mar 1, 2004 multi-path routing cse 525 course presentation dhanashri kelkar department of computer...

Mar 1, 2004

Multi-path Routing

CSE 525 Course Presentation

Dhanashri Kelkar

Department of Computer Science and EngineeringOGI School of Science and Engineering

Mar 1, 2004 Dhanashri Kelkar – OGI School of Science and Engineering

2

Multi-path Routing

• A. Akella, B. Maggs, S. Seshan, A. Shaikh, R. Sitaraman, "A Measurement-Based Analysis of Multihoming", ACM SIGCOMM 2003.

• D. Andersen, A. Snoeren, H. Balakrishnan, "Best-Path v. Multi-Path Overlay Routing", IMC 2003.


3

Multihoming Advantages – The Gist

• A study of multihoming performance and reliability ‣ Data collected from Akamai content

distribution network‣ High-volume content providers‣ Enterprises that mainly receive data

• Analysis:‣ Improve performance and reliability‣ Choosing right set of providers important


4

Multihoming

• Technique to achieve resilience to service interruptions

• Customer network having more than one external link, either to single ISP or to different providers

• Mainly used for reliability


5

K-Multihoming

• Customer network multihomed to K (K≥2) service providers

• Expect incremental performance


6

Multihoming – Two Models

• Enterprise perspective:‣ Route data being downloaded through

appropriate ISP

• Web server perspective:‣ Route data being provided through

appropriate ISP

• Does smart routing improve performance?

• Does choice of ISPs matter?


7

Data Collection – Enterprise Perspective2-Multihoming

• Data set A1‣ 27 monitoring nodes‣ Two nodes per city

connected to different ISP

‣ Every 6 min. nodes download objects from Akamai customers

‣ Log turnaround time for

request

AkamaiCustomer

ISP1 ISP2

Monitor1

Monitor2

Enterprise Stand-in tPM ix ,


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Data Collection – Enterprise PerspectiveK-Multihoming (K>2)

• Data set H1‣ Multiple Akamai

servers per city‣ Each server connected

to different ISP‣ Servers download from

customers periodically‣ Log avg turnaround

time each hour

AkamaiCustomer

ISP 1 ISP K

Server1

ServerK

Enterprise Stand-in tHT

kOP


9

Performance – 2-multihoming

• Use best provider for each download instead of single provider for all downloads

• Performance metric:

• Measures how much each ISP loses compared to multihoming solution (≥1)

tPNumvalid

tPMtPMN

i

ti ibestix

x ,

,/,,


10

Performance – K-Multihoming

• Performance metric:

• particular K-multihoming solution• Best multihoming obtained if we choose best of

all ISPs

tNumvalid

tHTtHTN t bestOP

OPk

k

/

kOP


11

Enterprise 2-Multihoming: Results

• 2-multihoming shows performance benefits but to varying degrees


12

Enterprise K-Multihoming Performance

• Each line represents different city

• No significant improvement after 4 or 5

• Knowing best ISP in advance is important


13

Data Collection – Web Server Perspective

ISP 1 ISP K

Server1

ServerK

Web-server Stand-in

Server2

ISP 2

Internet


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Web Server Perspective – Cont’d

• Data set A2:‣ In 5 metro areas, pick servers attached to

distinct upstream ISPs‣ Every 6 min. each server downloads 50 KB

object from other Akamai servers‣ Turnaround time for request


15

Web Server K-Multihoming

• Use Akamai servers to emulate multihomed data centers and their active clients

• Metric for comparison: same as with enterprises

• Not much benefit beyond K=4


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Reliability

• Data set containing traceroute measurements from nodes of keynote systems to Akamai servers‣ 50 geographically diverse keynote nodes,

2 per city‣ 20 Akamai servers per city (top 20 ISP)

• Information about IP-level connectivity

• Robustness to IP-level failures


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Reliability Metrics

• Fraction of total path diversity captured by solution

‣ Higher value shows better performance

• Degree of overlap in paths

‣ Lower value shows better performance

i

i

kik E

EOPR

20,

,1 50/1)(

i

ki

kikik E

EPOPR

,

,,2 50/1)(


18

Reliability Analysis

• For both metrics, significant difference in optimal, average, and worse solution‣ Difference about 80%

• Choosing ISPs very crucial


19

Conclusion

• Multihoming helps, at least 20% improvement on average ‣ But not much beyond 4 providers

• Careful choice necessary‣ Cannot just pick top individual performers‣ Poor choice can affect performance

significantly


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Best-path vs. Multi-path Routing

• Analysis of performance of reactive and mesh routing

• Reactive routing: measure path quality using probes and send on best path

• Mesh routing: send redundant duplicates


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Design

• Probe-based reactive overlay routing‣ Periodic probes for availability, latency, loss

rate‣ Best path performance

• Redundant multi-path routing‣ Sends redundant data to multiple paths‣ Path independence


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Routing Methods

‣ Direct Single packet, direct path‣ Direct direct 2 packets, direct, no spacing‣ DD 10ms 2 packets, direct, 10ms spacing‣ DD 20ms 2 packets, direct, 20ms spacing‣ Lat Reactive routing, min latency‣ Loss Reactive routing, min loss‣ Direct Rand 2 pkts, Redundant routing‣ Lat Loss 2 pkts, Redundant multi-path


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Duplication Reduces Loss Rate

• Type Loss %• direct 0.42• direct direct 0.30• dd 10ms 0.27• dd 20ms 0.27• Lat 0.43• Loss 0.33• Direct Rand 0.26• Lat Loss 0.23


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Measurement Summary

• Redundant beats reactive for low loss

• Reactive finds specific good paths‣ Latency improvements‣ Low loss paths

mar 1, 2004 multi-path routing cse 525 course presentation dhanashri kelkar department of computer...

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