HISTORY OF WIFI PART 2
WLAN with RF has some topology as follows
1. Centralized
The other name is a star network or hub based. This topology consists of the server (c) and some user terminals, where communication between terminals must go through the server first. The advantages are wide coverage area, relatively efficient transmission, and user terminal design is quite simple because of the complexity there is on the server. The weakness is the delay is large and if the server is damaged then the network can not work.
 |
| Image: Star Topology on WLAN |
2. Distributed
It can be called peer to peer, where all terminals can communicate with each other without the need for a server. Here, the server is required to connect the WLAN to another LAN. This topology can support mobile operators and is an ideal solution for ad hoc networks. The advantage if one terminal is broken then the network remains functioning, the delay is small and the complexity of planning is minimal. The disadvantage is that it does not have a network control unit (power control, access, and timing).
 |
| Image: Peer to peer topology |
3. Cellular network
This network is suitable to serve areas with wide coverage and mobile operation. This network utilizes the concept of the microcell, frequency reuse techniques, and handover techniques. The advantage is to combine the advantages and remove the weaknesses of the two topologies above. The disadvantage is that it has a high planning complexity.
 |
| Image: Mobile network topology |
4. Wireless LAN Components
4.1. Access Point (AP)
In WLAN, a tool for transmitting data is called an Access Point and connected to a LAN network via cable. The function of the AP is to send and receive data, as a data buffer between WLAN and Wired LAN, convert radio frequency (RF) signals into digital signals to be transmitted via cable or other WLAN devices transmitted by converted into radio frequency signals.
One AP can serve a number of users up to 30 users. Because with the increasing number of users connected to the AP then the speed obtained by each user will also be reduced. Here are some examples of AP products from some vendors.
Figure: Access Point from Linksys product, Symaster, Dlink
4.2 Extension Point
To solve specific problems in network topology, designers can add extension points to expand network coverage. Extension points work just like repeaters for clients in more remote places. Terms that between access points can communicate with each other, the channel settings in each AP must be the same. Additionally, the SSID (Service Set Identifier) used should also be the same. In practice in the field usually, for application extension point should be done by using the same AP brand.
Figure: Network using Extension Point
4.3 Antenna
The antenna is a tool to transform radio signals propagating to a conductor into electromagnetic waves propagating in the air. The antenna has resonance properties so the antenna will operate in a certain area.There are several types of antennas that can support WLAN implementations:
1. Omnidirectional gb2 antenna
That is the type of antenna that has a signaling pattern in all directions with the same power. To generate a large area coverage, the gain of the omnidirectional antenna should focus its power horizontally, regardless of the upward and downward be transmitting patterns, so that the antenna can be placed in the center of the base station. Thus the advantage of this type of antenna is that it can serve a larger number of users.However, the difficulty is in allocating frequencies for each cell to avoid interference
 |
| Image: Omnidirectional Antenna area coverage |
2. Directional antenna
Namely, the antenna that has a signal transmission pattern in one particular direction. This antenna is ideally used as a liaison between buildings or for areas that have small area coverage configurations such as in long hallways.
4.4 Wireless LAN Card
WLAN Card can be PCMCIA (Personal Computer Memory Card International Association), ISA Card, USB Card or Ethernet Card. PCMCIA is used for notebooks, while others are used on desktop computers.WLAN Card serves as an interface between the client network operating a system with air interface format to the AP. The special notebook that the latest output WLAN Cardnya already integrated into it. So it is not plasticity from outside.
 |
| Image: Wireless LAN Card |
Pros and Cons of Wireless LAN implementation
Advantages:
* Mobility and Higher Productivity, WLAN allows clients to access information in real-time as long as it is within WLAN coverage, thereby enhancing service quality and productivity. Users can work wherever they are from where they are located in the WLAN coverage area.
* Ease and speed of installation, because the infrastructure does not require cables then the installation is very easy and fast to implement, without the need to pull or install cable on the wall or floor.
* Flexible, with WLAN technology it is possible to build networks in areas that are impossible or difficult to reach by cables, for example in big cities, where cable infrastructure is not available.
* Lowering the cost of ownership, with one access point can already cover the entire area and maintenance costs cheap (only includes cell stations instead of as on the cable network covering the entire cable)
Weakness:
* Cost of expensive equipment (this weakness can be eliminated by developing and producing electronic component technology so as to reduce network costs),
* Large delay, the existence of radio propagation problems such as blocked, reflected and many sources of interference (this weakness can be overcome with modulation techniques, antenna diversity techniques, spread spectrum techniques etc.),
* The capacity of the network faces the limitations of the spectrum (the band cannot be widened but can be efficiently utilized with the help of various techniques such as spread spectrum / DS-CDMA) and data security (confidentiality) less assured (this weakness can be overcome for example with spread spectrum techniques)Click here to open HISTORY OF WIFI PART 1
Source: Internet