Tomography-based Overlay Network Monitoring and its

Applications

Joint work with David Bindel, Brian Chavez, Hanhee Song, and Randy H. Katz

UC Berkeley

Yan Chen

Problem FormulationGiven n end hosts on an overlay network and

O(n2) paths, how to select a minimal subset of paths to monitor so that the loss rates/latency of all other paths can be inferred.

• Key idea: select a basis set of k paths that completely describe all O(n2) paths (k «O(n2)) – Select and monitor k linearly independent paths to

compute the loss rates of basis set– Infer the loss rates of all other paths

End hosts

Overlay Network Operation Center

topology

measurements

1 2

1

2 3

1’

Real links (solid) and overlaypaths (dotted) going through them

Virtualization

Virtual links

1’ 2’

1

2

3

1’2’

4

k =1

k = 2

k = 3

3’

4’

Intuition through Topology Virtualization

1

1 2

12

3

• Virtual links: minimal path segments whose loss rates uniquely identified

• Can fully describe all paths

5

Efficiency and Adaptation

• Internet has moderate hierarchical structure [TGJ+02]

• For reasonably large n, (e.g., 100), k = O(nlogn)

• Tolerant to topology measurement errors• Incremental topology change detection and

update of monitoring paths– End host join/leave– Routing changes

Areas and Domains# of

hosts

US (40)

.edu 33

.org 3

.net 2

.gov 1

.us 1

Interna-tional (11)

Europe (6)

France 1

Sweden 1

Denmark 1

Germany 1

UK 2

Asia (2)Taiwan 1

Hong Kong 1

Canada 2

Australia 1

Experiments on Planet Lab

• 51 hosts, each from different organizations– 51 × 50 = 2,550 paths

• Simultaneous loss rate measurement– 300 trials– In each trial, send a 40-

byte UDP pkt to every other host

• Simultaneous topology measurement– Traceroute

• Experiments: 6/24 – 6/27– 100 experiments in peak

hours

• Loss rate distribution

• Accuracy– On average k = 872 out of 2550– Absolute error |p – p’|:

• Average 0.0027 for all paths, 0.0057 for lossy paths

– Small relative error and good lossy path inference

• Topology measurement error tolerance– On average 245 out of 2550 paths have no or

incomplete routing information– No router aliases resolved

lossrate

[0, 0.05)

lossy path [0.05, 1.0] (4.1%)

[0.05, 0.1) [0.1, 0.3) [0.3, 0.5) [0.5, 1.0) 1.0

% 95.9% 15.2% 31.0% 23.9% 4.3% 25.6%

Tomography-based Overlay Monitoring Results

Performance Improvement with Overlay

• With single-node relay• Loss rate improvement

– Among 10,980 lossy paths:– 5,705 paths (52.0%) have loss rate reduced by 0.05 or more– 3,084 paths (28.1%) change from lossy to non-lossy

• Throughput improvement– Estimated with

– 60,320 paths (24%) with non-zero loss rate, throughput computable

– Among them, 32,939 (54.6%) paths have throughput improved, 13,734 (22.8%) paths have throughput doubled or more

• Implications: use overlay path to bypass congestion or failures

lossraterttthroughput

5.1

SERVER

OVERLAY RELAYNODE

OVERLAY NETWORKOPERATION CENTER

CLIENT

3. Network congestion /failure

4. Detect congestion /failure

2. Register trigger

7. Skip-free streamingmedia recovery

6. Setup New Path

1. Setupconnection

5. Alert +New Overlay Path

X

UC Berkeley

UC San Diego

Stanford

HP Labs

Adaptive Overlay Streaming Media

• Implemented with Winamp client and SHOUTcast server• Congestion introduced with a Packet Shaper• Skip-free playback: server buffering and rewinding• Total adaptation time < 4 seconds

Pros and Cons About Planet Lab

+ Easy batch processing via SSH- No root privileges

– Many measurement tools don’t work!

- Limited tools– Only ping and traceroute– but people are adding more, like scriptroute

- Linux-only platform– New applications (multiplayer games, live

media) are mostly on Windows platform

- Limited programming language choices– Only C/C++ and perl, no Java

Backup Slides

Adaptive Streaming Media Architecture

Client 1

MEDIASOURCE

SERVER

SHOUTcastServer

Buffering Layer

Clie

nt 1

Clie

nt 2

Clie

nt 3

Clie

nt 4

FromSHOUTcast

server

Calculated

concatenationpoint

BU

FF

ER

ByteCounter

Client 2

Client 3

Client 4

INTERNET

Triggering /alert + new path

OVERLAY RELAY NODE

RELAY

Overlay Layer

Path Management

TCP/IP Layer

RELAY

CLIENT

Winamp client

TCP/IP Layer

Overlay Layer

Internet

Path Management

Winamp Video/Audio Filter

Byte Counter

TCP/IP Layer

OVERLAY NETWORKOPERATION CENTER