OSI means Open System Interconnect model. OSI means Open System Interconnect model. Developed by the International Organization for Standardization in Developed by the International Organization for Standardization in It consists of seven layers. It consists of seven layers. Each layer has a different but specific processing function. Each layer has a different but specific processing function. OSI Model

Advice Person Sales Take Not DoDo Please OSI Model Layers Application Presentation Session Transport Network Data Link Physical Layer - 7 Layer - 6 Layer - 5 Layer - 4 Layer - 3 Layer - 2 Layer - 1 Upper Layer or Software Layer Lower Layer or Hardware Layer Heart of OSI

Application Layer Application Layer is responsible for providing Networking Services to user. It also known as Desktop Layer. Identification of Services is done using Port Numbers. Ports are nothing but Socket i.e. Entry and Exit Point to the Layer Total No. Ports 0 – Reserved Ports 0 – 1023 Open Ports 1024 – Application Presentation Session Transport Network Data Link Physical Application

Example of HTTP request ClientWeb Server

Example of HTTP request ClientWeb Server HTTP Request Webpage HTTP Request Listen on Port 80 Sending HTTP Reply Webpage Received HTTP Reply Webpage

Example of FTP request ClientFTP Server ftp://ftp.microsoft.com

Example of FTP request FTP Request ftp://ftp.microsoft.com FTP Request Listen on Port 21 Sending FTP Reply Received FTP Reply ftp://ftp.microsoft.com ClientFTP Server

Examples of Networking Services Service Port No. HTTP80 FTP21 SMTP 25 TELNET23 TFTP69

Application How data flows from Application Layer Data Presentation Session Transport Network Data Link Physical

Presentation Layer Presentation Layer is responsible for converting data into standard format. Examples : ASCII, EBCDIC, JPEG, MPEG, BMP, MIDI, WAV, MP3 Following tasks are perform at Presentation layer : Encoding – Decoding Encryption – Decryption Compression – Decompression Application Presentation Session Transport Network Data Link Physical Presentation

How data flows from Presentation Layer Data Application Presentation Session Transport Network Data Link Physical

Session Layer Session Layer is responsible establishing, maintaining and terminating session. Session ID also works at Session Layer. Examples : RPC  Remote Procedure Call SQL  Structured Query language NFS  Network File System Application Presentation Session Transport Network Data Link Physical Session

How data flows from Session Layer Data Application Presentation Session Transport Network Data Link Physical

Transport Layer Transport Layer is responsible for end-to-end connectivity. It is also known as heart of OSI Layers. Following task are performed at Transport Layer : - Identifying Service Multiplexing & De-multiplexing Segmentation Sequencing & Reassembling Flow Control Error Correction Application Presentation Session Transport Network Data Link Physical Transport

Identifying Service Transmission Control Protocol Connection Oriented Acknowledgement Reliable Slower Port No. 6 e.g. HTTP, FTP, SMTP User Datagram Protocol Connection Less No Acknowledgement Unreliable Faster Port No. 17 e.g. DNS, DHCP, TFTP TCPUDP

Application Presentation Session Multiplexing & De-multiplexing Transport TCP - 6UDP - 17 Network Data Link Physical

Segmentation Hello! How are you ? Hello!HowAreYou? Hello! How are you ? AB

Sequencing & Reassembling Hello! How are you ? Hello! How AreYou? Hello! How are you ? AB You Hello! How ? Are Hello! How AreYou? you Hello! How ? are

Sequencing & Reassembling Hello! How are you ? Hello! 1/5 How 2/5 Are 3/5 You 4/5 ? 5/5 Hello! How are you ? AB Hello! 1/5 How 2/5 Are 3/5 You 4/5 ? 5/5 Hello! 1/5 How 2/5 Are 3/5 You 4/5 ? 5/5 Hello! How are you ?

Error Correction Hello! How are you ? Hello! 1/5 How 2/5 Are 3/5 You 4/5 ? 5/5 Hello! How are you ? Hello! 1/5 Are 3/5 You 4/5 ? 5/5 Hello! 1/5 Are 3/5 You 4/5 ? 5/5 Segment Missing Hello! 1/5 Are 3/5 You 4/5 ? 5/5 How 2/5 How 2/5 Hello! How are you ? Hello! How are you ? AB

Flow Control - Windowing Sending 3-window Received 3-window Ack-Rec- 3 Sending 5-window Received 4-window AB Ack. Received- 4 PC-A can send 4 Segment at a time to PC-B PC-A can send 4 Segment at a time to PC-B

How data flows from Transport Layer Data TH Segment Application Presentation Session Transport Network Data Link Physical

Network Layer Network Layer is responsible for providing best path to data to reach destination. Logical Addressing sits on this layer. Device working on Network Layer is Router. It is divided into two parts Routed Protocols e.g. IP, IPX, Apple Talk. Routing Protocols e.g. RIP, IGRP, OSPF, EIGRP Application Presentation Session Transport Network Data Link Physical Network

Routed Protocols Hello! How are you ? AB Segment Source IP Destination IP Source IP Destination IP Segment Hello! How are you ?

Routing Protocols A

How data flows from Network Layer Data Segment NH e.g. Router Packet Application Presentation Session Transport Network Data Link Physical

Data link Layer Datalink Layer is divided into two Sub Layers : LLC – Logical Link Control It talks about Wan protocols e.g. PPP, HDLC, Frame-relay MAC – Media Access Control It talks about Physical Address. It is 48 bit Addressing i.e. 12 digit Hexadecimal No. It is also responsible for Error Detection Device working on Data Link Layer is Switch, Bridge, NIC. Application Presentation Session Transport Network Data Link Physical Data Link

Error Detection – CRC Check Hello! How are you ? Packet Source MAC C Destination MAC C Error Detected C C AB PC-A CRC No PC-B CRC No Error Detected For Error Correction Contact Source Transport layer PC-A CRC No PC-B CRC No Error Detected For Error Correction Contact Source Transport layer

Error Detection – CRC Check Packet Source MAC C Destination MAC C Source MAC C Destination MAC C Packet Hello! How are you ? C C AB

e.g. Switch How data flows from Data Link Layer Data Segment DH Packet DT Application Presentation Session Transport Network Data Link Physical Packet Frame

Physical Layer Physical Layer is responsible for electrical, mechanical or procedural checks. Data will be converted in Binary that is 0’s & 1’s. Data will be in the form of electrical pulses if it is Coaxial or Twisted Pair cable and in the form of Light if it is Fiber Optic Cable. Devices working at Physical Layer are Hubs, Repeaters, Cables, Modems etc. Application Presentation Session Transport Network Data Link Physical

Physical Layer Example Frame Frame Hello! How are you ? AB

How data flows from Physical Layer Data Segment Packet Frame Bits e.g. Hub Application Presentation Session Transport Network Data Link Physical

Segment Packet Frame A B Packet Data Bits Data Segment Data Encapsulation & De-capsulation Packet Data Application Presentation Session Transport Network Data Link Physical Application Presentation Session Transport Network Data Link Physical Bits DHDTNH TH Segment Packet DT Packet DHDTDH NH Segment NHTH Data TH Frame Packet

Application Transport Internet Network Access Network Access Comparing OSI with TCP/IP Layers OSI LayersTCP/IP Layers Application Presentation Session Transport Network Data Link Physical