JP4539768B2 - Mobile station, handover method thereof, and communication system - Google Patents

Description

  The present invention relates to a handover of a mobile station that performs radio communication with a base station.

  Conventionally, a network system including IP telephone terminals that can be connected to a LAN in a remote environment using DHCP (Dynamic Host Configuration Protocol) is known (for example, see Patent Document 1). In Patent Document 1, a failure occurs in a connection between a router of a main station configured with a system control device and a DHCP server, and a router of a remote station configured with a backup system control device and an IP telephone terminal. However, by storing the IP address acquired from the DHCP server last time in the IP telephone terminal, it is possible to connect to the backup system controller using the IP address stored in the IP telephone terminal. That is disclosed.

On the other hand, in a mobile communication system including a base station and a mobile station, a technique (handover) is known in which a base station with a higher reception level and a mobile station appropriately switch a connected base station in order to perform wireless communication ( For example, see Patent Document 2).
JP 2006-217094 A JP 2004-56509 A

  By the way, a mobile station such as an IP telephone terminal cannot correctly transmit / receive data to / from a base station having a network address with a different segment. Therefore, if the mobile station is not sure whether the network address of the handover destination base station is the same segment or a different segment, the network address segment of the handover destination base station is different, so that data transmission / reception is correct. In order to prevent it from becoming impossible, the mobile station must re-acquire an IP address from the DHCP server. However, since it takes time to reacquire the IP address, the voice packet during that time is undelivered, and the sound interruption time becomes longer.

  Accordingly, an object of the present invention is to provide a mobile station, a handover method thereof, and a communication system that can reduce the sound interruption time during handover.

In order to achieve the above object, a mobile station according to the present invention provides:
A mobile station that performs radio communication with a base station,
Search means for performing a channel scan to search for a handover destination base station capable of communication;
PING transmission means for transmitting PING to a default gateway via the base station searched by the channel scan,
If there is a response to the PING, perform wireless communication with the IP address already acquired,
When there is no response to the PING, wireless communication is performed using the IP address reacquired from the DHCP server via the base station searched by the channel scan.

  Here, the mobile station according to the present invention includes authentication data transmission means for transmitting authentication data to the base station searched by the search means, and the PING transmission means is provided by the authentication data transmission means. It is preferable to transmit the PING after the authentication based on the transmitted authentication data is established.

In order to achieve the above object, the handover method according to the present invention includes:
A handover method of a mobile station that performs radio communication with a base station,
A search step of performing a channel scan for searching for a handover destination base station capable of communication;
A PING transmission step of transmitting a PING to a default gateway via the base station searched by the channel scan;
A first wireless communication step of performing wireless communication with an IP address that has already been acquired when there is a response to the PING;
A second wireless communication step of performing wireless communication with the IP address reacquired from the DHCP server via the base station searched by the channel scan when there is no response to the PING.

  Here, in the handover method according to the present invention, when the PING transmission step is executed after the authentication based on the authentication data transmitted from the mobile station to the base station searched by the channel scan is established. Is preferred.

In order to achieve the above object, a communication system according to the present invention includes:
A communication system comprising a mobile station, a plurality of base stations capable of wireless communication with the mobile station, and a DHCP server,
Search means for performing a channel scan for searching for a handover destination base station capable of communicating with the mobile station;
PING transmission means for transmitting PING to a default gateway via the base station searched by the channel scan,
The mobile station
If there is a response to the PING, perform wireless communication with the IP address already acquired,
When there is no response to the PING, wireless communication is performed using the IP address reacquired from the DHCP server via the base station searched by the channel scan.

  Here, the communication system according to the present invention includes authentication data transmission means for transmitting authentication data to the base station searched by the channel scan, and the PING transmission means includes the authentication data transmission means. It is preferable to transmit the PING after the authentication based on the authentication data transmitted by is established.

  According to the present invention, it is possible to shorten the sound interruption time during handover.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of a communication system 100 according to an embodiment of the present invention. The communication system 100 comprises an IP telephone terminal 100 that is an embodiment of a mobile station according to the present invention, and an access point (AP) that is a plurality of base stations capable of wireless communication with the IP telephone terminal 100. The communication system 100 includes two networks (subnets) having different IP address network address segments. The first network A and the second network B are connected via the routers 14 and 24, respectively. Note that the number of networks with different segments may be three or more.

  The network A includes a DHCP server 12, one or more access points (AP1 and AP2 are illustrated in FIG. 1), and a router 14. The DHCP server 12, AP 1, AP 2, and router 14 are connected to each other via the communication line 10.

  Similarly, the network B includes a DHCP server 22, one or more access points (AP3 is illustrated in FIG. 1), and a router 24. The DHCP server 22, AP 3, and router 24 are connected to each other via the communication line 20.

  The DHCP servers 12 and 22 are address management devices that automatically assign IP addresses. The APs 1, 2, and 3 are base stations that are arranged apart from each other and are connected to the IP telephone terminal 100 via a WLAN. The routers 14 and 24 are communication devices that interconnect the network A and the network B. A default gateway is mounted in the routers 14 and 24. The default gateway may not be mounted on the router but may be mounted on another host, for example, a DHCP server. Note that a call control server such as a SIP server may be connected to each of the communication line 10 of the network A and the communication line 20 of the network B.

  The IP telephone terminal 100 executes a channel scan for searching for a communicable base station in accordance with a decrease in reception level with a first base station (for example, AP1) in communication among a plurality of base stations, Handover is performed with a second base station (for example, AP2 or AP3) installed at a position distant from the first base station among the plurality of base stations. Note that the handover executed by the IP telephone terminal 100 may include a soft handover that is simultaneously connected to a plurality of base stations.

  Next, the operation when handover is performed will be described.

  FIG. 5 is a handover sequence using a DISCOVER message. If reception failure occurs while the wireless terminal and AP1 are transmitting and receiving audio data, the wireless terminal starts handover. The wireless terminal performs a channel scan to search for an AP that can communicate with itself. The wireless terminal transmits a probe request signal in the channel scan process. The wireless terminal recognizes that there is an AP that can communicate with itself by receiving a probe response signal that is a response signal from the AP to the probe request signal. The wireless terminal performs wireless authentication with the AP 2 searched as an AP that can communicate by channel scanning.

  Since the wireless terminal does not know at this point whether AP2 is the same segment as itself or a different segment, in order to prevent a communication failure due to the AP2 segment being different from its own segment, In order to re-assign IP address from the DHCP server, a DISCOVER command is transmitted with a broadcast address. The DHCP server that has received the DISCOVER message transmits an OFFER message for providing a candidate IP address that can be assigned to the wireless terminal. When the wireless terminal that has received the OFFER message determines that the IP address candidate included in the OFFER message may be adopted as its own IP address, the wireless terminal transmits a REQUEST message by broadcast. The DHCP server that has received the REQUEST message determines the IP address candidate as the official IP address of the wireless terminal, and transmits an ACK message that is a response signal to the REQUEST message. The wireless terminal that has received the ACK message transmits a REGISTER message to the SIP server to request its registration from the SIP server, and the SIP server transmits “200 OK” as a response signal thereto.

  However, since data transmission / reception with the DHCP server as shown in FIG. 5 usually takes several hundred milliseconds to several seconds, the silence time becomes longer due to interruption of transmission / reception of voice packets. However, considering the operation of an actual wireless IP phone, movement during a call is often a short distance, and handover is frequently performed between APs in the same segment. It is often unnecessary to request the DHCP server to reacquire the address. Therefore, if it is possible to know whether or not the destination network is a different segment, the call disconnection time at the time of handover can be shortened.

  Therefore, the wireless terminal transmits a PING to the default gateway via the handover destination base station before starting transmission / reception of the voice packet after completing the wireless authentication via the handover destination base station, If there is a response to the PING, the handover destination base station determines that it is the same segment as itself. After determining the same segment, the IP address lease time is confirmed. If the IP address lease time has not expired, the current IP address is used as it is to complete the handover promptly. The cut-off time can be shortened. On the other hand, if the response to PING times out, the handover destination base station determines that the segment is a different segment from itself, reacquires the IP address from the DHCP server, and performs handover with the reacquired IP address. Just do it. When the lease time of the IP address has expired, the IP address is reacquired in the same manner as when the response to PING times out. Even if a PING packet is not sent back due to a failure in the wireless path or the like when handover is performed in the same segment, it is only necessary to redo the IP address re-acquisition. It will not be.

  FIG. 2 is a block diagram of the configuration of the IP telephone terminal 100 according to the embodiment of the present invention. The IP telephone terminal 100 includes search means 110, authentication data transmission means 120, PING transmission means 130, and voice data transmission means 140. The searching means 110 performs a channel scan for searching for a handover-destination base station that can communicate with a decrease in the reception level with the communicating base station. Authentication data transmission means 120 transmits authentication data to the base station searched by channel scanning. The PING transmission unit 130 transmits the PING to the default gateway via the base station searched by the channel scan after the authentication based on the authentication data transmitted by the authentication data transmission unit 120 is established. When there is a response to the PING transmitted by the PING transmission unit 130, the voice data transmission unit 140 wirelessly communicates the voice data with the IP address already acquired from the DHCP server, and the PING transmitted by the PING transmission unit 130. If no response is received, the voice data is wirelessly communicated with the IP address reacquired from the DHCP server via the base station searched by the channel scan. For example, the microcomputer functions as the search unit 110, the authentication data transmission unit 120, the PING transmission unit 130, and the voice data transmission unit 140.

  FIG. 3 shows a handover sequence using a PING message. The sequence up to wireless authentication with the AP 2 is the same as in the case of FIG.

  After the wireless authentication is established, IP telephone terminal 100 transmits PING to the default gateway via AP 2 searched by channel scanning. The default gateway has a function of returning a response to a PING from a host in the same segment as itself, but not returning a response to a PING from a host in a segment different from itself. That is, when the default gateway belongs to the same segment as AP2 that is the handover destination of the IP telephone terminal 100 (in the case of FIG. 1, the default gateway is 14), the default gateway returns a response to PING. However, if it belongs to a different segment (if the default gateway is 24 in FIG. 1), the default gateway does not return a response to PING.

  As described above, when the IP telephone terminal 100 (for example, the IP address “192.168.12.20”) transmits a PING and receives a response from the default gateway, the channel-scanned AP and its default gateway are transmitted. Is determined to be the same segment as itself (for example, in the case of FIG. 1, AP2 of the IP address “192.168.12.20” and the default gateway 14 of the IP address “192.168.12.1”). After determining the same segment, the IP address lease time is confirmed. If the IP address lease time has not expired, the current IP address is used as it is and the handover is completed promptly. Can be shortened. On the other hand, when there is no PING response from the default gateway and a time-out occurs, the channel-scanned AP and the default gateway are determined to be different segments (for example, in the case of FIG. 1, the IP address “192.168 .. 13.30 ”AP3 and IP address“ 192.168.13.1 ”default gateway 24), and the IP address is reacquired from the DHCP server 22 via AP3 by broadcast, and the reacquired IP address is used. What is necessary is just to complete a hand-over with AP3. When the lease time of the IP address has expired, the IP address is reacquired in the same manner as when the response to PING times out.

  As described above, transmission / reception by PING is shorter in communication time than transmission / reception by DISCOVER message, and is normally completed in several tens of milliseconds. Therefore, the interruption time of transmission / reception of voice packets at the time of handover is suppressed, and The resumption of transmission / reception can be accelerated.

  In general, PING is used to confirm whether there is a partner (for example, PING is transmitted from the base station side to the mobile station side). Mobile station transmits a PING to the base station. That is, in this embodiment, it can also be confirmed that the communication is normally established by the establishment of the wireless authentication. By sending a PING after wireless authentication has been established, without having to wait for wireless authentication to be established or for communication confirmation, it is possible to take advantage of the PING transmission / reception time and realize a quick handover based on the presence or absence of a response to the PING. can do.

  In addition, the larger the system, the higher the cost of the corresponding equipment by developing a proprietary AP or wireless LAN switch (controller). However, according to this embodiment, an expensive wireless LAN switch is not used. Therefore, it is possible to realize a communication system capable of shortening the sound interruption time and completing the handover promptly regardless of the scale. In terms of software, the standard PING function does not require development and can be easily implemented in a wireless IP phone, which is cost-effective.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

  For example, FIG. 4 shows a handover sequence by an ARP (Address Resolution Protocol) command. By using an ARP command that has a faster response than PING, the call disconnection time can be further reduced.

  In other words, when performing a handover, an ARP is sent to the default gateway via the handover destination AP, and if there is a response, the voice such as an RTP (Real-time Transport Protocol) packet without changing the IP address.・ Send video data. Next, a PING packet is transmitted to the default gateway address. When a response is received, the channel-scanned AP and its default gateway are finally determined to be the same segment as itself, and the handover process is completed. By doing so, the transmission of the RTP packet can be resumed without waiting for the PING response, so that the call disconnection time can be shortened. Also, by sending a PING command after sending an ARP command, whether the segments are the same or different by checking the response to the PING even if the ARP response is returned even though it is a different segment Can be determined reliably.

  For example, a RADIUS server may be connected to the communication line 10 of the network A. The RADIUS server is an authentication server compatible with the RADIUS protocol. For example, the wireless terminal performs wireless authentication with a RADIUS server in the same segment as AP2 via AP2 searched as an AP that can communicate by channel scanning.

1 is an overall configuration diagram of a communication system 100 according to an embodiment of the present invention. 1 is a block diagram of a configuration of an IP telephone terminal 100 that is an embodiment of the present invention. FIG. This is a handover sequence using a PING message. It is a handover sequence by an ARP command. It is a handover sequence using a DISCOVER message.

Explanation of symbols

1, 2, 3 access point (AP)
10,20 Communication line 11,21 SIP server 12,22 DHCP server 14,24 Router (default gateway)
100 IP phone terminal

Claims (6)

A mobile station that performs radio communication with a base station,
Search means for performing a channel scan to search for a handover destination base station capable of communication;
PING transmission means for transmitting PING to a default gateway via the base station searched by the channel scan,
If there is a response to the PING, perform wireless communication with the IP address already acquired,
When there is no response to the PING, the mobile station performs wireless communication with the IP address reacquired from the DHCP server via the base station searched by the channel scan. Authentication data transmitting means for transmitting authentication data to the base station searched by the channel scan,
The mobile station according to claim 1, wherein the PING transmission unit transmits a PING after authentication based on the authentication data transmitted by the authentication data transmission unit is established. A handover method of a mobile station that performs radio communication with a base station,
A search step of performing a channel scan for searching for a handover destination base station capable of communication;
A PING transmission step of transmitting a PING to a default gateway via the base station searched by the channel scan;
A first wireless communication step of performing wireless communication with an IP address that has already been acquired when there is a response to the PING;
A second wireless communication step of performing wireless communication with an IP address reacquired from a DHCP server via a base station searched by the channel scan when there is no response to the PING. Over method.   The handover method according to claim 3, wherein the PING transmission step is executed after authentication based on authentication data transmitted from a mobile station to a base station searched by the channel scan is established. A communication system comprising a mobile station, a plurality of base stations capable of wireless communication with the mobile station, and a DHCP server,
Search means for performing a channel scan for searching for a handover destination base station capable of communicating with the mobile station;
PING transmission means for transmitting PING to a default gateway via the base station searched by the channel scan,
The mobile station
If there is a response to the PING, perform wireless communication with the IP address already acquired,
When there is no response to the PING, wireless communication is performed using the IP address reacquired from the DHCP server via the base station searched by the channel scan. Comprising authentication data transmitting means for transmitting authentication data to the base station searched by the channel scan;
6. The communication system according to claim 5, wherein the PING transmission unit transmits a PING after authentication based on the authentication data transmitted by the authentication data transmission unit is established.

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