On Fast Estimation of Network Bandwidth

There are several tools on the Internet that measure the bandwidth of an Internet link. These tools, however, have been shown to be a bit slow in regards to measuring the bandwidth. This is a direct result of the large amount of probe packets that these programs use in order to determine the bandwidth link, but is also affected by the tendency for these programs to find out more information about the characteristics of the link itself These tools send only a fixed Although the bandwidths obtained for links 1 and 7 both with We experienced a problem during our experiment with the Proposed technique: we could not obtain an ICMP response message from a router (node) along the path of probing. It seems that these particular occurences lend themselves towards a more secure default set-up. They did not respond, so out of the 11 links, only 3 of them were returned with information. We used links 1, 5, and 7 only with pchar for bandwidth estimation with δ = 1.0 x 10-9. FAST ADAPTIVE BANDWIDTH ESTIMATION 1) Measuring roundtrip times. Send probe packets of size s1, s2, s3, . , sn to the remote host and measure the corresponding RTT’s as r1, r2, . , rn from the responses of the remote node. Let R = be the corresponding measured RTT vector. The probe packets of different sizes can be sent in some random order with sufficient time interval in between them. It is important that the packet size must not exceed the maximum transmission unit (MTU) of the path to the CONCLUSION SIGNIFICANCE • Network Bandwidth is an Important Resource, knowledge of link bandwidths along a path can: • Avoid excessive packet loss, delay, and congestion • Plan delivery or data on a path for time-sensitive . number of probe packets, which can result in inaccurate results. Here, we use a regression-based, iterative technique to filter out queue delays from all measured RTTs. Our tests, which use the existing ICMP (Internet Control Message Protocol) based tools, are done along an Internet path and show that the proposed scheme is faster and similarly accurate. the proposed technique and pchar are close to each other, we observe some disparity of the results for link 5. As no information is available on the actual bandwidth of the link to us, it is not possible whether the proposed technique or pchar is inaccurate in the estimation of the bandwidth of the link. As can be seen from the table above, the proposed technique only needs 124 probe packets to estimate the bandwidth of link 7 compared to 1472 probe packets sent by pchar, which is less than 10% of the probe packets needed by pchar. F t d d ti filt i f d l remote node. 2) Calculating regression line. Interpolate a regression line for points (r1, s1), (r2, s2), . , (rn, sn) with their corresponding weights w1, w2, . , wn where wi = 1 for and then obtain the corresponding interpolated RTTs on the regression line as y1, y2, . , yn. Let Y = represent the corresponding vector. Find the slope of the line for the iteration with j = 0. Scatter Plot of RTTs data • Many tools currently available are not adaptive to network conditions such as congestion since they send a fixed amount of probe packets. NETWORK MODEL • as an a ap ve er ng o queue e ays from roundtrip times measured on variable sized probe packets sent from a host to two successive nodes along a path for a link produced accurate results • Fast filtering of queue delays is achieved through a weighted linear regression fit of the RTT data in an iterative manner • Selective probing and including certain data points on RTT with judicious 3) Filtering and selective probing. For 1 yi (i.e. the point is above the regression line) then discard ri and send a probe packet of si to the remote node to obtain a new RTT value. Set ri as the minimum of the previous RTT and the new RTT. 4) Iterating for convergence. For , if then set ; otherwise set . Next, interpolate a regression line with the filtered points (r1, s1), (r2, s2), . , (rn, sn) with weights w1, w2, . , wn and obtain the corresponding new interpolated RTTs on the METHODOLOGY REFERENCES 1. A.B. Downey, “Using pathchar to estimate Internet link characteristics,” Proc. ACM SIGCOMM’99, Cambridge, p(i): Signal propagation delay over link Li qu(i) : Upstream random queue delay at node i qd(i) : Downstream random queue delay at node i bu(i) : Upstream bandwidth of link Li bd(i) : Downstream bandwidth of link Li t(i) : Processing or forwarding delay at node i Notations Used for the Network Model are: selection of weights helps with the next iteration of linear regression fit • Produces similar results as other programs with less probe packets needed. (i.e. – Less intrusive) regression line as y1, y2, . , yn. Increment j and obtain the slope m(j) of the line as in step 2. If | m(j) – m(j-1) | / m(j) ≤ δ then stop; otherwise go back to step 3. It is to be noted that the constant δ has to be chosen carefully to ensure termination of the process without sacrificing accuracy too much. Filtering of Queue Delays EXPERIMENTAL RESULTS MA, September 1999. 2. V. Jacobson, “pathchar – a tool to infer characteristics of Internet Paths”, presented at the Mathematical Sciences Research Institute (MSRC), April 1997, ftp://ftp.ee. lbl.gov/pathchar 3. B.A. Mah, “pchar: a tool for measuring Internet path characteristics”, http://www.kitchenlab. org/www/bmah/Software/pchar/, last accessed on March 17, 2006. 4. V. Paxson, “End-to-end routing behavior in the Internet”, IEEE/ACM Transactions on Networking, vol. 5, pp. 601- 615, 1997. 5. W.R. Stevens, UNIX Networking Programming, Prentice Hall, 1997. 6. K. Lai and M. Baker. “Nettimer: a tool for measuring First, let us consider a path from node N0 to node Ni and let us suppose node N0 sends a packet of size s to node Ni and node Ni returns a packet of size r in response. The roundtrip time, Ts,r(i) of this communication as seen by node N0 is given by the following compressed equation: In order for our proposed technique to fairly be comared against the other programs we are using, we use the same ICMP protocol for probing and messaging as used in pathchar, clink, and pchar [1]-[3]. We chose pchar to be a representative of the existing tools that we have mentioned earlier. This probing was done on a path containing 11 links on the Internet. By default, pchar starts with a probe pcket of 32 bytes in size and has an increment of 32 bytes for every other packet afterwards. This will continue until the MTU (maximum transmissino unit) is reached. A path with an MTU of 1500 bytes will have pchar sending 1472 probe packets for each Node. Where C(i) can be regarded as a constant and is: And Q(i) is regarded as a total random queue delay and is: bottleneck link bandwidth,” Proceedings of the USENIX Symposium on Internet Technologies and Systems, March 2001. 7. L.P. Peterson and B.S. Davie, Computer Networks – A Systems Approach, 3rd Edition, Morgan Kaufmann, 2003. 8. M. Pucci, “Accuracy and expressiveness in adaptive bandwidth measurements,” Proceedings of the ISMA Bandwidth Estimation Workshop, San Diego, CA, December 2003. 9. V.J. Ribeiro, R.H. Riedi, R.G. Baraniuk, J. Navratil, and L. Cottrell, “pathChirp: efficient available bandwidth estimation for network paths,” Proceedings of Passive and Active Measurement Workshop, La Jolla, CA, April 2003. 10.A. Capone, L. Fratta, F. Martignon, “Bandwidth estimation Link No. of Probe Packets