JP4666503B2 - Communication system and relay method - Google Patents

Description

  The present invention relates to a technique for switching a data path in a network having a plurality of data paths, and for example, in a network having a plurality of gateway station apparatuses that relay a ground communication line and a satellite communication line, The present invention relates to a technology for switching data paths in a communication line and a satellite communication line.

For example, in a star-type satellite network in which a mobile terminal and a gateway station device (hereinafter also referred to as a gateway station, a gateway, a GW station, or a GW) are connected by wireless communication (satellite communication), the gateway is geographically separated as a countermeasure against failure. Therefore, the route control of the wired communication network (GW station replacement) is important.
In the GW station replacement, the service base (data transmission source) receives a replacement notice (LSA (Link-State Advertisement) notification) from the operating GW station before the replacement, performs a routing address switch, and switches between the service base and the GW station. This is accomplished by making a route change.

As another technique for switching communication routes in satellite communication, there is a technique disclosed in Patent Document 1.
JP 2004-080466 A

Here, a problem when switching the gateway of the duplex configuration in the above-described star type satellite network will be described.
As described above, the GW station replacement is achieved by the service base receiving the replacement notification (LSA notification) from the operating GW station before the replacement, switching the routing address, and changing the route between the service base and the GW station. At this time, in a route from the service base to the receiving terminal via the GW station / satellite, a time zone (transmission delay fluctuation) in which communication is not transmitted occurs for about 1 second.
Due to the occurrence of discontinuity in the signal from the service base to the terminal before and after the change, content transmission requiring time continuity, for example, image transmission, has a problem that the image freezes.
This problem will be described with reference to FIGS.

In FIG. 1, a plurality of service bases 20 are connected to a gateway station A 10 a and a gateway station B 10 b by a terrestrial wired communication network 30. The service base 20 is a server device that transmits image data, for example.
In FIG. 1, the gateway station A 10a is an operational gateway station, and the gateway station B 10b is a gateway station for backup. Also, each gateway station 10 is assumed to be compatible with, for example, the OSPF (Open Shortest Path First) protocol.
The gateway station A 10a and the gateway station B 10b can perform satellite communication with the satellite 50, respectively, and transmit data from the service base 20 to the satellite 50.
The satellite 50 can broadcast and transmit data from the gateway station A 10 a or the gateway station B 10 b to the plurality of terminals 40.

Each service base 20 transmits data to the gateway station A 10a until a GW station switching reason (for example, a failure such as a line down or a GW station operation stop for maintenance) occurs. When a GW station switching reason occurs, for example, when the line goes down, the gateway station A10a transmits an LSA to each service base 20, and the gateway station A10a and each service base 20 have an LSDB (Link-State Data Base). ) Is reconfigured, the gateway station A10a is switched to the gateway station B10b.
Depending on the capacity (power) of the processor used for the wired line and the number of routes, from the occurrence of the GW station switching event to the completion of the replacement of the gateway by reconstructing the LSDB, the service base passes through the GW station / satellite. In the path to the receiving terminal, a time zone (transmission delay fluctuation) in which communication is not transmitted occurs for about 1 second.

FIG. 11 shows a signal flow from content transmission (packet transmission) requiring time continuity to terminal reception by station switching.
(1) On the service base side, data is generated at the same time interval and transmitted from the router to the gateway station.
(2) The router of the gateway station A (A station) before the station change receives at the same time interval, and is transmitted from the A station to the satellite via the RF line at the same time interval (the frame position is the same) (packet 1). -3).
(3) The terminal receives the packet 1-3 from the satellite at the same time interval A.
(4) Delay variation (switching delay) occurs until the router of the gateway station B (B station) receives it due to the station change.
(5) The first transmission signal timing of the signal on the RF line in the B station is not the timing of the time extension of the transmission signal from the A station, and the transmission delay of the switching time is delayed (packet 4). (6) The terminal does not receive at the same time interval when switching. That is, the packet 4 is received at a time interval B longer than the time interval A.

As described above, discontinuity occurs in the signal from the service base to the terminal before and after the replacement, and thus there is a problem that the image freezes in content transmission that requires time continuity, for example, image transmission.
On the other hand, when dealing with this problem on the terminal side, all terminals are equipped with a buffer (large capacity memory) that compensates for long delay time fluctuations, which increases the cost of the terminal and, as a whole, a high-cost system. There was a problem.

  The present invention has been made, for example, in order to solve the above-described problems, and has as its main object to compensate for transmission delay fluctuations at the time of data path switching.

A communication system according to the present invention includes:
A first relay device that has a first buffer, receives data transmitted from a transmission source at a constant interval, stores the data in the first buffer, and transmits the data to a transmission destination at a constant transmission interval; ,
A second relay device that has a second buffer and backs up the first relay device;
A communication system for switching a data path from the first relay device to the second relay device in a predetermined case,
The first relay device is
When switching the data path from the first relay device to the second relay device, the timing difference between the data write timing to the first buffer and the data read timing from the first buffer. Set the time longer than the switching delay time
The second relay device is
The timing difference between the data write timing to the second buffer and the data read timing from the second buffer is determined from the timing difference between the write timing and the read timing in the first buffer. After switching the data path, the data transmitted from the transmission source at a certain interval is received, the data is written to and read from the second buffer at the timing difference, The read data is transmitted to the transmission destination at the same transmission interval as the transmission interval of the first relay device.

  According to the present invention, since the buffer configuration can absorb the switching delay time required for switching the data path, data can be transmitted at the same transmission interval as the transmission interval before switching even after switching of the relay device. Even when data that requires continuity is transmitted, discontinuity in data transmission does not occur.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a configuration example of a communication system according to the present embodiment.
FIG. 1 illustrates a star-type satellite network that connects a mobile terminal and a gateway station device (hereinafter also referred to as a gateway station, a gateway, a GW station, or a GW) by wireless communication (satellite communication).

In FIG. 1, a plurality of service bases 20 are connected to a gateway station A 10 a and a gateway station B 10 b by a terrestrial wired communication network 30. The service base 20 is a server device that transmits image data, for example. The service base 20 is a transmission source that transmits data to the terminal 40.
The gateway station A 10 a and the gateway station B 10 b can perform satellite communication with the satellite 50, respectively, and transmit data from the service base 20 to the satellite 50.
The gateway station A 10a and the gateway station B 10b are relay apparatuses that relay the ground wired communication network 30 and the satellite line.
In FIG. 1, the gateway station A 10a is an operational gateway station, and the gateway station B 10b is a gateway station for backup. For this reason, the gateway station A10a is an example of a first relay device, and the gateway station B10b is an example of a second relay device.
Also, each gateway station 10 is assumed to be compatible with, for example, the OSPF (Open Shortest Path First) protocol.
The satellite 50 can broadcast and transmit data from the gateway station A 10 a or the gateway station B 10 b to the plurality of terminals 40.
The terminal 40 receives data broadcast from the satellite 50. The terminal 40 is a data transmission destination.

FIG. 2 shows a configuration example of the gateway station 10 specialized for signal flow in the entire communication system shown in FIG. Note that both the gateway station A 10a and the gateway station B 10b in FIG. 1 have the configuration example shown in FIG.
An IP (Internet Protocol) network interface 100 is an interface with a terrestrial network (wired communication network 30).
The satellite packet generation / multiplexing unit 101 multiplexes packets received by the IP network interface 100 and generates data for transmission to the satellite 50.
The data copy buffer 102 supplies a write clock to the circular buffer 103 and writes data from the satellite packet generator / multiplexer 101 to the circular buffer 103.
The circular buffer 103 is a circular buffer of M bits length × N columns. The circular buffer 103 writes data from the data copy buffer 102 in accordance with a write clock from the data copy buffer 102 and stores accumulated data in accordance with a read clock from the modulator 104 to the modulator 104. Read out. The circular buffer of the gateway station A10a is an example of the first buffer, and the circular buffer of the gateway station B10b is an example of the second buffer. Note that the circulation buffer of the gateway station A 10a is represented as a circulation buffer 103a, and the circulation buffer of the gateway station B 10b is represented as a circulation buffer 103b.
The modulator 104 supplies a read clock to the circular buffer 103, generates a frame to be transmitted to the satellite 50 from the data read from the circular buffer 103, and transmits the frame to the satellite 50.
The switching control unit 105 performs switching control when switching the gateway station 10.
In the configuration of FIG. 2, only the circular buffer 103 is different from the conventional gateway station, and the detailed description of the configuration other than the circular buffer 103 is omitted below.

FIG. 3 is a diagram illustrating a hardware configuration example of the gateway station apparatus according to the present embodiment.
In FIG. 3, the gateway station apparatus 10 includes a CPU (Central Processing Unit) 137 that executes a program. The CPU 137 is connected via a bus 138 to a ROM (Read Only Memory) 139, a RAM (Random Access Memory) 140, a communication board 144, a CRT display device 141, a K / B (keyboard) 142, a mouse 143, an FDD (Flexible Disk Drive). 145, a magnetic disk device 146, a CDD (Compact Disc Drive) 186, a printer device 187, and a scanner device 188.
The RAM is an example of a volatile memory. ROM, FDD, CDD, and magnetic disk device are examples of nonvolatile memory. These storage devices constitute a circular buffer 103 and a data copy buffer 102.
The communication board 144 is connected to the terrestrial wired communication network 30 and the satellite line with the satellite 50.
The magnetic disk device 146 stores an operating system (OS) 147, a window system 148, a program group 149, and a file group 150. The program group is executed by the CPU 137, the OS 147, and the window system 148.

The program group 149 stores programs for executing functions described as “˜unit” or “˜device” in the description of the embodiment. The program is read and executed by the CPU.
In addition, an arrow portion of the flowchart described in the description of the embodiment described below mainly indicates input / output of data, and for the input / output of the data, data includes a magnetic disk device, an FD (Flexible Disk), an optical disk, It is recorded on other recording media such as CD (compact disc), MD (mini disc), DVD (Digital Versatile Disk). Alternatively, it is transmitted through a signal line or other transmission medium.

  Moreover, what is described as “˜unit” or “˜device” in the description of the embodiment may be realized by firmware stored in the ROM 139. Alternatively, it may be implemented by software alone, hardware alone, a combination of software and hardware, or a combination of firmware.

Next, details of the circular buffer 103 will be described.
The circulation buffer 103 is different from the conventional system in that (1) the capacity of the circulation buffer (memory) is slightly larger than the transmission delay fluctuation amount of about 1 second accompanying the station change. (2) When content that requires time continuity is started to be transmitted from the gateway station, it is read and transmitted with a time difference of about 1 second from writing to the memory in consideration of the delay time associated with switching. (3) In the replacement, the gateway station after replacement adjusts the timing by shortening the time difference from writing to memory to reading / transmission. (4) The controls (2) and (3) are performed for each content to be transmitted.

FIG. 4 shows an example of setting the address position (pointer) of the buffer (circular buffer 103a) of the gateway station A10a (before replacement) that starts transmitting content from the gateway station.
The circular buffer 103 is controlled so that the next of the memory final pointer is at the head of the memory. The writing direction and the reading direction are the same direction. The speed of writing follows the speed of the terrestrial network, the speed of reading depends on the speed transmitted by the gateway station, and the speeds (write clock frequency and read clock frequency) are independent. However, it is designed to have the same speed on average. That is, the write clock frequency and the read clock frequency are not completely the same, and there is a difference between the write clock frequency and the read clock frequency, and the difference varies. However, on average, it can be considered that the write clock frequency and the read clock frequency match. For this reason, the positional relationship (length) between the write pointer and the read pointer slightly fluctuates in a short time, but here it is not a major event, and the fluctuation can be ignored.

In the case of the write / read direction and the pointer positional relationship in FIG. 4, the read is performed after a long time difference from the write. That is, there is a long delay between the input and output signals of this buffer.
The position of the write pointer indicates the timing of writing data to the circular buffer 103a, and the position of the read pointer (A) indicates the timing of reading from the circular buffer 103a for the same data. That is, in the example of FIG. 4, it is shown that data is read after the time difference (A) has elapsed after the data has been written.

  FIG. 5 shows a pointer setting example of the circular buffer 103b of the gateway station B10b after replacement. In FIG. 5, reading is performed after a short time difference (B) from writing. There is a short delay between the input and output signals of this buffer.

FIG. 6 is a diagram in which FIG. 4 and FIG. 5 are overlapped. The difference between the time difference (A) shown in FIG. 4 and the time difference (B) shown in FIG. Equivalent to about 1 second).
Here, the time difference (B) is a time corresponding to the variation amount of the difference between the data write clock frequency to the circular buffer 103b and the data read clock frequency from the circular buffer 103b. As described above, on average, the write clock frequency and the data read clock frequency are considered to match, but instantaneously, there is a difference between the write clock frequency and the data read clock frequency, and Since this difference fluctuates, in order to absorb the instantaneous clock frequency difference, a time difference (B) larger than the maximum fluctuation width of the clock frequency difference is set.
For this reason, for example, a time (time difference (B)) corresponding to the variation amount of the difference between the data write clock frequency to the circular buffer 103b and the data read clock frequency from the circular buffer 103b and the switching delay time are added. The time difference is defined as a time difference (A).

FIG. 7 shows a signal flow by packet transmission and station switching in the present embodiment as a result of the setting shown in FIGS.
Even when a switching delay occurs in the terrestrial network as a result of the change of stations, packets at substantially equal time intervals A are received in terminal reception.
That is, in the gateway station B 10b, the buffer time B (the time difference (B) in FIG. 5) is obtained by subtracting the switching delay time from the buffer time A (corresponding to the time difference (A) in FIG. 4). )), Buffering transmission is performed, so that the switching delay time can be absorbed. For this reason, even when the data path is switched from the gateway station A10a to the gateway station B10b, the transmission interval transmitted to the satellite 50 is the same as the transmission interval before switching, and as a result, the reception interval at the terminal is also switched before switching. It can be kept the same later.
As described above, even after switching the gateway station, data can be transmitted at the same transmission interval as the transmission interval before the switching, and even when data requiring time continuity is transmitted, data transmission from the gateway station and terminal There will be no discontinuity in data reception.
Note that the gateway station A10a before switching can transmit the data stored in the circular buffer 103a to the satellite 50 during the switching process to the gateway station B10b or even after the switching process is completed (in the example of FIG. 7). Packets 2 and 3 can be transmitted to the satellite 50 during the switching process and even after the switching process is completed).

As described above, according to the present embodiment, in content transmission requiring time continuity, for example, image transmission, even if discontinuity occurs in the signal in the terrestrial network from the service base before and after the replacement to the gateway station, the image is not displayed. There is an advantage that the problem of freezing does not occur.
Also, in a star network, there are a small number of countermeasures (two in the case of duplication) for measures to take countermeasures for the root gateway station, and as a whole, a low-cost system is realized. There is an advantage that you can. Since measures are taken for the gateway station, there is no need for buffer processing at the terminal, and the buffer capacity (memory capacity) of the terminal can be suppressed.

As described above, in the present embodiment, the operation when the data path is switched from the gateway station A10a serving as the first relay device to the gateway station B10b serving as the second relay device has been described.
That is, in the gateway station A10a, the timing difference between the write timing of data to the circular buffer 103a (first buffer) and the read timing of the data from the circular buffer (first buffer) The switching delay time (maximum of about 1 second) that occurs when switching from the (first relay device) to the gateway station B10b (second relay device) is set to a longer time. In the gateway station B10b, the circular buffer 103b (first The timing difference between the data write timing to the second buffer) and the data read timing from the circular buffer 103b (second buffer) is the write timing and read timing in the circular buffer 103a (first buffer). Then, the gateway station B 10b obtains data transmitted from the service base 20 (transmission source) at regular intervals after the data path is switched, by subtracting the switching delay time (up to about 1 second) from the timing difference. The data is written to and read from the circular buffer 103b (second buffer) at the timing difference, and read to the terminal 40 (transmission destination) at the same transmission interval as the transmission interval of the gateway station A10a. Explained to send data.

  Further, in the present embodiment, the gateway station B10b has been transmitted from the service base 20 (transmission source) at regular intervals next to the last data before switching the data path transmitted to the gateway station A10a. The first data after switching the data path is received, and after the last data is transmitted, the first data is transmitted to the terminal 40 (transmission destination) at the same transmission interval as that of the gateway station A10a. explained.

  Further, in the present embodiment, the gateway station A10a performs the data write clock frequency to the circular buffer 103b (second buffer) and the data read clock frequency from the circular buffer 103b (second buffer) in the gateway station B10b. The time obtained by adding the time corresponding to the variation amount of the difference and the switching delay time is the data write timing to the circular buffer 103a (first buffer) and the data from the circular buffer 103a (first buffer). It has been explained that the timing difference from the read timing of.

Embodiment 2. FIG.
In the first embodiment, the capacity of the circular buffer (memory) is slightly larger than the transmission delay fluctuation amount of about 1 second accompanying the station change. However, in this embodiment, the circular buffer (memory) is provided. Is set to a capacity of 2 seconds or more.
In the present embodiment, it is assumed that the gateway station 10 is switched twice.

FIG. 8 shows an example of pointer setting of the circular buffer 103 of the gateway station 10 (before replacement) that starts transmitting content from the gateway station in the present embodiment.
FIG. 9 shows an example of pointer setting of the circular buffer 103 of the gateway station 10 after the first replacement.
FIG. 10 shows an example of pointer setting of the circular buffer 103 of the gateway station 10 after the second replacement.
In the gateway station 10 after the first replacement, the time difference (B) is set to a delay amount that is approximately ½ of the circular buffer from the relationship between the circular buffer capacity and the delay fluctuation amount.
That is, by setting time difference (A) = 2 × switching delay time (about 1 second) + time difference (C), even when the second gateway station is switched, the two switching delay times are absorbed. The data transmission interval from the gateway station and the reception interval at the terminal can be kept constant even after the second switching of the gateway station. The time difference (C) is set based on the same concept as the time difference (B) described in the first embodiment. That is, the time difference (C) is a time during which an instantaneous difference between the write clock frequency and the read clock frequency in the circulation buffer of the gateway station 10 after the second switching can be absorbed.

  In the first embodiment, there is a problem that cannot be dealt with when a station change event occurs again before content transmission requiring time continuity is completed. According to the present embodiment, when the gateway station has a two-station configuration, it can be replaced with the original gateway station that started the content transmission. As described above, the technique according to the present embodiment has an advantage of being able to cope with station switching up to two times.

Embodiment 3 FIG.
In the first embodiment, the capacity of the circular buffer (memory) is equipped with a capacity slightly exceeding the transmission delay fluctuation amount of about 1 second accompanying the station change. In the present embodiment, the method of the second embodiment is generalized so that the capacity of the circular buffer (memory) is N seconds (N times the switching delay time) or more. N is an integer of 2 or more.

  Thereby, according to this Embodiment, there exists a merit which can respond to a station change to N times.

  As described above, in the second and third embodiments, a time longer than N times the switching delay time (N is an integer of 2 or more) is a timing for writing data to the circular buffer and a timing for reading data from the circular buffer. The timing difference was explained.

  In the above embodiment, the star type satellite network in which the mobile terminal and the gateway station are connected by wireless communication has been described as an example. However, the present invention is not limited to this, and there are two or more relay devices. As long as the communication system is such that the data path is switched by switching the above, the method described in the above embodiment can be applied.

The figure which shows the structural example of the communication system which concerns on Embodiment 1-3. The figure which shows the structural example of the gateway station which concerns on Embodiment 1-3. The figure which shows the hardware structural example of the gateway station which concerns on Embodiment 1-3. The figure which shows the example of the address position (pointer) setting of the circular buffer of the gateway station before the switching which concerns on Embodiment 1. FIG. The figure which shows the example of the address position (pointer) setting of the circular buffer of the gateway station after the switching which concerns on Embodiment 1. FIG. The figure which shows the example of the address position (pointer) setting of the circular buffer of the gateway station before the switching which concerns on Embodiment 1, and after switching. The figure which shows the data flow at the time of the switching of the gateway station which concerns on Embodiment 1. FIG. The figure which shows the example of the address position (pointer) setting of the circular buffer of the gateway station before the switching which concerns on Embodiment 2. FIG. The figure which shows the example of the address position (pointer) setting of the circular buffer of the gateway station after the 1st switching based on Embodiment 2. FIG. The figure which shows the example of the address position (pointer) setting of the circular buffer of the gateway station after the 2nd switching based on Embodiment 2. FIG. The figure which shows the data flow at the time of the switching of the conventional gateway station.

Explanation of symbols

  10 gateway stations, 20 service bases, 30 wired communication networks, 40 terminals, 50 satellites, 100 IP network interfaces, 101 satellite packet generation / multiplexing units, 102 data copy buffers, 103 circulation buffers, 104 modulators, 105 switching control units.

Claims (6)

A first relay device that has a first buffer, receives data transmitted from a transmission source at a constant interval, stores the data in the first buffer, and transmits the data to a transmission destination at a constant transmission interval; ,
A second relay device that has a second buffer and backs up the first relay device;
A communication system for switching a data path from the first relay device to the second relay device in a predetermined case,
The first relay device is
When switching the data path from the first relay device to the second relay device, the timing difference between the data write timing to the first buffer and the data read timing from the first buffer. Set the time longer than the switching delay time
The second relay device is
The timing difference between the write timing of data to the second buffer and the read timing of the data from the second buffer is changed from the timing difference between the write timing and the read timing in the first buffer to the switching delay time. After switching the data path, the data transmitted from the transmission source at a certain interval is received, the data is written to and read from the second buffer at the timing difference, A communication system, wherein the read data is transmitted to the transmission destination at the same transmission interval as the transmission interval of the first relay device. The second relay device is
Receiving the first data after switching the data path transmitted from the transmission source at a fixed interval next to the last data before switching the data path transmitted to the first relay device; 2. The communication system according to claim 1, wherein after the last data is transmitted, the first data is transmitted to the transmission destination at the same transmission interval as the transmission interval of the first relay device. In the second relay device,
There is a difference between the data write clock frequency to the second buffer and the data read clock frequency from the second buffer, and the data write clock frequency to the second buffer and the second buffer The difference between the read clock frequency of the data from the buffer of the fluctuating and
The second relay device is
The timing difference between the data write timing to the second buffer and the data read timing from the second buffer is determined by the data write clock frequency to the second buffer and the data from the second buffer. A predetermined time longer than the maximum fluctuation width of the difference from the read clock frequency of
The first relay device is
The timing difference between the timing of reading data from the previous SL first of said first buffer and the write timing of data into the buffer, the said second write timing of data into the second buffer in the relay apparatus 2. The communication system according to claim 1 , wherein the switching delay time is added to a timing difference from a timing of reading data from the second buffer . 3. In the second relay device,
There is a difference between the data write clock frequency to the second buffer and the data read clock frequency from the second buffer, and the data write clock frequency to the second buffer and the second buffer The difference between the read clock frequency of the data from the buffer of the fluctuating and
The first relay device is
The timing difference between the timing of writing data to the first buffer and the timing of reading data from the first buffer, the clock frequency of writing data to the second buffer in the second relay device, and the timing A time obtained by adding N times (N is an integer of 2 or more) the switching delay time to a predetermined time longer than the maximum fluctuation width of the difference from the clock frequency for reading data from the second buffer. The communication system according to claim 1. The first relay device and the second relay device are respectively
The communication system according to claim 1, wherein data is broadcasted to a plurality of communication devices via a satellite line. A first relay process for receiving data transmitted from a transmission source at a constant interval and storing the data in a first buffer and transmitting the data to a transmission destination at a constant transmission interval;
A second relay process that backs up the first relay process using a second buffer;
A relay method for switching from the first relay process to the second relay process in a predetermined case,
The first relay process is
Switching delay caused when the timing difference between the timing of writing data to the first buffer and the timing of reading the data from the first buffer is switched from the first relay processing to the second relay processing Longer than the time,
The second relay process is
The timing difference between the data write timing to the second buffer and the data read timing from the second buffer is determined from the timing difference between the write timing and the read timing in the first buffer. After the switching from the first relay process, the data transmitted from the transmission source at regular intervals is received, and the data writing and data to the second buffer are performed at the timing difference. And reading the read data to the destination at the same transmission interval as the transmission interval of the first relay process.

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