tomography-based overlay network monitoring and its applications joint work with david bindel, brian...
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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
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