January 23, 2003 Week 3: Day 2
Welcome to Lesson 3 - Networking Media (Cont.)
Remember that the only difference between cabled computers and wireless computers
on a LAN is how they are connected. Wireless users are able to access the network
as if they were physically wired to it.
There are two kinds of wireless networks:
An ad-hoc, or peer-to-peer wireless network consists of a number of computers each equipped with a wireless networking interface card. Each computer can communicate directly with all of the other wireless enabled computers. They can share files and printers this way, but may not be able to access wired LAN resources, unless one of the computers acts as a bridge to the wired LAN using special software. (This is called "bridging")
Figure
1: Ad-Hoc or Peer-to Peer Networking.
Each computer with a wireless interface can communicate directly with all of
the others.
A wireless network can also use an access point, or base station. In this type of network the access point acts like a hub, providing connectivity for the wireless computers. It can connect (or "bridge") the wireless LAN to a wired LAN, allowing wireless computer access to LAN resources, such as file servers or existing Internet Connectivity.
There are two types of access points:
Dedicated
hardware access points (HAP) such as Lucent's WaveLAN, Apple's Airport Base
Station or WebGear's AviatorPRO. Hardware access points offer comprehensive
support of most wireless features, but check your requirements carefully.
Software Access Points which run on a computer equipped with a wireless network interface card as used in an ad-hoc or peer-to-peer wireless network. The Vicomsoft InterGate suites are software routers that can be used as a basic Software Access Point, and include features not commonly found in hardware solutions, such as Direct PPPoE support and extensive configuration flexibility, but may not offer the full range of wireless features defined in the 802.11 standard.
Each access point has a finite range within which a wireless connection can be maintained between the client computer and the access point. The actual distance varies depending upon the environment; manufacturers typically state both indoor and outdoor ranges to give a reasonable indication of reliable performance. Also it should be noted that when operating at the limits of range the performance may drop, as the quality of connection deteriorates and the system compensates.
Typical indoor ranges are 150-300 feet, but can be shorter if the building construction interferes with radio transmissions. Longer ranges are possible, but performance will degrade with distance. Outdoor ranges are quoted up to 1000 feet, but again this depends upon the environment.
A wireless computer can "roam" from one access point to another, with the software and hardware maintaining a steady network connection by monitoring the signal strength from in-range access points and locking on to the one with the best quality. Usually this is completely transparent to the user; they are not aware that a different access point is being used from area to area. Some access point configurations require security authentication when swapping access points, usually in the form of a password dialog box.
Access
points are required to have overlapping wireless areas to achieve this as can
be seen in the following diagram:
The measurement of electronic signals transmitted through the air is the number of cycles per second, or Hertz. This measurement affects the amount of data and the speed at which the data is sent. Generally, lower-frequency transmissions carry data more slowly over longer distances, whereas higher-frequency transmissions carry data more quickly over shorter distances. High frequency technologies often require a clear line of sight between the sender and the receiver.
Click
Here for the MiniLecture on Microwave Telecommunications
Williams Communications Global Interactive Map
I would like to end this lecture with a quick note on Cable Selection Criteria. Remember that there are 7 characteristics on which you would make your selection on what media to use when putting together your network:
Table 3-6 on page 87 is a good comparison table that you should study and remember for a midterm and/or final exam!
Have a good week and we will see you in Lesson 4!