Need Commercial AP's, Allied Telesys AT-WA7400 ???

Discussion in 'Wireless Internet' started by ToddAndMargo, Feb 11, 2008.

  1. ToddAndMargo

    ToddAndMargo Guest

    Hi All,

    I have a customer with d-link AP's in four separate
    co-located buildings (hotel rooms). The Building are
    all linked (wired) with Ethernet.

    The d-link AP's are not working so well. So, I was
    going to suggest he replace them with commercial AP's.
    Maybe even double the AP coverage in each building too.
    (And, you have to have commercial AP's for that.)

    Does anyone have any feed back on the Allied Telesys AT-WA7400?

    http://www.alliedtelesis.com/products/detail.aspx?pid=172&lid=52

    Anyone have any feedback on them? Any other units you like better?

    Many thanks,
    -T
     
    ToddAndMargo, Feb 11, 2008
    #1
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  2. ToddAndMargo

    John Navas Guest

    Why not? What's the problem?
    Best to know the problem before trying to fix it. That might be a waste
    of money, labor and time.
    Cisco Aironet.
     
    John Navas, Feb 11, 2008
    #2
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  3. ToddAndMargo

    ToddAndMargo Guest

    my guess it that most of the coverage is on a fringe
    and they have problems with too many users at one time
    for their poor $50.00 price tag

    Too much distance, too many users, too many metal objects
    in the way
    Customer is tired of powering off his AP's all the time
    to unjam them (about every 6 days). Are the Aironet's
    pretty much jam free?

    -T
     
    ToddAndMargo, Feb 11, 2008
    #3
  4. ToddAndMargo

    John Navas Guest

    Better not to guess -- better to do a site survey.
    Users shouldn't be an issue unless they are opening up too many
    connections (think peer-to-peer filesharing).
    Again, better to do a site survey than to guess.
    About as good as access points get.
     
    John Navas, Feb 11, 2008
    #4
  5. One AP per hotel building is not enough. You'll probably need at
    least one AP per floor (depending on type of construction).
    I'm suprised they work at all. How many walls are you going through
    between the AP and the guest's laptop? If it's more than one, you're
    going to have problems no matter what hardware you select.
    Good idea, especially since this is a commerical operation.
    Baloney. I can put a generic junk access point (or wireless router
    acting as an access point), next to the most exotic commercial access
    point I can find (Sonicwall), and as long as the TX power and antennas
    are the same, the range will be very close. In fact, I've done
    exactly that to justify using cheapo hardware to customer that
    insisted on blowing his budget on acronyms and buzzwords. You may get
    a few more feet of range or penetration using commercial quality
    hardware, but no way are you going to get double.
    No experience with this unit. Looking at the specs, it looks like a
    dual radio 802.11a and 802.11g access point, with impressive
    management and monitoring features. Lots of flexibility and control.
    However, nothing in the specs that I can see claims any better range
    or penetration. Such a box will certainly make it easier to manage
    and troubleshoot, but that's not what you're looking for.

    I don't like to make specific recommendations on hardware unless I
    know how it's going to be used, the network topology, expected
    traffic, number of users, building layout, available expertise, and of
    course the size of the budget.

    For other vendors, look at: Cisco, 3com, Proxim and Sonicwall. Also
    look at "wireless switch" offerings. See:
    <http://groups.google.com/group/alt.internet.wireless/msg/a448ba5fda43d5e5>

    Also, please read the Intel Wireless Hotspot Guide that has
    disappeared from Intel's web pile and that I've illegally archived
    (don't tell Intel) at:
    <http://802.11junk.com/jeffl/crud/Intel HotSpot Guide.pdf>
    There's a huge amount of good info in there on setting up a WLAN.
     
    Jeff Liebermann, Feb 11, 2008
    #5
  6. ToddAndMargo

    ToddAndMargo Guest

    Thank you for all the answers!

    I am going to walk the premises next Tuesday.
    Go over their blue prints too.

    Question: do you know of a piece of test equipment
    I can use to test signal strength of the current
    d-link's in the problem areas that the customer
    has tagged for me? (I guess I could make
    a crude measurement with a laptop.)

    Hmmmm. I wonder if all the d-links in the
    various (four) buildings are using the same
    channels.

    The customer may also just need to put UPS'es
    on all his AP's: sometimes it is just that easy.

    -T
     
    ToddAndMargo, Feb 11, 2008
    #6
  7. No. I have scripts that will crash literally anything. If it doesn't
    crash the AP, it will do the same to the router. For example,
    starting a file sharing program with hundreds of IP ports (streams)
    active, that will run the AP and router out of buffer space. Many of
    the WEP cracking tools are also inadvertant AP crashers. If your
    system doesn't have any QoS or Bandwidth Management, and you have an
    asymmetrical DSL or cable connection, then any user that is uploading
    heavily, will saturate the upstream bandwidth. That will cause the
    ACK's from downloads to get lost, making downloading slow or
    impossible. (Hint: You need Qos).

    Incidentally, I have some of my wireless router set to reboot nightly
    to avoid such problems. It seems to work and I haven't had any
    complaints since I started doing that. Perhaps a $10 digital lamp
    timer might be a better fix?
     
    Jeff Liebermann, Feb 11, 2008
    #7
  8. Jeff Liebermann, Feb 11, 2008
    #8
  9. ToddAndMargo

    John Navas Guest

    You're welcome.
    Good ideas. See
    <http://wireless.wikia.com/wiki/Wi-Fi#Site_Survey_Tools>

    I find that Network Stumbler on a laptop does a pretty good job.
    Very good question. Get the real answer with a site survey.
    Along with the rest of the network gear.
     
    John Navas, Feb 12, 2008
    #9
  10. ToddAndMargo

    ToddAndMargo Guest

    I am going to do the walk and blue print next Tuesday.
    I know there are four buildings (~200 rooms) and that
    a couple of them are multistory. I am not sure
    if it is a wood or steel (struts, etc.) either.
    The AT-WA7400 is only $300.00. I did not think it would blow the
    bank.

    I was looking for something that did not get a lot of complaints
    from the users and did not jam all the time. Basically, I
    was looking at spending a few more dollars to more reliability.
    Thank you!

    I am in process of reading it. It is a bit vague in spots.
    But, I don't think it was meant for a radio design engineer
    like myself. More of a non-techie user. Their convention
    hall example applies the closest, but they are not tell me
    things like max users per AP, signal strength to avoid
    swamping other AP's, etc., etc.. I guess it is time to
    start reading the AP's spec's.
     
    ToddAndMargo, Feb 12, 2008
    #10
  11. ToddAndMargo

    John Navas Guest

    [cough cough] I doubt that you can crash a Cisco Aironet access point
    with a script, and if the router is a serious Cisco as well, then you're
    going to have your work cut out for you there too.
     
    John Navas, Feb 12, 2008
    #11
  12. ToddAndMargo

    John Navas Guest

    The complaints tend to be associated with low-end routers that go into
    never never land for no good reason (e.g., too many filesharing
    connections. The best solution IMHO is to use access points, not
    routers, and back them up with a serious commercial (e.g., Cisco) wired
    router.
     
    John Navas, Feb 12, 2008
    #12
  13. Well, maybe you're right. I've never tried it with a Cisco AP. I
    probably should have said "...will crash most low end access points
    and wireless routers". Also, it's more than just scripts, but I don't
    wanna leak any details.

    However, I've got an AIR-AP1231G-A-K9 on order for a customer which I
    might try next week, time permitting. About $250 refurbished. I've
    also read rumors of various high end outdoor mesh and non-mesh access
    points getting crashed by probes, scans, ARP floods, MAC generators,
    and exploits. Some routers and AP's have watchdog timers, which helps
    recover from such attacks.
     
    Jeff Liebermann, Feb 12, 2008
    #13
  14. ToddAndMargo

    John Navas Guest

    Including SonicWALL, one of the reasons I use and recommend them.
     
    John Navas, Feb 12, 2008
    #14
  15. Look for aluminum foil backed insulation in the walls and ceilings.
    That blocks wireless (and cellular) traffic almost completely.

    One of the tricks I use is to "illuminate" the outside wall of a hotel
    or motel from a nearby building or pole. Penetration through the
    glass windows are MUCH better than through inside walls. This
    requires directional antennas with a very controlled pattern. Look
    into sector antennas or if you wanna build your own, AMOS or Franklin
    antennas. For example:
    <http://www.qsl.net/yu1aw/vhf_ant.htm>
    Good price for such a unit. I just bought a used Cisco
    AIR-AP1231G-A-K9 for about $250 (used) with the PoE adapters. I know
    that it's not fair comparing new and used prices, but I tend to buy
    what little Cisco I use on the used (refurbished) market. There are 4
    more used 1231 AP's on eBay for about the same price. Plan on having
    a spare handy. I also suspect that you'll need more than 4 radios to
    cover 200 rooms in multiple buildings and floors.
    Once you get away from commodity hardware (Linksys, Dlink, Belkin,
    Netgear), the overall quality and reliability improves. However,
    since the (used) price of an access point is about equal to the cost
    of a service call, methinks you'll do better to get something that can
    be remotely managed (and remotely rebooted). Also, my coffee shop
    routers increased dramatically in reliability since I started
    rebooting them nightly. Same with running some of them off gel cell
    batteries and chargers to isolate them from flaky AC power.
    It's also a bit old. It doesn't cover much of today's high fashion
    wireless technology, such as MIMO, roaming, QoS, and MultiMedia.
    However, it covers the basics, such as wall penetration, channel
    layout, and system sizing.
    If you want technical, I can bury you in heavy reading. The IEEE
    Communications Society (ComSoc) procedings are great, but very very
    very dense. Are you sure you want it more technical?
    Max users per AP is limited by the MAC address (bridging) table. Most
    small routers can barely handle a few users. See chart at:
    <http://www.smallnetbuilder.com/component/option,com_chart/Itemid,189/chart,124/>
    Some of the bottom of the line models are so bad, that they crash when
    they fill up the MAC address table (because they don't expire
    entries). The ARP table (MAC address to IP address) table also tends
    to fill and crash when full. Never mind running out of DHCP IP
    leases. Buffers is also a problem. Each user will open some number
    of IP sockets. Each socket requires a buffer. If the AP has too many
    users, or too many open sockets, it will run out of buffer space. How
    it handles running out of buffer RAM varies by implementation. Small
    AP's and routers are made for, ummm... small number of users.

    With better AP's and wireless routers, you get considerable relief
    with lots more working RAM and faster processors. The table and
    buffer problems may still be there, but the larger memory size means
    that you see them less frequently. You'll probably find the
    connection limit in the specs. As I vaguely recall, the Cisco 1241
    will do 2000 connections. Many university systems regularly handle
    well over 100 connections per AP, although many of these connections
    are idle and not moving traffic.

    Incidentally, you might find:
    <http://its.ucsc.edu/service_catalog/network_wireless/cruznet/maps/>
    of interest. That's the local university wireless network. If you
    click on a building it will show the wireless coverage in the
    building. It does NOT show the location of the wireless access
    points, or their number, but it will give you a very rough idea of how
    much area a single access point is expected to cover. There are about
    230 access points around the entire campus.
     
    Jeff Liebermann, Feb 12, 2008
    #15
  16. The 2nd thing to go is the memory. I forgot what was first.

    See:
    <http://www.cisco.com/warp/public/102/wlan/ap-faq.html>
    Q. How many clients can associate to the AP?
    A. The AP has the physical capacity to handle 2048 MAC addresses.
    However, because the AP is a shared medium and acts as a wireless
    hub, the performance of each user decreases as the number of users
    increases on an individual AP. Ideally, not more than 24 clients
    should associate with the AP because the throughput of the AP is
    reduced with each client that associates to the AP.
     
    Jeff Liebermann, Feb 12, 2008
    #16
  17. ToddAndMargo

    ToddAndMargo Guest

    Cool! Thank you!

    I can not wait to get to the customer's site and see
    what is actually going on!

    -T
     
    ToddAndMargo, Feb 12, 2008
    #17
  18. ToddAndMargo

    msg Guest

    Jeff Liebermann wrote:

    So overall do you think it is more cost-effective to use low-end APs
    with external watchdog hardware? This has been my solution so far
    (snmp controlled power supply).

    Michael
     
    msg, Feb 12, 2008
    #18
  19. ToddAndMargo

    msg Guest

    Jeff Liebermann wrote:

    Seems to cover routers.
    How many entries do you suppose are involved in that case?
    Most of these products have more RAM than high-end unix boxes of ten years
    prior, which could easily manage hundreds of arp entries, and why would an
    AP need an arp table for the wireless interface (see below)?
    On an access point?
    What sockets are opened for users on access points?

    <snip>

    I just need to understand what functionality is involved here; shouldn't
    an AP just do layer 2 bridging? With a smidgen of instrumentation that
    might require IP? This presumes that all security is handled offboard
    and the AP only bridges.

    Depending on your answers, I would ask why more folks don't build their
    own APs on standard hardware. I have always assumed that reliable but
    low-cost APs are sufficient for the basic bridging functions expected
    of an AP and should be able to service as many connections as the PHY
    and data paths permit.

    Regards,

    Michael
     
    msg, Feb 12, 2008
    #19
  20. ToddAndMargo

    John Navas Guest

    Layer 2 bridging uses a database to keep track of MAC addresses.
    See <http://en.wikipedia.org/wiki/Network_bridge>. To quote Jeff:
    "Max users per AP is limited by the MAC address (bridging) table."
    He then segued into talking about routers. Ignore that for bridging.
     
    John Navas, Feb 12, 2008
    #20
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