A METHOD OF SUPPORTING HANDOVER IN A MULTI-MODE MOBILE

STATION

TECHNICAL FIELD

The present invention relates to a method of supporting handover, and more

particularly, to a method of supporting handover in a multi-mode mobile station. Although

the present invention is suitable for a wide scope of applications, it is particularly suitable

for supporting handover of a multi-mode mobile station in a wireless mobile

communication system.

BACKGROUND ART

Generally, the object of IEEE 802.21 in progress for International Standardization of

Media Independent Handover between heterogeneous networks is to enhance user's

convenience for Mobile Station (MS) devices by providing seamless handover and service

continuity. Basic requirements' here include a MIH function, an event trigger (or event

service), a command service (CS) and an information service (IS) are defined as basic

requirements.

A mobile station (MS), which can also be referred to as a mobile subscriber station

(MSS) or a mobile terminal, is a multi-mode node that supports at least two interface types.

Here, the interface can be, for instance, a wire-line type interface such as 802.3-based

Ethernet, a wireless interface type based on IEEE 802.XX, such as IEEE 802.11, IEEE

802.15, IEEE 802.16 and the like, an interface type defined by cellular standardization

organization such as 3 ^rd Generation Partnership Project (3 GPP) and 3GPP2 and the like are

possible.

FIG. 1 is a diagram of protocol stack architecture of a multi-modal MS. Referring to

FIG. 1 , the multi-modal MS comprises a Physical (PHY) layer per mode and a Medium

Access Control (MAC) layer per mode. In addition, an MIH layer is placed below an

Internet Protocol (IP) layer.

The MIH should be defined between IEEE802-seri.es interfaces or between the 802-

series interfaces such as the above-mentioned non-802-series interfaces defined by the

cellular standardization organization such as 3GPP and 3GPP2. Moreover, a mobility

supporting protocol of an upper layer such as Mobile IP and SIP (session initiation protocol)

should be supported for the seamless handover service.

The MIH function is placed below the IP layer. Furthermore, the MIH function

facilitates the handover process by using the input values from Layer 2 such as trigger event

information and information of othel networks. Moreover, the MIH function can include

input values (e.g., user policy and configuration) which can affect the handover procedure.

In addition, general interfaces (e.g., the Mobile IP and the SIP) are defined between Layer 3

entities and the MIH Function. These interfaces provide information associated with

Layer 1 (i.e., PHY Layer) and Layer 2 (i.e., MAC Layer) as well as mobility management.

The MIH function uses an event service (ES) to acquire information on lower layers and the

network.

An Upper Management Entity (UPE) is located in the upper layer to monitor and

control statuses of various links in the MS. Furthermore, the UPE is used to perform

handover control function and device manager function. Here, the handover control

function and the device manager can be independently located or can be included in the

upper management entity.

In the present invention, the terms 'upper' and 'higher' are used interchangeably to

describe the upper/higher management entity, upper/higher layers, and a like.

Figure 2 illustrates a MS having a MIH function and a network having a functional

entity and transmission protocol, hi Figure 2, the dotted lines represent services such as a

primitive and the ES.

As illustrated in Figure 2, for faster handover, the network layer uses the

information from a link layer in order to quickly re-establish connection. The link layer

event can be used to predict the user's movement and also can be used prepare for handover

between the mobile terminal and the network. The trigger for handover procedure can be

initiated from the PHY layer and the MAC layer. Moreover, the source of the trigger can be

a local stack or a remote stack.

Figure 3 illustrates a structure of a trigger model. An event trigger provides

information related to the status of current signals, changes in status of other network,

predictable changes as well as changes in the PHY layer and the MAC layer and changes in

the properties of a certain network.

The event types can be classified into a PHY layer event, a MAC layer event, a

management event, an L3 event, and an application event. A basic trigger event is as

follows.

LinkJUp notification is delivered when a Layer 2 connection is established on the

specified link interface and when other upper layers can send higher layer packets. All

Layer 2 activities in establishing the link connectivity are determined to be completed at this

point of time. Here, the source of the LinkJUp event is the Local MAC and the Remote

MAC. Table 1 shows parameters of LinkJUp notification.

[Table 1]

Link_Down notification is delivered when a Layer 2 connection is broken on the

specified link and when no more packets can be sent on the specific link. Here, the source

of the Link_Down event is the Local MAC Table 2 shows parameters of Link_Down

notification.

[Table 2]

Link_GoingJDown notification is delivered when a Layer 2 connection is expected

(predicted) to go down (LinkJDown) within a certain time interval. Link_Going Down

event may be the indication to initiate handover procedures. Here, the source of the

Link_Going_Down event is the Local MAC and the Remote MAC. Table 3 shows

parameters of Link_Going_Down notification.

[Table 3]

Link_Going_Up notification is delivered when a Layer 2 connection is expected

(predicted) to go up (LinkJUp) within a certain time interval. Moreover, the notification is

used when excessive "amount of time is expanded in initializing the network. Here, the

source of the Link_Going_Up event is the Local MAC and the Remote MAC. Table 4

shows parameters of Link_Going_Up notification.

[Table 4]

Link_Event_Rollback indication is used in conjunction with Lirik_Going_Down.

That is, it combines Link_Going_Up and Link_Going_Down for use. More specifically, if

the link is no longer expected to go up (Link_Up) or go down (LirikJDown) in the specified

time interval, then a Link_Event_Rollback message is sent to the Event destination. Here,

the source of the Link Event Rollback event is the Local MAC and the Remote MAC.

Table 5 shows parameters of Link_Event_Rollback inciation.

[Table 5]

Link_Available indicates a new available link. That is, Link_Available indicates the

possibility that a new base station or a point of attachment (PoA) can provide better link

quality than that of the PoA (which can be also referred to as an access point, a base station,

or a network entity) to which the MS is connected. Here, the source of the Link_Available

event is the Local MAC and the ^" Remote MAC. Table 6 shows parameters of

Link Available.

[Table 6]

Link_Parameters_Change indicates changes in link parameters when specified

threshold levels are crossed. This may include link layer parameters such as speed of the

link, Quality of Service (QoS), ^" Bit Error Rate (BER), etc. The threshold level for each such

parameter can be configured through a separate command to link layer. Here, the source of

the Link_Parameters_Change event is the Local MAC and the Remote MAC. Table 7 show

parameters of Link_Parameters_Change.

[Table 7]

Figure 4 illustrates a trigger when establishing a new link due to decreased quality of

the current link.

An Information Service (IS) provides a framework by which a MIH Function both

in the mobile terminal and in the network can discover and obtain network information

within a geographical area to facilitate handovers. Here, the IS is accessible to any network.

The IS includes the following information elements, such as a link access parameter, a

security mechanism, a neighbor map, a location, a cost of link, and a provider and other

access information.

The conventional art defines the ES, CS, and IS for the MIH. However, when the ES,

CS, and IS are transmitted/received between a local stack and a remote stack based on the

MIH messages, there is not a defined MIH protocol procedure, a MIH header, and a

message format.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention is directed to a method of supporting handover in

a multi-mode mobile station that substantially obviates one or more problems due to

limitations and disadvantages of the related art.

An object of the present invention is to provide a method of discovering at least one

of a homogeneous and a heterogeneous network module to perform handover with in a

wireless mobile communication network.

Another object of the present invention is to provide an apparatus for discovering at

least one of a homogeneous and a heterogeneous network module to perform handover with

in a wireless mobile communication network.

Additional advantages, objects, and features of the invention will be set forth in part

in the description which follows and in part will become apparent to those having ordinary

skill in the art upon examination of the following or may be learned from practice of the

invention. The objectives and other advantages of the invention may be realized and

attained by the structure particularly pointed out in the written description and claims hereof

as well as the appended drawings.

To achieve these objects and other advantages and in accordance with the purpose of

the invention, as embodied and broadly described herein, a method discovering at least one

of a homogeneous and a heterogeneous network module to perform handover with in a

wireless mobile communication network includes establishing a network handover module

for converging information from at least one network interface module associated with at

least one of a homogeneous and a heterogeneous network handover module into a unified

presentation and transmitting a broadcast request message from a mobile station (MS) to a

source point of attachment (PoA) which transmits the broadcast request message to at least

one interface module to identify whether the at least one interface module supports at least

one of the homogeneous and the heterogeneous network handover module and a capability

of the at least one of the homogeneous and the heterogeneous network handover module.

The method further includes initiating a timer for a specified time period ¹ when the

broadcast request message is transmitted and receiving at least one response message from

the at least one interface module via the source PoA prior to expiration of the timer, wherein

the response message indicates that the at least one interface module supports at least one of

the homogeneous and the heterogeneous network handover module and the capability of the

at least one of the homogeneous and the heterogeneous network handover module.

In another aspect of the present invention, a method includes establishing a network

handover module for converging information from at least one network interface module

associated with at least one of a homogeneous and a heterogeneous network handover

module into a unified presentation and transmitting a request message from a mobile station

(MS) to a target module to identify whether the target module supports at least one of the

homogeneous and the heterogeneous network handover module and a capability of the at

least one of the homogeneous and a heterogeneous module, wherein the request message

includes an address of the target module. The method further includes initiating a timer for a

specified time period when the request message is transmitted and receiving a response

message from the target module prior to expiration of the timer, wherein the response

message indicates that the target module supports the at least one of the homogeneous and

the heterogeneous network handover module and a capability of the at least one of

the homogeneous and the heterogeneous module.

In further aspect of the present invention, an apparatus for discovering at least one of

a homogeneous and a heterogeneous network module to perform handover with in a

wireless mobile communication network includes a controller for establishing a network

handover module for converging information from at least one network interface module

associated with at least one of a homogeneous and a heterogeneous network handover

module into a unified presentation and for initiating a timer for a specified time period when

the broadcast request message is transmitted. The apparatus further includes a transmitter

for transmitting a broadcast request message from the apparatus to a source point of

attachment (PoA) which transmits the broadcast request message to at least one interface

module to identify whether the at least one interface module supports at least one of the

homogeneous and the heterogeneous network handover module and a capability of the at

least one of the homogeneous and the heterogeneous network handover module, and a

receiver for receiving #t least one response message from the at least one interface module

via the source PoA prior f> expiration of the timer, wherein the response message indicates

that the at least one interface module supports at least one of the homogeneous and the

heterogeneous network handover module and the capability of the at least one of the

homogeneous and the heterogeneous network handover module.

It is to be understood that both the foregoing general description and the following

detailed description of the present invention are exemplary and explanatory and are

intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding

of the invention and are incorporated in and constitute a part of this application, illustrate

embodiment(s) of the invention and together with the description serve to explain the

principle of the invention. In the drawings;

FIG. 1 is a diagram of protocol stack architecture of a multi-modal MS;

FIG. 2 illustrates a MS having a MIH function and a network having a functional

entity and transmission protocol;

FIG. 3 illustrates a structure of a trigger model;

FIG. 4 illustrates a trigger when establishing a new link due to "decreased quality of

the current link;

FIG. 5 illustrates an- architecture of a MIH event and a link event according to an

embodiment of the present invention;

FIG. 6 illustrates an architecture of a remote link event according an embodiment of

the present invention;

FIG. 7 illustrates an architecture of a remote MIH event according to an embodiment

of the present invention;

FIG. 8 illustrates an architecture of a MIH command and a link command according

to an embodiment of trie present invention;

FIG. 9 illustrates an architecture of a remote MIH command according to an

embodiment of the present invention;

FIG. 10 illustrates an architecture of a remote link command according to an

embodiment of the present invention;

FIG. 11 illustrates a flow of a media independent information service of a MS

according to an embodiment of the present invention;

FIG. 12 illustrates a relationship between MIH function and other protocol layers in

a protocol stack according to an embodiment of the present invention;

FIG. 13 illustrates a message format of a MIH packet according to an embodiment

of the present invention;

FIG. 14 illustrates a message format of a MIH packet according to another

embodiment of the present invention;

FIG. 15 illustrates a flow of an embodiment of the present invention;

FIG. 16 illustrates a flow of another embodiment of the present invention;

FIG. 17 illustrates a flow of yet another embodiment of the present invention;

FIG. 18 illustrates a flow of a further embodiment of the present invention;

FIG. 19 illustrates a flow of another embodiment of the present invention; and

FIG. 20 illustrates an exemplary diagram of an apparatus for discovering μn entity to

perform handover with in a wireless mobile communication system.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the preferred embodiments of the present

invention, examples of which are illustrated in the accompanying drawings. Wherever

possible, the same reference numbers will be used throughout the drawings to refer to the

same or like parts.

In the present application, the term mobile station (MS) can also be referred by a

mobile subscriber station (MSS), a mobile terminal (MT), a mobile node (MN), a terminal,

and a like.

Figure 5 illustrates an architecture of a MIH event and a link event according to an

embodiment of the present invention. More specifically, the MIH event includes event

information that is transmitted from the MIH to the upper management entity (UPE) or to

upper (or higher) layers. With respect to the conventional art, the MIH event corresponds to

event trigger. The link event is transmitted from the lower layers (e.g., MAC layer or

physical layer) to the MIH. Furthermore, the link event uses primitives used in interfaces

with the MAC layer or the physical (PHY) layer.

Figure 6 illustrates an architecture of a remote link event according an embodiment

of the present invention. .Referring to Figure 6, if an event is triggered from the lowers

layers of a local stack to the MIH in the same lower stack, the MIH of the local stack

transmits the event information to the MIH of the remote stack. Alternatively, if an event is

triggered from the lower layers of a remote stack to the MIH of the same remote stack, the

MIH of the remote stack transmits the event information to the MIH of the local stack.

Figure 7 illustrates an architecture of a remote MIH event according to an

embodiment of the present invention. In Figure 7, the MIH of the local stack triggers the

MIH event and transmits the event information to the MIH of the remote stacJc. After

receiving the event information, the MIH of the remote stack transmits the received event

information to the upper management entity (UPE) or to the upper layers. Alternatively, if

the MIH of the remote stack triggers an event to the MIH of the local stack, the MIH of the

local stack transmits the event information to upper layers of the local stack.

Figure 8 illustrates an architecture of a MIH command and a link command

according to an embodiment of the present invention. The MIH command is generated at

the UPE or the upper layers and transmitted to the MIH with instructions. The link

command is generated at the MIH and transmitted to the lower layers with instructions.

Figure 9 illustrates an architecture of a remote MIH command according to an

embodiment of the present invention. In Figure 9, the UPE or the upper layers of the local

stack generates and transmits the remote MIH command to the MIH. After receiving the

MIH command, the MIH transmits the received MIH command to the MIH of the remote

stack. Alternatively, the MIH command is transmitted from the upper layers of the remote

stack to the MIH of -the remote stack, and subsequently, the MIH of the remote stack

transmits the MIH command to the MIH of the local stack.

Figure 10 illustrates an architecture of a remote link command according to an

embodiment of the present invention. In Figure 10, the MIH of the local stack generates and

transmits the remote lihk command to the MIH of the remote stack. The MIH of the remote

stack then transmits the received remote link command to the lower layers of the remote

stack. Alternatively, the MIH of the remote stack transmits the remote link command to the

MIH of the local stack, which in turn, transmits the remote link command to the lower

layers of the local stack.

Figure 11 illustrates a flow of a media independent information service of a MS

according to an embodiment of the present invention. Initially, the MIH of the MS sends a

MIH_info. request message to the MAC of the MS to request for information service. Upon

receiving the request message, the MAC of the MS sends an Information Request Frame to

the MAC of a base station (BS). The MAC of the BS then sends the request by the MS to

the MIH of the BS via MIH_info. indication message. In response, the MIH of the BS sends

a media independent information service via MIH_info .response message to the MAC of

the BS. Then, the MAC of the BS sends an Information Response Frame to the MAC of the

MS. Upon receipt of 'the Information Response Frame, the MAC of the MS sends the

received information service to the MIH of the MS via MIH_info. confirm message.

MIH protocol comprises the following three stages. A first stage is defined by a

MIH capability discovery. This stage relates to discovering by the MIH of the MS or the

MIH of the BS/access router which entity of the network supports MIH function. Next,

MIH registration represents the next stage. In this stage, the MIHs of different entities

perform registration processes with each other in order to initiate MIH protocol. Lastly,

MIH message exchange 'stage represents two registered MIHs transmit/receive MIH

messages using a MIH payload and MIH protocol.

Figure 12 illustrates a relationship between MIH function and other protocol layers

in a protocol stack according to an embodiment of the present invention. Figure 13

illustrates a message format of a MIH packet according to an embodiment of the present

invention. The details of each field are as follows.

A 'Message Type' field (Octet 1) represents different messages based on message

type as shown in Table 8.

[Table 8]

A 'Length' field (Octet 1) represents a total length of the entire header including the

MIH message. A 'Sequence Number' field (Octet 1) represents a total count of message

transmissions. An 'IP' field (1 bit) indicates whether an internet protocol (IP) address

included in the header is associated with IPv4 or IPv6 (e.g., 0: IPv4, 1: IPv6). A 'F' field (1

bit) indicates whether the message is fragmented or not (e.g., 0: no fragmentation, 1:

fragmentation).

A 'Fragmentation Offset' field (Octet 1) indicates remaining number of packets

needed to form a complete message if one packet is insufficient to form a complete message.

A 'XID (Packet ID)' field (Octet 1) is used to match each request message to each

confirmation message.»A 'Source Hardware Type' field (4 bits) indicates a hardware type of

the transmitting end (e'.g.^OOOO: IEEE 802.3 interface, 0001 : IEEE 802.11 interface, 0010:

IEEE 802.16 interface, 0011: 3GPP interface, 0100: 3GPP2 interface, 0101-11111:

reserved).

A 'Destination Hardware Type' field (4 bits) indicates a hardware type of the

receiving end (e.g., 0000: IEEE 802.3 interface, 0001: IEEE 802.11 interface, 0010; IEEE

802.16 interface, 0011: 3GPP interface, 0100: 3GPP2 interface, 0101-11111: reserved). A

'Source Hardware Address' field represents aTiardware address of the transmitting end (e.g.,

Layer 2 address). A 'Source IP Address' field represents the IP address of the receiving end.

A 'Destination Hardware Address' field represents a hardware address of the transmitting

end (e.g., Layer 2 address). A 'Destination IP Address' field represents the IP address of the

receiving end. A 'MIH Message' includes actual messages of a remote event registration,

event, service, and command service in a Type, Length, Value (TLV) format.

Figure 14 illustrates a message format of a MIH packet according to another

embodiment of the presenfinvention. The details of each field of Figure 14 are as follows.

A 'Protocol Version' field represents a version of the MIH protocol, and the basic

value is 'OxOl.' A 'MIH Service ID' field is a identifier of the MIH service (e.g., 1: Event

Service; 2: Command Service; 3: Infoπnation Service). A 'MIH Opcode' field defines an

operation to the performed (e.g., 1: Request; 2: Response; 3: Indication). A 'Transaction ID'

field is used to match a request message to a response message. A 'Fr' field represents a

fragmentation flag (e.g., 1: current packet is fragmented at least once; 2: current packet is

not fragmented). A 'Fragment No.' field indicates a fragmentation number of a packet. A

'Message Length' field represents a total length of an entire message.

Furthermore, a 'MIH Function Identifier Length (MIHFL)' field indicates a length

of each 'Source/Destination MIH Identifier' field. A 'Source MIH Function Identifier' field

identifies the MIH of the transmitting end and can have a Layer 2 hardware address or an

IP -based Layer 3 address. Alternatively, this field can be a new MIH address identifier. A

'Destination MIH Function Identifier' field identifies the MIH of the receiving end and can

have ^r a ^* Layer 2 hardware address or an IP-based Layer 3 address. Alternatively, this field

can be a new MIH address identifier.

A 'MIH Message ID' field identifies an actual MIH message and is shown in Table

9.

[Table 9]

A 'MIH Message Data' field indicates a particular data of a MIH service.

As discussed above, the MIH packet can have a message format of Figure 13 or

Figure 14.

A signal message between MIHs can be classified by 'MIH Capability Discovery,'

'MlH Remote Event ^l Registration,' 'MIH Remote Event Service,' and 'MIH Remote

Command Service.

In order for the MS, the PoA (e.g., a wireless PoA, broadband wireless access

network BS, cellular system BS) ₃ a network entity (e.g., a router, foreign agent) to discover

MIH capability of the corresponding entity (e.g., a MS, PoA, network entity), the formats of

the MIH packet are used to classify different methods.

As a first method, if the MIH packet is represented by the format of Figure 13, a

MIH_Capability_Discover.request message and a MIH_Capability_Discovery.response

message can be used to discover a MIH capability of the corresponding entity.

The MIH_Capability_Discover.request message does not include a MIH message

payload and is included in a MIH header in which the 'Message Type' field is set to '1.'

This message can be transmitted via Layer 2 or Layer 3. If the transmitting entity does not

know the exact address of, the receiving entity, a broadcast message can be used to discover

which entity of the network possesses the MIH function. Alternatively, even though the

transmitting entity knows the address of the receiving entity, if the transmitting entity

desires to know whether the receiving entity has the MIH function, the message is sent in

unicast.

If the receiving entity of the MIH_Capability_Discovery .request message has the

MIH function, then it can respond by transmitting the MIH_Capability_Discovery.response

message. This message also does not include the MIH ^" message payload and is included

only in the MIH header in which the 'Message Type' field is set to '1.' As is the case in the

request message, this response message can be sent via Layer 2 or Layer 3. Here, the

destination address included in the MIH header is assigned with a duplicated source address

of the MIH_Capability_Discovery.request message, and the source address is assigned with

its own address. Further-more, the entity with the MIH function can advertise periodically its

MIH capability via Layer 2 or Layer 3.

As a second method, if the MIH packet is represented by the format of Figure 14,

the payload part of Figure 14 can be removed and transmit the MIH header only to the

corresponding entity in order to discover whether the corresponding entity has MIH

capability or not. After receiving the MIH header, the receiving entity responds by

transmitting its MIH header using the 'Source Address' field from the received header.

Such an action is possible if the receiving entity has the MIH capability.

As a third method, if the MIH packet is represented by the format of Figure 14, a

MIH message data can be removed and transmit the MIH header and a MIH Message

Identifier in order to discover whether the corresponding (receiving) entity has MIH

capability. Here, the MIH__Capability__Discover.request message and the

MIH_Capability_Discovery.response message can be further described as follows.

With respect ttT the MIH__Capability_Discover.request message, a MIH Message

Identifier can be set as MIH_Capability_Discover.request message and then transmitted.

This message can be transmitted via Layer 2 or Layer 3. If the transmitting entity does not

know the exact address of the receiving entity, a broadcast message can be used to discover

which entity of the network possesses the MIH function. Alternatively, even though the

transmitting entity knows the address of the receiving entity, if the transmitting entity

desires to know whether the receiving entity has the MIH function, the message is sent in

unicast.

If the receiving entity of the MIH_Capability_Discovery.request message has the

MIH function, then it pan respond by transmitting the MIH_Capability_Discovery .response

message. This message can be transmitted by including the parameters listed in Table 10 in

the MIH message data. As, is the case in the request message, this response message can be

sent via Layer 2 or Layer 3. Here, the destination address included in the MIH header is

assigned with a duplicated source address of the MIH_Capability_Discovery.request

message, and the source address is assigned with its own address. Furthermore, the entity

with the MIH function can advertise periodically its MIH capability via Layer 2 or Layer 3.

[Table 10]

As discussed above, a signal message between MIHs can be classified by 'MIH

Capability Discovery,' -'MIH Remote Event Registration,' 'MIH Remote Event Service,'

and 'MIH Remote Command Service.' Up to this point, the discussion has been with

respect to messages related to 'MIH Capability Discover.' Next, messages related to 'MIH

Registration' will be discussed.

A MIH_Event_Registration_request message is used by the MIH function which

desires to register an event service to be received in the remote stack. The details of which

are shown in Table 1 L

[Table 11]

A MIH_Event_Registration. confirm message is used to transmit the result of the

MIH_Event_Registration_request message. The details of which are shown in Table 12.

[Table 12]

A MIH_Event_Deregistration.request message is used to cancel registration of the

event service registered in the remote stack. The details of which are shown in Table 13.

[Table 13]

A MIHJEvent^Deregistration.request message is used to transmit the result of the

MIH_Event_Deregistration.request message. The details of which are shown in Table 14.

[Table 14]

Next, discussions related to 'MIH Event Service' will be presented. A

MIHJLink_Up.indication message is used by the MS or the PoA to transmit LinkJUp to the

remote stack. This message indicates to the remote stack that a new link has been

established. This message can be transmitted from the entities that have MIH capabilities to

not only the MS or the PoA but also to all the entities that support the MIH function. The

details of which are shown in Table 15.

[Table 15]

A MIH_Link_Down.indication message is used by the MS or the PoA to transmit

Link__Up to the remote stack. This message indicates to the remote stack that a new link has

been disconnected. This message can be transmitted from the entities that have MIH

capabilities to not only the MS or the PoA but also to all the entities that support the MIH

function. The details of which are shown in Table 16.

[Table 16]

'ReasonCode' from Table 16 includes various values. One of the values included is

a value labeled RC_EXPLICIT_DIS CONNECT which indicates that the link is down

because of explicit disconnect procedures initiated by client or network. Another value is

labeled RC PACKET TIMEOUT which indicates that the link is down because no

acknowledgements were received for transmitted packets within the specified time limit.

RCJF AIL-NORES OURCE value indicates that the link is down because there were no

resources to maintain the connection. Lastly, a value labeled RC_VENDOR_SPECIFIC

indicates a vendor specific reason code.

Next, discussions related to 'MIH Command Service' will be presented. First, there

is a 'MIH_Network_Address_Information.request' message which is transmitted to a

currently connected access point or the BS to request for new IP address information of a

new PoA before the MS attempts to perform handover with another interface network. After

receiving the message, if the new PoA has the address information of the foreign agent (FA)

or the access router, the new PoA sends the address information to the current PoA of the

MS. However, if the new PoA does not have the address information, the new. PoA sends

the address information to a new FA or a new access router. The details of which are shown

in Table 17.

[Table 17]

Second, there is a 'MIH_Network_Address_Information.response' message. This

message is transmitted by the new FA or access router to provide corresponding IP address

information in response to the 'MIH__Network_Address_Information.request' message. The

details of which are shown in Table 18.

[Table 18]

Figure 15 illustrates a flow of an embodiment of the present invention. More

specifically, the MS broadcasts the 'MIH_Capability_Discover.request/response' messages

to discover which entity in the network supports the MIH function and/or the MEH

capability. The terms 'entity' and 'module' can be interchangeably used throughout the

present application. In addition, the terms 'MIH function' and a 'network handover module'

can be used interchangeably.

The MIH function (the network handover module) refers to whether the entity has

the function to facilitate handover between heterogeneous networks and/or between

homogeneous networks. As for an entity which has MIH capability, this means that the

entity indicates which service list is supported by the MIH of the entity. The service list

includes a command service (CS), an event service (ES), and an information list (IS). It is

possible for the entity to have more than one service list.

First, a network handover module is established for converging information from at

least one network interface module (e.g., a wired-line broadband interface, a wireless

broadband interface, and a cellular interface) associated with at least one of a homogeneous

and a heterogeneous network handover module into a unified presentation. Thereafter, the

MS broadcasts via Layer 2 a 'MIH_Capability_Discover.request' message to determine

which entity in the network supports the MIH function. In addition, the message ban also be

broadcasted via Layer 3. If the message is sent via Layer 2, information in the 'Destination

Hardware Address' field of Figure 13 packet format can be broadcasted while information

in the 'Destination Address' field can be broadcasted as well. Here, a new 'Ethertype' field,

which has the capability to identify MIH capability, can be included in the Layer 2 message

header to identify the MIH message. Alternatively, if the message is sent via Layer 3, the

'Destination IP Address' field of Figure 13 packet format can be transmitted. Here, in order

for Layer 3 (e.g., IP layer) to identify this message as the MIH message, a 'protocol type'

field can be defined and included as a new MIH type.

Alternatively, the MS can transmit (unicast) via Layer 3 a

'MIH_Capability_Discover.request' message to determine whether a specific (or a target)

entity supports the MIH function and/or MIH capability. Here, homogeneous and/or

heterogeneous networks are applicable. In addition, the MS can transmit

'MIH_Capability_Discover.request' message via Layer 2. Here, the request message is

transmitted to a PoA first. Thereafter, the request message is then transmitted or relayed to a

specific entity to determine whether the specific entity supports the MIH function and/or

MIH capability.

Second, the MS can initiate a timer (Tl) when transmitting the

'MIH_Capability_Discover.request' message. In case where the message is transmitted to a

specific target (entity), if the 'MIH_Capability_Discover.response' message is not received

during the time set in the timer, the MS determines that there is no receiving entity. In case

where the message is broadcasted, if the 'MIH_Capability_Discover.response' message is

not received during the time set in the timer, the MS determines that there is no entity that

supports the MIH function. The PoA broadcasts via a Layer 2 link of the PoA.

If the request message is broadcasted via Layer 3, the PoA receives this message and

sends the message to a broadcast area of Layer 3 (e.g., a specified subnet, entire area),

which in turn transmits via Layer 3. In Figure 15, Po A3 does not have the MI ¹ H function

(MIHF) and therefore, cannot receive the MIH message. Furthermore, PoA3 cannot receive

the 'MIH_Capability_Discover.request' message and thus cannot respond to this message,

as illustrated in step 4.

However, PoA2 and the FA/access router, which supports the MIH function, can

receive the request message and send the 'MIH_Capability_Discover.response' message in

response to the request message, as shown in step 5. Thereafter, the MS receives the address

information included in the response message and determines which entity has the MIH

capability. Subsequently, the MS can send the address to the UPE or can keep this address

for use in future handovers.

Figure 16 illustrates a flow of another embodiment of the present invention. More

specifically, Figure 16 shows discovery of an entity that supports MIH function from a

plurality of entities or modules in the network initiated by PoAl. The difference from

Figure 15 is that here, the message is broadcasted (initiated) by PoAl (e.g., BS, access point,

network entity) instead of the MS. Beside this difference, the steps are same to those of

Figure 15.

Figure 17 illustrates a flow of yet another embodiment of the present invention.

More specifically, Figure 17 illustrates a failed scenario in discovering the entity having

MIH function capabilities.

First, the MS transmits a 'MIH__Capability_Discover.requesf message to PoAl to

determine whether PoA3, whose address information is known by the MS, supports the

MIH function. Upon transmission, the timer is initiated. PoAl looks at the destination

address of the message, determines that the message is targeted for Po A3, and transmits

(forwards) the message to PoA3. The message is then received by PoA3. Here, the MIH

packet format is used in transmission of the MIH message.

In this example, the PoA3 does not support MIHF and thus PoA3 cannot receive the

message and cannot respond to the message. Since the MS has not received the response

message prior to the expiration of the'timer, which was initiated at the transmission of the

'MIH_Capability_Discover.requesf message, the MS learns that PoA3 does not support the

MIH function based on the expired timer.

Figure 18 illustrates a flow of a further embodiment of the present invention.

Contrary to Figure 17, Figure 18 illustrates an example where the entity having the MIH

function capabilities is successfully discovered. The steps up to PoA3 receiving the message

is same as in Figure 17. However, since PoA2 supports the MIHF, PoA2 can receive the

'MIH_Caρability_Discover.request' message transmitted from the MS. In response, PoA2

can then send the 'MIH_Capability_Discover.response' message. Here, since the MS

receives the response message prior to the expiration of the timer, the MS can discover that

PoA2 supports the MIH function.

Figure 19 illustrates a flow of another embodiment of the present invention. More

specifically, the MS determines via Layer 3 whether the corresponding node

(entity/module) supports the MIH function.

The MS transmits a 'MIH_Capability_Discover.request' message using the IP

address discovered during link establishment with the corresponding node. At this time

(time of transmission), a timer is initiated. Upon receiving the request message, since the

corresponding node supports the MIH function, the corresponding node can receive the

message and respond by transmitting a 'MIH_Capability_Discover.response' message to

the MS. Since the response message is received by thVMS prior to the expiration of the

timer, the MS can discover that the corresponding node supports the MIH function.

Figure 20 illustrates an exemplary diagram of an apparatus for discovering an entity

to perform handover with in a wireless mobile communication system. More specifically, an

apparatus 200 (e.g., MS) comprises a transmitter 201, a receiver 202, and a controller 203.

The controller can be used to establish a network handover module for converging

information from at least one network interface module associated with at least one of a

homogeneous and a heterogeneous network handover module into a unified presentation.

The transmitter can be used to transmit messages such as a broadcast request message to a

PoA 210 (e.g., BS, access point, network entity) which can then transmit the broadcast

request message to at least one entity to identify at least one entity whether supports at least

one of MIH function and MIH capability. The receiver 202 can be used to receive at least

one response message from the at least one entity via the PoA 210 (e.g. BS, access point,

network entity) prior to expiration of a timer. Here, the response message indicates that the

at least one entity supports at least one of MIH function and MIH capability. Lastly, the

controller 203 can also be use to initiate a timer for a specified time period when the

broadcast request message is transmitted.

It will be apparent to those skilled in the art that various modifications and variations

can be made in the present invention without departing from the spirit or scope of the

inventions. Thus, it is intended that the present invention covers the modifications and

variations of this invention provided they come within the scope of the appended claims and

their equivalents.