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

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

“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. Introduction

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 Mbps, which means that the transfer ability of the network is million bits per second. 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. 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. Introduction (Cont’d)

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

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. Relation work (Cont’d)

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

Packet-Pair algorithm [3] Relation work (Cont’d) Bandwidth = Size/ Q b

Cartouche algorithm[4] Harfoush, Bestavros and Byers presented Cartouche algorithm. Cartouche probe [apm {pq} r-1 pm] 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 Relation work (Cont’d) Sender R1R i-1 R i R jRn Receiver R j+1

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

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

The problems of Cartouche algorithm Need to install software on receiver side. If the result will be inaccurate when the cross traffic becomes high. Our algorithm Sender RaRa+1RiRjRbRb+1 Receiver

Two steps: First, u se single-packet algorithm to check the network structure, get position of the bottleneck link L i. Our algorithm (Cont’d) RaRa+1RiRi+1RbRb+1 ReceiverSender LiLi

Our algorithm (Cont’d) Second step: Send [(Hdm r d) s ] probes to measure the bandwidth of bottleneck link. Size(H)>>Size(d)=Size(m), Dest(H)=L i, Dest(d)= L i+1 Dest(m)=Receiver dm…mdH…dm…mdH

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

Our algorithm (Cont’d) Dest(H)=L i, Dest(d)= L i+1 Dest(m)=Receiver Only the ICMP of packet d will be return from Router i+1 Ri dm…mdH When the probes reach bottleneck link: Ri+1 dm…md H dd ACK Receiver m…m

Our algorithm (Cont’d) 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. After the probes reach bottleneck link, ICMP packets come back ICMP RaRa+1Ri Sender dd ICMP dd

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

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. The improvement of our algorithm

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

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

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. Verify our algorithm (Cont’d)

1. Nielsen's Law of Internet Bandwidth 2. Using pathchar to Estimate Internet Link Characteristics Allen B. Downey ACM SIGCOMM '99 Pages: Congestion Avoidance and Control Van Jacobson, In Proceedings of ACM SIGCOMM‘98, Pages: 314— Measuring Bottleneck Bandwidth of Targeted Path Segments Khaled Harfoush, Azer Bestavros, John Byers Boston University, Network Simulator (NS), version 2

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