1. Load balancing of a wireless network
By: Vered Britshtein Shai Michaeli Boaz Aizenshtark
Instructor: Erez Biton

2. Background
Wireless LAN (IEEE ) 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)

3. introduction
A layer 2 protocol, very much compliant with Ethernet 802.3
It’s 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

4. 802.11 introduction – contd. 802.3 Ethernet segment AP A AP B MU4 MU2
Wireless connection
Wireless connection
MU4
To which AP should I go?
MU2
MU3
MU1

5. Project goals
The given topology: several AP’s which can communicate with each other, many MU associated with them randomly
Divide the MU between the AP’s so the load on each AP is equal
We define “Load” as a combination of different parameters – e.g. number of MU’s, current throughput, history

6. Implementation - flow
A server queries the AP’s 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

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

8. Implementation – details
The server communicates with the AP’s using SNMP (Simple Network Management Protocol)
The server will track each AP’s load and number of MU
The server holds an image of the AP’s ACL (Access Control List)

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

10. 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

11. 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 AP’s).
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

12. Algorithm – cons an pros
Assignment only
Reassignment allowed
Simple
Complicated
Overhead – a MU will be re-assigned only once at maximum
Overhead – each cycle many MU may be reassigned
Not flexible – the load between the AP’s may be unbalanced
Flexible – for each given network state we can choose the optimal distribution of MU

13. 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 Rate:The 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.

14. 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