Date of Award

8-2001

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Computer Science

Abstract

Computing stations networked on wireless LANs (wLANs) typically have a limited range of mobility: the station must always be within an access point’s coverage area. If a station moves outside of that area, and if it is unable to locate another base station within its range to perform a handover of communication connectivity responsibility, then it will ex perience a disruption in network services until it migrates into the coverage area of another wLAN. Typical causes for such losses of service include station migration to outside of the wLAN’s coverage area, changing environmental conditions, and “holes” within the cumu lative cell coverage area of multiple access points.

There could be several mobile stations simultaneously sharing the network in a wLAN. Each station may be stationary or in motion for part or all of its service life. How ever, in order to use the wLAN, it must be within service range of a access point. Theoreti cally, if a station is outside the access point’s coverage area, yet its own radio signal is within range of one of the stations which has connectivity with an access point, the isolated station could relay its network negotiations and traffic through a relay station which has direct communication with the access point. Therefore, the station nearer to the base sta tion acts as a relay point for the isolated station out of the access point’s range.

In this thesis, the author proposed, the design of a MAC Frame Relaying Protocol Extension which enables this type of dynamic relaying of network frames between stations in wLANs. It requires additional logic in the networking process on both the access point and the stations involved (both relay station and the isolated station) to support the bidirec tional forwarding of network traffic, and the definition of several new message types to support relay connection setup and data exchange. Both cryptography and digital signature concepts are employed to make secure the process of establishing of a relayed network session, and the exchange of data between the end stations.

To verify the validity of the protocol extension and to measure its performance, the protocol extension was implemented into an existing and widely accepted wireless network standard, IEEE 802.11. To study its effectiveness and impact on the wLAN protocol, the network simulation software, OPNET, was used. An existing model of IEEE 802.11 was enhanced with the additional logic introduced by the protocol extension.

Through simulation, it is proved that the logic presented by the protocol extension is able to function. In addition, the impact to overall network performance, and the quality of service the isolated station experiences during a relayed network session were quantita tively analyzed. Through the OPNET simulation, it was found that overall wLAN perfor mance diminished a moderate amount, while the isolated station experienced a far smaller level of throughput when engaged in a relayed network session, than it did in a normal network session.

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