1. CMPE 150- Introduction to Computer Networks 1 CMPE 150 Fall 2005 Lecture 18 Introduction to Computer Networks

2. CMPE 150- Introduction to Computer Networks 2 Announcements Midterm on 11.04. –In class, closed books/notes. Homework 3 is up. –Due on 11.07.05. Lab this week: discussion/review sessions for midterm. Lab next week: –Layer 2. –Ethernet.

3. CMPE 150- Introduction to Computer Networks 3 Today Finish MAC.

4. CMPE 150- Introduction to Computer Networks 4 Ethernet Cabling The most common kinds of Ethernet cabling.

5. CMPE 150- Introduction to Computer Networks 5 Ethernet Cabling (Cont’d) Three kinds of Ethernet cabling. (a) 10Base5, (b) 10Base2, (c) 10Base-T.

6. CMPE 150- Introduction to Computer Networks 6 Ethernet Topologies Cable topologies. (a) Linear, (b) Spine, (c) Tree, (d) Segmented.

7. CMPE 150- Introduction to Computer Networks 7 Switched Ethernet A simple example of switched Ethernet.

8. CMPE 150- Introduction to Computer Networks 8 Switched Ethernet (Cont’d) Point-to-point connections to multi-port hub acting like switch; no collisions. More efficient under high traffic load: break large shared Ethernet into smaller segments. Hub Switch

9. CMPE 150- Introduction to Computer Networks 9 Fast Ethernet IEEE 802.3u 100Mbps.

10. CMPE 150- Introduction to Computer Networks 10 Gigabit Ethernet (a) A two-station Ethernet. (b) A multistation Ethernet.. IEEE 802.11z.. All point to point.

11. CMPE 150- Introduction to Computer Networks 11 Gigabit Ethernet (Cont’d) Gigabit Ethernet cabling.

12. CMPE 150- Introduction to Computer Networks 12 Standardized MACs Topologies Bus Ring Round robin Reservation Contention Token bus (802.4) Polling (802.11) DQDB (802.6) CSMA/CD (802.3) CSMA(802.11) Token ring (802.5; FDDI) Techniques

13. CMPE 150- Introduction to Computer Networks 13 Wireless LANs

14. CMPE 150- Introduction to Computer Networks 14 Wireless LANs 2 modes of operation: –Infrastructure mode. –Ad hoc mode,

15. CMPE 150- Introduction to Computer Networks 15 Wireless LANs (a) Wireless networking with a base station. (b) Ad hoc networking.

16. CMPE 150- Introduction to Computer Networks 16 IEEE 802.11 IEEE standard for WLANs. Standardizes the PHY, MAC, and LLC. –LLC is the same as Ethernet.

17. CMPE 150- Introduction to Computer Networks 17 The 802.11 Protocol Stack Part of the 802.11 protocol stack.

18. CMPE 150- Introduction to Computer Networks 18 IEEE 802.11 Stack (Cont’d) Distributed access control mechanism (DCF) based on CSMA with optional centralized control (PCF). Physical Layer DCF PCF MAC layer Contention-free Service (polling) Contention Service (CSMA) LLC

19. CMPE 150- Introduction to Computer Networks 19 802.11 Distributed coordination function (DCF) uses CSMA-based protocol (e.g., ad hoc networks). CD does not make sense in wireless. –Hard for transmitter to distinguish its own transmission from incoming weak signals and noise. Point coordination function (PCF) uses polling to grant stations their turn to transmit (e.g., cellular networks).

20. CMPE 150- Introduction to Computer Networks 20 Why a new MAC for wireless?

21. CMPE 150- Introduction to Computer Networks 21 Why a new MAC for wireless? The range of a single radio may not cover the entire system.

22. CMPE 150- Introduction to Computer Networks 22 Why a new MAC for wireless? (a) The hidden station problem. (b) The exposed station problem.

23. CMPE 150- Introduction to Computer Networks 23 802.11 MAC DCF: CSMA or CSMA/CA. PCF; uses polling (centralized round-robin)

24. CMPE 150- Introduction to Computer Networks 24 What’s CSMA/CA? CSMA with collision avoidance. Radios are usually half-duplex. –Cannot send and listen at the same time. –CSMA/CD not possible. CSMA/CA means both physical- and virtual carrier sensing. –Tries to avoid hidden terminals.

25. CMPE 150- Introduction to Computer Networks 25 How does CSMA/CA work?

26. CMPE 150- Introduction to Computer Networks 26 802.11 Fragments A fragment burst.

27. CMPE 150- Introduction to Computer Networks 27 REVIEW

28. CMPE 150- Introduction to Computer Networks 28 REVIEW (1) Introduction, overview, terminology. The Telephone Network (PSTN or POTS). Addressing. Data networks. –Communication model. –System components. Connecting end systems: –Point-to-point (dedicated) link. –Multiple access (shared) link. –Switched point-to-point.

29. CMPE 150- Introduction to Computer Networks 29 REVIEW (2) Types of data networks: –Coverage: LAN, MAN, WAN. –Type of connection. –Topology. Protocols, Layering, Protocol Architecture (Stack), PDUs. Examples of protocol stacks. –OSI ISO. –TCP/IP. Protocol stack operation. –Encapsulation/de-encapsulation. –Overhead.

30. CMPE 150- Introduction to Computer Networks 30 REVIEW (3) Types of networks: –Circuit-, message-, and packet switching. Types of network services: –Connection versus connection-less service or datagram versus virtual circuit. Physical layer (PHY). –Function. –Analog versus digital transmission. –Digitization.

31. CMPE 150- Introduction to Computer Networks 31 REVIEW (4) PHY (Cont’d). –Sampling frequency. –Bit rate. –Signals and Systems. Fourier analysis. Nyquist’s Theorem. Shanon’s Theorem. Bandwidth. –Guided transmission. –More on the PSTN.

32. CMPE 150- Introduction to Computer Networks 32 REVIEW (5) PHY (Cont’d). –More on the PSTN. Components. Modems. Modulation. Baud rate versus bit rate. Full-, half-, and simplex transmission. Broadband access: ADSL, Cable, Wireless LL. Trunking. –Mux’ing and De-mux’ing. –Wireless transmission.

33. CMPE 150- Introduction to Computer Networks 33 REVIEW (6) PHY (Cont’d). –Wireless transmission. –Satellite. –Mobile phone system. DLL. –Functions. Framing, error-, and flow control. –Framing. Different framing mechanisms. Frame fields. –Error control. –Flow control.

34. CMPE 150- Introduction to Computer Networks 34 REVIEW (7) DLL. –Error control. Error detection versus error correction. Mechanisms for error detection/correction. –Error + Flow control protocols. Stop-and-Wait. ARQ. Sliding window. Go back N Selective repeat.

35. CMPE 150- Introduction to Computer Networks 35 REVIEW (8) DLL (Cont’d). –Window size and sequence numbers. –Bandwidth-delay product. –Example DLL protocols, MAC. –Why MACs? –Where is the MAC in the stack? –MACs and LANs. –Multiplexing. FDM, TDM. Dynamic TDM.

36. CMPE 150- Introduction to Computer Networks 36 REVIEW (9) MAC (Cont’d). –Types of MACs. –Contention-based MACs. Aloha family. CSMA family, Ethernet. –Ethernet MAC. –BEB. –Cabling. –Ethernet evolution. Wireless LANs. –IEEE 802.11.