Wireless FAQ
General FAQ
Advanced FAQ
Security FAQ
Basic FAQ
1. What is a Wireless LAN ?
Wireless LANs
provide all the functionality of wired LANs, without the need for physical
connections (wires). Data is modulated onto a radio frequency carrier and
transmitted through the ether. Typical bit-rates are 11Mbps and 54Mbps,
although in practice data throughput is half of this. Wireless LANs can be
formed simply by equipping PC's with wireless NICs. If connectivity
to a wired LAN is required an Access Point (AP) is used as a bridging device.
AP's are typically located close to the centre of the wireless client
population.
2. What
are the advantages of Wireless LANs ?
a.
Mobility:
Wireless LAN systems can provide LAN users with
access to real-time information anywhere in their organization. This mobility
supports productivity and service opportunities not possible with wired
networks.
b. Installation Speed and
Simplicity:
Installing a wireless LAN system can be fast and
easy and can eliminate the need to pull cable through walls and ceilings.
c. Installation Flexibility:
Wireless technology allows the network to go where
wire cannot go.
d. Reduced Cost-of-Ownership:
While the initial investment required for wireless
LAN hardware can be higher than the cost of wired LAN hardware, overall
installation expenses and life-cycle costs can be significantly lower.
Long-term cost benefits are greatest in dynamic environments requiring frequent
moves and changes.
e. Scalability:
Wireless LAN systems can be configured in a variety of topologies to
meet the needs of specific applications and installations. Configurations are
easily changed and range from peer-to-peer networks suitable for a small number
of users to full infrastructure networks of thousands of users that enable roaming
over a broad area.
3. What
are the disadvantages of Wireless LANs ?
The speed of Wireless LAN is still relative slower
than wired LAN. The most popular wired LAN is operated in 100Mbps, which is
almost 10 times of that of Wireless LAN (10Mbps). A faster wired LAN standard
(1000Mbps), which is 100 times faster, becomes popular as well. The setup cost
of Wireless LAN is relative high because the equipment cost including access
point and PCMCIA Wireless LAN card is higher than hubs and CAT 5 cables.
4. Where can you find wireless 802.11 networks ?
Airports,
hotels, and even coffee shops like Starbucks are deploying 802.11 networks so
people can wirelessly browse the Internet with their laptops. As these types of
networks increase, this will create additional security risk for the remote
user if not properly protected.
5. What is an Access Point ?
The AP (access point also known as a base station) is the wireless server that
with an antenna and a wired Ethernet connection that broadcasts information
using radio signals. AP typically act as
a bridge for the clients. It can pass information to wireless LAN cards that
have been installed in computers or laptops allowing those computers to connect
to the campus network and the Internet without wires.
6. What is IEEE 802.11 ?
The IEEE 802.11 is a wireless LAN industry
standard, and the objective of IEEE 802.11 is to make sure that different
manufactures' wireless LAN devices can communicate to each other.802.11
provides 1 or 2 Mbps transmission in the 2.4 GHz ISM band using either FHSS or
DSSS.
7. What is 802.11b ?
802.11b is the first revision of 802.11 standard allowing data
rates up to 11Mbps in the 2.4GHz ISM band. Also known as 802.11 High-Rate and
Wi-Fi. 802.11b only uses DSSS, the maximum speed of 11Mbps has fallbacks to
5.5, 2 and 1Mbps.
8. How fast is 802.11b ?
The IEEE
802.11b standard has a nominal speed of 11 megabits per second (Mbps). However,
depending on signal quality and how many other people are using the wireless
ethernet through a particular Access Point, usable speed will be much less (on
the order of 4 or 5 Mbps, which is still substantially faster than most dialup,
cable and DSL modems).
9. What is 802.11a ?
802.11a the second revision of 802.11 that operates in the unlicensed 5 GHz
band and allows transmission rates of up to 54Mbps. 802.11a uses OFDM
(orthogonal frequency division multiplexing) as opposed to FHSS or DSSS. Higher
data rates are possible by combining channels. Due to higher frequency, range
is less than lower frequency systems (i.e., 802.11b and 802.11g) and can
increase the cost of the overall solution because a greater number of access
points may be required. 802.11a is not directly compatible with 802.11b or
802.11g networks. In other words, a user equipped with an 802.11b or 802.11g
radio card will not be able to interface directly to an 802.11a access point.
Multi-mode NICs will solve this problem.
10. What is 802.11g ?
802.11g is an extension to 802.11b.
802.11g increases 802.11b's data rates to 54 Mbps and still utilize the
the 2.4 GHz ISM. Modulation is based upon OFDM (orthogonal frequency division
multiplexing) technology. An 802.11b radio card will interface directly with an
802.11g access point (and vice versa) at 11 Mbps or lower depending on range.
The range at 54 Mbps is less than for 802.11b operating at 11 Mbps.
11. Is
it possible to use products from a variety of vendors ?
Yes. As long as the products comply to the same IEEE 802.11 standard.
The Wi-Fi logo is used to define 802.11b compatible products. Wi-Fi5 is a
compatibility standard for 802.11a products running in the 5GHz band.
12. What is Wi-Fi ?
The Wi-Fi logo signifies that a product is interoperable with wireless
networking equipment from other vendors. A Wi-Fi logo product has been tested
and certified by the Wireless Ethernet Compatibility Alliance (WECA). The
Socket Wireless LAN Card is Wi-Fi certified, and that means that it will work
(interoperate) with any brand of Access Point that is also Wi-Fi certified.
13. What types of devices
use the 2.4GHz Band ?
Various spread spectrum radio communication applications use the 2.4 GHz
band. This includes WLAN systems (not necessarily of the type IEEE 802.11b), cordless phones, wireless medical telemetry
equipment and Bluetooth™ short-range wireless applications, which include
connecting printers to computers and connecting modems or hands-free kits to
mobile phones.
14. Does the 802.11
interfere with Bluetooth devices ?
Any time devices are operated in the same frequency
band, there is the potential for interference.
Both the 802.11b and Bluetooth devices occupy the same2.4-to-2.483-GHz
unlicensed frequency range-the same band. But a Bluetooth device would not
interfere with other 802.11 devices much more than another 802.11 device would
interefere. While more collisions are possible with the introduction of a
Bluetooth device, they are also possible with the introduction of another
802.11 device, or a new 2.4 GHz cordless phone for that matter. But, BlueTooth
devices are usually low-power, so the effects that a Bluetooth device may have
on an 802.11 network, if any, aren't far-reaching.
15. Can radio signals pass
through walls ?
Transmitting through a wall is possible depending upon the material used in its
construction. In general, metals and substances with a high water content do
not allow radio waves to pass through. Metals reflect radio waves and concrete
attenuates radio waves. The amount of attenuation suffered in passing through
concrete will be a function of its thickness and amount of metal re-enforcement
used.
16.
What
are potential factors that may causes interference among WLAN products ?
Factors of
interference:
1. Obstacles: walls, ceilings, furniture… etc.
2. Building Materials: metal door, aluminum studs.
3. Electrical devices: microwaves, monitors, electric motors.
Solution :
1.Minimizing the number of walls and ceilings
2.Antenna is positioned for best reception
3.Keep WLAN products away from electrical devices, eg: microwaves, monitors,
electric motors,…, etc.
4. Add additional APs if necessary.
17. What's the difference
between a WLAN and a WWAN ?
WLANs are generally
privately owned, wireless systems that are deployed in a corporation,
warehouse, hospital, or educational campus setting. Data rates are high and
there are no per-packet charges for data transmission.
WWANs are generally publicly shared data networks designed to provide coverage
in metropolitan areas and along traffic corridors. WWANs are owned by a service
provider or carrier. Data rates are low and charges are based on usage.
Specialized applications are characteristically designed around short, burst
messaging.
Advanced FAQ
1. What is Ad Hoc
mode ?
A wireless network
consists of a number of stations without access points. Without using an access
point or any connection to a wired network.
2. What is Infrastructure
mode ?
Infrastructure mode
implies connectivity to a wired communications infrastructure. If such
connectivity is required the Access Points must be used to connected to the
wired LAN backbone. Wireless clients have their configurations set for
"infrastructure mode" in order to utilize access points
relaying.
3. How many
Access Points are required in a given area ?
This depends on the
surrounding terrain, the diameter of the client population, and the number of
clients. If an area is large with dispersed pockets of populations then
extension points can be used for extend coverage.
4. What is
Direct-Sequence Spread Spectrum Technology – (DSSS) ?
DSSS spreads its
signal continuously over a wide frequency band. DSSS maps the information
bearing bit-pattern at the sending station into a higher data rate bit sequence
using a "chipping" code. The chipping code (also known as processing
gain) introduces redundancy which allows data recovery if certain bit errors
occur during transmission. The FCC rules the minimum processing gain should be
10, typical systems use processing gains of 20. IEEE 802.11b specifies the use
of DSSS.
5. What is Frequency-hopping Spread Spectrum
Technology – (FHSS) ?
FHSS uses a narrowband carrier which hops
through a predefined sequence of several frequencies at a specific rate. This
avoids problems with fixed channel narrowband noise and simple jamming. Both
transmitter and receiver must have their hopping sequences synchronized to
create the effect of a single "logical channel". To an unsynchronised
receivers an FHSS transmission appears to be short-duration impulse noise.
802.11 may use FHSS or DSSS.
6. Do I
need the same kind of antenna on both sides of a link ?
No. Provided the
antenna is optimally designed for 2.4GHz or 5GHz operation. WLAN NICs often
include an internal antenna which may provide sufficient reception.
7. Why the
2.4 Ghz Frequency range ?
This frequency range
has been set aside by the FCC, and is generally labeled the ISM band. A few
years ago Apple and several other large corporations requested that the FCC
allow the development of wireless networks within this frequency range. What we
have today is a protocol and system that allows for unlicensed use of radios
within a prescribed power level. The ISM band is populated by Industrial,
Scientific and Medical devices that are all low power devices, but can
interfere with each other.
8. What is Server Set ID (SSID) ?
SSID is a
configurable identification that allows clients to communicate to the
appropriate base station. With proper configuration, only clients that are
configured with the same SSID can communicate with base stations having the
same SSID. SSID from a security point of view acts as a simple single shared
password between base stations and clients.
9. What is an ESSID
?
ESSID stands for
Extended Service Set Identifier and identifies the wireless LAN. The ESSID of
the mobile device must match the ESSID of the AP to communicate with the AP.
The ESSID is a 32-character maximum string and is case-sensitive.
Security FAQ
1. How do I
secure the data across an Access Point's radio link ?
Enable Wired
Equivalency Protocol (WEP) to encrypt the payload of packets sent across a
radio link.
2. What is WEP ?
Wired Equivalent
Privacy. WEP is a security mechanism defined within the 802.11 standard and
designed to make the security of the wireless medium equal to that of a cable
(wire). WEP data encryption was designed to prevent access to the network by
"intruders" and to prevent the capture of wireless LAN traffic
through eavesdropping. WEP allows the administrator to define a set of
respective "Keys" for each wireless network user based on a "Key
String" passed through the WEP encryption algorithm. Access is denied by
anyone who does not have an assigned key. WEP comes in 40/64-bit and 128-bit
encryption key lengths. Note, WEP has shown to have fundamental flaws in its
key generation processing.
3. What is the difference between 40-bit and 64-bit
WEP ?
40 bit WEP & 64
bit WEP are the same encryption level and can interoperate. The lower level of
WEP encryption uses a 40 bit (10 Hex character) as "secret key" (set
by user), and a 24 bit " Initialization Vector " (not under user control)
(40+24=64). Some vendors refer to this level of WEP as 40 bit, others as 64
bit.
4. What is a WEP key ?
A WEP key is a user defined string of
characters used to encrypt and decrypt data.
5. A WEP key is a user defined string of characters used to encrypt and
decrypt data ?
No. 128-bit WEP will
not communicate with 64-bit WEP. Although 128 bit WEP also uses a 24 bit
Initialization Vector, but it uses a 104 bit as secret key. Users need to use
the same encryption level in order to make a connection.
6. Can the SSID be encrypted ?
WEP, the encryption
standard for 802.11, only encrypts the data packets not the 802.11 management
packets and the SSID is in the beacon and probe management messages. The SSID
is not encrypted if WEP is turned on. The SSID goes over the air in clear text.
This makes obtaining the SSID easy by sniffing 802.11 wireless traffic.
7. By
turning off the broadcast of SSID, can someone still sniff the SSID ?
Many APs by default have broadcasting the
SSID turned on. Sniffers typically will find the SSID in the broadcast beacon
packets. Turning off the broadcast of SSID in the beacon message (a common
practice) does not prevent getting the SSID; since the SSID is sent in the
clear in the probe message when a client associates to an AP, a sniffer just
has to wait for a valid user to associate to the network to see the SSID.
8. What are Insertion Attacks ?
The insertion attacks are based on placing unauthorized devices on the
wireless network without going through a security process and review.
9. What is Wireless Sniffer ?
An attacker can sniff and capture
legitimate traffic. Many of the sniffer tools for Ethernet are based on
capturing the first part of the connection session, where the data would
typically include the username and password. An intruder can masquerade as that
user by using this captured information. An intruder who monitors the wireless
network can apply this same attack principle on the wireless.
10. What is the difference between
Open System and Shared Key of Authentication Type ?
Open System:
The default
authentication service that simply announces the desire to associate with
another station or access point. A station can authenticate with any other
station or access point using open system authentication if the receiving station
designates open system authentication.
Share Key:
The optional authentication that involves a more rigorous exchange of
frames, ensuring that the requesting station is authentic. For a station to use
shared key authentication, it must implement WEP.
11. What is 802.1x ?
IEEE 802.1x
Port-Based Network Access Control is an IEEE (Institute of Electrical and
Electronics Engineers) standard, which specifies a standard mechanism for
authenticating, at the link layer (Layer 2), users' access to IEEE 802 networks
such as Ethernet (IEEE 802.3) and Wireless LAN (IEEE 802.11). For IEEE 802.11
WLAN, IEEE 802.1x authentication can be based on username/password or digital
certificate.
12. What is the difference between force-authorized, force-unauthorized and auto ?
force-authorized—disables 802.1X and causes the
port to transition to the authorized state without any authentication exchange
required. The port transmits and receives normal traffic without 802.1X-based
authentication of the client.
force-unauthorized—causes the port to remain in the unauthorized state,
ignoring all attempts by the client to authenticate. The switch cannot provide
authentication services to the client through the interface.
auto—enables 802.1X and causes the port to begin in the unauthorized state,
allowing only EAPOL frames to be sent and received through the port. The
authentication process begins when the link state of the port transitions from
down to up, or when an EAPOL-start frame is received. The switch requests the
identity of the client and begins relaying authentication messages between the
client and the authentication server. Each client attempting to access the
network is uniquely identified by the switch by using the client's MAC address.
13. What is AAA ?
AAA is the acronym for Authentication, Authorization,
and Accounting and refers to the idea of managing subscribers by controlling
their access to the network, verifying that they are who they say they are (via
login name and password or MAC address) and accounting for their network usage.
14. What is RADIUS ?
RADIUS stands for Remote Authentication Dial-In User
Service. RADIUS is a standard that has been implemented into several software
packages and networking devices. It allows user information to be sent to a
central database running on a RADIUS Server, where it is verified. RADIUS also
provides a mechanism for accounting.
All contents copyright © 2006 ZyXEL Communications Corporation.