1. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Networks zNetwork-based design. yCommunication analysis. ySystem performance analysis. zInternet. zInternet-enabled systems. zVehicles as networks. zSensor networks

2. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Communication analysis zFirst, understand delay for single message. zDelay for multiple messages depends on: ynetwork protocol; ydevices on network.

3. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Message delay zAssume: ysingle message; yno contention. zDelay: yt m = t x + t n + t r y = xmtr overhead + network xmit time + rcvr overhead

4. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Example: I 2 C message delay zNetwork transmission time dominates. zAssume 100 kbits/sec, one 8-bit byte. zNumber of bits in packet: yn packet = start + address + data + stop y = 1 + 8 + 8 + 1 = 18 bits zTime required to transmit: 1.8 x 10 -4 sec. z20 instructions on 8 MHz controller adds 2.5 x 10 -6 delay on xmtr, rcvr.

5. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Multiple messages zIf messages can interfere with each other, analysis is more complex. zModel total message delay: yt y = t d + t m y = wait time for network + message delay

6. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Arbitration and delay zFixed-priority arbitration introduces unbounded delay for all but highest- priority device. yUnless higher-priority devices are known to have limited rates that allow lower devices to transmit. zRound-robin arbitration introduces bounded delay proportional to N.

7. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Further complications zAcknowledgment time. zTransmission errors.

8. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Priority inversion in networks zIn many networks, a packet cannot be interrupted. zResult is priority inversion: ylow-priority message holds up higher-priority message. zDoesn’t cause deadlock, but can slow down important communications.

9. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Multihop networks zIn multihop networks, one node receives message, then retransmits to destination (or intermediate). ABC hop 1 hop 2 Network 1Network 2

10. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. System performance analysis zSystem analysis is difficult in general. ymultiprocessor performance analysis is hard; ycommunication performance analysis is hard. zSimple example: uncertainty in P1 finish time -> uncertainty in P2 start time. P1P2

11. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Analysis challenges zP2 and P3 can delay each other, even though they are in separate tasks. zDelays in P1 propagate to P2, then P3, then to P4. P2 P3 P1 P4

12. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Lower bounds on system zComputational requirements: ysum up process requirements over least-common multiple of periods, average over one period. z Communication requirements: yCount all transmissions in one period.

13. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Hardware platform design zNeed to choose: ynumber and types of PEs; ynumber and types of networks. zEvaluate a platform by allocating processes, scheduling processes and communication.

14. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. I/O-intensive systems zStart with I/O devices, then consider computation: yinventory required devices; yidentify critical deadlines; ychooses devices that can share PEs; yanalyze communication times; ychoose PEs to go with devices.

15. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Computation-intensive systems zStart with shortest-deadline tasks: yPut shortest-deadline tasks on separate PEs. yCheck for interference on critical communications. yAllocate low-priority tasks to common PEs wherever possible. zBalance loads wherever possible.

16. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Internet Protocol zInternet Protocol (IP) is basis for Internet. zProvides an internetworking standard: between two Ethernets, Ethernet and token ring, etc. zHigher-level services are built on top of IP.

17. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. IP in communication physical data link network transport presentation application session physical data link network transport presentation application session physical data link network node A router node B IP

18. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. IP packet zIncludes: yversion, service type, length ytime to live, protocol ysource and destination address ydata payload zMaximum data payload is 65,535 bytes.

19. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. IP addresses z32 bits in early IP, 128 bits in IPv6.  Typically written in form xxx.xx.xx.xx. zNames (foo.baz.com) translated to IP address by domain name server (DNS).

20. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Internet routing zBest effort routing: ydoesn’t guarantee data delivery at IP layer. zRouting can vary: ysession to session; ypacket to packet.

21. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Higher-level Internet services zTransmission Control Protocol (TCP) provides connection-oriented service. zQuality-of-service (QoS) guaranteed services are under development.

22. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. The Internet service stack IP UDP SNMP TCP User Datagram Protocol FTPHTTPSMTPtelnet

23. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Internet-enabled embedded system zInternet-enabled embedded system: any embedded system that includes an Internet interface (e.g., refrigerator). zInternet appliance: embedded system designed for a particular Internet task (e.g. email). zExamples: yCell phone. yLaser printer.

24. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Example: Javacam zHardware platform: yparallel-port camera; yNational Semi NS486SXF; y1.5 Mbytes memory. zUses memory-efficient Java Nanokernel.

25. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Javacam architecture Web browser QuickCam 486 Java nanokernel Java VM HTTP Quickcam server QuickCam applet

26. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Vehicles as networks z1/3 of cost of car/airplane is electronics/avionics. zDozens of microprocessors are used throughout the vehicle. zNetwork applications: yVehicle control. yInstrumentation. yCommunication. yPassenger entertainment systems.

27. CAN bus zFirst used in 1991. zSerial bus, 1 Mb/sec up to 40 m. zSynchronous bus. zLogic 0 dominates logic 1 on bus. zArbitrated with CSMA/AMP: yArbitration on message priority. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed.

28. CAN data frame z11 bit destination address. zRTR bit determines read/write from/to destination. zAny node can detect bus error, interrupt packet for retransmission. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed.

29. CAN controller zController implements physical and data link layers. zNo network layer needed---bus provides end-to-end connections. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed.

30. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Other vehicle busses zFlexRay is next generation: yTime triggered protocol. y10 Mb/s. zLocal Interconnect Network (LIN) connects devices in a small area (e.g., door). zPassenger entertainment networks: yBluetooth. yMedia Oriented Systems Transport (MOST).

31. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Avionics zAnything permanently attached to the aircraft must be certified by FAA/national agency. zTraditional architecture uses separate electronics for each instrument/device. yLine replaceable unit (LRU) can be physically removed and replaced. zFederated architecture shares processors across a subsystem (nav/comm, etc.)

32. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Sensor networks zWireless networks, small nodes. zAd hoc networks---organizes itself without system administrator: yMust be able to declare membership in network, find other networks. yMust be able to determine routes for data. yMust update configuration as nodes enter/leave.

33. © 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Node capabilities zMust be able to turn radio on/off quickly with low power overhead. yCommunication/computation power = 100x. zRadios should operate at several different power levels to avoid interference with other nodes. zMust buffer, route network traffic.