U.S. patent application number 10/690524 was filed with the patent office on 2004-04-29 for control device, handover control method and mobile communication system.
This patent application is currently assigned to NTT DoCoMo, Inc.. Invention is credited to Kawakami, Hiroshi, Okura, Akihito, Suzuki, Toshihiro, Yabusaki, Masami.
Application Number | 20040082329 10/690524 |
Document ID | / |
Family ID | 32089476 |
Filed Date | 2004-04-29 |
United States Patent
Application |
20040082329 |
Kind Code |
A1 |
Suzuki, Toshihiro ; et
al. |
April 29, 2004 |
Control device, handover control method and mobile communication
system
Abstract
An object of the present invention is to avoid packet loss and
implement a seamless handover by minimizing the handover latency
when a handover is implemented by a multihomed moving network (MN)
or a mobile host (MH). The present invention is a mobile
communication system that is constituted comprising an MN, a
plurality of AI each constituting an interface for the connection
to a core network at the MN, and a control device (MMF), wherein
the MMF dynamically changes the AI adopted as the connection
interface when a predetermined condition is satisfied on the basis
of the connection status to the core network at each AI or the
prediction information for a subsequent handover. In so doing, the
control device continues the transmission and receipt of data with
respect to an appropriate AI capable of maintaining a predetermined
communication quality, and maintains the connection to the core
network of another AI while causing this AI to enter a closed state
in which the transmission and receipt of data is disabled.
Inventors: |
Suzuki, Toshihiro;
(Kawasaki-shi, JP) ; Kawakami, Hiroshi;
(Yokosuka-shi, JP) ; Okura, Akihito;
(Yokohama-shi, JP) ; Yabusaki, Masami;
(Kashiwa-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
NTT DoCoMo, Inc.
Tokyo
JP
100-6150
|
Family ID: |
32089476 |
Appl. No.: |
10/690524 |
Filed: |
October 23, 2003 |
Current U.S.
Class: |
455/436 ;
370/331; 370/352 |
Current CPC
Class: |
H04W 84/005 20130101;
H04W 36/32 20130101; H04L 47/10 20130101; H04W 36/24 20130101 |
Class at
Publication: |
455/436 ;
370/352; 370/331 |
International
Class: |
H04Q 007/00; H04L
012/66; H04Q 007/20 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 28, 2002 |
JP |
2002-313092 |
Claims
What is claimed is:
1. A control device, which constitutes a mobile communication
system together with a mobile host, or a moving network comprising
a plurality of mobile hosts, and a plurality of mutually
connectable access interfaces each constituting an interface for
the connection to a core network at the mobile host or moving
network, and which serves to control a handover relating to the
connection to the core network at the access interfaces,
comprising: connection status acquiring means for acquiring
information on the connection status to the core network at each
access interface, from each access interface; handover predicting
means for predicting a subsequent handover on the basis of the
information on the connection status to the core network at each
access interface; and changing means for dynamically changing the
access interface adopted as the connection interface in accordance
with predetermined logic when a predetermined condition is
satisfied on the basis of the information on the connection status
to the core network at each access interface or the prediction
information for a subsequent handover.
2. The control device according to claim 1, wherein, upon
dynamically changing the access interface, the changing means
continue transmission and receipt of data with respect to an
appropriate access interface capable of maintaining a predetermined
communication quality, and maintain the connection to the core
network with respect to an access interface other than the
appropriate access interface while causing the access interface to
enter a closed state in which the transmission and receipt of data
is disabled.
3. The control device according to claim 1, wherein, upon
dynamically changing the access interface, the changing means
continue the transmission and receipt of data, when a mobile host
is connected to the appropriate access interface which is capable
of maintaining a predetermined communication quality and when the
access interface connected to the mobile host is connected to the
appropriate access interface; and continue communications by
establishing a connection between the mobile host and the
appropriate access interface or a connection between the access
interface connected to the mobile host and the appropriate access
interface, when the mobile host is not connected to the appropriate
access interface and the access interface connected to the mobile
host is not connected to the appropriate access interface.
4. The control device according to claim 1, further comprising:
downlink control means that perform control so that downlink data
from the core network is transmitted via an access router that is
connected to the appropriate access interface, among the access
routers in the core network.
5. The control device according to claim 1, wherein the connection
status acquiring means are constituted comprising: locational
relationship tracking means for tracking the locational
relationship of all the access interfaces connected to the mobile
hosts and the moving network; and information receiving means for
receiving information on the connection status between each access
interface and the core network, and switching information that
includes identification information for identifying the previous
access router and the destination access router at the time
switching occurs, as well as switching end time information, the
information being reported by each access interface; and wherein
the handover predicting means are constituted comprising: velocity
tracking means for tracking at least velocity information
pertaining to the mobile hosts and the moving network in accordance
with a predetermined tracking logic, on the basis of the locational
relationship of each access interface thus tracked and the
connection status information and switching information thus
received; and predicting means for predicting subsequent movement
and changes in the field strength based on the tracked
information.
6. The control device according to claim 5, wherein, for a mobile
host and moving network that are multihomed by means of two access
interfaces, upon recognizing, on the basis of the switching
information from each access interface, that the adjacent
switchings are executed by the same access router, the control
device tracks a value obtained by dividing the distance x by the
switching time difference t, as the velocity pertaining to the
mobile host and moving network, based on a switching time
difference t and a distance x between the access interfaces for the
adjacent switchings.
7. The control device according to claim 5, wherein, for a mobile
host and moving network that are multihomed by means of three or
more access interfaces, upon recognizing, on the basis of the
switching information from each access interface, that the adjacent
switchings are executed by the same access router, the control
device tracks, based on a plurality of combinations of the
switching time difference t and the distance x between the access
interfaces for the adjacent switchings, a direction which links the
two access interfaces and where the first-switched access interface
lies foremost as the direction of movement, and a value obtained by
dividing the distance x by the switching time difference t as the
velocity, with respect to each combination; and finds the vector
sum of the velocity vectors for each combination and tracks the
direction of movement and velocity of the mobile host and moving
network by means of the vector sum thus obtained.
8. The control device according to claim 1, wherein: the
predetermined condition is that the field strength between the
access interface and the core network should be less than a
predetermined threshold value.
9. The control device according to claim 1, wherein: the
predetermined condition is that a predicted value for the field
strength between the access interface and the core network which is
predicted on the basis of subsequent movement prediction should be
less than a predetermined threshold value.
10. The control device according to claim 1, wherein: the
predetermined logic is that of selecting an access interface that
corresponds with a maximum-value field strength from among the
field strengths between each access interface and-the core
network.
11. The control device according to claim 1, wherein: the
predetermined logic is that of selecting an access interface that
corresponds with a predicted value for the maximum-value field
strength from among predicted values for the field strengths
between each access interface and the core network, which are
predicted on the basis of subsequent movement prediction.
12. A handover control method by a mobile communication system that
is constituted comprising a mobile host, or a moving network
comprising a plurality of mobile hosts; a plurality of mutually
connectable access interfaces each constituting an interface for
the connection to a core network at the mobile host or moving
network; and a control device for controlling a handover relating
to the connection to the core network at the access interfaces,
wherein the control device dynamically changes the access interface
adopted as the connection interface in accordance with
predetermined logic when a predetermined condition is satisfied on
the basis of the connection status to the core network at-each
access interface or the prediction information for a subsequent
handover.
13. A mobile communication system that is constituted comprising a
mobile host, or a moving network comprising a plurality of mobile
hosts; a plurality of mutually connectable access interfaces each
constituting an interface for the connection to a core network at
the mobile host or moving network; and a control device for
controlling a handover relating to the connection to the core
network at the access interfaces, wherein the control device
comprises: connection status acquiring means for acquiring
information on the connection status to the core network at each
access interface, from each access interface; handover predicting
means for predicting a subsequent handover on the basis of the
information on the connection status to the core network at each
access interface; and changing means for dynamically changing the
access interface adopted as the connection interface in accordance
with predetermined logic when a predetermined condition is
satisfied on the basis of the information on the connection status
to the core network at each access interface or the prediction
information for a subsequent handover.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to control device, handover
control method and mobile communication system, and more
particularly, to handover control method by a mobile communication
system constituted comprising a mobile host, or a moving network
comprising a plurality of mobile hosts; a plurality of mutually
connectable access interfaces each constituting an interface for
the connection to a core network at the mobile host or moving
network; and a control device for controlling a handover relating
to the connection to the core network at the access interfaces, as
well as to the mobile communication system and a control device
that constitutes the mobile communication system.
[0003] 2. Related Background Art
[0004] The technology relating to a conventional multihoming moving
network and host mainly involves addressing, routing, and so forth.
More specifically, a routing protocol according to which it is
verified whether or not a plurality of addresses have been assigned
according to multihoming, and, if a plurality of addresses have
been assigned, even when a certain interface is disconnected, the
data destined for the address assigned to the interface can be
transmitted to the mobile host and network, has been proposed. In
addition, the principal object of multihoming is load sharing and
fault tolerant (for example, "Requirements for IPv6
Site-Multihoming Architectures" (see
http://www.ietf.org/internet-drafts/draft-ietf-multi6-m
ultihoming-requirements-07.txt)).
[0005] Further, a mobile host and moving network that are
multi-homed by means of a plurality of access interfaces exhibit
the characteristic that the communication quality of a line
connected to each access interface varies according to
movement.
[0006] However, conventionally, because a variation in the
communication quality of a line connected to each access interface
has not been predicted, the handover that pertains to the
connection to the core network at the access interface, has been
performed after one line is disconnected. Such handover is not
performed smoothly and a handover latency occurs, resulting in
packet loss.
[0007] The present invention was conceived in view of resolving the
above problems, an object thereof being to provide control device,
handover control method, and mobile communication system, which use
the merits of multihoming, and make it possible to avoid packet
loss and implement a seamless handover by minimizing the handover
latency when a handover is implemented by a moving network and
host.
SUMMARY OF THE INVENTION
[0008] In order to achieve the above object, the control device
according to the present invention is a control device, which
constitutes a mobile communication system together with a mobile
host, or a moving network comprising a plurality of mobile hosts,
and a plurality of mutually connectable access interfaces each
constituting an interface for the connection to a core network at
the mobile host or moving network, and which serves to control a
handover relating to the connection to the core network at the
access interfaces, comprising: connection status acquiring means
for acquiring information on the connection status to the core
network at each access interface, from each access interface;
handover predicting means for predicting a subsequent handover on
the basis of the information on the connection status to the core
network at each access interface; and changing means for
dynamically changing the access interface adopted as the connection
interface in accordance with predetermined logic when a
predetermined condition is satisfied on the basis of the
information on the connection status to the core network at each
access interface or the prediction information for a subsequent
handover.
[0009] In order to achieve the above object, the handover control
method according to the present invention is a handover control
method of a mobile communication system that is constituted
comprising a mobile host, or a moving network comprising a
plurality of mobile hosts; a plurality of mutually connectable
access interfaces each constituting an interface for the connection
to a core network at the mobile host or moving network; and a
control device for controlling a handover relating to the
connection to the core network at the access interfaces, wherein
the control device dynamically changes the access interface adopted
as the connection interface in accordance with predetermined logic
when a predetermined condition is satisfied on the basis of the
connection status to the core network at each access interface or
the prediction information for a subsequent handover.
[0010] In order to achieve the above object, the mobile
communication system according to the present invention is a mobile
communication system that is constituted comprising a mobile host,
or a moving network comprising a plurality of mobile hosts; a
plurality of mutually connectable access interfaces each
constituting an interface for the connection to a core network at
the mobile host or moving network; and a control device for
controlling a handover relating to the connection to the core
network at the access interfaces, wherein the control device
comprises: connection status acquiring means for acquiring
information on the connection status to the core network at each
access interface, from each access interface; handover predicting
means for predicting a subsequent handover on the basis of the
information on the connection status to the core network at each
access interface; and changing means for dynamically changing the
access interface adopted as the connection interface in accordance
with predetermined logic when a predetermined condition is
satisfied on the basis of the information on the connection status
to the core network at each access interface or the prediction
information for a subsequent handover.
[0011] According to these inventions, in the case of a mobile host
and network that are multihomed by means of a plurality of access
interfaces, attention is drawn to a characteristic according to
which the communication quality of the line connected to each
access interface varies with movement, or similar. Once the mobile
host and network has acquired information on the connection status
to the core network at each access interface or predicted a
subsequent handover, the access interface adopted as the connection
interface is dynamically changed on the basis of this connection
status information or subsequent handover prediction information.
Thus, when, conventionally, a handover latency is generated without
the variation in the communication quality of the line connected to
each access interface being predicted, packet loss can be avoided
and a seamless handover implemented by minimizing the handover
latency by means of the dynamic change to the access interface on
the basis of the connection status information or handover
prediction information.
[0012] Here, it is desirable that, upon dynamically changing the
access interface, changing means of the control device should
continue the transmission and receipt of data with respect to an
appropriate access interface capable of maintaining a predetermined
communication quality, and maintain the connection to the core
network with respect to an access interface other than the
appropriate access interface while causing the access interface to
enter a closed state in which the transmission and receipt of data
is disabled. In this case, the access interface change processing
is switched locally without propagation to the entire network or
informing the origin of the transmission as per an ordinary
handover procedure, and hence the switching time can be shortened.
An access interface other than the appropriate access interface is
afforded a closed state in which the transmission and receipt of
data is disabled without disconnecting the connection to the core
network. Hence, the effects of packet loss and a handover latency
as a result of performing the conventional non-local change
processing do not come to bear, whereby a seamless handover can be
implemented.
[0013] Further, here, upon dynamically changing the access
interface, changing means of the control device continue the
transmission and receipt of data, when a mobile host is -connected
to the appropriate access interface which is capable of maintaining
a predetermined communication quality and when the access interface
connected to the mobile host is connected to the appropriate access
interface. On the other hand, when the mobile host is not connected
to the appropriate access interface and the access interface
connected to the mobile host is not connected to the appropriate
access interface, changing means of the control device desirably
continue communications by establishing a connection between the
mobile host and the appropriate access interface or a connection
between the access interface connected to the mobile host and the
appropriate access interface.
[0014] Therefore, not only when the mobile host is connected to an
appropriate access interface that is capable of maintaining a
predetermined communication quality, but also when the access
interface to which the mobile host is connected, is connected to
the appropriate access interface, the transmission and receipt of
data in which a predetermined communication quality is maintained,
can be implemented by continuing the transmission and receipt of
data via the appropriate access interface. On the other hand, the
transmission and receipt of data in which a predetermined
communication quality is maintained, can be implemented by
continuing transmission by establishing a connection between the
mobile host and the appropriate access interface or a connection
between the access interface connected to the mobile host and the
appropriate access interface, when the mobile host is not connected
to the appropriate access interface and the access interface
connected to the mobile host is not connected to the appropriate
access interface.
[0015] Further, at such time, the control device desirably further
comprises downlink control means that perform control so that
downlink data from the core network is transmitted via an access
router that is connected to the appropriate access interface, among
the access routers in the core network. Therefore, the transmission
and receipt of data in which a predetermined communication quality
is maintained, can be implemented by performing controlling so that
downlink data from the core network is also transmitted and
received via the appropriate access interface.
[0016] By the way, a condition according to which the field
strength between the access interface and the core network should
be less than a predetermined threshold value can be adopted as the
predetermined condition constituting the turning point at which the
access interface is changed by the control device.
[0017] Further, a condition according to which a predicted value
for the field strength between the access interface and the core
network which is predicted on the basis of subsequent movement
prediction should be less than a predetermined threshold value can
also be adopted as the predetermined condition.
[0018] Meanwhile, a logic that involves selecting an access
interface that corresponds with a maximum-value field strength from
among the field strengths between each access interface and the
core network can be adopted as the predetermined logic used when
the access interface is dynamically changed by the control
device.
[0019] Further, a logic that involves selecting an access interface
that corresponds with a predicted value for the maximum-value field
strength from among predicted values for the field strengths
between each access interface and the core network, which are
predicted on the basis of subsequent movement prediction can be
adopted as the above predetermined logic.
[0020] By the way, the control device according to the present
invention is characterized in that the connection status acquiring
means are constituted comprising: locational relationship tracking
means for tracking the locational relationship of all the access
interfaces connected to the mobile hosts and the moving network;
and information receiving means for receiving information on the
connection status between each access interface and the core
network, and switching information that includes identification
information for identifying the previous access router and the
destination access router at the time switching occurs, as well as
switching end time information, the information being reported by
each access interface; and wherein the handover predicting means
are constituted comprising: velocity tracking means for tracking at
least velocity information pertaining to the mobile hosts and the
moving network in accordance with a predetermined tracking logic,
on the basis of the locational relationship of each access
interface thus tracked and the connection status information and
switching information thus received; and predicting means for
predicting subsequent movement and changes in the field strength
based on the tracked information.
[0021] Preferably the handover control method according to the
present invention, is characterized in that the control device
tracks the locational relationship of all the access interfaces
connected to the mobile hosts and the moving network; the control
device receives information on the connection status between each
access interface and the core network, and switching information
that includes identification information for identifying the
previous access router and the destination access router at the
switching time, as well as switching end time information, this
information being reported by each access interface; the control
device tracks at least velocity information pertaining to the
mobile hosts and moving network in accordance with a predetermined
tracking logic; and the control device predicts subsequent movement
and changes in the field strength, on the basis of the tracked
information.
[0022] According to these inventions, at least velocity information
pertaining to the mobile host and moving network is tracked in
accordance with a predetermined tracking logic, on the basis of the
locational relationship of each access interface thus tracked and
of the reported information on the connection status between each
access interface and the core network, and switching information
that includes identification information for identifying the
previous access router and the destination access router at the
time switching occurs, as well as switching end time information,
and subsequent movement and changes in the field strength are
predicted based on the tracked information. For this reason,
handover prediction information of favorable accuracy can be
obtained, and it is possible to implement a, seamless handover more
reliably.
[0023] Here, in the tracking of velocity information, for a mobile
host and moving network that are multihomed by means of two access
interfaces, upon recognizing, on the basis of the switching
information from each access interface, that the adjacent
switchings are executed by the same access router,
[0024] velocity tracking means of the control device desirably
tracks a value obtained by dividing the distance x by the switching
time difference t, as the velocity pertaining to the mobile host
and moving network, based on a switching time difference t and a
distance x between the access interfaces for the adjacent
switchings. In this case, the velocity of the mobile host and
moving network can be tracked with favorable accuracy.
[0025] Further, in the tracking of velocity information, for a
mobile host and moving network that are multihomed by means of
three or more access interfaces, upon recognizing, on the basis of
the switching information from each access interface, that the
adjacent switchings are executed by the same access router,
[0026] velocity tracking means of the control device desirably
tracks, based on a plurality of combinations of the switching time
difference t and the distance x between the access interfaces for
the adjacent switchings, a direction which links the two access
interfaces and where the first-switched access interface lies
foremost as the direction of movement, and a value obtained by
dividing the distance x by the switching time difference t as the
velocity, with respect to each combination; and finds the vector
sum of the velocity vectors for each combination and tracks the
direction of movement and velocity of the mobile host and moving
network by means of the vector sum thus obtained. In this case, the
direction of movement and velocity pertaining to the mobile host
and moving network, can be tracked with favorable accuracy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a constitutional view of the mobile communication
system of the first embodiment.
[0028] FIG. 2 is a function block constitutional view of the MMF of
the first embodiment.
[0029] FIG. 3A is a pre-handover state diagram which serves to
illustrate the logic of a seamless handover using multihoming, of a
multihoming moving network.
[0030] FIG. 3B is a state diagram of the state at the start of a
handover which serves to illustrate the logic of a seamless
handover using multihoming, of the multihoming moving network.
[0031] FIG. 3C is a state diagram after handover completion which
serves to illustrate the logic of a seamless handover using
multihoming, of the multihoming moving network.
[0032] FIG. 4A shows the state before the MMF issues a switching
instruction in the mode in which the MH is not aware of
switching.
[0033] FIG. 4B shows the state after the MMF issues a switching
instruction in the mode in which the MH is not aware of
switching.
[0034] FIG. 5 is a flowchart showing the MMF control operation of
the example in FIGS. 4A and 4B.
[0035] FIG. 6A shows the state before the MMF issues a switching
instruction in the mode in which the MH is aware of switching.
[0036] FIG. 6B shows the state after the MMF issues a switching
instruction in the mode in which the MH is aware of switching.
[0037] FIG. 7 is a flowchart showing the MMF control operation of
the example in FIGS. 6A and 6B.
[0038] FIG. 8 shows the initial state of the mobile communication
system of the second embodiment.
[0039] FIG. 9 is a function block constitutional view of the MMF of
the second embodiment.
[0040] FIG. 10 is a flowchart showing the velocity tracking
processing on the basis of information based on a single AI
combination.
[0041] FIG. 11 shows the state immediately after the NAI is
switched to the new AR.
[0042] FIG. 12 shows the state immediately after the OAI is
switched to the new AR.
[0043] FIG. 13 is a diagram which serves to illustrate the
processing in which a vector sum is calculated.
[0044] FIG. 14 is a flowchart showing the velocity and the
direction of movement tracking processing on the basis of
information based on a plurality of AI combinations.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0045] Various embodiments according to the present invention will
be described hereinbelow. Further, in the embodiment below, because
the case of the mobile host is included in substance by the case of
a moving network, only the case of the moving network will be
illustrated.
First Embodiment
[0046] FIG. 1 is a constitutional view of a mobile communication
system of a first embodiment. As shown in this figure, a mobile
communication system 1 is constituted by a core network 10, which
is constituted comprising a plurality of access routers (referred
to as "AR" hereinafter) 11, 12; and a moving network (referred to
as "MN" hereinafter) 20, which is constituted comprising a
plurality of access interfaces (referred to as "AI" hereinafter)
21, 22, a plurality of mobile hosts (referred to as "MH"
hereinafter) 31, 32, and a control device (referred to as "MMF"
hereinafter) 50, that is provided with a function for governing
mobile management and switching instructions (MMF: Mobility
Management Function). The MH 31 is connected to an AR (AR 11 in the
example in FIG. 1) on the side of the core network 10 via either
line 41 of the AI 21 or line 42 of the AI 22 (line 41 in the
example in FIG. 1), and thus transmits and receives data. The same
is true of the MH 32.
[0047] Further, the MN 20 moves from left to right in FIG. 1. Of
the two AI 21, 22, the AI 22 which lies foremost in the direction
of movement is called an NAI (New Access Interface), and the AI 21
that lies rearward in the direction of, movement is called an OAI
(Old Access Interface).
[0048] FIG. 2 is a function block constitutional view of the MMF 50
of the first embodiment. As shown in this figure, the MMF 50 is
constituted comprising a connection status acquisition section 51,
which acquires information from each AI on the connection status of
each AI to the core network 10; a handover prediction section 52,
which predicts a subsequent handover on the basis of the connection
status information for each AI thus acquired; a change section 53
for dynamically changing the AI adopted as the connection interface
in accordance with predetermined logic when a predetermined
condition is satisfied on the basis of the connection status
information for each AI or prediction information on a subsequent
handover; and a downlink control unit 54 that performs control so
that an MH is allowed to transmit downlink data from the core
network 10 via an AR, of the AR 11, 12 on the side of the core
network 10, which is connected to an AI (referred to as "FAI" (Fine
AI) hereinafter) that is capable of maintaining a predetermined
communication quality.
[0049] FIGS. 3A-3C show the logic for a handover using multihoming,
of the MN 20 has the multihoming function. As shown in FIG. 3A,
prior to the handover, the two AI 21, 22 are connected to the same
AR 11, and data packets are transmitted and received between the MN
20 and the core network 10 via the lines 41, 42 of the AI 21, 22
respectively. At the start of the handover, the NAI 22, which is
frontward in the direction of movement, transitionally enters a
mode in which same is connected to the new AR 12, as shown in FIG.
3B. At such time, the line 41 on the side of the OAI 21 is
disconnected in keeping with movement. However, this can be assumed
according to the function (velocity tracking function of the MN 20)
of the MMF 50 that will be described subsequently. For this reason,
the MMF 50 implements close processing (that is, processing to
disable the transmission and receipt of data although the line 41
is not disconnected) so that all the transmission data P1 and P2 is
transmitted by using the line 42 to which the NAI 22 is connected.
Further, after the handover has ended, the line 41 on the side of
the OAI 21 can then be connected to the new AR 12 as shown in FIG.
3C, and hence a data transfer using two lines as per the initial
state in FIG. 3A is feasible.
[0050] Switching processing is thus switched locally without
propagation to the entire network or informing the origin of the
transmission as per an ordinary handover procedure. Hence, packet
loss and a handover latency caused by a disconnection of the line
on the side of the OAI and by performing non-local switching
processing can be avoided, whereby a seamless handover can be
implemented.
[0051] Specific embodiments according to the handover control
method of the MN 20 equipped with multihoming function will be
described hereinbelow. Here, a mode in which the MH is not aware of
switching (FIGS. 4A, 4B, and 5) and a mode in which the MH is aware
of switching (FIGS. 6A, 6B, and 7) will be described in this
order.
[0052] FIGS. 4A and 4B are state transition diagrams for the mode
in which the MH is not aware of switching, and FIG. 5 is a
flowchart showing the MMF control operation for the example of
FIGS. 4A and 4B. Until the MMF 50 shown in FIG. 4A issues a
switching instruction, each AI 21, 22 reports the connection status
to the core network 10, to the MMF 50 at fixed intervals. As shown
in FIG. 5, the MMF 50 receives information on the connection status
between each AI and the core network 10 from each AI (S01), and, on
the basis of this connection status information, judges whether the
line quality of one AI is poor or not in light of a predetermined
condition (S02). The predetermined condition may be that the field
strength between the AI and core network 10 should be less than a
predetermined threshold value, and may be that a predicted value
for the field strength between the AI and the core network 10 that
is predicted on the basis of subsequent movement prediction should
be less than a predetermined threshold value.
[0053] If it is judged in S02 that the line quality of every AI is
not poor, processing returns to S01 and is repeated. If it is
judged in S02 that the line quality of one AI is poor, a switching
instruction is transmitted to the AI 21, 22 and the core network 10
(S03). More specifically, each of the AI 21, 22 is issued with an
instruction for a mutual connection therebetween, and, more
particularly, the OAI 21 receives an instruction to enter a closed
state, and the core network 10 receives an instruction to transmit
data via the AR 12 on the side of the FAI 22.
[0054] As shown in FIG. 4B, after the above-mentioned switching
instructions have been transmitted, the OAI 21, which has thus
received the switching instruction, causes the line 41 to enter a
closed state so that data is not transmitted or received, without
disconnecting the connection on the line 41 to the core network 10,
and establishes a connection to the NAI 22. Further, also in the
case of the core network 10, which has thus received a switching
instruction, the AR 11 connected to the OAI 21 causes the line 41
to enter a closed state so that data is not transmitted or
received, while still maintaining the connection on the line 41 to
the OAI 21.
[0055] Therefore, a portion of the data transmitted from the MN 20
to the core network 10 can be transmitted to the core network 10
via the side of the NAI 22 access line 42 by passing via the
connecting link between the OAI 21 and the NAI 22, without the MH
31, 32 in the MN 20 being aware of this operation. That is, as
shown in FIG. 4B, the transmission data P1 transmitted by the MH 31
to the core network 10 is transmitted to the core network 10 via
the side of the NAI 22 access line 42 together with the
transmission data P2 transmitted by the MH 32 to the core network
10.
[0056] Next, the mode in which the MH is aware of switching will be
described. FIGS. 6A and 6B are the state transition diagrams of the
mode in which the MH is aware of switching, and FIG. 7 is a
flowchart showing the MMF control operation of the example in FIGS.
6A and 6B. Until the MMF 50 shown in FIG. 6A issues a switching
instruction, each AI 21, 22 reports the connection status to the
core network 10, to the MMF 50 periodically. As shown in FIG. 7,
the MMF 50 receives information on the connection status between
each AI and the core network 10 from each AI (S11), and, on the
basis of this connection status information, it is judged whether
the line quality of one AI is poor or not in light of predetermined
conditions (S12). Similarly to the above-described mode in which
the MH is not aware of switching, the predetermined condition may
be that the field strength between the AI and core network 10
should be less than a predetermined threshold value, and may be
that a predicted value for the field strength between the AI and
the core network 10 that is predicted on the basis of subsequent
movement prediction should be less than a predetermined threshold
value.
[0057] If it is judged in S12 that the line quality of every AI is
not poor, processing returns to S11 and is repeated. If it is
judged in S12 that the line quality of one AI is poor, a switching
instruction is transmitted to the OAI 21, the core network 10, and
the MH 31 on the side of the OAI 21 (S13). More specifically, the
OAI 21 is issued with an instruction to enter a closed state, the
core network 10 receives an instruction to transmit data via the AR
12 on the side of the FAI 22, and the MH 31 receives an instruction
to connect to the NAI 22 instead of the OAI 21.
[0058] As shown in FIG. 6B, after the above-mentioned switching
instructions have been transmitted, the OAI 21, which has thus
received the switching instruction, causes the line 41 to enter a
closed state so that data is not transmitted or received, without
disconnecting the connection on the line 41 to the core network 10.
Further, also in the case of the core network 10, which has thus
received a switching instruction, the AR 11 connected to the OAI 21
causes the line 41 to enter a closed state so that data is not
transmitted or received, while still maintaining the connection on
the line 41 to the OAI 21. In addition, the MH 31 establishes a
connection to the NAI 22 instead of the OAI 21.
[0059] Therefore, with the side of the OAI 21 MH 31 in the MN 20
being aware of switching, the transmission data P1 transmitted by
the MH 31 to the core network 10, can be transmitted to the core
network 10 via the side of the NAI 22 access line 42 by way of the
connecting link between the MH 31 and the NAI 22, as per FIG.
6B.
[0060] In either the switching mode in which the MH is not aware of
switching or the switching mode in which the MH is aware of
switching, as described above, switching is performed locally
without propagation to the entire network or informing the origin
of the transmission, as is the case for an ordinary handover
procedure. Hence, packet loss and a handover latency caused by a
disconnection of the line on the side of the OAI and by performing
non-local switching processing can be avoided, whereby a seamless
handover can be implemented.
[0061] Further, although an example in which, in the MN 20, the AI
used to establish the connection to the core network 10 is switched
from the OAI 21 to the NAI 22, was described above, when the MMF 50
selects one switching-destination AI in a situation where three or
more AI are present, an AI corresponding with the maximum-value
field strength may be selected from among the field strengths
between each AI and the core network 10, for example. Furthermore,
an AI that corresponds with the predicted value for the
maximum-value field strength may be selected from among predicted
values for the field strengths between each AI and the core network
10 Which are predicted on the basis of subsequent movement
prediction.
Second Embodiment
[0062] FIG. 8 is a constitutional view of the initial state of a
mobile communication system lS of the second embodiment. As shown
in this figure, a mobile communication system lS is constituted by
the core network 10, which is constituted comprising a plurality of
AR 11, 12; and the MN 20, which is constituted comprising a
plurality of AI 21, 22, the MH 31, and a control device (MMF) 50
that is provided with a function for governing mobile management
and switching instructions (MMF: Mobility Management Function). The
MH 31 is connected to either AR on the side of the core network 10
via-either line 41 of the AI 21 or line 42 of the AI 22, and thus
transmits and receives data.
[0063] Further, the MN 20 moves from left to right in FIG. 8. Of
the two AI 21, 22, the AI 22 that lies foremost in the direction of
movement is called an NAI (New Access Interface), and the AI 21
that lies rearward in the direction of movement is called an OAI
(Old Access Interface). The MN 20 is therefore a moving network in
which the two AI 21, 22 are multihomed.
[0064] FIG. 9 is a function block constitutional view of the MMF 50
of the second embodiment. As shown in this figure, the fact that
the MMF 50 is constituted comprising the connection status
acquisition section 51, the handover prediction section 52, the
change section 53, and the downlink control unit 54, is the same as
for the MMF 50 of the first embodiment (FIG. 2). However, the
connection status acquisition section 51 is constituted comprising
a locational relationship tracking section 51A that tracks the
locational relationship of all the AI, an information receiver
section 51B that receives information on the connection status of
each AI to the core network 10, and switching information that
includes identification information for, identifying the switching
origin AR when switching occurs and the switching destination AR,
as well as switching end time information, the information being
reported by each AI. The handover prediction section 52 is
constituted comprising a velocity tracking section 52A for tracking
at least velocity information pertaining to the MN 20 in accordance
with a tracking logic (described later), on the basis of the
locational relationship of each AI thus tracked and the connection
status information and switching information thus received, and a
prediction section 52B for predicting subsequent movement and
changes in the field strength from the tracked information. The
velocity tracking section 52A pre-stores information on the
distance x between the two AI 21, 22, and, upon recognizing, on the
basis of the switching information from each AI, that adjacent
switching is with respect to the same AR, the velocity tracking
section 52A tracks, given a switching time difference t for the
adjacent switching and a distance x between the two AI, a value
obtained by dividing the distance x by the switching time
difference t as the velocity pertaining to the MN 20.
[0065] Velocity tracking processing, which is based on switching
information from a single AI combination (that is, the two AI 21,
22) executed by the MMF,50, will be described hereinbelow on the
basis of the flowchart of FIG. 10 and the state diagrams of FIGS.
8, 11, and 12. At the start of processing, the mobile communication
system is in the initial state of FIG. 8, and the AI 21, 22 report
the connection status to the core network 10, to the MMF 50
periodically.
[0066] As shown in FIG. 10, the MMF 50 receives information on the
connection status between each AI and the core network 10 from each
AI (S21), and, on the basis of this connection status information,
judges whether the line quality of one AI is poor or not in light
of predetermined conditions (S22). Just like the first embodiment,
the predetermined conditions may be that the field strength between
the AI and core network 10 should be less than a predetermined
threshold value, and may be that a predicted value for the field
strength between the AI and the core network 10 predicted on the
basis of subsequent movement prediction, should be less than a
predetermined threshold value.
[0067] If it is judged in S22 that the line quality of every AI is
not poor, processing returns to S21 and is repeated. If it is
judged in S22 that the line quality of one AI is poor, a switching
instruction is transmitted to the AI 21 and the core network 10
(S23). Here, in the initial state of FIG. 8 (a state where each AI
is connected to the same AR 11), because the MN 20 moves to the
right in FIG. 8, first the quality of the line 42 of the NAI 22
deteriorates and the quality of the line 42 is judged to be poor in
S22. For this reason, the MMF 50 transmits a switching instruction
for the NAI 22-and core network 10 to switch the connection
destination of the NAI 22 from the current AR 11 to the new AR.
[0068] As shown in FIG. 11, the NAI 22 and core network 10, which
have thus received the switching instruction, switch the connection
destination of the NAI 22 to the new AR 12, and hence the AR 12 and
NAI 22 are connected by the line 42. Further, location information
on the new AR 12 and information about the time (switching time) t1
when switching to the AR 12 has completed, are transmitted to the
MMF 50.
[0069] The MMF 50 receives the location information on the, new AR
12 and the information about the switching time t1 from the NAI 22,
and cumulatively stores them (S24) Because, at this time, only one
AI 22 is switched, S25 yields a negative judgment, and processing
returns to S21, whereupon the processing of step S21 and subsequent
steps are executed once again.
[0070] Further, in the state of FIG. 11, because the MN 20 moves
again to the right in FIG. 8, the quality of the line 41 of the OAI
21 then deteriorates and it is thus judged in S22 that the quality
of the line 41 is poor. For this reason, the MMF 50 transmits a
switching instruction for the OAI 21 and the core network 10 to
switch the connection destination of the OAI 21 from the current AR
11 to the new AR.
[0071] As shown in FIG. 12, the OAI 21 and core network 10, which
have thus received the switching instruction, switch the connection
destination of the OAI 21 to the new AR 12, and hence the AR 12 and
OAI 21 are connected by the line 41. Further, location information
on the new AR 12 and information about the time (switching time) t2
when switching to the AR 12 has completed, is transmitted to the
MMF 50.
[0072] The MMF 50 receives the location information on the new AR
12 and the information about the switching time t2 from the OAI 21,
and cumulatively stores them (S24) Because, at this time, the
location information on the new AR and the information about the
switching time have been received from both of the two AI, S25
yields an affirmative judgment, and processing proceeds to S26.
[0073] In S26, the velocity tracking section 52A recognizes that
the switching between the two AI 22, 21 is the switching between
the same AR, by the fact that the location information on the new
AR 12 of the NAI 22 corresponds to the location information on the
new AR 12 of the OAI 21. In addition, the velocity tracking section
52A obtains a value by dividing the pre-prepared distance x between
the AI 21, 22 by the switching time difference t (where t is
equivalent to (t2-t1)) for the two switching events, and tracks the
value as the velocity pertaining to the MN 20. Further, at such
time, the velocity tracking section 52A is able to track the
direction of movement in which the NAI 22 locates forward side and
the OAI 21 locates backward side, as the direction of movement of
the MN 20. In addition, in S27, the prediction section 52B is able
to predict the subsequent movement of the MN 20 and change in the
field strength on the basis of the velocity and the direction of
movement of the MN 20.
[0074] Further, although MN velocity tracking was described in the
above description on the basis of the switching information from
one combination of AIs (that is, the two AI 21, 22), the velocity
and the direction of movement of the MN can be tracked as detailed
below, on the basis of switching information from plural
combinations of AIs (that is, three or more AI), by applying the
above-described technology to practical use.
[0075] That is, the processing of FIG. 14 is executed by the MMF
50. In S31 and S32, the velocity tracking section 52A executes the
above-described velocity tracking processing in FIG. 10, for each
of a plurality of combinations of the AIs. For example, two
velocity vectors v1, v2 are obtained as shown in FIG. 13 on the
basis of the switching information from two combinations of AIs.
Here, the direction of each velocity vector is equivalent to the
tracked direction of movement, and the size of each velocity vector
is equivalent to a value for the tracked velocity.
[0076] Further, the velocity tracking section 52A calculates a
vector sum in S33, and, in S34, tracks the direction of movement
and the velocity of the MN on the basis of the vector obtained. In
the example in FIG. 13, a synthesized vector V is obtained by
calculating the vector sum of the two velocity vectors v1, v2, and
the direction of movement of the MN can be tracked on the basis of
the direction of the synthesized vector V, and the velocity of the
MN can be tracked on the basis of the size of this synthesized
vector V. In addition, in S35, the prediction section 52B is able
to predict the subsequent movement and change in the field strength
of the MN 20 on the basis of the velocity and direction of movement
of the tracked MN 20.
[0077] As described above, the velocity and direction of movement
of the MN 20 can also be tracked on the basis of either the
switching information from one combination of AIs (two AIs) or
switching information from a plurality of combinations of AIs
(three or more AIs), and the subsequent movement and change in the
field strength is predicted on the basis of the tracked
information. For this reason, handover prediction information of
favorable accuracy can be obtained, and it is possible to implement
a seamless handover more reliably.
[0078] Further, although a case where the present invention was
applied to an MN (moving network) was described in each of the
above-described embodiments, the same effects can be obtained by
performing a similar operation also in a case where the present
invention is applied to an MH (mobile host).
[0079] As described hereinabove, according to the present
invention, in the case of a mobile host and network that are
multihomed by means of a plurality of access interfaces, attention
is drawn to a characteristic in which the communication quality of
the line connected to each access interface varies according to
movement, and once information on the connection status of each
access interface to the core network has been acquired or a
subsequent handover predicted, the access interface adopted as the
connection interface is dynamically changed on the basis of this
connection status information or subsequent handover prediction
information. Thus, conventionally, when a handover latency is
generated without the variation in the communication quality of the
line connected to each access interface being predicted, packet
loss can be avoided and a seamless handover can be implemented, by
minimizing the handover latency by means of the dynamic change to
the access interface on the basis of the connection status
information or handover prediction information.
* * * * *
References