WiFi Demystified – Part I
By on August 12th, 2009

Wireless LAN or WLAN or simply Wifi is a highly under-utilized technology in India. Even with the availability of cheap hardware for both the client as well as the Gateway-side, the ignorance about this technology and it’s facade of complexity has led to the under-use of this highly convinient technology.

For example, it is surprising that you can go and sit on a cyber-cafe PC and pay as less as Rs.10/- per hour for internet, but cannot go to the same facility and use your own Laptop for the SAME bandwidth. The logic here, cry the owners, is that there is no way to control Wifi connections. Sigh, if they only knew about open source HotSpot softwares like ChilliSpot.

This article, however does not deal with the nuances of WHY Wifi is so under-utilized. Rather, we are going to familiarize ourselves with some Wifi terms and configurations which maybe useful for configuring our Laptops and residential AccessPoints (or Wifi Routers). Please note that the settings mentioned here are for the Home or SOHO (Small Office Home   Office) user, rather than network administrators of Enterprises.

Quick WiFi Glossary

AP : Access Points are the “server”-side or the gateways which connect wireless clients with the Wired network-side. For Eg., A Laptop will connect Wirelessly to an AP which, in turn, will have a Wired connection to the internet infrastructure. Nowadays, most APs are just logical entities within a full-fledged home residential gateway router. For example, the D-Link and the LinkSys home routers have an AP component to let wireless clients connect to them.

STAs : Wireless clients, like a Laptop or a Network printer are also called Stations or STAs in short. This term is used interchangeable with “Clients”

WLAN : Wireless LAN refers to a LAN network with all the nodes connected to the gateway Wirelessly

Beacon : In brash terms, this is the wireless packet advertised in the air so that clients can sniff it and connect to it.

Scan : Scanning refers to “sniffing” the surrounding to see if any APs are present and advertising any beacons. It basically displays all the SSIDs

Wireless LAN’s Basic Configuration Parameters

SSID : A Service Set Identfier,   is the name given to a particular WLAN network. Unlike a wired connection, where a client physically connects itself to the Gateway, wireless clients “associate” themselves to a network name or SSID. This name is present in the AP’s beacon. Thus, when a client is asked to “scan” the network, it shows a list of all the SSIDs in the surrounding area. The SSID can be as absurd or as intuitive as the user wishes. Ex. “Accounts”, “RaseelWifi” or “PirateofArbian” , as long as it’s within 32 characters.

Mode : Wifi operates in 3 different modes referred to as the “a”, “b” and the “g” mode , corresponding to the 802.11a , 802.11b and 802.11g IEEE specifications respecticvely. Mode “a” operates on the 5 Ghz frequencies with a Transmit Rate of upto 54 Mbps and most modern clients may not have support for this mode. Mode “b” and “g” operate on the 2.5 Ghz frequency range and have transmit rates of upto 11 Mbps and 54 Mbps respectively. Mode “b” is a legacy mode and is present in the most APs for backward comptability. The AP can be configured to set in a “bg” mode so that most clients will work without any issue. However, if you are sure that your client supports “g only” mode, it is advisable to set the router in “g” mode.

Channel : Wifi networks operate on the 2.4Ghz and 5 GHz range. The actual frequency consists of upto 14 channgels separated by 200 MHz starting from 2.412 Ghz. and 4.9 GHz respectively. Some of these channels are overlapping (2, 3,4, etc.) while some are the primary channels like (1, 6 and 11). However, it is sufficient to configure the channels to “Auto” mode and let the AP intelligently decide on which channel to operate on. It takes this decision based on minimum interfernce on that frequency.

Max Transmit Rate : This is the Maximum Transmit Rate between the AP and the client. This parameter too can be set to “Auto” mode so that the AP can decide on the optimum rate. This is especially useful when your network may have Clients with “b only” mode which transmit at a max rate of 11 Mbps, as well as clients with “g only” mode with a max transmit rate of 54 Mbps. However, in order to manage bandwidth effectively and to limit interference, some network administrators might limit the rate to a lower value like 5.5 Mpbs or 36 Mbps.

Power : The power unit for transmission in Wifi can be dBm or mW (milliwatts). A dBm is a standard unit for measuring levels of power in relation to a 1 milliwatt reference signal. Most APs have a max power value of 20 dBm or 100 mW which covers an area of 100 meters without any obstructions. Again, this parameter can be set to “Auto” in some APs so that maximum througput can be achieved.

Advanced Wifi Configurations

Now, let’s look at some more advanced configuration and terms regarding Wifi which a user can feel free to tamper with. However, leaving these values to the default ones should be fine for most users.

DTIM Period : Delivery Taffic Indication Message Period is the interval in which DTIM message will be included in the beacon. This helps to have minimum collision and in effect, increased throughput. In cases where there is not much interference, or where the number of clients is limited, the DTIM interval has little or no significance. Usually a value of 1 or 2

Hidden SSID : You can enable this option to hide the SSID of your network so that unauthorised clients will not be able to “see” your network when they scan. However, an autorised user having the correct security credentials and knows the hidden SSID, will be able to enter it in his Wifi configuration utility and connect directly to the AP without seeing it in the list after scanning.

Country and Regulatory domain : Different countries have different rules and regulations regarding Wifi. Hence it is mandatory for the APs to include this information in the beacons. For example, the United Stated supports only Channels 1-13 while Mexico might support 1-14. These are Specification nuances and the user need not be bothered. And in some cases, the APs will come pre-configured with the country setting and there might be no option to change this on the APs config UI.

Antetnna Diversity : This referes to the usage of Rx and Tx antennas. Some APs may have only one antenna in which case this option is either not present or of no use. In some APs, you may be allowed to use Antenna 1 for Rx and 2 for Tx. This will improve the APs performace.

80211N or MIMO : 802.11n is a new proposed specification from IEEE and as of writing this article it was due to be released “any day now”. However, the markets are already flooded with products which support the “802.11N Draft” specs. This mode increases throughput considerably (upto 300 Mbps) provided the client has 802.11N support too. MIMO stands for Multiple-In-Multple-Out and makes uses of clever ways to make use of Antenna, obstructions in the surrounding ,etc to enhance throuput. This mode works alongwith the a,b and g modes mentioned previously for backward compatibilty.

Multiple SSID : This is a very innovative use of the Wifi technology to group users. With this feature, a single AP can be configured to beacon more than one SSID with their own security, throughput and other settings. Thus, I can configure my AP to have the following SSIDs, “Guests” , “Trusted”, “Highest”. No points for guessing that I will have some low security like WEP and lower transmit rate, say 2 Mpbs and a different channel,say 2 for “Guests” SSID and better configuration for the other SSIDs. However, it must be noted that this will hamper the overall performance of the AP since the total bandwidth of the AP is divided.

WMM or WME : Wireless MultiMedia or Wifi MultiMedia Extensions is an advnaced Wireless configuration which implements the Qos functionality in Wireless. By configuring WMM parameters we can have better throughout for specific applications like Voice (over IP), Video and regulate bandwidth for other normal applications like Web surfing, etc.   I will not dvelve deeper into this since very few residential gateways will offer this as an configurable option.

UAPSD : Unscheduled Automatic Power Save Delivery is a feature that uses WMM to save the APs power depending upon the type of traffic. Again, as WMM may not be offered UAPSD also might be absent and more info is out of the scope of this document.

While the above parameters are enough to configure an AP and make it functional, there is no security associated with them. Security settings for Wifi are covered in a separate post.

Author: Raseel Bhagat

Raseel Bhagat has written and can be contacted at raseel@techie-buzz.com.
 
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