1. Advanced Computer Networks1 Efficient Policies for Carrying Traffic Over Flow-Switched Networks Anja Feldmann, Jenifer Rexford, and Ramon Caceres Presenters: Tauhid, Reji and Murshed

2. Advanced Computer Networks2 Objective Increase the efficiency of the switching technique Reduce the overhead for establishing and maintaining the dedicated route or shortcut for flow

3. Advanced Computer Networks3 Introduction A possible solution could be grouping series of related data packets into flows and sending the flows through a shortcut path Benefits: improve performance and capitalizing on QoS of the switches Drawbacks: consume network resources to create and maintain dedicated path for the flow Different definition and criteria are necessary for flow construction and shortcut creation and maintenance

4. Advanced Computer Networks4 Introduction (Contd.) Three parameters determine the flow and shortcut decisions: aggregation: level for traffic combination timeout: time interval of any flow trigger: traffic quantity or number of packets for constituting a flow

5. Advanced Computer Networks5 Introduction (Contd.) The effects of varying these parameters were explored on three metrics of interest: percentage of traffic following the shortcut shortcut setup rate number of simultaneous shortcut

6. Advanced Computer Networks6 Trace Collection of Packets The Extensive packet-level trace collection was carried out on T1 line of AT&T Research Lab. Several aspects were considered as: -the traffic trace reflects the dominance of WWW -long continuous traffic traces were observed -the endpoint machines were taken for consideration -all the flow and shortcut parameters were evaluated on various parameters

7. Advanced Computer Networks7 Trace Collection of Packets (Contd.) The T1 line connects the AT&T Lab to the external internet. The Ethernet segment carries all traffic to and from the T1 line at a speed of 10-Mbits/s The Sniffer was equipped with tcdump to collect information of 100 00 packets in raw binary format.

8. Advanced Computer Networks8 Trace Collection of Packets (Contd.) Tcdump read each packet and generated an ASCII log Perl script classified each packet into flows Splus function processed all the log files on different performance metrics

9. Advanced Computer Networks9 Trace Collection of Packets (Contd.) From the optional field of the web request messages, the operating system of the client machine was identified. Linux and/or Windows systems were classified as personal computers IP address associated with multiple types of machines such as Windows and SunOS are classifies as Proxy Servers

10. Advanced Computer Networks10 Hourly average throughput of the Ethernet segment

11. Advanced Computer Networks11 The packet size distribution of the network traffic

12. Advanced Computer Networks12 Trace Collection of Packets (Contd.) Half of the outgoing traffic consists of 40 bytes TCP acknowledgement packets, so the average packet size became 123 bytes More than 60% of the incoming packets have 552, 567, or 1500 bytes, that correspond to common maximum transfer unit size on the Internet Using tcpreduce tool, the FTP, HTTP, SMTP, DNS, etc. data transfer were measured

13. Advanced Computer Networks13 Flow Size Distributions Mixture of flows between 100 and 100,000 bytes Majority of flows within range of 50 to 1000 bytes 1/3 of flows between 1000 – 10,000 bytes. 1/3 between 100 – 1000 bytes

14. Advanced Computer Networks14 Cumulative Distribution

15. Advanced Computer Networks15 Derivative of Cumulative Distribution

16. Advanced Computer Networks16 Density of the logarithm of the flow sizes

17. Advanced Computer Networks17 Flow sizes of Web Traffic SMTP (email) – large concentration of 1000 byte flows, remaining flows around 3000 bytes Telnet – Bytes per flow is typically less than 100 bytes HTTP has the largest bytes per flow. Flows fall into 3 main categories –1. Less than 150 bytes, from failed TCP sessions and error messages. –2. 150 – 300 bytes, from cache hit messages. –3. Greater than 300 bytes, actual web page transfers.

18. Advanced Computer Networks18 Flow sizes of Traffic

19. Advanced Computer Networks19 Flow duration of Web Traffic Duration of SMTP traffic falls between 0.01 seconds and 100 seconds, with high concentration between.01 and 1 second Telnet flows typically have the longest duration. Data shows duration up to 17 minutes. Usually around 100 seconds HTTP Flow duration typically around 1 second, but can last up to 100 seconds

20. Advanced Computer Networks20 Flow duration of Traffic

21. Advanced Computer Networks21 HTTP Flows by Machine Type End point machines have unique flow characteristics Flow duration for modem connection is longer Traffic to proxy servers tend to be a mixture of shorter and longer flows Larger transfers have higher throughputs since TCP window grows

22. Advanced Computer Networks22 Flow duration for different machines

23. Advanced Computer Networks23 Combining Multiple Web Responses 3 different levels of end-point aggregation –Port-to-port: Combines packets with the same IP address and port numbers at both end-points. –Host-level: Combines different TCP session from the same Web server to the same Web client. –Net-to-Net: Aggregating hosts that share the first 16 bits of the IP address.

24. Advanced Computer Networks24 Flow sizes for web responses

25. Advanced Computer Networks25 Flow sizes for web responses

26. Advanced Computer Networks26 Proportion of Shortcut Traffic With a trigger of 10 – 20 packets, network can avoid establishing shortcuts for short-lived flows. X-packet trigger less effective for host-to-host using packet trigger since aggregation increases number of packets thus triggering too early

27. Advanced Computer Networks27 Percent of shortcut traffic (port-to-port)

28. Advanced Computer Networks28 Percent of shortcut traffic (host-to-host)

29. Advanced Computer Networks29 Shortcut Setup Rate

30. Advanced Computer Networks30 Shortcut Setup Rate (Contd.)

31. Advanced Computer Networks31 Shortcut Setup Rate (Contd.) Setup rate is lower for larger packet size Setup rate is lower for higher timeout

32. Advanced Computer Networks32 Simultaneous Shortcut Connections

33. Advanced Computer Networks33 Simultaneous Shortcut Connections (Contd.) 0-packet trigger 75.8 shortcuts in average 10-packet trigger reduces the average no of simultaneous shortcuts by a factor of 3.3 (75.8 to 23.6) –Reason: higher packet trigger causes less shortcut connections For stable operation during heavy load, coarser aggregation and larger triggers may be necessary

34. Advanced Computer Networks34 Simultaneous Shortcut Connections (Contd.)

35. Advanced Computer Networks35 Simultaneous Shortcut Connections (Contd.) 12 sec timeout causes 4.3 shortcuts 300 sec timeout causes 44.5 shortcuts Larger timeout increases no of shortcuts, as a result it reduces signaling load Establishment of shortcuts is limited by no of connections, or the signaling capacity of the switch, or both Substantial network overhead reduction is possible by timeouts, triggers, end-point aggregation

36. Advanced Computer Networks36 Traffic Flows Along Partial Routes As the hop count increases, the numbers increases exponentially. ( EX: first seven hops have 26, 71, 137, 267, 409, 916, 1508 different outcomes, respectively.)

37. Advanced Computer Networks37 Partial Route Aggregation

38. Advanced Computer Networks38 Partial Route Aggregation (Contd.) Aggregating traffic along a portion of the routes decreases both the setup rate and the number of simultaneous connection –Seven hop: Setup rate = 20%,No. of Shortcuts = 11% –Three hop: Setup rate = 37%,No of Shortcuts = 16% Percent of Byte in Shortcuts –End-to-End:92.2% –Seven hop:94.0% –Three hop:96.0%

39. Advanced Computer Networks39 Partial Route Aggregation (Contd.) Partial-route aggregation reduces network overheads while increasing the proportion of shortcut traffic Partial-route aggregation combines transforms from replicas of the same web site, as well as related servers at the same institution Partial route flows benefit more from larger timeout values –As seen in Table III for 60 sec and 300 sec.

40. Advanced Computer Networks40 Summary Flow characteristics vary with endpoint type (modem, personal computer, compute servers, proxy servers) Aggregating consecutive and concurrent transfers from the same web server yields substantial benefits

41. Advanced Computer Networks41 Summary (Contd.) Aggregation and triggers both reduce overhead, but the reductions are not multiplicative Variability in traffic load changes with time scale Aggregating traffic along portions of the route between the source and destination yields additional reduction in network overhead

42. Advanced Computer Networks42 Future Work To evaluate specific new policies that balance the short-term tradeoffs between processor and network load To investigate the policy and performance implications of combining traffic along a portion of the route To study more detailed breakdown of web traffic by content type, as well as the implications of push technology and the new features in the emerging HTTP standards