Wireless Local Area Networks

Wireless LANs

In the 80s they replaced wired LANs. Avoid the cost of installation, facilitate the transfer, etc.

But it was surpassed by:

The Architects included in their design expensive pre-wired for data applications. Security in twisted pairs for LAN networks. Alternative to the LAN network. There will be a wired network and stationary workstations with LAN servers.

These WIRELESS LANs do not require cables to transmit signals, but instead use radio or infrared waves to send packets (data sets) through the air.

Most WIRELESS LAN networks use distributed spectrum technology, which offers a limited bandwidth -generally less than 11 Mbps-, which is shared with other devices on the spectrum.

Wireless LAN technology offers Growing Businesses the ability to have seamless networks that are fast, secure and easy to configure.

Services

Wireless LANs (WLANs) offer several advantages over conventional LANs (Ethernet, Token-Ring, fiber optics) because they can be mobile. The benefits are obvious for laptops and desktops, as the user can truly roam from point to point and stay connected to the LAN and its resources.

The benefits for the desktop, business system and server market are not so obvious. The network can be established without the expense and hassle of laying cables and installing connectors in walls. Additionally, wireless networks are flexible, since desktop machines can be moved around without any infrastructure work. This is particularly useful when setting up temporary sites or when working in "fixed" locations that periodically change locations, such as companies that relocate to a larger office when they exceed the capacity of their current facilities.

Until the availability of the IEEE standard 802.11(which defines Media Access Control and Physical Layer characteristics, specific to Wireless LANs), the only wireless networking solutions available were low speed, original design devices. This standard established a 2Mbps system in 1997. The IEEE expansion 802.11b, approved in 1999, increased the speed to 11 Mbps. This offers roughly the same range of performance as a card Ethernet of 10 Mbps. The IEEE standard 802.11a is being considered, and could increase speeds to 25 Mbps or more.

Operation

The PC Card in the notebook computer receives and transmits digital information over a 2,4 GHz radio frequency. The card converts the radio signal into digital data (actually small packets of information) that the PC can understand and process.

The PCI card connects to a desktop computer and works similarly to the PC Card, except that it is dedicated to Laptops.

The software access point allows a PC connected to a network Ethernet (a very common type of local area network) can act as a hardware access point.

The hardware access point receives and transmits information in a similar way to the PC Card. connects to the network Ethernet via an RJ-45 connector and handles incoming and outgoing traffic between the fixed network and WIRELESS LAN users or "clients", thus acting as a wireless hub. In other words, the hardware access point acts as a gateway or on-ramp for wireless users to access a wired LAN.

It is important to note that, just like on a motorway during peak traffic hours, the more users at the access point, the slower the traffic. The hardware access point connects to a hub, switch, or router, but can also connect directly to a server using a cable adapter.

Infrastructure mode.- When the infrastructure mode is selected (on the PC using the configuration utility), the user can send and receive radio signals (information) through an access point, which can be through hardware or software. This access point connects to a conventional network via a cable, receives the radio signal from the client and converts it to a digital format that the network and the server can understand and process. If the user requests information (for example, a web page), the access point sends a radio signal to the user's PC on the WIRELESS LAN. Access points are located at network connections where any computer, printer, or other network device would connect using an RJ-45 cable (similar to a phone jack, but slightly larger).

Peer mode: When peer to peer mode is selected, users connect to other computers (either laptops or desktops) equipped with high-speed IEEE 802.11b wireless products. This mode is used when wired networks do not exist when a group of users want to set up their own network for collaboration and file sharing. At the server/network end, the IT manager must install a software package, which her department must push to the appropriate server.

This software package allows you to configure, manage, and control the tracking of wireless traffic over the network.

Each hardware access point offers a throughput of up to 11 Mbps. This capacity is suitable for the following activities:

* 50 mostly inactive users who occasionally check text emails.
* Top 25 users who use email services heavily and upload or download files of moderate size.
* 10 to 20 users who are constantly connected to the network and work with large files.

To increase capacity, more access points can be added, giving users more opportunity to enter the network. It is important to note that networks are considered optimized when the access points correspond to different channels.

Example: A company can establish 3 access points (with a range of up to 100 meters each) in 3 adjacent offices, each set to a different channel. In theory, this would allow multiple users to "share" a total capacity of up to 33 Mbps (although no user could reach speeds greater than 11 Mbps). In reality, since clients communicate with the access point that offers them the strongest signal, bandwidth is not necessarily evenly distributed among all users.

Wired LAN backbone such as an Ethernet. Connect several servers, workstations, or routers to connect to another network. There is a Control Module that functions as an interface with the wireless LAN.

Multi-Cell Wireless LAN There are several control modules interconnected by a wired LAN. Each module services multiple wireless end systems within its transmission range.

Configuration and Structuring of a Wireless LAN

To configure and structure a Wireless LAN, an Access Point must be available, which complies with the IEEE 802.11 standard, consisting of protocol software and a card for wireless networks. With this product, the configuration of wireless networks in Infrastructure mode is facilitated, providing greater security in the control of access to the network by wireless equipment.

The IEEE specification has chosen the ICM band (Industrial, Scientific and Medical use) of 2 GHz for the definition of the Wireless LAN standard, which guarantees its global validity as it is a band available worldwide. The ICM band is for commercial use without a license, limiting the transmission power for wireless local networks to 4 mW. The link speed between the wireless devices is 100 Mbps, the maximum speed defined in the IEEE2 standard, with direct sequence spread spectrum (DSSS) signal modulation. With this modulation technique, each bit of data to be transmitted is replaced by an equivalent 802.11-bit sequence that is easily recognizable by the receiver, so that even if part of the transmission signal is affected by interference, the receiver can still reconstruct information from the received signal.

The Access Point is composed of:

* A WIRELESS LAN card (Wireless LAN.)

* Software protocol for Wireless LAN networks 802.11.

It acts as a bridge between the wireless network and a fixed network (Ethernet). The only connectors are the power and fixed cable, 10Base-T (RJ-45) connector. There are also two antennas that stand upright during use. Complies with IEEE 802.11b (High Speed ​​Streaming Spread Spectrum) standard. Allows a temperature between 0 - 40ºC (temp. in operation) Humidity: 95% (without condensation)

General operation of a wireless LAN card:

Complies with IEEE802.11 standard. Range: 50 meters in dense offices, 100 meters in open offices, 800 meters outdoors. Intermediate frequency: 280 MHz. Frequency range: 2,4 GHz (from 2.412 MHz to 2.484 MHz). Antenna: External omnidirectional.

Wireless LAN Access Point Software:

The "Software Access Point" (SAP) package. It is a program that is installed on a computer equipped with an Access Point unit and offers the functionality of the same.

Wireless LAN Uses

Nomad Access

* Allows an unguided link between a LAN hub or server and a data terminal
mobile with antenna (laptop).
* User can move around with laptop and connect with servers
Wireless LAN from different places.

Card for Notebook, which is used to configure the Notebook for Wireless LANs, has integrated antenna and can transmit 11 Mbits/second

Another of the great advantages derived from the use of the Access Point is the possibility of linking a wireless network with an Ethernet cable network. Both wired and wireless networks would thus be integrated into a single global network, so that any PC on the wired network can communicate with any PC on the wireless network and vice versa.

Bearing in mind that in the Infrastructure network the PC that has access control can be any device on the network, the use of the Access Point allows the current Ethernet cable networks to be expanded only on the basis of the installation of new points with devices wireless, without the need to continue installing network cables. * The use of the Access Point, in the extension of existing Ethernet cable networks, is especially indicated in links between floors of the same building, between nearby buildings and/or between nearby premises but without continuity.

For this, the so-called Bridge is used. The Bridge or Bridge complies with the IEEE802.11 standard and is made up of the protocol software for wireless networks and a wireless network card.

The purpose of the Bridge is the union (or bridge) between two networks of traditional cables (Ethernet), separated by a certain physical space, which make their union by cable impossible or difficult.

The use of the Bridge allows easy interconnection between two cable networks located in nearby locations, on different floors or even in separate buildings, saving the user costly infrastructure works (ditches, wiring, etc.,).

The solution provided by the use of the Bridge against point-to-point or temporary links, via a switched telephone network, provides a much higher speed in data transfer (up to 60 times more), without more costs than the use of the Bridge itself.

Interconnection of Ethernet Networks through Bridge

Wireless networks can be configured in the following environments:

1.- Network "ad-hoc":

It is the one in which all computers (desktop and/or laptop) equipped with wireless network cards can communicate with each other directly. It is a peer network (without a central server) established temporarily to meet an immediate need, thus forming a temporary network.

2.- Infrastructure Network.

It is the one in which all the computers (desktops and/or laptops) equipped with wireless network cards work in a hierarchical order, whereby one of the computers on the network is the link point between all the PCs on the same network. . Access control is carried out from that computer, as a security measure for the rest of the equipment that forms part of the network. To configure the Infrastructure network, it is required that an Access Point be installed on the computer chosen to take control, in accordance with the IEEE 802.11 standard.

Typical Wireless Lan Applications

Link of independent physical areas through Access Points:

The link between wireless networks located on different floors of the same building is a perfect example of the use of the Access Point to link between independent wireless networks, through minimal Ethernet cabling, in situations where the coverage of the antennas is limited due to obstacles. important.

Links or Interconnection between Buildings:

* In the connection of LANs located in neighboring buildings, whether they are wired LANs or not, an unguided link is used between the buildings, the connected devices are bridges or routing devices.

* This point to point link is not itself a LAN, but this application is used in Wireless LANs.

The combination of the Access Point and the Bridge allows to carry out the link between two wireless areas, when it is impossible or too expensive to make this connection through a cable.

For a similar situation between two existing Ethernet networks, the Bridge that allows both to be linked wirelessly, overcoming the obstacles that prevented their connection by means of a cable via radio.

Wireless networks in the same physical area:

Two or more wireless networks, both in Ad-Hoc and Infrastructure mode, can coexist simultaneously in the same physical area of ​​coverage of their antennas, in a completely transparent way to the users of each of the networks. In addition, through a simple channel assignment operation in its configuration, both networks can operate at full capacity of their 2 Mbps bandwidth.

Wireless LAN Requirements:

In addition to including the requirements of any other LAN networks, including:

* High capacity
* Coverage of small distances
* Full connectivity of connected stations
* Diffusion capacity

There is a set of specific needs for Wireless LAN environments:

Performance: The use of the MAC protocol must be efficient to maximize capacity.

Number of Nodes: they can support many nodes by using multiple cells.

Connection to the LAN Trunk: interconnection with stations located on a wired backbone LAN occurs. Infrastructure Wireless LANs are supported by Control Modules that connect both types of LANs, nomadic users and ad hoc Wireless LANs.

Service area: The coverage area has a typical diameter between 100 and 300 meters.

Battery Consumption: When mobile users use wireless adapters they need long battery life.

Rebustness in the transmission and security: The design of a wireless LAN must allow reliable transmissions even in noisy environments and must offer a certain level of security against eavesdropping.

Orderly network operation: It is likely that two or more networks operate in some area where interference between them is possible, this frustrates the operation of the MAC algorithm and may allow unauthorized access to a particular LAN.

License-free operation: Users would prefer to work over wireless LANs that do not require a license for the frequency band used by the network.

Without intervention/nomadic : The MAC protocol used should allow mobile stations to move from one cell to another.

Dynamic configuration: The MAC addressing and network management aspects of the LAN should allow for dynamic and automatic insertion, removal and movement of end systems without affecting other users.

Wireless Lan Technologies

Wireless LANs are generally classified according to the transmission technique used. The current ones are in the following categories:

Infrared LAN (IR)

A single cell in an IR LAN is limited to a single room since infrared light is not capable of passing through opaque walls.

spread spectrum LAN

In most cases, these LANs operate in the ISM bands, which do not require an FCC license for use in the US. These LANs make use of spread spectrum transmission technology.

narrow band microwave

These LANs operate in the microwave range. some of these products at frequencies where the FCC license is required, and others at some ISM bands.

The table summarizes some of the main characteristics of these three technologies:

Glossary

Ethernet

Ethernet is a 10 to 1000 Mbps network that uses dedicated cables in the home or office. Users must be physically connected to the network at all times in order to access it.

802.1110

The medium access control (MAC) and physical characteristics of wireless local area networks are defined in this standard. The media access control unit of this standard is designed to support physical layer units as they are added according to spectrum availability. This standard includes three physical layer units: two radio units (both operating in the 2400 to 2500 MHz band) and one baseband infrared unit. One of the radio units uses the frequency hopping spread spectrum technique, while the other uses the direct sequence spread spectrum technique.

Cell

A coverage area that encompasses multiple computers provided by the access point. Also called microcell.

Canal

Specifies the default channel (802.11 standard).

direct sequence

It is the method that wireless cards use to transmit data over the frequency spectrum. The other method is frequency hopping. Direct sequence spreads data over a range of frequencies (channel), while frequency hopping switches from one narrow band to another approximately 10 times per second.

PCMCIA

Acronym for the International Personal Computer Memory Card Association. They are also used to designate a physical device that is currently called a PC Card.

roaming

In an infrastructure network, this is when a wireless PC moves out of range of the access point it was previously connected to and communicates through a different access point. By physically distributing access points throughout the network environment, computers can always connect, regardless of where they are located or moved.

Domain

It is one formed by a group of associated stations to establish direct communication.