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Wireless Networking General FAQ

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February 8, 2006 5:19:30 PM

Wireless Networking General FAQ
Questions
  • What's the difference between Short and Long Preamble?
  • Can two Access Points communicate with each other?
  • Does 'enhanced' 802.11b really run at 22Mbps?
  • Can most USB Wireless Client Adapters be used with Apple computers out of the box?
  • Can I swap the radio card in my wireless router?
  • What are the performance tradeoffs between integrated PCI cards, USB adapters, and PC card/adapter combinations?
  • Are there any 802.11b PCMCIA cards that can accept an external antenna?
  • Are there any multiport wireless routers that have both WAN dialup support and removable antenna(s)?
  • What is SSID Broadcast?
  • What is antenna diversity?
  • Why do most wireless routers have two antennas while most wireless access points only have one?
  • What is WDS?
  • Can all 802.11b products perform Ad Hoc networking?
  • Are there wireless routers that support dialup WAN connection?
  • I want to set up an 802.11a-only WLAN, but should I buy 11a-only products?
  • I want to set up a wireless network for my neighborhood. Can you tell me what to buy and how to do it?
  • What does the Basic Rate setting in an access point or wireless router do and how does it differ from the Transmit Rate setting?
  • Can I add a wireless LAN card to my Ethernet-connected computer and have it act like an access point for other wireless computers?
  • When connecting a gaming console to the Internet via a wireless connection is an 802.11g adapter better than an 802.11b?
  • Will wireless keyboards interfere with my wireless network?
  • Should I buy 802.11a - only products?
  • What is the maximum number of wireless clients that can be networked using Ad Hoc mode, i.e. w/o access point?
  • Will a wireless LAN card work worldwide?
  • Where can I find construction details and test data for wireless LAN products?
  • Is there a tool that will give you a better indication of wireless signal strength than the meter built into WinXP or many wireless clients?
  • Can I connect wireless LAN adapters running in Ad Hoc mode to a wired LAN?
  • How can I prevent a wireless laptop from losing connection when moving between multiple Access Points?
  • Can I connect multiple signal boosters (like Hawking's HSB1) and a high-gain antenna together to get an even stronger signal?
  • Can wireless products sold in the United States be used in other countries?
  • How are 'gaming' wireless bridges different from non-gaming products?
  • My WLAN has multiple access points. Is there a way I can get my wireless notebook to automatically connect to the AP with the strongest signal?
  • Will 802.11b/g products purchased in one country work in another?
  • What will affect a wireless network signal around an average home?
  • Is there a wireless router or AP that can keep users isolated from each other?
  • Do wireless network cards need to support WMM (802.11e) or is it only a function of a wireless access point?

    Answers
  • What's the difference between Short and Long Preamble?
    The preamble is part of the IEEE 802.11b physical layer specification, and specifically, part of the Physical Layer Convergence Protocol (PLCP). All 802.11b devices must support the long preamble format, but may optionally support the short preamble.
    If your device supports the short preamble and you are having trouble getting it to communicate with other 802.11b devices, make sure that it is set to use the long preamble.

  • Can two Access Points communicate with each other?
    Maybe. Older Access Points only had one mode and could communicate only with wireless clients. However, newer Access Points sometimes include "bridging" modes, which can be used for Access Point to Access Point communication. See http://www.tomsnetworking.com/Sections-article15-page2.php this part of the TomsNetworking Wireless Need-To-Know for more info.

  • Does 'enhanced' 802.11b really run at 22Mbps?
    Nope. The http://www.tomsnetworking.com/Sections-article13-page2.php First TomsNetworking Rule of Wireless Networking holds for these latest wireless networking products too. Our testing has shown that you can get a speed boost to about 6.5 - 7Mbps (vs. a typical 4Mbps normal 802.11b best-case speed). But you get the boost only under strong-signal conditions, and your speed will degrade more than it does with normal 802.11b as your signal level decreases.
    For more info, see http://www.tomsnetworking.com/Reviews-7-ProdID-DWL900APplus.php theTomsNetworking review of D-Link's DWL-900AP+ enhanced Access Point.

  • Can most USB Wireless Client Adapters be used with Apple computers out of the box?
    No. Most of the available wireless adapters work with Windows-based machines only.

  • Can I swap the radio card in my wireless router?
    If your wireless router is a "wireless ready" model that allows you to insert a CardBus or mini-PCI card radio, in most cases you'll be limited to whichever card the manufacturer recommends. This is because the radio card's driver software is part of the router's firmware, and different cards require different drivers.
    Most of the "wireless-ready" products use 802.11b cards, and it will be interesting to see if router firmware upgrades will be available to allow the use of 802.11a/b or a/b/g dual-band cards.

  • What are the performance tradeoffs between integrated PCI cards, USB adapters, and PC card/adapter combinations?
    See http://www.tomsnetworking.com/Sections-article15-page1.php this part of TomsNetworking's Wireless NTK.

  • Are there any wireless cards that can accept an external antenna?
    Not many manufacturers provide this feature, mainly because it complicates their certification process. But there are a few products to be found:
    - Buffalo Technology's http://buffalotech.com/products/product-detail.php?productid=110&categoryid=7 WLI-CB-G54HP High Power Wireless Notebook Adapter
    - SMC's http://www.smc.com/index.cfm?event=viewProduct&localeCode=EN_USA&pid=346 SMC2532W-B EliteConnect 2.4GHz 802.11b High Power Wireless PC Card

  • What is SSID Broadcast?
    This is a function performed by an Access Point that transmits its name so that wireless stations searching for a network connection can 'discover' it. It's what allows your wireless adapter's client manager program or Windows XP's built-in wireless software to give you a list of the in-range Access Points.
    The ability to disable SSID broadcast essentially makes your Access Point invisible unless a wireless client already knows the SSID, or is using tools that monitor or 'sniff' traffic from an AP's associated clients.

  • What is antenna diversity?
    Antenna diversity is a function included in most wireless LAN equipment that has two antennas.In simple terms, diversity monitors the signal from each antenna and automatically switches to the one with the better signal. The user usually has no control over this function.There are also other forms of diversity, which are described http://www.antennasonline.com/ast_newsletter2_9-04.htm here.

  • Why do most wireless routers have two antennas while most wireless access points only have one?
    No, this isn't some plot to get higher sales for wireless routers at the expense of Access Points. The number of antennas is purely a design choice by the product's manufacturer. Note that sometimes there is a second, fixed position antenna located inside the access point.

  • What is WDS?
    WDS stands for Wireless Distribution System. It is a special Access Point mode that enables single-radio APs to be wirelessly connected vs. relying on connection to an Ethernet network. WDS encompasses both wireless bridging in which WDS APs communicate only with each other and don't allow wireless clients or Stations to access them, and wireless repeating in which APs communicate with each other and with wireless Stations.
    The downside of the repeating mode is that wireless throughput is cut in half for each AP that data flows through before hitting the wired network.

  • Can all 802.11 products perform Ad Hoc networking?
    Yes. Ad Hoc mode, in which 802.11b clients communicate directly with each other instead of through an Access Point, is available on all 802.11b client products.

  • Are there wireless routers that support dialup WAN connection?
    Routers that support dialup connections are getting tougher to find and wireless versions even tougher. But the http://www.alwaysonwireless.com/ WiFlyer is an 802.11b router with both a built-in dialup modem and Ethernet WAN interface.

  • I want to set up an 802.11a-only WLAN, but should I buy 11a-only products?
    Dual-band products are probably a better choice, since they're less expensive than 11a-only products and more readily available. Just disable the 11b/g radio when you set up the AP or router. Do the same on the client cards, if the manufacturer's client application allows it.

  • I want to set up a wireless network for my neighborhood. Can you tell me what to buy and how to do it?
    There are a number of websites that can help your quest to become a Wireless ISP (WISP).For commercial, i.e. pricey, solutions, try http://www.wipop.com/ WiPOP.com. It's mainly a marketing-oriented companion site to WISP equipment provider YDI.com, but it has useful info and pre-packaged solutions if you're in a hurry and have plenty of money to spend.
    If you're looking for a lower-budget solution, you should check out the various "Community Wireless" sites. http://www.nycwireless.net/ NYCwireless has one of the better organized sites and includes a http://www.nycwireless.net/buildnode_start.html "Getting Started with Free Wireless Networks" article.

  • What does the Basic Rate setting in an access point or wireless router do and how does it differ from the Transmit Rate setting?
    The Basic Rate set is the rates that all clients that want to associate with a given access point must support. For 802.11b WLANs, these will be 1, 2, 5.5 and 11Mbps. This information is transmitted by an access point as mandatory rates in the Supported Rates element of various management frames.All current-generation 802.11b products support the 1,2,5.5 and 11Mbps basic rate set. However some very old 802.11b clients may only be able to associate with APs advertising a 1, 2Mbps basic rate set. This is why some APs allow you to change this setting.The Transmit Rate setting is used to set the fastest rate that an AP or wireless router will send data. It can be used to force a lower rate in order to trade off speed for more reliable connection in WLANs where many clients are operating at low signal levels.
    We recommend Matthew Gast's http://www.oreilly.com/catalog/802dot112/ 802.11Wireless Networks: The Definitive Guide book as a great resource for looking up the definitions of wireless networking terms.

  • Can I add a wireless LAN card to my Ethernet-connected computer and have it act like an access point for other wireless computers?
    Yes! It won't act exactly like an access point, but will work essentially the same. See this http://www.tomsnetworking.com/Sections-article53.php TomsNetworking article .

  • When connecting a gaming console to the Internet via a wireless connection is an 802.11g adapter better than an 802.11b?
    Most broadband connections run about 1-2Mbps best case, and best case throughput runs between 4 - 6Mbps and 18 - 20Mbps for 802.11b and 11g products respectively. Typical best-case response (ping) times for either standard run below 5ms. So if you have a strong wireless connection, either product won't stand in your way of being quick on the trigger in on-line frag-fests.The main argument in favor of 11g would be for longer-range / weaker signal connections. 11b products will drop down to about 1-2Mbps?still fast enough for a broadband connection?but the response time tends to degrade to the tens of milliseconds. Even worse, though is that the connection gets very "bursty" as the adapter constantly switches between different transmit rates to try to lower its error rate. Since 11g products also use the 2.4GHz band, their signals will degrade at about the same rate as 11b products'. But since 11g throughput starts out higher, with well-designed products, you should see higher throughput at equivalent range. The more important factor, however, is response time, which from our experience tends to stay down below 5ms even under weaker signal conditions.
    So bottom line: Strong signal?shouldn't matter; Weak signal?11g has the edge.

  • Will wireless keyboards interfere with my wireless network?
    Generally no. Wireless keyboards and mice using infra-red technology certainly won't, and most others use frequencies in the 900MHz range. The possible exception are Bluetooth keyboards and mice, which might interfere, but probably to an extent that you wouldn't notice.

  • Should I buy 802.11a - only products?
    In general, no. Most 802.11a products you'll find are based on first-generation chipsets from Atheros. These products had range problems that gave 802.11a "poor range" reputation that persists even today.We recommend purchasing only dual-band products if you want to use 802.11a. These products are generally based on current-generation Atheros chipsets which have essentially the same or better range than competing 802.11b or 11g products.

  • What is the maximum number of wireless clients that can be networked using Ad Hoc mode, i.e. w/o access point?
    The theoretical limit, which is the same as in Ethernet, is determined by the 48 bit MAC address field in each wireless data frame.The practical limit is determined by constraints that may be built into client drivers. As a rule of thumb, Ad Hoc networks with 16 to 32 stations should be possible.

  • Will a wireless LAN card work worldwide?
    As long as it is an 802.11b or 11g card, it should work fine using channels 1-11. Using an 802.11a card is a little more difficult, since different frequency bands are supported in different countries.

  • Where can I find construction details and test data for wireless LAN products?
    Wireless LAN products sold in the U.S. must be certified by the Federal Communications Commission (FCC). The certification process requires that the manufacturer submit detailed information about a product including external and internal construction detail photos and test reports.The https://gullfoss2.fcc.gov/prod/oet/cf/eas/reports/GenericSearch.cfm FCC website has search tools that can find a product by its FCC ID (usually found on the serial number label of the product) and also find manufacturers' three-character 'Grantee Code' that is helpful for general product searches.

  • Is there a tool that will give you a better indication of wireless signal strength than the meter built into WinXP or many wireless clients?
    If you're running a Windows machine, then Marius Milner's http://www.stumbler.net/ NetStumbler is probably your best bet. The latest version runs on only WinXP and 2000 but supports many more wireless cards than before. There's also a "ministumbler" version for PocketPC. It's free, but you'll probably find it so useful that you should consider making a http://www.stumbler.net/donate donation to support Marius' work.

  • Can I connect wireless LAN adapters running in Ad Hoc mode to a wired LAN?
    Generally no. WLAN clients running in Ad Hoc mode communicate with each other and not with Access Points or wireless routers.However, there is a trick you can use if one of your LAN's computers is running WinXP or other operating system that allows bridging network adapters. See http://www.tomsnetworking.com/Sections-article53-page1.php this TomsNetworking How To for more info.

  • How can I prevent a wireless laptop from losing connection when moving between multiple Access Points?
    The concept of "roaming", i.e. moving among access points, was not high on the priority list for the framers of the 802.11 series of specifications. As a result, roaming performance varies widely from product to product and for SOHO-grade equipment tends toward the terrible.Roaming logic is built into wireless client software (and sometimes firmware) and tends to be set so that clients hang on to the signal they have until the AP signal pretty much completely disappears. We've occasionally seen a wireless client that has allows a selection of optimizing for range or speed, but the control is usually buried deep in the network properties."Enterprise" grade products, especially entire WLAN management / security systems tend to have faster roaming switchover times, but much higher prices.

  • Can I connect multiple signal boosters (like Hawking's HSB1) and a high-gain antenna together to get an even stronger signal?
    It all depends on how strong a signal your current equipment has. To stay within FCC requirements, signal boosters limit their output power to 30dBm or 1W (or in the HSB1's case, 20dBM or 0.5W). If one booster amplifies your signal up to its limit, adding another won't help and could hurt by distorting the signal and raising the error rate. Depending on the signal booster design, you could also damage the second booster by overloading its input. Adding a higher-gain antenna, on the other hand, will increase gain, no matter what the power level, since its gain doesn't use active (powered) amplification and doesn't have power output limiting.

  • Can wireless products sold in the United States be used in other countries?
    In general, these products will work as long as you can supply the proper AC power requirements, as long as you have a "matched set" of components, i.e. AP or wireless router and client adapters. Intermixing U.S. and locally-sourced products, can be a little trickier, however.802.11b and 11g products, which operate in the 2.4GHz frequency band can be used without technical or legal problems. However, channel selection limitations must be observed.The situation is more complicated for 802.11a products, which operate in three 5GHz frequency bands. The issue, again, is mixing U.S. and locally-sourced products, which might not interoperate due to channel selection limitations.http://www.vnunet.com/features/1143145 This article provides some good insight into the issues.

  • How are 'gaming' wireless bridges different from non-gaming products?
    Some "gaming" wireless bridges have auto-setup features that allow them to connect to unsecured WLANs without having to run a computer-based setup utility. But if you are running a WEP or WPA-secured wireless LAN (as you should be), you'll need to fire up either a utility or log into a web-based admin server in the device to properly set it up. As long as your gaming device has an Ethernet port, you should be able to use any wireless bridge product with it.

  • My WLAN has multiple access points. Is there a way I can get my wireless notebook to automatically connect to the AP with the strongest signal?
    Multiple AP WLANs usually assign the same SSID to all APs, so if you're using WinXP's built-in wireless utility, you will see only one "network".The client utilities that come with wireless adapters might allow you to see multiple APs with the same SSID, but since you select a network by SSID and not MAC address of the AP, you won't be able to select a specific AP.The only reliable way to allow selection of specific APs is to assign each one a unique SSID. Note that this might force you to have to manually re-connect when you move out of an AP's range.

  • Will 802.11b/g products purchased in one country work in another?
    Maybe. Since most manufacturers don't like making country-specific products, the chipsets used in these products are capable of operating in all 14 channels. However, operating systems and drivers localized for specific countries may lock operation to only the frequencies allowed in that country.Some products handle this issue by asking the user to specify the country of operation upon first use. In other cases, the user can go into the Advanced properties settings and set the channels used.See http://en.wikipedia.org/wiki/IEEE_802.11 this Wikipedia article for a list of the allowed 802.11b/g channels in major countries / world regions.

  • What will affect a wireless network signal around an average home?
    WLAN interferers can be grouped into four categories: things with high water content, metal, RF (radio frequency) generators and dense materials. The first group includes fish tanks, water heaters, hot tubs and such.Metal-related problems can come from obvious things such as filing cabinets, foil-backed insulation, and metal bookcases. But they can also include not-so-obvious things such as tinted windows that use metal-based films and aluminum window screens.Things that can generate RF strong enough to overpower your wireless LAN include microwave ovens, 2.4 and 5GHz cordless phones (but not DECT or 900MHz models), baby monitors and lots more.Finally, dense building materials like filled cinder block, brick, rock fireplace walls, adobe or stucco construction will significantly knock your wireless signal strength down.

  • Is there a wireless router or AP that can keep users isolated from each other?
    Yes. Most of Linksys' wireless routers, most notably the venerable http://www.tomsnetworking.com/Reviews-39-ProdID-WRT54G.php WRT54G, have an "AP isolation" feature that keeps wireless users from communicating with each other.Buffalo Technology's wireless routers, such as the http://www.tomsnetworking.com/Reviews-182-ProdID-WZRRSG54.php WZR-RS-G54 have a similar feature, called "Privacy Separator".

  • Do wireless network cards need to support WMM (802.11e) or is it only a function of a wireless access point?
    802.11e specifies enhancements to the Media Access Control (MAC) layer of 802.11 networks. So it must be supported in all WLAN devices in order to work.
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