabling the LAN

Media Characteristics: Cable length

Cost

Ease of installation

Susceptibility to interference

Ethernet Cabling TypesCoaxial

Fiber Optic

Space

Category 5 unshielded twisted-pair cable (Cat 5 UTP)

Cabling is an integral part of building any network.

Cabling standards are a set of specifications for the installation and testing of cables.

Standards specify types of cables to use in specific environments, conductor materials, pin outs, wire sizes, shielding, cable lengths, connector types and performance limits.

Twisted Pair Cable

Twisted pair cable is most commonly used in network installations

The TIA/EIA organization defines two different patterns, or wiring schemes, called T568A and T568B.

Each wiring scheme defines the pin out, or order of wire connections, on the end of the cable.

There are two types of twisted pair cable STP,UTP

(Cat 5 UTP) is mainly used in network installations.

Unshielded Twisted Pair (UTP)

Unshielded twisted-pair cable (UTP) is a four-pair wire medium used in a variety of networks.

TIA/EIA-568-A contains specifications governing cable performance.

RJ-45 connectorUTP Cable Types

Straight-Through

Crossover

Rollover

RJ-45 Connector

Straight-through Cable

A Straight-through cable is the most common cable type.

It maps a wire to the same pins on both ends of the cable.

Straight-through cables used for following connections, Switch to router

Switch to PC or server

Hub to PC or server

Crossover Cable

A crossover cable uses both wiring schemes.

The wires on the cable are crossed over so that the receive signal pins on the RJ-45 connector on one end are connected to the transmit signal pins on the RJ-45 connector on the other end.

Crossover cables used for following connections,Switch to switch

Switch to hub

Hub to hub

Router to router

PC to PC

Router to PC

Rollover Cable

Rollover cable (also known as Cisco console cable) is a type of null-modem cable that is most commonly used to connect a computer terminal to a router's console port.

Cisco routers and switches are normally configured over their console ports.

The pin outs on one end are reversed from the other, as if the wire had been rolled over and you were viewing it from the other side.

Rollover cables used for following connectionsConnect a terminal to a console port.

Wireless Network

802.11 standard specifies the operating parameters of wireless local area networks (WLAN)

The 802.11 wireless networks operate in two basic modes: 1.Infrastructure mode 2.Ad-hoc mode

Infrastructure Mode

Wireless Network Security

Wired Equivalent Privacy (WEP): The original encryption protocol developed for wireless networks.WEP encryption is based on the RC4 stream cipheroperationWi-Fi Protected Access (WPA):Most current WPA implementations use a preshared key (PSK), commonly referred to as WPA Personal, and the Temporal Key Integrity Protocol (TKIP, pronounced tee-kip) for encryption.

WPA Enterprise uses an authentication server to generate keys or certificatesWi-Fi Protected Access version 2 (WPA2): Based on the 802.11i wireless security standard.

The most significant enhancement to WPA2 over WPA is the use of the Advanced Encryption Standard (AES) for encryption

WEP vs WPA vs WPA2

WEP

WPA

WPA2

ENCRYPTION

RC4

RC4

AES

KEY ROTATION

NONE

Dynamic Session Keys

Dynamic Session Keys

KEY DISTRIBUTION

Manually typed into each device

Automatic distribution available

Automatic distribution available

AUTHENTICATION

Uses WEP key as Authentication

Can use 802.1x & EAP

Can use 802.1x & EAP

Data Link Layer

Switching-Providing MAC address

Framing-Send blocks of data (frames) between physical devices

Dealing with transmission errors(Node-Node Error Control)

Regulating data flow(Flow control)

It mainly uses the hardware device Switches.

Switches

Switches do following functions,

Hardware address learning

Intelligent forwarding of frames

Loop avoidance

Switches support three methods of forwarding frames.

Store-and-Forward method

Cut-Through (Real Time) method

Fragment-Free (Modified Cut-Through) method

Spanning Tree Protocol(STP)

Switches (and bridges) needed a mechanism to prevent loops from forming.

Switches utilize the Spanning Tree Protocol (STP) to maintain a loop-free environment.

STP Process

To maintain a loop-free environment, STP performs the following functions:

A Root Bridge is elected

Root Ports are identified

Designated Ports are identified

If a loop exists, a port is placed in Blocking state. If the loop is

removed the blocked port is activated again.

STP Process

Point to Point protocol

PPP is a data-link layer protocol, PPP uses a stack of other protocols to establish the link, to authenticate the parties involved, and to carry the network layer data.Three sets of protocols are used by PPP: Link control protocol

Authentication protocol

Network control protocol

Link Control Protocol (LCP)

It is responsible for establishing, maintaining, configuring, and terminating links.

It also provides negotiation mechanisms to set options between endpoints.

Both endpoints of the link must reach an agreement about the options before the link can be established.

When PPP is carrying an LCP packet, it is either in the establishing state or in the terminating state.

All LCP packets are carried in the data field of the PPP frame.

Authentication Protocols

Authentication plays a very important role in PPP because PPP is designed for use over dial-up links where verification of user identity is necessary.

Authentication means validating the identity of a user who needs to access a set of resources.

PPP uses two protocols for authentication: Password Authentication Protocol (PAP)

Challenge Handshake Authentication Protocol (CHAP)

Password Authentication Protocol (PAP)

The user who wants to access a system sends an ID (identification) and a password.The system checks the validity of the identification and password and either accepts or denies a connection.

Challenge Handshake Authentication Protocol (CHAP)

The CHAP protocol is a three-way handshaking authentication protocol that provides greater security than PAP.In this method, the password is kept secret; it is never sent on-line.

Network Control Protocol (NCP)

After the link is established and authentication (if any) is successful, the connection goes on the networking state.

NCP is a set of control protocols to allow the encapsulation of data coming from network layer protocols into the PPP frame.

The set of packets that establish and terminate a network layer connection is called Internetwork Protocol Control Protocol (IPCP).

NCP Example

Network Layer

Routing and Forwarding

Logical addressing

Transport packet from sending to receiving hostsA logical address contains two components: Network ID identifies which network a host belongs to. Host ID uniquely identifies the host on that network.Logical addressing protocols include

Internetwork Packet Exchange (IPX)

Internet Protocol (IP).

IPv4 address Classes

Class First Octet Range Default Subnet Mask

Class A 1 126 255.0.0.0

Class B 128 191 255.255.0.0

Class C 192 223 255.255.255.0

Class D 224 239 -

Class E 240 255 -

Ranges 127.x.x.x are reserved for the loopback or localhost.

127.0.0.1 is a comman Loopback address.

Routing And Forwarding

1

2

3

0111

value in arrivingpackets header

routing algorithm

local forwarding table

header value

output link

0100010101111001

3221

Routing algorithm determines

end-end-path through network

Forwarding table determineslocal forwarding at this router

Routing-Determine route taken by packets from source to destination

Forwarding-Move packets from routers input to appropriate router output

Transport Layer

This layer is responsible for the reliable transfer of data, by ensuring that data arrives at its destination error-free and in order.

It provides Port number to specifies the Application.

It is Host-to-Host layer.

Transport layer communication falls under two categories:

Connection-oriented requires that a connection with specific agreed-upon parameters be established before data is sent.(TCP)

Connectionless requires no connection before data is sent.(UDP)

Some common Port numbers

Port Number Transport Protocol Application

20, 21 TCP FTP

22 TCP SSH

23 TCP Telnet

25 TCP SMTP

53 TCP/UDP DNS

80 TCP HTTP

110 TCP POP3

443 TCP SSL

666 TCP Doom

Transmission Control Protocol(TCP)

Connection establishment connections are established, maintained, and ultimately terminated between devices.

Segmentation and sequencing data is segmented into smaller pieces for transport. Each segment is assigned a sequence number, so that the receiving device can reassemble the data on arrival.

Acknowledgments receipt of data is confirmed through the use of acknowledgments. If a segment is lost, data can be retransmitted to guarantee delivery.

Flow control (or windowing) data transfer rate is negotiated to prevent congestion.

Connection Termination.

TCP Process

User Datagram Protocol(UDP)

The User Datagram Protocol (UDP) is a connectionless,unreliable transport protocol.

UDP experiences less latency(High speed transmission)

It provides no three-way handshake, no flow-control, no sequencing, and no acknowledgment of data receipt.

UDP essentially forwards the segment

UDP ideal for applications that require speed over reliability. For example, DNS primarily uses UDP as its transport protocol

Session Layer

The session layer is responsible for dialog
control and synchronization.

The session layer defines how to start, control and end conversations (called sessions) between applications.

This includes starting, stopping, and re-synchronizing communications between applications on two computers.

The session layer offers provisions for efficient data transfer.Session layer Protocols,

Structured Query Language (SQL)

Remote Procedure Call (RPC)

Network File system(NFS)

Basic Functions for the Session Layer

Managing multiple sessionsA computer can establish multiple sessions with several other computers

e.g., session 1: exchanging information over the World Wide Web with www.yahoo.comsession 2: exchanging information over the World Wide Web with www.google.comsession 3: exchanging information over the World Wide Web with www.espn.comTwo computers can also establish multiple sessions,

e.g., function 1: exchanging information over the World Wide Web; function 2: exchanging information over the FTP; function 3: exchanging information over the email

Session layer Examples

Software

music

news

Presentation Layer

The presentation layer is responsible for translation, compression, and encryption.

This layer controls the formatting and syntax of user data for the application layer.

This ensures that data from the sending application can be understood by the receiving application.

Examples of Presentation layer formats include: Text - RTF, ASCII, EBCDIC Images - GIF, JPG, TIF Audio - MIDI, MP3, WAV Movies - MPEG, AVI, MOV

Presentation Layer Protocols

This layer has two protocols for secure purpose of transmission

1.Transport layer Security Protocols(TLS)

The primary goal of the TLS protocol is to provide privacy and data integrity between two communicating applications

In practice, used to protect information transmitted between browsers and Web servers

2.Secured Socket Layer protocols(SSL)SSL is an Internet security protocol used by Internet browsers and Web servers to transmit sensitive information.

Both protocols works on three features like Confidentiality, integrity, and Availability.

SSL/TLS

Cryptography

Cryptography is the practice and study of hiding information. It is the Art or Science of converting a plain intelligible data into an unintelligible data and again retransforming that message into its original form.It provides Confidentiality, Integrity, Accuracy.Encryption The process of converting plain text into an unintelligible format (cipher text) is called Encryption.Decryption The process of converting cipher text into a plain text is called Decryption

Symmetric And Asymmetric Key Methods

Symmetric Key Cryptography (Secret Key Cryptography)Same Key is used by both partiesAdvantagesSimpler and FasterDisadvantagesLess Secured

Asymmetric Key Cryptography (Public Key Cryptography)2 different keys are usedUsers get the Key from an Certificate AuthorityAdvantagesMore SecuredAuthenticationDisadvantagesRelatively Complex

Application Layer

It mainly provides user interface

Everything at this layer is application-specific.

This layer provides application services for file transfers, e-mail, and other network software services

This layer handles issues like network transparency, resource allocation and problem partitioning.

Application Layer Protocols

DNS- Domain Name systemHTTP - Hyper Text Transfer ProtocolFTP - File Transfer ProtocolPOP 3-Post Office ProtocolIMAP- Internet Message Access protocolSMTP - Simple Mail Transfer ProtocolTelnet - Remote Access

Domain Name system(DNS)

DNS is a host name to IP address translation service.

DNS is a distributed database implemented in a hierarchy of name servers.

An application level protocol for message exchange between clients and servers.

Root DNS Servers

com DNS servers

org DNS servers

edu DNS servers

poly.eduDNS servers

umass.eduDNS servers

yahoo.comDNS servers

amazon.comDNS servers

pbs.orgDNS servers

DNS Process

Hyper Text Transfer Protocol(HTTP)

HTTP is the protocol that supports communication between web browsers and web servers

It provides web services.

HTTP can support multiple request-reply exchanges over a single TCP connection.

The well known TCP port for HTTP servers is port 80.

File Transfer Protocol(FTP)

File Transfer Protocol (FTP) is the standard mechanism provided by TCP/IP for copying a file from one host to another.FTP uses the services of TCP. It needs two TCP connections.The well-known port 21 is used for the control connection and the well-known port 20 for the data connection.

Electronics Mail(SMTP,POP3,IMAP)

SMTP-Uses TCP to reliably transfer email message from client to server, port 25.

It is a push protocol; it pushes the message from the client to the server.

POP- Protocol used to retrieve email from a mail server.

It stores and forwards messages

IMAP- Keep all messages in one place(The server).

Allows user to organize messages in folders.

Electronics Mailing

Internet

POPStore

IMAPstore

Mail Server

MailClient

Internet Message Access Protocol

IMAP

SMTP

SMTP

MailClient

POP

SMTP

Telnet

It is the standard TCP/IP protocol

Telnet allows a user to log into a computer across an internet.

Telnet establishes a TCP connection and then passes keystrokes from the users keyboard directly to the remote computer .

Telnet offers three basic services .1. It defines a network virtual terminal that provides a standard interface to remote systems.2. Telnet includes a mechanism that allows the client and server to negotiate options .3. Telnet treats both ends of the connection symmetrically.

TELNET Operation

THANK YOU