ISO OSI reference model ppt

osi reference model ppt presentation and osi reference model with example ppt and comparison of osi and tcp reference model ppt
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Dr.ShivJindal,India,Teacher
Published Date:19-07-2017
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Review of Networking and Design Concepts (II) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1Overview  Protocols, layering, encapsulation  Function-placement: End-to-end principle  Implementation: App-layer framing, ILF  Interface design: functionality, technology, performance  Rules of thumb in system design  Chapter 1,2,11 in Doug Comer book  Reading: Saltzer, Reed, Clark: "End-to-End arguments in System Design"  Reading: Clark: "The Design Philosophy of the DARPA Internet Protocols":  Reading: RFC 2775: Internet Transparency: In HTML Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 2Protocols Human protocol vs Computer network protocol: A series of functions performed at different locations. Hi TCP connection req. Hi TCP connection Got the reply. time? Get http://www.rpi.edu/index.htm 2:00 file time Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 3Why Layering? (FTP – File Transfer Protocol, NFS – Network File Transfer, HTTP – World Wide Web protocol) FTP NFS HTTP Application Telnet Coaxial Fiber Packet Transmission cable optic radio Media  No layering: each new application has to be re-implemented for every network technology Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 4Why Layering?  Solution: introduce an intermediate layer that provides a unique abstraction for various network technologies FTP NFS HTTP Telnet Application Intermediate layer Coaxial Fiber Packet Transmission cable optic radio Media Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 5What is Layering?  A technique to organize a network system into a succession of logically distinct entities, such that the service provided by one entity is solely based on the service provided by the previous (lower level) entity Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 6Layering  Advantages Modularity – protocols easier to manage and maintain Abstract functionality –lower layers can be changed without affecting the upper layers Reuse – upper layers can reuse the functionality provided by lower layers  Disadvantages Information hiding – inefficient implementations Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 7Protocols  Building blocks of a network architecture  Each protocol object has two different interfaces  service interface: defines operations on this protocol  peer-to-peer interface: defines messages exchanged with peer L L i+1 i+1 service interface L L i i peer interface Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 8ISO OSI Reference Model  Seven layers Lower three layers are peer-to-peer Next four layers are end-to-end Application Application Presentation Presentation Session Session Transport Transport Network Network Network Datalink Datalink Datalink Physical Physical Physical Physical medium Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 9Encapsulation  A layer can use only the service provided by the layer immediate below it  Each layer may change and add a header to data packet data data data data data data data data data data data data data data Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 10OSI vs. TCP/IP  OSI: conceptually define services, interfaces, protocols  Internet: provide a successful implementation Telnet FTP DNS Application Application Presentation Session TCP UDP Transport Transport IP Network Internet Datalink Host-to- Packet LAN network radio Physical OSI TCP Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 11Example: Transport Protocol (Logical Communication) data application  take data from app transport transport  add addressing, network link reliability check info physical to form “datagram” ack network  send datagram to application link transport physical data peer network  wait for peer to ack link data physical receipt application application transport transport transport  analogy: post office network network link link physical physical (Source: Kurose & Ross) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 12Example: Transport Protocol (Physical Communication) data application transport network link physical network application link transport physical network link data physical application application transport transport network network link link physical physical (Source: Kurose & Ross) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 13Key questions  How to decompose the complex system functionality into protocol layers?  What functions to be placed at which levels?  Can a function be placed at multiple levels ? Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 14Common View of the Telco Network Brick Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 15Common View of the IP Network Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 16End-to-End Argument  “…functions placed at the lower levels may be redundant or of little value when compared to the cost of providing them at the lower level…”  “…sometimes an incomplete version of the function provided by the communication system (lower levels) may be useful as a performance enhancement…”  This leads to a philosophy diametrically opposite to the telephone world which sports dumb end- systems (the telephone) and intelligent networks. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 17Example: Reliable File Transfer Host A Host B Appl. Appl. OS OS OK  Solution 1: make each step reliable, and then concatenate them  Solution 2: end-to-end check and retry Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 18Discussion  Solution 1 not complete What happens if the sender or/and receiver misbehave?  The receiver has to do the check anyway  Thus, full functionality can be entirely implemented at application layer; no need for reliability from lower layers  Is there any need to implement reliability at lower layers? Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 19Discussion  Yes, but only to improve performance  Example: assume a high error rate on communication network then, a reliable communication service at datalink layer might help Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 20