Networking Fundamentals: Layering, Multiplexing, and Communication Challenges

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

2. 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 2 2 2 2 2

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. Communication channels are multiplexed

5. Data flow on an isochronous link

6. A data communication network

7. Asynchronously multiplexed link

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

10. Packet forwarding (store and forward) networks

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. Queuing delays versus utilization.

13. Recovery of lost packets

14. Duplicate requests

15. Delays and recovery lead to duplicate response

17. Layering • Simplify the design • Example- RPC

18. Client-server communication based on RPC

21. Example of layered design

22. Data link layer

23. Network layer

24. End-to-end (transport) layer

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. 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. 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. 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. Serial transmission

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

31. Signal attenuation and shape distortion

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. Sender bit stuffing procedure

34. Receiver bit stuffing procedure

35. A network protocol may use multiple data link protocols

36. Multiple transport and data link protocols

37. Sending a frame

38. Receiving a frame