5.7 WLAN Topologies
A WLAN can be configured in several ways:
2. Access point configuration
3. Multiple access points with access points
5.7.1 Peer to Peer
In a Peer to Peer configuration, wireless devices are directly connected to each other as shown in the figure. P2P configurations are often called ad-hoc configurations as they do not require administration or pre-configuration. They also do not use any access points because each of the wireless adapters communicates directly with another adapter without first going to a central location.
P2P networks are very useful when a group of users need to communicate with each other in an unstructured way.
Figure 5.11 Peer-to-Peer Topology
5.7.2 WLAN Configuration with Access Points
P2P networks can be expanded by adding access points (AP – Access Point) to the configuration. Access points can serve as signal signals between devices thus expanding the coverage area.
Figure 5.12 Configuring an access point WLAN
In an office or home environment, access points can be used to enable multiple users to access the same fast connection without having to plug in any computer. In a corporate environment, several access points can work together to provide wireless coverage for the entire building. The coverage area of an access point is called a microcell. To provide coverage in large spaces, microcells can intersect with each other, allowing users to move freely from one cell to another without disconnecting. The movement from the coverage area of one access point to one coverage area of another access point is called roaming. Roaming is enabled by a relay mechanism (hand off) according to which one access point passes to the next point the information for the client. The whole process is invisible to the client. For example, the following figure shows the plan of a floor and how wireless coverage can be created for it.
Figure 5.13 Plan of a floor with WLAN coverage
Figure 5.14 example of an access point WLAN network
5.7.3 Multiple access points
In more advanced configurations access points can be used to connect wireless networks to cable networks as in Figure 5.15. In addition to access points, extension points (EPs) are used, which connect several access points. These devices expand the network coverage area by sending signals to client devices, other EPs or access points. These do not need to be connected to cable networks. Another WLAN device is the steering antenna. These types of antennas amplify the signal and send it several miles away. At the destination the antenna connects to an access point which creates WLAN connection to the rest of the network.
Figure 5.15 Multiple infrastructure with access points
5.8 Wireless personal area network (WPAN)
The market for personal wireless networks is expanding very quickly. People today use many more electronic devices in offices, homes and public spaces and consequently the need for communication between them arises. Examples of devices that need to be connected are desktop computers, laptops, printers, microphones, boxes, cell phones, barcode readers and sensors. Connecting such devices can be difficult if classic cable methods are used, moreover, it is not at all comfortable even if the devices do not need to be moved. If mobility comes into play, the issue becomes even more challenging. The above issue is a good excuse to use WPAN technology. The main features of a WPAN are:
• Short distance communication.
• Low power consumption.
• Low cost.
• Small personal nets.
To have these features a WPAN must achieve two main goals:
• wide application in the market and
• interaction between devices.
The three current WPAN standards are IrDA, Bluetooth and IEEE 802.15. All three standards enable the creation of ad-hoc networks between devices.
IrDA (Infrared Data Association) is an international organization that creates and promotes infrared data communication standards. IrDA has a set of protocols that support a wide range of applications and devices.
IrDA protocols use IrDA DATA as the sending / receiving mechanism and IrDA CONTROL as the control mechanism.
The qualities of infrared communication are:
. Communication range up to one meter, although a distance of 2m can often be reached.
. Low power consumption option up to 20cm. It consumes 10 times less energy than full implementation.
. Two-way communication.
. Data transmission at speeds from 9600 bps to 4Mbps.
Theoretically using Ir for data transfer is a good idea. Unfortunately this type of communication is not widely used for real purposes. This is due to the technical challenges that accompany Ir. For two devices to communicate with infrared they must have a straight line of sight with each other and not have physical barriers between them. In many office environments this restriction is not practical for many peripherals such as printers or scanners.
Application is most common on smaller, mobile devices. For this reason most desktop computers do not have infrared devices. However, there are some areas where infrared rays are used very often. The IrDA CONTROL standard allows wireless peripherals such as keyboards, mouse and marking devices to interact wirelessly with devices.