Aim: Study experiment on WLAN.

Theory:

Wireless LAN

Awireless local area network(WLAN) links two or more devices using some wireless distribution method (typicallyspread-spectrumorOFDMradio), and usually providing a connection through an access point to the wider Internet. This gives users the mobility to move around within a local coverage area and still be connected to the network. Most modern WLANs are based onIEEE 802.11standards, marketed under theWi-Fibrand name. WLANs were once called LAWNs (for local area wireless network) by the Department of Defence.

Architecture

Components of WLAN architecture are:

  1. Stations

All components that can connect into a wireless medium in a network are referred to as stations. All stations are equipped with wireless network interface controllers (WNICs). Wireless stations fall into one of two categories: access points, and clients. Access points (APs), normally routers, are base stations for the wireless network. They transmit and receive radio frequencies for wireless enabled devices to communicate with. Wireless clients can be mobile devices such as laptops, personal digital assistants, IP phones and other smartphones, or fixed devices such as desktops and workstations that are equipped with a wireless network interface.

  1. Basic service set

The basic service set (BSS) is a set of all stations that can communicate with each other. Every BSS has an identification (ID) called the BSSID, which is the MAC address of the access point servicing the BSS.

There are two types of BSS: Independent BSS (also referred to as IBSS), and infrastructure BSS. An independent BSS (IBSS) is an ad-hoc network that contains no access points, which means they can not connect to any other basic service set.

  1. Extended service set

An extended service set (ESS) is a set of connected BSSs. Access points in an ESS are connected by a distribution system. Each ESS has an ID called the SSID which is a 32-byte (maximum) character string.

  1. Distribution system

A distribution system (DS) connects access points in an extended service set. The concept of a DS can be used to increase network coverage through roaming between cells.

DS can be wired or wireless. Current wireless distribution systems are mostly based on WDS or MESH protocols, though other systems are in use.

Ad-hoc wireless LAN networks

Fig 1: Ad-hoc Wireless LAN

On wireless computer networks, ad-hoc mode is a method for wireless devices to directly communicate with each other. Operating in ad-hoc mode allows all wireless devices within range of each other to discover and communicate in peer-to-peer fashion without involving central access points.

To set up an ad-hoc wireless network, each wireless adapter must be configured for ad-hoc mode. In addition, all wireless adapters on the ad-hoc network must use the same SSID and the same channel number.

An ad-hoc network tends to feature a small group of devices all in very close proximity to each other. Performance suffers as the number of devices grows, and a large ad-hoc network quickly becomes difficult to manage. Ad-hoc networks cannot bridge to wired LANs or to the Internet without installing a special-purpose gateway.

Ad hoc networks make sense when needing to build a small, all-wireless LAN quickly and spend the minimum amount of money on equipment. Ad hoc networks also work well as a temporary fallback mechanism if normally-available infrastructure mode gear (access points or routers) stop functioning.

Minimal configuration and quick deployment make ad hoc networks suitable for emergency situations like natural disasters or military conflicts. The presence of dynamic and adaptive routing protocols enables ad hoc networks to be formed quickly.

Here are some of the benefits of an ad-hoc network:

  • Ad-hoc networks are simple to set up. Plug in your wireless network adapters, configure the software, and you're off and running.
  • Ad-hoc networks are inexpensive. You save the cost of purchasing an access point.
  • Ad-hoc networks are fast. Throughput rates between two wireless network adapters are twice as fast as when you use an access point.

Wireless LAN based on Infrastructure

Fig 2:Infrastructure based Wireless LAN

Many WLANs of today need an infrastructure network. Infrastructure mode wireless networking bridges (joins) a wireless network to a wired Ethernet network. Infrastructure mode wireless also supports central connection points for WLAN clients. Infrastructure network not only provides access to other networks but also includes forwarding functions, medium access control etc.

A wireless access point (AP) is required for infrastructure mode wireless networking. To join the WLAN, the AP and all wireless clients must be configured to use the same SSID. The AP is then cabled to the wired network to allow wireless clients access to, for example, Internet connections or printers. Additional APs can be added to the WLAN to increase the reach of the infrastructure and support any number of wireless clients. In infrastructure based wireless LAN networks the communication takes place only between wireless node and access point, no direct communication between two nodes is possible.

In infrastructure based wireless LAN networks, each Basic service set must consists of an Access Point and we can connect two BSS together to form an ESS (Extended service set) with help of distribution system.

Compared to the alternative, ad-hoc wireless networks, infrastructure mode networks offer the advantage of scalability, centralized security management and improved reach. The disadvantage of infrastructure wireless networks is simply the additional cost to purchase AP hardware.

An infrastructure network enables you to:

  • Connect to a wired network.

An access point lets you easily expand a wired network with wireless capability. Your wired and wirelessly networked computers can communicate with each other. This is the most obvious strength of an infrastructure setup.

  • Extend your wireless network's range.

Placing an access point in between two wireless network adapters doubles their range.

  • Utilize roaming ability.

If you add multiple access points to your network, as you might in an office or large home, users can roam between interlocking access point cells, without ever losing a connection to the network.

  • Share the Internet.

Probably the most useful device in a simple wireless LAN is an access point with a built-in router and firewall. The router allows you to share Internet access between all your computers, and the firewall hides your network, helping to keep network-savvy hoodlums at bay. Some of these multifunction access points include a (wired) hub as well, for plugging in several computers connected to your network by Ethernet.

Ad-hoc vs Infrastructure based Wireless LAN

Ad-hoc based Wireless LAN / Infrastructure based Wireless LAN
Ad Hoc Mode does not require an access point, it's easier to set up, especially in a small or temporary network. / Infrastructure mode needs access point, which must be configured properly in order to provide services.
Ad Hoc Mode connections are limited, for example between two laptops, to the power available in the laptops. / Infrastructure takes advantage of the high power of an access point to cover wide areas.
As the Ad Hoc topology changes, throughput and range will change, sometimes in unanticipated ways. / Network topology, throughput and range do not change in unanticipated ways.
In an Ad Hoc network with many computers, the amount of interference for all computers will go up, since each is trying to use the same frequency channel. / Unlike Ad-hoc networks, the central access point manages the channel to keep interference as low as possible.
In Ad Hoc Mode, chains of computers will connect to pass your data, if your computer is not directly in range. On the other hand, you do not have control over the path your data takes. The automatic configuration routines may send your data through several computers, causing significant network delays. / In infrastructure mode, the access point itself provide access to another device and networks using high speed wired connection which significantly reduce network delays.
Ad-hoc networks are inexpensive. You save the cost of purchasing an access point. / Infrastructure base networks are expensive than Ad hoc networks since they need an Access point.

Advantages of Wireless LANs

  1. People can access the network from where they want; they are no longer limited by the length of the cable
  2. Some cities have started to offer Wireless LANs. This means that people can access the internet even outside their normal work environment, for example when they ride the train home.
  3. Setting up a wireless LAN can be done with one box (called Access point). This box can handle a varying number of connections at the same time. Wired networks require cables to be laid. This can be difficult for certain places.
  4. Access points can serve a varying number of computers.

Disadvantages of Wireless LANs

  1. Wireless LANs use radio waves to communicate. Special care needs to be taken to encrypt information. Also the signal is much worse, and more bandwidth needs to be spent on error correction.
  2. A typical IEEE 802.11 access point has a range of meters from where devices can connect. To extend the range more access points are needed.
  3. There are many reliability problems, especially those connected to interference from other devices.
  4. Wireless LANs are much slower than wired ones; this may not matter for most users though, because the bottleneck in a home network is usually the speed of the ADSL line (used to connect to the Internet)

Bluetooth

Bluetooth is the name given to a new technology standard using short-range radio links, intended to replace the cable(s) connecting portable and/or fixed electronic devices. The standard defines a uniform structure for a wide range of devices to communicate with each other, with minimal user effort.

Its key features are robustness, low complexity, low power and low cost.Bluetooth uses Frequency Hop Spread Spectrum (FHSS) to avoid any interference. A Bluetooth channel is divided into time slots each 625 micro second in length. The devices hop through these timeslots making 1600 hops per second. This trades bandwidth efficiency for reliability, integrity and security.

Bluetooth radios operate in the unlicensed ISM band at 2.4 Gigahertz using 79 channels between 2.402 GHz to 2.480 GHz (23 channels in some countries). The range for Bluetooth communication is 0-30 feet (10 meters) with a power consumption of 0dBm (1mW). This distance can be increased to 100 meters by amplifying the power to 20dBm. The Bluetooth radio system is optimized for mobility.

Bluetooth supports two kinds of links: Asynchronous Connectionless (ACL) links for data transmission and Synchronous Connection oriented (SCO) links for audio/voice transmission. The gross Bluetooth data rate is 1 Mbps while the maximum effective rate on an asymmetric ACL link is 721 Kbps in either direction and 57.6 Kbps in the return direction. A symmetric ACL link allows data rates of 432.6 Kbps. Bluetooth also supports up to three 64Kbps SCO channels per device. These channels are guaranteed bandwidth for transmission.

Piconet

A piconet is the type of connection that is formed between two or more Bluetooth-enabled devices such as modern cell phones or PDAs. Bluetooth enabled devices are "peer units" in that they are able to act as either master or slave. However, when a piconet is formed between two or more devices, one device takes the role of 'master', and all other devices assume a 'slave' role for synchronization reasons. Piconets have a 3-bit address space, which limits the maximum size of a piconet to 8 devices (23 = 8), i.e. 1 master and 7 slaves.

The master of the piconet determines the hopping pattern and the slaves have to synchronize to this pattern. Each piconet has its own unique pattern. If a device want to became a part of piconet then it has to follow the hopping pattern of that piconet.The first step in transmission in any piconet is sending clock and device id by master.

Fig 3:Piconet

Apart from masters and slaves, in a piconet, there can be 200 parked devices and infinite number of standby devices. When a slave completes its data transfer, a parked device gets chance to become slave and a standby device gets chance to become parked device.

Scatternet

A scatternet is a number of interconnected piconets that supports communication between more than 8 devices. Scatternets can be formed when a member of one piconet (either the master or one of the slaves) elects to participate as a slave in a second, separate piconet. The device participating in both piconets can relay data between members of both ad-hoc networks. However, the basic bluetooth protocol does not support this relaying - the host software of each device would need to manage it. Using this approach, it is possible to join together numerous piconets into a large scatternet, and to expand the physical size of the network beyond Bluetooth's limited range.

Fig 4:Scatternet

If a device wants to participate in more than one piconet, it has to synchronize to the hopping sequence of the piconet it wants to join. If a device acts as slave in one piconet, it simply starts synchronizing with the hopping sequence of the piconet it wants to join. After synchronization, it acts as slave in this piconet and no longer participates in its former piconet. But before leaving piconet, a slave informs the current master that it will be unavailable for certain amount of time.

A master can also leave its piconet and act as a slave in another piconet. Communication between different piconets takes place by device jumping back and forth between these nets. If this is done periodically, for instance, isochronous data streams can be forwarded from one piconet to another. However, scatternets are not yet supported by all devices.

Advantages of Bluetooth

  1. Wireless

As you probably already know, there are many benefits and advantages to using wireless devices. Along with improving safety as a result of eliminating wires you don't need, wireless also offers you plenty of other advantages.

  1. Bluetooth is actually inexpensive

The technology of Bluetooth is cheap for companies to implement, which results in lower costs for the company. These savings are then passed from the company on to you.

  1. Bluetooth is automatic

Bluetooth doesn't have you set up a connection or push any buttons. When two or more devices enter a range of up to 30 feet of each other, they will automatically begin to communicate without you having to do anything.

  1. Standardized protocol

Bluetooth is standardized wireless, meaning that a high level of compatibility among devices isguaranteed. Bluetooth will connect devices to each other, even if they aren't the same model.

  1. Low interference

Bluetooth devices almost always avoid interference from other wireless devices. Bluetooth uses a technique known as frequency hopping, and also low power wireless signals.

  1. Low energy consumption

As a result of Bluetooth using low power signals, the technology requires very little energy and will use less battery or electrical power as a result. This is an excellent benefit for mobile devices,as Bluetooth won't drain the battery.

  1. Sharing voice and data

The standard for Bluetooth will allow compatible devices to share data and voice communications. This is great for mobile phones and headsets, as Bluetooth simplifies driving and talking on your cell phone.

  1. Instant PAN (Personal Area Network)

You can connect up to seven Bluetooth devices to each other within a range of up to 30 feet, forming a piconet or PAN. For a single room, you canalso set up multiple piconets.

  1. Upgradeable

Upgradeable is the standard for Bluetooth. There are newer versions of Bluetooth in the works,which offer many new advantages and backward compatible with older versions.

  1. The technology stays

Bluetooth technology is a world-wide, universal wireless standard. With it being as popular asit is, you can count on it being around for years to come. As more and more devices start to useBluetooth technology, more manufacturers will be eager to make their products compatible. A chain reaction will occur, making Bluetooth the standard for cutting edge wireless.

Disadvantages of Bluetooth

  1. Though the transfer speeds are impressive at around 1 Mbps, certain other technologies like Infrared can offer speeds up to 4 Mbps. This is an area that can be improved on in the near future.
  2. Even though the security is good, it is even better on Infrared. This is because of the comparatively larger range of Bluetooth and also the lack of a line of sight. Someone who knows how to hack such networks can do so eventually.
  3. The battery usage during a single transfer is negligible, but there are some people who leave the device switched on in their devices. This inevitably eats into the battery of these devices, and lowers the battery life considerably.

Conclusion:Hence we have studied Wireless LAN and Bluetooth.