U.S. patent application number 11/790273 was filed with the patent office on 2008-08-14 for fast handover method, apparatus, and medium.
This patent application is currently assigned to Samsung Electronics Co., Ltd.. Invention is credited to Yong-lun Lim, Soo-hong Park.
Application Number | 20080192691 11/790273 |
Document ID | / |
Family ID | 37886053 |
Filed Date | 2008-08-14 |
United States Patent
Application |
20080192691 |
Kind Code |
A1 |
Park; Soo-hong ; et
al. |
August 14, 2008 |
Fast handover method, apparatus, and medium
Abstract
A fast handover apparatus, method, and medium for performing a
fast handover in a wireless LAN environment. The fast handover
method includes (a) determining whether a beacon signal input from
an access point (AP) to a mobile node (MN) contains border
information indicating that the AP is located at the border of its
subnet, the AP connecting the MN to a wired network; and (b)
selectively performing a handover between subnets based on the
determination results obtained in (a). Accordingly, unnecessary
communications between an MN and an AR are prevented by providing
predetermined information, based on which the MN can determine
whether to perform only an L2 handover or both the L2 handover and
an L3 handover.
Inventors: |
Park; Soo-hong; (Yongin-si,
KR) ; Lim; Yong-lun; (Seoul, KR) |
Correspondence
Address: |
STAAS & HALSEY LLP
SUITE 700, 1201 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Assignee: |
Samsung Electronics Co.,
Ltd.
Suwon-si
KR
|
Family ID: |
37886053 |
Appl. No.: |
11/790273 |
Filed: |
April 24, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11079696 |
Mar 14, 2005 |
7196320 |
|
|
11790273 |
|
|
|
|
60552197 |
Mar 12, 2004 |
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Current U.S.
Class: |
370/331 ;
455/436 |
Current CPC
Class: |
G01P 3/486 20130101;
G01D 5/34723 20130101; G01D 5/363 20130101 |
Class at
Publication: |
370/331 ;
455/436 |
International
Class: |
H04Q 7/00 20060101
H04Q007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 9, 2004 |
KR |
2004-24508 |
Claims
1. A repeater, which connects a mobile node and an access router,
periodically broadcasting predetermined information for determining
whether a handover in an IP layer is required to a cell in which
the mobile node belongs.
2. The repeater of claim 1, wherein the predetermined information
indicates that the repeater is located on a border of a subnet
managed by the access router.
3. The repeater of claim 1, wherein the predetermined information
is recorded in a reserved field of a capability information field
of a frame body field of an IEEE 802.11 beacon frame.
4. The repeater of claim 1, wherein the predetermined information
is recorded in a subtype field of a frame control field of an IEEE
802.11 management frame.
5. A recording medium having recorded thereon a frame in which a
repeater, connecting a mobile node and an access router,
periodically broadcasts to a cell in which the mobile node belongs
to, wherein the frame comprises predetermined information for
determining whether the mobile node requires a handover in an IP
layer.
6. The recording medium of claim 5, wherein the predetermined
information indicates that the repeater is located on a border of a
subnet managed by the access router.
7. The recording medium of claim 5, wherein the frame is an
IEEE802.11 beacon frame and the predetermined information is
recorded in a reserved field of a capability information field of a
frame body field of the IEEE 802.11 beacon frame.
8. The recording medium of claim 5, wherein the frame is an IEEE
802.11 management frame and predetermined information is recorded
in a subtype field of a frame control field of the IEEE 802.11
management frame.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This Application claims benefit under 35 U.S.C. .sctn. 120
as a continuation of co-pending application Ser. No. 11/078,696,
filed Mar. 14, 2005, and entitled "FAST HANDOVER METHOD, APPARATUS,
AND MEDIUM", now pending, which is hereby incorporated by reference
in its entirety into this application. This application claims the
benefit of U.S. Provisional Application No. 60/552,197, filed on
Mar. 12, 2004, in the U.S. Patent & Trademark Office, the
disclosure of which is incorporated herein in its entirety by
reference. This application also claims the benefit of Korean
Patent Application No. 10-2004-0024508 filed on Apr. 9, 2004, in
the Korean Intellectual Property Office, the disclosure of which is
incorporated herein in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a handover apparatus and
method that perform a handover in a wireless local area network
(LAN) environment, and more particularly, to a fast handover
apparatus and method that performs a fast handover in an Institute
of Electrical and Electronics Engineers (IEEE) 802.11-based
wireless LAN environment.
[0004] 2. Description of the Related Art
[0005] As the number of subscribers to mobile communication
services rapidly increases, and mobile communication services
become more diversified so that they can provide multimedia
communications, the demand for seamless communications becomes
stronger. Accordingly, the importance of a handover in an IEEE
802.11-based wireless LAN environment also becomes much
stronger.
[0006] FIG. 1 is a diagram illustrating a conventional wireless LAN
environment. Referring to FIG. 1, the conventional wireless LAN
environment includes a mobile node (MN) 1, a first access point
(AP) 21, a second AP 22, a third AP 23, a fourth AP 24, a first
access router (AR) 31, and a second AR 32.
[0007] The conventional wireless LAN environment will be described
in detail in the following supposing that the MN 1 sequentially
passes through a cell managed by the first AP 21, a cell managed by
the second AP 22, a cell managed by the third AP 23, and a cell
managed by the fourth AP 24.
[0008] Each of the first through fourth APs 21 through 24 informs
the MN 1, which is constantly on the move, of which AP the MN 1 can
access a wired network by periodically transmitting a beacon signal
to the MN 1.
[0009] The MN 1 receives a beacon signal from the first AP 21, as
marked by `211`, and then recognizes based on the received beacon
signal that it is currently located within the cell managed by the
first AP 21. Accordingly, the MN 1 can access the wired network via
the first AP 21.
[0010] Thereafter, the MN 1 receives a beacon signal from the
second AP 22, as marked by `221`, and then recognizes based on the
received beacon signal that it has moved from the cell managed by
the first AP 21 to the cell managed by the second AP 22.
Accordingly, the MN 1 performs a handover in a link layer. In other
words, the MN 1 recognizes that it is currently located in the cell
managed by the second AP 22 and switches its link layer's
connection from the first AP 21 to the second AP 22. According to
the open systems interconnection (OSI) reference model, the link
layer corresponds to Layer 2. Thus, the handover performed in the
link layer is called a Layer 2 handover or L2 handover.
Accordingly, the MN 1 can keep accessing the wired network via the
second AP 22.
[0011] Thereafter, the MN 1 transmits information indicating that
it has moved from the first AP 21 to the second AP 22 to the first
AR 31 via the second AP 22, as marked by `222`. Then, the first AR
31 recognizes that the MN 1 has not yet escaped from its subnet
based on the fact that it has received the information from the MN
1 via the second AP 22, rather than via another AR.
[0012] Thereafter, the first AR 31 transmits information indicating
that the MN 1 has not yet escaped from the subnet managed by the
first AR 31 to the MN 1 via the second AP 22, as marked by `223`.
Then, the MN 1 recognizes that it is still located in the subnet
managed by the first AR 31 and determines that there is no need to
generate a new Internet protocol (IP) address for a new subnet.
Accordingly, the MN 1 does not perform a handover in an IP layer.
According to the OSI reference model, the IP layer corresponds to
Layer 3. Thus, the handover performed in the IP layer is called a
Layer 3 handover or L3 handover.
[0013] Thereafter, the MN 1 receives a beacon signal from the
second AP 22, as marked by `224`, and recognizes based on the
received beacon signal that it is still located in the cell managed
by the second AP 22. Accordingly, the MN 1 can keep accessing the
wired network via the second AP 22.
[0014] Thereafter, the MN 1 receives a beacon signal from the third
AP 23, as marked by `231`, and recognizes based on the received
beacon signal that it has moved from the cell managed by the second
AP 22 to the cell managed by the third AP 23. Accordingly, the MN 1
performs a L2 handover. In other words, the MN 1 recognizes that it
is currently located in the cell managed by the third AP 23 and
switches it link layer connection from the second AP 22 to the
third AP 23. Thus, the MN 1 can keep accessing the wired network
via the third AP 23.
[0015] Thereafter, the MN 1 transmits information indicating that
it has moved from the cell managed by the second AP 22 to the cell
managed by the third AP 23 to the first AR 31 via the third access
point 23 and the second AR 32, as marked by `232`. Then, the first
AR 31 recognizes that the MN 1 has escaped from its subnet based on
the fact that it has received the information from the MN 1 via
another AR, i.e., the second AR 32.
[0016] Thereafter, the first AR 31 transmits information indicating
that the MN 1 has escaped from the subnet managed by the first AR
31 to the MN 1 via the second AR 32 and the third AP 23, as marked
by `233`. Then, the MN 1 recognizes that it has escaped from the
subnet managed by the first AR 31 and is currently located in the
subnet managed by the second AR 32. Accordingly, the MN performs a
L3 handover, which will be described in detail in the
following.
[0017] The MN 1 issues a request for a network prefix of the subnet
managed by the second AR 32 to the second AR 32 via the third AP
23, as marked by `234`, in order to generate a new IP address for
the subnet managed by the second AR 32. The MN 1 receives the
network prefix of the subnet managed by the second AR 32 from the
second AR 32 and generates a new IP address based on the received
network prefix. Thereafter, the MN 1 performs communications in the
subnet managed by the second AR 32 using the new IP address.
[0018] Thereafter, the MN 1 receives a beacon signal from the third
AP 23, as marked by `235`, and recognizes based on the received
beacon signal that it is still located in the cell managed by the
third AP 23. Accordingly, the MN 1 can keep accessing the wired
network via the third AP 23.
[0019] Thereafter, the MN 1 receives a beacon signal from the
fourth AP 24, as marked by `241`, and recognizes that it has moved
from the cell managed by the third AP 23 to the cell managed by the
fourth AP 24. Accordingly, the MN 1 performs a L2 handover. In
other words, the MN 1 recognizes that it is currently located in
the cell managed by the fourth AP 24 and switches its link layer
connection from the third AP 23 to the fourth AP 24. Accordingly,
the MN 1 can keep accessing the wired network via the fourth AP
24.
[0020] The MN 1 transmits information indicating that it has moved
from the cell managed by the third AP 23 to the cell managed by the
fourth AP 24 to the second AR 32 via the fourth AP 24, as marked by
`242`. The second AR 32 recognizes that the MN 1 has not yet
escaped from its subnet based on the fact that it has received the
information from the MN 1 via the fourth AP 24, rather than via
another AR.
[0021] Thereafter, the second AR 32 transmits information
indicating that the MN 1 has not yet escaped the subnet managed by
the second AR to the MN 1 via the fourth AP 24, as marked by `243`.
Then, the MN 1 recognizes that it is still located in the subnet
managed by the second AR 32 and determines that there is no need to
generate a new IP address for a new subnet. Accordingly, the MN 1
does not perform a L3 handover.
[0022] As described above, a MN does not know about whether it has
moved from one subnet to another subnet. Thus, in order to obtain
information on whether the MN has moved from one subnet to another
subnet, the MN communicates with an AR. In other words, the MN
communicates with an AR in order to determine whether to perform
only an L2 handover or both the L2 handover and an L3 handover. The
MN obtains predetermined information, based on which it determines
whether to perform only the L2 handover or both of the L2 handover
and the L3 handover, from the AR while communicating with the AR.
However, the communication of the MN with the AR should be
performed through the mediation of an AP whenever the MN moves from
one cell to another cell, which serves as an impediment to the
realization of a fast handover.
SUMMARY OF THE INVENTION
[0023] Embodiments of the present invention provide a fast handover
apparatus, method, and medium which prevent unnecessary
communications between an MN and an AR by providing the MN with
information, based on which the MN can determine whether to perform
only an L2 handover or both the L2 handover and an L3 handover.
[0024] Additional aspects and/or advantages of the invention will
be set forth in part in the description which follows and, in part,
will be obvious from the description, or may be learned by practice
of the invention.
[0025] According to an aspect of the present invention, there is
provided a fast handover method, which is performed in a mobile
node (MN). The fast handover method includes (a) determining
whether a beacon signal input from an access point (AP) to the MN
contains border information indicating that the AP is located at
the border of its subnet, the AP connecting the MN to a wired
network; and (b) selectively performing a handover between subnets
based on the determination results obtained in (a).
[0026] According to another aspect of the present invention, there
is provided a fast handover apparatus, which is installed in an MN.
The fast handover apparatus includes a border information
determination unit, which determines whether a beacon signal input
from an AP to the MN contains border information indicating that
the AP is located at the border of its subnet, the AP connecting
the MN to a wired network; and a handover unit, which selectively
performs a handover between subnets based on the determination
results obtained by the border information determination unit.
[0027] According to another aspect of the present invention, there
is provided a fast handover method, which is performed in an MN.
The fast handover method includes (a) determining whether a signal
received from an AP is a border signal indicating that the AP is
located at the border of its subnet, the AP connecting the MN to a
wired network; and (b) selectively performing a handover between
subnets based on the determination results obtained in (a).
[0028] According to another aspect of the present invention, there
is provided a computer-readable recording medium, on which a
computer program for executing a fast handover method, which is
performed in an MN, is recorded. Here, the fast handover (a)
determining whether a beacon signal input from an access point (AP)
to the MN contains border information indicating that the AP is
located at the border of its subnet, the AP connecting the MN to a
wired network; and (b) selectively performing a handover between
subnets based on the determination results obtained in (a).
[0029] According to another aspect of the present invention, there
is provided a computer-readable recording medium, on which a
computer program for executing a fast handover method, which is
performed in an MN, is recorded. Here, the fast handover includes
(a) determining whether a signal received from an AP is a border
signal indicating that the AP is located at the border of its
subnet, the AP connecting the MN to a wired network; and (b)
selectively performing a handover between subnets based on the
determination results obtained in (a).
[0030] To achieve the above and/or other aspects and advantages,
embodiments of the present invention include a fast handover
method, which is performed in a mobile node (MN), the fast handover
method including determining whether a beacon signal, transmitted
from an access point (AP) in a current subnet to the MN in the
current, contains border information indicating that the AP is
located at the border of the current subnet; and determining
whether the MN has moved within the current subnet or has moved
from one subnet to the current subnet based on whether the beacon
signal contains border information.
[0031] The method may further include increasing a count value of a
counter if the beacon signal is determined to contain the border
information. If the count value is not less than two, the MN may be
determined to have moved from one subnet to another subnet.
[0032] The fast handover method may further include determining
whether a signal received by the MN is a beacon signal designating
a current cell managed by the AP; determining whether the MN has
moved within the current cell or has moved from one cell in one AP
to the current cell managed by the AP; and performing a handover
from the one AP to the current AP if it is determined that the MN
has moved from the one cell of the one AP to the current cell of
the AP.
[0033] The handover between cells may be a link layer handover, and
the handover between subnets may be an Internet protocol (IP) layer
handover. The border information may be recorded in a reserved
field of a capability information field of a frame body field of an
IEEE 802.11 beacon frame.
[0034] To achieve the above and/or other aspects and advantages,
embodiments of the present invention include a fast handover
apparatus, which may be installed in an MN, the fast handover
apparatus including a border information determination unit, which
determines whether a beacon signal transmitted from an AP to the MN
contains border information indicating that the AP is located at
the border of its subnet; and a handover unit, which selectively
performs a handover between subnets based on whether the beacon
signal contains border information.
[0035] The fast handover apparatus may further include a counter,
which increases a count value of a counter if the border
information determination unit determines that the beacon signal
contains the border information; and a subnet change determination
unit, which determines whether the MN has moved from one subnet to
another subnet based on the count value. If the count value is less
than two, the subnet change determination unit may determine that
the MN has moved from one subnet to another subnet.
[0036] The fast handover apparatus may further include a beacon
signal determination unit, which determines whether a signal
received from the AP is a beacon signal designating a cell managed
by the AP, wherein the handover unit selectively performs a
handover between cells based on the determination results obtained
by the beacon signal determination unit. The handover between cells
may be a link layer handover, and the handover between subnets may
be an IP layer handover. The border information may be recorded in
a reserved field of a capability information field of a frame body
field of an IEEE 802.11 beacon frame.
[0037] To achieve the above and/or other aspects and advantages,
embodiments of the present invention include a fast handover
method, which is performed in an MN, the fast handover method
including determining whether a signal received from an AP is a
border signal indicating that the AP is located at the border of
its subnet; and determining whether the MN has moved within the
current subnet or has moved from one subnet to the current subnet
based on whether the signal is the border signal.
[0038] The fast handover method may further include increasing a
count value of a counter if the received signal is determined to be
the border signal; and determining whether the MN has moved from
one subnet to another subnet based on the count value. If the count
value is not less than two, the MN is determined to have moved from
one subnet to another subnet.
[0039] The fast handover method may further include determining
whether the signal received by the MN is a beacon signal
designating a current cell managed by the AP; determining whether
the MN has moved within the current cell or has moved from one cell
in one AP to the current cell managed by the AP; and performing a
handover at the link layer from the one AP to the current AP if it
is determined that the MN has moved from the one cell of the one AP
to the current cell of the AP. The fast handover method between
cells is a link layer handover, and the handover between subnets is
an Internet protocol (IP) layer handover. The border information
may be recorded in a reserved field of a capability information
field of a frame body field of an IEEE 802.11 beacon frame.
[0040] To achieve the above and/or other aspects and advantages,
embodiments of the present invention include a computer-readable
recording medium, on which a computer program for executing a fast
handover method, which is performed in an MN, is recorded, the fast
handover including determining whether a beacon signal transmitted
from an access point (AP) and received by the MN contains border
information indicating that the AP is located at the border of its
subnet, the AP connecting the MN to a wired network; and
selectively performing a handover between subnets based on whether
the beacon signal contains border information.
[0041] To achieve the above and/or other aspects and advantages,
embodiments of the present invention include a computer-readable
recording medium, on which a computer program for executing a fast
handover method, which is performed in an MN, is recorded, the fast
handover including determining whether a signal received from an AP
is a border signal indicating that the AP is located at the border
of its subnet, the AP connecting the MN to a wired network; and
selectively performing a handover between subnets based on whether
the signal is the border signal.
[0042] A computer-readable data transmission medium containing a
data structure may include border information recorded in a
reserved field of a capability information field of a frame body
field of an IEEE 802.11 beacon frame.
[0043] A computer-readable data transmission medium containing a
data structure may include border information recorded in a type
field and a subtype field of a frame control field of an IEEE
802.11 management frame. The type field may have a value of zero,
and the subtype field has a value of FFFF.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] These and/or other aspects and advantages of the invention
will become apparent and more readily appreciated from the
following description of the embodiments, taken in conjunction with
the accompanying drawings of which:
[0045] FIG. 1 is a diagram illustrating a conventional wireless LAN
environment;
[0046] FIG. 2 is a diagram illustrating a wireless LAN environment
according to an exemplary embodiment of the present invention;
[0047] FIG. 3 is a block diagram illustrating fast handover
apparatuses according to an exemplary embodiment of the present
invention;
[0048] FIG. 4 is a diagram illustrating the format of a beacon
frame according to an exemplary embodiment of the present
invention;
[0049] FIGS. 5 and 6 are flowcharts of fast handover methods
according to an exemplary embodiment of the present invention;
[0050] FIG. 7 is a block diagram illustrating fast handover
apparatuses according to another exemplary embodiment of the
present invention;
[0051] FIG. 8 is a diagram illustrating the format of a border
frame according to an exemplary embodiment of the present
invention; and
[0052] FIGS. 9 and 10 are flowcharts of fast handover methods
according to another exemplary embodiment of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0053] Reference will now be made in detail to exemplary
embodiments of the present invention, examples of which are
illustrated in the accompanying drawings, wherein like reference
numerals refer to the like elements throughout. The exemplary
embodiments are described below to explain the present invention by
referring to the figures.
[0054] FIG. 2 is a diagram illustrating a wireless LAN environment
according to an exemplary embodiment of the present invention.
Referring to FIG. 2, the wireless LAN environment includes a MN 4,
a first AP 51, a second AP 52, a third AP 53, a fourth AP 54, a
first AR 61, and a second AR 62.
[0055] The wireless LAN environment according to an exemplary
embodiment of the present invention will be described in detail as
the MN 4 sequentially passes through a cell managed by the first AP
51, a cell managed by the second AP 52, a cell managed by the third
AP 53, and a cell managed by the fourth AP 54. It is understood
that the MN 4 may move among the cells in any manner and that the
wireless LAN environment of exemplary embodiments will accommodate
such movement of the MN 4.
[0056] Each of the first through fourth APs 51 through 54 informs
the stationary or moving MN4 in its cell, as to which of the first
through fourth APs 51 through 54 can be used by the MN 4 to access
a wired network by periodically transmitting a beacon signal to the
MN 4 in its cell. In addition, the second AP 52, which is located
at the border of a subnet managed by the first AR 61, and the third
AP 53, which is located at the border of a subnet managed by the
second AR 62, additionally transmit information indicating that
they are located at the borders of their respective subnets to the
MN 4.
[0057] The MN 4 receives a beacon signal from the first AP 51, as
marked by `511`, and recognizes based on the received beacon signal
that it is currently located in the cell managed by the first AP
51. Accordingly, the MN 4 can access the wired network via the
first AP 51.
[0058] Thereafter, the MN 4 receives a beacon signal from the
second AP 52, as marked by `521` and then recognizes based on the
received beacon signal that it has moved from the cell managed by
the first AP 51 to the cell managed by the second AP 52.
Accordingly, the MN 4 performs a handover in a link layer, i.e., an
L2 handover. In other words, the MN 4 recognizes that it is
currently located in the cell managed by the second AP 52 and
switches its link layer connection from the first AP 51 to the
second AP 52. Therefore, the MN 4 can keep accessing the wired
network via the second AP 52. Since the second AP 52 is located at
the border of the subnet managed by the first AR 61, the MN 4
receives information indicating that the second AP 52 is located at
the border of the subnet managed by the first AR 61 from the second
AP 52.
[0059] Thereafter, the MN 4 receives a beacon signal from the
second AP 52, as marked by `522`, and recognizes based on the
received beacon signal that it is still located in the cell managed
by the second AP 52. Accordingly, the MN 4 can keep accessing the
wired network via the second AP 52. Since the second AP 52 is
located at the border of the subnet managed by the first AR 61, the
MN 4 receives the information indicating that the second AP 52 is
located at the border of the subnet managed by the first AR 61 from
the second AP 52.
[0060] Thereafter, the MN 4 receives a beacon signal from the third
AP 53, as marked by `531`, and recognizes based on the received
beacon signal that it has moved from the cell managed by the second
AP 52 from the cell managed by the third AP 53. Accordingly, the MN
4 performs an L2 handover. In other words, the MN 4 recognizes that
it is currently located in the cell managed by the third AP 53 and
switches its link layer connection from the second AP 52 to the
third AP 53. Accordingly, the MN 4 can keep accessing the wired
network via the third AP 53. Since the third AP 53 is located at
the border of the subnet managed by the second AR 62, the MN 4
receives information indicating that the third AP 53 is located at
the border of the subnet managed by the second AR 62 from the third
AP 53. Thereafter, the MN 4 determines that it has moved from one
subnet to another subnet after receiving the information,
indicating that the second AP 52 is located at the border of the
subnet managed by the first AR 61, and then the information,
indicating that the third AP 53 is located at the border of the
subnet managed by the second AR 62, from the second AP 52 and the
third AP 53, respectively.
[0061] Thereafter, the MN 4 transmits information indicating that
it has moved from the cell managed by the second AP 52 to the cell
managed by the third AP 53 to the first AR 61 via the third AP 53
and the second AR 62, as marked by `532`. Then, the first AR 61
recognizes that the MN 4 has escaped from its subnet based on the
fact that it has received the information indicating that the MN 4
has moved from the cell managed by the second AP 52 to the cell
managed by the third AP 53 from the MN 4 via another AR, i.e., the
second AR 62.
[0062] Thereafter, the first AR 61 transmits information indicating
that the MN 4 has escaped from the subnet managed by the first AR
61 to the MN 4 via the second AR 62 and the third AP 53. Then, the
MN 4 confirms its earlier determination that it has escaped from
the subnet managed by the first AR 61 and is currently located in
the subnet managed by the second AR 62. Accordingly, the MN 4
performs a handover in an IP layer, i.e., an L3 handover, which
will be described in detail in the following.
[0063] The MN 4 issues a request for a network prefix of the subnet
managed by the second AR 62 to the second AR 62 via the third AP 53
in order to generate a new IP address that can be used in the
subnet managed by the second AR 62. The MN 4 receives the network
prefix of the subnet managed by the second AR 62 from the second AR
62 and generates a new IP address based on the received network
prefix. Accordingly, the MN 4 performs communications in the subnet
managed by the second AR 62 using the new IP address.
[0064] Thereafter, the MN 4 receives a beacon signal from the third
AP 53, as marked by `535`, and recognizes based on the received
beacon signal that it is still located in the cell managed by the
third AP 53. Accordingly, the MN 4 can keep accessing the wired
network via the third AP 53.
[0065] Thereafter, the MN 4 receives a beacon signal from the
fourth AP 54, as marked by `541`, and recognizes based on the
received beacon signal that it has moved from the cell managed by
the third AP 53 to the cell managed by the fourth AP 54.
Accordingly, the MN 4 performs an L2 handover. In other words, the
MN 4 recognizes that it is currently located in the cell managed by
the fourth AP 54 and switches its link layer connection from the
third AP 53 to the fourth AP 54. Accordingly, the MN 4 can keep
accessing the wired network via the fourth AP 54.
[0066] As described above, the MN 4 communicates with an AR only
when it is determined that the MN 4 has moved from one subnet to
another subnet. Thus, it is possible to prevent unnecessary
communications between the MN 4 and the AR.
[0067] FIG. 3 is a block diagram illustrating fast handover
apparatuses according to an exemplary embodiment of the present
invention. Referring to FIG. 3, the fast handover apparatuses are
respectively installed in a second AP 52, a third AP 53, and an MN
4. The fast handover apparatus installed in the second AP 52
includes a beacon signal generation unit 521, a border information
insertion unit 522, and a signal transmission unit 523. The fast
handover apparatus installed in the third AP 53 includes a beacon
signal generation unit 531, a border information insertion unit
532, and a signal transmission unit 533. The fast handover
apparatuses can achieve a fast handover by inserting border
information indicating that the second and third APs 52 and 53 are
located at the borders of their respective subnets in a beacon
frame and then transmitting the beacon frame to a MN 4.
[0068] The beacon signal generation unit 521 generates a first
beacon signal designating a cell managed by the second AP 52. The
beacon signal generation unit 521 generates a second beacon signal
designating a cell managed by the third AP 53. Therefore, if the MN
4 receives the first or second beacon signal, then the MN 4
recognizes that it is located in the cell managed by the second AP
52 or the third AP 53. The first and second beacon signals are IEEE
802.11 beacon frames.
[0069] The border information insertion unit 522 inserts first
border information indicating that the second AP 52 is located at
the border of its subnet in the first beacon signal generated by
the beacon signal generation unit 521. The border information
insertion unit 532 inserts second border information indicating
that the third AP 53 is located at the border of its subnet in the
second beacon signal generated by the beacon signal generation unit
531.
[0070] When designing a network, a network designer divides the
network into several subnets and additionally install border
information insertion units (e.g., the border information insertion
units 522 and 532) in APs that are located at the borders of their
respective subnets so that the APs can inform MNs within their
cells of the fact that they are located at the borders of their
respective subnets.
[0071] In the present embodiment, the border information insertion
units 522 and 532 are simply added to the second and third APs 52
and 53, respectively. Thus, it is possible to minimize
modifications to the structures of the second and third APs 52 and
53.
[0072] FIG. 4 is a diagram illustrating the format of a beacon
frame according to an exemplary embodiment of the present
invention. Referring to FIG. 4, a management frame, which is
created based on the IEEE 802.11 standard, includes a frame control
field 401, a duration field 402, a destination address field 403, a
source address field 404, a basic service set (BSS) identification
(ID) field 405, a sequence control field 406, a frame body field
407, and a frame check sequence field 408.
[0073] The frame control field 401 includes a protocol version
field 4011, a type field 4012, a subtype field 4013, and other
fields.
[0074] According to the IEEE 802.11 standard, a beacon frame is one
type of management frame having a subtype field value of 1000. When
a beacon frame has a type field value of 0, it is a management
frame. The frame body field 407 includes a time stamp field 4071, a
beacon interval field 4072, a capability information field 4073, a
traffic indication map (TIM) field 4074, and other fields.
[0075] The capability information field 4073 includes an extended
service set (ESS) field 40731, an independent BSS (IBSS) field
40732, a contention free (CF) pollable field 40733, a CF poll
request field 40734, a privacy field 40735, and a reserved field
40736.
[0076] Referring to FIG. 4, border information may be contained in
one bit of the reserved field 40736 of the capability information
field 4073 of the frame body field 407. Hereinafter, the bit of the
reserved field 40736 where the border information is contained will
be referred to as a border flag or B flag. If the B flag is set to
a value of 1, an AP is located at the border of its subnet. The
border information insertion units 522 and 532 are not installed in
fast handover apparatuses of APs that are not located at the
borders of their respective subnets. Thus, each of the fast
handover apparatuses in the APs that are not located at the borders
of their respective subnets only include a beacon signal generation
unit and a signal transmission unit and transmit a beacon frame
whose B flag is set to a value of 0. If an AP transmits a beacon
frame whose B flag is set to a value of 0 to the MN 4, the MN 4
determines that the AP is not located at the border of its
subnet.
[0077] Referring to FIG. 3, the signal transmission unit 523
transmits a beacon frame in which the first border information is
inserted by the border information insertion unit 522 to the MN 4.
The signal transmission unit 533 transmits a beacon frame in which
the second border information is inserted by the border information
insertion unit 532 to the MN 4. The signal transmission unit 523 or
533 notifies the MN 4, which is constantly on the move within the
cell managed by the second AP 52 or the third AP 53, that the MN 4
is currently located in the cell managed by the second AP 52 or the
third AP 53 by periodically transmitting a beacon signal to the MN
4.
[0078] The fast handover apparatus installed in the MN 4 includes a
signal receipt unit 41, a beacon signal determination unit 42, a
cell ID checking unit 43, a cell change determination unit 44, a
border information determination unit 45, a counter 46, a subnet
change determination unit 47, and a handover unit 48. The handover
unit 48 includes a link layer handover unit 481 and an IP layer
handover unit 482.
[0079] The signal receipt unit 41 receives a signal from the second
AP 52 or the third AP 53. If the MN 4 is located in the cell
managed by the second AP 52, it receives a signal from the second
AP 52. If the MN 4 is located in the cell managed by the third AP
53, it receives a signal from the third AP 53.
[0080] The beacon signal determination unit 42 determines whether
the signal received from the second AP 52 or the third AP 53 is a
beacon signal designating the cell managed by the second AP 52 or
the third AP 53. As described above, the beacon signal
determination unit 42 may determine whether the received signal is
a beacon signal with reference to a value recorded in a subtype
field (4013) of a type field (4012) of the received signal. If the
type field of the received signal has a value of 0, and the subtype
field of the received signal has a value of 1000, then the beacon
signal determination unit 42 determines the received signal as a
beacon signal.
[0081] If the beacon signal determination unit 42 determines the
received signal as a beacon signal, the cell ID checking unit 43
checks cell ID included in the received signal. As described above,
a beacon frame, which is one type of management frame, includes a
BSS ID field (405). According to the IEEE 802.11 standard, a BSS
corresponds to a cell managed by an AP, and ID of the BSS, i.e.,
cell ID, is contained in a BSS ID field of a beacon signal.
Accordingly, the cell ID checking unit 43 checks cell ID
referencing a BSS ID field of the received signal.
[0082] The cell change determination unit 44 determines whether the
MN 4 has moved from one cell to another cell based on the cell ID
(hereinafter referred to as current cell ID) checked by the cell ID
unit 43. If the current cell ID is not identical to previous cell
ID, the cell change determination unit 44 determines that the MN 4
has moved from one cell to another cell.
[0083] The handover unit 48 selectively performs a handover based
on the determination results output from the beacon signal
determination unit 42. Specifically, if the cell change
determination unit 44 determines that the MN 4 has moved from one
cell to another cell, the link layer handover unit 481 included in
the handover unit 48 performs an L2 handover so that the MN 4
switches its link layer connection from the second AP 52 to the
third AP 53.
[0084] If the beacon signal determination unit 42 determines the
received signal as a beacon frame, the border information
determination unit 46 determines whether the received signal has
border information indicating that the second AP 52 or the third AP
53 is located at the border of its subnet by referencing a reserved
field (40736) of a capability information field (4073) of a frame
body field (407) of the received signal.
[0085] If the border information determination unit 45 determines
that the received signal has the border information, the counter 46
increases a count value by 1. In other words, if the border
information determination unit 45 confirms that a B flag of the
received signal has a value of 1, the counter 46 increases the
count value by 1.
[0086] The subnet change determination unit 47 determines whether
the MN 4 has moved from one subnet to another subnet based on the
count value of the counter 46. In other words, if the count value
is not smaller than 2, the subnet change determination unit 47
determines that the MN 4 has moved from one subnet to another
subnet. For example, if the count value of the counter 46 is 1, the
MN 4 is determined to have received a beacon signal only from the
second AP 52 or the third AP 53. Supposing that the MN 4 has
received the beacon signal only from the third AP 53, the MN 4
recognizes that it is currently located near the border of the
subnet where the second AP 52 is located but cannot determine
whether it has entered a new subnet. In particular, the count value
may also be 1 when the MN 4 has moved to the border of the subnet
where the third AP 53 is located and then turns back to the subnet
where the second AP 52. Thus, a count value of 1 is not reliable
enough to determine that the MN 4 has moved from one subnet to
another subnet.
[0087] However, if the count value is 2, the MN 4 is determined to
have received two beacon signals from the second AP 52 and the
third AP 53. Therefore, the MN 4 recognizes based on the two beacon
signals that it has moved from the subnet where the second AP 52 is
located to the subnet where the third AP 53 is located. In general,
if the counter value of the counter 46 is not smaller than 2, the
MN 4 is determined to have received at least 2 beacon signals from
at least two different APs that are located at the borders of their
respective subnets. Thus, the MN 4 can recognize based on the
beacon signals that it has moved from one subnet to another
subnet.
[0088] However, if the MN 4 receives a plurality of beacon signals
from the second AP 52 while moving about in the subnet where the
second AP 52 is located or if the MN 4 moves back and forth between
the border of the subnet where the second AP 52 is located and the
border of the subnet where the third AP 53 is located, the count
value of the counter 46 may be not smaller than 2. In order to
solve this problem, the counter 46 must be set to count a plurality
of beacon signals whose BSS ID fields (405) designate the same cell
ID as 1.
[0089] The handover unit 48 selectively performs a handover based
on the determination results output from the border information
determination unit 45. Specifically, if the subnet change
determination unit 47 determines that the MN 4 has moved from one
subnet to another subnet, the IP layer handover unit 482 included
in the handover unit 48 performs an L3 handover. Accordingly, the
MN 4 receives a network prefix of the subnet that it has entered
and generates a new IP address that can be used in the
corresponding subnet.
[0090] FIGS. 5 and 6 are flowcharts of a fast handover method
according to an exemplary embodiment of the present invention.
Specifically, FIG. 5 is a flowchart of a fast handover method
according to an exemplary embodiment of the present invention,
which is performed in an AP, and FIG. 6 is a flowchart of a fast
handover method according to an exemplary embodiment of the present
invention, which is performed in an MN.
[0091] Referring to FIG. 5, in operation 501, an AP generates a
beacon signal designating a cell managed by it.
[0092] In operation 502, the AP inserts border information
indicating that the AP is located at the border of its subnet in
the beacon signal generated in operation 501.
[0093] In operation 503, the AP transmits the beacon signal in
which the border information is inserted to an MN.
[0094] Referring to FIG. 6, in operation 601, an MN receives a
signal from an AP.
[0095] In operation 602, the MN determines whether the received
signal is a beacon signal designating a cell managed by the AP.
[0096] In operation 603, if the received signal is determined to be
a beacon signal designating the cell managed by the AP, the MN
checks cell ID included in the received signal.
[0097] In operation 604, the MN determines whether it has moved
from one cell to another cell based on the cell ID checked in
operation 603.
[0098] In operation 605, the MN selectively performs a handover
based on the determination results obtained in operation 604.
Specifically, if the MN is determined to have moved from one cell
to another cell in operation 604, it performs an L2 handover.
[0099] In operation 606, the MN determines whether the received
signal includes border information indicating that the AP is
located at the border of its subnet by referencing a reserved field
(40736) of a capability information field (4073) of a frame body
field (407) of the received signal.
[0100] In operation 607, the MN increases a count value of a
counter if the received signal is determined to include the border
information, particularly, if a B flag of the received signal is
set to a value of 1.
[0101] In operation 608, the MN determines whether it has moved
from one subnet to another subnet based on the count value.
Specifically, if the count value is not smaller than 2, the MN
determines that it has moved from one subnet to another subnet.
[0102] In operation 609, the MN selectively performs a handover
based on the determination results obtained in operation 608.
Specifically, if the MN is determined to have moved from one subnet
to another subnet, it performs an L3 handover.
[0103] In operation 610, the MN resets the counter to a value of 0
in order to prevent a count value of 2 or higher from being falsely
interpreted as indicating that the MN has moved from one subnet to
another subnet.
[0104] FIG. 7 is a block diagram of fast handover apparatuses
according to another exemplary embodiment of the present invention.
Referring to FIG. 7, the fast handover apparatuses are respectively
installed in a second AP 52, a third AP 53, and an MN 4. The fast
handover apparatus installed in the second AP 52 includes a beacon
signal generation unit 524, a border signal generation unit 525,
and a signal transmission unit 526. The fast handover apparatus
installed in the third AP 53 includes a beacon signal generation
unit 534, a border signal generation unit 535, and a signal
transmission unit 536. The fast handover apparatuses can achieve a
fast handover by transmitting border signals indicating that the
second and third APs 52 and 53 are located at the borders of their
respective subnets to an MN 4.
[0105] The beacon signal generation unit 524 generates a first
beacon signal designating a cell managed by the second AP 52. The
beacon signal generation unit 534 generates a second beacon signal
designating a cell managed by the third AP 53. Therefore, if the MN
4 receives the first or second beacon signal, then the MN 4
recognizes that it is located in the cell managed by the second AP
52 or the third AP 53. The first and second beacon signals are IEEE
802.11 beacon frames.
[0106] The border signal generation unit 525 generates a first
border signal indicating that the second AP 52 is located at the
border of its subnet. The border signal generation unit 535
generates a second border signal indicating that the third AP 53 is
located at the border of its subnet.
[0107] When designing a network, a network designer divides the
network into several subnets and additionally install border signal
generation units (e.g., the border signal generation units 525 and
535) in APs that are located at the borders of their respective
subnets so that the APs can inform MNs within their cells of the
fact that they are located at the borders of their respective
subnets.
[0108] In the present embodiment, the border signal generation
units 525 and 535 are simply added to the structures of the second
and third APs 52 and 53, respectively. Thus, it is possible to
minimize modifications to the structures of the second and third
APs 52 and 53.
[0109] FIG. 8 is a diagram illustrating the format of a border
frame according to an exemplary embodiment of the present
invention. Referring to FIG. 8, a management frame, which is
created based on the IEEE 802.11 standard, includes a frame control
field 801, a duration field 802, a destination address field 803, a
source address field 804, a BSS ID field 805, a sequence control
field 806, a frame body field 807, and a frame check sequence field
808.
[0110] The frame control field 801 includes a protocol version
field 8011, a type field 8012, a subtype field 8013, and other
fields.
[0111] A subtype field of a frame control field of a management
frame may be used to define a new signal or a new frame indicating
that an AP is located at the border of its subnet. The new frame
will be referred to as a border frame in the following. If a
subtype field of a border frame is set to a value of FFFF, the
border frame indicates that a corresponding AP is located at the
border of its subnet. FFFF may be any value that has not yet been
designated by the IEEE 802.11 standard. If a type field of the
border frame has a value of 0, the border frame is one type of
management frame. Fast handover apparatuses of APs that are not
located at the borders of their respective subnets only include a
beacon signal generation unit (524 or 534) and a signal
transmission unit (526 or 536) and thus do not transmit a border
frame to the MN 4 because they do not have a border information
generation unit (525 or 535). If an AP does not transmit a border
frame to the MN 4, the MN 4 determines that the AP is not located
at the border of its subnet.
[0112] Referring to FIG. 7, the signal transmission unit 526
transmits a beacon frame generated by the beacon signal generation
unit 524 and a border signal generated by the border signal
generation unit 525 to the MN 4. The signal transmission unit 536
transmits a beacon signal, generated by the beacon signal
generation unit 534, and a border signal, generated by the border
signal generation unit 535, to the MN 5. The signal transmission
unit 526 or 536 notifies the MN 4, which is constantly on the move
within the cell managed by the second AP 52 or the third AP 53,
that the MN 4 is currently located in the cell managed by the
second AP 52 or the third AP 53 by periodically transmitting a
beacon signal to the MN 4.
[0113] The fast handover apparatus installed in the MN 4 includes a
signal receipt unit 410, a beacon signal determination unit 411, a
cell ID checking unit 412, a cell change determination unit 413, a
border signal determination unit 414, a counter 415, a subnet
change determination unit 416, and a handover unit 417. The
handover unit 417 includes a link layer handover unit 4171 and an
IP layer handover unit 4172.
[0114] The signal receipt unit 410 receives a signal from the
second AP 52 or the third AP 53. If the MN 4 is located in the cell
managed by the second AP 52, it receives a signal from the second
AP 52. If the MN 4 is located in the cell managed by the third AP
53, it receives a signal from the third AP 53.
[0115] The beacon signal determination unit 411 determines whether
the signal received from the second AP 52 or the third AP 53 is a
beacon signal designating the cell managed by the second AP 52 or
the third AP 53. As described above, the beacon signal
determination unit 411 may determine whether the received signal is
a beacon signal with reference to a value recorded in a subtype
field (4013) of a type field (4012) of the received signal. If the
type field of the received signal has a value of 0, and the subtype
field of the received signal has a value of 1000, then the beacon
signal determination unit 411 determines the received signal as a
beacon signal (FIG. 4).
[0116] If the beacon signal determination unit 411 determines the
received signal as a beacon signal, the cell ID checking unit 412
checks cell ID included in the received signal. As described above,
the cell ID checking unit 412 checks cell ID referencing a BSS ID
field (405) of the received signal.
[0117] The cell change checking unit 413 determines whether the MN
4 has moved from one cell to another cell based on the cell ID
(hereinafter referred to as current cell ID) checked by the cell ID
unit 43. If the current cell ID is not identical to previous cell
ID, the cell change checking unit 413 determines that the MN 4 has
moved from one cell to another cell.
[0118] The handover unit 417 selectively performs a handover based
on the determination results output from the beacon signal
determination unit 411. Specifically, if the cell change checking
unit 413 determines that the MN 4 has moved from one cell to
another cell, the link layer handover unit 4171 included in the
handover unit 417 performs an L2 handover so that the MN 4 switches
its link layer connection from the second AP 52 to the third AP
53.
[0119] The border signal determination unit 414 determines whether
the received signal is a border signal indicating that the second
AP 52 or the third AP 53 is located at the border of its subnet. As
described above, the border signal determination unit 414
determines whether the received signal is a border signal by
referencing a type field (8012) and a subtype field (8013) of a
frame control field (801) of the received signal. If the type field
of the received signal has a value of 0, and the subtype field of
the received signal has a value of FFFF, the border signal
determination unit 414 determines that the received signal is a
border signal (FIG. 8).
[0120] If the border signal determination unit 414 determines that
the received signal is a border signal, the counter 415 increases a
count value by 1. In other words, if the border signal
determination unit 414 confirms that the type field of the received
signal has a value of 0, and the subtype field of the received
signal has a value of FFFF, the counter 415 increases the count
value by 1.
[0121] The subnet change determination unit 416 determines whether
the MN 4 has moved from one subnet to another subnet based on the
count value of the counter 415. In other words, if the count value
is not smaller than 2, the subnet change determination unit 416
determines that the MN 4 has moved from one subnet to another
subnet. The counter 415 counts a plurality of border signals whose
BSS ID fields (405) designate the same cell ID as 1.
[0122] The handover unit 417 selectively performs a handover based
on the determination results output from the border information
checking unit 414. Specifically, if the subnet change determination
unit 416 determines that the MN 4 has moved from one subnet to
another subnet, the IP layer handover unit 4172 included in the
handover unit 417 performs an L3 handover. Accordingly, the MN 4
receives a network prefix of the subnet that it has entered and
generates a new IP address that can be used in the corresponding
subnet.
[0123] FIGS. 9 and 10 are flowcharts of fast handovers method
according to an exemplary embodiment of the present invention.
Specifically, FIG. 9 is a flowchart of a fast handover method
according to an exemplary embodiment of the present invention,
which is performed in an AP, and FIG. 10 is a flowchart of a fast
handover method according to an exemplary embodiment of the present
invention, which is performed in an MN.
[0124] Referring to FIG. 9, in operation 901, an AP generates a
beacon signal designating a cell managed by it.
[0125] In operation 902, the AP transmits the beacon signal
generated in operation 501 to an MN.
[0126] In operation 903, the AP generates a border signal
indicating that the AP is located at the border of its subnet. The
AP generates the beacon signal and then the border signal so that
the MN performs an L2 handover ahead of an L3 handover or performs
the L2 handover and the L3 handover at the same time.
[0127] In 904, the AP transmits the borer signal generated in
operation 903 to the MN.
[0128] Referring to FIG. 10, in operation 101, an MN receives a
signal from an AP.
[0129] In operation 102, the MN determines whether the received
signal is a beacon signal designating a cell managed by the AP.
[0130] In operation 103, if the received signal is determined to be
a beacon signal designating the cell managed by the AP, the MN
checks cell ID included in the received signal.
[0131] In operation 104, the MN determines whether it has moved
from one cell to another cell based on the cell ID checked in
operation 103.
[0132] In operation 105, the MN selectively performs a handover
based on the determination results obtained in operation 104.
Specifically, if the MN is determined to have moved from one cell
to another cell in operation 104, then the MN performs an L2
handover.
[0133] In operation 106, the MN determines whether the received
signal is a border signal indicating that the AP is located at the
border of its subnet by referencing a type field (8012) and a
subtype field (8013) of a frame control field (801) of the received
signal.
[0134] In operation 107, the MN increases a count value of a
counter if the received signal is determined to be a border signal,
particularly, if the type field of the received signal has a value
of 0, and the subtype field of the received signal has a value of
FFFF.
[0135] In operation 108, the MN determines whether it has moved
from one subnet to another subnet based on the count value.
Specifically, if the count value is not smaller than 2, the MN
determines that it has moved from one subnet to another subnet.
[0136] In operation 109, the MN selectively performs a handover
based on the determination results obtained in operation 108.
Specifically, if the MN is determined to have moved from one subnet
to another subnet, it performs an L3 handover.
[0137] In operation 110, the MN resets the counter to a value of 0
in order to prevent a count value of 2 or higher from being falsely
interpreted as indicating that the MN has moved from one subnet to
another subnet.
[0138] The fast handover methods according to the exemplary
embodiments of the present invention may be written as a computer
program so that they are executed in a common digital computer or
any other computing device. The computer program may be stored in a
computer-readable data storage medium so that it is read and
executed by a computer or any other computing device. Examples of
the computer-readable data storage medium include a magnetic
recording medium (e.g., a ROM, a floppy disc, or a hard disc), an
optical recording medium (e.g., a CD-ROM or a DVD), and a carrier
wave medium (e.g., data transmission through the Internet).
Examples of the computer-readable data storage medium further
include any type of transmission medium including networks, which
may be wired networks, wireless networks or any combination
thereof.
[0139] According to the present invention, it is possible to
prevent unnecessary communications between an MN and an AR by
providing predetermined information, based on which the MN can
determine whether to perform only an L2 handover or both the L2
handover and an L3 handover. In other words, the MN and the AR
communicate with each other only when the MN is determined to have
moved from a subnet managed by the AR to a subnet managed by
another AR. Accordingly, it is possible to achieve a fast
handover.
[0140] In addition, it is possible to minimize modifications to the
structure of existing APs by simply adding new elements suggested
in this disclosure to the existing APs.
[0141] While the present invention has been shown and described
with reference to exemplary embodiments thereof, it will be
understood by those of ordinary skill in the art that various
changes may be made therein without departing from the principles,
spirit, and scope of the present invention as defined by the claims
and their equivalents.
* * * * *