KR102326764B1 - Method of improving mobility and security of time synchronization protocol using status information of neighbor nodes in wireless ad hoc networks - Google Patents

Abstract

Disclosed is a method for improving mobility and security of a time synchronization protocol in a wireless ad hoc network. A method for improving mobility and security of a time synchronization protocol in a wireless ad hoc network according to an embodiment includes recognizing states of a plurality of neighboring nodes of a node, and based on the states of the plurality of neighboring nodes, the plurality of neighbors Determining a node to be included in calculation of an average value for network time synchronization of the node from among the nodes, and performing network time synchronization of the node by using the node to be included in the calculation of the average value.

Description

Method of improving mobility and security of time synchronization protocol by using status information of neighboring nodes in a wireless ad hoc network

The following embodiments relate to a method of improving mobility and security of a time synchronization protocol by using state information of a neighbor node in a wireless ad hoc network.

The average-based consensus time synchronization protocol has been widely used in wireless sensor networks and ad hoc networks because it has robustness to the single point of failure problem due to the distributed design. In this type of distributed protocol, each node is designed to have the same role as the other nodes in the network. However, due to the distributed design, there may be a problem that a certain node that is not synchronized may have a negative effect on other nodes in the system. In particular, in a wireless ad hoc network, a new node (or a new node) may frequently join, and the time synchronization of the existing network may be broken due to the new node. In addition, a malicious node may propagate incorrect time synchronization information to the network with malicious intent. As such, the average-based consensus protocol has vulnerabilities in a dynamic and hostile environment.

Embodiments recognize the states of a plurality of neighboring nodes, and based on the state information of the plurality of neighboring nodes, a technique for determining a node to be included in an average value calculation for network time synchronization (or a time synchronization value averaging process of each node) can provide

However, the technical problems are not limited to the above-described technical problems, and other technical problems may exist.

A method for improving mobility and security of a time synchronization protocol in a wireless ad hoc network according to an embodiment includes recognizing states of a plurality of neighboring nodes of a node, and based on the states of the plurality of neighboring nodes, the plurality of neighbors Determining a node to be included in calculation of an average value for network time synchronization of the node from among the nodes, and performing network time synchronization of the node by using the node to be included in the calculation of the average value.

The recognizing may include a synchronous node whose time is synchronized with the node, an asynchronous node whose time is not synchronized, and the wireless ad hoc network for the plurality of neighboring nodes based on a relative clock speed between each of the plurality of neighboring nodes and the node. It may include the step of determining as a new node newly joined to the .

The determining includes determining the plurality of neighboring nodes as the new node and the existing node already included in the wireless ad-hoc network, based on whether a message is transmitted/received between each of the plurality of neighboring nodes and the node; and determining the nodes determined as the existing nodes as the synchronous node and the asynchronous node based on a relative clock speed between each of the nodes determined as the existing nodes and the nodes.

The determining of the nodes to be included in the average value calculation includes comparing the number of synchronous nodes with the number of asynchronous nodes and the number of new nodes, and based on a comparison result, at least one of the synchronous node and the asynchronous node. and determining as a node to be included in the average value calculation.

In the step of determining the at least one node as a node to be included in the average value calculation, when the number of synchronous nodes is greater than the number of asynchronous nodes and the number of new nodes, determining only the synchronous node as a node to be included in the average value calculation or, when the number of synchronous nodes is smaller than the number of asynchronous nodes and the number of new nodes, determining the synchronous node and the asynchronous node as nodes to be included in the average value calculation.

1 is a diagram for explaining a wireless ad hoc network environment according to an embodiment.
FIG. 2 is a flowchart illustrating an operation of classifying a state of a neighbor node, and an operation of compensating for a clock speed and an offset, performed in each node in the wireless ad hoc network environment shown in FIG. 1 .
3 is an algorithm for explaining an operation of classifying the state of a neighboring node.
4 is a schematic block diagram of a node according to an embodiment.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, since various changes may be made to the embodiments, the scope of the patent application is not limited or limited by these embodiments. It should be understood that all modifications, equivalents and substitutes for the embodiments are included in the scope of the rights.

The terms used in the examples are used for description purposes only, and should not be construed as limiting. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present specification, terms such as “comprise” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiment belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. does not

In addition, in the description with reference to the accompanying drawings, the same components are given the same reference numerals regardless of the reference numerals, and the overlapping description thereof will be omitted. In the description of the embodiment, if it is determined that a detailed description of a related known technology may unnecessarily obscure the gist of the embodiment, the detailed description thereof will be omitted.

In addition, in describing the components of the embodiment, terms such as first, second, A, B, (a), (b), etc. may be used. These terms are only for distinguishing the components from other components, and the essence, order, or order of the components are not limited by the terms. When it is described that a component is “connected”, “coupled” or “connected” to another component, the component may be directly connected or connected to the other component, but another component is between each component. It will be understood that may also be "connected", "coupled" or "connected".

Components included in one embodiment and components having a common function will be described using the same names in other embodiments. Unless otherwise stated, a description described in one embodiment may be applied to another embodiment, and a detailed description in the overlapping range will be omitted.

1 is a diagram for explaining a wireless ad hoc network environment according to an embodiment.

A wireless ad hoc network environment consists of a plurality of nodes. Each node performs network time synchronization through an average-based consensus protocol based on the state of neighboring nodes. Embodiments are improvements to the average-based consensus protocol based on neighbor node status. Through this, the embodiments isolate the malicious nodes when there is a malicious node trying to break the network time synchronization in a wireless ad hoc network environment, and allow the network time synchronization to be performed quickly, so that the network time caused by frequent changes such as node mobility Overcome motivational difficulties.

Before describing the average-based consensus protocol based on the neighbor node state according to an embodiment, the operation of the average-based consensus protocol will be described.

Each node contains two clocks. One clock may be a hardware clock, and the other clock may be a local (software) clock.

의 hardware clock 값

는 다음과 같이 계산된다.The hardware clock indicates the time counted by an external crystal oscillator, and the increase rate of the hardware clock varies depending on the hardware and the surrounding environment. node

hardware clock value of

is calculated as

[Equation 1]

는 hardware clock의 속도이고

는 hardware clock offset이다. hardware clock은 연속적으로 실행되고 수정할 수 없기 때문에 local clock을 기준으로 시간을 표현하고 동기화하도록 정의한다.here

is the speed of the hardware clock

is the hardware clock offset. Since the hardware clock runs continuously and cannot be modified, it is defined to express and synchronize time with respect to the local clock.

의 local clock 값

는 다음과 같이 계산된다.node

local clock value of

is calculated as

[Equation 2]

는 logical clock 속도이고

는 logical clock offset이다.here

is the logical clock speed

is the logical clock offset.

이 동일해지도록

와

를 추정하는 것이다. 평균 컨센서스 기반의 시간 동기화 프로토콜에서 각 노드는 인접 노드의 상대적인 속도에 따라 logical clock 속도를 조정한다.The goal of the time synchronization protocol is the logical clock value of each node.

to be the same

Wow

is to estimate In the average consensus-based time synchronization protocol, each node adjusts the logical clock speed according to the relative speed of the adjacent node.

와

의 상대적인 속도는 다음과 같은 두 개의 식으로 계산된다.nodes next to each other

Wow

The relative speed of is calculated by the following two equations.

[Equation 3]

In each iteration situation, the new clock speed is calculated as follows.

[Equation 4]

는 노드

의 1-홉 이웃들의 집합이다. clock offset 값도 유사한 방법으로, 아래의 식과 같이 계산할 수 있다.here

is the node

is the set of 1-hop neighbors of . The clock offset value can also be calculated in a similar way, as shown in the following formula.

[Equation 5]

Each node calculates an average value based on the clock information of all neighboring nodes and corrects the current clock value. At this time, when each node recognizes the state of a node adjacent to each node and determines that it is a node that inhibits network time synchronization, it is better not to include a node that is hindered in time synchronization calculation. A neighboring node adjacent to each node may be a node located in the wireless ad hoc network and located in the vicinity of each node.

Embodiments recognize the state of a neighboring node in the time synchronization calculation described in the average-based consensus protocol, and reflect the state of the neighboring node in the time synchronization calculation. For example, each node in the wireless ad hoc network recognizes the states of a plurality of neighboring nodes, and calculates an average value for network time synchronization based on the state information of the plurality of neighboring nodes (or the time synchronization value averaging process of each node) You can decide which nodes to include in . In this case, each node may recognize the state of the neighbor node as a neighbor node synchronized with each node, a neighbor node newly joined to the wireless ad hoc network, or a neighbor node unsynchronized with each node. A synchronized neighbor node may be referred to as a synchronous node, an unsynchronized neighbor node may be referred to as an asynchronous node, and a neighbor node newly joined to the wireless ad hoc network may be referred to as a new node. The new node may be a malicious node.

A node for synchronizing the time of each node among a plurality of neighboring nodes of each node by determining whether the node is a new node, a synchronous node, or an asynchronous node for each neighboring node, and determining whether the time synchronization of the network is in a stable state can be decided

For example, each node may determine the plurality of neighboring nodes as a synchronous node, an asynchronous node, and a new node based on each of the plurality of neighboring nodes and a relative clock speed between each node. Specifically, each node may determine the plurality of neighboring nodes as a new node and an existing node already included in the wireless ad-hoc network based on each of the plurality of neighboring nodes and whether a message is transmitted/received between each node. Each node may determine nodes determined as existing nodes as synchronous nodes and/or asynchronous nodes based on each of the nodes determined as existing nodes and a relative clock speed between each node.

Each node may compare the number of asynchronous nodes and the number of new nodes with the number of synchronous nodes to determine whether the time synchronization of the network is in a stable state. The time synchronization of the network is stable when the number of synchronous nodes is greater than the number of asynchronous nodes and the number of new nodes. can mean The time synchronization of the network is in an unstable state when the number of synchronous nodes is smaller than the number of asynchronous nodes and the number of new nodes. For example, when the number of synchronization nodes is not a majority (super-majority, 2/3 or more), the time synchronization of the network may be said to be in an unstable state.

Each node may decide not to exclude the asynchronous node from the average value calculation when the time synchronization of the network is in a stable state, and may decide not to exclude the asynchronous node from the average value calculation when the time synchronization of the network is in an unstable state. Each node can perform average value calculation and correction including all nodes in an unstable state of time synchronization in which asynchronous nodes occupy a majority. When the time synchronization of the network is in a stable state, each node may determine a synchronization node as a node for synchronizing each node. When the time synchronization of the network is in an unstable state, each node may determine a synchronous node or an asynchronous node as a node for synchronizing each node.

Each node may average the clock values of the determined nodes, and synchronize the time of each node with the time of the determined node based on the averaged clock value. The determined node may be a neighbor node determined to synchronize time of each node among the plurality of neighboring nodes.

Through this, each node improves the average-based consensus time synchronization protocol even in the dynamic and hostile environment of the wireless ad hoc network to improve the mobility and security of the time synchronization protocol, asynchronous nodes, newly joined new nodes and/or malicious It can reduce the negative influence from the node.

The above-described method may be independently performed in a distributed manner for each individual node. For example, even in a network environment in which the majority of nodes are synchronized, the judgment on synchronization/asynchronization may be different from the point of view of each node, and specific asynchronous nodes may be excluded from the point of view of the majority of synchronized nodes. On the other hand, from the point of view of asynchronous nodes, the majority of the remaining synchronized nodes can be regarded as asynchronous nodes.

The time synchronization process involves two sub-processes: sending and receiving messages. In the initial stage, the network is in an asynchronous state because the clock values of all nodes are different. Then, each node initiates the synchronization process by exchanging timing messages. Each node transmits a time synchronization message every time synchronization period T, where T means a synchronization period. That is, each node sends one time synchronization message every time synchronization period T, and receives messages from all neighboring nodes. In this case, some messages may be lost depending on the wireless network environment, and even in the packet loss environment, there is no significant obstacle to achieving network time synchronization. Therefore, it is not necessary for each node to receive all messages.

In the time synchronization process, each node may 1) determine the state of its neighboring node, and 2) calculate correction values for clock speed and offset.

By default, each node starts in a standby state.

When each node receives a time-synchronized message from a neighbor, it immediately joins this neighbor to a newly joined node, synchronized node, or synchronized node before storing timing information in memory. An unsynchronized node is classified into three states.

In addition, whenever the time synchronization period T expires, the corrected clock offset and clock skew are calculated according to Equations 4 and 5, and then the timing message is transmitted as a new clock value. In this case, in the process of calculating the time synchronization correction value, whether or not to include neighboring nodes may be differently applied according to the number of synchronous neighboring nodes and the number of asynchronous neighboring nodes. (If the synchronous node is super-majority, except for the asynchronous node, otherwise, the correction value is calculated based on the time synchronization value of all nodes)

FIG. 2 is a flowchart for explaining a state classification operation of a neighbor node performed at each node in the wireless ad hoc network environment shown in FIG. 1 and an operation of compensating for clock speed and offset, and FIG. It is an algorithm for explaining the operation.

As shown in FIG. 2 , each node may 1) determine the state of a neighboring node (flow chart on the left), and 2) calculate clock speed and offset correction values.

1) State classification of neighboring nodes

Each node has a synchronization round variable called CurSeq to monitor the current synchronization round after power is turned on, and CurSeq increases by 1 for each time synchronization period. Each node may store a timestamp and time synchronization information of the received time synchronization message together with a seq field in memory whenever it receives a time synchronization message from a neighboring node. At this time, the time synchronization message of each node does not include seq information (sequence information, or sequence number), and is used to track the history of the time synchronization message received from each neighbor node. The rules for assigning seq information, that is, seq values, are as follows.

· If the received time-synchronization message is transmitted in advance from a node that does not exist in memory, this node (message) is considered as a new joining node (or new node). Therefore, the value of the seq field in the entry is always set to 0 (line 13 of Algorithm 1).

If the received time-synchronized message is sent from a node that is considered asynchronous (an existing node), the value of the seq field in the input is set to the negative value of CurSeq (lines 5-7 of Algorithm 1). The existing node may be a node already included in the wireless ad hoc network. The detailed criteria for distinguishing a synchronized node from a non-synchronized node will be described again in the next paragraph.

· When the received time-synchronization message is transmitted from a node considered to be a synchronized node, the value of the seq field is set to the curSeq value (lines 8-10 of Algorithm 1).

As in line 4 of Algorithm 1, the criterion of whether to classify a neighbor node as a synchronized node or an asynchronous node can be identified by the relative clock skew (related clock skew). For example, in an average-based time synchronization protocol, each node gradually converges to the same clock rate as each node undergoes a time synchronization process. That is, in the theoretical condition, after the time synchronization between the two nodes is completed, the clock speed of each node is kept constant. At this time, the theoretical condition means that there is no communication delay in the message delivery process. There may be some fluctuations in the clock speed. Therefore, it is impossible to determine whether the time synchronization is based on the condition that the clock rates between the two nodes exactly match. Instead, as shown in Equation 6 below, the threshold is based on the maximum delay time (or maximum transmission delay time) D and the maximum clock speed ρ. value can be determined. At this time, by applying the MAC layer timestamping technique, the message delay time is 5 us or less, and accordingly, the threshold value θ can be set very small.

[Equation 6]

Accordingly, when a node's clock speed is suddenly changed or a time synchronization message is received from a malicious node, the relative clock speed difference is very large. Based on this, as shown in Equation 7 below, it is possible to determine whether the neighboring node is a synchronized node or not.

[Equation 7]

2) Compensation of clock speed and offset

When the time synchronization period T expires, each node starts calculating clock speed and offset correction values according to Equations (4) and (5). In this case, the neighbor nodes included in the time synchronization correction are applied differently depending on the number of synchronized neighbor nodes, and the detailed rules are as follows.

· If the number of synchronized neighbors is equal to or more than double the number of unsynchronized neighbors, each node includes only synchronized neighbors in the calculation. Since consensus-based time synchronization is a kind of Byzantine fault tolerance (BFT) system, it has been proven that the consensus of all nodes can be derived through a two-thirds agreement between nodes in the BFT system. Accordingly, each node can derive synchronization of the entire network through more than half of the synchronized neighboring nodes, and non-synchronized neighboring nodes can adjust clocks according to the remaining synchronized neighboring nodes.

Conversely, if the number of synchronized neighboring nodes is less than twice the number of unsynchronized neighboring nodes, each node counts all neighboring nodes except the newly joined node. That is, each node can be regarded as a state in which most of the neighboring nodes in the network are in a state of synchronization, and the clock speed can be matched by averaging the clock values of all neighboring nodes.

The existence of asynchronous nodes is unavoidable in real network environments, especially in dynamic and hostile environments. 1 to 3 , a node having a clock different from the common clock of the network is regarded as an unsynchronized node, and the unsynchronized node cannot recognize its state. That is, from the point of view of the unsynchronized node, the state of all neighboring nodes neighboring the unsynchronized node can be recognized as the unsynchronized state. Therefore, the desynchronized node must average the clock speed and offset using the time synchronization values of all neighboring nodes in order to calculate the correction values. Conversely, from the point of view of the remaining nodes in the network, it can be recognized that there are a small number of unsynchronized nodes in the network. Accordingly, the synchronized nodes in the network may exclude the unsynchronized nodes from the correction value calculation process for a temporary period (eg, the period until the unsynchronized nodes are synchronized with the clock speed of the synchronized nodes).

As a result, an unsynchronized node cannot cause any negative impact on its neighboring nodes and can quickly synchronize with the network. In addition, even when the network topology is changed due to node mobility in a mobile environment, it is possible to achieve fast time synchronization by excluding incorrect time information of the mobile node from the calculation of the correction value.

4 is a schematic block diagram of a node according to an embodiment.

The node 100 may include a first memory 110 , a second memory 130 , and a processor 150 .

The first memory 110 may store instructions (or programs) executable by the processor 150 . For example, the instructions may include instructions for executing an operation of the processor 150 and/or an operation of each component of the processor 150 .

The second memory 130 may store various information about the node, such as the time synchronization message, CurSeq, timestamp, time synchronization information, and Seq field described with reference to FIGS. 1 to 3 .

The processor 150 may process data stored in the first memory 130 . The processor 130 may execute computer-readable codes (eg, software) stored in the first memory 130 and instructions induced by the processor 150 .

The processor 150 may store, in the second memory 130 , things to be stored during the operation of classifying the state of the neighboring node and the operation of compensating the clock speed and offset described in FIGS. 2 and 3 .

The processor 150 may be a hardware-implemented data processing device having a circuit having a physical structure for executing desired operations. For example, desired operations may include code or instructions included in a program.

For example, a data processing device implemented as hardware includes a microprocessor, a central processing unit, a processor core, a multi-core processor, and a multiprocessor. , an Application-Specific Integrated Circuit (ASIC), and a Field Programmable Gate Array (FPGA).

The processor 150 may control the overall operation of the node 100 . In addition, the processor 135 may perform the network time synchronization method substantially the same through the average-based consensus protocol based on the neighbor node state according to an embodiment in FIGS. 1 to 3 . Accordingly, a detailed description of the processor 150 will be omitted.

The method according to the embodiment may be implemented in the form of program instructions that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, etc. alone or in combination. The program instructions recorded on the medium may be specially designed and configured for the embodiment, or may be known and available to those skilled in the art of computer software. Examples of the computer-readable recording medium include magnetic media such as hard disks, floppy disks and magnetic tapes, optical media such as CD-ROMs and DVDs, and magnetic such as floppy disks. - includes magneto-optical media, and hardware devices specially configured to store and carry out program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include not only machine language codes such as those generated by a compiler, but also high-level language codes that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the embodiments, and vice versa.

Software may comprise a computer program, code, instructions, or a combination of one or more of these, which configures a processing device to operate as desired or is independently or collectively processed You can command the device. The software and/or data may be any kind of machine, component, physical device, virtual equipment, computer storage medium or device, to be interpreted by or to provide instructions or data to the processing device. , or may be permanently or temporarily embody in a transmitted signal wave. The software may be distributed over networked computer systems, and stored or executed in a distributed manner. Software and data may be stored in one or more computer-readable recording media.

As described above, although the embodiments have been described with reference to the limited drawings, those skilled in the art may apply various technical modifications and variations based on the above. For example, the described techniques are performed in a different order than the described method, and/or the described components of the system, structure, apparatus, circuit, etc. are combined or combined in a different form than the described method, or other components Or substituted or substituted by equivalents may achieve an appropriate result.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (5)

A method for improving mobility and security of a time synchronization protocol in a wireless ad hoc network, the method comprising:
recognizing the state of a plurality of neighboring nodes of the node;
determining a node to be included in calculating an average value for network time synchronization of the node from among the plurality of neighboring nodes based on states of the plurality of neighboring nodes; and
performing network time synchronization of the node using a node to be included in the average value calculation
including,
The step of determining the node to be included in the average value calculation comprises:
Among the plurality of neighboring nodes, the number of synchronized nodes whose time is synchronized with the node, the number of asynchronous nodes whose time is not synchronized, and the number of new nodes newly joined to the wireless ad-hoc network are compared and included in the average value calculation Deciding which node to do
including,
The comparison and determining a node to be included in the calculation of the average value comprises:
determining, when the number of synchronous nodes is greater than the number of asynchronous nodes and the number of new nodes, determining only the synchronous node as a node to be included in the average value calculation; and
When the number of synchronous nodes is smaller than the number of asynchronous nodes and the number of new nodes, determining the synchronous node and the asynchronous node as nodes to be included in the average value calculation;
A method comprising
According to claim 1,
The recognizing step is
Based on the relative clock speed between each of the plurality of neighboring nodes and the node, the plurality of neighboring nodes are identified as a synchronous node whose time is synchronized with the node, an asynchronous node whose time is not synchronized, and a new member newly joined to the wireless ad hoc network. Steps to determine with nodes
A method comprising
3. The method of claim 2,
The step of determining as a new node newly joined to the wireless ad hoc network includes:
determining the plurality of neighbor nodes as the new node and the existing node already included in the wireless ad hoc network based on whether a message is transmitted/received between each of the plurality of neighbor nodes; and
Determining the nodes determined as the existing nodes as the synchronous node and the asynchronous node based on a relative clock speed between each of the nodes determined as the existing nodes and the nodes
A method comprising
4. The method of claim 3,
The comparison and determining a node to be included in the calculation of the average value comprises:
comparing the number of synchronous nodes with the number of asynchronous nodes and the number of new nodes; and
determining at least one of the synchronous node and the asynchronous node as a node to be included in the average value calculation based on a comparison result
A method comprising
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