Optimizing Network Performance In Replicated Hosting

1
Optimizing Network Performance In Replicated
Hosting

• Peter Steenkiste (CMU)
• with
• Ningning Hu (CMU),
• Oliver Spatscheck (ATT),
• Jia Wang (ATT)

2
Motivation

• The question of how to use latency to select a
  replicated web server has been well studied
• How about using available bandwidth?

?
3
Outline

• Pathneck
• Internet end user RTT distribution and access
  bandwidth distribution
• Optimization results
• For RTT
• For bandwidth
• For data transmission time

4
Pathneck Recursive Packet Train (RPT)

• Two measurement packets are dropped at each
  router
• ICMP packets allow source to estimate train
  length at each hop
• Changes in train length provide bounds on the
  available bandwidth of each link

5
Pathneck Operation
S
R1
R2
R3
6
Pathneck Properties

• Pathneck is an active probing tool designed for
  locating Internet bottlenecks
• It is efficient and effective
• Also provide route, delay, and bandwidth
  information
• For technical detail please see
  www.cs.cmu.edu/hnn/pathneck
• We improve Pathneck to cover the last hop
• This allows us to measure the RTT and the access
  bandwidth of many end users.

7
Methodology

• Measurement sources 18 nodes from a large tier-1
  ISP
• 14 in the US, 3 in Europe, and 1 in East-Asia
• Large fraction of paths cover other ISPs
• Play the role of possible replica sites
• Measurement destinations 164,130 IP addresses
  from different prefixes
• 67,271 IPs correspond to real online hosts
• Firewalls etc sometime require us to use
  intermediate node as virtual destination
• Play the role of clients accessing the web

8
Results

• Internet end user RTT distribution and access
  bandwidth distribution
• Optimization results
• For RTT
• For bandwidth
• For data transmission time

9
RTT Distribution
Europe
US-NE
East-Asia

• The RTT views of Internet clients from
  different geographical locations are
  significantly different

10
Bandwidth Distribution
Europe
East-Asia
US-NE

• The bandwidth views are much more alike

11
End Access Bandwidth Distribution
Limited by downstream bandwidth of measurement
source
62.5 lt 10Mbps
50 lt 4.2Mbps
40 lt 2.2Mbps

• Low access bandwidth still dominates among end
  users

12
Bottleneck Location Distribution

• 75 of bottleneck links are at the last two hop
• Little chance to avoid these bottlenecks using
  replication
• However, when access bandwidth is higher than
  40Mbps, content replication can help to improve
  performance

13
Results

• Internet end user RTT distribution and access
  bandwidth distribution
• Optimization results
• For RTT
• For bandwidth
• For data transmission time

14
Optimization Algorithm

• We use simple greedy algorithm to optimize the
  performance of our replication infrastructure
• In each step, select the replication node that
  has the largest marginal utility
• Greedy algorithm has been shown to be able to
  obtain results very close to the optimal results
• For our study, it is only 0.1 worse than the
  optimal results from brute-force search

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RTT Optimization
US-Central
East-Asia
US-West
Europe
US-East

• RTT optimization results have a clear
  geographical pattern
• The first 5 replicas provide most of the benefit

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Marginal Utility of RTT Optimization

• The first 5 nodes have significant improvement
  (i.e., larger than 5)
• Marginal utility the relative performance
  improvement from a specific node

17
Bandwidth Optimization

• The first 2 replicas provide most of the benefit

18
Marginal Utility for B.W. Optimization

• Only the first 2 (3) nodes have significant
  improvement

19
For Well-provisioned Access Links
74
35
54Mbps

• Replication can indeed improve bandwidth
  performance for end users with access bandwidth
  larger than 40Mbps

20
Data Transmission Time

• End-users data transmission time depends on
  delay, bandwidth, and data size
• We estimate data transmission time using a
  simplified TCP model a slow start and congestion
  avoidance phase
• Assumes no packet loss
• Slow start transfer time is delay sensitive
• Congestion avoidance bandwidth sensitive
• Data size determines whether replication should
  optimize delay or bandwidth
• Use slow-start size as cross over point
• Results 70 of paths have slow-start size larger
  than 10KB
• Larger than the average web page

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Data Transmission Time (2)

• The transmission times for 10KB, 100KB, 1MB and
  10MB are 0.4s, 1.1s, 6.4s, and 59.2s, respectively

22
Related Work

• Content replication with different optimization
  metrics
• Geographic location, network hops and latency,
• Retrieval costs, update cost, storage cost,
• QoS guarantee,
• Greedy algorithm used in replica selection

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Conclusion

• Quantify Internet end-node access-bandwidth
  distribution and bottleneck location distribution
• Two differences distinguish the optimization on
  bandwidth and on RTT
• Geographic location is not important for
  bandwidth optimization
• For throughput, only well-provisioned end users
  can benefit from content replication