Simultaneous association with more than one ESS in WLAN environment
Original Publication Date: 2003-Jul-17
Included in the Prior Art Database: 2003-Jul-17
AbstractA method to provide extended mobility is presented for an end unit in WLAN or WLAN – like environment.
association with more than one ESS in WLAN environment
By Baruh Hason
A method to provide extended mobility is presented for an end unit in WLAN or WLAN – like environment.
Present protocol specifications related to WLAN (Wireless Local Area Network) do not provide mobility, as it is customary in the wireless/cellular communication world. The specifications in 802.11 identify three sorts of transitions:
· No transition,
· BSS (Basic Service Set)-transition and
· ESS (Extended Service Set)-transition.
While the first two can be achieved by the services defined by 802.11, the third, which represents the mobility as in the cellular communication, is left outside the scope of this standard. A wireless end unit (EU) moving from the coverage area of one ESS to the coverage area of another ESS, very probably, will experience a disruption or disconnection in an ongoing communication session – conducted with other peer EU(s). Connections at two levels should be reestablished during this transition: AP (Access Point) association and IP subnet membership of the EU (only if the two ESS belong to separate IP subnets). During the course of the transition, when the association with the older ESS is broken the ability of conducting upper layer message exchange using the old IP address is inhibited as well. As a result the ongoing session not only is broken but also cannot contribute to any network or application layer handover procedure.
If the coverage areas of the two ESS have an overlapping region there is no reason in breaking the AP association with the old ESS before making a new AP association with the new ESS. If the AP association to both ESS can be maintained for a period of time, which will enable an upper layer handover procedure, then the possibility of maintaining the continuation of an upper layer session is also gained.
Problem To Be Solved
We would like to provide a mechanism, which will allow some sort of communication continuity for protocol layers above the link layer in WLAN environment. Using the terms used in WLAN standards we would like to provide a mechanism, which will allow ESS – transition with minimum disruption.
This problem is not relevant in wire-line LAN environments since an end unit, in wire-line LAN, is not expected to move from one LAN segment (in the sense of IP subnet) to another LAN segment while an application using the communication services of the LAN is active. If a wire-line end unit is expected to be active in two IP subnets then it is provided two MAC layer connections with two separate link layer addresses.
In the wireless world the technology known as soft handover enables a mobile station to communicate with more than one base station simultaneously. However, the decision of adding a handover leg is made by a central decision agent. In a broader sense an auxiliary agent is needed...