System and method for providing a push to talk over cellular service

A system and method are provided that provide Push to talk over Cellular (PoC) service via a PoC server. The method includes receiving, by the PoC server, a PoC group call request for requesting a PoC connection for a PoC group from a first User Equipment (UE); extracting information regarding a cell where a second UE that belonged to the PoC group is located, according to the received PoC group call request; comparing a number of current PoC connections corresponding to a cell with a maximum number of PoC connections to the cell; and establishing a PoC connection with the second UE, if the number of current PoC connections is less than the maximum number of PoC connections.

PRIORITY

This application claims priority under 35 U.S.C. §119(a) to a Korean Patent Application No. 10-2011-0100577, which was filed in the Korean Intellectual Property Office on Oct. 4, 2011, the entire disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a Push to talk over Cellular (PoC) service, and more particularly, to a system and method that efficiently manages a connection while providing the PoC service.

2. Description of the Related Art

The 3rdGeneration Partnership Project Internet Protocol (IP) Multimedia Subsystem (3GPP IMS) standard includes a standard regarding a PoC service and a Push-To-Talk (PTT) specification. The PTT, which is also known as Press-To-Transmit, is a method of conversing on half-duplex communication lines, where users set a transmission mode or a reception mode by operating a switch.

For example, users set a PTT device to a transmission mode by pressing the mode switch and revert to reception mode by releasing the mode switch. That is, a PTT device user A talks into a microphone while pressing the mode switch of the user A's PTT device, and another user B, who has subscribed to the same PTT group as user A, stands by, without pressing a mode switch of user B's PTT device. Accordingly, user B can hear what user A is saying via user B's PTT device. A typical example of a device using PTT is a handheld transceiver or a walkie-talkie.

PoC services refer to PTT services that are provided via a cellular communication network. Cellular communication networks support full-duplex via Frequency Division Multiplexing (FDM), Time Division Multiplexing (TDM), etc. If the networks use PoC services, they can transmit messages to a User Equipment (UE) that is not currently connected thereto, instead of half-duplex communication, because cellular mobile phones and cellular communication networks employ PoC services.

PoC services are provided based on PoC groups. For example, if a PoC group, G1, includes PoC devices, A, B, and C, data that device A transmits to group G1in a transmission mode can be shared by devices B and C.

Further, one PoC device may be subscribed to a number of PoC groups. In that case, the PoC device selects which of the PoC groups it wants to transmit a corresponding message to or receive a corresponding message from.

A PoC application server identifies a PoC group session or the number of connections, executed according to the request of user equipment, in an environment where services are provided, according to a conventional IMS standard, via a mobile communication network. However, if communication congestion occurs in a PoC group in a cell, the PoC application server detects the congestion and controls the group calls.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-described problems, and provides at least the advantages described below.

An aspect of the present invention is to provide a system and method for controlling communication congestion in a PoC group based on cells and providing a PoC service.

In accordance with an aspect of the present invention, a method for providing a PoC service via a PoC server is provided. The method includes receiving, by the PoC server, a PoC group call request for requesting a PoC connection for a PoC group from a first User Equipment (UE); extracting information regarding a cell where a second UE that belonged to the PoC group is located, according to the received PoC group call request; comparing a number of current PoC connections corresponding to a cell with a maximum number of PoC connections to the cell; and establishing a PoC connection with the second UE, if the number of current PoC connections is less than the maximum number of PoC connections.

In accordance with another aspect of the present invention, a PoC application server for providing a PoC service is provided. The PoC application server includes a communication unit for receiving a PoC group call request for requesting a PoC connection for a PoC group from a first User Equipment (UE); a controller for extracting information regarding a cell where a second UE that belonged to the PoC group is located, according to the received PoC group call request, and comparing a number of current PoC connections corresponding to a cell with a maximum number of PoC connections to the cell. The communication unit establishes a PoC connection with the second UE, if the number of current PoC connections is less than the maximum number of PoC connections.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1illustrates a network that provides PoC services according to an embodiment of the invention.

Referring toFIG. 1, the PoC service network includes a PoC application server (hereinafter referred to as a PoC server)150, an IP Multimedia Subsystem Core Network (IMS CN)170, and a Home Subscriber Server (HSS)160. The IMS CN170includes a Session Initiation Protocol/Internet Protocol Core (SIP/IP)175for controlling calls and sessions. For example, the PoC serving network may support communication according to Mobile-Wimax (M-Wimax) and/or Long Term Evolution (LTE).

As illustrated inFIG. 1, the PoC service network includes UE111, UE112, a first Radio Access Station (RAS)114, a first Access Control Router (ACR)116, UE121, UE122, a second Radio Access Station (RAS)124, and a second Access Control Router (ACR)126, which communicate with each other according to M-Wimax.

In addition, the PoC service network includes UE131, UE132, a first eNode B (eNB)134, a first System Architecture Evolution Gateway (SAE-GW)136, UE141, UE142, a second eNB144, and a second SAE-GW146, which communicate with each other according to LTE.

Although the communication standard of UEs111,112,121, and122differs from that of UEs131,132,141, and142, they all serve as UEs for cellular communication. Likewise, although the communication standard of RASs114and124differs from that of eNBs134and144, they all serve as base stations. Therefore, RASs114and124and eNBs134and144are commonly referred to herein as base stations.

In addition, although the communication standard of ACRs116and126differs from that of SAE-GWs136and146, they all serve as routers. Therefore, ACRs116and126and SAE-GWs136and146are commonly referred to herein as routers.

UEs111,112,121,122,131,132,141, and142provide standard client functions proposed in the IMS standard, e.g., a Voice over Internet Protocol (VoIP) service request, a PoC group selection, and a PoC group call request, a function for controlling a right to talk, a function for providing location information when a service is requested, a function for providing information regarding an altered location, etc.

The base stations114,124,134, and144and the routers116,126,136, and146serve as agents that provide cellular services to the UEs111,112,121,122,131,132,141, and142.

The IMS CN170establishes a connection or disconnects according to the request of a VoIP service or the request of PoC group communication. Specifically, the IMS CN170receives an SIP signaling message from UE, parses the SIP signaling message, and processes the received SIP signaling message according to its service profile information or initial Filter Criteria (iFC). The IMS CN170transmits the received SIP message to a corresponding application server or a called service subscriber.

The PoC server150registers a PoC group according to a user or administrator request. The PoC server150receives a PoC group call request from a UE and establishes or controls the session/connection of the PoC group according to the request. The PoC server150controls call congestion, registers location information regarding base stations, and sets the number of limited connections by base stations. The PoC server150manages location information regarding the UE in real time.

The HSS160authenticates subscribers in IMS networks, and manages service profiles. The HSS160authenticates subscribers, cooperating with the IMS CN170, and transfers profile information regarding permitted subscribers to the IMS CN170. If a subscriber requests a service, the IMS CN170provides the subscriber with the service using profile information regarding the service previously provided.

FIG. 2is a signal flow diagram illustrating a method for establishing configuration information regarding a PoC server, according to an embodiment of the invention.

Referring toFIG. 2, the PoC server150may include Location Base Resource Control (LBRC) as a location information control module. An administrator or operator may access PoC server150, via open interface (e.g., Web, Graphic User Interface (GUI), etc.), for example, and set the configuration information in step210. The administrator or operator may also set PoC group information and/or cell-based management information, for example. For example, the PoC group information and cell-based management information are configured as follows.

1) PoC Group Information

PoC group information refers to information regarding PoC groups managed by a PoC server. PoC group information regarding one PoC group includes at least four fields, e.g., an IDentifier (ID), a Name, Members, and a Priority.ID: Identifier of the PoC group.Name: Name of the PoC group.Members: Identifiers of members subscribed to the PoC group.Priority: Priority of the PoC group (e.g., 0-9, Variable).

It should be understood that the field names described above are exemplary and may be altered.

For example, the field, Name, is not an essential element, and the field, Priority, may be omitted from the PoC group information if priority is not taken into consideration.

2) Cell-Based Management InformationTotal_Assigned_CellIds: Total number of cells that are allocated.Total_Configured_Cellids: Total number of cells that are configured.Total_Attached_UEs: Total number of UEs that are registered.Total_Attached_UEs_Per_[ ]Cellid: Number of UEs registered in respective cells.Total_GroupCall_Sessions: Total number of PoC connections that are being executed.Total_GroupCall_Sessions_Per_[ ]Cellid: Number of PoC connections that are being executed in respective cells.Total_VoipCall_Sessions: Total number of VoIP sessions that are being executed.Total_VoipCall_Sessions_Per_[ ]Cellid: Number of VoIP sessions that are being executed in respective cells.Threshold Values: Values when call congestions reach a critical state (number of limited connections). The number of limited connections may be set differently according to respective cells. It includes Max_GroupCall_Sessions_Per_[ ]Cellid and Max_VoipCall_Sessions_Per_[ ]Cellid.Max_GroupCall_Sessions_Per_[ ]Cellid: Number of PoC group connections that can be simultaneously processed in respective cells.Max_VoipCall_Sessions_Per_[ ]Cellid: Number of VoIP secessions that can be simultaneously processed in respective cells.

It should be understood that the names of data described above are exemplary and may be altered.

Further, the data, Total_VoipCall_Sessions, Total_VoipCall_Sessions_Per_[ ]Cellid, and Max_VoipCall_Sessions_Per_[ ]Cellid, may be omitted if the PoC server does not manage the number of VoIP connections.

FIG. 3is a signal flow diagram illustrating a method for registering a PoC service for a UE, according to an embodiment of the invention.

When the UE is turned on, it may automatically execute a service registration procedure. Alternatively, the service registration procedure may be executed when the service subscriber operates the UE.

Referring toFIG. 3, UE111transmits a registration message, REGISTER, to an SIP/IP Core A175a, in step301. In step302, the SIP/IP Core A175atransmits a command, User-Authorization-Request (UAR), to the HSS160. In step303, the HSS160transmits a command, User-Authorization-Answer (UAA), in response to the UAR, to the SIP/IP Core A175a. In step304, the SIP/IP Core A175atransmits a command, Multimedia-Ruth-Request (MAR), to the HSS160. In step350, the HSS160transmits a command, Multimedia-Ruth-Answer (MAA), in response to the MAR, to the SIP/IP Core A175a. In step306, the SIP/IP Core A175atransmits a401Unauthorized message, confirming that the current UE111has not been authorized, to the UE111.

In step307, the UE111transmits a registration message, REGISTER, to the SIP/IP Core A175a. In step308, the SIP/IP Core A175atransmits a command, User-Authorization-Request (UAR), to the HSS160. In step309, the HSS160transmits a command, User-Authorization-Answer (UAA), in response to the UAR, to the SIP/IP Core A175a. In step310, the SIP/IP Core A175atransmits a command, Server-Assignment-Request (SAR), to the HSS160. In step311, the HSS160transmits a command, Server-Assignment-Answer (SAA), in response to the SAR, to the SIP/IP Core A175a. In step312, the SIP/IP Core A175atransmits a 200 OK message, confirming that the current UE111has been registered in the HSS160, to the UE111.

For example, the REGISTER messages transmitted from the UE111to the SIP/IP Core A175in steps301and307include information regarding a cell that the UE111belonged to or information regarding a location where the UE111is located. For example, the location information regarding UE111may include at least one of the following.P-Access-Network-Info: IEEE-802.16: wimax-location=0000400121f6: if the UE111to the SIP/IP Core A175communicate according to M-WiMAX.P-Access-Network-Info: 3GPP-E-UTRAN-FDD: e-utran-cell-id-3gpp=0000400121f6: if the UE111to the SIP/IP Core A175communicate according to LTE-FDD.P-Access-Network-Info: 3GPP-E-UTRAN-TDD: e-utran-cell-id-3gpp=0000400121f6: if the UE111to the SIP/IP Core A175communicate according to LTE-TDD.

The REGISTER messages, transmitted from the UE111to the SIP/IP Core A175in steps301and307, optionally include information regarding a cell that the UE111belonged to or information regarding a location where the UE111is located.

Alternatively, the information regarding a cell that the UE111belonged to or information regarding a location where the UE111is located may be transmitted from the UE111to the SIP/IP Core A175aat different steps.

Referring againFIG. 3, the SIP/IP Core A175atransmits a registration message, REGISTER, to the PoC server150in step313. The REGISTER message in step313may include information regarding a cell that the UE111belonged to or information regarding a location where the UE111is located, which is included in the REGISTER messages at steps301and307.

After receiving the REGISTER message, the PoC server150increases Total_Attached_UE (the total number of registered UEs) by one. The PoC server150identifies a cell that the UE111belonged to, based on the information regarding a cell that the UE111belonged to or information regarding a location where the UE111is located, included in the REGISTER message. The PoC server150increases Total_Attached_UEs_Per_[ ]Cellid for a cell that the UE111belonged to (i.e., the number of UEs registered in a corresponding cell) by one.

In step314, the PoC server150transmits a 200 OK message to the SIP/IP Core A175a. In step315, the PoC server150transmits a SUBSCRIBE message to the SIP/IP Core A175a. In step316, the SIP/IP Core A175atransmits a 200 OK message to the PoC server150. In step317, the SIP/IP Core A175atransmits a NOTIFY message to the PoC server150. In step318, the PoC server150transmits a 200 OK message to the SIP/IP Core A175a.

Alternatively, the information regarding a cell that the UE111belonged to or information regarding a location where the UE111is located may be transmitted from the SIP/IP Core A175ato PoC server150at any other steps other than step313. In such a case, the PoC server150receives the information and then increases Total_Attached_UE (the total number of registered UEs) and Total_Attached_UEs_Per_[ ]Cellid (the number of UEs registered in a corresponding cell), by one, respectively.

As described above referring toFIG. 3, the registration message, REGISTER, according to an embodiment of the invention includes information regarding a cell that the UE belonged to (or information regarding a location where the UE is located), and the PoC server150records the number of UEs registered in a corresponding cell based on the information in the message.

FIG. 4is a signal flow diagram illustrating a method for releasing a PoC service according to an embodiment of the invention.

When a UE is turned off or the user operates the UE and selects a service release option, the UE performs the service release procedure.

Referring toFIG. 4, the UE111transmits a registration message, REGISTER, to the SIP/IP Core A175ain step401. The REGISTER message may include information regarding a cell that the UE111belonged to or information regarding a location where the UE111is located. For example, location information regarding the UE111may be expressed as shown below, i.e., the same as the service registration procedure illustrated inFIG. 3.P-Access-Network-Info: IEEE-802.16: wimax-location=0000400121f6: if the UE111to the SIP/IP Core A175communicate according to M-WiMAX.P-Access-Network-Info: 3GPP-E-UTRAN-FDD: e-utran-cell-id-3gpp=0000400121f6: if the UE111to the SIP/IP Core A175communicate according to LTE-FDD.P-Access-Network-Info: 3GPP-E-UTRAN-TDD: e-utran-cell-id-3gpp=0000400121f6: if the UE111to the SIP/IP Core A175communicate according to LTE-TDD.

In step402, the SIP/IP Core A175atransmits a command, UAR, to the HSS160. In step403, the HSS160transmits a command, UAA, in response to the UAR, to the SIP/IP Core A175a. In step404, the SIP/IP Core A175atransmits a command, Server-Assignment-Request (SAR), to the HSS160. In step405, the HSS160transmits a command, Server-Assignment-Answer (SAA), in response to the SAR, to the SIP/IP Core A175a. In step406, the SIP/IP Core A175atransmits a 200 OK message, confirming that the service has been released, to the UE111.

In step407, the SIP/IP Core A175atransmits a registration message, REGISTER, to the PoC server150. The REGISTER message in step407may include information regarding a cell that the UE111belonged to or information regarding a location where the UE111is located, which is included in the REGISTER messages in step401.

After receiving the REGISTER message, the PoC server150decreases Total_Attached_UE (the total number of registered UEs) by one. The PoC server150identifies a cell that the UE111belonged to, based on the information regarding a cell that the UE111belonged to or information regarding a location where the UE111is located, included in the REGISTER message. The PoC server150decreases Total_Attached_UEs_Per_[ ]Cellid for a cell that the UE111belonged to (i.e., the number of UEs registered in a corresponding cell) by one.

In step408, the PoC server150transmits a 200 OK message to the SIP/IP Core A175a. In step409, the PoC server150transmits a SUBSCRIBE message to the SIP/IP Core A175a. In step410, the SIP/IP Core A175atransmits q 200 OK message to the PoC server150. In step411, the SIP/IP Core A175atransmits a NOTIFY message to the PoC server150. In step412, the PoC server150transmits a 200 OK message to the SIP/IP Core A175a.

FIG. 5is a signal flow diagram illustrating a method for processing a PoC group call request, according to an embodiment of the invention.

Referring toFIG. 5, in step501, the UE111transmits an invitation message, INVITE, to SIP/IP Core A175a. The INVITE message requests a PoC group call setting, and may also be referred to as a PoC group call request. The PoC group call request may include an identifier of a PoC group that needs to perform PoC communication.

For example, a user can operate the UE111and select a first PoC group and the PoC group call, thereby executing PoC communication. The UE111performs the transmission of an invitation message according to the user operation. The invitation message includes an identifier of the first PoC group.

Herein, it is assumed that the UE111and the UE121have belonged to the selected first PoC group.

In step502, the SIP/IP Core A175atransmits a 100 Trying message to the UE111.

In step503, the SIP/IP Core A175atransmits an INVITE message to the PoC server150. The INVITE message in step503includes the identifier of the first PoC group included in the INVITE message in step501. The INVITE message in step503may also include information included in the INVITE message in step501. In steps504and505, the, a 100 Trying message and a 180 Ringing message are transmitted from the PoC server150to the SIP/IP Core A175a. In step506, a 180 Ringing message is transmitted from the SIP/IP Core A175ato the UE111.

PoC server150extracts information regarding the UE111and the UE121that belonged to a corresponding group, according to the identifier of a group included in the INVITE message transmitted in step503. The PoC server150identifies a cell that UE111and UE121belonged to. For example, the PoC server150identifies information regarding a cell that the UE111and the UE121belonged to, referring to external other entities.

Alternatively, the PoC server150stores information regarding cells that UEs belonged to in the storage unit, and manages/uses it if necessary.

PoC server150identifies the number of current PoC connections to a cell that the UE121belonged to (Total_GroupCall_Sessions_Per_[ ]Cellid). If the number of current PoC connections to a corresponding cell is less than the number of PoC connections that can perform a simultaneous process in the cell (Max_GroupCall_Sessions_Per_[ ]Cellid), i.e., the maximum number of PoC connections to a corresponding cell, the PoC server150increases the total number of PoC connections Total_GroupCall_Sessions and the number of PoC connections to a corresponding cell (Total_GroupCall_Sessions_Per_[ ]Cellid), by one, respectively. Likewise, the PoC server150applies this procedure to the UE111.

The method illustrated inFIG. 5is implemented when a number of current PoC connections to a corresponding cell is less than the maximum number of PoC connections to the cell. The other cases will be explained referring toFIGS. 6,7A, and7B.

In step507, if the number of current PoC connections is less than the maximum number of PoC connections to the cell, the PoC server150transmits an INVITE message to the SIP/IP Core A175. Thereafter, the INVITE message is transmitted through a second ACR126to the UE121at steps508to528, thereby establishing a PoC connection between the UEs111and121via the PoC server150.

FIG. 6is a signal flow diagram illustrating a method for processing a PoC group call request, according to an embodiment of the invention.

Referring toFIG. 6, in step600, the PoC connection is ongoing in the first PoC group including the UE111and the UE121. Herein, it is assumed that the UE121and the UE122belong to the same cell, and the cell that the UE121and the UE122belonged to is in a state where the number of current PoC connections is equal to or greater than the maximum number of PoC connections, i.e., a PoC call congestion state. The second PoC group includes the UE111and the UE122.

In step601, the UE122transmits an invitation message, INVITE, to an SIP/IP Core B175bwhile the PoC connection of the first PoC group is ongoing. The INVITE message refers to a PoC group call request message for the second PoC group.

In step602, the SIP/IP Core B175btransmits a 100 Trying message to the UE122, and in step603, the SIP/IP Core B175btransmits an INVITE message for the second PoC group to the PoC server150.

In steps604and605, the PoC server150transmits a 100 Trying message and a 180 Ringing message to the SIP/IP Core B175b.

In step606, the SIP/IP Core B175btransmits a 180 Ringing message to the UE122.

In step607, the PoC server150analyzes and identifies the received INVITE message as a message for the second PoC group. PoC server150identifies whether the UE111and the UE122belong to the second PoC group. PoC server150may also identify a cell that the UE111and the UE122belonged to, and determine whether an additional PoC connection can be established in the cell. Because the number of current PoC connections to a cell that the UE122belonged to is equal to or greater than the maximum number of PoC connections, the PoC server150cannot process the PoC group call request via the procedure illustrated inFIG. 5. Accordingly, the PoC server150detects a PoC connection of a PoC group with the lowest priority, from among the PoC connections for the current cell. As described above referring toFIG. 2, PoC groups have priority values.

InFIG. 6, it is assumed that: a PoC connection of a PoC group with the lowest priority, from among PoC connections to a current, corresponding cell, is defined as a first PoC group; the priority of the first PoC group is 8; the priority of the second PoC group is 5; and the higher the priority the faster the process of the connection.

The priority of the first PoC group is greater than that of the second PoC group. The PoC server150compares a priority of a PoC group that attempts a new connection with that of a PoC group with the lowest priority, from among the PoC connections to the cell. If the PoC server150ascertains that a priority of a PoC group that attempts a new connection is less than that of a PoC group that is currently connected to the cell, it rejects the new connection request. However, if PoC server150ascertains that a priority of a PoC group that attempts a new connection is equal to or greater than that of a PoC group that is currently connected to the cell, it disconnects the current connection and processes the new connection request. Because the priority of the first PoC group that is currently connected to the cell is greater than that of the second PoC group that attempts a new connection inFIG. 6, the PoC server150rejects the connection request of the second PoC group in step607.

In steps608and609, the PoC server150transmits a 406 Not Acceptable message, rejecting the connection, through the SIP/IP Core B175b, to the UE122. In steps610and611, a 200 Ok message is transmitted from the UE122to the SIP/IP Core B175b, and then to the PoC server150.

Because the connection request of the UE122is rejected, a connection is no longer executed with respect to the other UEs in the second PoC group. However, it should be understood that the method illustrated inFIG. 6may be modified in such a way that, although the connection request of the UE122is rejected, a PoC connection may be performed in the other UEs in the second PoC group, so that they can establish a PoC connection with each other.

FIGS. 7A and 7Bare signal flow diagrams illustrating a method for processing a PoC group call request, according to an embodiment of the invention. Specifically, inFIGS. 7A and7B, it is assumed that the UE121and the UE122belong to the same cell; the cell that UE121and UE122belonged to is in a state where the number of current PoC connections is equal to or greater than the maximum number of PoC connections, i.e., a PoC call congestion state; and the cell that the UE111belonged to is in a PoC call congestion state. The second PoC group includes the UE111and the UE122. Basically, the method illustrated inFIGS. 7A and 7Bis implemented in the same environment as the method illustrated inFIG. 6, except that the PoC groups have different priorities.

Referring toFIG. 7A, the PoC connection is ongoing in the first PoC group including the UE111and the UE121in step700.

Because steps701to706are identical to steps601to606inFIG. 6, which were already described above, the detailed description will be omitted in the following description.

In step707, the PoC server150analyzes and identifies the received INVITE message as a message for the second PoC group. The PoC server150identifies whether the UE111and the UE122belong to the second PoC group. The PoC server150may also identify a cell that the UE111and the UE122belonged to, and determine whether an additional PoC connection can be established in the cell. Because the number of current PoC connections to a cell that the UE122belonged to is equal to or greater than the maximum number of PoC connections, the PoC server150cannot process the PoC group call request in step707. Accordingly, the PoC server150detects a PoC connection of a PoC group with the lowest priority, from among the PoC connections for the current cell.

As described above referring toFIG. 2, PoC groups have respective priority values.

InFIGS. 7A and 7B, it is assumed that a PoC connection of a PoC group with the lowest priority, from among PoC connections to a current, correspond cell, is defined as a first PoC group; the priority of the first PoC group is 3; the priority of the second PoC group is 5; and the higher the priority the faster the process of the connection. The priority of the second PoC group is greater than that of the first PoC group.

The PoC server150compares a priority of a PoC group that attempts a new connection with that of a PoC group with the lowest priority, from among the PoC connections to the cell. If the PoC server150ascertains that a priority of a PoC group that attempts a new connection is less than that of a PoC group that is currently connected to the cell, it rejects the new connection request. However, if the PoC server150ascertains that a priority of a PoC group that attempts a new connection is equal to or greater than that of a PoC group that is currently connected to the cell, it disconnects the current connection and processes the new connection request. Because the method illustrated inFIGS. 7A and 7Bis implemented in such a way that the priority of the first PoC group that is currently connected to the cell is less than that of the second PoC group that attempts a new connection, the PoC server150releases the connection of the first PoC group with respect to the cell that the UE121and the UE122belonged to and processes the connection of the second PoC group. In addition, the PoC server150releases the connection of the first PoC group with respect to the cell that the UE111belonged to and processes the connection of the second PoC group.

In steps708to712, the PoC connection of Group 1 is released between the PoC server150and the UE121. Likewise, the PoC connection of Group 1 is released between PoC server150and UE111via steps713to717.

In steps718to733, the PoC connection of Group 2 is established between the UE111and the UE122, via PoC server150.

InFIGS. 7A and 7B, because the number of actual PoC connections does not vary, this was not described. However, if there is a change in the number of actual PoC connections, the PoC server150reflects the change in the data and stores the result.

FIG. 8is a signal flow diagram illustrating a method for terminating a PoC group call according to an embodiment of the invention. InFIG. 8, it is assumed that a PoC group connection has already been established between the UE111and the UE121.

Referring toFIG. 8, the UE111transmits a PoC group disconnection request message, BYE, to the SIP/IP Core A175ain step801. For example, a user operates the UE111and requests to terminate the PoC connection to PoC group1. In step802, the SIP/IP Core A175atransmits the received disconnection request, BYE, to the PoC server150. The 200 OK message is transmitted from the PoC server150to the SIP/IP Core A175a, and then to the UE111in step803and804. In step805, the PoC connection is released between the PoC server150and the UE111. The disconnection request is transmitted from the PoC server150, via the SIP/IP Core A175aand the ACR126, to the UE121in steps806to808. The 200 OK message is transmitted from the UE121, via the ACR126and the SIP/IP Core A175a, to the PoC server150in steps809to811. Therefore, the PoC connection is released between the PoC server150and the UE121in step812.

During the processes, the total number of PoC connections (Total_GroupCall_Sessions) is reduced by two. In addition, the numbers of PoC connections (Total_Attached_UEs_Per_[ ]Cellid) for a cell that the UE111belonged to and a cell that the UE121belonged to are reduced, by one, respectively. The PoC server150reflects information regarding the change to data stored therein.

FIG. 9is a signal flow diagram illustrating a method for processing movement operations of UE, according to an embodiment of the invention. InFIG. 9, it is assumed that a PoC connection has been established between the UE111and the PoC server150; and the UE111moves from a first cell to a second cell.

Referring toFIG. 9, in step901, the UE111transmits a PoC update message, UPDATE, to the SIP/IP Core A175a. In step902, the SIP/IP Core A175atransmits the received PoC update message to the PoC server150. The PoC update message includes identification information regarding a cell where the UE111is newly located after it moves or information regarding a location where the UE is located. The format of the cell identification information or the location information may be identical to or similar to that of the embodiment illustrated inFIG. 3.

For example, the location information regarding UE111may include at least one of the following.P-Access-Network-Info: IEEE-802.16: wimax-location=0000400121f6: if the SIP/IP Core A175aand the UE111communicate according to M-WiMAX.P-Access-Network-Info: 3GPP-E-UTRAN-FDD: e-utran-cell-id-3gpp=0000400121f6: if the SIP/IP Core A175aand the UE111communicate according to LTE-FDD.P-Access-Network-Info: 3GPP-E-UTRAN-TDD: e-utran-cell-id-3gpp=0000400121f6: if the SIP/IP Core A175aand the UE111communicate according to LTE-TDD.

The PoC server150analyzes the received PoC update message and detects the identification information regarding a cell to which the UE111newly moves. The PoC server150extracts information regarding the old location where the UE111was located before it moved to the new location, according to information that the PoC server150has stored or via another method. The PoC server150may store information regarding cells that UEs have been connected to.

In the modification, the PoC update message may include identification information regarding a cell where the UE111was located before it moved or information regarding a location where the UE is currently located. In that case, the PoC server150analyzes the PoC update message and detects location information before and after the UE111moves.

The PoC server150decreases the total number of PoC connections for cells where the UE111was originally located, by one, and increases the total number of PoC connections for cells where the UE111is newly located, by one, according to the detected information. InFIG. 9, it is assumed that a cell where the UE is newly located is not in a PoC connection congestion state. If a cell where the UE is newly located is in a PoC connection congestion state, the priorities of PoC groups are compared with each other and the PoC connection of a PoC group with the lowest priority is released, as described in the embodiments referring toFIGS. 6,7A, and7B. In the modification, if UE moves, PoC connections may all be maintained irrespective of congestion states.

In steps903and904, the 200 OK message is transmitted from the PoC server150, via the SIP/IP Core A175a, to the UE111.

FIG. 10is a schematic block diagram illustrating a PoC server according to an embodiment of the invention.

Referring toFIG. 10, the PoC server150includes a communication unit1010, a controller1020, and a storage unit1030. The communication unit1010receives a PoC group call request for requesting a PoC connection to a specific PoC group from UE111.

After receiving the PoC group call request, the controller1020extracts information regarding cells where the other UEs that belonged to the PoC group are located and compares the number of current PoC connections corresponding to the cell with the maximum number of PoC connections corresponding to the cell. If the controller1020ascertains that the number of current PoC connections is less than the maximum number of PoC connections, the controller1020controls the communication unit1010to establish PoC connections with the other UEs. However, if the number of current PoC connections is equal to or greater than the maximum number of PoC connections, the controller1020releases old connections according to the priorities and processes or rejects new connections, as was described above referring toFIGS. 2 to 9.

The storage unit1030stores PoC group information and cell based management information, as described above referring toFIG. 2.

Again, the PoC group information refers to information regarding PoC groups managed by a PoC server and may include at least four fields, e.g., ID, Name, Members, and Priority, as described above.

When the PoC connection is released or established, or the UE moves, the controller1020updates Total_GroupCall_Sessions and Total_VoipCall_Sessions_Per_[ ]Cellid, stored in the storage unit1030. In addition, when information regarding the UE is registered/removed in/from PoC server150, the controller1020updates Total_Attached_UEs and Total_Attached_UEs_Per_[ ]Cellid, stored in the storage unit1030. The updating processes are performed in the same way as described above referring toFIGS. 2 to 9.

As described above, the system and method for providing PoC services according to the above-described embodiments of the invention can properly control communication congestion in PoC groups based on cells.

In addition, it should be understood that the process and the operations of the mobile device, described above, can be performed via computer programming instructions. These computer programming instructions can be installed to processors of data processing equipment that can be programmed, special computers, or universal computers.

In order to implement a particular mode, the computer programming instructions can also be stored in a computer available memory or computer readable memory that support computers or data processing equipment that can be programmed. Therefore, the instructions, stored in the computer available memory or computer readable memory, can be installed to the products, and perform the functions therein. In addition, because the computer programming instructions can also be installed to computers or data processing equipment that can be programmed, they can create processes that perform a series of operations therein.

In the above-described embodiments, the terminology, component ‘˜unit,’ refers to a hardware element such as a PGGA, an ASIC, etc., or combination of a software element and a hardware element, and performs a corresponding function.

The terms or words described in the description and the claims should not be limited by a general or lexical meaning, instead should be analyzed as a meaning and a concept through which the inventor defines and describes the invention at his most effort, to comply with the idea of the invention.

Although various embodiments of the present invention have been described in detail hereinabove, it should be understood that many variations and modifications of the basic inventive concept herein described, which may be apparent to those skilled in the art, will still fall within the spirit and scope of the embodiments of the invention as defined in the appended claims and their equivalents.