Transcript Data Set 3

Control Plane Issues
in the Internet:
Personal Perspective
2005.4.8. Friday
Dept. of Computer Science and Engineering
Seoul National University
Sue B. Moon
Division of Computer Science
Dept. of EECS
KAIST
Overview
• Personal Perspective
– Single-Hop Delay
– Point-to-Point Delay
– Routing Anomaly
– Path Multiplicity as a Value-Added Service
2
Personal Experience at Sprint
• When I first arrived, I heard …
– “No loss” on Sprint backbone network
– “Almost no delay”
– “Cadillac brand of IP service”
3
Monitors in
San Jose PoP
* All monitored links are OC3
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Min/Avg/Max Delay per
Minute
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Link Utilization
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Single-Hop Delay Distribution
7
Delay w/o Transmission Time (TT)
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Minimum Router Transit Time (MRTT)
9
Is the queue
work-conserving?
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Delay w/o TX and MRTT
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Min/Avg/Max Delay without
Cisco Router Idiosyncracies
12
Summary of Single-Hop Delay
• Packet size is a major factor
• Non-work-conserving behavior of a
router is a main cause behind large
delay (> 1ms)
• Not much queueing observed
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Point-to-Point Delay
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Delay Distributions
Data Set 3
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Hourly Delay Distributions
Data Set 3
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Identification of Constant Factors:
Multi-Paths
• Equal Cost Multi Paths (ECMP)
– Src/Dst addresses, Router ID
Data Set 3
Path 3
Path 2
Path 1
Min delay of src/dst flow (Data Set 3)
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Three Paths Connectivity
• Data Set 3
Fiber prop.delay
28ms
32ms
34ms
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Path Separation of Data Set 3
• TTL difference
• Minimum delay of flow (src ip, dst ip)
Path 1
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Identification of Constant Factors:
Packet Size
• Path transit time
– Propagation + packet processing (packet size)
d fixed  p  : p  


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Removing Constant Factors
d var : d  d fixed  p 
Data Set 3
Path1
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Variable Delay: Bulk
Data Set 3, Path 1
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Variable Delay: Bulk (cont’d)
Data Set 3
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Impact
of Bottleneck Link Load
90
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Variable Delay Revisited: Tail
Data Set 3, Path 1
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Peaks in Variable Delay
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Closer Look
• Queue
Build up &
Drain
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Summary of Pt-to-Pt Delay
• Not much queueing most of the time
• Severe congestion when bottleneck link
utililization > 90%
• Congestion periods longer than 1 sec
– Exact causes unknown
– Possible causes
• Route changes
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Routing Loop
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Issues in "Good" Routing
• Misbehaving routing protocols
– BGP misconfigurations
– Pathological behaviors
– Frequent changes
• Even under normal circumstances
– Transient behaviors
– Inter/intra-domain routing not well
understood
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Scenario
for a Transient Routing Loop
In Normal Operation
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When a link fails, R1 is the
first to detect.
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R3 is updated before R2.
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Finally R2 is updated, and the
loop is resolved.
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CDF of Routing Loop Duration
in Time
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VoIP experimental setup
[Boutremans2002]
• Traffic injected in the network:
– 200 byte UDP packets
– every 5ms.
• Packets captured and timestamped at
end-systems.
• Traceroute runs continuously during the
experiment.
• Induced link failures on purpose to
evalute convergence time and impact on
e2e connections
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Information Sources
• IS-IS & BGP listener logs
• Router logs from both ends of
“failing” links
• Controlled bi-directional VoIP traffic
between Reston and ATL
• SNMP data
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Delays (1 sec timescale)
~3.4ms
~2.6ms
3 links up
2 links down
2 links up
3 links down
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When the two interfaces went
down …
6.6 seconds
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When three links came back up
Traffic “black-holed”
for 0.975 seconds
For 30 secs packets
follow a shorter path
Traffic “black-holed”
for 1.745 seconds
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Approaches To Fix It
• Fine-tuning parameters
– Timer values [Alattinoglu2002]
• Modify Routing Protocols
– Suppress advertisement and perform local
rerouting using a backwarding table
[Lee04]
– Centralized path computation
[Feamster04,Rexford04]
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Our Approach
• Key Idea:
– Find disjoint overlay path and send duplicate
packets
• Assumptions
– Sender and receiver both within an AS
– Bidirectional link weights
– Extra income for extra b/w consumption
• Pros and cons
– Advantages
• No modification to current infrastructure
• Selective use by only those that need it
– Disadvantages
• Extra b/w consumption
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Provisioning
for Interactive Streaming
• Interactive Streaming
– Not a driving force behind b/w
– A candidate for growing revenue
• Examples
– VoIP gradually taking over PSTN traffic
– Remote video viewing at door by cell
phone
– Online game traffic
• "Good" routing more important than
bandwidth
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Basic Ideas
source
destination
candidate relay nodes!!!
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Resilient to Failures
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What I have learned …
• No loss, almost no delay
– Almost. I gained insight into causes
behind
• Debunking the myths [Odlyzko2005]
–
–
–
–
Streaming real-time traffic
QoS
Content is king
Usage-sensitive pricing
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Other Issues Tackled
• Traffic Matrix Estimation
– Inspired by tomography in other fields
– Before arrival of efficient NetFlow
• Network Anomaly Detection
– NIDS, IDS => PCA-based global
monitoring
• Optimization
– Cross-layer resource allocation
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Future Work
• Personal perspective
– More into creating value-added services
– MPLS/VPN performance issues
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Acknowledgements
• Thank D. Papagiannaki, B.-Y. Choi, U. Hengartner, C.
Boutresmans, G. Iannaccone, and M. Cha for help with the
slides.
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