JP2984910B2 - Data flow control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a data flow control method, and more particularly to a data flow control method of a layer 4 (OSI reference model / transport layer) in a node that executes a communication protocol process.

[0002]

2. Description of the Related Art Generally, a layer 4 (OSI reference model / transport layer) such as a TCP protocol widely used in the Internet is based on a data flow control called a window system. In particular, since it is intended for a network environment in which networks and nodes having different performances coexist, control for adjusting and transmitting data flow control parameters based on the assumption that available resources are unknown is performed.

FIG. 8 is a flow chart showing a conventional data flow control processing operation (for example, "TCP / IP").
Network Construction by Vol. " I, section 12.20 and Vol. II section 14.7-section 14.8,
D. Comer, Translated by Murai, Kyoritsu Publishing, etc.). Here, the receiving window size (adwnd) declared by the receiving side
In addition, parameters such as a congestion window size (cwnd) and a slow start threshold (ssthresh) are provided.

There are two different flow control methods.
It has two phases, namely a slow start phase and a congestion avoidance phase. The number of packets that can be transmitted at a certain point in time is min (cwnd, adwnd) (however, min (A, B) indicates that either A or B takes a smaller value), and with the variation of each parameter, It changes during communication.

After the connection is set, data flow control is started. First, ssth is set as a flow control parameter.
The reset is initialized to adwnd and the cwnd is initialized to one data packet (step 80). Subsequently, a slow start phase is entered, one data packet is transmitted, and the reception of an acknowledgment packet is waited (step 81).

If an acknowledgment packet is received within a predetermined time after the packet transmission (step 81: acknowledgment reception), cwnd indicating the transmittable amount is set to the threshold s.
sthresh is determined (step 8
2) If cwnd is smaller than ssthresh (step 82: YES), cwnd is doubled (step 83), and the process returns to step 81 to transmit the next packet. As a result, until the transmittable amount cwnd reaches the threshold value ssthresh, the cwnd increases by twice (1, 2, 4, 8,...) Every time an acknowledgment is received as a slow start phase (FIG. 5B )reference).

On the other hand, in step 82, cwnd is s
sthresh is reached (step 82: N
O), enter the congestion avoidance phase and set cwnd to 1 / cwn
It increases by d (step 84), and returns to step 81 to transmit the next packet. As a result, cwnd becomes ss
When thresh is reached, cwnd increases by 1 / cwnd each time an acknowledgment is received as a congestion avoidance phase, and the immediately preceding packet transmission amount c
When all acknowledgments for wnd are received, cwn
d increases by one data packet, and increases moderately compared to the initial slow start phase.

In step 81, if an acknowledgment is not received within a predetermined time after the packet transmission (step 81: acknowledgment timeout), it is considered that packet loss has occurred due to congestion and ssthre
sh is set to min (cwnd, adwnd) / 2 and cwnd is set to "1" (step 8).
5) Returning to step 81, the next packet is transmitted.

[0009]

Therefore, in such a conventional data flow control method, congestion is likely to occur in a non-uniform network environment in which networks and nodes having different performances coexist, and the data transmission time is limited by the line transmission time. It operates efficiently on a line much larger than the propagation delay time, for example, a medium-to-low-speed line such as 64 Kbps. However, when the magnitude relationship between the data transmission time and the propagation delay time is reversed, an acknowledgment wait after data transmission is performed. The state becomes relatively large, and there is a problem that the line utilization rate decreases and the line capacity cannot be used effectively.

FIG. 9 is an explanatory diagram showing a data transfer required time, where tha is a packet processing time required for packet processing on the transmission side and the reception side, and tp is a data packet transmission time required for transmitting a data packet from the transmission side. ,
tak is an acknowledgment packet transmission time required to transmit an acknowledgment packet from the receiving side, and d is a propagation delay time required to transfer various packets between transmission and reception. Generally, in a medium-to-low speed line such as 64 Kbps, the packet transfer speed is low, so that the data transmission time, that is, the sum of the data packet transmission time and the acknowledgment packet transmission time (tp + tak) is compared with the propagation delay time (d × 2). ) Is larger.

However, in a relatively uniform network environment composed of an ultra-high-speed line ranging from 150 Mbps to several Gbps and an ultra-high-performance processing device, it is important that the resource capacity (the line speed and the memory capacity of the buffer) is rarely insufficient. Since it can be considered, congestion is relatively unlikely to occur, and the magnitude relationship between the data transmission time (tp + tak) and the propagation delay time (d × 2) is reversed. For example, when an 8 Kbyte packet is transferred between Tokyo and Osaka (about 600 km), the propagation delay time of the optical fiber is 5 μsec / Km, so the round trip propagation delay time (d × 2) is 6 msec, but the data transmission time is (Tp + tak) is 27 μs for a 2.4 Gbps line
c, or 1 sec for a 64 Kbps line, and the magnitude relationship between the propagation delay time and the data transmission time differs between the medium and low speed lines and the ultra high speed line.

In the conventional data flow control method, after the connection setting is completed, the congestion window size cwnd =
Transmission starts from "1", and every time an acknowledgment is received, the transmission amount that can be transmitted next is doubled and the transmission amount is sequentially increased. In a relatively uniform network environment composed of processing devices, as described above, since the propagation delay time occupies a large proportion, the acknowledgment wait state after data transmission, that is, the line idle state becomes relatively large, and the line There has been a problem that the usage rate is greatly reduced.

Similarly, when a packet is lost, the congestion window size is set to cwnd = “1”, and the transmission amount is sequentially increased every time an acknowledgment is received. Even if the buffer load is reduced and a large amount of information can be transferred, the increased line capacity cannot be used effectively due to the reduced load, and it takes time to maximize the line capacity. Cannot be used effectively, and there is a problem that transfer time is required from the viewpoint of the application. An object of the present invention is to solve such a problem, and to provide a data flow control method capable of realizing high throughput by effectively using a line and shortening a transfer required time viewed from an application side. It is an object.

[0014]

In order to achieve the above object, a data flow control method according to the present invention comprises:
A buffer load status indicator indicating the buffer load status of the relay node is provided in the protocol header of the I reference model layer 4 so that the relay node can store its own buffer at the time of packet relay.
If the usage rate does not reach the specified value, the buffer load status
Set the bear display to “0” and the buffer usage rate reaches the specified value
The buffer load status display to "1"
Then, the transmitting end node performs layer 4 protocol processing.
After receiving the connection setting request packet,
Negative buffer for returned connection setup response packet
Check the load status display, and see “0” in the buffer load status display.
If set, the receiver's specified receive window
Buffer the transmission data packet size up to
If “1” is set in the load bear display, send
Data packet volume is increased sequentially from small amount
Things.

Therefore, when "0" is set in the buffer load status indicator of the connection setting response packet returned from the receiving side after the transmission of the connection setting request packet, the transmitting end node determines whether the buffering state of the receiving side is equal to the predetermined value. When the transmission data packet amount is permitted up to the reception window size of “1” and “1” is set, the transmission data packet amount is sequentially increased from a small amount.

The relay node sets the buffer load status display to "0" when the buffer usage rate does not reach the predetermined value at the time of packet relay, and sets the buffer usage rate to the predetermined value when the buffer usage rate has reached the predetermined value. , Set the buffer load status display to “1”, and the transmitting end node transmits one data packet first by layer 4 protocol processing, and then the buffer load status of the acknowledgment packet returned from the receiving side. Check the display, and display "0" in the buffer load status display.
Is set, the amount of transmission data packets is permitted up to a predetermined reception window size on the receiving side, and if "1" is set in the buffer load status display, the transmission data packet amount is reduced from a small amount. It is designed to increase sequentially. Therefore, if “0” is set in the buffer load status indicator of the acknowledgment packet returned from the receiving side in response to one data packet transmitted first, the transmitting end node determines whether the receiving end has a predetermined The transmission data packet amount is allowed up to the reception window size of
When “1” is set, the transmission data packet amount is sequentially increased from a small amount.

[0017]

Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a data transmission system according to a data flow control method according to an embodiment of the present invention. In FIG. 1, reference numerals 1a and 1b denote end nodes for transmitting and receiving desired data via the communication line 3 and the transfer node 2.

In the end nodes 1a and 1b, reference numeral 12 denotes a lower layer processing unit for performing protocol processing of layer 3 and below, and here, layer 1 (OSI reference model / physical layer) for providing electrical consistency with the communication line 3 ), A layer 2 (OSI reference model / data link layer) for assembling / disassembling a frame, and a layer 3 (OSI reference model / network layer) for routing, etc., are subjected to protocol processing.

Reference numeral 11 denotes a buffer used for various data transmission / reception processing, 13 denotes a layer 4 processing unit for performing data transmission / reception processing based on connection release and flow control, etc.
An application processing unit 4 provides various data communication services to the user. In the relay node 2, reference numeral 21 denotes a buffer used for various data relay processing,
2 is the same as the lower layer processing unit 12 described above,
3 is a lower layer processing unit that performs the protocol processing of No. 3.

FIG. 2 is an explanatory diagram showing a header configuration of the layer 4, and compared with the conventional header configuration,
The buffer load state display (Cong) indicating the usage rate of the buffer 21 is additionally provided. This buffer load display is set to Cong = "0" at the time of packet transmission by the layer 4 processing unit 13 of the end node 1a (1b).
When the usage rate of the buffer 21 of the relay node 2 reaches a predetermined value, the lower layer processing unit 22 of the relay node 2
Sets Cong = “1”, otherwise Cong
It is assumed that g is set to “0”.

Next, the processing operation of the data flow control according to the first embodiment of the present invention will be described with reference to FIG. FIG. 3 is a flowchart showing the processing operation of the data flow control according to the first embodiment of the present invention.
A case where data is transmitted from the end node 1a to the end node 1b via the relay node 2 will be described as an example.

Here, in addition to the reception window size (adwnd) declared by the receiving side as the receivable capacity, parameters such as a congestion window size (cwnd) and a slow start threshold (ssthresh) are provided. Further, the number of packets that can be transmitted at a certain point in time is min (cwnd, adwnd) (where min
(A, B) indicates that either A or B takes a smaller value), which changes during communication with the fluctuation of each parameter.

In the end node 1a, a predetermined connection setting request packet is transmitted by the layer 4 processing unit 13 based on the communication request from the application processing unit 14 (step 30), and a connection setting response packet corresponding to the connection setting request packet is transmitted. (Step 31). When the connection setting response packet is not received within a predetermined time after the transmission of the connection setting request packet (step 31: setting response timeout), only when the number of retransmissions is equal to or less than a predetermined limit value (step 32: YES). Returning to step 30, the connection setting request packet is retransmitted, and ends abnormally when the retransmission count exceeds the limit (step 3).
2: NO).

On the other hand, in a normal state, a connection setting response packet is returned from the receiving end node 1b in response to the connection setting request packet received via the relay node 2. In the relay node 2, the buffer 21
Only when the usage rate of the connection setting response packet reaches a predetermined limit value, the lower layer
ong = “1”, otherwise Cong =
Set to “0”.

Therefore, when a connection setting response packet is received within a predetermined time after the transmission of the connection setting request packet, the buffer load status indication Con stored in the layer 4 header of the received packet.
The value of g is checked, and if Cong = “0” (step 31: setting response reception / Cong = 0), the slow start threshold ssthresh = adwnd is initialized and the congestion window size cwnd = sst
hresh is initialized (step 33). This allows min (cwnd, adwn) to be transmitted from the start of data transmission.
Continuous transmission of a large number of packets determined by d) is permitted.

On the other hand, if the received connection setting response packet is Cong = “1” in step 31 (step 31: setting response reception / Cong = 1),
Initially, ssthresh = adwnd and cwnd = “1” (step 3
4). As a result, the operation enters the same slow start phase as described above (see FIG. 8).

Thus, ssthresh and c
After the initial setting of wnd, min (cwnd, adwnd) packets are transmitted based on these parameters, and the reception of an acknowledgment for the packets is waited (step 3).
5). Here, when the acknowledgment is received within a predetermined time after the packet transmission, the Cong stored in the layer 4 header of the received packet is checked in the same manner as described above (step 31).

If Cong = "1" (step 3
5: acknowledgment response / Cong = 1), it is determined whether or not cwnd indicating the transmittable amount is smaller than threshold ssthresh (step 36), and cwnd is ssthresh.
If smaller (step 36: YES), cwn
d is incremented by 1 (step 37Y), and the process returns to step 35 to transmit the next packet. Thereby, the transmittable amount cw
Until nd reaches the threshold value ssthresh, every time an acknowledgment is received as a slow start phase, cwn
d is increased by 1 (1, 2, 3, 4...).

On the other hand, in step 36, cwnd becomes s.
sthresh is reached (step 36: N
O), enter the congestion avoidance phase and set cwnd to 1 / cwn
It increases by d (step 37N), and returns to step 35 to transmit the next packet. Thereby, cwnd becomes s
When sthresh is reached, every time an acknowledgment is received as the congestion avoidance phase, cwnd is 1 / cwnd
When all acknowledgments to the previous packet transmission amount cwnd are received, cw
nd increases by one data packet, and increases moderately compared to the slow start phase.

In step 35, the acknowledgment received within a predetermined time after the packet transmission is changed to Cong =
If it is "0" (Step 35: Receive acknowledgment / Co
ng = 0), set cwnd = adwnd (step 38), and return to step 35 to transmit the next packet. Thereby, continuous transmission of a large number of packets equal to the reception window size is permitted from the next data transmission.

In step 35, if no acknowledgment is received within a predetermined time after the packet transmission (step 35: acknowledgment timeout), it is considered that packet loss has occurred due to congestion, and ssthre
sh is set to min (cwnd, adwnd) / 2, and cwnd is set to “1” (step 3).
9) Return to step 35 and transmit the next packet.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 4 is a flowchart showing a processing operation of data flow control according to the second embodiment of the present invention.
A case where data communication is always performed, that is, a case of a PVC (permanent virtual channel call) connection that does not require a connection setup and release procedure will be described as an example.

First, layer 4 of originating end node 1a
The processing unit 13 controls the slow start threshold ssthres
h = adwnd and the congestion window size cwnd = "1" (step 4)
0). Subsequently, in response to a data transmission request from the application processing unit 14, the lower layer processing unit 12 is requested to transmit one data packet, and the receiving end node 1b
It waits for the receipt of an acknowledgment (step 41).

If an acknowledgment packet is received within a predetermined time after the transmission of the data packet, the buffer load status indicator Con of the layer 4 header of the acknowledgment packet is received.
g is checked, and if Cong = "0" (step 41: acknowledgment response / Cong = 0), cwnd = s
sthresh. As a result, continuous transmission of a large number of packets determined by min (cwnd, adwnd) is permitted from the next data transmission, and the process shifts to the packet transmission processing described above (step 35 in FIG. 3).

On the other hand, if it is determined in step 41 that the received acknowledgment packet is Cong = “1” (step 41: acknowledgment reception / Cong = 1), the above-described operation is performed (see FIG. 3).
Steps 36, 37Y, and 37N), the operation starts in the same slow start phase.
cwnd is incremented by one each time an acknowledgment response of ong = “1” is received.

In step 41, if the acknowledgment packet has not been received within a predetermined time after the transmission of the data packet (step 41: acknowledgment timeout), the cwnd = "1" is maintained as described above (FIG. 3). The process proceeds to the packet transmission process of step 35). The subsequent processing is the same as that described above (steps 35 to 39 in FIG. 3).
Here, it is omitted.

As described above, the buffer load status indication for indicating the load status of the buffer 21 of the relay node 2 is provided in the protocol header of the layer 4 and the buffer load status is displayed at the relay node 2 according to the load status of the buffer 21. In addition to setting the display, the transmission end node 1a confirms the buffer load state display, and the buffer 21 of the relay node 2
The transmission data packet amount is determined according to the load state of the network, so even when the magnitude relationship between the data transmission time and the propagation delay time is reversed, high throughput can be realized by effectively using the line, and application The required transfer time as viewed from the side can be reduced.

FIG. 5 is an explanatory diagram showing a change in the amount of transmission data packets. FIG. 5A shows a case where the amount of transmission data packets increases at one time in response to the reception of an acknowledgment of Cong = "0" (step 38). , (B) shows the case where the number of transmission packets is increased one by one in response to the reception of the acknowledgment with Cong = “1” (Step 37Y: equivalent to the conventional slow start phase). Thereby, it is understood that when the load state of the buffer 21 of the relay node 2 is small, the transmittable amount cwnd increases at a time according to Cong = 0.

As shown in FIG. 6, according to the present invention, the acknowledgment packet corresponding to the first transmitted data packet is Cong
= “0”, the next transmittable amount cwnd is set to the receiving-side receivable amount adwnd, so that the line capacity can be used effectively thereafter, whereas the conventional slow start phase operation Then, transmittable amount cwnd
Gradually increases, and a transmission pause state is entered on the way, so that the line capacity cannot be used effectively.

Therefore, when transferring a predetermined data amount Df, the time Tfo is required in the present invention, while the time Tfo is required in the conventional method. Further, as an example, the line speed is 2.4 Gbps, one relay node,
Assuming that the transfer data amount is 10 MB, the packet length is 8 KB, and the packet processing time in the node is approximately equal to one data packet transmission time, the line utilization rate Rf and the required transfer time Tf are shown in FIG.
It changes as shown in (a) and (b).

This is because the ratio of the transmission delay time increases from the data transmission time as the communication distance L increases.
According to the conventional method, an acknowledgment wait state after data transmission,
In other words, the line availability state becomes relatively large, and the line utilization rate Rf and the required transfer time Tf are significantly deteriorated. On the other hand, in the present invention, since the acknowledgment wait state after data transmission is relatively small, the communication distance Even if L increases, deterioration of the line utilization rate Rf and the required transfer time Tf is suppressed. Therefore, for example, between Tokyo and Osaka (communication distance L = 600
Km), it can be seen that according to the present invention, the line utilization rate can be improved by a factor of 1.8 and the required transfer time Tf can be reduced to about 比較 as compared with the related art.

[0042]

As described above, according to the present invention, the OSI
A buffer load status indicator indicating the buffer load status of the relay node is provided in the protocol header of the reference model layer 4 so that the relay node can store its own buffer at the time of packet relay.
If the buffer usage does not reach the specified value, the buffer load
Set the status display to "0" and set the buffer usage rate to the specified value.
If it has reached, set the buffer load status indicator to “1”.
After receiving the connection setting request packet in the layer 4 protocol processing of the transmitting end node,
Negative buffer for returned connection setup response packet
If “0” is set in the load status display, the receiving side
Transmitted data packets up to a given receive window size
Amount is permitted, and if “1” is set,
Data packet volume is increased sequentially from a small amount.
It is.

Therefore, the data transmission time and the propagation delay
The line is effective even when the relationship between the size is reversed
High throughput can be realized by using
The required transfer time as viewed from the side can be reduced. Ma
In addition, if a connection needs to be set at the start of communication, it is possible to determine the amount of data packets to be transmitted and to quickly determine the amount of data packets to be transmitted by using the packets used for setting the connection. It becomes possible to transmit an amount of data packets according to the load state.

In the layer 4 protocol processing of the transmitting end node, one data packet is transmitted first, and then the buffer load state display of the acknowledgment packet returned from the receiving side is confirmed. "0"
Is set, the amount of transmission data packets is permitted up to a predetermined reception window size on the receiving side, and if "1" is set in the buffer load status display, the transmission data packet amount is reduced from a small amount. If the connection setting is not necessary at the start of communication, the amount of data packet transmission can be determined quickly in the shortest time from the start of data packet transmission. It is possible to transmit a small amount of data packets.

[Brief description of the drawings]

FIG. 1 is a block diagram of a data transmission system according to a data flow control method according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing a layer 4 protocol header.

FIG. 3 is a flowchart showing a data flow control operation according to the first embodiment of the present invention.

FIG. 4 is a flowchart showing a data flow control operation according to a second embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a change in a transmission data packet amount.

FIG. 6 is an explanatory diagram showing a relationship between an accumulated transfer information amount and an elapsed time.

FIG. 7 is an explanatory diagram showing a relationship between a communication distance, a line utilization rate, and a required transfer time.

FIG. 8 is a flowchart showing a conventional data flow control operation.

FIG. 9 is an explanatory diagram showing a data transfer required time RTT.

[Explanation of symbols]

1a, 1b end node, 11 buffer, 12 lower layer processing unit, 13 layer 4 processing unit, 14 application processing unit, 2 relay node, 21 buffer
22: lower layer processing unit, 3: communication line.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-63-24742 (JP, A) JP-A-8-251226 (JP, A) JP-A-3-283940 (JP, A) JP-A-3-283940 45051 (JP, A) JP-A-2-14645 (JP, A) JP-A-2-16840 (JP, A) JP-A-62-285532 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04L 12/56 H04L 12/28

Claims (2)

(57) [Claims] 1. A data flow control method for performing desired data transmission using a data packet by executing a predetermined communication protocol process between a relay node and an end node connected via a communication line. by providing a buffer load condition display indicating the buffer load status of the relay node to the protocol headers OSI reference model layer 4, the relay node, the self buffer utilization during packet relay
If the value does not reach the specified value, display the buffer load status
Is set to “0” and the buffer usage rate reaches a predetermined value.
The buffer load status display to "1"
Then, the transmitting end node performs the layer 4 protocol processing,
Returned from the receiving side after sending the connection setting request packet
Connection setting response packet buffer load status
Check the buffer status display and see “0” in the buffer load status display.
If set, the receiver's specified receive window
The size of the transmitted data packet up to the
When "1" is set in the load status display,
A data flow control method characterized by sequentially increasing a transmission data packet amount from a small amount . 2. The data flow control method according to claim 1, wherein the relay node has its own buffer usage rate at the time of packet relay.
If the value does not reach the specified value, display the buffer load status
Is set to “0” and the buffer usage rate reaches a predetermined value.
If the buffer load state bear display is set to "1"
Then, the transmitting end node performs the layer 4 protocol processing,
First, transmit one data packet, and then return from the receiving side.
Check the buffer load status indication of the transmitted acknowledgment packet.
And the buffer load status display is set to "0"
If there is a
To allow the amount of transmitted data packets, and
If "1" is set in the status display, the transmission data
A data flow control method characterized by sequentially increasing a packet amount from a small amount .