Ad-Hoc and Infrastructure Modes

When architecting an 802.11 network, there are two modes in which you can operate: Ad-Hoc and Infrastructure. In Ad-Hoc mode (see image above), sometimes called “IBSS” or “Independent Basic Services Set”, all devices operate in a peer-to-peer mode.There are no access points used in this topology, as all devices communicate directly with all other devices.
In Infrastructure mode, an AP is connected to a wired infrastructure (such as Ethernet) and all of the wireless devices communicate with the AP. Even if two wireless devices are located right next to each other, all communication between the devices occurs through an AP. When using Infrastructure mode, a collection of wireless devices connected to an AP is referred to as a Basic Service Set (BSS).
If two or more BSSs are connected together using a “Distribution System” (such as wired Ethernet), the collection of BSSs is referred to as an Extended Service Set (ESS).

Top Mobile Broadband Deals in UK

A mobile broadband revolution is sweeping the nation, as more of us come to expect high-speed and often wireless internet access at home we are starting to explore broadband access as an option for when we're on the move to.
For you in UK, here's Top Mobile Broadband deals comparing speed, monthly cost, and bandwidth offered.

1. Vodafone Mobile Broadband - USB Stick
   7.2Mbps | 3GB | 12 months | £ 15.00
2. 3 Mobile Broadband Max - USB Stick
   3.6Mbps | 15GB | 24 months | £ 15.00
3. O2 Mobile Broadband - USB Stick
   3.6Mbps | 3GB | 24 months | £ 9.79

802.11g

To keep up with the 54-Mbps speed claims of 802.11a, the 802.11g protocol was ratified in 2003. This protocol took the OFDM modulation technique of 802.11a and applied it to the 2.4 GHz spectrum of 802.11b. Because it operated in 2.4 GHz, it was possible to remain backwards-compatible with 802.11b equipment. 802.11g radios support both OFDM and DSSS modulation techniques. Therefore, an 802.11g device would, in theory, be compatible with an original 1 or 2 Mbps 802.11 DSSS device from 1997.
Keep in mind that a typical residential or small business hotspot has a DSL or similar connection behind it providing the bandwidth to the Access Point.These broadband connections typically provide speeds in the 1.5 to 3 Mbps range. Obviously, the bottleneck in a Wi-Fi deployment is usually the DSL (or even T1) pipe.Therefore, the advantages of higher speed wireless connections (such as 802.11g) are often limited because of the Internet connection.The only exception would be if there is a large number of data transfers between wireless clients and PCs on the local area network (or between two wireless PCs). In those cases (such as gaming or local file transfers), users will notice a significant speed increase when using 802.11g,  compared to slower wireless protocols, such as 802.11b. In many large-scale community wireless networks, a system of repeaters will be used to enhance coverage in dead spots. Because each repeater (such as WDS) reduces the bandwidth by half, using 802.11g (and 54 Mbps) is often desirable.The logic here is that you can halve 54 Mbps more times then you can halve 11 Mbps, and yet still wind up with a useable, decent bandwidth speed for the client.
The pros and cons of 802.11g are as follows:

• Upside: Relatively fast speed; compatible with 802.11b
• Downside: Interference from other 2.4 GHz devices; only three non-overlapping channels

802.11a

Although 802.11a was released around the same time as 802.11b, it never achieved the same critical mass or wide scale acceptance.This was despite 802.11a’s superior 54-Mbps speed. (Before 802.11g was released, 802.11a was the fastest Wi-Fi protocol available.) 802.11a operates in the 5 GHz spectrum and has 12 non-overlapping channels. As a result of this higher frequency, 802.11a has a much harder time penetrating through obstacles, such as walls and other objects.This results in a range much lower than 802.11b.
One major advantage of 802.11a is that it is less prone to interference from other 5 GHz devices simply because there are fewer 802.11a and 5 GHz cordless devices deployed in the real world to compete with. Unlike 2.4 GHz (which is flooded with competing devices), 5 GHz remains relatively unused.This trend, however, is changing as more and more cordless phones and other gadgets are migrating to the less crowded 5 GHz spectrum. However, for the time being, 802.11a makes an excellent choice for building-to-building and backhaul solutions where line of sight is available. Also, 802.11 offers 11 non-overlapping channels. See Table 1.2 for a list of 802.11a channels.The pros and cons of 802.11a are as follows:

• Upside: Relatively fast speed; more non-overlapping channels than 802.11b/g; 5 GHz spectrum is less crowded
• Downside: More expensive; shorter range

802.11b

For many years, 802.11b was widely regarded as the most popular form of Wi-Fi. It utilizes frequencies in the 2.4 GHz range (2.400–2.485GHz) and has 11 channels. However, only three of these channels are truly non-overlapping. See Table 1.1 for a list of all channels.The range (distance) for 802.11b can vary widely, but each access point (with default antennas) typically covers a few hundred feet (indoors) or a few thousand feet (outdoors).With specialized, external antennas, this range can be greatly increased. 802.11b operates in the Industrial, Scientific, and Medical (ISM) unlicensed spectrum.

The top speed for 802.11b is 11 Mbps, but it will auto-negotiate down to rates of 5.5, 2, and 1 Mbps as the signal strength deteriorates.These speeds include a relatively high amount of “overhead,” as required by the protocol to operate. Keep in mind that actual throughput (for all 802.11 flavors) is typically about 50–60 percent of the advertised speeds. In other words, even under ideal circumstances, the actual data throughput (say, transferring a file) is usually around a maximum of 5–6 Mbps.
So many people have discovered the joys of wireless networking that 802.11b is quickly becoming a victim of its own success. Specifically, the level of Wi-Fi congestion found in any major metropolitan area is raising the RF noise floor and rendering many long distance links unusable.The pros and cons of 802.11b are as follows:

• Upside: Most popular and widely available; least expensive; good coverage
• Downside: Relatively slow speed; interference from other 2.4 GHz devices; only three nonoverlapping channels
  

Introduction to Wi-Fi

Welcome to the world of “wireless magic.” 802.11 (Wi-Fi) wireless LANs have exploded onto the
scene with an excitement not seen since the introduction of the Internet itself. Getting rid of the
wires means getting rid of the hassle.With Wi-Fi, you can roam through your favorite coffee shop,
boardroom or living room, all the while maintaining the convenience of high-speed connectivity.
With Wi-Fi, life is good!
Once you’ve gone through the experience of setting up a local Wi-Fi network, your first instinct is
likely to think that “bigger is better.” Expanding the coverage and increasing the network cloud enables
you to share Internet resources with others as a community service. As long as you’re not breaking the
law (or violating your ISP’s terms of service), you should listen to that creative instinct and start getting
together with your neighbors (or others in your community) and begin planning a community wireless
network! This book is all about the challenges, thrills, and adventures of such an effort, started in San
Diego, and known as “SoCalFreeNet.” By offering this roadmap to you, the reader, we hope to inspire
more such efforts in neighborhoods all around the world.