Load balancing of a wireless network

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Load balancing of a wireless network

• By Vered Britshtein Shai Michaeli Boaz
  Aizenshtark
• Instructor Erez Biton

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Background

• Wireless LAN (IEEE 802.11) will probably become
  the most popular networking solution in years to
  come
• The spec describes the system in layer 2 (MAC),
  so the higher levels of management are not
  defined
• This leaves room for management entities which
  reside above level 2, but below level 3 (the IP
  layer)

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802.11 introduction

• A layer 2 protocol, very much compliant with
  Ethernet 802.3
• Its main purpose is to dynamically and
  transparently connect mobile/stationary units to
  an Ethernet segment, though it can be used in
  other configurations as well
• There are two entities in an ESS (Extended
  Service Set Ethernet connectivity in mortal
  language)1. AP Access Point provides
  Ethernet connection to the WLAN (acts
  as a switch)2. MU Mobile Unit the customer
• Basically, A mobile unit can be associated with
  any AP within range, but must be associated with
  only one at any given time

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802.11 introduction contd.
802.3 Ethernet segment
A
B
AP
AP
Wireless connection
Wireless connection
MU2
MU3
MU1
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Project goals

• The given topology several APs which can
  communicate with each other, many MU associated
  with them randomly
• Divide the MU between the APs so the load on
  each AP is equal
• We define Load as a combination of different
  parameters e.g. number of MUs, current
  throughput, history

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Implementation - flow

• A server queries the APs of the MU which are
  associated with it, the load, history etc.
• The server then runs a load balancing algorithm
  and finds the optimal distribution of the MU
• The server commands the AP to disassociate with
  selected MU, forcing the MU to re-associate with
  another AP

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Implementation flow example
Server
Get rid of MU2!
Allow MU2 to join
AP2
AP1
AP2 sucks!
MU3
MU4
MU2
MU1
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Implementation details

• The server communicates with the APs using SNMP
  (Simple Network Management Protocol)
• The server will track each APs load and number
  of MU
• The server holds an image of the APs ACL (Access
  Control List)

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Implementation - Server
Load balancing Algorithm
Database
Server API
To be implemented
Implemented
OS SNMP stack
Ethernet
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Implementation - Algorithm

• First we intend to implement a simple algorithm
  (balance the number of MU in each AP)
• Second, we will implement a more complex
  algorithm which will take into account other
  parameters. We did not yet decide on this
  algorithm

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Algorithm costs benefits

• MU is not connected to the closest AP we may
  damage the MU communication with the AP.
• We should consider that MU may have difficulties
  finding another AP in that case, we may want
  the algorithm to do only assignments when a new
  MU arrives, but not reassignments (moving MU
  between APs).
• Reassignment time when disconnecting a MU, we
  should consider the roaming time (how long will
  the unit stay disconnected). This is another
  calculation in favor of choosing an algorithm
  which does assignments only.
• Reassignment policy we can either force a MU to
  a specific AP, or just force it out of a specific
  AP, allowing it to reassociate with any other AP

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Algorithm cons an pros
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Implementation statistics

• Statistics given of the AP are for the load
  calculating
• Packets Seen packets received on Ethernet
  interface
• Packets Sent total packets sent out
• Any Collision packets affected by at least one
  collision
• Current Mus Specifies the current number of MUs
  associated with this AP.
• Information given on each MU
• Current Transmit RateThe current rate the AP
  transmits data to the station
• Packets Sent The packets sent by the AP to the
  MU.
• Packets Received The packets received by the AP
  from the MU.
• Bytes Sent The bytes sent by the AP to the MU.
• Bytes Received The bytes received by the AP from
  the MU.

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Schedule

• Wireless ramp-up 2 weeks done
• Hardware ramp-up 1 week done
• SNMP ramp-up 3 weeks in progress
• Implement SNMP manager 4 weeks
• Implement a simple algorithm 2 weeks
• Implement a complex algorithm 3 weeks