JP2773631B2 - Packet transmission method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a packet transmission system, and more particularly to a CCSDS (Consultive Co.).
mmitee for Space Data Sy
stems) relates to a packet transmission method for transmitting a packet conforming to the international standard.

[0002]

2. Description of the Related Art Conventionally, as a packet transmission method of a space data system, a method of multiplexing and transmitting packets in accordance with the CCSDS international standard has been known. In this conventional system, as shown in FIG. 4, variable-length packet data 41 and 42 to be transmitted from a user are multiplexed to generate a fixed-length frame 43 arranged in a data field, and this is transmitted from a satellite to the ground. Send to the station (or vice versa).

Here, in FIG. 4, 43a is a header, 43b
Indicates a data field portion where packet data 41 is multiplexed and arranged, and 43c indicates a data field portion where packet data 42 is multiplexed and arranged. When all the packet data cannot be multiplexed in the data field of the frame 43, the remaining data portion is multiplexed and arranged in the data field of the frame to be transmitted next. Therefore, the header 43
a contains at least the position information of the first packet multiplexed from the beginning in the data field.

As described above, conventionally, when multiplexing the packet data, the packet data 41 and 42 are packed in the frame 43 and transmitted when the data field becomes full. However, packet data is input irregularly, is input intermittently, and may not be input for a relatively long time. Therefore,
Conventionally, when a predetermined time has elapsed, a frame is transmitted as a timeout even if packet data is not multiplexed to fill the data field.

[0005]

Therefore, in this conventional packet transmission system, a delay time is inevitably generated until a packet is filled up with a data field of a frame or until a timeout occurs. If this time-out period is shortened, the frame will be transmitted with many empty areas in the data field in the frame.
Packet transmission efficiency decreases.

On the other hand, if the time-out period is made longer,
When the average packet residence time is long and the frequency of occurrence of packets is low, a large delay time occurs, which is particularly disadvantageous in a space data system having many packets that are critical to the delay time, such as remote control commands and real-time commands.

[0007] The present invention has been made in view of the above points,
Packets that are prioritized for transmission are immediately transmitted even if packets are not fully multiplexed in the data field.
An object of the present invention is to provide a packet transmission method capable of reducing a delay time of a critical packet without lowering packet transmission efficiency.

[0008]

According to the present invention, there is provided a buffer for storing a packet having an identification flag indicating whether or not the packet is a priority packet in a header portion.
A flag detection unit for detecting an identification flag of a packet sequentially extracted from the buffer, a release timing generation unit for outputting a release timing signal when an identification flag detection signal is input from the flag detection unit, and a fill packet for generating a fill packet A generation unit and a packet from a buffer are multiplexed in a data field, and a fixed-length frame having a header including at least the position information of the first packet in the data field is generated and output, and the release timing generation unit And a multiplexing unit for generating and outputting a frame in which the empty area of the data field is filled with the fill packet when the release timing signal is input.

The release timing generator generates and outputs a release timing signal as a timeout when a predetermined time has elapsed after the reset, and the multiplexing unit resets the release timing generator by transmitting a frame. In this case, a plurality of packets can be multiplexed into a frame and transmitted, which is preferable in terms of packet transmission efficiency.

[0010]

According to the present invention, when a priority packet is transmitted, an identification flag arranged in the priority packet is detected by the flag detection unit, and a release timing signal is output from the release timing generation unit to the multiplexing unit based on the detection output. Therefore, after the multiplexing unit multiplexes the above priority packet in the data field in the frame, immediately fills the empty area of the data field with the fill packet from the fill packet generating unit without waiting for the input of the next packet and fixes it. A long frame can be generated and transmitted.

[0011]

Next, an embodiment of the present invention will be described. FIG. 1 is a block diagram showing an embodiment of a packet transmission system according to the present invention. In FIG. 1, a buffer 1 is a circuit for sequentially storing packets input from a user. The format of this input packet is, as indicated by 10 in FIG.
And a variable-length secondary header 10b, which is control information freely defined by the user, and a variable-length data field 10c, and are variable-length data as a whole. In some cases, the secondary header 10b is not used.

In this embodiment, whether or not to multiplex in a packet is left to the secondary header 10 which is left to the user.
A priority packet / normal packet identification flag (hereinafter, referred to as a priority flag) 11 indicating whether the packet 10 is a priority packet to be transmitted with priority or a normal packet is arranged in, for example, the first bit of b. There is a characteristic in that.

The priority flag check unit 2 in FIG. 1 passes the packet from the buffer 1 as it is and outputs it to the multiplexing unit 6, while checking the presence or absence of the priority flag of the secondary header in the packet and outputting the check result. I do.
Release timing generator 3 is priority flag checker 2
A release timing signal is generated when a priority flag detection signal is input or when a time-out is detected based on a reference time signal from the time generation unit 4. The time generator 4 generates a reference time signal.

The Fill packet generation unit 5 includes a header having a predetermined value (for example, all “1”), a predetermined value (for example, a fixed value of “1” or “0”, or “1”). And fill data of alternating values of "0") are sequentially output to form a fill packet.
The multiplexing unit 6 multiplexes the packets input from the buffer 1 via the priority flag checking unit 2 and generates a fixed-length frame by adding a fixed-length header. When a signal is input, a frame is generated in which a fill packet is filled in an empty area (remaining data field) of the data field. The frame is, for example, 10200 bits.

Next, the operation of the embodiment shown in FIG.
This will be described with reference to FIGS. The packets of the format shown in FIG. 2A separately input from each user are stored in the buffer 1 and then sequentially taken out and input to the priority flag check unit 2 (step 3 in FIG. 3).
0). The priority flag checker 2 checks whether or not the secondary header of the input packet has a priority flag (step 31 in FIG. 3), and supplies the detection result of the priority flag to the release timing generator 3.

When the detection signal of the priority flag is input, the release timing generator 3 determines that the input packet is a priority packet, and supplies a release timing signal to the multiplexer 6 (step 32 in FIG. 3). When the detection signal of the priority flag is not input, the input packet is determined to be a normal packet, and the release timing signal is not output.

Further, the release timing generator 3 is shown in FIG.
The counting of the reference time signal input from the time generating section 4 from the initial value is started by the reset signal input of step 38 described later by a routine different from the main routine of the flowchart shown in FIG. When the specified timeout period is reached,
It is configured to output a release timing signal.

The multiplexing unit 6 multiplexes and packs the packet from the buffer 1 input via the priority flag checking unit 2 into the data field of the frame (step 3 in FIG. 3).
3). At this time, the multiplexing unit 6 monitors whether or not a release timing signal has been input from the release timing generating unit 3 (step 34 in FIG. 3). If not, the multiplexing unit 6 monitors whether or not the packet has been packed to the full frame. (Step 35 in FIG. 3). On the other hand, when the release timing signal is input, a fill packet is packed in an empty area of the frame (step 36 in FIG. 3).

Accordingly, for example, as shown in FIG. 2B, when the packet is input in the order of the normal packet 12 and the priority packet 13 as shown in FIG. After the normal packet 12 is multiplexed in the first part 20b of the data field and the priority packet 13 is multiplexed in the data field part 20c, the multiplexing unit 6 continues to receive the above-mentioned release timing signal. 5 (see FIG. 2)
14) of (B) is multiplexed to fill the remaining data field portion 20d of the frame, and a header 20a is added to the top to generate a frame 20.

Further, as shown in FIG. 2B, only normal packets include 15, 16, 17,. . . , The multiplexing unit 6 converts these into the data field portion 2 immediately after the header 21a as shown in FIG.
1b, 21c, 21d,. . . Multiplex to frame 21
Generate At this time, the multiplexing unit 6 multiplexes a normal packet to fill the data field of the frame 21 or fills the remaining data field portion with a fill packet when a timeout occurs before the data field is full, and the fixed length is fixed. Generate a frame.

In this way, when the multiplexing unit 6 determines at step 35 in FIG. 3 that the frame is full, or after filling the empty area of the frame with the fill packet at step 36, the multiplexing unit 6 generates the generated CCSDS international standard. Is transmitted (step 37), and the release timing generator 3 is reset (step 38). Thereafter, the operation from step 30 is started again. The frames 20 and 21 to be transmitted may be further multiplexed in the data field of a fixed-length frame to form another frame before transmission.

As described above, according to this embodiment, the priority flag is provided in the secondary header of the space priority packet, and when the priority packet is multiplexed with the frame, the empty area is immediately filled with the fill packet and the fixed-length frame is transmitted. Since the packet is transmitted, the priority packet can be transmitted immediately without being stagnated in the multiplexing unit 6, and a relatively long timeout can be taken for the normal packet, so that the packet transmission efficiency is the same as the conventional one. Can be secured to the extent.

The present invention is not limited to the above embodiment. For example, it is not always necessary to provide a timeout, and a packet to be transmitted is transmitted after being multiplexed with a frame conforming to the CCSDS international standard. Of course, the present invention is not limited to this.

[0024]

As described above, according to the present invention,
At the time of sending a priority packet, the multiplexing unit multiplexes the above-mentioned priority packet in the data field in the frame, and immediately fills the fill packet from the fill packet generating unit into an empty area of the data field without waiting for the input of the next packet. Filling to generate and send fixed-length frames allows packets that are critical to the delay time, such as remote control commands and real-time commands, to be sent immediately without stagnating in the multiplexing section. Time can be reduced.

In addition, normal packets other than priority packets can be transmitted by multiplexing a plurality of packets into a frame within a relatively long time-out, so that packet transmission efficiency is prevented from lowering than before. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a diagram illustrating a signal format and the like of each unit in FIG. 1;

FIG. 3 is a flowchart for explaining the operation of FIG. 1;

FIG. 4 is an explanatory diagram of an example of a conventional method.

[Explanation of symbols]

Reference Signs List 1 buffer 2 priority flag check unit 3 release timing generation unit 4 time generation unit 5 fill packet generation unit 6 multiplexing unit 10 packet 10a primary header 10b secondary header 10c data field 11 priority packet / normal packet identification flag (priority flag) 20, 21 flame

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04L 12/56

Claims (3)

(57) [Claims] A buffer for storing a packet having an identification flag indicating whether or not the packet is a priority packet in a header portion; a flag detection unit for detecting the identification flag of the packet sequentially extracted from the buffer; A release timing generation unit that outputs a release timing signal when the identification flag detection signal is input from the flag detection unit; a fill packet generation unit that generates a fill packet; packets from the buffer are multiplexed in a data field; Generating and outputting a fixed-length frame having a header including at least the position information of the first packet of the data field, and, when the release timing signal is input from the release timing generating section, Filled in the empty area of the data field Packet transmission method characterized by having a multiplexing unit for generating and outputting a beam. 2. The release timing generating section generates and outputs a release timing signal as a timeout when a predetermined time has elapsed after resetting, and the multiplexing section resets the release timing generating section by transmitting a frame. 2. The packet transmission method according to claim 1, wherein: 3. The packet includes a primary header including at least a packet length, a sequence number, and an address, and data arranged in a data field.
3. The packet transmission method according to claim 1, wherein the identification flag is arranged in a secondary header multiplexed in the frame following the primary header by a user.