WO2003015315A1

WO2003015315A1 - Handover/roaming mechanism supporting system in a short-range wireless network based on the bluetooch

Info

Publication number: WO2003015315A1
Application number: PCT/KR2002/001533
Authority: WO
Inventors: Hyun-Sang Jang
Original assignee: Initium Co., Ltd.
Priority date: 2001-08-09
Filing date: 2002-08-09
Publication date: 2003-02-20
Also published as: KR20030013757A; KR100388421B1

Abstract

The present invention relates to a handover/roaming mechanism supporting system in a short-range wireless network based on the Bluetooth including a Promineo-access point (Promineo-AP) which is a network access point (NAP) for connecting a Bluetooth user apparatus through the LAN, at least one Promineo-data terminal (Promenio-DT) loaded with Bluetooth client application software for supporting handover/roaming mechanism, and a Promineo-roaming agent (Promineo-RA) for supporting the handover/roaming mechanism on a wired backbone and managing all the Bluetooth apparatuses within the service area.

Description

HANDOVER/ROAMING MECHANISM SUPPORTING SYSTEM IN A

SHORT-RANGE WIRELESS NETWORK BASED ON THE BLUETOOTH

TECHNICAL FIELD '

The present invention relates to a short-range wireless

communication network based on the Bluetooth, and in particularly to a

handover/roaming mechanism supporting system which can extend a

service area in a short-range wireless communication network using the

Bluetooth.

BACKGROUND ART

The Bluetooth which is one of the short-range wireless data

communication standards such as the IrDA (Infrared Data Association),

wireless LAN (IEEE 802.11) and SWAP (Shared Wireless Access Protocol)

is a communication standard for a variety of electronic apparatuses. The

five corporations, Ericsson, Nokia, IBM, Toshiba' and Intel have composed

a consortium called Bluetooth SIG (Special Interest Group) in May, 1998,

and defined the Bluetooth Spec. 1.0 in the first forum held in England in

June, 1999. The Bluetooth Spec. 1.0 prescribes a data rate of 1Mbps and a

transmission distance of 10 to 100m. Member companies have increased to 1900 for about one year, arousing interest of the field. Since the Bluetooth

transmits and receives electric waves according to spread spectrum

frequency hopping which sets up 79 channels having a bandwidth of 1MHz

in 2.4GHz band and changing the channels 1600 times per second, it can be

wirelessly connected to a notebook computer, cellular phone, PDA, digital

camera, printer, MP3 player and home network apparatus, stably transmit

and receive data, and reduce the price and power consumption. It is thus

expected that demands for the Bluetooth will be remarkably increased.

Compared with the wireless LAN of IEEE 802.11b which is another

short-range wireless technology using 2.4GHz band, the Bluetooth which

has the transmission distance within 10 ~ 100 meters needs to extend a

service area through the handover/roaming mechanism as in the wide area

wireless communication network in order to guarantee user mobility.

However, the Bluetooth which is designated for removing cables or

considers PAN (Personal Area Network) does not handle the

handover/roaming mechanism in current Spec. vl.l.

DISCLOSURE OF THE INVENTION

Accordingly, it is an object of the present invention to allow the

Bluetooth standardized by the Bluetooth SIG and IEEE 802.15, solve problems due to frequent inquiries/connections during the movement of a

generalized Bluetooth user apparatus, and overcome using distance limits

which are one of disadvantages of the Bluetooth by extending a service

area through a handover/roaming mechanism supporting system.

To achieve the above-described object of the invention, a

handover/roaming mechanism supporting system in a short-range wireless

network based on the Bluetooth includes at least one Promineo-access

point (Promineo-AP) which is a network access point (NAP) for connecting

a Bluetooth user apparatus through the LAN, at least one Promineo-data

terminal (Promineo-DT) loaded with Bluetooth client application software

for supporting handover/roaming mechanism, and a Promineo-roaming

agent (Promineo-RA) for supporting the handover/roaming mechanism on

a wired backbone and managing all the Bluetooth apparatuses within the

service area. The Promineo-AP connects the Promineo-DT through the

LAN, informs the Promineo-RA of BD_ADDR and clock_offset information

of the DT, sets up connection according to a command from the

Promineo-RA and performs a proxy operation for relaying a PPP diagram,

and the Promineo-RA serves as a PPP server for processing PPP

connection to the DT in a sub-network including the NAPs, recovers the

PPP connection through tunnel end point redirection after the handover mechanism is completed, and thus maintains the previous PPP connection

state during the handover/roaming mechanism regardless of disconnection

of the Bluetooth link.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a basic structure view illustrating a handover/roaming

mechanism supporting system in a short-range wireless network based on

the Bluetooth in accordance with a preferred embodiment of the present

invention;

Fig. 2 shows PPP termination in the RA;

Fig. 3 shows an initial connection setup in accordance with the

preferred embodiment of the present invention;

Fig. 4 shows measurement of a clock offset in accordance with the

preferred embodiment of the present invention;

Fig. 5 shows link loss detection and handover mechanism based on a

radio signal strength indicator (RSSI);

Fig. 6 shows link loss detection and handover mechanism based on a

link supervision timer; and

Fig. 7 shows one example of network constitution. BEST MODE FOR CARRYING OUT THE INVENTION

Example 1

Fig. 1 is a basic structure view illustrating a handover/roaming

mechanism supporting system in a short-range wireless network based on

the Bluetooth in accordance with a preferred embodiment of the present

invention. Referring to Fig. 1, the handover/roaming mechanism supporting

system includes a Promineo-AP which is a NAP for connecting a Bluetooth

user apparatus through the LAN, a Promineo-DT which is a data terminal

loaded with Bluetooth client application software for supporting

handover/roaming mechanism, and a Promineo-RA which is a roaming

agent for supporting the handover/roaming mechanism on a wired

backbone and managing all the Bluetooth apparatuses within the service

area.

The Promineo-AP can include up to four Bluetooth modules. The

each Bluetooth module can be used to connect the DTs through the LAN or

can be used for pre-paging to detect the position of the DT adjacent to the

AP. In addition, the Promineo-AP is positioned between the DT and the RA

for informing the RA of BD_ADDR and clock-offset information of the DT

and performing relay operations such as connection setup according to a

command from the RA. A PPP server exists in the RA, not the AP, when the RA is used for handover/roaming support. In this case, the AP merely

performs a proxy operation for relaying a PPP diagram between the DT

and the RA.

The Promineo-RA serves as a PPP server for processing PPP

connection to the DT in a sub-network including the NAPs. The

Promineo-RA performs a tunneling operation with the NAPs for receiving

data through an internet and transmitting them to an appropriate NAP,

buffers IP packets when the DT moves to a different NAP, and redirects

them to the NAP. In addition, the Promineo-RA stores and manages

information (status, position, BD_ADDR and clock-offset) of the DT

existing in the sub-network, manages the handover mechanism and

provides an appropriate command to the NAP. For example, when the DT

connected to one NAP moves away from it, the Promineo-RA transmits a

pre-paging command to the adjacent NAPs to detect the position of the DT.

When the DT is disconnected, the Promineo-RA determines an NAP most

adjacent to the DT according to the pre-encoded geometric information of

the deployed NAPs, and commands the NAP to connect the DT.

The Promineo-DT uses a PPP associated RFCOMM (serial cable

emulation protocol) model defined in the Bluetooth LAN access profile

(LAP). Moreover, the DT has a few additional functions for supporting the

handover mechanism. That is, when the DT is disconnected during the

handover mechanism, it should maintain the PPP session until the handover

mechanism is completed. In order to receive a connection request from a

new AP, the DT has a function of entering into a continuous page scan

mode. The DT satisfying the aforementioned conditions can be the

Promineo-DT.

The LAP which is a network connection standard of the Bluetooth

Spec. 1.1 executes network connection through the PPP on the RFCOMM

which is a serial communication emulation layer. Whenever the user

apparatus changes connection from one NAP to another NAP due to

movement, inquiries/connections must be performed as well as the PPP

connection must be newly attempted. Accordingly, time consumption is

increased due to inquiries/connections and information on the previous

connection is lost due to the new PPP connection. That is, it generates time

delay due to the handover mechanism and packet loss due to disconnection

of the PPP.

Therefore, the existing PPP connection state must be maintained

during the handover/roaming mechanism, regardless of disconnection of

the Bluetooth link. For this, the Promineo-AP of the invention is designed to be operated in a dual mode, for individually supporting the generalized

LAP and the handover/roaming mechanism. That is, when the RA is not

used, the Promineo-AP is operated as the generalized NAP including a PPP

server and network address translation (NAT). In addition, in order to

support the handover/roaming mechanism, the PPP server is positioned

not on the NAP but on the RA, and the NAP managed by the RA performs a

proxy operation for relaying a PPP diagram through tunneling as shown in

Fig. 2. Therefore, the PPP connection on the RA is valid during the NAP to

NAP handover mechanism of the user apparatus. When the handover

mechanism is completed, the RA recovers the PPP connection through

tunnel end point redirection.

In addition, in order to reduce the packet loss and improve packet

transmission, the RA performs packet buffering in consideration of the time

delay generated due to the handover mechanism and a data transfer rate.

Since the user apparatus does not sense that the PPP service is executed

not in the NAP which is the connection object but in the RA, it cannot

distinguish this connection from the general network connection using the

LAP.

Fig. 3 shows an initial connection setup in accordance with the

preferred embodiment of the present invention. The DT is initially connected to the network according to the LAP.

That is, the DT performs inquiries and paging to the network, and enters

the Piconet called as the Bluetooth network composed of a master and

corresponding slaves through a master/slave switch. Here, the AP is the

master and the DT is the slave.

When connection is finished, the AP confirms whether the DT is the

Promineo-DT or general DT (by using a name request or SDP).

Fig. 4 shows measurement of the clock offset in accordance with the

preferred embodiment of the present invention.

When the DT connected to one AP (APi) is disconnected from the

AP and connected to another AP (AP2), the AP₂ needs clock_offset

information between the DT and AP₂ for faster paging.

For this, the Bluetooth modules of the APs can calculate a relative

clock offset between the DT and the AP₂ by using the clock offset between

the DT and the previously-connected APi and the offset between the APi

and the AP₂ stored in the RA through the inquiry to the APs.

The clock offset is calculated between the two Bluetooth modules

existing in one AP through the inquiry. Since the data communication is

disabled during the inquiry, it is executed by using the secondary Bluetooth

module. Actually, only 5 upper bits (1.28sec resolution) of the clock offset value lδbits are used for paging. The calculated clock offset value needs

not to be updated for an extended period of time even in consideration of a

clock drift.

Fig. 5 shows link loss detection and handover mechanism based on a

radio signal strength indicator (RSSI).

When a radio signal strength measurement value read from the AP

(API) connected to the DT is lower than a predetermined value

Link_lost_th, the AP forcibly disconnects itself from the DT by using

HCI_disconnect_command. Here, the reason code of OxFF is used as

reason code which is one of the elements of the HCI_disconnect_command,

so that this disconnection can be distinguished from disconnections due to

authentication failure or the like (For User Ended Connection, 0x13 is

used). The disconnected DT enters into the R0 page scan mode and

performs continuous page scan. The RA transmits handover initiation

command to one (AP₂) of the adjacent APs for connection according to

predetermined position information (explained below). While the DT is

being connected, the APi cannot communicate with the

previously-connected DTs. When the DT maintains the R0 page scan mode,

it can respond within a first page train (10ms), which is very short.

Fig. 6 shows link loss detection and handover mechanism based on a link supervision timer.

When it is difficult to use the RSSI, link loss must be detected by

using the link supervision timer. A basic value of a link supervision timeout

is 20 seconds. However, the basic value must be reduced (to about 1

second) by using HCI_write_link_supervision_timeout command to

decrease a delay time due to the handover mechanism, after the DT is

connected to the APi. When the link supervision timer is used, if the timer

expires, the DT and the APi receive HCI_disconnect_complete event

(reason code: connection timeout 0x08). Thereafter, the DT enters into the

R0 page scan mode, and the APi informs the RA of disconnection. The RA

transmits a command to the APs adjacent to the APi to sequentially attempt

connection to the DT.

In this case, the link supervision timeout must be reduced, which

may seriously restrict a number of the slaves entering into a park mode.

The two methods presume that the DT is operated in the R0 page

scan mode after disconnection. The Promineo-DT performs the

continuous page scan for a predetermined time (bw_page_scan_timeout:

basic value 2.56 seconds) after disconnection.

On the other hand, when the DT is not the Promineo-DT and thus

not operated as described above (AP confirms it after initial connection setup), paging for new connection may take a long time. When the DT is

disconnected from an AP and the handover mechanism starts, the PPP

session must be maintained. After the DT is connected to a new AP,

connection of the RFCOMM is simply performed. For this, Promineo-DT

software exists between the RFCOMM and the PPP of the DT to maintain

the PPP session.

Since the packet loss by the handover mechanism may seriously

increase delay, the RA has packet buffers in each session, stores packets

during the disconnection period and transmits them right after the

handover mechanism, thereby minimizing the total handover delay. Here, a

size of the packet buffer is dependent upon the handover delay and the

packet transfer rate.

The above-explained process of the handover mechanism will now>

be summarized.

When the Promineo-DT enters the service area of the Bluetooth

network system and intends to be connected to the network, it is

connected to the adjacent Promineo-AP using LAN access profile. When

the Promineo-DT is disconnected from the Promineo-APo, it needs to be

connected to another AP. The APs adjacent to the APo form a candidate

group which the Promineo-DT can be connected to after the handover mechanism. The candidate APs are indicated by APi, AP2,'", AP_n.

When the handover measurement value (for example, RSSI) is lower

than a predetermined critical value, the APo initiates the handover

mechanism as follows:

1. The APo informs the Promineo-RA of initiation of the handover

mechanism. The Promineo-RA stores packets toward the Promineo-DT.

2. The APo ends connection to the Promineo-DT. Here, 1 byte of the

reason command parameter showing the reason for connection termination

must be set up in the HCI-DISCONNECT command. In order to distinguish

the disconnection from disconnections due to other reasons such as

deficiency of the AP resources or power failure, the reason parameter is

set up as OxFF, namely one of the values reserved for future use in the

current version of the Bluetooth specifications.

3. The DT enters into the continuous page scan mode for

T_handover_timeout seconds. T_handover_timeout seconds should be long enough to

allow all the APs of the candidate group to page the DT.

4. The APo selects the APs from the candidate group so that the

distance among the APs can be long enough to prevent interferences

during the paging process. The APo transmits handover command

messages including the Promineo-DT information to the selected APs. 5. The selected APs intend to page the Promineo-DT by using

BD_ADDR of the Promineo-DT. The selected APs transmit paging

messages for T_page_timeout sufficiently long to compensate for possible

wireless channel errors.

6-1. When all the selected APs fail to be connected to the

Promineo-DT, the APo selects another APs from the candidate group and

repeats steps 4 and 5.

6-2. When the AP succeeds in connection setup to the

Promineo-DT, the AP transmits a handover success message to the APo.

The master/slave switching does not occur during the handover

mechanism, since the access point initiates the connection establishment.

When receiving the message, the APo directly informs the Promineo-RA of

completion of the handover mechanism. The Promineo-RA re-transmits

the packets to the Promineo-DT by generating a new PPP channel or

renewing a routing table.

7. When all the APs of the candidate group APi, AP₂,-, AP_n fail to

connect to the Promineo-DT, if the Promineo-DT re-enters the allowable

range of the APo, the APo intends to finally page the Promineo-DT.

8. In the case that any of the APs cannot be connected to the

Promineo-DT, the handover mechanism fails and the resources allocated to the Promineo-DT are released.

The main object of the handover mechanism is that the APs

alternately perform paging when the Promineo-DT maintains the

continuous page scan mode. In order to guarantee successful handover

mechanism, the candidate group must be selected to cover the whole areas

which the user moves during the handover mechanism.

In addition, the Promineo-AP can include a plurality of Bluetooth

modules, and thus can be connected to a module different from the

previously-connected module in the same AP.

A Promineo protocol is defined between the AP and the RA for the

handover mechanism. The Promineo protocol is divided into a Promineo

command from the RA to the AP and a Promineo event from the AP to the

RA, and transmitted in XML data form for extensibility.

The Promineo protocol for the handover/roaming mechanism will

now be described.

1. LAP<->LAP protocol

The LAPs communicate with each other by using an UDP channel.

Each LAP generates UDP sockets having a standardized port number and

transmits messages through the UDP sockets. The LAP receiving the

message guarantees reliability of the channel by transmitting ACK. When the sender does not receive the ACK for a predetermined time

after transmitting the message, the sender judges that packet loss has

been generated and re-transmits the message. When the message is

normally transmitted but the ACK is lost, the LAP may receive a redundant

message. In order to ignore the redundant message, a sequence number is

added to the message. When the sequence number of the received

message is identical to that of the previously-received message, the LAP

ignores the received message.

1 byte (0-255) is used to display the sequence number. The sender

and the receiver record and use finally-transmitted and received numbers.

For example, when LAP1 transmits/receives messages to/from LAP2 and

LAP3, the LAP1 should memorize the sequence numbers of the messages

respectively transmitted to the LAP2 and LAP3. In addition, it must record

the sequence numbers of the messages from the LAP2 and LAP3.

When the message where a payload length is added to a message

header is damaged, the LAP1 requests re-transmission by sending NACK.

The whole structure of the message is shown in following Table 1 :

Message

0x00 SEQ. NUM MSG length MSG type Arguments

ACK

NACK

The message is divided into a command type and an event type. The

command type message commands the receiver to perform a specific

operation, and the event type message notifies a command execution

result.

Command Type

BW_SEND_BUF_DA bd_addr,

TA_COMMAND buf_data

Event Type

2. Communication between LAP<->RA

The LAP and the RA communicate with each other in the same

manner as the LAP to LAP communication. The RA generates one UDP

socket and communicates with the LAP through the UDP socket. The RA

confirms the LAP transmitting the message according to sender sockaddr,

and performs a necessary operation (or LAP identifier is added to the

message so that the RA can confirm the LAP transmitting the message).

Identically to the LAP to LAP communication, reliability of communication

is improved by using ACK.

Table 3 shows message types used for the communication.

3. Inter-Process Communication

In the LAP, one process is allocated to each DT. The DT process

forks processes as many as MAX_DT (a number of modules is 4, and when

7 DTs are connected to each module, a number of processes is 28) in the

LAP initialization time point to prevent overload. Accordingly, the main

process and MAX_DT DT processes exist in the LAP.

■ Main process: LAP to LAP communication, RA communication,

BT module control using a stack interface. The main process

examines a connection state of the DT by reading RSSI value at

a predetermined interval. When the handover mechanism is necessary, the main process informs the DT process to interrupt

data transmission and buffer data.

■ DT process: TCP data channel setup for data transmission and

reception to/from the RA. When the DT is connected, the DT

process opens the BT driver (open ttyBT#) and transmits data

between the RA and DT.

The main process and the DT process transmit/receive messages

according to pipe and FIFO. Table 4 shows types of the messages between

the two processes.

Message for transmitting buffered data to the main dt process

BUFFERED_DAT process after the DT process starts the handover -$ main A mechanism (receiving LINK_LOW_POWER_EVENT)

Message for transmitting data by main -> dt

WRITE_BUFFER BW_SEND_BUF_DATA_COMMAND to the DT process

ED_DATA process after connection to new LAP is completed

during the handover mechanism

Message for confirming that buffered data are all dt process

transmitted to the DT. When the main process -^ main

COMPLETE_WRI receives the message, it directly transmits

TE_BUF_DATA BW_HANDOVER_C0MPLETE_EVENT to the agent

to set up a transmission path to the DT and starts

transmission.

In order to perform the handover/roaming mechanism, geographical

positions (position information) of each AP module are stored. The position

information can be used to select the candidate group during the handover

mechanism. The position information is stored in an adjacent matrix form. The RA stores the whole position information and the AP stores nodes

adjacent its modules. The RA reads the position information of the APs

stored in a script form, stores it in its adjacent matrix, and transmits it to

each AP. A node of the graph is BT module of the AP and an edge indicates

a relative distance. The relative distance is divided into 1) near, 2) overlap

(40% overlap) and 3) tangent (tangent areas). In the case of the roaming

mechanism due to movement, the module displayed as 'overlap' is set up as

the handover destination, and in the case of load balancing for congestion,

the handover mechanism is performed on the module displayed as 'near'.

The position information is executed when the Promineo-AP is installed,

and re-executed when the installation position of the Promineo-AP is

changed. The embodiment of the position information will now be

explained.

■ In the RA,

- The RA must know topologies of the whole modules existing

within the LAN, which modules belong to the same LAP, and

adjacent modules of the module if only one module exists.

- Each LAP has a consecutive number starting from 0.

- The numbers of the modules are displayed in pairs of LAP

number-LAP module number (0~3) (for example, module 2-1 : first module from second LAP).

- Adjacent matrix formation

a. declaration : int adj_matrix [module number] [module

number]

b. index i : LAP number*4+ LAP module number

ex) module 2-1 : I = 2*4+ 1 = 7

d. adj_matrix[i] [j] : edge weight between module i and

module j, which is the same as adj_matrix [j ] [i] .

c. index j is converted into module number

- LAP number : j%4

- LAP module number : j - j%4 (for example, j = 15 =>

module 3-3)

d. search for identical module in index j

- distinguish which modules belong to the same LAP by LAP

module numbers (for example, switch(LAP module number))

case 3 : j-3, j-2, j-1 belong to the same LAP

case 2 : j-2, j-1, j+ 1 belong to the same LAP

case 1 : j-1, j+ 1, j+ 2 belong to the same LAP

case 0 : j+ 1, j+ 2, j+ 3 belong to the same LAP e. Edge size is shown as integers.

When the integer is over a predetermined value, it is

deemed to be a long distance.

In the LAP,

Each LAP must be informed of which topology their Modules

compose, whether they are adjacent to modules of another

LAP, and numbers of the adjacent modules.

Adjacent matrix formation

a. declaration : int adj_matrix[4] [module number]

b. index i : LAP module number

c. hereinafter, the same as the RA case

Fig. 7 shows one example of network constitution. Following tables

show adjacent matrixes in the network constitution of Fig. 7.

Adjacent matrix of RA

0 1 2 3 4 5 6 7

0 3 4

1 3 4

2 4 3 6 2 3 3 4 3 2 5 7

4 6 2 2 4

5 2 5 2 1 4

6 3 7 4 1 3

7 4 3

modulelD o-o 0-1 0-2 0-3 1-0 1-1 1-2 1-3

Adjacent matrix of LAPO

Adjacent matrix of LAP1

A method for enabling the handover mechanism between a mobile

terminal (PAN user : PANU) having the Bluetooth wireless interface and

the NAP in a state where the PANU is connected to a network

infrastructure through the NAP according to the Bluetooth PAN profile will

now be explained.

The NAP includes the Bluetooth wireless interface and the Ethernet

interface and exchanges packets between the PANU and the wireless

network. As defined in the PAN profile, the NAP is operated in one of

Layer 2 bridge and Layer 3 router. Here, it is presumed that the NAP is

operated in the bridge which is a basic operation mode of the PAN profile. The NAP connects Bluetooth Network Encapsulation Protocols (BNEP),

regards Ethernet ports as valid bridge ports, and converts and exchanges

packets there between (namely, BNEP packet <-> Ethernet packet).

The handover mechanism by the PAN profile will now be explained.

1. Connection to NAP of PANU

The PANU is connected to the NAP according to the PAN profile for

generating BNEP connection.

2. Initiation of handover mechanism

The NAP monitors information obtained from the Bluetooth module

(link quality, signal strength or distance). When the connection state to the

specific PANU (hereinafter, referred to as 'PANUO') is deteriorated or the

distance is increased, the handover mechanism is initiated.

3. Order of handover mechanism

(1) The NAP previously connected to the PANUO (hereinafter,

referred to as 'NAPO') is disconnected from the PANUO. In addition, the

NAPO informs the Promineo-RA of initiation of the handover mechanism on

the PANUO.

(2) The PANUO recognizes disconnection for the handover

mechanism by confirming a reason code parameter of the disconnection

command, and enters into the continuous page scan mode. (3) While the handover mechanism is being performed, the NAPO

buffers data transmitted to the PANUO in the memory in the Ethernet

packet form.

(4) The NAPO transmits the handover command message including

PANUO information sequentially to the adjacent NAPs (similar to the

above-described candidate group of the handover mechanism according to

the position information order). The NAPs receiving the handover

command message perform paging for T_page_timeout to attempt connection to

the PANUO.

(5) The NAP succeeding in paging the PANUO (hereinafter, referred

to as 'NAP1') generates BNEP connection to the PANUO, and transmits the

handover success message to the NAPO and the Promineo-RA to notify it.

(6) The NAPO interrupts buffering of the packets transmitted to the

PANUO by removing MAC address (BD_ADDR) of PANUO in the entry of its

packet filtering database, and transmits the handover success

acknowledge message to the NAP1. In addition, the NAPO transmits the

buffered Ethernet packets to the NAP1.

(7) The NAP1 receiving the handover success acknowledge

message adds MAC address (BD_ADDR) of the PANUO to the entry of its

packet filtering database, receives the packets transmitted to the PANUO and buffers them in its memory. The NAP1 transmits the whole Ethernet

packets stored in the NAPO to the PANUO, and transmits its received

packets to the PANUO.

In addition, the NAP can include a plurality of Bluetooth modules.

Accordingly, the NAP can be connected from a module different from the

previously-connected module in the same NAP.

INDUSTRIAL APPLICABILITY

As described above, the present inventions allow the Bluetooth to

solve problems due to frequent inquiries/connections during the movement

of the generalized Bluetooth user apparatus, and overcomes distance limit

which is the one of disadvantages of the Bluetooth by extending the

service area through the handover/roaming mechanism supporting system.

Claims

WHAT IS CLAIMED IS:

1. A handover/roaming mechanism supporting system in a

short-range wireless network based on the Bluetooth, comprising:

at least one Promineo-access point (Promineo-AP) which is a

network access point (NAP) for connecting a Bluetooth user apparatus

through the LAN;

at least one Promineo-data terminal (Promineo-DT) loaded with

Bluetooth client application software for supporting handover/roaming

mechanism; and

a Promineo-roaming agent (Promineo-RA) for supporting the

handover/roaming mechanism on a wired backbone and managing all the

Bluetooth apparatuses within the service area, wherein the Promineo-AP

connects the Promineo-DT through the LAN, informs the RA of BD_ADDR

and clock_offset information of the DT, sets up connection according to a

command from the RA and performs a proxy operation for relaying a PPP

diagram, and the Promineo-RA serves as a PPP server for processing PPP

connection to the DT in a sub-network including the NAPs, recovers the

PPP connection through tunnel end point redirection after the handover

mechanism is completed, and thus maintains the previous PPP connection state during the handover/roaming mechanism regardless of disconnection

of the Bluetooth link.

2. The system of claim 1, wherein the Promineo-RA buffers packets

by PPP sessions in consideration of time delay generated due to the

handover mechanism and a data transfer rate in order to remove packet

loss and improve packet transmission.

3. The system of either claim 1 or 2, which processes commands

and events between the Promineo-AP and the RA by using a

predetermined Promineo protocol.

4. The system of either claim 1 or 2, wherein clock offset

information between the DT for determining a paging/connection time

between the DT and the Promineo-AP and the newly-connected AP (AP2)

is calculated as a relative clock offset between the DT and the AP2 by

using the clock offset between the DT and the previously-connected AP

(API) and the clock offset between the API and the AP2 stored in the RA

through the inquiry to the APs.

5. The system of claim 1, which is operated according to LAN

access profile and/or PAN profile.

6. The system of claim 1, wherein the Promineo-AP performs a

main process for executing communication between the plurality of

Promineo-APs and communication to the Promineo-RA, controlling BT

module by using a stack interface, and examining a connection state of the

Promineo-DT by reading a radio signal strength indicator (RSSI) value at a

predetermined interval; and performs a DT process for setting up TCP data

channel for data transmission and reception to/from the Promineo-RA, and

opening a BT driver when the Promineo-DT is connected, and transmitting

data between the Promineo-RA and the Promineo-DT, wherein, when the

handover mechanism is necessary, the main process interrupts connection

to the Promineo-DT and the DT process receives and buffers data

transmitted to the DT.

7. The system of claim 6, wherein the DT disconnected from the

Promineo-AP enters into a continuous page scan mode (R0 page scan

mode) to reduce the delay of the whole handover mechanism.

8. The system of claim 1, wherein, when the Promineo-AP is

installed, the Promineo-RA generates and stores position information

comprised of adjacent matrixes showing relative distances to the

Promineo-APs, and when the handover mechanism is necessary, the

Promineo-RA determines the Promineo-AP to be connected according to

the position information.

9. The system of either claim 1 or 8, wherein, each of the

Promineo-APs comprises a plurality of Bluetooth modules, and when the

multiple Bluetooth modules are installed, the Promineo-AP generates and

stores position information comprised of adjacent matrixes showing

relative distances between the modules of the Promineo-AP and relative

distances to modules of another Promineo-AP, and when the handover

mechanism is necessary, the Promineo-AP determines the module to be

connected according to the position information.