monitoring persistently congested internet links
DESCRIPTION
Monitoring Persistently Congested Internet Links. Leiwen (Karl) Deng Aleksandar Kuzmanovic Northwestern University. http://networks.cs.northwestern.edu. Objective. New probing methods that can improve measurement observability for core congestion - PowerPoint PPT PresentationTRANSCRIPT
Monitoring Persistently CongestedInternet Links
Leiwen (Karl) Deng
Aleksandar Kuzmanovic
Northwestern University
http://networks.cs.northwestern.edu
2Karl Deng Monitoring Persistently Congested Internet Links
Objective
New probing methods that can improve measurement observability for core congestionPong – a tool specialized in measuring a subset of non-edge links exhibiting repetitive congestion– Can reveal systematic problems such as routing
pathologies, poorly-engineered network policies, or non-cooperative inter-AS relationships
Lightweight: monitoring in addition to on-demand measuring– A building block of a large scale triggered
monitoring system for Internet congestion
3Karl Deng Monitoring Persistently Congested Internet Links
Repetitive Congestion
We focus on locating and monitoring non-edge links that exhibit repetitive congestion– Queuing delay as congestion indicator
– Queue building-up repetitively happens on time scales of one or more minutes.
4Karl Deng Monitoring Persistently Congested Internet Links
Methodology Highlights
Coordinated probing– Probe from both endpoints of a path– Combine end-to-end probes with (TTL limited)
probes to intermediate routers
Infer underlying path topology conditions– Implicit inference– Based on measured queuing delays on different
probing paths
Use statistics over longer time scales
Quantify measurement accuracy– Link measurability score
5Karl Deng Monitoring Persistently Congested Internet Links
S D
Probe
fs
db
f (“forward”) probe b (“backward”) probe
s (“source”) probe d (“destination”) probe
, ,
,
A Simplified Case – Symmetric Path
Coordinated Probing
6Karl Deng Monitoring Persistently Congested Internet Links
S D
fs
db
Δfs
Δfd
Half-path queuing delay
Locating
Congested
Links
Tracing
Congestion
Status
Probe
Δd
Δb
Δf
Δs
Coordinated Probing
7Karl Deng Monitoring Persistently Congested Internet Links
Infer Underlying Path Topology Conditions
S D
fs
db
Probe
Δd
Δb
Δf
Δs
Condition: Δf +Δb ≈Δs +Δd
Path Pattern: 4-p probing scenario
8Karl Deng Monitoring Persistently Congested Internet Links
S D
fs
bd
Observed by b probe only Paired d probe
CongestionPair up
Fsd probing
S D
fs
b
No suitable d probes to pair up with this s probe
Congestion
Fsb probing
Probing technique Condition
4-p probing Δf +Δb ≈Δs +Δd
Δf ≈Δs +ΔdFsd probing
Δs ≈Δf +ΔbFsb probing
unconditional2-p probing
S D
fs
bd
Paired d probe
Congestion
4-p probing
Pair up
Δfs
Δfd
Estimates of half-path queuing delay
Probe Probe
Probe
Infer Underlying Path Topology Conditions
9Karl Deng Monitoring Persistently Congested Internet Links
Probing technique Condition
4-p probing
Fsd probing
Fsb probing
2-p probing
Δf +Δb ≈Δs +Δd
Δf ≈Δs +Δd
Δs ≈Δf +Δb
unconditional
max(Δf +Δb, Δs +Δd)QoM4p = 1 −|(Δf +Δb) − (Δs +Δd)|
max(Δf, Δs +Δd)QoMfsd = 1 −|(Δf − (Δs +Δd)|
QoMfsb = 1 −|(Δs − (Δf +Δb)|max(Δs, Δf +Δb)
Dem
ote
Pro
mo
te
(Last resort)
Definition of QoM
Select Probing Techniques
Adjust probing technique online based on quality of measurability (QoM)
10Karl Deng Monitoring Persistently Congested Internet Links
S D
Probe Probe Probe Probe Probe
Δfs ΔfdΔfs ΔfdΔfs ΔfdΔfs Δfs Δfd Δfd
Probe all nodes simultaneously
Locating Congested Links
Perform coordinated probing for all intermediate nodes
11Karl Deng Monitoring Persistently Congested Internet Links
Correlate probes to neighboring nodes
S D
Probe Probe
Switch Point Approach
Congested link is identified
Congestion
Locating Congested Links
12Karl Deng Monitoring Persistently Congested Internet Links
S DLink C (Identified congested link)
Link C
Congestion Status
Time
Congestion
Use fast rate end-to-end probing
Tracing Congestion Status
fffffffffffffff
13Karl Deng Monitoring Persistently Congested Internet Links
1 2 3 4 5 6 7 81 3 4 6 72 5
0.37s on/off 0.71s on/off 0.53s on/off
0.47s on/off 0.83s on/off
12111098 10 119
Topology: 12 nodes (PCs), 11 links
Link: 100Mbps, 2ms
Cross traffic: Each consists of 3 parallel TCP flows, 50% time on and 50% time off.
Build multiple bottlenecks: Cross traffics are added to corresponding links concurrently.
Emulab Experiment Example
14Karl Deng Monitoring Persistently Congested Internet Links
1 2 3 4 5 6 7 81 3 4 6 72 5
0.37s on/off 0.71s on/off 0.53s on/off
12111098 10 119
At the Beginning
Emulab Experiment Example
15Karl Deng Monitoring Persistently Congested Internet Links
1 2 3 4 5 6 7 81 3 4 6 72 5
0.37s on/off 0.71s on/off 0.53s on/off
0.47s on/off 0.83s on/off
12111098 10 119
After adding backward bottlenecks
Emulab Experiment Example
16Karl Deng Monitoring Persistently Congested Internet Links
1 2 3 4 5 6 7 81 3 4 6 72 5
0.37s on/off 0.71s on/off 0.53s on/off
12111098 10 119
0.29s on/off 0.63s on/off
After adding two more forward bottlenecks
Emulab Experiment Example
17Karl Deng Monitoring Persistently Congested Internet Links
Optimizing Pong in the Internet
Set queuing delay threshold– Based on distribution of queuing delay samples
Tune other parameters based on experiments on the PlanetLabMinimize measurement errors– Detect and react to anomalies (clock skews, router alterations, ICMP
queuing, etc)– Use instantaneous quality of measurement value as sample weight
Quantify measurement quality– Help select vantage points
18Karl Deng Monitoring Persistently Congested Internet Links
Quantify Measurement Quality
Help select vantage points
Link measurability score1. Probing technique and quality of measurability
2. Queuing delay threshold quality
3. Observability score• Congestion observed on a less frequently congested link
can be blurred by a much more frequently congested link on the same path.
19Karl Deng Monitoring Persistently Congested Internet Links
Conclusion
Pong – a tool specialized in measuring a subset of non-edge links exhibiting repetitive congestion
Coordinated probing
Infer underlying path topology conditions
Select probing techniques online– Quality of measurability
Quantify measurement quality– Link measurability score
20Karl Deng Monitoring Persistently Congested Internet Links
Thank you!
Questions?