Wireless Basics

The technology that it is being, wireless networks in today's world has it's own stage in networking. Since, wired connections are a necessity but when we are conversing about the modern day enterprise networks, we have to look at the bigger picture.

?Suppose your manager roams all over the campus and requires connectivity all over the place. Well, clearly giving a wired connection to the person would work but seriously..everywhere?! This is where wireless networks comes handy so that, no manual cable and wired connections work through ceiling and walls is required. Also, there can be other examples too for wireless networks requirement.

Infrastructure networking - Networking with AP

The Access Point aka AP, is the center and the Basic Service Set ambassador for wireless network infrastructure but wait, there's more coming on this topic later. So, AP is central device which will establish wireless connections with the other wireless stations. The AP does this by creating a Basic Service Area or Cell i.e. covering the range where AP's signal are reachable. Here, what an AP creates is called Basic Service Set (BSS) which is a collection of an AP and it's associated stations.

?Our Access Point will be identified by the stations via a Basic Service Set Identifier (BSSID) which is derived form it's own radio mac. Although, when we(humans) usually tries to identify it by using it's Service Set Identifier (SSID) which is a text string eg, NetworkFloor1 or simply as AP1, AP2. The AP does so by generating beacon frames(wireless management frames) at regular intervals to show WLAN existence.

Distribution System

Also, in short known as DS is an uplink wired connection from AP at Switch (Access), in case we if want to establish a wired and wireless connection in order to make our devices from both ends to communicate. The dot1q trunk between the AP and switch will allow the hosts on each of the wired and wireless ends to communicate via the defined mapping of WLAN-VLAN.

For doing so, the AP will broadcast different SSIDs using it's own radio MAC, different for each SSID. Although, the overall range covered by the AP will be same.

???It can also be wireless if interconnection of AP is wireless then it is called Wireless DS or WDS.

Extended Service Set (ESS)

By joining or combining two or more APs (each forming BSS) we form an Extended Service Set which appears to be as a single bigger BSS and the overall area will be known as Extended Service Area (ESA). This is particularly helpful when we more like want to extend the connectivity of a wireless station. In order to accomplish this we could just place two or more APs having different BSSIDs but broadcasting identical SSID. So, while roaming within a campus, a user would still be connected to the same network.

Bands and Frequencies - lets have a discussion

Unlicensed and Licensed : One might think them of as something related to laws or commissioned to but that's not exactly the case. In general terms, the licensed bands are allowed to be used by the company that licensed them, whereas the unlicensed bands are used by anyone who wants to use them.

?????????Some types of unlicensed radio bands are as follows -

?????????Industrial,Scientific, Medical (ISM)

?????????Unlicensed National Information Infrastructure (U-NII)

?????????Unlicensed Personal Communications Services (UPCS)

IEEE 802.11 networks do have several choices of wireless bands, without requirement to lease the frequencies from government. However, the downside of unlicensed frequencies or bands is that if anyone uses same frequency ranges can leads in causing interference for the signals you are transmitting. So, the unlicensed bands may be used by anyone, following the government guidelines and regulations, these guidelines cover the issues like intrusion on neighboring frequencies leading to interference. Some groups have helped to develop standards for these radio bands.

Some examples are:

FCC (Federal Communications Commission)

IEEE (Institute of Electrical and Electronics Engineers)

Wi-Fi Alliance

ETSI (European Telecommunications Standards Institute)

ITU-R (International Telecommunication Union, Radiocommunication Sector)

WLANA (WLAN Association)

What's with the Signals

Now, if we talk about acting upon computer data over wires either fiber or copper we have light/optical and electrical signals respectively for both. But if we want to send wireless signals we have light waves or Radio Frequencies (RF).

?So there we have it, and we can identify a wave at a frequency.

Modulations allows to add data to the wave changing it's form. These changes includes the amplitude, the frequency and the phase. Remember, whatever is done before the transmission to the wave is modulation and can be undone at receiver end i.e. demodulation, if receiver understands the modifications.

Here, in wireless also there were interoperability issues. So, IEEE resolved this issue by developing standards around WLAN communications e.g., 802.11a, 802.11b, etc.

?Overall, we can use two distinct bands 2.4-GHz and 5-GHz of RF frequency spectrum.

In 2.4-GHz portion working range lies between 2.4000-2.4835 GHz which is broken into 14 unique channel (can referred to as Channel numbers) so, that it'll be easier to remember. Each one is 22MHz wide except the last but the center of each is at least 5MHz apart. The drawback here is the overlapping between consecutive channels resulting in interference thus, preventing optimum communication. The Recommendation is to use Channel 1,6,11 and even 14. This band is used by IEEE 802.11b/g/n networking and also, in bluetooth and cordless phones which might again leads to interference if any of other device other than your own device generates signal in that frequency range. Hence, 2.4 GHz RF band also known to as heavily congested.

Another that we have is 5-GHz RF band, that gives working range of 5.150-5.825 GHz which broken into 24 unique channels each 20 MHz wide and center of each channel is at least 20 MHz apart.Thus, the biggest benefit of 5 GHz portion of spectrum is non-overlapping channels.

The 5-GHz band actually contains the following four separate and distinct bands:

5.150 to 5.250 GHz

5.250 to 5.350 GHz

5.470 to 5.725 GHz

5.725 to 5.825 GHz

Obviously, the operation between wireless devices and AP should all be done on same band. The devices and AP must also share compatibility with parts of 802.11 standard they supports.

Amendments

Both AP and wireless clients can be compatible with one or more amendments however, both can communicate only if they both support and agree on the same amendment. Usually, an AP can operate on both bands simultaneously to support any clients they might present on whereas, on the other hand clients associates with AP on one band at a time. Although, a wireless client can also switch to a different band if signal conditions got any better which depends on it's internal configuration, Wireless adapter, OS, etc.