WDS performance

My understanding is that WDS cuts the bandwidth in half. If your AEBS are G, then the WDS part of your network is running at 50% of G speed (or may 25% if you have to go through 2 AEBS to get to the TC!) rather than at 100% of N speed. That is quite a hit.

My personal experience is that with the AEBSn connected to ADSL modem setup as a WDS main, with AX setup as WDS remote, I can still get 6MB download from AirDisks. To me that means I'm getting n speeds to the AEBS (I installed my own Airport N card in my MBP, prior to that I was getting about 2MB download).

With the Airports switched around (AX as WDS main and connected to ADSL, AEBS as WDS remote) I only get Wireless G speeds.

Since WDS is an 802.11g feature, using WDS forces the Time Capsule to operate in the slower 802.11g mode.

Furthermore EACH WDS link cuts your available wireless bandwidth in half. If you have 3 stations you would have 2 WDS links. Therefore you available wireless bandwidth would be 1/4 (1/2*1/2) of it's potential. If you were in a perfect environment that would mean your maximum wireless bandwidth would be 54/4 = 13 Mbps.

"Since WDS is an 802.11g feature, using WDS forces the Time Capsule to operate in the slower 802.11g mode"

I know we've discussed this before Duane. But do you still think that an 802.11n connection to the TC (acting as WDS main) is not possible? Otherwise it seems hard to explain my Airdisk transfer speeds.

If you have an 802.11n AX and an 802.11n AEBS you should be able to use the 802.11n feature "extend network" instead of WDS to wirelessly connect the 2.

That wasn't what I asked, but thanks for the info anyway 🙂 Interesting to hear about the Express N but my WDS consists of, obviously, a AEBSn and a regular Express G.

ince WDS is an 802.11g feature, using WDS forces the Time Capsule to operate in the slower 802.11g mode

I don't think that's right either.

In the document "Designing Airport Networks" page 42. It states:

"You can connect AirPort Extreme 802.11n Base Stations or Time Capsules and use the
5 GHz frequency band in the network. Only client computers that have 802.11n wireless
cards installed can join the network. If you want client computers using 802.11b or
802.11g wireless cards to join the network, set up the network using the 2.4 GHz
frequency band, or add 802.11g AirPort Extreme or AirPort Express to the network. "

From that, I am assuming that WDS works on both 5GHz and 2.4GHz bands.

Furthermore EACH WDS link cuts your available wireless bandwidth in half.

To be more accurate, your should say each additional HOP (from one cell to another) will cut your bandwidth in half. I would configure the WDS in a star configuration, and make TC (with Internet WAN port) the WDS main. All traffic from the remote cell will only take a max of two hops to reach the TC. Of course, if you are in the same cell as TC, then there is still just 1 hop, and no performance degradation. If you go from one cell to another cell, it will take three hops, that hopefully, that isn't going to happen too often.

In the material you quoted from "Designing AirPort Networks" there is zero reference to WDS so I don't see how you can reach your conclusion.

The problem is not the number of hops. The problem is that EVERY base station in a WDS setup is using the SAME channel. Therefore if ANY base station is communicating wirelessly with ANYTHING no other traffic is allowed on the ENTIRE network.

Under the section "Setting up WDS network", page 42 says: "You can connect AirPort Extreme 802.11n Base Stations or Time Capsules and use the 5 GHz frequency band in the network. "

Doesn't that imply the WDS can operate in 5GHz band?

All Ethernet (wire or wireless) use the same technology, carrier sense multiple access with collision detection (CSMA/CD). Which means, if any base station is talking, no other traffic is allowed on the entire network. This has nothing to do with WDS.

The additional overhead the WDS impose is the number of hops to reach the destination cell. If one Mac in the remote WDS cell, and it has to talk to the TC in the main cell. The Mac must first talk to the remote WDS BS, the remote BS then relay the message to TC in the main cell. So that's two hops. That's means you are taking twice the bandwidth. In the meantime, as you've noted above, nobody in the entire network is allowed to talk.

If the same Mac is talking to another Mac in the main cell, that will make it three hops.

On a WDS network, the number hops for any given Mac to reach TC is important, that's why I've suggested using a star configuration to minimize the number of hops.

michaelawhite wrote:
I have 1 time capsule 1TB and two extreme base stations all running in a 3 station WDS. Seems to work generally...
..My first time machine backup would not complete via wireless and I was forced to connect to time capsule by Ethernet to get time machine to work at all. Is that because the WDS is slow. All stations have good signal to each other.

I'd have to write that WDS might be a bit of a Time Machine killer in terms of performance. I tried it , but abandoned it as an option as data rates were much lower, defeating the point imo of having a home 802.11n network. This is why my TC is set in +extend wireless network mode+ , allowing the AEBS to be 5GHz N mode.

I noticed some lively discussion in the rest of the topic:

My understanding is that WDS cuts the bandwidth in half.

Approx 1/2 per hop, if you think about it WDS works well for say a network where you want to cover a large area with wireless for internet surfin', but isn't so good for networks where data rate acrosss netowrk is criticl, and for TC this is a factor I think.

Since WDS is an 802.11g feature, using WDS forces the Time Capsule to operate in the slower 802.11g mode.

I don't think WDS is just an 802.11 feature, it may have first come along when 802.11g was ats its height, but 802.11N routers can operate WDS, AEBS N being a prime example.

In the material you quoted from "Designing AirPort Networks" there is zero reference to WDS so I don't see how you can reach your conclusion.

It's not ideal document for in-depth info on the AEBSN implementation of WDS.

The problem is not the number of hops. The problem is that EVERY base station in a WDS setup is using the SAME channel. Therefore if ANY base station is communicating wirelessly with ANYTHING no other traffic is allowed on the ENTIRE network.

The exact logic of this statement does not seem applicable to the AEBS as I use it at home.

Under the section "Setting up WDS network", page 42 says: "You can connect AirPort Extreme 802.11n Base Stations or Time Capsules and use the 5 GHz frequency band in the network. " Doesn't that imply the WDS can operate in 5GHz band?

AS near as I can tell in WDS mode you only have option of 802.11N (b/g compatible radio mode).

Doesn't that imply the WDS can operate in 5GHz band?

No. In the 5 GHz band you use 802.11n's new "extend network" feature... although operationally very similar to WDS it is not WDS.

Which means, if any base station is talking, no other traffic is allowed on the entire network.

Not true. In a multiple wireless base station network with an Ethernet backbone the base stations are configured to different channels to reduce/eliminate RF interference. This allows multiple wireless clients to broadcast at the same time to different base stations using different channels. True the data would then be subject to collision detection if it drops out to the Ethernet backbone but the wireless communication is not limited to a single client/single base station at a given time.

No. In the 5 GHz band you use 802.11n's new "extend network" feature... although operationally very similar to WDS it is not WDS.

I use the +extend network+ feature to create a 802.11N 5GHz network (avoiding 2.4GHz interference) with AEBS N and TC, and this gives me better networking speeds across my network than say making it an 802.11b/g compatible network. However, Apple does seem to describe it as a form of WDS. Quoting from the +Extending the range of an 802.11n network+ : "AirPort Utility makes it simple to extend the range of an 802.11n network if you are connecting another 802.11n base station or a Time Capsule. Connecting two 802.11n devices greatly simplifies the WDS setup process...

Not true. In a multiple wireless base station network with an Ethernet backbone the base stations are configured to different channels to reduce/eliminate RF interference.

I thought we were talking about WDS, which all WDS cell operate in the same channel and roaming is possible.

Anyway, I also thought the new "extending a network" mode is built on top of the WDS protocol. IMO, network layer are exactly the same. The difference is only at the application layer. Instead of user setting up main/relay/remote WDS manually, the new mode let the base station broadcast the WDS service via Bonjour, so the MAC address can be linked up automatically. I might be wrong, but I don't think Apple would reinvent the wheel, they are not really a networking company like Lucent/Agere.