OSI ModelOSI Model

Joan Baez Dimatira, RECEJoan Baez Dimatira, RECE06/18/1406/18/14

An attempt for a framework for developing An attempt for a framework for developing networking technologiesnetworking technologies

OSI became a tool for explaining the OSI became a tool for explaining the Networking in generalNetworking in general

Before OSI was created people created Before OSI was created people created their Software/Hardware as they wanted it their Software/Hardware as they wanted it to be. There was not any compatibility. to be. There was not any compatibility. Now OSI is used as a rule set for all Now OSI is used as a rule set for all vendors to create their Software/Hardware vendors to create their Software/Hardware by using the standards.by using the standards.

How OSI was created and howHow OSI was created and how

Open Systems Interconnection (OSI) is a set Open Systems Interconnection (OSI) is a set of internationally recognized, non-proprietary of internationally recognized, non-proprietary standards for networking and for operating standards for networking and for operating system involved in networking functions.system involved in networking functions.

7 Layers7 Layers

All People Seem To Need Data Processing

• Each layer support the layers above it and offers services to the layers below

• Each layer performs unique and specific task

• A layer only has knowledge of its neighbour layers only

• A layer service is independent of the implementation

LAYER 7 – The APPLICATION Layer

• The top layer of the OSI model

• Provides a set of interfaces for sending and receiving applications to gain access to and use network services, such as: networked file transfer, message handling and database query processing

• Examples of such applications are spreadsheet programs, word processing programs, and bank terminal programs.

• Applications and Services run on it• Enables human network to interface the underlying data

network• Applications on that layer (E-mail clients, web browsers,

Chats, etc.) – top-stack applications (As people are on the top of the stack)

• Applications provide people with a way to create message• Application layer services establish an interface to the

network• Protocols provide the rules and formats that govern how

data is treated• Protocols on the destination and the host must match

Application layer(Layer 7)

• The application layer is responsible for providing services to the user.

• Coding and conversion of Application layer data to ensure that data from the source device can be interpreted by the appropriate application on the destination device.

• Compression of the data in a manner that can be decompressed by the destination device.

• Encryption of the data for transmission and the decryption of data upon receipt by the destination.

• This is the layer at which application programmers consider data structure and presentation

• Examples: GIF, JPEG, TIFF, etc.

LAYER 6 – The PRESENTATION Layer

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

LAYER 5 – The SESSION Layer• Enables two networked resources to hold ongoing

communications (called a session) across a network

• Applications on either end of the session are able to ex change data for the duration of the session

• This layer is: Responsible for initiating, maintaining and terminating sessions

• Responsible for security and access control to session information (via session participant identification)

• Responsible for synchronization services, and for checkpoint services

• Examples :- SQL, ASP(AppleTalk Session Protocol)

• The session layer is responsible for dialog control, authentication, permission and synchronization.

LAYER 4 – The TRANSPORT Layer• Manages the transmission of data across a network

• Manages the flow of data between parties by segmenting long data streams into smaller data chunks (based on allowed “packet” size for a given transmission medium)

• Reassembles chunks into their original sequence at the receiving end

• Provides acknowledgements of successful transmissions and requests resends for packets which arrive with errors- retransmission

• Layer 4 protocols include TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).

• The transport layer is responsible for the delivery of a message from one process to another.

LAYER 3 – The NETWORK Layer

• Handles addressing messages for delivery, as well as translating logical network addresses and names into their physical counterparts

• Responsible for deciding how to route transmissions between computers

• This layer also handles the decisions needed to get data from one point to the next point along a network path

• This layer also handles packet switching and network congestion control

• Examples :- IP, IPX, AppleTalk.

• The network layer is responsible for the delivery of individual packets from

• the source host to the destination host.

LAYER 2 – The DATA LINK Layer

• Handles special data frames (packets) between the Network layer and the Physical layer

• At the receiving end, this layer packages raw data from the physical layer into data frames for delivery to the Network layer

• At the sending end this layer handles conversion of data into raw formats that can be handled by the Physical Layer

• Examples :- Ethernet, Frame Relay, FDDI.

2.1. Logical Link Control (LLC ) – Establishment and control of logical links between local devices on a

network.

2.2. Media Access Control (MAC) – The procedures used by devices to control access to the network

medium.• Frame sequencing • Frame acknowledgment • Addressing• Frame delimiting• Frame error checking• PDU: frame

• The data link layer is responsible for moving frames from one hop (node) to the next.

LAYER 1 – The PHYSICAL Layer• Converts bits into electronic signals for outgoing messages

• Converts electronic signals into bits for incoming messages

• This layer manages the interface between the the computer and the network medium (coax, twisted pair, etc.)

• This layer tells the driver software for the MAU (media attachment unit, ex. network interface cards (NICs, modems, etc.)) what needs to be sent across the medium

• The bottom layer of the OSI model

• Examples :- EIA/TIA-232, RJ45, NRZ.

• The physical layer is responsible for movements of• individual bits from one hop (node) to the next.

Remember

• A convenient aid for remembering the OSI layer names is to use the first letter of each word in the phrase:

• All People Seem To Need Data Processing