KR101841143B1 - Method and device for scheduling flow of packet for reducing delay time due to retransmit of packet - Google Patents

Abstract

According to the present invention there is provided a method for scheduling a packet flow for shortening the delay due to retransmission of a packet, the method comprising the steps of: (a) receiving a query from an external object; (b) prioritizing for a response to the query ; And (c) transmitting a packet according to the priority order, wherein the step of designating the priority order comprises: generating a packet for the response and transmitting the packet to another server; when the target packet is a retransmission packet, A higher priority is assigned to the retransmission packet than a packet.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a packet scheduling method and apparatus for shortening a delay due to retransmission of a packet,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for packet flow scheduling for shortening a delay due to retransmission of a packet, and more particularly, to a method and apparatus for reducing a delay due to retransmission of a packet And more particularly, to a method and apparatus for packet flow scheduling.

The data center is composed of a number of computer servers and switches, and is a foundation for a wide variety of applications such as social network services, web search engines, and big data analysis.

The data center receives a query from a user terminal. The query is divided into a plurality of network flows and assigned to a plurality of servers in the data center. Each server that has completed the task notifies the central server that it has processed the query results, which is transmitted over the network. The query completion time is determined by the completion time of the slowest flow among the divided network flows since all distributed work results must be collected before the query is completed.

Here, query completion time is an important factor. If the query completion time is slow, the user is not satisfied with the service quality and the probability of utilizing other services increases, and such user deviation may lead to a decrease in the profit of the data center utilizing service provider.

Conventional methods for minimizing query completion time on a data center network are as follows. First, the data center network congestion control scheme reduces the transmission rate of the transmission server in proportion to the network congestion. Data center network load balancing is a technique that distributes network traffic evenly throughout the network, rather than driving it to a specific path. All of these techniques are based on reducing the probability of occurrence of packet loss in a flow. This is because when the packet loss of a flow occurs, the flow completion time is slowed down due to packet retransmission, so that the query completion time determined by the completion time of the slowest flow also becomes slow.

 However, the above conventional methods have a problem that the query completion time can not be minimized in the case of loss of flow that can not be avoided through software technology such as failure of network equipment. In addition, since conventional methods require ECN (Explicit Congestion Notification) and a large number of priority queues, it can be applied only to expensive switches. Therefore, it is applied to data centers such as universities and small and medium enterprises where the equipment replacement cost is limited, it's difficult. In addition, since large-scale data centers use data center resource sharing among a large number of operators, the number of priority queues is utilized because many of them use reservation based on the amount of money when the priority queue is utilized. it's difficult.

In this regard, Patent No. 10-1350755 (Attorney Dates: 2014.01.10) discloses a cost-based scheduling method and system for multiple workflows in cloud computing.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and apparatus for scheduling a flow that minimizes the delay time of a flow due to packet retransmission.

Accordingly, it is an object of the present invention to provide a service response speed improvement by minimizing a query completion time.

It is another object of the present invention to make it possible to use a flow delay time minimization technique even in a low-cost switch equipment.

According to an embodiment of the present invention, a method for scheduling a packet flow for shortening a delay due to retransmission of a packet, the method comprising the steps of: (a) receiving a query from an external object; (b) Assigning a priority to the response; And (c) transmitting a packet according to the priority order, wherein the step of designating the priority order comprises: generating a packet for the response and transmitting the packet to another server; when the target packet is a retransmission packet, A higher priority is assigned to the retransmission packet than a packet.

According to another embodiment of the present invention, there is provided an apparatus for scheduling a packet flow for shortening a delay caused by retransmission of a packet, the apparatus comprising: a memory for storing a program for performing a flow scheduling method of a packet for shortening a delay due to retransmission of a packet; And a processor for executing the program, wherein the processor, in response to execution of the program, receives a query from an external object, prioritizes for a response to the query, In the process of designating the priority, a packet for the response is generated and transmitted to another server. If the target packet is a retransmission packet, a higher priority is assigned to the retransmission packet than another packet.

The present invention minimizes a delay time of a flow caused by retransmission of a lost packet, thereby shortening a service response speed and providing a more comfortable and quick service to a user. Operators can also generate more revenue from users based on the rapid service effectiveness of these data centers. Further, since the present invention does not require ECN (Explicit Congestion Notification) and requires a small number of priority queues, it can be applied to a data center composed of low-cost switches, thus saving the cost of constructing and maintaining a data center.

1 is a schematic diagram of a system according to an embodiment of the present invention.
2 is a block diagram of a configuration of a server according to an embodiment of the present invention.
3 is a block diagram of the configuration of the transmitter of FIG.
FIG. 4 is a conceptual diagram for explaining the operation of the transmitter and the switch of FIG. 2;
5 to 7 are graphs of experimental results for comparing the performance of an embodiment of the present invention with the performance of the prior art.
8 is a flowchart illustrating a flow scheduling method of a packet for shortening a delay due to retransmission of a packet according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, when a part is referred to as being "connected" to another part, it includes not only "directly connected" but also "electrically connected" with another part in between . Also, when an element is referred to as "comprising ", it means that it can include other elements as well, without departing from the other elements unless specifically stated otherwise.

In this specification, the term " part " includes a unit realized by hardware, a unit realized by software, and a unit realized by using both. Further, one unit may be implemented using two or more hardware, or two or more units may be implemented by one hardware. On the other hand, 'to' is not limited to software or hardware, 'to' may be configured to be an addressable storage medium, and may be configured to play one or more processors. Thus, by way of example, 'parts' may refer to components such as software components, object-oriented software components, class components and task components, and processes, functions, , Subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. The functions provided in the components and components may be further combined with a smaller number of components and components or further components and components. In addition, the components and components may be implemented to play back one or more CPUs in a device or a secure multimedia card.

The "user terminal" mentioned below may be implemented as a computer or a portable terminal capable of accessing a server or other terminal through a network. Here, the computer includes, for example, a notebook computer, a desktop computer, a laptop computer, and the like, each of which is equipped with a web browser (WEB Browser), and the portable terminal may be a wireless communication device , International Mobile Telecommunication (IMT) -2000, Code Division Multiple Access (CDMA) -2000, W-CDMA (W-CDMA), Wireless Broadband Internet (WIBRO), Long Term Evolution A handheld-based wireless communication device such as a cellular phone, a tablet PC, and the like. The term "network" may also be used in a wired network such as a local area network (LAN), a wide area network (WAN) or a value added network (VAN) And may be implemented in all kinds of wireless networks, such as communication networks.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

Referring to Figure 1, the system according to one embodiment of the present invention may be a data center 10.

The data center 10 includes a plurality of servers 100 hierarchically connected via a network.

Specifically, it may be constituted by a central server 100a for receiving a query from a user terminal and a plurality of lower servers 100b and 100c for distributing the work of the central server 100.

Many services (for example, portal search service, SNS service) utilize the data center 10 due to an increase in traffic due to an increase in the number of connected users of each online service, an increase in data amount to be processed, and the like.

For example, when a query including a search term for a specific topic is transmitted from a user terminal and received by the central server 100a, the central server 100a distributes the query through a plurality of the subordinate servers 100b and 100c . That is, a packet is transmitted to each of the lower servers 100b to search for a response value corresponding to the query.

At this time, a flow is defined for each path between the lowest server 100c and the central server 100a. After the request packet is transmitted in accordance with the flow in the central server 100a, a response packet including the response value is transmitted to the lowest server 100c To the central server 100a, thereby completing the flow. That is, a flow refers to a set of all packets transmitted from a specific destination to a specific destination, and is information indicating a continuous flow of packets, and may be composed of one or more packets. At this time, the time required from the transmission of the first packet to the reception of the last packet can be referred to as a flow completion time. In the data center 10, a packet is transmitted to the lower servers 100b and 100c for each flow, and a response value to the query is transmitted to the user terminal only when all the responses are received. Here, the response value and the flow are transmitted to the central server 100a by the lowest server 100c. If the response value of any one of the flows is not received even though the response value generated in the various flows is received, The query is not terminated. That is, even if a delay occurs in only one of the flows, a delay occurs in the query.

On the other hand, the delay of the flow can greatly affect the delay of the query if a loss occurs in the transmitted packet and a situation that retransmission occurs occurs.

Accordingly, an embodiment of the present invention shortens the total delay time through scheduling for a retransmission packet.

Hereinafter, the present invention will be described in detail with reference to FIG. 2 through FIG.

The server 100 according to an exemplary embodiment of the present invention may be a central server 100a of the data center 10, but since an embodiment of the present invention is not applicable to the central server 100a , And may be applied to all the servers 100.

The server 100 according to an embodiment of the present invention includes a processor that executes a program stored in a program (or an application) that performs a flow scheduling method of a packet to shorten a delay due to retransmission of a packet, . Here, the processor can perform various functions according to the execution of programs stored in the memory, and the detailed components included in the processor can be represented by the receiving unit 110, the transmitting unit 120, and the switch unit 130 according to each function .

The receiving unit 110 may receive a query from an external object. For example, a query may be received from a user terminal. At this time, the query may include various information. For example, it may include a search term for a specific issue, or may include request information to search for a friend on the SNS. Alternatively, the receiving unit 110 may receive a packet requesting a specific response value from an external server.

In order to respond to the query, the transmitter 120 generates a packet and transmits it to another server (or a lower server). When the target packet is a retransmission packet, the transmitter 120 designates a higher priority for the retransmission packet than other packets.

The transmission unit 120 includes a flow size determination unit 121 and a priority determination unit 122. [

The flow size determination unit 121 determines whether a packet to be transmitted is a retransmission packet. At this time, it is possible to determine whether the packet is a retransmission packet through the retransmission timer or the Fast Retransmit technique provided by TCP NewReno. When a retransmission timer is used and an object acknowledgment message is not received from the lower server 100b or 100c within a predetermined time after the target packet is transmitted to the lower server 100b or 100c, And judges the packet as a retransmitted packet.

Next, the packet size determination unit 121 compares the flow size of the target packet with a predetermined threshold value when the target packet is a retransmission packet. At this time, the size of the flow of the target packet can be determined through the size of the accumulated data of the acknowledgment message for the flow of the target packet. The acknowledgment message is an acknowledgment signal transmitted from the server 100 that has received the packet to the server 100 that has transmitted the packet. The central server 100a transmits an acknowledgment message from the past to the present every time an acknowledgment message is generated. And the size of the data of the recording medium.

The priority specification unit 122 designates a priority value for a target packet according to the comparison result between the retransmission packet and the flow size of the target packet and the threshold value. Referring to FIG. 4, a first priority value is designated for a target packet having a size of cumulative data of an acknowledgment message less than a threshold value among target packets determined to be a retransmission packet. The first priority value may be zero. On the other hand, a second priority value is designated for the target packets whose accumulated data size exceeds the threshold value. The second priority value may be one. Generally, since the cumulative data size of a general packet acknowledgment message is less than a certain size, 1 is specified for the target packets exceeding the threshold value. Also, even when the target packet is not a retransmission packet, a second priority value can be designated as a general packet.

At this time, the first and second priority values may be recorded in the Differentiated Service Code Point (DSCP) field of the IP header of the target packet.

The switch unit 130 sequentially transmits the packets according to the designated priority order. The switch unit 130 may include an input port, a switch fabric, and an output port with reference to FIG. At this time, the classifier is included in the input port, and the transmission order of the packets can be determined according to the priority value through the classifier. That is, packets having a priority value of 0 and 1 are sorted separately into priority queues, and packets having a priority value of 0 are transmitted first, and packets having a priority value of 1 are transmitted later do. Accordingly, the retransmission packet is transmitted first.

As described above, since the embodiment of the present invention can provide the effect of shortening the delay time even through the switch device having only two priority queues, it is possible to use the low-cost switch device. This can reduce the cost of establishing the data center 10.

5 to 7 are graphs showing query completion times according to changes in network traffic load of the present invention and prior arts by performing simulation through the ns-3 network simulator.

In this experimental example, a three-layer Fat-tree network topology in which 54 servers 100 equipped with a 1 Gbps network interface exists is used, and each switch port has a buffer size of 100 KB. The minimum retransmission timer value (RTOmin) was set to 10 ms. A standard ECMP routing algorithm was used for the routing and load balancing method, and a switch with two priority queues was used as the network switch.

In the graph, TCP refers to TCP NewReno, TFS refers to an embodiment of the present invention using TCP NewReno as a TCP protocol, DCTCP (Data Center TCP) refers to a TCP protocol using ECN, and TFSDCTCP refers to DCTCP Lt; RTI ID = 0.0 > TCP < / RTI > protocol.

In relation to the y-axis value of the graph, FIG. 5 shows the average query end time, FIG. 6 shows the middle value of the query end time, and FIG. 7 shows the query end time corresponding to 99.9 percentile. 5 through 7, it can be seen that one embodiment of the present invention for most traffic loads shows a better query end time than TCP, and another embodiment of the present invention provides a better query end time than DCTCP Can be seen. Finally, it can be seen that other embodiments of the present invention exhibit the best performance.

Hereinafter, with reference to FIG. 8, a flow scheduling method of a packet for shortening a delay due to retransmission of a packet according to an embodiment of the present invention will be described in detail.

Since the following method is performed by the above-described server 100, even if there is an omitted item, the above-mentioned contents are replaced.

First, the server 100 according to an embodiment of the present invention determines whether the target packet is a retransmission packet (S110).

Then, the server 100 determines whether the flow size of the packet is equal to or less than a preset threshold (S120).

If the flow size of the packet is less than or equal to a preset threshold value, a high priority value is recorded in the DSCP field of the IP header of the target packet (S140).

However, if the flow size of the packet exceeds the preset threshold value, a low priority value is written in the DSCP field of the IP header of the target packet (S130). In addition, even when the target packet is not a retransmission packet, a low priority value is recorded in the DSCP field.

The server 100 schedules according to the designated priority and transmits the packet (S150). As a result, among the retransmission packets, packets having a large flow size are transmitted first, and general packets and packets having a small flow size are transmitted in a rearranged order, thereby minimizing the flow delay time due to packet loss.

One embodiment of the present invention may also be embodied in the form of a recording medium including instructions executable by a computer, such as program modules, being executed by a computer. Computer readable media can be any available media that can be accessed by a computer and includes both volatile and nonvolatile media, removable and non-removable media. In addition, the computer-readable medium may include both computer storage media and communication media. Computer storage media includes both volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Communication media typically includes any information delivery media, including computer readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave, or other transport mechanism.

While the methods and systems of the present invention have been described in connection with specific embodiments, some or all of those elements or operations may be implemented using a computer system having a general purpose hardware architecture.

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims rather than the detailed description and all changes or modifications derived from the meaning and scope of the claims and their equivalents are to be construed as being included within the scope of the present invention do.

100: server 110:
120: transmitting unit 130:

Claims (13)

A method for scheduling a packet flow for shortening a delay caused by a retransmission of a packet, which is performed by a server,
(a) receiving a query from an external object;
(b) assigning a priority for a response to the query; And
(c) transmitting a packet according to the priority order,
The step of designating the priority order may include generating a packet for the response and transmitting the packet to another server, wherein when the target packet is a retransmission packet, a higher priority is assigned to the retransmission packet than another packet,
The step (b) may further comprise: (b-1) determining whether the target packet is a retransmission packet; (b-2) comparing the flow size of the target packet with a predetermined threshold value when the target packet is a retransmission packet; And (b-3) designating a priority value for the target packet according to whether the retransmission packet is a packet or a comparison result between a flow size of the target packet and a threshold value,
Wherein the step (b-1) further comprises: a retransmission timer for determining the transmitted target packet as a retransmission packet when the target packet is not received from the another server within a preset time after the target packet is transmitted to the another server; It is determined whether the packet is a retransmission packet through the Fast Retransmit technique provided by TCP NewReno,
Wherein the flow is information on a path through which the target packet travels until it is transmitted from a source to a destination, wherein the delay is shortened due to retransmission of the packet. The method according to claim 1,
The server comprises:
Wherein a plurality of servers belong to a data center in which to perform a distributed search to respond to a query of a user terminal. 3. The method of claim 2,
If the data center comprises a central server receiving the query from a user terminal and a plurality of lower servers for distributing the work of the central server,
Wherein the server performing the scheduling method corresponds to the central server and the other server corresponds to the lower server. The method of claim 3,
The server for performing the scheduling method comprises:
Generating a plurality of packets for searching for a response to the query and transmitting the plurality of packets to a plurality of other servers, waiting until receiving all the responses to the transmitted packets from the plurality of other servers, To the user terminal. The method of claim < RTI ID = 0.0 > 1, < / RTI > delete delete delete The method according to claim 1,
The step (b-2)
Comparing the size of the accumulated data of the acknowledgment message for the flow of the target packet with the threshold value when it is determined that the target packet is a retransmitted packet based on a case in which the acknowledgment message is not received from the other server The method comprising the steps of: receiving a packet; 9. The method of claim 8,
The acknowledgment message is an acknowledgment signal transmitted from the server that received the packet to the server that transmitted the packet.
Wherein the size of the data of the acknowledgment message from the past to the present is cumulatively recorded every time the acknowledgment message is generated, in order to shorten the delay due to the retransmission of the packet. The method according to claim 1,
The step (b-3)
Designates a first priority value for the target packet when the flow size of the target packet is less than or equal to the threshold value,
And designating a second priority value lower than the first priority value for the target packet when the flow size of the target packet exceeds the threshold or the target packet is not a retransmission packet. To reduce the delay due to retransmission of the packet. 11. The method of claim 10,
Wherein the first and second priority values are recorded in a Differentiated Service Code Point (DSCP) field of the IP header of the target packet. The method according to claim 1,
The step (c)
Arranging target packets in different queues according to the priority through a classifier; And
And transmitting from the target packets arranged in the queue having the highest priority a packet delayed by the retransmission of the packet. An apparatus for packet flow scheduling for shortening a delay due to retransmission of packets,
A memory for storing a program for performing a flow scheduling method of a packet for shortening a delay due to retransmission of a packet; And
And a processor for executing the program,
The processor, in response to execution of the program, receives a query from an external object, assigns a priority for a response to the query, transmits a packet according to the priority, and assigns the priority , Generates a packet for the response, and transmits the packet to another server. If the target packet is a retransmission packet, the retransmission packet is assigned a higher priority than another packet,
Wherein the control unit determines whether the target packet is a retransmission packet in the process of designating the priority and compares the flow size of the target packet with a predetermined threshold value when the target packet is a retransmission packet, A priority value for the target packet is specified according to a result of comparison between a flow size of a packet and a threshold value,
When it is determined that the target packet is a retransmission packet, if the target packet is not received from the other server within a preset time after the target packet is transmitted to the other server, the transmitted target packet is determined as a retransmission packet A retransmission timer or a Fast Retransmit technique provided by TCP NewReno to determine whether the packet is a retransmission packet,
Wherein the flow is information related to a path that the target packet travels from the source to the destination until the packet is delayed due to retransmission of the packet.

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