KR100372842B1 - Handoff method for terminal mobility support - Google Patents

Abstract

The present invention relates to a handoff method for terminal mobility supporting handoff of a mobile terminal without establishing a new H.323 call. In the prior art, first, a call may be broken if a new H.323 call is not made completely in the overlapped region. Second, bandwidth is wasted because two H.323 calls are established. Third, if the other terminal does not have a multipoint video conferencing controller function, handoff is not supported, and the delay is increased when the multipoint video conferencing controller is separated from the corresponding terminal. The more serious case is that both are mobile terminals, and the current multipoint video conferencing controller function alone cannot fully support handoff in this case. Thus, existing multipoint videoconferencing controllers cannot support the new mobile H.323. Since the present invention does not use the multipoint videoconferencing controller function, it is possible to handle handoff without regard to the multipoint videoconferencing controller. In addition, since the number of incoming and outgoing messages can be reduced and the delay for a new TCP connection can be reduced, the handoff can be performed more quickly in the overlapping interval between two cells. Since one call continues to be used, there is no waste of bandwidth. It also maintains backward compatibility because it does not affect existing H.323 messages.

Description

Handoff method for terminal mobility {HANDOFF METHOD FOR TERMINAL MOBILITY SUPPORT}

The present invention relates to a handoff method for terminal mobility in H.323, and more particularly, to a method for supporting handoff of a mobile terminal without establishing a new H.323 call.

H.323 is a protocol for multimedia cooperative applications standardized by the International Telecommunication Union (ITU) for video conferencing and Internet phones. H.323 consists of H.225, H.245, RTP / RTCP and various codecs. As mobility support on the Internet becomes important, ITU is standardizing "H.323 annex H" (hereinafter referred to as "mobile H.323") to support mobility in H.323.

Handoff is the most important part of mobility. The best way to support handoff is to use mobile Internet Protocol (IP). However, using mobile IP increases delay with triangular routing. Thus, this method is not suitable for transmitting delay sensitive multimedia data.

Existing schemes allow a mobile terminal to make a new call to a multipoint controller (MC) of the other party using a care-of-address (COA) of a foreign agent (FA) of a new cell. To set. At this time, if a new call is established, the mobile terminal hangs up the existing call. However, in this method, if the new call setup is not completed until the mobile terminal leaves the overlapped section, the call may be disconnected because no data is received. Then, the bandwidth is doubled until the handoff is completed, and the handoff cannot be supported when there is no multipoint video conferencing controller.

Liao proposed H.323 mobility support method using multi-point video conferencing controller. When a handoff occurs, the mobile terminal opens a new Transmission Control Protocol (TCP) and establishes a new call following all call setup procedures. In this case, call setting is performed by using the multipoint video conference controller of the other party, so there must be a multipoint video conference controller. Once the call setup is complete, the existing call is removed through the multipoint video conferencing controller. The existing call must be maintained until the new call is completely established, otherwise the call may be dropped.

The ITU is currently working on standardization to support mobility in H.323. For mobility, not only mobility of terminals, users, and services, but also methods for mobility management have been standardized. Call setup is similar to H.323. For handoff, we used multipoint video conferencing controller like Liao's method.

Wedlund and Schulzrinne proposed mobility support using the Session Initiation Protocol (SIP). This uses the redirect mode of SIP as a method of managing mobility in the application layer of the IP network. In this method, mobile IP is used for TCP connection and UDP (User Datagram Protocol) is used for multimedia session.

Cceres and Padmanabhan proposed a hierarchical mobility management method. This uses locality in the user's mobility, which means that the mobile node only moves around. Therefore, in a small area, that is, the handoff between base stations in the same network can be efficiently performed.

1 is a step-by-step diagram illustrating a handoff method currently being performed in standardization for mobile H.323, which is a representative handoff method proposed by Liao to support mobility in H.323. In this case, it is assumed that the mobile terminal moves to a new zone while the multimedia session is open and the call is in progress.

In the figure, the H.323 mobile terminal sends a Gatekeeper Request (GRQ) message of a new zone (step 1).

The foreign gatekeeper of the new zone sends a Gatekeeper Confirm (GCF) message and a COA in response to the gatekeeper finder message to the mobile terminal to receive it (step 2).

The mobile terminal sends a registration request (RRQ) message (step 3).

The external gatekeeper of the new zone sends a RegistrationConfirm (RCQ) message in response to the registration message to be received by the mobile terminal (step 4).

The mobile terminal sends an AdmissionRequest (ARQ) message (step 5).

The external gatekeeper of the new zone sends an AdmissionConfirm (ACF) message in response to the call grant message to allocate bandwidth to the mobile station to complete the registration procedure (step 6). At this time, the external gatekeeper sends a location request (LRQ) message to the second gatekeeper while the predetermined step is performed (step 7). Thereafter, the second gatekeeper sends a location confirmation (LCF) message to the external gatekeeper (step 8).

After this registration procedure, the mobile terminal sends a Setup H.225 message to the H.323 counterpart terminal with the multipoint video conferencing controller (step 9).

The opposite terminal transmits a call processing message to the mobile terminal to establish a call between the mobile terminals (step 10).

The other terminal transmits an AdmissionRequest (ARQ) message to the second gatekeeper (step 11).

The second gatekeeper sends an AdmissionConfirm (ACF) message to the opposite terminal in response to the call grant message (step 12).

The opposite terminal transmits an alerting message to the mobile terminal (step 13).

The other terminal transmits a Connect message to the mobile terminal (step 14).

The mobile terminal transmits capability information on its codec and the like to the other terminal (step 15).

The opposite terminal transmits the capability acceptance message of the opponent to the mobile terminal (step 16).

The opposite terminal transmits capability information on its codec and the like to the mobile terminal (step 17).

The mobile terminal transmits the capability acceptance message of the opponent to the other terminal (step 18).

The mobile terminal transmits the master / slave decision message to the other terminal (step 19).

The opposite terminal transmits the master / slave decision completion message to the mobile terminal to allow master / slave relationship in step 19 (step 20).

The mobile terminal transmits a logical channel open message to the opposite terminal (step 21).

The opposite terminal sends a logical channel open accept message to the mobile terminal (step 22).

The opposite terminal sends a logical channel open message to the mobile terminal (step 23).

The mobile terminal sends a logical channel open confirmation message to the opposite terminal (step 24).

Steps 15 to 24 are the negotiation procedure specified in H.245.

All these procedures must be completed in the overlapping intervals of the two cells. After all procedures for handoff are completed, the mobile terminal establishes a new connection such as a TCP connection such as H.225, H.245, and UDP for multimedia transmission, and terminates the existing call. At this time, a message (not shown in the drawing) such as DRQ (DisengageRequest) and URQ (UnregistrationRequest) is used.

The first and second gatekeepers shown in FIG. 1 correspond to H.323 terminals, respectively.

FIG. 3A is a schematic diagram illustrating the handoff method shown in FIG. 1 in which a mobile terminal 14 in a cell 12 is adjacent to a H.323 fixed terminal 10 having a multipoint video conferencing controller. When moving into the zone of cell 16, a new H.323 call must be made perfectly in the overlapping area of the two cells 12, 16. The solid line between the fixed terminal 10 and the mobile terminal 14 indicates the flow of multimedia data (UDP), and the broken line indicates the flow of call signal processing (TCP), respectively.

In this prior art, first, a call may be broken if a new H.323 call is not made completely in the overlapped region. Second, bandwidth is wasted because two H.323 calls are established. Third, if the other terminal does not have a multipoint video conferencing controller function, handoff is not supported, and the delay is increased when the multipoint video conferencing controller is separated from the corresponding terminal. The more serious case is that both are mobile terminals, and the current multipoint video conferencing controller function alone cannot fully support handoff in this case. Thus, existing multipoint videoconferencing controllers cannot support the new mobile H.323.

The present invention provides a handoff method for terminal mobility that supports handoff of a mobile terminal without establishing a new H.323 call by a method of closing a logical channel and opening a logical channel with a new address. The purpose is to provide.

According to an aspect of the present invention, there is provided a handoff system for providing a handoff to a mobile terminal moving from a zone having a gatekeeper to a specific zone with a specific gatekeeper during a call with a counterpart terminal. A first step of receiving a call from the specific gatekeeper; A second step of the mobile terminal requesting the opposite terminal to close a logical channel; A third step of the mobile terminal requesting a new mode from the opposite terminal; A fourth step in which the opposite terminal accepts closing the logical channel to the mobile terminal; A fifth step of accepting a new mode by the opposite terminal to the mobile terminal; A sixth step in which the opposite terminal notifies the mobile terminal of closing a logical channel; A seventh step in which the opposite terminal requests the mobile terminal to open a new logical channel; And an eighth step of the mobile terminal accepting a new logical channel opening to the opposite terminal.

1 is a step-by-step diagram showing a handoff method currently being performed in standardization for mobile H.323;

2 is a step-by-step diagram illustrating a handoff method for terminal mobility of H.323 according to the present invention;

3A is a schematic diagram for explaining the handoff method shown in FIG. 1;

3B is a schematic diagram for explaining the handoff method shown in FIG. 2;

4 is a diagram illustrating a network configuration for explaining the handoff method illustrated in FIG. 2.

<Description of the symbols for the main parts of the drawings>

20, 50: fixed terminal 22: home agent

24, 28, 30, 36: cell 26, 32: mobile terminal

34, 38, 52: 1st, 2nd, 3rd gatekeeper

40: Internet 42, 44, 46: first, second, third router

Hereinafter, the embodiment of the present invention will be described in detail with reference to the following drawings.

2 is a step-by-step diagram illustrating a handoff method for terminal mobility of H.323 according to the present invention. In this case, it is assumed that the mobile terminal moves to a new zone while the multimedia session is open and the call is in progress. Unless otherwise specified, the same steps in FIGS. 1 and 2 are considered to perform different performances.

In the figure, the H.323 mobile station sends a gatekeeper search message for the new zone (step 1). The external gatekeeper of the new zone sends a gatekeeper search confirmation message and a COA in response to the gatekeeper search message to be received by the mobile terminal (step 2). The mobile terminal sends a registration message (step 3). The external gatekeeper of the new zone sends a registration confirmation message in response to the registration message to be received by the mobile terminal (step 4). The mobile terminal sends a call authorization message (step 5). The external gatekeeper of the new zone sends a call grant confirmation message in response to the call grant message and allocates bandwidth to the mobile station to complete the registration process (step 6).

The process of steps 1 to 6 is the same as the steps 1 to 6 of FIG. Steps 1 to 6 are typical procedures for exchanging information to determine the location of the mobile terminal rather than for handoff. This enables roaming services of the mobile terminal.

Next, the mobile terminal transmits a logical channel close request message to the opposite terminal (step 7).

The mobile terminal sends a request message for the new mode to the other terminal (step 8).

The opposite terminal sends a logical channel close acceptance message to the mobile terminal (step 9).

The opposite terminal sends a new mode accept message to the mobile terminal (step 10).

The opposite terminal sends a logical channel close message to the mobile terminal (step 11).

The opposite terminal sends a new logical channel open message to the mobile terminal (step 12).

The mobile terminal sends a new logical channel open accept message to the opposite terminal (step 13).

In such a case, there is something to consider. If a new environment including a bandwidth reaches a new environment, the existing codec cannot be used as it is, and a new codec must be used. Therefore, for this case, it adapts to the new environment change obtained through the call permission message with the external gatekeeper of the newly moved zone through the request message for the new mode of step 8. When a new logical channel is opened, the DRQ message is used like the conventional method to return the existing bandwidth.

In addition, in order to open a new logical channel, the COA of the mobile terminal that has moved must be informed to the other terminal. That is, this can be solved by putting the IP address in 'H2250LogicalChannelParameters' in step 13. In this way, a new logical channel is opened to handle the handoff while using the existing call.

FIG. 3B is a schematic diagram illustrating the handoff method shown in FIG. 2, in which the mobile terminal 26 in the cell 24 is talking to the H.323 fixed terminal 20 having no multipoint video conferencing controller. When moved to the zone of the adjacent cell 28, a new H.323 call must be made completely under the control of the home agent 22 in the overlapped area of the two cells 24, 28. The solid line between the fixed terminal 20 and the mobile terminal 26 represents the flow of multimedia data (UDP), and the broken line between the mobile terminal 26 and the home agent 22 represents the flow of call signal processing (TCP), respectively.

4 is a diagram illustrating a network configuration for explaining the handoff method illustrated in FIG. 2, wherein each cell 30, 36 connects to the Internet 40 through the first and second routers 42 and 44, respectively. The fixed terminal 50 connects to the Internet 40 via the third router 46. In this case, the first gatekeeper 34 is an H.323 mobile terminal in the cell 30, the second gatekeeper 38 is an H.323 mobile terminal in the cell 36, and the third gatekeeper 52 is predetermined. Each fixed terminal connected to the network is managed.

In the figure, the mobile terminal 32 in the cell 30 is adjacent to the adjacent cell (while making a call through the fixed terminal 50, the first router 42, the Internet 40, and the third router 46). Moving to 36, the handoff is completed at the overlapping portion between the two cells (30, 36). After completion of the hand hop, the mobile terminal 32 receives the management of the second gatekeeper 38 and connects to the Internet 40 through the second router 44.

The handoff method according to the present invention described above considers two points.

First, when a handoff occurs, it does not set up a new call, but simply replaces a logical channel to support the handoff, thereby shortening the handoff time. This method avoids the use of a multipoint videoconferencing controller, which may be the biggest disadvantage of the existing method, and satisfies the time constraint of ending the handoff operation in the overlapped section of two cells.

The second adapts to a new H.323 zone when a handoff occurs. In order to adapt to new environment changes, a request message for a new mode called RequestMode is used among H.245 control messages. You can use this message to adapt to bandwidth in new zones, etc.

The control channel according to the present invention described above uses TCP for mobile IP, and the logical channel for multimedia uses UDP using COA.

As described above, the present invention relates to a protocol above the transport layer, and assumes that the lower network layer uses mobile IP. However, there may be other protocols at the network layer, including similar cellular IP.

As described above, since the present invention does not use the multipoint videoconferencing controller function, the handoff can be processed without regard to the multipoint videoconferencing controller. In addition, since the number of incoming and outgoing messages can be reduced and the delay for a new TCP connection can be reduced, the handoff can be performed more quickly in the overlapping interval between two cells. Since one call continues to be used, there is no waste of bandwidth. It also maintains backward compatibility because it does not affect existing H.323 messages.

Claims (3)

A handoff system for providing a handoff to a mobile terminal moving from a zone with a gatekeeper to a zone with a specific gatekeeper in a call with the other terminal in a zone with a gatekeeper: A first step in which the mobile terminal receives a call from the specific gatekeeper; A second step of the mobile terminal requesting the opposite terminal to close a logical channel; A third step of the mobile terminal requesting a new mode from the opposite terminal; A fourth step in which the opposite terminal accepts closing the logical channel to the mobile terminal; A fifth step of accepting a new mode by the opposite terminal to the mobile terminal; A sixth step in which the opposite terminal notifies the mobile terminal of closing a logical channel; A seventh step in which the opposite terminal requests the mobile terminal to open a new logical channel; And an eighth step of the mobile terminal accepting opening of a new logical channel to the opposite terminal. The method of claim 1, The mobile terminal and the other terminal is a handoff method for terminal mobility, characterized in that the H.323 terminal. The method according to any one of claims 1 to 2, The opposite terminal is a mobile terminal or a fixed terminal handoff method for the terminal mobility, characterized in that.