Lec02 layering

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Lec02 layering

  1. 1. CS425: Computer Networks Bhaskaran Raman [braman] AT [cse.iitk.ac.in]http://www.cse.iitk.ac.in/users/braman/cs425/ Department of CSE, IIT Kanpur Jul-Dec 2006 Lecture 02: Fri, 04 Aug 2006
  2. 2. Updates/Announcements● Course web-page is up● Lecture times (CS101): – Mon 11-12, Fri 5-6:30● Tutorial times (CS101): – Tue 4:30-6, Wed 11-12:30, Thu 5:30-7 – May be reduced to one hour● Will have to move to LHC if needed
  3. 3. Recap and Lecture Outline● Recap: – What is a network? – What is a protocol?● Lecture outline: – What are the required/desirable functionalities? – How to structure them? – Concepts of layering, encapsulation – Physical layer encoding (Kameswari Chebrolu)
  4. 4. Required/Desired Functionalities● Modulation, ● Multiplexing, demodulation demultiplexing● Encoding ● Quality-of-Service● Framing ● Security● Detect, correct errors ● Compression● Medium Access Control ● Naming, addressing● Routing ● Application● Reliability● In-order delivery
  5. 5. OSI Layering ● What is layering? Application – “ Structuring technique Presentation which permits the network... to be viewed Session as logically composed of Transport a succession of layers, each wrapping the lower Network layers and isolating them Link-Layer-Ctrl from higher layers” Medium-Access [Zim80] Physical   
  6. 6. Advantages of Layering ● Handle heterogeneity ● Software reuse, modularity ● Allows extensibility, new technologies   
  7. 7. Inter-Layer Communication Layer N+1 Layer N+1 Downcall Upcall Layer N Layer N Layer N-1 Layer N-1 PHY Host-1 Host-2 Interface definition between layers is crucial   
  8. 8. Encapsulation & Decapsulation Layer N+1 Layer N+1 Layer N Layer N Layer N-1 Layer N-1 PHY Host-1 Host-2 Each layer adds/removes its header   
  9. 9. Logical Communication between Layers at the Same Level Application Application Logical Transport Transport Logical Network Network Logical LLC/MAC LLC/MAC Logical PHY PHY PHY  Host-1   Host-2
  10. 10. End-to-end versus Hop-by-hop Application Application Logical Transport Transport Logical Network Network Network Network Logical Logical Logical LLC/MAC LLC/MAC LLC/MAC LLC/MAC Logical Logical Logical PHY PHY PHY PHY PHY PHY PHY End-Host-1 Intermediate- Intermediate- End-Host-2 Host-1 Host-2   
  11. 11. Summary of Concepts ● Layering ● Inter-layer communication ● Encapsulation ● End-to-end versus hop-by-hop communication ● Concepts not covered from Chapter-1 of Peterson book: – Packet switching – Sockets – Protocol graph  – Bandwidth-Delay Product (BDP)  

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