Re: [WISPA] WDS PtMP
Ok I didn't realize that you where utilizing the WDS station mode. So you basically have a normal AP/station setup but it is just bridged. Are you using N-stream? The WDS-station mode really was designed so that N-stream could be used on a WDS / Bridge network. WDS - station is a proprietary mode developed by MT if my understanding is correct. If so the likely the issue will be resolved with the polling feature available with N-stream. The reason I state this is because from the information provided the issue has became a problem as more load has been applied to the solution. The solution is more then capable of handling the throughput so this would indicate an interference source. As 802.11 is the solution you are seeing more retransmissions as the wait-before-talk mechanism is causing high latency issues. Assuming the interference is self generated and antenna choices are limited the Polling feature in N-stream likely is your best bet for fixing this. I currently use N-stream over WDS for one of my main back hauls to a new bandwidth source and it has performed flawlessly for 6 months. This is using 2.9.28 software. It has been upgraded since installation and I am not sure what version of the software we started with. Anthony Will Tom DeReggi wrote: To be clear, Mikrotik us being used, and the 4 remote building are in wds station mode and only configured to talk to the 1 central master WDS AP, the four client WDS radios are not configured to talk to each other. So all the CPE radios only have one hop to the APconnected to the Internet backhaul. My theory for design was... I had a 10 mbps backhaul. The WDS PtMP would have 16mbps (54 mbps modulation), to help with waste from re-transmissions. All clients are bandwidth managed (priority weighted method) centrally on other end of backhaul, to also assist with fair transmission time. Also radios use CDMA/CA, with the CA also assisting. The question is, is this enough to let it work well with only four buildings. I'm starting to think that it might not be. But the problem shouldn't be that they hear each other. we want them to hear each other, so they don't transmit at the same time. Thats what 802.11 needs. Hidden node happens because CPEs don't hear each other, and don;t know someone else is transmitting, from my understanding. Part of my question is, Does WDS work differently when in Mikrotik Station WDS mode than a normal WDS AP? Tom DeReggi RapidDSL Wireless, Inc IntAirNet- Fixed Wireless Broadband - Original Message - From: Anthony Will [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Saturday, October 07, 2006 11:57 AM Subject: Re: [WISPA] WDS PtMP It would seem to me that as your load increased your WDS/APs are transmitting over each other as clients are trying to transmit to the central AP. client --WDS/AP transmitting carrier beacons or other data to client and passing onto to --WDS/AP--WDS/AP--Client (transmitting to local AP) In this scenario you have the two clients talking and one AP all trying to talk at the same time and thus raising your noise floor because they are all on the same channel. There is not a feature in standard WDS to coordinate who can talk and who can not talk other then the standard CDMA layer of the 802.11 protocol. This will create issues as the more load you have on this setup the more self interference and retransmissions you will incur. The big thing the mesh brings to the table is the ability to help coordinate all of this traffic so that you can utilize the spectrum more efficiently. At least that is my opinion as soon as someone actually does it. You likely are going to have to switch to a station /AP solution for this setup because everything is to close and can hear each other. This will destroy your bridge setup unless you change to a propitiatory system such as Trango, Canopy, etc. One other thing to note is that this is all half duplex so you might have two many hops and thus running out of bandwidth. Anthony Will Broadband Corp. Tom DeReggi wrote: Background In standard WIFI, a principle exists called hidden note, where two CPEs transmit at the same time and colide because they do not hear each other. There are three ways to get around that, using WIFI between Client and AP. 1) Polling (Karlnet, Nstream, Proprietary), 2) Use Omnis, so radios can hear each other if in close proximity, 3) RTS/CTS which effectively solves the problem at a significant performance degregation. A well know problem with well known solutions. Issue. How does this play our with WDS? AP to AP communication. Sure in PtP its a non-issue, because there are only two radios involved to complete the link. But WDS allows PtMP operation. How does WDS commuication work? Does the Hidden Node problem exist with PtMP WDS? And if so, is there a way to address it? If so, will it help to make the CPE's Omnis, so
RE: [WISPA] WDS PtMP
2) My primary goal in the original post was to learn the difference between Wifi Station/client and Wifi WDS at the protocol level on how the protocol makes communications. For example, can they both do CTS/RTS? Unless the WDS protocol is fully understood, its not possible to design networks optimally using WDS. Tom, Unlike WiFi, there is no recognized standard of interoperability amongst WDS implementations -- the spec itself is rather vague when outlining WDS, basically saying more like this is what it is and what it has to do rather than this is exactly how it needs to be done -- to my knowledge, there's no WDS interoperability requirement for WiFi certification -- so YMMV depending on the vendor implementation Btw -- coming to our roadshow? -Charles --- WiNOG Wireless Roadshows Coming to a City Near You http://www.winog.com -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Tom DeReggi Sent: Saturday, October 07, 2006 8:34 PM To: WISPA General List Subject: Re: [WISPA] WDS PtMP Marlon, For clarification 1) Yes 5.250-5.350 is for outdoor, but I temporarilly put my radio to a channel under 5.25 which is in the 5.1 band for indoor only use, for the temporary testing. 3) Mikrotik actually has several WDS modes. They may not all necesarilly operate the same at the protocol level. 4) Also, the reason the network was done this way was that only one of the five buildings had LOS to our network. All clients within the building are done with wires. Normally we would have done this site with Trango PtMP, but when it was installed (1.5years ago), Trango had a short range packet loss problem and no Omni AP option. Cosmetic requirements from Property owner for the main site, would not allow Sector AP antennas for each remote buildings, so Omni was required. WDS was required as Standard Wifi was not true bridging. This was actually an excellent case study site for Mikrotik acting as both the radio and VLAN switch w/9 ethernet ports on CPEs. 5) There are many ways to improve the network, the problem, is I'm looking to be as least disruptive as possible, and don;t want to use the customer base as guinee pigs, so looking to better understand WDS at the protocol level. One of our consideration, is that we may leave the Mikrotiks as the Building routers, and repalce the outdoor stuff with Trango, not that it has good short range gear. But there is no reason to do that unless WDS is truly the cause. We have not proven that for certain yet. We can also solve it, by adding a second WDS Master AP, and then we'd split the load and have redundancy. Tom DeReggi RapidDSL Wireless, Inc IntAirNet- Fixed Wireless Broadband - Original Message - From: Marlon K. Schafer (509) 982-2181 [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Friday, October 06, 2006 1:27 PM Subject: Re: [WISPA] WDS PtMP - Original Message - From: Tom DeReggi To: WISPA General List Sent: Friday, October 06, 2006 9:09 AM Subject: [WISPA] WDS PtMP Background In standard WIFI, a principle exists called hidden note, where two CPEs transmit at the same time and colide because they do not hear each other. There are three ways to get around that, using WIFI between Client and AP. 1) Polling (Karlnet, Nstream, Proprietary), 2) Use Omnis, so radios can hear each other if in close proximity, 3) RTS/CTS which effectively solves the problem at a significant performance degregation. A well know problem with well known solutions. mks: Close. It's when two CPE talk at the same time and the AP can't hear one of them because the other one is louder. This is part of why you should never build a network using the same size antennas everywhere. And why more power isn't always better. I try to keep all of my cpe within about 10 dB of each other. mks: It can ALSO be where two cpe talk at the same time because they don't know each other exists. This causes a collision at the ap (it can't understand either one of them) and after a random backoff time they'll each try again. mks: The easy fix to that problem is usually to just add another ap as you've filled up the one you already have :-). Issue. How does this play our with WDS? AP to AP communication. Sure in PtP its a non-issue, because there are only two radios involved to complete the link. But WDS allows PtMP operation. How does WDS commuication work? Does the Hidden Node problem exist with PtMP WDS? And if so, is there a way to address it? If so, will it help to make the CPE's Omnis, so they hear each other? mks: As I understand it, wds is simply a way for a cpe unit to ALSO act as an ap. Much like AdHoc mode. Except this time you can put in WDS units only where needed so that you can go around a corner or two. With AdHoc the whole network would have to be that way. My
Re: [WISPA] WDS PtMP
On thing I forgot to mention is that every single packet transmitted is going to be retransmitted on all the WDS/AP connected together on the wireless side. With sustained traffic that would mean that all of them are transmitting and receiving the 2 megs mentioned. And we can assume that these units are not exactly all the same distance or under the same exact load so there will be very tiny differences when each unit will be retransmitting that 2 meg of traffic. I am not real happy with the way I explained this let me know if it makes any sense :) Anthony Will Broadband Corp. Anthony Will wrote: It would seem to me that as your load increased your WDS/APs are transmitting over each other as clients are trying to transmit to the central AP. client --WDS/AP transmitting carrier beacons or other data to client and passing onto to --WDS/AP--WDS/AP--Client (transmitting to local AP) In this scenario you have the two clients talking and one AP all trying to talk at the same time and thus raising your noise floor because they are all on the same channel. There is not a feature in standard WDS to coordinate who can talk and who can not talk other then the standard CDMA layer of the 802.11 protocol. This will create issues as the more load you have on this setup the more self interference and retransmissions you will incur. The big thing the mesh brings to the table is the ability to help coordinate all of this traffic so that you can utilize the spectrum more efficiently. At least that is my opinion as soon as someone actually does it. You likely are going to have to switch to a station /AP solution for this setup because everything is to close and can hear each other. This will destroy your bridge setup unless you change to a propitiatory system such as Trango, Canopy, etc. One other thing to note is that this is all half duplex so you might have two many hops and thus running out of bandwidth. Anthony Will Broadband Corp. Tom DeReggi wrote: Background In standard WIFI, a principle exists called hidden note, where two CPEs transmit at the same time and colide because they do not hear each other. There are three ways to get around that, using WIFI between Client and AP. 1) Polling (Karlnet, Nstream, Proprietary), 2) Use Omnis, so radios can hear each other if in close proximity, 3) RTS/CTS which effectively solves the problem at a significant performance degregation. A well know problem with well known solutions. Issue. How does this play our with WDS? AP to AP communication. Sure in PtP its a non-issue, because there are only two radios involved to complete the link. But WDS allows PtMP operation. How does WDS commuication work? Does the Hidden Node problem exist with PtMP WDS? And if so, is there a way to address it? If so, will it help to make the CPE's Omnis, so they hear each other? My confusion is how WDS/WDS works compared to Station/AP modes. Example application: Using 802.11a gear. 5 seperate MTU buildings, spread out within 300 yards of each other. 1 is a Master AP Site, with an Omni, and a second backhaul radio to the Internet. 4 of the 5 have a direction CPE style antenna pointing to the Master Antenna. WDS is used to allow the radios to operate as true transparent bridges, and to pass per client (5-10 clients per MTU) large packet VLAN traffic. (Note: There is a reason we did not select Nstreme w/ Polling. It may have been an incompatibilty with WDS or inabilty to do transparent bridging with large packets, which standard 802.11 station mode does not support under protocol. May have been early version of Firmware, not sure if still an issue) Why I thought it might be an issue: Surveys show low noise. However, as more clients have been taken on (2 mbps average sustained throughput all combined), the Link quality started to degregate as if the noise floor was rising. As a tempoirary measure, we switched to 5.2Ghz (indoor only FREQ, which appeared not to have any detectable noise in standard 802.11 based survey tools, and was chosen because non-detectable carrier grade gear would not use those channels). Its hard to believe that the noise floor would be that high using that freq. So I'm wondering if the noise that I'm hearing is actually my own CPEs within this project? The symptom was sparatic higher latency, what typically would happen if 802.11a had frequent retransmissions (native prorocol ARQ). I can look at stats to see if there are re-transmissions, but that data is pointless, as what I want to know is, is the retransmisison because my own noise or someone elses. Its hard to tell with WiFi, as WiFi doesn't transmit when its not in use. So testing in the middle of the night, when clients and users in town are off, may not be meaningful. Its also possible, that I just have a failing
Re: [WISPA] WDS PtMP
Marlon, For clarification 1) Yes 5.250-5.350 is for outdoor, but I temporarilly put my radio to a channel under 5.25 which is in the 5.1 band for indoor only use, for the temporary testing. 2) My primary goal in the original post was to learn the difference between Wifi Station/client and Wifi WDS at the protocol level on how the protocol makes communications. For example, can they both do CTS/RTS? Unless the WDS protocol is fully understood, its not possible to design networks optimally using WDS. 3) Mikrotik actually has several WDS modes. They may not all necesarilly operate the same at the protocol level. 4) Also, the reason the network was done this way was that only one of the five buildings had LOS to our network. All clients within the building are done with wires. Normally we would have done this site with Trango PtMP, but when it was installed (1.5years ago), Trango had a short range packet loss problem and no Omni AP option. Cosmetic requirements from Property owner for the main site, would not allow Sector AP antennas for each remote buildings, so Omni was required. WDS was required as Standard Wifi was not true bridging. This was actually an excellent case study site for Mikrotik acting as both the radio and VLAN switch w/9 ethernet ports on CPEs. 5) There are many ways to improve the network, the problem, is I'm looking to be as least disruptive as possible, and don;t want to use the customer base as guinee pigs, so looking to better understand WDS at the protocol level. One of our consideration, is that we may leave the Mikrotiks as the Building routers, and repalce the outdoor stuff with Trango, not that it has good short range gear. But there is no reason to do that unless WDS is truly the cause. We have not proven that for certain yet. We can also solve it, by adding a second WDS Master AP, and then we'd split the load and have redundancy. Tom DeReggi RapidDSL Wireless, Inc IntAirNet- Fixed Wireless Broadband - Original Message - From: Marlon K. Schafer (509) 982-2181 [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Friday, October 06, 2006 1:27 PM Subject: Re: [WISPA] WDS PtMP - Original Message - From: Tom DeReggi To: WISPA General List Sent: Friday, October 06, 2006 9:09 AM Subject: [WISPA] WDS PtMP Background In standard WIFI, a principle exists called hidden note, where two CPEs transmit at the same time and colide because they do not hear each other. There are three ways to get around that, using WIFI between Client and AP. 1) Polling (Karlnet, Nstream, Proprietary), 2) Use Omnis, so radios can hear each other if in close proximity, 3) RTS/CTS which effectively solves the problem at a significant performance degregation. A well know problem with well known solutions. mks: Close. It's when two CPE talk at the same time and the AP can't hear one of them because the other one is louder. This is part of why you should never build a network using the same size antennas everywhere. And why more power isn't always better. I try to keep all of my cpe within about 10 dB of each other. mks: It can ALSO be where two cpe talk at the same time because they don't know each other exists. This causes a collision at the ap (it can't understand either one of them) and after a random backoff time they'll each try again. mks: The easy fix to that problem is usually to just add another ap as you've filled up the one you already have :-). Issue. How does this play our with WDS? AP to AP communication. Sure in PtP its a non-issue, because there are only two radios involved to complete the link. But WDS allows PtMP operation. How does WDS commuication work? Does the Hidden Node problem exist with PtMP WDS? And if so, is there a way to address it? If so, will it help to make the CPE's Omnis, so they hear each other? mks: As I understand it, wds is simply a way for a cpe unit to ALSO act as an ap. Much like AdHoc mode. Except this time you can put in WDS units only where needed so that you can go around a corner or two. With AdHoc the whole network would have to be that way. My confusion is how WDS/WDS works compared to Station/AP modes. Example application: Using 802.11a gear. 5 seperate MTU buildings, spread out within 300 yards of each other. 1 is a Master AP Site, with an Omni, and a second backhaul radio to the Internet. 4 of the 5 have a direction CPE style antenna pointing to the Master Antenna. WDS is used to allow the radios to operate as true transparent bridges, and to pass per client (5-10 clients per MTU) large packet VLAN traffic. (Note: There is a reason we did not select Nstreme w/ Polling. It may have been an incompatibilty with WDS or inabilty to do transparent bridging with large packets, which standard 802.11 station mode does not support under protocol. May have been early version of Firmware, not sure if still an issue) Why I
Re: [WISPA] WDS PtMP
To be clear, Mikrotik us being used, and the 4 remote building are in wds station mode and only configured to talk to the 1 central master WDS AP, the four client WDS radios are not configured to talk to each other. So all the CPE radios only have one hop to the APconnected to the Internet backhaul. My theory for design was... I had a 10 mbps backhaul. The WDS PtMP would have 16mbps (54 mbps modulation), to help with waste from re-transmissions. All clients are bandwidth managed (priority weighted method) centrally on other end of backhaul, to also assist with fair transmission time. Also radios use CDMA/CA, with the CA also assisting. The question is, is this enough to let it work well with only four buildings. I'm starting to think that it might not be. But the problem shouldn't be that they hear each other. we want them to hear each other, so they don't transmit at the same time. Thats what 802.11 needs. Hidden node happens because CPEs don't hear each other, and don;t know someone else is transmitting, from my understanding. Part of my question is, Does WDS work differently when in Mikrotik Station WDS mode than a normal WDS AP? Tom DeReggi RapidDSL Wireless, Inc IntAirNet- Fixed Wireless Broadband - Original Message - From: Anthony Will [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Saturday, October 07, 2006 11:57 AM Subject: Re: [WISPA] WDS PtMP It would seem to me that as your load increased your WDS/APs are transmitting over each other as clients are trying to transmit to the central AP. client --WDS/AP transmitting carrier beacons or other data to client and passing onto to --WDS/AP--WDS/AP--Client (transmitting to local AP) In this scenario you have the two clients talking and one AP all trying to talk at the same time and thus raising your noise floor because they are all on the same channel. There is not a feature in standard WDS to coordinate who can talk and who can not talk other then the standard CDMA layer of the 802.11 protocol. This will create issues as the more load you have on this setup the more self interference and retransmissions you will incur. The big thing the mesh brings to the table is the ability to help coordinate all of this traffic so that you can utilize the spectrum more efficiently. At least that is my opinion as soon as someone actually does it. You likely are going to have to switch to a station /AP solution for this setup because everything is to close and can hear each other. This will destroy your bridge setup unless you change to a propitiatory system such as Trango, Canopy, etc. One other thing to note is that this is all half duplex so you might have two many hops and thus running out of bandwidth. Anthony Will Broadband Corp. Tom DeReggi wrote: Background In standard WIFI, a principle exists called hidden note, where two CPEs transmit at the same time and colide because they do not hear each other. There are three ways to get around that, using WIFI between Client and AP. 1) Polling (Karlnet, Nstream, Proprietary), 2) Use Omnis, so radios can hear each other if in close proximity, 3) RTS/CTS which effectively solves the problem at a significant performance degregation. A well know problem with well known solutions. Issue. How does this play our with WDS? AP to AP communication. Sure in PtP its a non-issue, because there are only two radios involved to complete the link. But WDS allows PtMP operation. How does WDS commuication work? Does the Hidden Node problem exist with PtMP WDS? And if so, is there a way to address it? If so, will it help to make the CPE's Omnis, so they hear each other? My confusion is how WDS/WDS works compared to Station/AP modes. Example application: Using 802.11a gear. 5 seperate MTU buildings, spread out within 300 yards of each other. 1 is a Master AP Site, with an Omni, and a second backhaul radio to the Internet. 4 of the 5 have a direction CPE style antenna pointing to the Master Antenna. WDS is used to allow the radios to operate as true transparent bridges, and to pass per client (5-10 clients per MTU) large packet VLAN traffic. (Note: There is a reason we did not select Nstreme w/ Polling. It may have been an incompatibilty with WDS or inabilty to do transparent bridging with large packets, which standard 802.11 station mode does not support under protocol. May have been early version of Firmware, not sure if still an issue) Why I thought it might be an issue: Surveys show low noise. However, as more clients have been taken on (2 mbps average sustained throughput all combined), the Link quality started to degregate as if the noise floor was rising. As a tempoirary measure, we switched to 5.2Ghz (indoor only FREQ, which appeared not to have any detectable noise in standard 802.11 based survey tools, and was chosen because non-detectable carrier grade gear would not use those channels). Its hard to believe
Re: [WISPA] WDS PtMP
every single packet transmitted is going to be retransmitted on all the WDS/AP connected together on the wireless side. Is that really true, in this type of configuration, Mikrotik 4 stationsWDS, 1 AP WDS? I'm not sure that these units re-transmit the data. Remember their is no data that needs to pass between the 4 remote client buildings. Also remember that none of the subscribers are using wireless, they are all using wired connection, only the 4 MTU building roofs have a station WDS radio. Tom DeReggi RapidDSL Wireless, Inc IntAirNet- Fixed Wireless Broadband - Original Message - From: Anthony Will [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Saturday, October 07, 2006 12:07 PM Subject: Re: [WISPA] WDS PtMP On thing I forgot to mention is that every single packet transmitted is going to be retransmitted on all the WDS/AP connected together on the wireless side. With sustained traffic that would mean that all of them are transmitting and receiving the 2 megs mentioned. And we can assume that these units are not exactly all the same distance or under the same exact load so there will be very tiny differences when each unit will be retransmitting that 2 meg of traffic. I am not real happy with the way I explained this let me know if it makes any sense :) Anthony Will Broadband Corp. Anthony Will wrote: It would seem to me that as your load increased your WDS/APs are transmitting over each other as clients are trying to transmit to the central AP. client --WDS/AP transmitting carrier beacons or other data to client and passing onto to --WDS/AP--WDS/AP--Client (transmitting to local AP) In this scenario you have the two clients talking and one AP all trying to talk at the same time and thus raising your noise floor because they are all on the same channel. There is not a feature in standard WDS to coordinate who can talk and who can not talk other then the standard CDMA layer of the 802.11 protocol. This will create issues as the more load you have on this setup the more self interference and retransmissions you will incur. The big thing the mesh brings to the table is the ability to help coordinate all of this traffic so that you can utilize the spectrum more efficiently. At least that is my opinion as soon as someone actually does it. You likely are going to have to switch to a station /AP solution for this setup because everything is to close and can hear each other. This will destroy your bridge setup unless you change to a propitiatory system such as Trango, Canopy, etc. One other thing to note is that this is all half duplex so you might have two many hops and thus running out of bandwidth. Anthony Will Broadband Corp. Tom DeReggi wrote: Background In standard WIFI, a principle exists called hidden note, where two CPEs transmit at the same time and colide because they do not hear each other. There are three ways to get around that, using WIFI between Client and AP. 1) Polling (Karlnet, Nstream, Proprietary), 2) Use Omnis, so radios can hear each other if in close proximity, 3) RTS/CTS which effectively solves the problem at a significant performance degregation. A well know problem with well known solutions. Issue. How does this play our with WDS? AP to AP communication. Sure in PtP its a non-issue, because there are only two radios involved to complete the link. But WDS allows PtMP operation. How does WDS commuication work? Does the Hidden Node problem exist with PtMP WDS? And if so, is there a way to address it? If so, will it help to make the CPE's Omnis, so they hear each other? My confusion is how WDS/WDS works compared to Station/AP modes. Example application: Using 802.11a gear. 5 seperate MTU buildings, spread out within 300 yards of each other. 1 is a Master AP Site, with an Omni, and a second backhaul radio to the Internet. 4 of the 5 have a direction CPE style antenna pointing to the Master Antenna. WDS is used to allow the radios to operate as true transparent bridges, and to pass per client (5-10 clients per MTU) large packet VLAN traffic. (Note: There is a reason we did not select Nstreme w/ Polling. It may have been an incompatibilty with WDS or inabilty to do transparent bridging with large packets, which standard 802.11 station mode does not support under protocol. May have been early version of Firmware, not sure if still an issue) Why I thought it might be an issue: Surveys show low noise. However, as more clients have been taken on (2 mbps average sustained throughput all combined), the Link quality started to degregate as if the noise floor was rising. As a tempoirary measure, we switched to 5.2Ghz (indoor only FREQ, which appeared not to have any detectable noise in standard 802.11 based survey tools, and was chosen because non-detectable carrier grade gear would not use those channels). Its hard to believe that the noise floor would be that high using
Re: [WISPA] WDS PtMP
To be clear... Client1 -wire---\ ___ WDS Station --RF\ Client2 -wire---/\_ WDS AP --wire--Backhaul to Internet / Client3 -wire---\ ___ WDS Station --RF---/ Client4 -wire---/ Tom DeReggi RapidDSL Wireless, Inc IntAirNet- Fixed Wireless Broadband - Original Message - From: Anthony Will [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Saturday, October 07, 2006 12:07 PM Subject: Re: [WISPA] WDS PtMP On thing I forgot to mention is that every single packet transmitted is going to be retransmitted on all the WDS/AP connected together on the wireless side. With sustained traffic that would mean that all of them are transmitting and receiving the 2 megs mentioned. And we can assume that these units are not exactly all the same distance or under the same exact load so there will be very tiny differences when each unit will be retransmitting that 2 meg of traffic. I am not real happy with the way I explained this let me know if it makes any sense :) Anthony Will Broadband Corp. Anthony Will wrote: It would seem to me that as your load increased your WDS/APs are transmitting over each other as clients are trying to transmit to the central AP. client --WDS/AP transmitting carrier beacons or other data to client and passing onto to --WDS/AP--WDS/AP--Client (transmitting to local AP) In this scenario you have the two clients talking and one AP all trying to talk at the same time and thus raising your noise floor because they are all on the same channel. There is not a feature in standard WDS to coordinate who can talk and who can not talk other then the standard CDMA layer of the 802.11 protocol. This will create issues as the more load you have on this setup the more self interference and retransmissions you will incur. The big thing the mesh brings to the table is the ability to help coordinate all of this traffic so that you can utilize the spectrum more efficiently. At least that is my opinion as soon as someone actually does it. You likely are going to have to switch to a station /AP solution for this setup because everything is to close and can hear each other. This will destroy your bridge setup unless you change to a propitiatory system such as Trango, Canopy, etc. One other thing to note is that this is all half duplex so you might have two many hops and thus running out of bandwidth. Anthony Will Broadband Corp. Tom DeReggi wrote: Background In standard WIFI, a principle exists called hidden note, where two CPEs transmit at the same time and colide because they do not hear each other. There are three ways to get around that, using WIFI between Client and AP. 1) Polling (Karlnet, Nstream, Proprietary), 2) Use Omnis, so radios can hear each other if in close proximity, 3) RTS/CTS which effectively solves the problem at a significant performance degregation. A well know problem with well known solutions. Issue. How does this play our with WDS? AP to AP communication. Sure in PtP its a non-issue, because there are only two radios involved to complete the link. But WDS allows PtMP operation. How does WDS commuication work? Does the Hidden Node problem exist with PtMP WDS? And if so, is there a way to address it? If so, will it help to make the CPE's Omnis, so they hear each other? My confusion is how WDS/WDS works compared to Station/AP modes. Example application: Using 802.11a gear. 5 seperate MTU buildings, spread out within 300 yards of each other. 1 is a Master AP Site, with an Omni, and a second backhaul radio to the Internet. 4 of the 5 have a direction CPE style antenna pointing to the Master Antenna. WDS is used to allow the radios to operate as true transparent bridges, and to pass per client (5-10 clients per MTU) large packet VLAN traffic. (Note: There is a reason we did not select Nstreme w/ Polling. It may have been an incompatibilty with WDS or inabilty to do transparent bridging with large packets, which standard 802.11 station mode does not support under protocol. May have been early version of Firmware, not sure if still an issue) Why I thought it might be an issue: Surveys show low noise. However, as more clients have been taken on (2 mbps average sustained throughput all combined), the Link quality started to degregate as if the noise floor was rising. As a tempoirary measure, we switched to 5.2Ghz (indoor only FREQ, which appeared not to have any detectable noise in standard 802.11 based survey tools, and was chosen because non-detectable carrier grade gear would not use those channels). Its hard to believe that the noise floor would be that high using that freq. So I'm wondering if the noise that I'm hearing is actually my own CPEs within this project? The symptom was sparatic higher latency, what typically would happen if 802.11a had frequent
[WISPA] WDS PtMP
Background In standard WIFI, a principle exists called hidden note, where two CPEs transmit at the same time andcolidebecause they do not hear each other. There are three ways to get around that, using WIFI between Client and AP. 1) Polling (Karlnet, Nstream, Proprietary), 2) Use Omnis, so radios can hear each other if in close proximity, 3) RTS/CTSwhich effectively solves the problem at asignificant performance degregation. A well know problem with well known solutions. Issue. How does this play our with WDS?AP to AP communication. Sure in PtP its a non-issue, because there are onlytwo radios involved to complete the link. But WDS allows PtMP operation. How does WDS commuication work? Does the Hidden Node problem exist with PtMP WDS? And if so, is there a way to address it? If so, will it help to make the CPE's Omnis, so they hear each other? My confusion is how WDS/WDSworks compared to Station/AP modes. Exampleapplication: Using 802.11a gear. 5 seperate MTUbuildings, spread outwithin 300 yards of each other. 1 is a Master AP Site, with an Omni, and a secondbackhaul radio to the Internet. 4 of the 5 have a direction CPE style antenna pointing to the Master Antenna. WDS is used to allow the radios to operate as true transparent bridges, and to pass per client (5-10 clients per MTU) large packet VLAN traffic. (Note: There is a reason we did not select Nstreme w/ Polling. It may have been an incompatibilty with WDS or inabilty to do transparent bridging with large packets, which standard 802.11 station mode does not support under protocol. May have been early version of Firmware, not sure if still an issue) Why I thought it might be an issue: Surveys show low noise. However, as moreclients have been taken on (2 mbps average sustained throughput all combined),the Link quality started to degregate as if the noise floor was rising. As a tempoirary measure, we switched to 5.2Ghz (indoor only FREQ, which appeared not to have any detectable noise in standard 802.11 based survey tools, and was chosen becausenon-detectable carrier grade gear would not use those channels). Its hard to believe that the noise floor would be that high using that freq. So I'm wondering if the noise that I'm hearing is actually my own CPEs within this project? The symptom was sparatic higher latency, what typically would happen if 802.11ahad frequent retransmissions (native prorocol ARQ). I can look at stats to see if there are re-transmissions, but that data is pointless, as what I want to know is, is the retransmisison because my own noise or someone elses. Its hard to tell with WiFi, as WiFi doesn't transmit when its not in use. So testing in the middle of the night, when clients and users in town are off, may not be meaningful. Its also possible, that I just have a failing radio card or two, and a totally different cause. Tom DeReggiRapidDSL Wireless, IncIntAirNet- Fixed Wireless Broadband -- WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/
Re: [WISPA] WDS PtMP
- Original Message - From: Tom DeReggi To: WISPA General List Sent: Friday, October 06, 2006 9:09 AM Subject: [WISPA] WDS PtMP Background In standard WIFI, a principle exists called hidden note, where two CPEs transmit at the same time and colide because they do not hear each other. There are three ways to get around that, using WIFI between Client and AP. 1) Polling (Karlnet, Nstream, Proprietary), 2) Use Omnis, so radios can hear each other if in close proximity, 3) RTS/CTS which effectively solves the problem at a significant performance degregation. A well know problem with well known solutions. mks: Close. It's when two CPE talk at the same time and the AP can't hear one of them because the other one is louder. This is part of why you should never build a network using the same size antennas everywhere. And why more power isn't always better. I try to keep all of my cpe within about 10 dB of each other. mks: It can ALSO be where two cpe talk at the same time because they don't know each other exists. This causes a collision at the ap (it can't understand either one of them) and after a random backoff time they'll each try again. mks: The easy fix to that problem is usually to just add another ap as you've filled up the one you already have :-). Issue. How does this play our with WDS? AP to AP communication. Sure in PtP its a non-issue, because there are only two radios involved to complete the link. But WDS allows PtMP operation. How does WDS commuication work? Does the Hidden Node problem exist with PtMP WDS? And if so, is there a way to address it? If so, will it help to make the CPE's Omnis, so they hear each other? mks: As I understand it, wds is simply a way for a cpe unit to ALSO act as an ap. Much like AdHoc mode. Except this time you can put in WDS units only where needed so that you can go around a corner or two. With AdHoc the whole network would have to be that way. My confusion is how WDS/WDS works compared to Station/AP modes. Example application: Using 802.11a gear. 5 seperate MTU buildings, spread out within 300 yards of each other. 1 is a Master AP Site, with an Omni, and a second backhaul radio to the Internet. 4 of the 5 have a direction CPE style antenna pointing to the Master Antenna. WDS is used to allow the radios to operate as true transparent bridges, and to pass per client (5-10 clients per MTU) large packet VLAN traffic. (Note: There is a reason we did not select Nstreme w/ Polling. It may have been an incompatibilty with WDS or inabilty to do transparent bridging with large packets, which standard 802.11 station mode does not support under protocol. May have been early version of Firmware, not sure if still an issue) Why I thought it might be an issue: Surveys show low noise. However, as more clients have been taken on (2 mbps average sustained throughput all combined), the Link quality started to degregate as if the noise floor was rising. As a tempoirary measure, we switched to 5.2Ghz (indoor only FREQ, which appeared not to have any detectable noise in standard 802.11 based survey tools, and was chosen because non-detectable carrier grade gear would not use those channels). Its hard to believe that the noise floor would be that high using that freq. So I'm wondering if the noise that I'm hearing is actually my own CPEs within this project? The symptom was sparatic higher latency, what typically would happen if 802.11a had frequent retransmissions (native prorocol ARQ). mks: 5.2 gig is also usable outdoors. I use 5.2 and 5.3 anywhere I can! Because most others don't :-). But the smart ones do. It's the 5.1 ghz band that's indoor only. mks: I think what you are probably seeing is indeed the effects of all mesh networks that use single radio systems. They all use the same channel and try to at the same time. That's why I've never liked standard mesh systems. I don't think they (and feedback such as yours seems to uphold this) will ever scale to any real use. Sure, put it in an office and feel free to do email and an occasional print job, but don't do much more than that with mesh. I can look at stats to see if there are re-transmissions, but that data is pointless, as what I want to know is, is the retransmisison because my own noise or someone elses. Its hard to tell with WiFi, as WiFi doesn't transmit when its not in use. So testing in the middle of the night, when clients and users in town are off, may not be meaningful. Its also possible, that I just have a failing radio card or two, and a totally different cause. mks: Well, first, try changing channels around and see if it has any measureable effect. Next, get ahold of a spectrum analyzer (Bob M. isn't that far from you, or I can ship mine out to you). mks: Next, build a proper network! grin. Put in a 5 gig ptmp and/or ptp system to link up all of the buildings back to the internet
