Repeater problem

Hi there,

I've got two d-link access points. A 2100AP working as access point and
a G700AP working as repeater. I've enabled RTS/CTS on the 2100AP and set
threshold to 512 bytes. Packet fragmentation is set to 2048 bytes.

Should the two devices have the same RTS/CTS and packet fragmentation
configuration? In other words, if I set RTS/CTS threshold to 512 bytes
on the 2100AP, should I set the G700AP to 512 too or should I just leave
it at its default level (2346 bytes)?

andrias

On Mon, 11 Sep 2006 20:38:31 +0200, Andrias Sundskard
<(E-Mail Removed)> wrote:

>I've got two d-link access points. A 2100AP working as access point and
>a G700AP working as repeater. I've enabled RTS/CTS on the 2100AP and set
>threshold to 512 bytes. Packet fragmentation is set to 2048 bytes.
>
>Should the two devices have the same RTS/CTS and packet fragmentation
>configuration? In other words, if I set RTS/CTS threshold to 512 bytes
>on the 2100AP, should I set the G700AP to 512 too or should I just leave
>it at its default level (2346 bytes)?

Leave it at the default level. Also, they do NOT need to be the same
on each link. When the fragmentation threshold is set to the maximum
packet size of 2346 or something similar, this value effectively turns
off packet fragmentation.

The only time you want to use packet fragmentation is when you have a
high non-802.11 interference problem. The idea is that smaller
packets have a better chance of making it through impulse and
transcient interference than large packets. The fragmentation
threshold sets the largest packet that can be sent before it should be
fragmented. In effect, it sets the maximum 802.11 packet size.

CTS/RTS threshold is similar. You only want to enable that if you
have a serious hidden node problem. That's where you have multiple
clients that can all hear the central access point, but which can't
hear each other. With a sufficiently large number of such clients,
the chances of collisions (simultaneous transmissions) are high.
CTS/RTS flow control allows the central access point to control the
client radios transmission times and thus prevent collisions.

The problem is that the CTS/RTS management packets take some air time,
especially since management packets are sent at the slowest 1Mbit/sec
speed. It makes little sense to send flow control packets for very
small data packets. Just send the small data packets and just resend
if there is a collision. Only large packets really need CTS/RTS flow
control. Therefore, the CTS/RTS threshold is the minimum packet size
that the system will send CTS/RTS flow control. If set to the largest
packet size (2346 ???), then CTS/RTS is effectively turned off because
all packets are less than the minimum. My guess(tm) is that you don't
need CTS/RTS flow control unless you have more than 5 concurrent
users, with widely seperated locations.


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558 (E-Mail Removed)
# http://802.11junk.com (E-Mail Removed)
# http://www.LearnByDestroying.com AE6KS

Jeff Liebermann wrote:
> On Mon, 11 Sep 2006 20:38:31 +0200, Andrias Sundskard
> <(E-Mail Removed)> wrote:
>
>> I've got two d-link access points. A 2100AP working as access point and
>> a G700AP working as repeater. I've enabled RTS/CTS on the 2100AP and set
>> threshold to 512 bytes. Packet fragmentation is set to 2048 bytes.
>>
>> Should the two devices have the same RTS/CTS and packet fragmentation
>> configuration? In other words, if I set RTS/CTS threshold to 512 bytes
>> on the 2100AP, should I set the G700AP to 512 too or should I just leave
>> it at its default level (2346 bytes)?
>
> Leave it at the default level. Also, they do NOT need to be the same
> on each link. When the fragmentation threshold is set to the maximum
> packet size of 2346 or something similar, this value effectively turns
> off packet fragmentation.
>
> The only time you want to use packet fragmentation is when you have a
> high non-802.11 interference problem. The idea is that smaller
> packets have a better chance of making it through impulse and
> transcient interference than large packets. The fragmentation
> threshold sets the largest packet that can be sent before it should be
> fragmented. In effect, it sets the maximum 802.11 packet size.
>
> CTS/RTS threshold is similar. You only want to enable that if you
> have a serious hidden node problem. That's where you have multiple
> clients that can all hear the central access point, but which can't
> hear each other. With a sufficiently large number of such clients,
> the chances of collisions (simultaneous transmissions) are high.
> CTS/RTS flow control allows the central access point to control the
> client radios transmission times and thus prevent collisions.
>
> The problem is that the CTS/RTS management packets take some air time,
> especially since management packets are sent at the slowest 1Mbit/sec
> speed. It makes little sense to send flow control packets for very
> small data packets. Just send the small data packets and just resend
> if there is a collision. Only large packets really need CTS/RTS flow
> control. Therefore, the CTS/RTS threshold is the minimum packet size
> that the system will send CTS/RTS flow control. If set to the largest
> packet size (2346 ???), then CTS/RTS is effectively turned off because
> all packets are less than the minimum. My guess(tm) is that you don't
> need CTS/RTS flow control unless you have more than 5 concurrent
> users, with widely seperated locations.
>
>
Thank you very much for that very good and detailed answer.

andrias