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Hi,

I have a small doubt regarding TPC (Transmit power control).

Two APs which are nearby reduce their power to reduce the interference.

If the above two APs are in different channels whether they will reduce power or not ?
How does Cisco, Aruba behave ?
What are the advantages of it ?

One advantage which I can think is
Load balance But anything else ..

Please help me to solve the mystery .......
No body mentions this point explicitly.

With regards,
Murali

Hii Murali ,

Answer to your questions is in the implemetation by the vendor , but TPC can help in following scenarios :

1. If the signal from two AP's are interfering , then the transmit power can be reduced.

2. Apposite of the same is true , if the client is conneted to the AP at low signal , and AP is not workinf at full power , it can increase the power so as to bring the client out of coverage hole.

Actually there always be a complex algorithm working behind which will trigger the power increase or decrease and usually has some threshold value above which the TPC comes in play.


For more information on the Product specific behaviour , you can go through the Product information guides .

Hope this helps

Hi,

As far as my tech knowledge is concerned, the TPC implementation is not so complex as it looks.At a very basic level it is a substraction.

Can anyone guide me to any one implementation of Cisco or Arubas TPC mechanisms or any other good technical paper regarding this or problems associated with it practically ?

With regards,
Murali

From my reading, DFS and TPC are implemented mainly to adhere to regulatory constraints and rules and the DFS is to avoid interfering with radar in the 5GHz spectrum. DFS and TPC are not required in the 2.4GHz radios, but are required in the 5GHz radios. Here are links to Cisco that talk about the regulations and how to configure Cisco's TPC/DFS.

Cisco Transmit Power Control and DFS:
http://tinyurl.com/24rkqk

Also, for Cisco DFS/TPC:
http://tinyurl.com/245olb

FCC Rules on DFS/TPC:
http://tinyurl.com/255zt8

Cisco Press:
http://safari.ciscopress.com/1587051648/ch03lev1sec4

Cisco Networkers Presentation:
http://tinyurl.com/yphl7s

Hi Murli,

Most of the WLAN products have their own proprietary way of reducing channel interference and coverage overlap. The center idea is to optimize coverage overlap and make sure no 2 channels stay next to each other so that stations have better throughput.

Hence here there are two things that needs to be taken care of,

1. Co Channel interference
2. Coverage overlap

there is usually a threshold value set by each vendor for both the params. APs (basically Thin APs) monitor the traffic for both the above params, if any one hits the threshold ... Algorithm kicks in and AP power level or channel is changed accordingly.

For Ex: while scanning the RF when the WLAN switch gets a report that there is a situation where there are 2 APs with same channel it might run an algorithm to find out if it meets the threshold value to shift channel so that interference is optimal. if it does channels are not changed, if it does not then channels are changed to interference reduced.

P.S. Any vendor can only reduce or optimize RF for less interference and better throughput but cannot negate performance issues completely from RF.

I would go with "codeman14150" reply, TPC and DFS is only to guarantee that the TX Power and channel is by the Govt specs for the country.

- thanks
Vinu

If you have a large network, say 9 AP's or more, and are only using channles 1,6,11, power control will greatly improve performance by minimizing interference.

Remember, throughput is a function of singnal to noise and bandwidth. Improving the S/N increases the throughtput (and the happiness of your customers).

Hi Vinu,

I agree to the to the first point (Co-channel Interference).

But What is dis-advantage if there is coverage overlap ?Actually it is better for roaming and avoid coverage holes.

Can you explain the dis-advantages for coverage over-lap ?

With regards,
Murali

Hi Murali,

The idea of TPC is to avoid interference...

2 APs can have complete overlap in the coverage area and have no interference when they operate in non-overlapping channels!
Thus, hence, TPC is necessary for APs in overlapping areas.

Load balancing is required but based on load... This is but independent of channel as long as stations support them.

Hope this helps!

Rgrds,
Kiran

Hi Murli,

Coverage overlap as got its advantages. Overlap of say 20% is good for roaming (threshold is defined by each vendor). But more than this there will be unnecessary interference.

The main idea of reducing or increasing power is to maintain an optimal coverage overlap.

thanks