Wireless FAQ

General FAQ

1. What is a Wireless LAN?
2. What are the main advantages of Wireless LANs?
3. What are the disadvantages of Wireless LANs?
4. Where can you find wireless 802.11 networks?
5. What is an Access Point?
6. What is IEEE 802.11?
7. What is IEEE 802.11b?
8. How fast is 802.11b?
9. What is IEEE 802.11a?
10. What is IEEE 802.11g?
11. Is it possible to use products from a variety of vendors ?
12. What is Wi-Fi?
13. What types of devices use the 2.4GHz Band?
14. Does Bluetooth interfer with wireless 802.11 LAN?
15. Can radio signals pass through walls?
16. What are potential factors that may cause interference among WLAN products?
17. What's the difference between a WLAN and a WWAN?

Advanced FAQ

1. What is Ad Hoc mode ?
2. What is Infrastructure mode?
3. How many Access Points are required in a given area ?
4. What is Direct-Sequence Spread Spectrum Technology – (DSSS) ?
5. What is Frequency-hopping Spread Spectrum Technology – (FHSS) ?
6. Do I need the same kind of antenna on both sides of a link ?
7. Why the 2.4 Ghz Frequency range ?
8. What is Server Set ID (SSID)?
9. What is an ESSID ?

Security FAQ

1. How do I secure the data across an Access Point's radio link?
2. What is WEP?
3. What is the difference between 40-bit and 64-bit WEP ?
4. What is a WEP key?
5. Can 128-bit WEP communicate with 64-bit WEP?
6. Can the SSID be encrypted?
7. By turning off the broadcast of SSID, can someone still sniff the SSID?
8. What are Insertion Attacks?
9. What is Wireless Sniffer?
10. What is the difference between Open System and Shared Key of Authentication Type?
11. What is 802.1x?
12. What is the difference between force-authorized, force-unauthorized and auto?
13. What is AAA?
14. What is RADIUS?
15. What is WPA/WPA2?

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 acts 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 it is known as 802.11 High-Rate and Wi-Fi. 802.11b only uses the 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 utilise 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 connect to the wired LAN backbone. Wireless clients have their configurations set for "infrastructure mode" in order to utilise 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. Can 128-bit WEP communicate with 64-bit WEP?
No. 128-bit WEP can 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.

15. What is WPA/WPA2?

WPA is designed for use with an 802.1X authentication server, which distributes different keys to each user. The Wi-Fi Alliance calls the pre-shared key version WPA-Personal or WPA2-Personal and the 802.1X authentication version WPA-Enterprise or WPA2-Enterprise.

Data is encrypted using the RC4 stream cipher, with a 128-bit key and a 48-bit initialization vector (IV). WPA uses Temporal Key Integrity Protocol (TKIP), which dynamically changes keys as the system is used. When combined with the much larger IV to defeat the well-known key recovery attacks on WEP.

The cyclic redundancy check (CRC) used in WEP is inherently insecure; it is possible to alter the payload and update the message CRC without knowing the WEP key. A more secure message authentication code (usually known as a MAC, but here termed a MIC for "Message Integrity Code") is used in WPA, an algorithm named "Michael". The MIC used in WPA includes a frame counter, which prevents replay attacks being executed; this was another weakness in WEP.

WPA was formulated as an intermediate step towards improved 802.11 security for two reasons: first, 802.11i's work lasted far longer than originally anticipated, spanning four years, during a period of ever-increasing worries about wireless security; second, it encompasses as a subset of 802.11i only elements that were backwards compatible with WEP for even the earliest 802.11b adopters. WPA firmware upgrades have been provided for the vast majority of wireless network interface cards ever shipped; 802.11 access points sold before 2003 generally needed to be replaced.

By increasing the size of the keys and IVs, reducing the number of packets sent with related keys, and adding a secure message verification system, WPA makes breaking into a Wireless LAN far more difficult. The Michael algorithm was the strongest that WPA designers could come up with that would still work with most older network cards; however it is subject to a packet forgery attack. To limit this risk, WPA networks shut down for 60 seconds whenever an attempted attack is detected.

WPA2 is the certified form of IEEE 802.11i tested by the Wi-Fi Alliance. WPA2 implements the mandatory elements of 802.11i. In particular, the Michael algorithm is replaced by a message authentication code, CCMP, that is considered fully secure and RC4 is replaced by AES.

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