2 Content Introduction to the OSI layer How OSI was created and why Comparison with TCP/IPLayers :Application layerPresentation layerSession layerTransport layerNetwork layerData link layerPhysical layerConclusionResources
3 Introduction to the OSI layer Open Systems Interconnection (OSI)Each layer support the layers above it and offers services to the layers belowEach layer performs unique and specific taskA layer only has knowledge of its neighbour layers onlyA layer service is independent of the implementation
4 How OSI was created and how An attempt for a framework for developing networking technologiesOSI became a tool for explaining the Networking in generalBefore OSI was created people created their Software/Hardware as they wanted it to be. There was not any compatibility. Now OSI is used as a rule set for all vendors to create their Software/Hardware by using the standards.
5 Protocol Reference Model of OSI II OSI Overview1. OSI - layered framework for the design of network systems that allows communication across all types of computer systems.2. The OSI 7 Layers. ( Brief functional overview. )3. Vertical and horizontal communication between the layers using interfaces. (defines what information and services should the layer provide to the layer above it. )
6 Layers Each layer contains a logical grouping of functions Each function receive an input(one or more) and produces an output6
7 Protocol Reference Model of OSI I History1. The need for standardization- many vendors, no interoperability- no common framework2. ISO and CCITT came up withOSI (Open System Intercommunication) in 1984.3. OSI Protocol Suite – unaccepted by vendors and users. (TCP won)4. OSI – a standard, which allows communication between different systems without requiring changes to the logic of the underlying hardware and software.
8 Protocol Reference Model of OSI Layer abstraction and the path of the message
9 Protocol Reference Model of OSI OSI Overview4. Data Encapsulationa) PDU conception – each protocol on the diff. layer has its own format.b) Headers are added while a packet is going down the stack at each layer.c) Trailers are usually added on the second layer.
10 Comparison with TCP/IP Pretty similar to OSITCP/IP has less layers(four)Main difference in layers is after layer 4
12 Application layer(Layer 7) Applications and Services run on itEnables human network to interface the underlying data networkApplications on that layer ( 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 messageApplication layer services establish an interface to the networkProtocols provide the rules and formats that govern how data is treatedProtocols on the destination and the host must match
13 Protocol Reference Model of OSI III The OSI Layers7. Application LayerProvides user interfaces and support for servicesResource sharing and device redirectionRemote file accessRemote printer accessInter-process communicationNetwork managementDirectory servicesElectronic messaging (such as mail)Network virtual terminals
14 Presentation layer(Layer 6) 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 presentationExamples: GIF, JPEG, TIFF, etc.Sometimes n distinction is made between the presentation and application layers. For example http/https. HTTP is generally regarded as an application layer protocol although it has Presentation layer aspects such as the ability t identify character encoding for roper conversion
15 Protocol Reference Model of OSI The OSI Layers6. Presentation LayerTranslation (connects different computer systems)Compression (transmission efficiency)Encryption (SSL security)
16 Session layer(Layer 5)Functions at this layer create and maintain dialogs between source and destination applicationsAuthenticationPermissionsSession Restoration (Checkpoint or recovery)
17 Protocol Reference Model of OSI The OSI Layers5. Session LayerSession establishment, maintenance and termination (Deciding who sends, and when.)Session support (security, name recognition, logging )
18 Transport layer(Layer 4) Tracking the individual communication between applications on the source and destination hostsSegmenting data and managing each pieceReassembling the segments into streams of application dataIdentifying the different applicationsConversation MultiplexingSegmentsConnection-oriented conversationsReliable deliveryOrdered data reconstructionFlow controlTCP – Web BrowserUDP – Video Streaming Applications
19 Protocol Reference Model of OSI The OSI Layers4. Transport LayerConnectionless and connection- oriented servicesProcess-Level AddressingMultiplexing and DemultiplexingSegmentation, Packaging and ReassemblyConnection Establishment, Management and TerminationAcknowledgments and RetransmissionsFlow Control
20 Network layer(Layer 3) Addressing (IPV4) Encapsulation (Inserts a header with source and destination IPs)Routing (Move a packet over the Internet)Decapsulation (Open the packet and check the destination host)IP is connectionless
21 Protocol Reference Model of OSI The OSI Layers3. Network LayerLogical AddressingRouting (where the packet is destinated to)Datagram EncapsulationFragmentation and Reassembly (handling too big packets )Error Handling and Diagnostics ( using status messages for example )
22 Protocol Reference Model of OSI End to end packet delivery
23 Data link layer(Layer 2) It is the role of the OSI Data Link layer to prepare Network layer packets for transmission and to control access to the physical media.Allows the upper layers to access the media using techniques such as framingControls how data is placed onto the media and is received from the media using techniques such as media access control and error detectionFrame - The Data Link layer PDUNode - The Layer 2 notation for network devices connected to a common mediumMedia/medium - The physical means for the transfer of information between two nodesNetwork - Two or more nodes connected to a common mediumThe Data Link layer is responsible for the exchange of frames between nodes over the media of a physical network.
24 Protocol Reference Model of OSI The OSI Layers2. Data Link Layer2.1. 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 sequencingFrame acknowledgmentAddressingFrame delimitingFrame error checkingPDU: frame
25 Physical layer (Layer 1) The role of the Physical layer is to encode the binary digits that represent Data Link layer frames into signals and to transmit and receive these signals across the physical media that connect network devices.Copper cableFiberWireless
26 Protocol Reference Model of OSI The OSI LayersPhysical LayerDefinition of Hardware Specifications (of cables, connectors, wireless radio transceivers, network interface cards )Encoding and Signaling (bit representation)Data Transmission and Reception (half duplex, full duplex )Topology and Physical Network Design (mesh, ring, bus)PDU: bit
28 Conclusion The way people learn Networking A standard for software A standard for hardwareSeven layers architectureEach layer independent on the othersSimilar to TCP/IP(TCP/IP explained)OSI is used as a model for developing network aware applications(Here I mean that people use its structure to model software)