Rogue access point detection in wireless networks
Methods to detect rogue access points (APs) and prevent unauthorized wireless access to services provided by a communication network are provided. A mobile station (MS) reports to a serving AP the received signal strength (RSS) for all APs in the area it travels. The serving AP detect a rogue AP based on inconsistencies perceived in the RSS reports, assessed during the handover phase or whilst the communication is active.
1. A method for a mobile station (MS) to detect a rogue access point (AP) in a wireless access network containing legitimate APs, comprising:
maintaining at each legitimate AP of said wireless access network, a neighbor database containing AP data for all legitimate APs in a service area;
requesting, from said MS roaming in said service area, a handover from a serving AP to one of a list of candidate APs in said service area;
collecting, at the MS, AP presence information from all of said candidate APs, and reporting said AP presence information to said serving AP;
calculating an effective path loss value for each candidate AP;
determining whether a distance between the MS and a particular candidate AP is known, and, when the distance is known:
calculating an expected path loss value for the particular candidate AP;
comparing the effective oath loss value to the expected path loss value for the particular candidate AP; and
determining that the particular candidate AP is a rogue AP when the effective path loss value and the expected path loss value have a mismatch greater than a threshold when the distance is unknown;
determining, at said serving AP, if said AP presence information is consistent with said AP data maintained at said serving AP;
when said AP presence information and said AP data are inconsistent, randomly removing one candidate AP from the list of candidate APs, and repeating the removal step until the AP presence information is consistent with the AP data maintained at the serving AP; and
identifying the last removed candidate AP as the rogue AP.
2. The method of claim 1 , wherein said AP presence information includes for each candidate AP, a received signal strength (RSS) value associated with a respective AP identification (ID).
3. The method of claim 2 , wherein said AP data includes, for each candidate AP in said service area, an identification (ID) of said respective AP associated with AP location data an effective isotropic radiated power (EIRP) value of said respective AP.
4. The method of claim 3 , further comprising:
calculating the effective path loss value based on the respective RSS and EIRP values for said particular candidate AP.
5. The method of claim 3 , further comprising:
calculating an effective path loss based on the respective RSS and EIRP values for said particular candidate AP; and
estimating the distance between said MS and said particular candidate AP based on the effective path loss.
6. The method of claim 4 , further comprising;
using a scanner to determine the distance.
7. The method of claim 4 , further comprising:
advising said MS to use said particular candidate AP if the expected path loss is consistent with said effective path loss for said particular candidate AP.
8. The method of claim 5 , further comprising: determining if an assumed current location of said MS is consistent with the AP data.
9. The method of claim 5 , further comprising:
estimating the distance of said MS between a minimum distance and a maximum distance.
10. The method of claim 8 , further comprising:
advising said MS to use any of said candidate APs if said assumed current location of said MS is consistent with the AP data.
11. The method of claim 8 , further comprising:
randomly selecting a candidate AP and removing said selected candidate AP from said list;
determining if said estimated distance recalculated without the RSS value for the removed candidate AP is consistent with the AP data; and
advising said MS to use any of said candidate APs except the removed candidate AP if the expected path loss is consistent with said effective path loss.
12. The method of claim 9 , further comprising:
electing a probability that said estimated distance is equal to an actual current distance between said MS and said candidate AP;
calculating said minimum and maximum distance according to said probability and the effective path loss for the candidate AP; and
providing a geometrical representation of said minimum and said maximum distances for all candidate APs.
13. The method of claim 11 , further comprising:
replacing said removed candidate AP with another AP from said list of candidate APs.
14. The method of claim 12 , wherein said geometrical representation comprises a plurality of annuli, wherein each candidate AP is in the center of a respective annulus having radii equal to said minimum and said maximum distances, respectively.
15. The method of claim 12 , wherein said geometrical representation comprises a plurality of disks, wherein each candidate AP is in the center of a respective disk having a radius equal to said maximum distance.
16. The method of claim 12 , wherein said geometrical representation comprises a plurality of sectors, for candidate APs that are equipped with sectorized antennae.
17. The method of claim 12 , further comprising:
determining if said geometrical representation has a non-empty intersection, indicating that it is plausible for the MS to be located within an intersection area.
18. A method for a mobile station (MS) to detect a rogue access point (AP) in a wireless access network, containing legitimate APs, comprising:
maintaining at each legitimate AP of said wireless access network, a neighbor database containing AP data for all legitimate APs in a service area;
collecting, at the MS roaming in said service area, a data set including a received signal strength (RSS) value for a list of candidate APs in said service area, and reporting said data set to a serving AP;
calculating an effective path loss value for each candidate AP;
determining whether a distance between the MS and a particular candidate AP is known, and, when the distance is known:
calculating an expected path loss value for the particular candidate AP;
comparing the effective path loss value to the expected path loss value for the particular candidate AP; and
determining that the particular candidate AP is a rogue AP when the effective path loss value and the expected path loss value have a mismatch greater than a threshold when the distance is unknown:
determining at said serving AP if the RSS value in said data set is consistent with said AP data maintained at said serving AP;
when the RSS value in said data set and said AP data are inconsistent, randomly removing one candidate AP from the list of candidate APs, and repeating the removal step until the AP presence information is consistent with the AP data maintained at the serving AP; and
identifying the last removed candidate AP as the rogue AP.
19. The method of claim 18 , wherein said AP data includes, for each AP in said service area, an identification (ID) of said respective AP, associated with AP location data and an effective isotropic radiated power (EIRP) value of said respective AP.
20. The method of claim 18 , wherein said data set includes for all APs in said service area, an ID of each said AP and the RSS value.
21. The method of claim 18 , further comprising advising said MS to use the candidate AP in said data set if the expected path loss is consistent with said effective path loss value for all said paths.
22. The method of claim 19 , further comprising:
calculating the effective path loss value based on the respective EIRP and RSS values for the particular candidate AP;
estimating the distance between an assumed current location of said MS and the particular candidate AP based on the effective path loss value;
determining if said assumed current location of said MS is consistent with the AP data; and
advising said MS to use the candidate AP if said assumed current location of said MS is consistent with the AP data.