Wireless Howto: Background Knowledge Next Previous Contents

2. Background Knowledge

2.1 What about Wireless?

Wireless is a new technology that can help you to connect computers at distance. It works with Wireless cards with a TX/RX inside at 2.4 GHz while the software interface is Ethernet-like, with an hardware address different for each card in the world. Typical transmit power is 10-20 mW till 100mW (see standard IEEE 802.11 and FCC/CEPT licenses).

2.2 What's the max distance between radio cards?

The most important thing in Wireless communications is the line of sight clear: you MUST SEE (with eyes or with a binocular) the antenna from the other end or you can have (at most) a little tree between them.

The distance depends on the antenna and (eventually amplifier) used: 2-300 meters with a omnidirectional antenna; 1 km with a directive one; 2-3 km with a omnidirectional amplified (200mW); some km with parabolic antenna. 50-60 km with parabolic or directive antenna amplified (some Watts).

Be aware that it is not always legal to amplifier Wireless cards, cause you could violate FCC/CEPT (and also your country relative) specifics.

2.3 What's the difference between wired and Wireless network?

Wired networks are very simple to setup (at least at low level). Wireless networks are very difficult to setup, to manage, to debug... Typical problem with wired networks like hardware install, software install, debug and so on become very critical with Wireless:

  1. You have to choose the right Wireless card: there are many cards from many vendor with many requirement and specs. If you want to create a little LAN/WAN you have to buy IEEE 802.11 compliant Wireless cards with an Access Point.
  2. Many cards are PCMCIA, so you have to install pcmcia Linux source first.
  3. You have to test it with 2 running systems, first at very short distance, then you can get far.
  4. You should test it at any weather (typically rain).
  5. Finally be happy for setting up.

If you installed a repeater (Linux box that has many Wireless and wired cards) you may have problem editing its configuration at distance!

2.4 What I need to know to setup a Wireless network?

There are a number of requirement to setup a Wireless network;

software requirement: 

  1. Generic network knowledge like IP address, netmask, routing... covered by generic Linux NET3-4-HOWTO; *
  2. Specific network knowledge like proxy arp, bridging, proc fs, contained in Proxy-ARP-Subnet, Bridge Mini-Howto and in Linux Kernel Source (2.2.x or 2.4.x) under Documentation/networking/ ip-sysctl.txt) *
  3. Wireless network knowledge like access mode (ADHOC, INFRASTRUCTURE and ACCESS POINT), channel concept, outdoor and indoor defines and so on that you can find in any document concerning Wireless: IEEE standard 802.11, CEPT, etc.

non software requirement: 

  1. Minimal experience in antennas, physical mounting, pointing
  2. Pc hardware installation with particular attention to not produce interference between different Wireless Cards (if required).

finally a great luck!

* All Howtos needed by this document can be retrieved from http://www.linuxdoc.org

2.5 Why should I setup a Wireless network and what I expect from it?

Why? Because you're not satisfied of wired network!

With Wireless cards you can go across garden, parks, houses, (but you MUST SEE the other end!).

High Level Protocol used in Wireless Cards are the same used in Ethernet cards: TCP/IP over Wireless Ethernet-like but make attention to Windows Sharing Application, cause if you use Linux to forward, you are warned that a ip forwarder doesn't let pass through broadcast messages (see more on NetBIOS protocol): in this case you should use a WINS server to support Network Browsing (see Samba doc).

Wireless let you create a little LAN/WAN with a central point of access (maybe with Internet Access!) and give access to anyone by air!

Imagine a country all cabled by radio machines.

Imagine a network that can connect all country people together, sharing files, audio applications, video applications at high bandwidth (like cable network).

All that can be done (and it's already done in some country) using Wireless cards with Wireless Access Point and Wireless Linux Boxes that can operate as repeater (at IP level such as router or, if you want, at data-link level, with bridge driver, see more at Bridge Http Link or Bridge Ftp Link

2.6 What Wireless cards are covered by this howto?

In this howto I start with a generic configuration (to introduce Wireless networking), then I describe an example for each card I knew directly, with some trick you can use to improve its performance.

Wireless Card list: 

  1. Proxim Symphony - http://www.proxim.com
  2. Webgear AviatorPRO 2.4 (pcmcia support needed) - http://www.webgear.com
  3. Lucent Wavelan I, II, Orinoco - http://www.lucent.com and http://www.orinocowireless.com
  4. Cabletron - http://www.cabletron.com
  5. YDI am930_isa - http://www.ydi.com
  6. Siemens Radio Modem (Dect) - http://www.siemens.com
  7. RadioLan (5 GHZ) - http://www.radiolan.com

For a very more exhaustive list see Jean Tourrilhes Wireless Howto.

Siemens Radio Modem is not a really 802.11 Wireless card, they are modems that you can attach to serial and they act as modem (at 1800 MHz, so DECT technology). Appendix B describe their use.

RadioLan cards work at 5.4GHz in a Windows 9x environment and with a RadioLan Access Point that bridges between Wired and Wireless networks (there are no Linux driver as I know).

2.7 How much do they cost?

Wireless cards listed above are very low expansive: they start from very few hundred of dollars up to some thousand of dollars for Access Point that have 2 Wireless card (Lucent, for example) that can act as a bridge.

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