IPv6 topology dynamic detection method and system based on variable dimension prefix space tree

Abstract

The invention relates to the technical field of network measurement, in particular to an IPv6 topology dynamic detection method and system based on a variable-dimension prefix space tree, and the method comprises the steps: constructing the variable-dimension prefix space tree based on a seed address and a prefix list; generating a pre-scanning target prefix and executing pre-scanning; updating weight information of the prefix space tree according to detection feedback; then circularly executing the following steps until the number of the sent data packets exceeds the budget; generating a target prefix based on the prefix space tree; performing topology detection on the target prefix; and updating weight information of the prefix space tree according to detection feedback. The prefix information is introduced to guide hierarchical clustering, the detection target is dynamically generated by adopting heuristic learning, the coverage range is expanded by utilizing a space tree expansion mechanism, and the breadth and efficiency of topology detection are improved.

Description

Technical Field

[0001] The present invention relates to the field of network measurement technology, and in particular to an IPv6 topology dynamic detection method and system based on a variable-dimensional prefix space tree. Background Art

[0002] As IPv6 adoption grows rapidly, it is critical to develop Internet-wide IPv6 topology detection tools. Although researchers have conducted extensive research in the field of topology detection, most of the existing research is limited to IPv4. The huge address space and unique prefix allocation strategy of IPv6 make IPv6 topology detection technology face different challenges from IPv4 topology detection. In the field of IPv6 topology detection, researchers have made many attempts. Yarrp6 proposed by Beverly et al. first provided a topology detection method specifically suitable for IPv6 networks, but its target generation method is static, the detection space is limited and cannot be expanded. 6Search proposed by Liu et al. first used a heuristic learning method, but its detection range can only be limited to a small number of prefixes. Edgy proposed by ERIK C.RYE et al. relies on TraceRoute seed sets for subnet discovery, and its detection range is limited to its inferred edge / 48 subnet. Xmap proposed by Li et al. uses RFC4443 regulations to expose address information, but the detection range is still too large.

[0003] Although the above methods have achieved certain results in IPv6 topology detection, there are still problems such as limited coverage and low detection efficiency. In particular, the detection targets of most methods are strictly limited to seed addresses and BGP prefix lists, and it is impossible to perform a detailed scan of the entire IPv6 topology space. In addition, existing IPv6 topology detection algorithms are usually offline algorithms, which means that they cannot be dynamically adjusted according to real-time detection results. Therefore, there is an urgent need for a method that can achieve large-scale and efficient topology detection of IPv6 networks under a limited budget. Summary of the invention

[0004] The purpose of the present invention is to propose a method and system for dynamic detection of IPv6 topology based on a variable-dimensional prefix space tree, so as to solve the problems of limited coverage and low detection efficiency of IPv6 topology detection in the prior art, and to improve the breadth and efficiency of topology detection.

[0005] To achieve the above purpose, the technical solution adopted is:

[0006] A method for dynamic detection of IPv6 topology based on a variable-dimensional prefix space tree, comprising:

[0007] Based on the seed address and prefix list, a variable-dimensional prefix space tree is constructed;

[0008] Generate pre-scan target prefix and perform pre-scan;

[0009] Update the weight information of the prefix space tree according to the detection feedback;

[0010] The following steps are then executed in a loop until the number of packets sent exceeds the budget;

[0011] Generate a target prefix based on the prefix space tree;

[0012] Perform topology detection on the target prefix;

[0013] Update the weight information of the prefix space tree according to the detection feedback.

[0014] According to the IPv6 topology dynamic detection method based on the variable-dimensional prefix space tree of the present invention, further, constructing the variable-dimensional prefix space tree includes: first creating a root node representing the entire IPv6 address space, and counting all seed addresses and prefix lists into the root node; then starting from the root node, recursively performing node splitting.

[0015] According to the IPv6 topology dynamic detection method based on the variable-dimensional prefix space tree of the present invention, further, the node splitting is recursively performed according to the following rules:

[0016] If a node contains a prefix whose prefix length is greater than the node's own prefix length, it will be split according to the shortest prefix length;

[0017] If the node does not contain a prefix whose prefix length is greater than the prefix length of the node itself, the node is split according to the set default dimension;

[0018] If the split node contains a prefix, and the length of the shortest prefix is ​​greater than the prefix length of the node, the node is marked as a virtual node, and the virtual node does not participate in the hierarchical relationship construction;

[0019] If the prefix of a child node differs from the prefix of the parent node only in the prefix length, the child node is marked as a zero node;

[0020] If the prefix length of a node reaches the specified maximum value, or when it does not have a prefix longer than its own prefix length and the number of seed addresses is less than or equal to 1, the node splitting is stopped.

[0021] According to the IPv6 topology dynamic detection method based on the variable-dimensional prefix space tree of the present invention, further, generating a pre-scan target prefix includes: starting from the root node of the prefix space tree, hierarchical traversal, until encountering a leaf node or a non-virtual node whose prefix length is greater than or equal to the starting prefix length, selecting the following prefixes as pre-scan targets:

[0022] The prefix length is equal to the starting prefix length;

[0023] The prefix length is less than the starting prefix length and does not contain any further subnetting information;

[0024] The prefix length is greater than the starting prefix length, but the prefix length of its parent prefix is ​​less than the starting prefix length;

[0025] Perform a topology probe on the selected pre-scan target prefix.

[0026] According to the IPv6 topology dynamic detection method based on the variable-dimensional prefix space tree of the present invention, further, the weight information of the prefix space tree is updated according to the detection feedback to update the ID advantage level of the node ID, wherein the ID advantage level is used to evaluate a subtree with a certain node as the root node, reflecting the comparative advantage of a certain exploration direction relative to other exploration directions.

[0027] According to the IPv6 topology dynamic detection method based on the variable-dimensional prefix space tree of the present invention, further, generating a target prefix based on the prefix space tree includes: evaluating the node advantage level of the candidate prefixes, the node advantage level being calculated based on the ID advantage level; selecting prefixes with high expected values ​​therefrom, and generating their sub-prefixes as target prefixes; and expanding the selected space tree sub-nodes whose prefix lengths do not reach the maximum prefix length.

[0028] According to the IPv6 topology dynamic detection method based on the variable-dimensional prefix space tree of the present invention, further, extending the selected space tree child node whose prefix length does not reach the maximum prefix length includes:

[0029] Calculate the node advantage level of the selected leaf node and assign it to the ID advantage level of the node ID;

[0030] The prefix is ​​expanded according to the set expansion dimension to generate a sub-prefix as a detection target, and the generated sub-prefix only constructs a prefix hierarchical relationship at the parent-child relationship level.

[0031] According to the IPv6 topology dynamic detection method based on the variable-dimensional prefix space tree of the present invention, further, topology detection of the target prefix includes: splicing the target prefix with ::1 or other fixed IID to generate the target address; constructing a detection data packet for all addresses with a set initial Hop Limit, and performing stateless synchronous detection in a random order; iteratively generating detection targets according to detection feedback until topology detection is completed for all target addresses.

[0032] According to the IPv6 topology dynamic detection method based on the variable-dimensional prefix space tree of the present invention, the method further includes setting an alias prefix avoidance strategy: ① if a previously responded interface is encountered during forward detection of a target address, the forward detection of the target address is terminated immediately; ② a port that the other party cannot open is used as the destination port of the UDP detection module; ③ a seed address that does not contain an alias is used; ④ the maximum prefix length is limited.

[0033] Furthermore, the present invention also proposes an IPv6 topology dynamic detection system based on a variable-dimensional prefix space tree, comprising a prefix generator, a topology detection module and a scanner; the prefix generator is used to construct a variable-dimensional prefix space tree and generate a target prefix; the topology detection module is used to control the topology detection process for the target prefix; the scanner is used to perform detection and return the detection result;

[0034] The prefix generator contains:

[0035] A prefix space tree construction module, used for constructing a variable-dimensional prefix space tree based on a seed address and a prefix list;

[0036] A pre-scan module, used for generating a pre-scan target prefix and performing a pre-scan;

[0037] A weight updating module, used to update the weight information of the prefix space tree according to the detection feedback;

[0038] A prefix generation module, used for generating a target prefix based on a prefix space tree;

[0039] The topology detection module includes:

[0040] A target generation module is used to generate a specific detection target based on the target prefix and detection feedback;

[0041] A detection control module, used for controlling the scanner to perform detection;

[0042] Feedback processing module, used to process detection feedback and pass it to the prefix generator.

[0043] The beneficial effects achieved by adopting the above technical solution are:

[0044] 1. The present invention introduces prefix information to guide hierarchical clustering, constructs a variable-dimensional prefix space tree, and more accurately characterizes the hierarchical relationship between prefixes, providing a good foundation for subsequent target prefix generation.

[0045] 2. The present invention adopts a dynamic target prefix generation method based on heuristic learning, and adjusts the detection direction in real time according to the correlation between the prefix hierarchy relationship and the topological distribution, thereby improving the detection efficiency.

[0046] 3. The present invention utilizes the space tree expansion mechanism to realize the exploration of unknown IPv6 space and expand the coverage of topology detection.

[0047] 4. The present invention adopts a variety of alias prefix avoidance strategies, which effectively reduces invalid detection of alias prefixes and further improves detection efficiency.

[0048] 5. The system of the present invention is modularly designed, and the scanner adopts stateless detection technology, which can realize high-speed and large-scale IPv6 topology detection.

[0049] The present invention can be applied to network security analysis, network performance optimization, network structure research, etc., and provides a powerful tool for the management and research of IPv6 networks. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings of the embodiments of the present invention, wherein the drawings are only used to illustrate some embodiments of the present invention, but not to limit all embodiments of the present invention thereto.

[0051] Figure 1 It is a flow chart of a method for dynamic detection of IPv6 topology based on a variable-dimensional prefix space tree according to an embodiment of the present invention;

[0052] Figure 2 is a schematic diagram of constructing a variable-dimensional prefix space tree according to an embodiment of the present invention;

[0053] Figure 3 Schematic diagram of the process of generating a pre-scan target prefix according to an embodiment of the present invention;

[0054] Figure 4 is a schematic diagram of a prefix space tree expansion mechanism according to an embodiment of the present invention;

[0055] Figure 5 is a schematic diagram of associated nodes of a certain ID in an embodiment of the present invention;

[0056] Figure 6 is a schematic diagram of an association ID of a node in an embodiment of the present invention;

[0057] Figure 7 It is a structural block diagram of an IPv6 topology dynamic detection system based on a variable-dimensional prefix space tree according to an embodiment of the present invention. DETAILED DESCRIPTION

[0058] The following will be combined with the drawings of specific embodiments of the present invention to clearly and completely describe the exemplary scheme of the embodiment of the present invention. Unless otherwise defined, the technical terms or scientific terms used in the present invention should be the common meanings understood by people with ordinary skills in the field.

[0059] like Figure 1 As shown, this embodiment discloses a method for dynamic detection of IPv6 topology based on a variable-dimensional prefix space tree. The core idea of ​​the method is to dynamically generate a target prefix by using the hierarchical relationship between prefixes and detection feedback, and to expand the detection coverage through a space tree expansion mechanism. The method comprises the following steps:

[0060] Step S1: construct a variable-dimensional prefix space tree based on the seed address and the prefix list.

[0061] like Figure 2 As shown, the construction process of the variable-dimensional prefix space tree is as follows:

[0062] (1) Create a root node that represents the entire IPv6 address space and include all seed addresses and prefix lists in the root node.

[0063] (2) Starting from the root node, recursively execute the following node splitting rules:

[0064] ① If a node contains a prefix whose prefix length is greater than the node's own prefix length, it will be split according to the shortest prefix length.

[0065] ② If the node does not contain a prefix whose prefix length is greater than the prefix length of the node itself, the node is split according to the set default dimension (such as 4 bits).

[0066] ③If the split node contains a prefix, and the length of the shortest prefix is ​​greater than the prefix length of the node, the node is marked as a virtual node, and the virtual node does not participate in the hierarchical relationship construction.

[0067] ④ If the prefix of a child node differs from the prefix of its parent node only in prefix length, mark the child node as a zero node.

[0068] ⑤ If the prefix length of the node reaches the specified maximum value (such as 64), or when it does not have a prefix longer than its own prefix length and the number of seed addresses is less than or equal to 1, stop splitting the node.

[0069] Step S2: Generate a pre-scan target prefix and perform a pre-scan.

[0070] like Figure 3 As shown in the figure, the generation process of the pre-scan target prefix is ​​as follows: start the hierarchical traversal from the root node of the prefix space tree until a leaf node or a non-virtual node with a prefix length greater than or equal to the starting prefix length is encountered, and select the following prefixes as pre-scan targets:

[0071] ① The prefix length is equal to the starting prefix length.

[0072] ② The prefix length is less than the starting prefix length and does not contain any further subnet division information.

[0073] ③The prefix length is greater than the starting prefix length, but the prefix length of its parent prefix is ​​less than the starting prefix length.

[0074] Perform a topology probe on the selected pre-scan target prefix.

[0075] Step S3: Update the weight information of the prefix space tree according to the detection feedback.

[0076] The ID advantage level of the node ID is updated according to the detection feedback. The ID advantage level is used to evaluate the subtree with a certain node as the root node, reflecting the comparative advantage of a certain exploration direction over other exploration directions.

[0077] The formula for calculating the ID advantage level is:

[0078]

[0079] Among them, ID represents the unique identifier generated by the prefix tree for the node when the node is created; L t (ID) represents the ID advantage level of a node ID at time t; C t (ID) represents the sum of the number of data packets sent by all nodes associated with this ID at time t; R t (ID) represents the sum of the number of newly discovered unique interfaces of all nodes associated with this ID at time t; N t (ID) represents the set of nodes associated with the ID at time t, such as Figure 5 As shown; α represents the learning rate.

[0080] Step S4: Generate a target prefix based on the prefix space tree.

[0081] (1) Calculate the node advantage level based on the ID advantage level. The node advantage level is used to evaluate a single node and directly reflects the comparative advantage of a prefix compared to other prefixes.

[0082] The calculation formula of node advantage level is:

[0083]

[0084] Among them, A i,t represents the node advantage level of node i at time t; M i,t represents the associated ID set of node i at time t, such as Figure 6 As shown; for each IDj(j∈M i,t ), L j,t represents the ID advantage level of ID j at time t.

[0085] (2) Evaluate the advantages of candidate prefixes.

[0086] (3) Select a prefix with a high expected value and generate its sub-prefix as the target prefix. Expand the selected tree sub-nodes whose prefix length does not reach the maximum prefix length.

[0087] like Figure 4 As shown, the steps of expanding the tree child nodes of the space tree include:

[0088] ① Calculate the node advantage level of the selected leaf node and assign it to the ID advantage level of the node ID.

[0089] ② Expand the prefix according to the set expansion dimension (such as 4 bits) to generate a sub-prefix as the detection target. The generated sub-prefix only constructs a prefix hierarchical relationship at the parent-child relationship level.

[0090] Step S5: Perform topology detection on the target prefix.

[0091] (1) Concatenate the target prefix with ::1 or other fixed IID to generate the target address.

[0092] (2) Construct a detection data packet for all addresses with a set initial Hop Limit (such as 16), and perform stateless synchronous detection in a random order.

[0093] For each destination address:

[0094] If the response address is an address that has been responded to before, the detection of the target address is terminated directly.

[0095] If a response is received from the target (including normal response, port or protocol unreachable, target address unreachable), terminate forward detection (detection in the direction away from the local machine); calculate the distance between the target and the local machine, and set it as the next Hop Limit of backward detection (detection in the direction close to the local machine) of the destination address after subtracting one.

[0096] If it is other types, such as the survival time is 0 or no response, the next Hop Limit of the forward detection and the next Hop Limit of the backward detection are set to the initial Hop Limit plus one and the initial Hop Limit minus one respectively.

[0097] (3) Iteratively generate detection targets based on detection feedback until all target addresses complete topology detection.

[0098] For each destination address:

[0099] If the forward detection has not terminated, the next Hop Limit of the forward detection is the current Hop Limit of the forward detection plus one.

[0100] If the backward detection is not terminated, the next Hop Limit of the backward detection is the current Hop Limit of the backward detection minus one.

[0101] Forward detection stop conditions: receiving a response from the target; not receiving any response for a specified number of consecutive times in forward detection; the Hop Limit of the data packet to be constructed exceeds the maximum Hop Limit; the response address is the address that has been responded to previously.

[0102] Backward detection stop condition: the response address is the address that has been responded to previously; it reaches the local address (Hop Limit = 0).

[0103] Forward detection and backward detection are carried out simultaneously without interfering with each other.

[0104] Step S6: Repeat steps S3 to S5 until the number of data packets sent exceeds the budget.

[0105] This embodiment also includes the following alias prefix avoidance strategy:

[0106] ① If an interface that has previously responded is encountered during forward detection of a target address, the forward detection of the target address will be terminated immediately.

[0107] ② Use a port that the other party cannot open as the destination port of the UDP detection module.

[0108] ③Use a seed address that does not contain an alias.

[0109] ④ Limit the maximum prefix length (such as 64).

[0110] like Figure 7 As shown, this embodiment also discloses an IPv6 topology dynamic detection system based on a variable-dimensional prefix space tree, comprising a prefix generator, a topology detection module and a scanner; the prefix generator is used to construct a variable-dimensional prefix space tree and generate a target prefix; the topology detection module is used to control the topology detection process for the target prefix; the scanner is used to perform detection and return the detection results.

[0111] The prefix generator is the core component of the system and contains:

[0112] The prefix space tree construction module is used to construct a variable-dimensional prefix space tree based on the seed address and the prefix list. The prefix space tree can effectively represent the hierarchical relationship between prefixes and can be expanded during the detection process.

[0113] A pre-scan module, used for generating a pre-scan target prefix and performing a pre-scan;

[0114] A weight updating module, used to update the weight information of the prefix space tree according to the detection feedback;

[0115] The prefix generation module is used to generate a target prefix based on the prefix space tree. The prefix generation module generates the prefix that is most likely to obtain high returns according to the hierarchical relationship between prefixes and detection feedback, and dynamically adjusts the detection direction according to the detection feedback.

[0116] The topology detection module includes:

[0117] The target generation module is used to generate a specific detection target (a combination of IP address and HopLimit) according to the target prefix and detection feedback;

[0118] A detection control module, used for controlling the scanner to perform detection;

[0119] A feedback processing module, used to process the detection feedback and pass it to the prefix generator;

[0120] Scanner: It uses stateless detection technology for high-speed scanning and provides customizable UDP, TCP, and ICMP detection modules.

[0121] Those skilled in the art will appreciate that all or part of the steps in the above method can be completed by instructing related hardware through a program, and the program can be stored in a computer-readable storage medium, such as a read-only memory, a disk or an optical disk. Optionally, all or part of the steps in the above embodiment can also be implemented using one or more integrated circuits, and accordingly, each module / unit in the above embodiment can be implemented in the form of hardware or in the form of software function modules. The present invention is not limited to any specific form of combination of hardware and software.

[0122] Finally, it should be noted that the above-described embodiments are only specific implementations of the present invention, which are used to illustrate the technical solutions of the present invention, rather than to limit them. The protection scope of the present invention is not limited thereto. Although the present invention is described in detail with reference to the above-described embodiments, ordinary technicians in the field should understand that any technician familiar with the technical field can still modify the technical solutions recorded in the above-described embodiments within the technical scope disclosed by the present invention, or can easily think of changes, or make equivalent replacements for some of the technical features therein; and these modifications, changes or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for dynamic detection of IPv6 topology based on a variable-dimensional prefix space tree, characterized in that: Include: Based on the seed address and prefix list, a variable-dimensional prefix space tree is constructed; Generate pre-scan target prefix and perform pre-scan; Update the weight information of the prefix space tree according to the detection feedback; The following steps are then executed in a loop until the number of packets sent exceeds the budget; Generate a target prefix based on the prefix space tree; Perform topology detection on the target prefix; Update the weight information of the prefix space tree according to the detection feedback.

2. The method for dynamic IPv6 topology detection based on a variable-dimensional prefix space tree according to claim 1, characterized in that: Constructing a variable-dimensional prefix space tree includes: firstly creating a root node representing the entire IPv6 address space, and counting all seed addresses and prefix lists into the root node; then starting from the root node, recursively performing node splitting.

3. The method for dynamic IPv6 topology detection based on a variable-dimensional prefix space tree according to claim 2, characterized in that: Recursive node splitting is performed according to the following rules: If a node contains a prefix whose prefix length is greater than the node's own prefix length, it will be split according to the shortest prefix length; If the node does not contain a prefix whose prefix length is greater than the prefix length of the node itself, the node is split according to the set default dimension; If the split node contains a prefix, and the length of the shortest prefix is ​​greater than the prefix length of the node, the node is marked as a virtual node, and the virtual node does not participate in the hierarchical relationship construction; If the prefix of a child node differs from the prefix of the parent node only in the prefix length, the child node is marked as a zero node; If the prefix length of a node reaches the specified maximum value, or when it does not have a prefix longer than its own prefix length and the number of seed addresses is less than or equal to 1, the node splitting is stopped.

4. The method for dynamic IPv6 topology detection based on a variable-dimensional prefix space tree according to claim 1, characterized in that: Generating a pre-scan target prefix includes: starting from the root node of the prefix space tree, hierarchical traversal until a leaf node or a non-virtual node with a prefix length greater than or equal to the starting prefix length is encountered, and selecting the following prefixes as pre-scan targets: The prefix length is equal to the starting prefix length; The prefix length is less than the starting prefix length and does not contain any further subnetting information; The prefix length is greater than the starting prefix length, but the prefix length of its parent prefix is ​​less than the starting prefix length; Perform a topology probe on the selected pre-scan target prefix.

5. The method for dynamic IPv6 topology detection based on a variable-dimensional prefix space tree according to claim 1, characterized in that: The weight information of the prefix space tree is updated according to the detection feedback to update the ID advantage level of the node ID, where the ID advantage level is used to evaluate the subtree with a certain node as the root node, reflecting the comparative advantage of a certain exploration direction over other exploration directions.

6. The method for dynamic IPv6 topology detection based on a variable-dimensional prefix space tree according to claim 5, characterized in that: Generating a target prefix based on the prefix space tree includes: evaluating the node advantage level of the candidate prefixes, where the node advantage level is calculated based on the ID advantage level; selecting a prefix with a high expected value, and generating its sub-prefix as the target prefix; The selected space tree child nodes whose prefix lengths do not reach the maximum prefix length are expanded.

7. The method for dynamic IPv6 topology detection based on a variable-dimensional prefix space tree according to claim 6, characterized in that: The selected space tree child nodes whose prefix length does not reach the maximum prefix length are expanded to include: Calculate the node advantage level of the selected leaf node and assign it to the ID advantage level of the node ID; The prefix is ​​expanded according to the set expansion dimension to generate a sub-prefix as a detection target, and the generated sub-prefix only constructs a prefix hierarchical relationship at the parent-child relationship level.

8. The method for dynamic IPv6 topology detection based on a variable-dimensional prefix space tree according to claim 1, characterized in that:The topology detection of the target prefix includes: concatenating the target prefix with ::1 or other fixed IID to generate the target address; constructing detection packets for all addresses with the set initial Hop Limit, and performing stateless synchronous detection in random order; The detection targets are iteratively generated according to the detection feedback until all target addresses complete the topology detection.

9. The method for dynamic IPv6 topology detection based on a variable-dimensional prefix space tree according to claim 1, characterized in that: The method also includes setting an alias prefix avoidance strategy: ① if a previously responded interface is encountered during forward detection of a target address, the forward detection of the target address is terminated immediately; ② a port that the other party cannot open is used as the destination port of the UDP detection module; ③ a seed address that does not contain an alias is used; ④ the maximum prefix length is limited.

10. An IPv6 topology dynamic detection system based on a variable-dimensional prefix space tree, characterized in that: It includes a prefix generator, a topology detection module and a scanner; the prefix generator is used to construct a variable-dimensional prefix space tree and generate a target prefix; the topology detection module is used to control the topology detection process for the target prefix; the scanner is used to perform detection and return the detection result; The prefix generator contains: A prefix space tree construction module, used for constructing a variable-dimensional prefix space tree based on a seed address and a prefix list; A pre-scan module, used for generating a pre-scan target prefix and performing a pre-scan; A weight updating module, used to update the weight information of the prefix space tree according to the detection feedback; A prefix generation module, used for generating a target prefix based on a prefix space tree; The topology detection module includes: A target generation module is used to generate a specific detection target based on the target prefix and detection feedback; A detection control module, used for controlling the scanner to perform detection; Feedback processing module, used to process detection feedback and pass it to the prefix generator.

Images