Performance Comparison of Two Wireless Mesh Networks

1
Performance Comparison of Two Wireless Mesh
Networks

• Rongdi Chen
• crd02_at_csnet.cs.tsinghua.edu.cn
• Network Research Center of Tsinghua Univ.

2
Outline

• Background
• Demonstrational wireless network project
• Tropos MetroMesh Vs Nortel WMN
• Measurement setup
• Results comparison
• Future works
• Conclusions

3
Mesh Networking

• Anytime and anywhere WLAN technology
• Traditional WLAN limited by wires
• Free Access Points from a wired infrastructure
  Mesh
• 802.11s, Mesh Networking, is standardizing a
  dynamically self-configuring multi-hop Wireless
  Distribution System (WDS).

ESS MESH
FREE
IEEE 802.11
the
APs
4
Mesh Networking
Internet
Internet Gateway
5
Advantages and Challenges

• Eliminate the limitation of wired infrastructure
• Span coverage areas from hot-spots to hot-zones
• Ease deployment and ensure reliability
• Auto-discovering
• Self-organizing
• Auto-configuring
• Self-healing
• Fast roaming
• However, still need considerable research efforts
• Throughput drops significantly as the number of
  hops increases
• Available MAC and routing protocols do not have
  enough scalability

6
Demonstrational wireless network
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Tropos MetroMesh Vs Nortel WMN

• Real mesh solutions
• Radio technology
• Tropos MetroMesh Single-band, single-radio
• Nortels WMN Dual-band, dual-radio
• Routing protocol
• Tropos Predictive Wireless Routing Protocol
• Nortel OSPF

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Multi-band, multi-radio Vs Single-band, single
radio

• Multi-radio better capacity
• A radio cannot transmit and receive at the same
  time

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Multi-band, multi-radio Vs Single-band, single
radio

• 5 GHz suffers much more attenuation than 2.4 GHz

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Routing efficiency

• PWRP predictive wireless routing protocol
• dynamically selects the end-to-end path based on
  packet error rates
• minimize total retransmissions and create
  subscriber capacity
• OSPF
• insensitive to packet errors
• do nothing to limit the resulting retransmissions

Conclusion Both two solutions have their own
advantages and disadvantages that can affect the
network performance.
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Measurement setup

• Software IxChariot version 5.4 Console
  Endpoint
• Hardware
• Console Intel P4 3.0 GHz processor, 1GB RAM,
  Windows XP
• Client IBM T30 laptop, Intel P4 mobile 2.2 GHz,
  1GB RAM, Cisco AIRONET 340 series
  wireless LAN adapter (802.11b), Windows XP

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Tropos performance test

• Topology

Node 02
IxChariot Console
Gateway 02
Node 01
Node 03
Gateway 01

• End-to-end throughput

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Nortel performance test

• Topology

DHCP Server
AP1
AP_at_NAP
AP2
6
FTP, RADIUS, Optivity Server
Router_at_NAP (PP 1424)
Wireless Gateway (WG7250)
1
11
IxChariot Console
AP3
1

• End-to-end throughput

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Performance results

• Nortel 802.11b throughput

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Performance results

• Tropos 802.11b throughput

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Comparisons

• Both solutions have performance degradation
  problem.
• Multi-hop throughput degradation
• Tropos in 1/n fashion
• Nortel in fashion
• Normally, Nortel separates the access link and
  transit link by using different frequency bands,
  can have better performance, then

Why?
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Analysis

• Retransmissions cause performance decline
• Hop retransmissions limited by number of hops
• Packet errors caused by interference, multi-path
  fading maybe unlimited on error-prone links
• Hop retransmissions can cause performance decline
  up to 1/n
• Tropos PWRP dynamically selects the best link
  lowest packet error rates
• Nortel OSPF insensitive to packet errors
• During the test
• Tropos two hops topology was quite steady and it
  had nice link quality (shown on the network
  management system) little packet errors, 1/n
  pattern reasonable
• Nortel 3 hops topology was configured fixed may
  exist a lot of packet errors, so the throughput
  decline significantly

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Thoughts and Future works

• The biggest advantage of mesh is its wireless
  backhaul, more hops, more advantage. But more
  hops mean more performance degradation.
• tradeoff
• Routing protocols and routing costs both affect
  the performance.
• tradeoff

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Conclusions

• Deployed two demonstrational wireless mesh
  networks in our campus for further research
• Observed the actual throughput degradation of the
  two mesh networks
• Compared two real wireless mesh solutions and
  make an explanation for the multi-hop throughput
  degradation
• Pointed out the future works

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Thanks for your kind attention!
Any idea or other suggestions?