OSI and Layers

OSI MODEL

Model or main architectural reference for network that describe how data and network information communicated from a computer application to another computer application via transmission media.

OSI is not a hardware but a guide for vendors so that their devices can run in the network.

FUNCTION

Help network designer to understand every function from each layers that connected with the data communication flow and to simplify the understanding,utilization,design,data processing and vendor uniformity standard.

OSI Model divided into 7 Layers, with each character and function.

Each layer must can communicate with another layer that stands above or below them directly pass by series of protocol and standardization.

Every layer are responsible particulary to data communication process.

Every layer are responsible to create hardware interconnection, while the other layer responsible to corect troubles when the data transfer process is running.

OSI Layers Model divided by two group:

- Lower Layer

- Upper Layer

These 4 layer are included in ‘Lower Layer’:

Pshycal layer

Responsible for data process to bit and transfer it via media as cable and maintain physical connection from system to another system, specificating volt,cable speed, and pin compotition.

example: EIA/TIA-232, V.35,etc

Function :

• Representating bits depend from the media and protocol used

• Change voltage from high to low and vice versa

• Define voltage need,mechanical,procedural and functional,defend and non active physical connection between.

Data Link Layer:

Provide links for data, package it to frames that connected with ‘Hardware’ and then carry it via media. Manage Physical layer communication between connection system and error management.

Function

• Framing

• Convert bit to bytes and then to frames

• Provide acess to media using MAC address

• Only Detect ‘Error’ not repair it

• Provide Physical transmision from data

• Handle flow control

• Make sure that messages will be sent by devices that correspond in LAN using MAC address

• Translate from upper layer to physical layer bits belowa

• Create encapsulations which cover the real data

• Encapsulations will be taken off after package was sent to below layer

• Identificate tools in the network

• The package will not changed in the progress

• Put hardware address in the filter table and remeber which port that received the frames

• Determine the tolls location and mapping the tools on the network

Example : 802.3/ 802.2/ HDLC

Network Layer

Doesn’t care where the host is this layer will only find the best way to reach it and locate it in the network to deliver package.

Function

• Responsible to determine network address

• Decide best route that must be taken along the progress

• Keep queue traffic in the network

• Data in this layer is in the package form

• Provide logical addresing

• Error notifications, flow control

• Delivering intertools traffic which not connected in local network

This is example how this layer works:

- Package was received by router interface,

- Router will check the destination IP address, then

- Router check destination network address in it’s routing table.

- If data wasn’t found in the routing entry table so the data will be dropped

- If founded, router interface will spend data package that covered become data frame and sent to local network/neighbour router interface

Transport Layer

Function

• Segmentating and reassembling data from upper layer to become a same data flow

• Provide transport service from point to point

• Create a logical connection between sender host and destination host

• Provide Multiplexing mechanism(Technique to send and receive different kinds of data in the same time by one network media)

• Connection-oriented

• Made connection-oriented communication by creating session on the other remote tools

These 3 are included in ‘Upper Layer’:

Session layer

Function

• Determine how 2 terminal guard, maintain and manage connection

• Maintain so that data from each application still separated

• Established, Managed, Stopped session between application

• Responsible to form, manage, and decide sessions between upper layers

• Dialog Control between nodes

• Coordinate systems and determine their communication type

 (simplex,half dulplex, full duplex)

• Maintain separating data from many application which use network(SQL)

Presentation Layer

Function

• Responsible to how data converted and formatted to transfer data.

(Convertion .gif and .jpg)

• This layer create convertion code, data translation, encrypt and convert

• Menyajikan data

• Translating services

• Handle processes like ecryption,data type, data format, data structur

Application Layer

Function

• Communicate services to user application

• Responsible to information trade netween computer applications

like(email program, other services that run in the network)