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Address Reservation

Discussion in 'Cisco/Linksys Wireless Routers' started by MadDog-2000, Nov 14, 2004.

  1. MadDog-2000

    MadDog-2000 Network Guru Member

    Hello everyone,

    I just bought the WRT54GS because my Netgear WGR614 failed a few days ago. I immediately flashed the WRT54GS with Alchemy 6.0 and it works just fine. My old Netgear had something called Address Reservation, where the DHCP statically assigns or reserves an IP for a specific PC, using its MAC adress, that is on a list. Where can I find that feature in the WRT54GS (no, I don't just wanna setup static IPs)?

    Also, under Port Forwarding there are only 13 rules I can create but I need to make more, is there a way to increase the number of rules I can make?

    Finally, I would like attach a waveguide antenna (can antenna) to one of the RP-TNC connectors and point it to my neighbours house, who is also planning on buying a WRT54GS, so we can enable WDS. Anyway, can I attach the directional antenna on one connector (for both send and receive) and have the regular antenna (for both send and receive) on the other connector for close range connectivity?

  2. dscline

    dscline Network Guru Member

    Everything I've read suggests that diversity tuning allows both antennas to be used for reception, but only one antenna sends. If true, you couldn't use it in this manner.
  3. Toxic

    Toxic Administrator Staff Member

    best bet is to ask in sveasoft forums as Alchemy is not yet supported here.

    Static DHCP is in Management.
  4. MadDog-2000

    MadDog-2000 Network Guru Member

    Thanks, I found it. The Alchemy firmware is great but it is not very well organzied and structured. Sveasoft could probably prevent a lot of confusion by doing a better job on the menu structure and feature description. I used to have a Netgear router and the web menu in those is so much better. Even WiFi-Box's firmware is in many cases easier to find and understand.

    This makes more sense then hiding the Static DHCP fuction in the Management section and then calling it DHCPd.

    If they made a firmware with a better layout, that looks like Netgear's, plus all the advanced features, it would be perfect.
  5. MadDog-2000

    MadDog-2000 Network Guru Member

    I did some more research and it seems highly unlikely that one antenna is for both sending and receiving, while the other is for receiving only! First of all, each wireless router/radio is a transceiver, which means it transfers and receives signals. If one antenna could only receive that would mean that it is internally connected to a receiver chip only and the other antenna is hooked up to a transceiver chip. This is totally illogical and would imply that Linksys soldered a transceiver and a receiver chip on the same board, which would raise manufacturing costs.

    Another proof that both antennas can send and receive is that they are internally hooked up to the same curcuit, which ultimately connects to a single transceiver chip. Here is a picture that shows that both antennas are hooked together and can both send and receive.


    Finally, if you look at WiFi Box’s firmware, which has a better description, you can see that by default both antennas are set to diversity, which implies both antennas must be able to do both.

  6. AbNormal

    AbNormal Network Guru Member

    In theory, the answer is "not very well", but some have reported a degree of success.

    A signal transmitted at 2.4GHz can take several paths towards the receiving end: the direct (shortest) path, plus a number of reflected signals that bounce off metal, such as heating ducts, and appliances. Depending on what lies in between the transmitter and receiver, the direct path may not have the best line of sight, and therefore the reflected paths (at that precise moment) may result in the better signal. This is why the WRT54 has two antennas, with a diversity switch. The receiver can switch over to the antenna that is receiving the best signal. So in reality, only one antenna is used, but both are used to determine which was best.

    Once the the diversity function determines the best antenna for the moment, then it will re-use this same antenna to transmit on, if "diversity" is selected for the transmit antenna. There is no such thing as "transmit diversity" as this is really only a receiver function. The transmitter only ever transmits on a single antenna, but the transmitter will follow the receiver's antenna preference, in the case.

    Remember also that the WRT only has a single transceiver. This means that it first receives data, then retransmits it, if repeating to another wireless client. In this specific scenario, the router would have no way of knowing whether the intended client was in the local vicinity (standard antenna), or outdoors off the directional high gain antenna. This is where you may run into problems.

    It may work when clients are only talking back to the access point, in order to reach either the wired LAN, or internet. But for wireless client to wireless client, when each is "off" a different antenna, I doubt how reliable it might be.

    YMMV, of course!

  7. dscline

    dscline Network Guru Member

    No, my understanding is that there is only a single radio, but the diversity circuit always switches to the same antenna during sends. I don't know that that's correct, but I researched the issue (because I have a similar need), and that's the conclusion I've come to based on what I've read. Here are a couple of examples, though I can't vouch for their accuracy:



    There was another page I remember finding that was more of a "professional" review, that didn't specifically say how the WRT54G operated, but basically said something to the effect of "all the routers we've seen select from both antennas for receive, but use only one for transmit", or something like that.

    However, here is a page that supports AbNormal's post stating that the transmit follows the receive antenna:


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