Bottleneck Bandwidth Estimation

1. Bottleneck Bandwidth Estimation Instructor: Dr. Aggarwal Present by: Jason Wei

2. Outline • Introduction of bandwidth estimation • Related Work • Our algorithm and experiment • Summary

3. Introduction • “A high-end user's connection speed grows by 50% per year” [1] • Monitoring the performance of the network, especially the network bandwidth, still is a challenging research topic.

4. Introduction (Cont’d) What is network bandwidth? The bandwidth of a network, also called throughput, is given by the number of bits that can be transmitted over the network in a certain period of time. For example, the bandwidth of a STS-1 network is 51.840 Mbps, which means that the transfer ability of the network is 51.840 million bits per second.

5. Introduction (Cont’d) • Bottleneck link bandwidth If there is no other traffic in the path, bottleneck link bandwidth is the maximum throughput that the path can provide from source to destination. It is limited by the bottleneck link’s underlying capacity. • Available bandwidth Available bandwidth is the maximum rate that the path can provide to a flow without reducing the rate of the cross traffic.

6. Introduction (Cont’d) Why measure bandwidth? • Network users benefit from knowing the bandwidth. • Measuring bandwidth is the key to congestion control and QoS (Qualities of Service). • Dynamical server selection • It is important to know bandwidth for mobile computing.

7. Relation work Bottleneck link bandwidth measurement can be divided into two categories: • Single-packet algorithms • packet-pair algorithms

8. Relation work (Cont’d) Single-packet algorithm • Use time-to-live (TTL) field in IP packet. TTL is used to monitor and remove the packets. • Once TTL is decremented to zero, the packet will be discarded and the router will send back an ICMP time exceeded packet to the original sender • By sending out a series of probe packets with different values of TTL. Bandwidth and latency of each link can be calculated by using statistics to analyze the time when error packets are received.

9. Relation work (Cont’d) Single-packet algorithm RTT= q1 + (lat1 + size/bwn1) + q2 + forward + q3 + (lat2+error_size/bwn2) + q4[2]

10. Relation work (Cont’d) Packet-Pair algorithm [3] Bandwidth = Size/Qb

11. Relation work (Cont’d) Cartouche algorithm[4] • Harfoush, Bestavros and Byers presented Cartouche algorithm. • Cartouche probe [apm {pq}r-1pm] can measure the bottleneck bandwidth of targeted path segments (i,j). s(p)>s(m)=s(q),D(a)=i, D(p)=D(q)=j, D(m)=A R1 Ri-1 R i R j Rj+1 Rn Sender Receiver

12. Relation work (Cont’d) Before the target path segment:

13. Relation work (Cont’d) After the target path segment:

14. Our algorithm The problems of Cartouche algorithm • Need to install software on receiver side. • If the result will be inaccurate when the cross traffic becomes high. Ra Ra+1 Ri Rj Rb Rb+1 Sender Receiver

15. Our algorithm (Cont’d) Two steps: • First, use single-packet algorithm to check the network structure, get position of the bottleneck link Li. Li Ra Ra+1 Ri Ri+1 Rb Rb+1 Sender Receiver

16. Our algorithm (Cont’d) Second step: Send [(Hdmrd)s] probes to measure the bandwidth of bottleneck link. Size(H)>>Size(d)=Size(m), Dest(H)=Li, Dest(d)= Li+1 Dest(m)=Receiver

17. Our algorithm (Cont’d) Before probes reach bottleneck link: • Size(H)>>Size(d)=Size(m) • If there is cross traffic between the sender and Ri , because of s(H )>>s(d), the interval between d still should be same. Ra Ra+1 Ri Sender

18. Our algorithm (Cont’d) When the probes reach bottleneck link: • Dest(H)=Li, Dest(d)= Li+1 Dest(m)=Receiver • Only the ICMP of packet d will be return from Router i+1 Ri Ri+1 Receiver H ACK ACK

19. Our algorithm (Cont’d) After the probes reach bottleneck link, ICMP packets come back • If there is no cross traffic, the interval of d can be keep. • If the interval of d is large enough, the time they pass the link with cross traffic should be same. Ra Ra+1 Ri Sender ICMP ICMP

20. Our algorithm (Cont’d) • Send several times of (Hdmrd) • Record the interval of d and analyze them to get the interval Idd. (The minimum value of them may be the value we need) • Bandwidth=Size(d)*(r+1)/ Idd

21. The improvement of our algorithm Compared with single-packet algorithm: • Both use ACK, so we do not need to install software on receiver side. • We just use single-packet algorithm to check the network structure (the position of the network bottleneck link) • Our algorithm is accurate than single-packet algorithm in the case that cross traffic exists.

22. The improvement of our algorithm (Cont’d) Compared with Cartouche algorithm: • We use ACK. So we do not need to install software on receiver side.

23. Verify our algorithm • Current work: Make my own network simulator to verify our algorithm. (partly finished)

24. Verify our algorithm (Cont’d) Next Step: • Use Network Simulator[5]to demo the algorithm. • If possible, set up a real network with routers, computers, and cross traffic, implement the algorithm.

25. Reference 1. Nielsen's Law of Internet Bandwidth http://www.useit.com/alertbox/980405.html 2. Using pathchar to Estimate Internet Link Characteristics Allen B. Downey ACM SIGCOMM '99 Pages: 241-250 3. Congestion Avoidance and Control Van Jacobson, In Proceedings of ACM SIGCOMM‘98, Pages: 314—329 4. Measuring Bottleneck Bandwidth of Targeted Path Segments Khaled Harfoush, Azer Bestavros, John Byers Boston University, 2001 5. Network Simulator (NS), version 2 http://www.isi.edu/nsnam/ns/

26. Summary • Introduce the basic network bandwidth algorithms.(Single packet, packet pair) • Cartouche algorithm and problems • Our algorithm