another newbie WLAN question (access points)

wild_eyed

access points

what things must you consider before installing multiple access points in a large room / warehous sort-a-thing

zAbbo

nodes per AP

Ap channels

Wep Encryption

AP Placement(centralised)

//is this a exam question?

wild_eyed

its a small 5 marker. not in notes.

zAbbo

ohh the sneaky russian.

The main thing here is which channel they are operating on, and weither the 2 AP`s are to be directly connected, or connected via the wired network backbone

# Range and Coverage
Since wireless LAN is a radio based technology, connectivity and throughput performance between devices diminishes with increased distance (range) between devices. Additionally, obstructions such as walls and furniture will cause signal reflections. This phenomenon is known as multipath fading. The consequence of multipath fading is that areas in the LAN could become “dead spots” or “nulls” for the radio signal. As the transmitted radio signal reflects, it can behave in an additive fashion (known as “constructive interference”) or in a subtractive fashion (known as “destructive interference”) at the receiving device. This could be imagined as waves in a pool of water where “peaks” are additive and “troughs” are subtractive. Troughs will be prone to exhibiting dead spot characteristics. Dead spots in the wireless LAN cause coverage in the building to be inconsistent. Although dead spots are difficult to predict they can be compensated for by physically moving the wireless equipment (usually dead spots are small and highly localized) or by re-orienting the device’s antenna (if possible). Higher quality wireless LAN equipment will implement a receiver function known as an “equalizer” which is designed to compensate for multipath effects. In addition to an equalizer, a technique known as antenna diversity is necessary to mitigate the effect of dead spots. In summary, the effects of multipath are well understood and easily overcome even if the location of dead spots is highly dependent upon both site characteristics and equipment placement.

# Throughput (data rate) vs. connection reliability

Wireless LAN technology is designed to make maintaining a connection between two devices as reliable and consistent as possible. Since the speed of the connection between wireless devices will vary as range and signal quality varies, the wireless devices will intentionally sacrifice throughput (data rate or connection speed as measured in bits per second) in exchange for maintaining a reliable connection. In other words, a reliable connection at a lower speed is preferred over an unreliable connection at a higher speed (i.e., it is easier to maintain the connection if data rate is deliberately reduced, or put another way, lower data rates will tolerate a higher range and/or worse signal quality). This characteristic is known as fallback. As example, an 802.11b system will fallback from 11 Mbps to 5.5 Mbps as range increases or signal quality decreases. Subsequent fallbacks from 5.5 Mbps to 2 Mbps and 1 Mbps are also supported. Wireless LAN devices requiring higher performance should be placed closer to one another.

# Interference and coexistence

802.11b operates in a range of radio frequencies known as an “unlicensed” band (i.e. the FCC does NOT require the use of a license in order to operate a radio transmitter in this range). This means that commercially available radio devices other than wireless LAN devices are permitted to use the same frequency band as 802.11b. Consequently, these co-existing radio devices can interfere or “jam” the wireless LAN (and vice versa). Ironically, the most troublesome devices are cordless telephones and microwave ovens.

Fortunately, higher quality cordless phones tend to “listen” for a clear channel before becoming active and will thus avoid interfering with a wireless LAN (i.e., the cordless phone seeks a clear channel for itself so naturally avoids being interfered with or being a source of interference).

Jamming from microwave ovens is more severe but is usually restricted to the upper frequency range for 802.11b (it should be noted that 802.11b divides the available frequency band into 11 channels. The higher numbered channels are most susceptible to microwave oven interference). In each instance, jamming occurs only when the cordless telephone or microwave oven is active.

# Security

Much has been publicized in the mass media recently about security problems with wireless LANs. Although it cannot be denied that the encryption algorithms currently used in 802.11 are flawed, the fact is that security breaches of a wireless LAN require a deliberate attempt to access the network by an intruder. The primary issue is that many current users of wireless LAN have opted NOT to turn on security features. If users were to enable the security features currently available (including only allowing known systems access to the network and enabling WEP aka Wired Equivalent Privacy encryption) the intruder’s work is much harder. Much as a burglar will bypass a house whose doors and windows are securely locked, so too will a hacker tend to bypass a network where security measures are enabled.

Capt'n Midnight

If it was for the real world rather than an exam you'd have to take into account the different radiation limits in different licencing areas.

For 5GHz equipment the allowed frequencies are also different. And for external use of 5GHz in this country you have to register with Comreg.

etc. etc.