الرحیم بسم الرحمن الله

Information & Communication Technology Institute

Group Members:

1: Rehmatullah *** Class: Fourth

2: Sonia ***N/of solid: 1-30

3: Nasrin *** Delivery time: 15 minutes

4: Ghullam Ali

Title of Project: OSI Reference Model (OSI Layers)

Voice Over Ip book page number: 110

CONTENTS OF LECTURE

• Brief introduction to OSI Reference Model.

• What are OSI layers and their main concepts.

• Introduction to Application layer

• Application layer functions.

• Application Layer Hardware.

• Application Layer Protocols and Standards.

CONTENTS OF LECTURE

Introduction to Presentation layer

• Presentation layer functions.

• Presentation Layer Hardware

• Presentation Layer Protocols and Standards

Introduction to Session layer

• Session layer functions.

• Session Layer Hardware

• Session Layer Protocols and Standards

OSI REFERENCE MODEL

International Standards Organization/Open System Interconnection (ISO/OSI) model is a standard reference model for communication between two end users in a network.

It is reference model for how applications can communicate over a network.

The purpose of the OSI reference model is to guide vendors and developers so the digital communication products and software programs they create will interoperate, and to facilitate clear comparisons among communications tools.

Most vendors in telecommunications describe their products and services in relation to

the OSI model.

THE MAIN CONCEPT OF OSI LAYERS

The main concept of OSI is that the process of communication between two endpoints in a telecommunication network can be divided into seven groups of related layers.

Each communicating user or program is at a computer that can provide those seven layers of function. So in a given message between users, there will be a flow of data down through the layers in the source computer, across the network and then up through the layers in the receiving computer.

The seven layers are having some applications a like, operating systems, network card device drivers and networking hardware that enable a system to put a signal on a network cable or out over Wi-Fi or other wireless protocol.

The seven layer Model describes seven layers of interaction for an information system communication over a network , presenting a stack of layers representing major function areas that are generally required or useful for data communication between nodes in a distributed environment.

The OSI (Open Systems Interconnection) model is used to understand how networks or systems operate. In trying to understand this model, it is best to look at it based on its seven layers.

We'll take a look at the OSI model broken down into these seven layers, focusing specifically on the Application , presentation and session layer.

THE MAIN CONCEPT OF OSI LAYERS

WHAT ARE THE OSI LAYERS?

• These are seven layers of OSI Model.

The Application layer ISO /OSI, Layer seven, is the top layer of both the OSI and TCP/IP models. It is the layer that provides the interface between the applications we use to communicate and the underlying network over which our messages are transmitted.

The application layer provides the interface to the communications environment which is used by the application process. It is responsible for communicating application process parameters.

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

APPLICATION LAYER

APPLICATION LAYER

Application layer ISO OSI on the transmitting host, proceeding down the hierarchy to the Physical layer, then passing over the communications channel to the destination host, where the information proceeds back up the hierarchy, ending at the Application layer.

The figure depicts the steps in this process

APPLICATION LAYER FUNCTIONS

An application function describes the internal behavior of a component; for the user of a component that performs an application function.

Now that we have a basic understanding of how the seven layers work, let's focus more on what the Application Layer does.

• In this layer, data can be generated using applications like Microsoft Excel or streaming audio and video data. But it is also used to transfer information across the internet or through email.

• Provides interface between software applications and network for interpreting application requests and requirements.

It provides services directly to user applications. It enables to access the network. It provides user interfaces and support for services such as email, remote file access and transfer, shared database management and other types of distributed information services.

1: File Transfer: It allows a user to access, retrieve and manage files in a remote computer.

2 :Mail services: It provides the basis for email forwarding and storage facilities.

3: Directory services: It provides distributes database sources and access for global information about various objects and services.

APPLICATION LAYER FUNCTIONS

APPLICATION LAYER HARDWARE

Content Filtering /firewall :Network layer firewalls, also called packet filters, operate at a relatively low level of the TCP/IP protocol stack, not allowing packets to pass through the firewall unless they match the established rule set. The firewall administrator may define the rules; or default rules may apply.

Firewall: is a network security system that controls the incoming and outgoing network traffic based on an applied rule set.

Application-layer firewalls work on the application level of the TCP/IP stack ,they block other packets (usually dropping them without acknowledgment to the sender

APPLICATION LAYER HARDWARE

Proxy Servers: Also called a "proxy," The word proxy means "to act on behalf of another," it is a computer system or router that breaks the connection between sender and receiver.

Functioning as a relay between client and server, proxy servers help prevent an attacker from invading a private network and are one of several tools used to build a firewall.

All requests from clients to the Internet go to the proxy server first. The proxy evaluates the request, and if allowed, re-establishes it on the outbound side to the Internet.

  

CONT..………

• Gateways: An Application Layer Gateway (ALG) is a software component that is designed to manage specific protocols such as SIP/FTP the ALG intercepts and analyzes the specified traffic, allocates resources, and defines dynamic policies to permit the traffic to pass securely through the Networks device.

• Application Switches: Switches a switch actually checks for the destination MAC address and forward it to the relevant port to reach that computer only. This way, switches reduce traffic and divide the collision domain into segments, this is very sufficient for busy LANs and it also protects frames from being sniffed by other computers sharing the same segment.

 APPLICATION LAYER PROTOCOLS AND STANDARD

Application layer, uses protocols to specify what messages are exchanged between the source and destination hosts, the syntax of the control commands, the type and format of the data being transmitted, and the appropriate methods for error notification and recovery.

Application layer ISO OSI protocols are used by both, thesource and destination devices during a communication session. In order for the communications to be successful, the application layer protocols implemented on the source and destination host

must match.

Some common protocols of Application layer are (BOOTP, DHCP, DNS, FTP, HTTP, HTTPS, IMAP4, PING, POP3, NTP, SFTP, SMTP, Telnet, TFTP)

1: Bootp: lets a network user be automatically configured (receive an IP address) and have an operating system booted without user involvement. The BOOTP server, managed by a network administrator, automatically assigns the IP address from a pool of addresses for a certain duration of time.

2: IMAP (Internet Message Access Protocol) is a standard protocol for accessing e-mail from your local server. IMAP is a client/server protocol in which e-mail is received and held for you by your Internet server.

APPLICATION LAYER PROTOCOLS

CONT …

• Dynamic Host Configuration Protocol (DHCP): enables devices on a network to obtain IP addresses and other information from a DHCP server. This service automates the assignment of IP addresses, subnet masks, gateway and other IP networking parameter

• Domain Name System (DNS), an Internet service that translates domain names into IP add. domain names are alphabetic, they're easier to remember. Internet is really based on IP addresses. We use a domain name, therefore, a DNS service must translate the name into IP address. Ex: domain name www.example.com might translate to 198.105.232.4

Trivial File Transfer Protocol, TFTP: is used when a file transfer does not require an acknowledgment during file transfer. TFTP is used often in router configuration.

CONT.…

• File Transfer Protocol(FTP). It is an Internet service specially designed to establish a connection to a particular Internet server (or computer), so that users are able to transfer files (download) to their computer or to transfer (upload) their own files to the server (computer).

• Secure File Transfer Protocol(SFTP). The Secure File Transfer Protocol ensures that data is securely transferred using a private and safe data stream.no clear text, data are transferred as like as passwords.

• Simple Mail Transfer Protocols.(SMTP). is used between email servers and clients on each end that need to send mail. SMTP is used by email clients to send mail to the mail server.

CONT…

Hypertext Transfer Protocol, HTTP is a set of standards that allow users of the World Wide Web to exchange information found on web pages.

Hypertext Transfer Protocol Secure, HTTPS :is a secure method of accessing or sending information across a web page. All data sent over HTTPS is encrypted before it is sent, Because data is encrypted over HTTPS, it is slower than HTTP.

Network Time Protocol or NTP: is a method that allows devices to synchronize their clocks times through a network.

Secure File Transfer Protocol SFTP: is a network protocol that provides file transfer and manipulation functionality over any reliable data stream.

CONT…

• Post Office Protocol3, POP3 is used for electronic messaging across the Internet. POP3 is a protocol that involves both a server and a client. A POP3 server receives an e-mail message and holds it for the user. POP3 does not allow a client to send mail, only to receive it.

• Telecommunication Network ,TelNet: a virtual terminal protocol allowing a user logged on to one TCP/IP host to access other hosts on the network. Many people use remote control applications to access computers at their workplace from outside the network.

• Packet Internet Groper, PING: It uses to send echo request and echo reply messages that determine the validity of an IP address.

PRESENTAION LAYER

As layer six and second from the top of the OSI model, it is primarily responsible for managing the two networking characteristics: protocol and architecture.

Protocol defines a standard set of guidelines under which the network operates.

Network's architecture determines what protocol applies.

The presentation layer converts the data sent by the application layer of the transmitting node into an acceptable data format based on the applicable network protocol and architecture.

It is different from the other layers in two key respects. First, it has a much more limited and specific function than the other layers; Second, it is used much less often than the other layers; in many types of connections it is not required.

PRESENTATION LAYER FUNCTIONS

As a functional part of the OSI model the presentation layer performs a multitude of data conversion algorithms and character translation functions. These include:

• Character-Code Translation: The presentation layer translates from the American standard code for information interchange (ASCII) to the extended binary coded decimal interchange code (EBCDIC).

• Data Conversion: The sixth layer also performs bit order reversal functions, converts CR (byte code for a carriage return) to CR/LF, (byte code for a carriage return with a line feed) and converts integer numbers to floating point numbers.

• Data Compression: The presentation layer reduces the number of bits requiring transmission, which improves the data throughput.

• Data Encryption and Decryption: Encryption is needed for security purposes when sending data across networks. An encryption algorithm is used during transmission, while a decryption algorithm is used at the receiving node. Encryption and decryption typically involves the secure sockets layer (SSL) protocol, which has become more popular when used by the presentation layer.

• Data Translation: Networks provide the capability of connecting different types of computers, servers and mainframes on the same network and may employ different character sets. The presentation layer is responsible for fixing any irregularities while making translations transparent between networked systems.

PRESENTATION LAYER FUNCTIONS

PRESENTATION LAYER PROTOCOL AND STANDARD

• MIME (Multi-Purpose Internet Mail Extensions) is an extension of the original Internet E-mail protocol that lets people use the protocol to exchange different kinds of data files on the Internet: audio, video, images, application programs, and other kinds

• SSL (Secure Sockets Layer) is a standard security technology for establishing an encrypted link between a server and a client-typically a web server (website) and a browser; or a mail server and a mail client (e.g., Outlook).

SSL allows sensitive information such as credit card numbers, social security numbers, and login credentials to be transmitted securely.

PRESENTATION LAYER PROTOCOL

• Transport Layer Security (TLS) is a protocol that ensures privacy between communicating applications and their users on the Internet. When a server and client communicate, TLS ensures that no third party may eavesdrop or tamper with any message.

PRESENTATION LAYER HARDWARE:

Gateways,

Proxy Servers,

Application Switches,

Content Filtering Firewalls

SESSION LAYER

This is the fifth layer of OSI model The name of this layer tells you much about what it is designed to do: to allow devices to establish and manage sessions.

In general terms, a session is a persistent logical linking of two software application processes, to allow them to exchange data over a prolonged period of time.

In some discussions, these sessions are called dialogs; they are roughly compare to a telephone call made between two people.

This layer establishes dialog control between the two computers in a session, regulating which side transmits, and when and how long it transmits.

This layer sets up, coordinates and conversations. Services include authentication and reconnection after an interruption.

The session layer provides the mechanism for opening, closing and managing a session between end-user application processes,

SESSION LAYER

Session layer functions

The session layer defines how to start, control and end conversations (called sessions) between applications. This includes the control and management of multiple bi-directional messages using dialogue control.

• It also synchronizes dialogue between two hosts and manages their data exchange.

• The session layer offers provisions for efficient data transfer. It performs name-recognition and other functions, such as security, that are needed to allow two applications to communicate over the network.

• The session layer establishes, manages, , and terminates user connections. A session is an exchange of message between computers. It synchronizes user tasks.

SESSION LAYER CREATING CONNECTION

Three method used to establish and end connection between computer applications:

1:Sender sends Synchronization message to request a session to the receiver

2:Receiver replies by sending acknowledgment message to acknowledge the Synchronization message sent by the sender, and SYN message to request a session to the sender.

3: Sender replies by sending ACK message to acknowledge the SYN message sent by the receiver

SESSION LAYER CREATING CONNECTION

Creating connectionPICTURE OF CREATING CONNECTION

Session layer protocol and standard

Protocols specify how data inside the messages is structured and the types of messages that are sent between source and destination ,protocols provide the rules and formats that govern how data is treated.

Some common protocol used in session layer are as the following:

Network basic input output system , NetBIOS: provides a communication interface between the application program and the attached medium. All communication functions from the physical layer through the session layer are handled by NetBIOS, A NetBIOS session is a logical connection between any two names on the network.

SESSION LAYER PROTOCOLS AND SATANDARD

Server Message Block ,SMB: The Server Message Block (SMB) is a client/server file sharing protocol. Message Block (SMB) in the late 1980s to describe the structure of shared network resources, such as directories, files, printers, and serial ports. It is a request-response protocol.

The SMB protocol describes file system access and how clients can make requests for files.

SESSION LAYER PROTOCOLS AND SATANDARD

Network File System (NFS): is a client/server application that lets a computer user view and optionally store and update file on a remote computer as though they were on the user's own computer. The user's system needs to have an NFS client and the other computer needs the NFS server. Both of them require that you also have TCP/IP installed since the NFS server and client use TCP/IP as the program that sends the files and updates back and forth.

NetWare Core Protocol (NCP): provided connections and flow control between processes running on different host computers. Application services, such as email and file transfer, were built on top of NCP, using it to handle connections to other host computers.

SESSION LAYER PROTOCOLS AND SATANDARD

Gateways,

Proxy Servers,

Application Switches,

Content Filtering Firewalls

SESSION LARYER HARDWARE

OSI Reference Model : It is reference model for how applications can communicate over a network

Application layer: provides the interface between the applications we use to communicate

Application layer function : Provides interface between software applications and network for interpreting application requests.

Application layer hardware: Content Filtering /firewall ,Proxy server, Gateways , Switches.

Application layer protocols : are (BOOTP, DHCP, DNS, FTP, HTTP, HTTPS, IMAP4, PING, POP3, NTP, SFTP, SMTP, Telnet, TFTP)

SUMMARIZATION

Presentation layer : primarily responsible for managing the two networking characteristics: protocol and architecture.

Presentation layer function: Code Translation, Data conversion, Data Compression , data Encryption and Decryption, Data translation.

Presentation layer protocols:(MIME,SSL, TLS)

Presentation layer hardware: Filtering /firewall ,Proxy server, Gateways , Switches.

Session layer: to allow devices to establish and manage sessions.

Session layer function: session layer establishes, manages, , and terminates user connections, also synchronizes dialogue between two hosts‘.

SUMMARIZATION

Session layer protocols:(NetBIOS , SMB, NFS,NCP)

Session layer hardware : Filtering /firewall ,Proxy server, Gateways , Switches.

SUMMARIZATION

…THE END…

If any questions?Reference:. www.nwk.iso/osi.it.com