1 / 25

ECE 7750 Distributed Control Systems FISP1 Topic: Network Delay Mitigation

ECE 7750 Distributed Control Systems FISP1 Topic: Network Delay Mitigation. Prepared by : Nathan Erni Dept. of Electrical and Computer Engineering Utah State University E: nate.erni@aggiemail.usu.edu; T: ( 435)232-7526;. 2/18/2010. Overview. Problem Statement UDP vs. TCP

elata
Download Presentation

ECE 7750 Distributed Control Systems FISP1 Topic: Network Delay Mitigation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ECE 7750 Distributed Control SystemsFISP1 Topic: Network Delay Mitigation Prepared by: Nathan Erni Dept. of Electrical and Computer Engineering Utah State University E: nate.erni@aggiemail.usu.edu; T: (435)232-7526; 2/18/2010

  2. Overview • Problem Statement • UDP vs. TCP • Things to Consider • UDP • What causes Delay • TCP • How are packets lost • What causes Delay • Measurement Resources • Summary • Further Work • References • Questions

  3. Problem Statement Network Delay

  4. UDP vs. TCP • User Datagram Protocol (UDP) • Connectionless • Header information is reduced, thus packet size is lighter • Reduction in processing time • Assumes packet arrival. Does not rebroadcast • Mainly used in short communication links (LAN) • Latency can be as low as packet Round Trip Time (RTT) • Best type of protocol to reduce latency. Most common are Real Time Protocol (RTP) and Real Time Control Protocol (RTCP) run under the UDP protocol. • Can have Missing packets, duplicate packets, or packet in wrong order • Transmission Control Protocol (TCP) • Connection-Oriented • 3-way communication before data transfer • Rebroadcasts packets if lost • Insures that packets arrive • Processing time increased • Keeps track of order • Mainly used in long distance communication links (WAN)

  5. Things to Consider • Understand your system that you want to control and pick what protocol works best for you. • Where is your controller located compared to the plant? • How will your system respond to packet loss and delay? • How much bandwidth does your controller have on the network? Is it shared?

  6. User Datagram Protocol • What Causes Delay? • Hub • All network data it receives on one port will be immediately transmitted out all the other ports, so each computer must take it's turn before sending data. • Switch • Acts like a smart hub. All network data it receives will be directed to only the destination port. This frees up bandwidth for all other lines.

  7. Application Presentation Session Transport Network Datalink Physical Two LANS Joined by a Subnet Application Presentation Session Transport Router 1 Router 2 Network Network Network Network Network Datalink Datalink Datalink Datalink Datalink Physical Physical Physical Physical Physical LAN 1 Transmission Line LAN 2 ~http://www.neng.usu.edu/classes/ece/6600/slides.html

  8. Transmission Control Protocol • How are Packets Lost? • Data Collision • Two packets are sent on the same line • Buffer Overflow • Packets are transmitted too fast for the receiving end • Noise • Noise corrupts data causing packet to be disregarded

  9. Transmission Control Protocol • How to Avoid Packets Lost? • Data Collision • No avoidance • Buffer Overflow • Receiver’s buffer size can be increased or sender’s buffer size can be decreased • Noise • No avoidance (assuming no access to physical layer)

  10. Transmission Control Protocol • Sending and Resending Packets • Window Size • Allocation of how many packets can be sent during a time duration • Sending Protocol • Stop and Wait • Go Back N • Selective Repeat

  11. Transmission Control Protocol Sender’s Window • Window Size 0123 1234 2345 3456 4567 5678 Sender Receiver 0123 1234 2345 3456 4567 5678 Receiver’s Window ~http://www.neng.usu.edu/classes/ece/6600/slides.html

  12. Station 1 Time Station 2 Transmission Control Protocol • Stop and Wait • Go Back N • Selective Repeat ~http://www.neng.usu.edu/classes/ece/6600/slides.html

  13. Transmission Control Protocol • What Causes Delay? • Address Resolution Protocol (ARP) Cache Timeout • No association with MAC address and IP address of receiver • Unused Bandwidth • Free bandwidth on the line • Buffer Overflow • Packets are transmitted too fast for the receiving end

  14. Transmission Control Protocol • How to Mitigate Delay? • Address Resolution Protocol (ARP) Cache Timeout • ARP associates the receivers MAC address with the current IP address. If this address is not know a broadcast packet is sent out requesting the receivers information. The association only stays in ARP cache for 4 seconds. Each time a packet is sent the ARP cache is updated, thus transmission delay can me mitigated if packets are sent less than every 4 seconds. This elevates the need for sending ARP packets. • To view ARP cache type “arp –a” in command window

  15. Transmission Control Protocol • How to Mitigate Delay? • Unused Bandwidth • Find the Narrow Link and push bandwidth to that limit. • Example: Consider a narrow link of 10 Mbps and a Round Trip Time (RTT) of 50 ms. The in flight data should be (10 Mbps) * (0.025 ms) = 250 Kbits. ~http://fasterdata.es.net/TCP-tuning/TCP-Tuning-Tutorial.pdf

  16. Transmission Control Protocol • How to Mitigate Delay? • Buffer Overflow • Maximize Buffer Size • Default TCP send/receive buffers are 64 KB, and default maximum size is 256 KB. This is 10 to 150 times too small • Good buffer size • Buffer size = Bandwidth*RTT • Example: Consider a narrow link of 500 Mbps (62 Mbytes/sec) and a Round Trip Time (RTT) of 50 ms. The buffer size should be (62 Mbytes/sec) * (0.05 seconds) = 3.1 Mbytes • Caution: Do not set the buffer size too big or too many packets will be sent at once and data will be lost

  17. Transmission Control Protocol • Comparison ~http://fasterdata.es.net/TCP-tuning/TCP-Tuning-Tutorial.pdf

  18. Transmission Control Protocol • One more thought. Parallel Streaming ~http://fasterdata.es.net/TCP-tuning/TCP-Tuning-Tutorial.pdf

  19. Measurement Resources • Tracert – measures delay to each node • Command Window “tracert google.com” • Iperf– measures Interval, Transfer, and Bandwidth • http://dast.nlanr.net/Projects/Iperf/ • Pathrate – measures the capacity of the narrow link • http://www.pathrate.org • Pathload – measures the available bandwidth • http://www.pathrate.org • Pipechar – measures hop-by-hop available bandwidth • http://dsd.lbl.gov/NCS/ • Tcpdump – TCP header information for source/destination address • ftp://ftp.ee.lbl.gov/ • Tcptrace – plots output analysis • http://www.ncne.nlanr.net?TCP/testrig/

  20. Summary • UDP • Latency as low as RTT • Risk packet loss, duplication, or wrong order • TCP • Latency increase from UDP due to processing time • Insures packet transfer is correct • Latency Mitigation • Avoid Hubs and Routers in LAN • Reduce unnecessary Nodes • Keep MAC/IP Correlation in ARP Cache • Utilize the Narrow Link Bandwidth • Maximize Buffer Settings • Use Parallel Streams

  21. Further Work • If time permitted, I would like to complete the below tasks. • Implementation of the tuning process in a real control system and measure the actual speed increase in both a LAN and WAN system for the UDP and TCP protocols. • Research other protocols to see if their RTT is faster or characteristics are better then UDP/TCP. • Research topics on measurement of how much delay a system can handle before becoming unstable. • Create a quick reference tuning guide/software that will allow you to measure desired information and change parameters within a network.

  22. References • TCP Tuning Techniques for High-Speed wide-Area Networks • http://fasterdata.es.net/TCP-tuning/TCP-Tuning-Tutorial.pdf • Computer Networking Course Website ECE6600 • http://www.neng.usu.edu/classes/ece/6600/slides.html • Minimizing Average Network Delay for Ultra-Wideband Wireless Networks • http://www4.ncsu.edu/~mlsichit/Research/Publications/wcncUWB.pdf • Stability Analysis of Networked Control Systems with Data Dropout and Transmission Delays • http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=4594178&isnumber=4592780 • Topics in High-Performance Messaging • http://www.29west.com/docs/THPM/packet-loss-myths.html

  23. References • Stability of Networked Control Systems in the Presence of Packet Loss • http://www.ecse.rpi.edu/~babak/cdc2003_camera_ready.pdf • Packet Loss Myths • http://www.29west.com/docs/THPM/packet-loss-myths.html • Network Latency • http://smutz.us/techtips/NetworkLatency.html • Using UDP socket connections for low-latency and loss-tolerant scenarios in AIR 2 (Part 1) • http://www.insideria.com/2009/11/udp-socket-connections-for-los-1.html • Comparative analysis – TCP – UDP • http://www.laynetworks.com/Comparative%20analysis_TCP%20Vs%20UDP.htm • Switches vs. Hubs • http://www.networkclue.com/hardware/network/switches-vs-hubs.aspx

  24. Questions?

  25. Extra Material

More Related