Seamless handoff for a wireless lan/wired lan internetworking

• US 5,875,185 A
• Filed: 10/10/1995
• Issued: 02/23/1999
• Est. Priority Date: 10/10/1995
• Status: Expired due to Term

• Current Assignee: A10 Networks Incorporated
• Original Assignee: Industrial Technology Research Institute
• Inventors: Wang, Yao-Tzung, Huang, Nen-Fu, Lin, Tzung-Pao
• Primary Examiner(s): VU, HUY DUY
• Application Number:
  US08/544,386
• Time in Patent Office: 1,232 Days
• Field of Search: 370/310, 370/313, 370/315, 370/328, 370/338, 370/331, 370/352, 370/353, 370/354, 370/355, 370/356, 370/362, 370/357, 370/386, 370/389, 370/392, 370/395, 370/396, 370/397 , 370/400, 370/401, 370/402, 370/409, 370/384, 370/351, 370/360, 455/33.2, 455/54.1, 455/54.2, 455/56.1, 455/432, 455/433, 455/436, 455/437, 455/438, 455/439, 455/440, 455/442, 455/443, 455/444, 455/445, 379/58, 379/59, 379/60, 340/826, 340/827
• US Class Current: 370/331
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection
• CPC Class Codes: H04W 40/36 due to handover
• CPC Class Codes: H04W 8/24 Transfer of terminal data
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]
• CPC Class Codes: H04W 88/08 Access point devices
• CPC Class Codes: H04W 92/02 Inter-networking arrangements

Abstract

An exclusive VCC is maintained between each two communicating work stations (MT pair). The handoff method differs if the MT moves to a coverage area having a base station connected to the same switch as the previous coverage area (intra-switch mobility) or to a coverage area having a base station connected to a different switch than the previous coverage area (inter-switch mobility). In intra-switch mobility, the switch changes the path directly to the new base station and eliminates the path through the original base station. In inter-switch mobility, the switch performs the path set-up. The path may be elongated from the switch connected to the original BS, to the new BS, rather than from the original BS to the new BS. This eliminates the path through the original base station. The exclusive VCC between the MT pair permits path elongation to be minimized.

Claims

1. A handoff method for a wireless local area network servicing at least two mobile terminals, when a first mobile terminal moves from a first coverage area covered by a first base station connected to a switch to a second coverage area covered by a second base station connected to the same switch, the method comprising the steps of:

a. the first mobile terminal issuing to the first base station a location message containing the location of the second base station;

b. the first mobile terminal issuing to the second base station a connection message containing virtual channel connections for the first mobile terminal;

c. the first base station issuing a routing message containing the location of the first and second base stations and the virtual channel connections for the first mobile terminal;

d. the switch altering the virtual channel connections for the first mobile terminal to reflect the move to the second coverage area; and

e. the switch issuing to the second base station a complete message containing the altered virtual channel connections for the first mobile terminal.

2. The method of claim 1, wherein the step of altering comprises eliminating the first base station from the virtual channel connection.

3. A handoff method for a wireless local area network servicing at least two mobile terminals, when a first mobile terminal moves from a first coverage area covered by a first base station connected to a first switch to a second coverage area covered by a second base station connected to a second switch, the first and second switches connected by a local area network, the method comprising the steps of:

a. the first mobile terminal issuing to the first base station a location message containing the location of the second base station;

b. the first mobile terminal issuing to the second base station a connection message containing virtual channel connections for the first mobile terminal;

c. the first base station issuing a routing message containing the location of the first and second base stations and the virtual channel connections for the first mobile terminal;

d. the first switch issuing, via the second switch, to the second base station a couple message containing the virtual channel connections for the first mobile terminal; and

e. the first switch updating the virtual channel connections for the first mobile terminal to reflect the move to the second coverage area.

4. The method of claim 3, further comprising the step of after issuing the routing message, establishing a switched virtual connection to the second base station.

5. The method of claim 3, wherein before the step of issuing the couple message:

a. determining if a loop exists in the first switch; and

b. if a loop is determined to exist, eliminating the loop.

6. The method of claim 5, wherein the steps of determining and eliminating are performed for a plurality of switches.

7. A handoff method for a wireless local area network servicing at least two mobile terminals, and having at least two base stations and at least two switches;

each mobile terminal being in wireless communication with a base station covering a coverage area, each base station being connected to a switch, and the switches being connected by a wired local area network (LAN), the method comprising the steps of;

a. designating a virtual channel connection (VCC) between a first and a second mobile terminal; and

b. altering the VCC between the first and second mobile terminals when the second mobile terminal moves from a first base station to a second base station, where;

(1) if the first and second base stations are connected to the same switch, altering the VCC in the first switch, deleting the VCC in the first base station, and adding the altered VCC in the second base station; and

(2) if the first and second base stations are connected to a first and a second switch, respectively, establishing an elongated path by;

1. creating a switched virtual connection (SVC) from the first base station to the second base station via the first and second switches;

2. deleting the VCC in the first base station,

3. after deleting the VCC in the first base station, determining if a loop exists in a switch in the SVC;

4. if a loop is determined to exist in a switch, eliminating the loop;

5. altering the VCC to delete the eliminated loop; and

6. sending to the second base station a couple message containing the VCC for the second mobile terminal.

8. The method of claim 7, wherein steps 3-5 are repeated for a plurality of switches.