1. COP 5611 Operating Systems Spring 2010 Dan C. Marinescu Office: HEC 439 B Office hours: M-Wd 2:00-3:00 PM

2. 2 22222 Lecture 9 Reading Assignment: Chapter 7 from the online textbook HW1 due today. Remember: A progress report for the project is due on every Monday till week 12. Last time: Thread coordination and scheduling  Multi-level memories  I/O bottleneck Today:  Network properties  Layering  Data link layer Next time  Network layer

3. 3 Properties of Networks Physical limitations:  Speed of light  finite communication latency  Hostile environments  Limited channel capacity  limited bandwidth Channels are shared - multiplexed  Why: Support any-to-any communication Share costs  How Isochronous multiplexing – scheduled access  TDM  FDM Asynchronous multiplexing

4. 4 Communication channels are multiplexed

5. 5 Data flow on an isochronous link

6. 6 A data communication network

7. 7 Asynchronously multiplexed link

8. 8 Communication Continuous versus bursty  The old phone network versus data networks  Human versus computer communication Connection-oriented versus connectionless communication Packet-forwarding networks  Routing problem  Delays

9. 9

10. 10 Packet forwarding (store and forward) networks

11. 11 Problems in packet forwarding networks Delay  Propagation delay  Transmission delay  Processing delay  Queuing delay Resources are finite and a worst case design is not feasible  heavy tail distributions of resource needs Buffer overflow and discarded packets  Adaptive rate modulated by information regarding network congestion  Timers and packet retransmission  Duplicate packets

12. 12 Queuing delays versus utilization.

13. 13 Recovery of lost packets

14. 14 Duplicate requests

15. 15 Delays and recovery lead to duplicate response

16. 16

17. 17 Layering Simplify the design Example- RPC

18. 18 Client-server communication based on RPC

19. 19

20. 20

21. 21 Example of layered design

22. 22 Data link layer

23. 23 Network layer

24. 24 End-to-end (transport) layer

25. 25 How many layers should a network model have? OSI –has 7 layers Internet is based on a model including  Application  Transport  Network  Data Link  Physical Layer Applications are very diverse and it makes no sense for a lower layer to implement functions required by higher layers. The end-to-end argument  application knows best

26. 26 Network composition Mapped composition  some layers of a network are composed of basic data-link, network, and transport layers of another network. Overlay networks Internetworking  interconnect several networks together, e.g., the Internet

27. 27 Network composition. The overlay network Gnutella uses for its link layer an end-to-end transport protocol of the Internet. In turn, the Internet uses for one of its links an end-to-end transport protocol of a dial-up phone system

28. 28 More about the link layer Function: push bits from one place to another Analog worlds Capacity of a communication channel Capacity of a noisy communication channel C= B x log (1+ signal/noise) B is the bandwidth in Hz signal/noise – ratio of signal power to noise power Signals attenuation Signals are distorted over long distances

29. 29 Serial transmission

30. 30 How to push bits from A to B which do not share the same clock? First raise the READY line

31. 31 Signal attenuation and shape distortion

32. 32 Framing A pattern of bits serve as a frame delimiter – e.g., seven 1’s Bit stuffing:  The sender: add a 0 whenever it encounters a pattern of six 1’s in data  The receiver: remove a 0 following a pattern of six 1’s in data Add a frame header Add a frame trailer

33. 33 Sender bit stuffing procedure

34. 34 Receiver bit stuffing procedure

35. 35 A network protocol may use multiple data link protocols

36. 36 Multiple transport and data link protocols

37. 37 Sending a frame

38. 38 Receiving a frame