Shortslot Override
Values are Long and Short and Auto, default value is Auto
The Help file says..v
nothing.
How it Works:
The setting "Shortslot Override" refers to Short Slot Times - The amount of time a device waits after a collision before retransmitting a packet. You can increase throughput on 802.11g, 2.4-GHz radios by enabling Shortslot override (most .11g radios enable this by default). Reducing the slot time from the standard 20 microseconds to the 9-microsecond short slot time decreases the overall backoff, which increases throughput. Backoff, which is a multiple of the slot time, is the random length of time a station waits before sending a packet on the LAN.
Many 802.11g radios support Shortslot override, but some do not. When Shortslot override is enabled, the wireless device uses the short slot time only when all clients associated to the 802.11g, 2.4-GHz radio support Shortslot override. Shortslot override is an 802.11g-only feature and does not apply to 802.11a radios.
SUMMARY: Slot times should transition from 20us to 9us when a "pure" .11g environment exists for that AP.
Comments? anyone want to add to this? _________________ Location (urban) - 1x Linksys EA8500 (AP wlan0 & wlan1 enabled)
1x Asus 68u (Repeater Bridge w/VAP) - wl0 disabled
1x Asus 87u (Client Bridge) - wl1 disabled
it may be that bluetooth colocation only works with one bluetooth chipset...
http://www.nxp.com/acrobat_download/literature/9397/75015951.pdf _________________ Conventional wisdom among radio guys is that $1 spent on antennas is worth $10 spent on amplifiers. Solve RF problems with antennas to the greatest extent possible before increasing power.
I have updated CTS Protection, RTS and Fragmentation as well..
I think it makes thinks a lot clearer to me anyways what each of these parameters is used for and when to use them. _________________ Location (urban) - 1x Linksys EA8500 (AP wlan0 & wlan1 enabled)
1x Asus 68u (Repeater Bridge w/VAP) - wl0 disabled
1x Asus 87u (Client Bridge) - wl1 disabled
Sensitivity Range (ACK Timing)
Default Value: 2000 meters ( a 1KM Wifi Link)
Help file says..
Adjusts the ack timing in Atheros typical way based on the maximum distance in meters .A value of 0 disables ack timing completely for broadcom firmwares. On Atheros based firmwares a value of 0 will turn into auto ack timing mode
How it works:
1.) AP sends a message: Everybody wait X time for a response
2.) Client receives
3.) Client sends a response to the AP called and ACK - Acknowledges the command waiting for X time.
4.) AP sees the ACK
5.) Other Clients and AP are free to send
-Ack timing adjustment is used for distance links when the time needed to tramit is greater then than the amount of time the sender waits before retrying to transmit the same packet again.
-You want to set the ack timing to 2x the distance between bridged routers measured in meters.
-If the ACK timing is too high it will not affect the throughput that much. If the ACK time is too low it can drop your throughput to the point of being unusable and can even make the system not connect.
-Recommended setting is to 0 for a household network. Which for linksys users means dd-wrt doesn't use ACK timing at all.
Joined: 13 Nov 2008 Posts: 5266 Location: CENTRAL Midnowhere
Posted: Wed Apr 29, 2009 0:23 Post subject:
I am fairly certain ack timing doesn't do anything, although that might only be for broadcom. I have had my household settings at 2000, and my long distance link at 0, and never found any difference. What you have is what you should set it too, but it might not really matter. [/i] _________________ Warning: I'm "out of my element!"
http://www.youtube.com/watch?v=MjYJ7zZ9BRw&NR=1
This thread is now linked in note 16 of the peacock thread sticky. _________________ SIG:
I'm trying to teach you to fish, not give you a fish. If you just want a fish, wait for a fisherman who hands them out. I'm more of a fishing instructor.
LOM: "If you show that you have not bothered to read the forum announcements or to follow the advices in them then the level of help available for you will drop substantially, also known as Murrkf's law.."
Post it to google community or something? I have no idea...
wiki or sticky[/list] _________________ Conventional wisdom among radio guys is that $1 spent on antennas is worth $10 spent on amplifiers. Solve RF problems with antennas to the greatest extent possible before increasing power.
I'm gonna update CTS with this info.....any thoughts \ edits anyone would like to make?
CTS Protection
The default value is set to Auto.
The help file says...
When set to Auto, a protection mechanism will ensure that your Wireless-B devices will connect to the Wireless-G router when many Wireless-G devices are present. However, performance of your Wireless-G devices may be decreased.
How it works:
CTS Protection mode is a is a protection mechanism that operates on the physical (PHY) level frame. In its default configuration dd-wrt uses it to provide a way of ensuring coexistence between the legacy and the new wifi devices. Adding to that by using CTS and modifying RTS threshold value you can tweak operation of the CTS protection mechanism this can then be combined with the Fragmentation Threshold tweak to help troubleshoot\fix connectivity and\or performance issues etc. Remember tweaking the CTS\RTS process and the Fragmentation Threshold value often comes at a price usually by decreasing the overall throughput to the WLAN.
At a very high level summary of the process when multiple devices are connected to an access point, they can occasionally be transmitting data to the access point at the same time because neither one can see the other client well enough to determine if it is transmitting on the channel or not. When this happens, the AP will discard both pieces of colliding data, thus contributing to error rates. CTS (clear to send) protection skirts this issue by delegating which device gets to transmit at a given time.
Once CTS \RTS Protection is configured correctly within your WLAN environment there are specific scenarios that occur and the software will activate the CTS\RTS protection mechanisms;
Here are a few examples of what triggers CTS to be employed by the dd-wrt router software.
CTS Protection trigger 1; - NON-default dd-wrt behaviour -This is the trigger that a user is impacting by changing the RTS threshold default to a lower value.
A client that wants to use the radio channel to send data packet(s) of a size that is equal or above the defined RTS threshold value.
CTS Protection trigger 2; -default dd-wrt behaviour
A 802.11g client attempts to connect to a SSID that is using channel bonding. Transmissions using a 40 MHz channel in the presence of 802.11a or 802.11g clients require using CTS protection mode. This will apply the CTS protection mechanism on both 20 MHz halves of the 40 MHz channel, to prevent interference with legacy devices and allow proper operation of the 802.11a and 802.11g clients.
CTS Protection trigger 3; -default dd-wrt behaviour
If you are running in mixed wireless mode on a 802.11n router and you have 802.11b clients in your environment. CTS Protection is used to allow the 802.11b client to operate correctly and also not to interfere with the operation of the 802.11a,g, and N client transmissions.
Also;
- An 11b device associates to the AP. - same as trigger 3
- An 11b AP on the same channel can be heard by the AP - variant on trigger 3
- The AP hears an 11g AP that is in protection because of an 11b device associated. -another variantion of the trigger 3 event.
**NOTE: Trigger 1 will never happen on the dd-wrt default configuration due to the the value of the RTS Threshold value being 2347 and the the Fragmentation Threshold value being 2346. Based on the data packet fragmentation threshold default value at 2346 in size dd-wrt will apply fragmentation to all packets. Becasue of this fragmentaion process the 2347 packet size needed to trigger the RTS threshold is never reached.
For a closer look at what happens in one of these cases lets look at a case like trigger number 1 list above and the steps in the CTS\RTS protection process.
example. A client that wants to use the radio channel to send data packet(s) of a size that is equal or above the defined RTS threshold value.
Steps in the CTS\RTS Protection process
1.) The client wishing to send date over the channel first sends an RTS (request to send) packet to the AP.
2.) In turn the AP responds with a CTS broadcast packet to the WLAN and declares to all the clienbts on the entire WLAN that the specific client who sent the RTS packet as the "owner" of the channel and then the AP listens only to that client until it is done transmitting.
3.)The process is repeated for all request to transfer data,which for whatever reason triggers the CTS\RTS protection mechanisms, on a first come first serve basis.
Implementing CTS\RTS Protection on top of the defaul dd-wrt configuration;
1.) The AP running dd-wrt has the CTS Protection mode is set to Auto by default and then you could adjust the RTS threshold value to something lower then 2346(Which is the default fragmentation threshold value on dd-wrt) on the AP.
2.) All clients connected to the dd-wrt AP are configured for CTS\RTS mode as apposed to disabled or CTS-Self mode.
***NOTE Typically the The RTS Threshold value on dd-wrt is lowered to address or troublehsoot some sort of connectivity or preformance issue with a client or all clients on a WLAN. Adjusting the value is a balenacing act between getting your problem fixed and lossing overall WLAN speed. The more times CTS procetion mode is triggered in a period of time "its frequency" the more impact it will have; good or bad. So start with 2340, then 2320, 2300 etc...
-If your trying to tweak out every drop of preformance in an ideal setup then you can disable this on the AP and clients. Test again to see if it helps for better results, it should.
-If you want to try 40MHz with your 802.11n clients you might want to start with CTS Protection set to Auto. You do this incase you have 802.11a or g or even some N clients that do not support 40GHz transmissions or "channel bonding" as it is sometimes called.
-If you have a 802.11n based router running in mixed wireless mode that you want to connect 802.11b clients you need to have CTS protection mode set to Auto meaning enabled.
-If CTS Protection makes things faster a network redesign might be needed.
-"CTS to self" based protection - an alternate implementation method of CTS; where by the device willing to send frames over the WLAN first sends a CTS frame to itself. "CTS to self" based protection has less overhead, but it must be taken into account that this only protects against devices receiving CTS frame (e.g. if there are 2 "hidden" stations, there is no use for them to use "CTS to self" protection, because they will not be able to receive CTS sent by other station - in this case stations must use RTS/CTS so that other station knows not to transmit by seeing CTS transmitted by AP).If you have set the CTS protection mode to disabled on the dd-wrt AP, then this is a good choice for the client configuration. _________________ Location (urban) - 1x Linksys EA8500 (AP wlan0 & wlan1 enabled)
1x Asus 68u (Repeater Bridge w/VAP) - wl0 disabled
1x Asus 87u (Client Bridge) - wl1 disabled
Joined: 13 Nov 2008 Posts: 5266 Location: CENTRAL Midnowhere
Posted: Mon May 04, 2009 18:00 Post subject:
I think this is WAY too technical. You need a guide to be simple and easy to read. Provide links to the technical detail; explain what it means in words that almost all can understand. Focus on what a person should "do".
And I disagree too technical. If you are not interested in the 'too technical' stuff you probably should not be mucking with advanced wireless settings
And I disagree too technical. If you are not interested in the 'too technical' stuff you probably should not be mucking with advanced wireless settings
Is this thread supposed to be elitist? I guess the decision has to be made as to who it is being written for. That will determion tne the technical level.
The suggestion was to provide links to the technical info, not to omit it entirely.
