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

Bottleneck Bandwidth Bottleneck Bandwidth EstimationEstimation

Instructor: Dr. AggarwalInstructor: Dr. Aggarwal

Present by: Jason WeiPresent by: Jason Wei

• Introduction of bandwidth estimation

• Related Work

• Our algorithm and experiment

• Summary

OutlineOutline

• “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.

IntroductionIntroduction

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.

Introduction (Cont’d)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)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)Introduction (Cont’d)

Bottleneck link bandwidth measurement can be divided into two categories:

• Single-packet algorithms

• packet-pair algorithms

Relation workRelation 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)Relation work (Cont’d)

Single-packet algorithm

Relation work (Cont’d)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)Relation work (Cont’d)

Bandwidth = Size/Q b

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

Relation work (Cont’d)Relation work (Cont’d)

Sender R1 Ri-1 R i R j Rn ReceiverRj+1

Relation work (Cont’d)Relation work (Cont’d)

Before the target path segment:

Relation work (Cont’d)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 algorithmOur algorithm

Sender Ra Ra+1 Ri Rj Rb Rb+1 Receiver

Two steps:• First, use single-packet algorithm to check the

network structure, get position of the bottleneck link Li.

Our algorithm (Cont’d)Our algorithm (Cont’d)

Ra Ra+1 Ri Ri+1 Rb Rb+1 ReceiverSender

Li

Our algorithm (Cont’d)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

d m … m d H … d m … m d H

Our algorithm (Cont’d)Our algorithm (Cont’d)

• 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 RiSender

d m … m d H d m … m d H

Before probes reach bottleneck link:

Our algorithm (Cont’d)Our algorithm (Cont’d)

• Dest(H)=Li, Dest(d)= Li+1 Dest(m)=Receiver

• Only the ICMP of packet d will be return from Router i+1

Ri

d m … m d H

When the probes reach bottleneck link:

Ri+1

d m … m d

H

d dACK

ACK

Receiver

m … m

Our algorithm (Cont’d)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

Ra Ra+1 RiSender

d d

ICMP

d 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

Our algorithm (Cont’d)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 The improvement of our algorithmalgorithm

Compared with Cartouche algorithm:

• We use ACK. So we do not need to install software on receiver side.

The improvement of our The improvement of our algorithm (Cont’d)algorithm (Cont’d)

Verify our algorithmVerify 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)Verify our algorithm (Cont’d)

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/

ReferenceReference

• Introduce the basic network bandwidth algorithms.(Single packet, packet pair)

• Cartouche algorithm and problems

• Our algorithm

SummarySummary