Bridge (WDS) with only 1 custom + 1 stock

Discussion in 'Tomato Firmware' started by leesiulung, Oct 31, 2007.

  1. leesiulung

    leesiulung LI Guru Member

    I have a Buffalo WHR-G54S and flashed it with Tomato to use as my main router, but now my needs changed. I need network/internet access for a few devices that only has ethernet far away from the router with internet access.

    So idea is to use my current el-cheap Linksys 802.11b router as is for internet access and Buffalo for bridging. However, I might be wrong but it seems you can only do WDS with two routers having the same Tomato firmware.

    Is there a way around this?

    Help would be much appreciated! :)
  2. RonWessels

    RonWessels Network Guru Member

    There might be a way around this.

    Some Linksys wireless routers enable something called "Lazy WDS". Essentially, this is WDS without the requirement to specify the remote WDS MAC address. It is used to enable usage of the WRE54G (Range Expander / Repeater).

    If you configure your Tomato router to establish a WDS connection with your Linksys, it might actually work. It's certainly worth trying anyway.
  3. HennieM

    HennieM Network Guru Member

    Also, you don't have to have Tomato on all your WDS routers. The WDS protocol is a sort of standard, so any 2 routers that supports WDS should be able to WDS with one another. The only snag is the encryption - not all WDS implementations can support WPA, so you might have to drop security to WEP or none.

    If you try the "Lazy" as suggested by Ron, start off with no encryption. If that works, go to WEP,.... etc.
  4. leesiulung

    leesiulung LI Guru Member

    So it turns out, what I really want is Wireless Ethernet Bridge (WET) mode. Here is my setup:

    Linksys Router (left alone on ip -> Buffalo (tomato set to WET) -> devices (get's internet access i.e. PC, printer etc)

    How do I setup the ip's though for the Buffalo device. Does it needs it own block of ip's or do the DHCP handling happen at the linksys router?

    The linksys router has the following:

    What do I setup my Buffalo (WET mode) to?
  5. digitalgeek

    digitalgeek Network Guru Member

    WET will not allow the Buffalo to act as an access point. Only the linksys unit will accept wireless clients.

    All the setup can be done easily from the Tomato basic setup. The buffalo will become a wireless client of the linksys. The linksys should host DHCP, and internet; requiring you to disable the unused services on the buffalo.
  6. leesiulung

    leesiulung LI Guru Member

    Is that the difference between WET and WDS? The fact that WDS can act as a wireless access point and wireless ethernet bridge (i.e. allow ethernet connections) while WET is just that wireless ethernet bridge without wireless access point functionality.

    Can you confirm?


    PS, I just ordered a WRT54GL yesterday! All excited and can't wait for it to arrive.
  7. digitalgeek

    digitalgeek Network Guru Member

    correct... wds will cost you half your bandwidth, Wet utilizes the entire bandwidth...
  8. leesiulung

    leesiulung LI Guru Member

    So it appears, WDS is slower than WET? I wonder why that is the case?

    So for gaming, would you recommend WET or WDS?

    I do not need the Wireless Access Point functionality since both units are fairly close. With WET I did not need to enter MAC addresses and such, while with WDS I did... Wonder if that has any impact?
  9. RonWessels

    RonWessels Network Guru Member

    With all due respect digitalgeek, you are wrong, or at best misleading.

    What halves the bandwidth is when you have WDS+AP. Because there is only one radio, when a wireless client is communicating, the radio spends half the time receiving packets from the client and half the time forwarding packets over WDS. If you have two routers available for one side of the WDS connection, you could use one for the WDS link and the second for the access point functionality and get full bandwidth, since each radio now only has one task. Similarly if you have a wired client attached to a WDS+AP router, you get full bandwidth, because the radio is only being used to forward over the WDS link.

    WDS is designed as a wireless point-to-point link. WET is simply using the router's radio to emulate a wireless network adapter. [ The difference between WET and Client mode is that WET bridges the radio to the LAN, where client mode treats the radio as the WAN. In other words, under WET, your wired clients are on the same network as the wireless. Under client mode, the router is NAT'ing the connection. ]

    Under OpenWRT, you can apparently set up WET+AP on your radio. This would have the same halving of bandwidth that WDS+AP has, because once again, you have only one radio that must perform two tasks.
  10. HennieM

    HennieM Network Guru Member

    Slight correction Ron - it's not only WDS+AP that halves bandwidth, it's every time where a device needs to re-transmit by wireless (1 radio) what it receives. This is how I understand it:
    To AAA:1     |     1        |        1/2             1/4     |         1/8
                 |              |                                |
               wired        wireless                          wireless
                 |              |                                |
               clientA       clientB                           clientD
    Any client talking to device AAA will do so at the lowest speed indicated.
      e.g.  clientA will talk to AAA at full [wired] speed (over 0 wireless nodes)
            clientB will talk to AAA at 1/2 speed (over 1 repeating-, and 1 non-repeating WDS node)
            clientC will talk to AAA at 1/8 speed (over 3 repeating-, and 1 non-repeating WDS nodes)
    clientA will talk to clientB at 1/2 speed (over 1 repeating-, and 1 non-repeating WDS nodes)
    clientB will talk to clientC at 1/8 speed (over 3 repeating WDS nodes)
    clientD will talk to clientC at 1/2 speed (over 1 repeating non-WDS node [it's the AP that repeats, not WDS])
    Also, it might not be quite true that if a signal has to traverse 2 repeating nodes, that speed would now be 1/2 x 1/2 = 1/4 - the latency may be a bit higher, but the speed may very well be better than 1/4 as the transmit period of the 1st node is also the receive period of the 2nd node. However, as with WDS all nodes share the same channel, only one device can transmit at any particular time.
  11. RonWessels

    RonWessels Network Guru Member

    Oh, I'm _so_ glad you brought that up.

    Firstly, while I was talking about a single wireless router-to-router link, you are correct that every time a radio in the chain of communication must do double-duty, bandwidth is (potentially) lost. However, unless you can produce experimental results to the contrary, I do not believe that each double-duty halves the bandwidth in aggregate. In fact, I believe that in ideal cases, multiple WDS hops can be attained with an overall bandwidth reduction of 1/2 (ie. the same as for 1 link).

    Let's look at your example, and consider a packet stream from clientB to clientC. Assume each packet takes time T to transmit wirelessly.

    At time 0, clientB begins transmitting packet #1 to WDS+AP_1.
    At time T, WDS+AP_1 finishes receiving packet #1 and begins transmitting it to WDS_2.
    At time 2T, WDS_2 finishes receiving packet #1 and begins transmitting it to WDS+AP_2.
    However, since WDS+AP_1 has finished re-transmitting the packet, also at time 2T, clientB can transmit packet #2 to WDS+AP_1, since its radio is available.

    Iterate through the chain and you can see that clientB is obtaining half the wireless bandwidth talking to clientC, transmitting a packet at time 0, 2T, 4T, 6T, ...

    Even if it were the case that clientB cannot transmit the second packet until clientC receives the first one, that is still 1/4 bandwidth, not 1/8 bandwidth. Again, look at the timings.

    At time 0, clientB begins transmitting packet #1 to WDS+AP_1.
    At time T, WDS+AP_1 finishes receiving packet #1 and begins transmitting it to WDS_2.
    At time 2T, WDS_2 finishes receiving packet #1 and begins transmitting it to WDS+AP_2.
    At time 3T, WDS+AP_2 finishes receiving packet #1 and begins transmitting it to clientC.
    At time 4T, clientC finishes receiving packet #1.

    In other words, packet transmissions happen at 0, 4T, 8T, ..., so the effective bandwidth is at worst 1/4 and not 1/8. But why should the clientB<->WDS+AP_1 link care about what is happening on the WDS+AP_2<->clientC link? Presumably clientB can't hear WDS+AP_2, or it would connect there directly.
  12. leesiulung

    leesiulung LI Guru Member

    I understand that half the bandwidth is taken if the router has to do two things at once with one antenna i.e. WDS + AP and also that there is an additional delay as the signal is being retransmitted. However I fali to see the difference between WET and Client Mode.

    My setup is as follows:

    Linksys WRT54GL (recently acquired)
    Buffalo WHR-XXX (some flavor)

    Both are installed with Tomato firmware. The WRT54GL is currently used as my main router connected to the cable modem. The Buffalo router is connected to my gaming systems and computers via CAt5e cable. I want to bridge the Buffalo router to my WRT54GL wirelessly so I can access internet from my gaming system and computer. Since I do not need an additional Access Point. What is the optimum configuration for speed and avoid latency?

    Bandwidth is not a big issue with me, but rather latency affects game play signficantly. Suggestions would be much appreciated. :biggrin:
  13. RonWessels

    RonWessels Network Guru Member

    Oh WELL, if you're going to bring YOUR thread back to your ORIGINAL point ... :)

    Quite frankly, I think the only difference in speed / latency that you might see, if you see anything at all, will only be seen if you run benchmarks and look for that last 1%.

    Personally, I'd probably configure your Buffalo in WET mode, only because it means that, if anything happens to either router, you just have to replace the failed unit without having to reconfigure the other unit.
  14. HennieM

    HennieM Network Guru Member

    @RonWessels: You may very well be correct (and I really hope you are). As I mentioned
    Also, I know very little about OFDM, CSMA/CD and all the cool protocols, so I assume that only one device on an entire WDS system can Tx at a time, which may also be wrong.
    One day I think I'll set up such an experiment....

    A nice WET/Client/etc. discussion here: . Tomato just has "WET" and "Wireless Client", while other firmwares also mention "Client bridge". In my mind WET and Client Bridge modes are the same thing as it's all one transparent subnet, while Wireless Client mode allows different subnets, and therefore routing.
    You don't want to fiddle with routing, so WET is the answer as suggested by Ron.
  15. leesiulung

    leesiulung LI Guru Member

    Guys, thanks for answering my questions.

    A few more though.... :biggrin:

    1. In WET mode, who dishes out the ip (DHCP)?

    2. Does the Linksys configured as a router see the attached devices to the Buffalo as a wireless client? As opposed to overwriting the MAC address like HennieM suggested.

    Basically this question is really, how does the Linksys router see all the clients connected to the Buffalo via Cat5e?

    3. In relation to the above question are there any difference here between WDS or WET?

    I'm just interrested as there is no real difference. I will probably stick to WET with probably lower power requirements since it doesn't have to act as a AP and only wirelessly transmits when something is connected to the Buffalo.
  16. RonWessels

    RonWessels Network Guru Member

    1) DHCP is handled by whoever handles DHCP for the wireless network (probably the Linksys). In other words, make sure the DHCP server is off on your Buffalo.

    (2) & (3) I'm not completely certain, but I suspect, in your particular application, the effective difference between WET and WDS will be what MAC addresses are reported to the Linksys. Particularly if there is only one wired device attached to the Buffalo. Try it and see what happens.

    By the way, you can configure your Buffalo to WDS only. WDS and WDS+AP are two separate settings.
  17. leesiulung

    leesiulung LI Guru Member


    I thought WDS automatically had AP...

    Then I'm confused why one would need WDS+AP? Does the AP dish out IP's too?
  18. HennieM

    HennieM Network Guru Member

    WDS, AP, WDS+AP, WET, Client, etc. are just different modes of operating the wireless interface on a wireless router or access point, but have nothing to do with DHCP or "dishing out IPs". DHCP (Dynamic Host Configuration Protocol) is a daemon or service that runs on some machine - if you run a DHCP server somewhere on your subnet/network, that DHCP server is dishing out the IPs - not only to wireless clients, but also to wired clients - i.e. to any client that is configured to obtain IP address/network parameters via DHCP or BOOTP.

    Thus, you can run a DHCP server on the Buffalo, or on the WRT, or on some other machine that's always connected to your network. You just have to make sure that (i) the DHCP server dishes out the right IPs, subnet mask, gateway address, etc., and (ii) that only ONE DHCP server is running on your net. If you run 2 DHCP servers on your net, you may get conflicting IP addresses, etc.

    The easiest is usually to have the device that connects your network to the internet run the DHCP server.

    WDS is for linking 2 (or more) WDS devices together, but cannot link to wireless clients. AP is for linking to wireless clients. WDS+AP is for linking WDS devices AND wireless clients together.
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