UNDERSTANDING OSI REFERENCE MODEL

DEVELOPMENT HISTORY ABOUT OSI  THE MODEL

IN THE LATE 1970 TWO GROUPS CAME TOGETHER WITH THE GOAL OF TO DEFINE A SPECIFIC STANDARD FOR THE ARCHITECTURE OF NETWORKING SYSTEMS.
ONE KNOW AS INTERNATIONAL ORGANIZATION  FOR STANDARDIZATION  (ISO) AND THE OTHER INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULATIVE COMMITTEE.

EACH ORGANIZATION DEVELOPS A DOCUMENT AND IN 1983 THE DOCUMENTS  WERE MERGE TOGETHER. 

 

TO FORM THE REFERENCE MODEL OF THE  OPEN SYSTEM INTERCONNECT IN 1984. AND THE CONCEPT OF THE SEVEN LAYERS WAS PROVIDER BY CHARLES BACH MAN. EACH LAYER WORKS DIRECTLY WITH THE LAYER BENEAT IT, AND PROVIDE SERVICES FOR LAYER ABOVE IT.

                                                  WHAT IS AN OSI MODEL

MEANING OF THE ABBREVIATION IS OPEN SYSTEM INTERCONNECT. OSI IS A REFERENCE MODEL ARCHITECTURE THAT ENABLE DIFFERENT NETWORK TO COMMUNICATE RELIABLE BETWEEN DIFFERENT SYSTEM.

       

         SOME ADVANTAGES OF THE OSI REFERENCE MODEL

  1. ALLOWS DIFFERENT VENDORS OF NETWORKS TO INTER OPERATE.

   2. IT ALLOWS VARIOUS TYPES OF NETWORK  AND HARDWARE TO COMMUNICATE.

3. DIVIDES NETWORK COMMUNICATION INTO SMALLER AND SIMPLER FORM COMPONENT WHICH AID IN TROUBLE SHOOTING.

   4.IT ENCOURAGES INDUSTRIAL STANDARDIZATION BY DEFINING WHAT STANDARDS OCCUR AT EACH LAYER OF THE MODEL.

   5.IT PREVENT CHANGES IN ONE LAYER FROM AFFECTING THE OTHER LAYER.

PHYSICAL LAYER

IT REPRESENTS THE NETWORK MEDIA AND DEVICES.ITS MAIN FUNCTION IS TO PROVIDE AN INTERFACE FOR TRANSMISSION OF INFORMATION. ITS CHARACTERISTICS ARE PHYSICAL DATA RATES AND PHYSICAL CONNECTORS. 

SOME DEVICES THAT WORK AT THESE LAYER HUBS, NIC, REPEATERS, MODEM. SOME PROTOCOLS THAT WORK AT THESE LAYER ARE DSL, USB, ISDN, IRDA.

DATALINK LAYER

IT REPRESENTS WAYS OF TRANSFERRING DATA BETWEEN DEVICES. BY THE USE OF FRAMES. ITS MAIN CHARACTERS IT IMPLEMENT FLOW CONTROL,SUPPORT POINT TO POINT AS WELL AS BROADCAST INFORMATION AND HALF DUPLEX AND FULL DUPLEX COMMUNICATION.  

SOME DEVICES THAT WORK AT THIS LAYER ARE SWITCHES, NETWORK ADAPTER, BRIDGES, WIRELESS ACCESS POINT.SOME PROTOCOLS THAT WORK AT THIS LAYER ARE PPP, CDP, FDDI, LAPD.

NETWORK  LAYER   

IT’S THE LAYER RESPONSIBLE FOR MOVING DATA AROUND A NETWORK OF NETWORKS. KNOWN AS AN INTERNET WORK OR INTERNET.ITS PROVIDES ADDRESS PATHS FOR FRAMES (PACKETS). ITS HANDLES CONGESTION IN THE NETWORK AND FRAGMENTS PACKETS AND PROVIDES OPTIMUM PATH FOR PACKETS.

SOME  DEVICES THAT OPERATE AT THESE LAYER ROUTERS, BASIC FIREWALLS, LAYER 3 SWITCHES.  SOME PROTOCOLS THAT WORK AT THIS LAYER IP, ICMP, ARP, IGMP

TRANSPORT LAYER

ITS KNOW AS AN END TO END LAYER PROTOCOL RESPONSIBLE FOR ENSURING RELIABLE DELIVERY OF DATA. DUE TO ITS RELIABLE MECHANISM IT HELPS TO EXCHANGE DATA BETWEEN TWO PROCESS IN DIFFERENT COMPUTERS AND PROVIDES CONNECTION FOR SERVICES ORIENTED.  IT BREAKS MESSAGES FROM THE SESSION LAYER INTO PACKET FORMAT.  

 SOME  DEVICES THAT WORKS AT THIS LAYER MULTI LAYER SWITCHES, FIREWALLS, IDS.  SOME PROTOCOLS THAT WORK AT THIS LAYER TCP,UDP.

SESSION LAYER

ITS HELPS TO  START, CONTROL AND END CONVERSATIONS KNOWN AS (SESSIONS) BETWEEN APPLICATIONS. ITS ALSO RESPONSIBLE FOR TERMINATING CONNECTION. ITS ALSO PROVIDES SERVICES LIKE DIALOGUE AND DISCIPLINE. 

SOME  DEVICES THAT OPERATE  AT THIS LAYER OF THE OSI REFERENCE MODEL ARE  WALKIE TALKIE, GATEWAY. SOME PROTOCOLS THAT WORK AT THESE LAYER OF THE OSI MODEL NFS,SIP,PTP, (TLS/SSL).

PRESENTATION LAYER

ITS  THE SECOND LAYER FROM THE TOP OF THE OSI REFERENCE LAYER MODEL. IT DEFINES A FORMAT OR STANDARD IN WHICH DATA NEEDS TO BE EXCHANGE BETWEEN TWO COMMUNICATION ENTITIES . AND ALSO PRESENTS DATA TO THE APPLICATION LAYER.COMPRESSION AND ENCRYPTION.  THIS LAYER MAKES IT POSSIBLE FOR COMPUTERS WITH DIFFERENT REPRESENTATION TO COMMUNICATE.  

 SOME DEVICES THAT WORKS AT THIS LAYER OF THE OSI MODEL COMPUTERS AND MOBILE PHONES .  SOME PROTOCOLS THAT WORK AT THESE LAYER OF THE OSI MODEL ARE HTTP, TLS,SSL.

 APPLICATION LAYER

ITS THE HIGHEST LAYER OF THE OSI MODEL.  IT PROVIDES SERVICES FOR AN APPLICATION PROGARM TO ENSURE  EFFECTIVE COMMUNICATION WITH ANOTHER APPLICATION PROGARM IN A NETWORK IS POSSIBLE. IT INTERACTS WITH THE APPLICATION PROGARMS. SUCH AS FILE TRANSFER, ELECTRONIC MAIL, REMOTE LOGIN AND SO ON.ITS THE ENDING OF DATA TRANSFER. AT THIS POINT DATA IS A VISUAL FORM.  

SOME DEVICES THAT WORK AT THESE LAYER OF THE OSI MODEL PROXY AND FIREWALL SERVERS. SOME PROTOCOLS THAT WORKS AT THESE LAYER OF THE OSI MODEL TFTP,DNS,SMTP,SNMP.

 THE OSI REFERENCE MODEL IS A TOOL THAT HELPS TO SIMPLIFY NETWORK  DESIGN, MANAGE AND TROUBLESHOOT NETWORKS IT’S A PRIMARY ARCHITECTURE FOR INTER COMPUTER COMMUNICATIONS.

 TAGS: PHYSICAL LAYER= BINARY TRANSMISSION,DATA-LINK LAYER= MEDIA ACCESS,NETWORK LAYER= ADDRESS PATH (PACKETS), TRANSPORT LAYER= END TO END CONNECTIONS,SESSION LAYER= INTER HOST COMMUNICATION,PRESENTATION LAYER= DATA REPRESENTATION,APPLICATION LAYER=  NETWORK PROCESS TO APPLICATION.