JP2945341B2 - Flow control method and communication network having flow control function - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow control method, for example, a flow control method corresponding to handover (switching of base stations by movement) when an ATM method is applied to a micro-cell type multimedia mobile communication network. And a communication network having a flow control function.

[0002]

2. Description of the Related Art In recent years, research and development on high-speed and multimedia transmission in mobile communication have been actively conducted.
In such a system, in order to keep transmission power low, the radio communication range covered by one radio base station in a conventional automobile or mobile phone is several km (macro cell).
On the other hand, the wireless communication range (micro cell) is about 100 m. When the wireless communication range is small as described above, a mobile station moving at a high speed immediately goes out of the communication range, so that a function for performing handover between wireless base stations is required. Note that handover refers to switching of a radio base station in order to continue a call even if the mobile station moves between radio zones during a call.

Conventionally, there is a PHS as a narrow system with a radio communication range of about 100 m. However, a mobile station moving at a speed of a pedestrian is assumed as a target of a call, and a handover of a mobile station moving at a high speed cannot be performed. . In addition, in the conventional car telephone system, there is an instantaneous interruption of 0.7 to 0.8 seconds when switching channels during a call. This occurs because the data flowing through the transmission line during the handover is simply discarded. Due to this momentary interruption, phenomena such as skipping and deterioration of image quality occur in the case of transmission of audio and moving images, and in the case of computer data transmission, data loss occurs, data retransmission occurs, and traffic congestion occurs. There was a problem. In the case of a microcell, a handover occurs in a shorter cycle than in a macrocell, so this problem becomes more remarkable.

[0004] In a mobile communication system, there are a radio portion between a mobile station and a radio base station, and a wired portion connecting the radio base station, the serving control station, and the gateway control station. As the wired part, a dedicated network is used in the automobile / mobile phone system, and an N-ISDN network is used in the PHS. However, in all cases, the service quality is based on voice, and the video and computer data are integrated and transmitted. Was incapacitated.
Therefore, as a wired network for high-speed multimedia transmission, A
A network based on the TM method is promising.

[0005]

In order to adopt the ATM system in the wired part of the mobile communication network, the ATM cells are reserved during the handover process, and the ATM cells are reserved after the handover process.
There is a need for a flow control method that releases the reserved cells and sends the reserved ATM cells to prevent loss of the ATM cells. In addition, it is necessary to transmit the ATM cells at a transmission rate higher than the steady state (at the time of call setting) from immediately after the release of the hold of the ATM cells until the stay of the ATM cells is resolved. At this time, if the transmission band on the output ATM transmission line exceeds the “free” capacity, congestion occurs. Therefore, in order to avoid congestion inside the ATM node, it is necessary to allocate a transmission band while leaving a certain margin in the transmission band, and to control the transmission speed so as not to exceed the allocated band. In addition, leaving a margin in the transmission band lowers the line efficiency, so it is necessary to stop the transmission band for a limited period as much as possible.

The present invention relates to a mobile communication network adopting an ATM system for a wired portion, wherein an ATM system is used before a handover process.
The present invention relates to a flow control method for starting cell holding, releasing the ATM cell holding after a handover process, and transmitting the held ATM cell to prevent loss of the ATM cell. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the conventional technology and to increase the transmission rate band instantaneously until the reservation of the ATM cell is canceled without changing the conventional hardware configuration as much as possible. An object of the present invention is to provide a flow control method in an ATM node and a communication network having the function, which can be controlled and can increase a line efficiency by limiting a period in which a margin of a transmission speed band is required.

[0007]

In order to achieve the above object, according to the present invention, a buffer terminal device includes an input / output A
The buffer terminal device is connected to the cell switch via the TM transmission path, and can set an input buffer for storing ATM cells for each ATM virtual channel and a transmission rate for each ATM virtual channel. And a cell transmission module for transmitting the ATM cell stored in the step (a).

[0008] At the start of the ATM virtual channel switching process, the cell switch control device selects the AT to be switched.
The M virtual channel is selected, and the cell switch is switched so that the ATM cell is transferred to the buffer terminal device. Then, the buffer terminal stores the ATM cell. At the end of the ATM virtual channel switching process, the cell switch control device selects an output ATM transmission line through which the switched ATM virtual channel passes, and outputs the output ATM transmission line in order to eliminate the accumulation of ATM cells in the buffer terminal device.
A large transmission rate within a permissible range is determined based on the band usage status of the TM transmission path, a band is secured, and the buffer cell terminal transmits the ATM cell at the transmission rate.

After the accumulation of the ATM cells is eliminated, the cell switch control device selects an ATM virtual channel to be switched and directly outputs the ATM virtual channel to the output buffer on the input transmission line in order to directly connect without passing through the buffer terminal device. The AT
An ATM cell of the M virtual channel is set to be stored, whereby the ATM cell is temporarily stored during connection switching.

At the end of the ATM virtual channel switching process, the cell switch control device selects an output ATM transmission path through which the switched ATM virtual channel passes, and
In order to eliminate the stagnation of TM cells, the transmission rate at which the storage of the ATM cells can be canceled is determined from the band usage status of the output ATM transmission line, the bandwidth is secured, and the transmission is set at the transmission rate. Send the cell. After the stagnation is eliminated, the cell switch controller releases the extra band of the output ATM transmission line.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 is a block diagram showing a configuration of a mobile communication network as an example of a communication network to which the present invention is applied. The mobile communication network has a hierarchical structure. The gateway control station 1 is an ATM node (exchange) located at the top of the hierarchy, and the serving control stations 2, 3 located at lower levels.
As well as other communication networks 9 and 10.

The serving control stations 2 and 3 are ATM nodes located below the gateway control station 1 and only one layer is shown in FIG. 2, but may be a plurality of layers. The lowest base station control stations 2 and 3 include radio base stations 4 to
7 is connected. Each of the radio base stations 4 to 7 performs radio connection with the mobile station 8 located in the predetermined service area 11 to 14, respectively. When the mobile station 8 moves to another cell, a handover process as described later is performed. To switch the wireless base station.

FIG. 1 is a block diagram showing an embodiment of the present invention in which a new radio base station 5 and an old radio base station 4 are connected to the same serving control station 2. Mobile station 8
Communicates with the wireless base station 4 via a wireless line.
The wireless base stations 4 and 5 and the located control station 2 are connected to each other via input / output ATM transmission lines. Further, the serving control station 2 is connected to another serving control station or a gateway control station, which is an upstream station, via an input / output ATM transmission line, and a terminating ATM node containing a communication partner terminal of the mobile station 8 is located beyond that. It shall be.

The serving control station 2 includes a cell switch 20, a cell switch control device 21, input control modules 22 and 30, which exist for each input ATM transmission line, an output buffer 24, and output destination tables 23 and 31. The output buffer 24 is a buffer memory for cells arranged in a stage preceding the cell switch 20 on the input ATM transmission line.

The output destination tables 23 and 31 are respectively provided before the cell switch 20 in the input ATM transmission line, and based on the ATM virtual channel identifier at the time of cell input,
This is a table from which a virtual channel identifier (and an ATM virtual channel identifier at the time of output) when the cell passes through the cell switch and output ATM transmission line information can be searched. The cell switch 20, the cell switch control device 21, and the input control modules 22 and 30 are configured to be commonly referred to. (Note that, regarding the virtual channel identifier, both when the cell is input to the switch 20 and when the cell is output,
The conversion of the virtual channel using the table is performed. The input control modules 22 and 30 are each provided with an input ATM.
The transmission path is monitored, and the output destination tables 23 and 31 are searched with the ATM virtual channel identifier of the input cell.
If the TM transmission path information is "pending", the cell is stored in the output buffer 24. If it is not “reserved”, it is rewritten to the virtual channel identifier when passing through the cell switch and passed to the cell switch 20. The information cell for connection control such as call setting is transferred to the cell switch control device 21 via the cell switch 20. Further, when the “hold” is released, the cells stored in the buffer 24 are transmitted to the cell switch 20 at the set transmission rate.

The buffer terminal device 25 includes input buffers 26, 27, 28 and a cell transmission module 29. The input buffers 26, 27, and 28 are buffer memories for cells that perform a FIFO operation, and are secured and released as needed for each virtual channel. Cell transmission module 29
Transmits cells at a transmission rate set for each virtual channel.

FIGS. 3 to 8 are explanatory diagrams showing the flow control operation in the ATM node. FIG. 3 shows a state before the start of handover of the serving control station to be switched. The radio base stations 4 and 5 form an adjacent radio zone, and the mobile station 8 is located in the radio zone of the radio base station 4. Cells are input to the cell switch 20 on a virtual channel (a) on the input transmission line, and cells are output on a virtual channel (b) on the output transmission line J1. Then, when the mobile station 8 moves to the wireless zone of the wireless base station 5, a handover is performed. At this time, the bandwidth management status of the output transmission line J2 to which the new wireless base station 5 is connected is determined by the total bandwidth 100 (% or actual) as shown in the bandwidth management table 40 for the output transmission line J2 in FIG. Are allocated to the normal band 70 and the spare band 30, both of which are unused.

FIG. 4 shows a state in which the serving control station is performing a handover. In response to the instruction from the cell switch control device 21, the buffer terminal device 25 transmits the virtual channel (d)
, And its output is set to a prohibited state (indicated by a cross in the figure). The cell switch control device 21 changes the output destination table 23 so that cells of the virtual channel (a) in the input transmission line are transmitted to the output transmission line J3 as the virtual channel (d).
Therefore, the cell addressed to the mobile station 8 stays in the input buffer 26. It is assumed that the transmission speed of the cell at this time is 10.

FIG. 5 shows a transitional state in which the state of cells remaining in the input buffer 26 after the handover of the serving control station is to be eliminated. The cell switch control device 21 changes the output destination table 31 so that the virtual channel (d) in the input transmission line from the buffer terminal device 25 is transmitted to the output transmission line J2 as the virtual channel (c).

As in the present invention, A is used before the handover process.
Start holding the TM cell, and after the handover process, the ATM
In the flow control method for preventing the loss of the ATM cell by releasing the reserved cell and transmitting the reserved ATM cell, immediately after the released of the reserved ATM cell is released until the released ATM cell is released. During this period, it is necessary to transmit cells at a transmission rate higher than the steady state (at the time of call setup). At this time, if the transmission speed band in the output ATM transmission line exceeds the “vacancy”, congestion occurs. So, A
In order to avoid congestion inside the TM node, it is necessary to allocate a transmission speed band while leaving a certain margin in the transmission speed band, and to control the transmission speed so as not to exceed the range. In addition, since always having a margin in the transmission speed band decreases the line efficiency, it is necessary to stop securing the margin band in a limited period as much as possible.

In this embodiment, the normal band 10 and the margin band 10 are secured from the band management table 40 of the output transmission line J2. The normal band secured in the output transmission line J2 is the same band as the input ATM virtual channel. As described above, the surplus bandwidth is determined based on the current traffic situation such as the unused bandwidth, the capability of the terminal, and the like.

When the band is secured, the cell switch control device 21 instructs the buffer terminal device 25 to transmit cells of the virtual channel (d) at the transmission speed 20.
Therefore, cells flow into the buffer terminal device 25 at the transmission rate of 10, but cells flow out at the transmission rate of 20, so that after a predetermined time, all cells staying in the buffer are sent out, and the staying time is reduced. Will be resolved.

FIG. 6 shows a state in which the staying state of the cells in the input buffer 26 of the buffer terminal device 25 has been canceled after the handover of the serving control station. The cell switch control device 21 controls the virtual channel (a) in the input transmission path.
The output destination table 23 is changed so as to “hold” the cell. Due to this change, the input cell of the corresponding virtual channel is held in the output buffer 24 on the input transmission line. Therefore, after all the cells that have passed through the input buffer 26 of the buffer terminal device 25 have been sent to the output transmission line J2, the input buffer 26 becomes empty.

FIG. 7 shows a state in which a cell in the output buffer 24 on the input transmission line is to be released from the suspended state after all the cells that have passed through the buffer terminal device 25 have been transmitted to the output transmission line J2. The state is shown. The cell switch control device 21 changes the cell of the virtual channel (a) in the input transmission line to the virtual channel (c), and changes the output destination table 23 so that the cell is transmitted to the output transmission line J2.
Further, the output transmission speed of the output buffer 24 is set to 20. With this setting, the input virtual channel (a) is connected to the virtual channel (c) connected to the new radio base station 5, and the cells in the output buffer 24 are transmitted at the transmission rate 20. Of the cell at the time of is eliminated.

FIG. 8 shows a steady state after a handover of the serving control station. The cell switch control device 21 releases the margin band 10 from the band management table 40 of the output transmission line J2.

Although the processing in the ATM node in which switching is performed between the radio base stations accommodated in the own station has been described above, the processing may be performed when the mobile station moves to the service area of the radio base station accommodated in another ATM node. is there. In such a case, the routed handover start notification cell and handover end notification cell are successively passed through the serving control station or the gateway control station to the ATM node accommodating the partner terminal device communicating with the mobile station 8. Transferred. Then, each ATM node determines the station to be switched from the contents of the handover start notification cell, and does nothing when switching is performed higher or lower than the own station. Such processing is performed.

While the embodiment has been disclosed above, the present invention may be modified as follows. In the embodiment, the method of disconnecting the buffer terminal device by switching back is disclosed. However, communication may be performed via the buffer terminal device until the end of the call without switching back. If there is no margin in the output transmission band, only the normal band is secured and communication is performed via the buffer terminal device. Then, when there is a margin in the output transmission band, or when the input cells are interrupted and the stay of the cells in the buffer terminal device is eliminated, the switching back may be executed.

In the embodiment, an example in which a cell is held using a buffer terminal device is disclosed. However, a configuration in which a cell is held at the time of handover in an output buffer 24 associated with an input control module is also conceivable. In this case, it is necessary to increase the capacity of the output buffer, but the control is simplified. The buffer terminal device can accommodate a large number of virtual channels with one device, but a plurality of buffer terminal devices may be provided to increase the capacity or the like.
INDUSTRIAL APPLICABILITY The present invention is not limited to processing at the time of handover in a mobile communication system, and is applicable to processing of switching a virtual channel in order to avoid detour or congestion at the time of a failure in any cell or packet switching system.

[0029]

As described above, according to the present invention, the buffer terminal device is provided, and the cell is reserved by the device. Therefore, the buffer terminal device can be simply used without changing the conventional hardware configuration. There is an effect that it can be implemented only by adding a terminal device for use. In addition, by securing an input buffer for each virtual channel and transmitting cells at the specified transmission rate, it is possible to control an increase in bandwidth for eliminating the hold state in the buffer after handover, and to avoid congestion. is there. Furthermore, only the transient band after the handover requires the normal band and the extra band, and only the normal band is required in the steady state, so that the line efficiency is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a serving control station according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a mobile communication network to which the present invention is applied.

FIG. 3 is an explanatory diagram illustrating a flow control operation in an ATM node.

FIG. 4 is an explanatory diagram illustrating a flow control operation in an ATM node.

FIG. 5 is an explanatory diagram illustrating a flow control operation in the ATM node.

FIG. 6 is an explanatory diagram showing a flow control operation in the ATM node.

FIG. 7 is an explanatory diagram illustrating a flow control operation in the ATM node.

FIG. 8 is an explanatory diagram illustrating a flow control operation in the ATM node.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Gate control station, 2, 3 ... Location control station, 4-7 ... Wireless base station, 8 ... Mobile station, 11-14 ... Service area, 20
... cell switch, 21 ... cell switch control device, 22,
Reference numeral 30: input control module, 23, 31: output destination table, 24: output buffer, 25: buffer terminal device,
26 to 28: input buffer, 29: cell transmission module, 40: bandwidth management table

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) H04L 12/28 H04L 12/56 H04Q 7/22

Claims (7)

(57) [Claims] 1. A communication network for performing communication by transmitting cells via a virtual channel established between nodes, comprising: buffer means for temporarily storing cells; The buffered cells are temporarily stored in the buffer unit, and the virtual channel is switched to another path. Determine a large transmission rate, secure the bandwidth of the output transmission path, send out the stored cells at the transmission rate, and release the extra bandwidth of the output transmission path after the cell stagnation is resolved. Characteristic flow control method. 2. The buffer means is provided in a terminal device accommodated in a cell switch of a node, wherein the terminal device comprises: a buffer unit; and a transmission rate specified by a cell in the buffer unit. 2. The flow according to claim 1, further comprising: a cell transmitting unit for transmitting the input virtual channel to the terminal device via a cell switch when input cells are stored in the buffer unit. Control method. 3. After the cell stays in the buffer means is eliminated, the input cells are temporarily stored in a second buffer means provided between the input transmission line and the cell switch, and the input virtual channel is stored in the cell switch. Is disconnected from the terminal device and directly reconnected to the output virtual channel, and the second cell transmitting means for transmitting cells in the second buffer means uses the band of the output transmission line to eliminate the stagnation of cells. Based on the situation, a transmission rate higher than the input virtual channel is determined, a band of the output transmission path is secured, and the stored cells are transmitted at the transmission rate. 3. The flow control method according to claim 2, wherein an extra band is released. 4. The buffer means is provided in an input control means provided between an input transmission line and a cell switch at a node, wherein the input control means stores the buffer means and a cell in the buffer means. 2. A cell transmission means for transmitting at a specified transmission rate.
3. The flow control method according to 1. 5. The communication network communicates via a virtual channel established between a radio base station in which a mobile station is located and a node to which a communication partner device of the mobile station is connected. A flow control method for a mobile communication network, wherein the flow control according to claim 1 is performed when a virtual channel is switched when a mobile station moves to a wireless zone of another wireless base station. 6. A communication network for performing communication by transmitting cells via virtual channels established between nodes, wherein the nodes include a cell switch, cell switch control means, and a buffer housed in the cell switch. Terminal means for buffering, the buffering means comprises buffer means for temporarily accumulating cells, and cell transmitting means for transmitting cells at a set transmission rate. Via the cell switch, temporarily connect to the buffer terminal means, accumulate cells in the buffer means, connect the output of the buffer terminal means with the output virtual channel after switching, the connection Later, based on the bandwidth usage of the output transmission line, a transmission rate higher than the input virtual channel is determined, and the bandwidth of the output transmission line is determined. Is ensured, the stored cells are transmitted to the output virtual channel at the transmission rate, the stagnation of the cells in the buffer means is eliminated, and after the stagnation of the cells is eliminated,
A communication network having a flow control function, wherein an extra band of an output transmission line is released. 7. A radio base station is provided at the lowest level, and has a hierarchical structure in which a serving control station and a gateway control station are positioned above the base station. Each station functions as a node, and each station is connected by an input / output transmission path. In a mobile communication network, a mobile station communicates via a virtual channel established between a radio base station in which the mobile station is located and a terminal node accommodating a communication partner of the mobile station. A communication network having a flow control function for executing the flow control method according to any one of claims 1 to 5 in a virtual channel switching process that occurs when a mobile station moves to a wireless zone of another wireless base station.