A PDT digital trunking cross-switch encryption group monitoring method

Abstract

The present invention discloses a PDT digital cluster cross-exchange encryption group monitoring method, which overcomes the problems of low security level of the encryption talk group and low security performance of the base station and the terminal in the prior art, and comprises the following steps: the subordinate exchange records the monitoring of non-local area codes; the subordinate exchange initiates a call request, and the call request contains a high-level encrypted voice stream and a non-encrypted voice stream; the superior exchange transfers the high-level encrypted voice stream to the encryption group member terminal 2 roaming to the superior exchange, and transfers the non-encrypted voice stream to the command and dispatch terminal; the encrypted voice initiated by the terminal 1 of the subordinate exchange is decrypted, and the subordinate exchange forwards the encrypted voice and the non-encrypted voice to the superior exchange; the superior exchange transfers the encrypted voice to the terminal 2, and transfers the non-encrypted voice to the command and dispatch terminal, so as to realize the encryption group monitoring. The service demand of the superior exchange command and dispatch agent to temporarily monitor the talk group of the subordinate exchange is met, and the encryption level of the conversation of the encryption group members is maintained at the same time.

Description

Technical Field

[0001] The invention relates to the field of digital cluster communication security, and in particular to a PDT digital cluster cross-exchange encryption group monitoring method. Background Art

[0002] The voice encryption of the PDT digital trunking system is implemented in an end-to-end manner, that is, the terminal that initiates the speech encrypts the voice through its own encryption card, and then transmits it to the base station through wireless transmission, and then transmits it to the local exchange through the IP network, and then transmits it to the group-attributed exchange, and then transmits it to the exchange and base station where other group members visit through the group-attributed exchange, and finally transmits it to the receiving terminal through the wireless transmission of the base station. The receiving terminal transmits the secret words to the receiving terminal's own encryption card for voice decryption, realizing the complete voice encryption communication process.

[0003] The encryption group is opened in the home exchange, and only supports encryption and decryption communications by users with the same area code as the encryption group. In actual combat, the command and dispatch agent of the exchange of the superior administrative unit (referred to as the superior exchange) often needs to temporarily monitor the calls of the exchange of the subordinate administrative unit (referred to as the subordinate exchange) to understand the command and dispatch situation in real time. Because the area code of the command and dispatch agent of the superior administrative unit is different from that of the encryption group, the command and dispatch agent cannot decrypt the encryption group. The usual practice is to reduce the security encryption level of the encryption group or not encrypt it, but this reduces the security of the entire call. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems of low security level of encrypted talk groups in PDT digital cluster systems and low security performance of base stations and terminals in the prior art, and to provide a PDT digital cluster cross-exchange encryption group monitoring method. Under the premise of not reducing the encryption level of the encryption group, the overall architecture of the interconnection of the PDT exchange system is followed to enable the upper exchange to monitor the voice of the lower exchange encryption group.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A PDT digital trunking cross-switch encryption group monitoring method, characterized in that it includes the following steps: S1: Subordinate exchange records are not monitored by local area codes; S2: The lower-level switch initiates a call request, which includes a high-level encrypted voice stream and a non-encrypted voice stream; S3: The upper switch transfers the high-level encrypted voice stream to the encryption group member terminal 2 roaming to the upper switch, and transfers the unencrypted voice stream to the command and dispatch terminal to enter the encryption group monitoring; S4: decrypt the encrypted voice initiated by terminal 1 of the lower-level switch, and the lower-level switch forwards the encrypted voice and the unencrypted voice to the upper-level switch; S5: The upper level switch transfers the encrypted voice to the terminal 2 and transfers the unencrypted voice to the command and dispatch terminal to implement encryption group monitoring.

[0006] The present invention provides a PDT digital cluster cross-exchange encryption group monitoring method, which follows the overall architecture of the PDT exchange system interconnection. When the encryption group is talking, the encrypted voice initiated by terminal 1 is decrypted, and the encrypted voice and the decrypted non-encrypted voice are sent to the upper-level exchange together. The upper-level exchange sends the high-level encrypted voice stream to terminal 2, and the non-encrypted voice is sent to the command and dispatch terminal. In this way, the high-level encrypted voice stream is always transmitted on the wireless interface between the base station and the terminal, and the command and dispatch terminal of the upper-level exchange obtains the non-encrypted voice and can monitor normally. The non-encrypted voice is transmitted in the IP private network, so the security can be guaranteed, eliminating the potential safety hazards.

[0007] Preferably, the decryption of the encrypted voice initiated by the terminal 1 of the lower-level switch includes: the encrypted voice initiated by the terminal 1 is transmitted to the lower-level switch after passing through the lower-level base station, and the lower-level switch hands the encrypted voice to the local encryption and decryption server to obtain unencrypted voice.

[0008] The lower level switch forwards the encrypted voice of the lower level base station and the decrypted non-encrypted voice to the upper level switch.

[0009] Preferably, the step S3 also includes that the upper-level exchange forwards the high-level encrypted voice stream to the upper-level base station, the upper-level base station initiates an encryption group call request to terminal 2, and terminal 2 enters the encryption group call; after the command and dispatch terminal receives the non-encrypted voice stream, it also enters the encryption group call.

[0010] Preferably, in step S2, the terminal 1 of the lower-level exchange initiates an encryption group call, and transmits the encrypted call request to the lower-level exchange through the base station. If the lower-level exchange finds that the encryption group has the participation of the command and dispatch terminal user of the upper-level exchange with a non-local area code, and the member terminal 2 of the encryption group roams to the upper-level exchange, a call request is initiated to the upper-level exchange.

[0011] The message body of the call request indicates that the current call provides two types of voice streams (high-level encrypted voice stream and non-encrypted voice stream).

[0012] Preferably, the switch to which the base station initiating the group call belongs each time is a temporary group call controller.

[0013] Preferably, the temporary group call controller searches for base stations to which users registered in the current call group belong in the entire network, and directly forwards the call to all base stations that need to participate.

[0014] Voice and handoff during a call reduces the extra processing and network delays caused by the involvement of multiple switches, achieving a time-saving method.

[0015] Preferably, multiple switches in the PDT digital trunking system manage their own base stations respectively and process their own mobility management services.

[0016] In this way, only one exchange in the current group participates in the group call service processing, but the group call service is established normally. Since there are fewer exchanges involved, the service processing delay of the exchange participation and the network delay through multiple exchanges are reduced, achieving the purpose of shortening the group call establishment time.

[0017] Preferably, multiple switches of the PDT digital trunking system all serve as group call controllers.

[0018] The general mode is that the group call controller can only be undertaken by one interconnected switch. In the present invention, multiple switches can be used as group call controllers, which shortens the time for establishing a group call.

[0019] Preferably, multiple switches in the PDT digital trunking system share mobile user information and device network topology information through a database.

[0020] Through data interaction, each exchange can perceive all base station information and user mobility data in the entire network.

[0021] Preferably, in step S1, after receiving the monitoring request of the scheduling terminal from the upper-level switch, the lower-level switch records the event of users with non-local area codes in the current encryption group participating in the call.

[0022] Therefore, the present invention has the following beneficial effects: the security level of the encryption group is not reduced on the wireless interface between the base station and the terminal, and the overall architecture of the interconnection of the PDT exchange system is followed. When the encryption group is talking, the encrypted voice initiated by terminal 1 is decrypted, and the encrypted voice and the decrypted non-encrypted voice are sent to the upper-level exchange together. The upper-level exchange sends the high-level encrypted voice stream to terminal 2, and the non-encrypted voice is sent to the command and dispatch terminal. In this way, the high-level encrypted voice stream is always transmitted on the wireless interface between the base station and the terminal, and the command and dispatch terminal of the upper-level exchange obtains non-encrypted voice and can monitor normally. The non-encrypted voice is transmitted in the IP private network, and the security can be guaranteed, eliminating the potential safety hazards. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The figure is a specific operation flow chart of the method of the present invention.

[0024] Figure 2 This is a schematic diagram of the traditional encrypted group call monitoring process.

[0025] Figure 3 This is a schematic diagram of the encryption group monitoring process of the present invention. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments: Embodiment 1: like Figure 1 In the illustrated embodiment, a method for PDT digital cluster cross-switch encryption group monitoring can be seen, and its operation process is as follows: Step 1, the subordinate switch records the non-local area code for monitoring; Step 2, the subordinate switch initiates a call request, and the call request includes a high-level encrypted voice stream and a non-encrypted voice stream; Step 3, the superior switch transfers the high-level encrypted voice stream to the encryption group member terminal 2 roaming to the superior switch, and transfers the non-encrypted voice stream to the command and dispatch terminal to enter the encryption group monitoring; Step 4, the encrypted voice initiated by the terminal 1 of the subordinate switch is decrypted, and the subordinate switch forwards the encrypted voice and the non-encrypted voice to the superior switch; Step 5, the superior switch transfers the encrypted voice to the terminal 2, and transfers the non-encrypted voice to the command and dispatch terminal to realize the encryption group monitoring.

[0027] The present embodiment provides a PDT digital cluster cross-exchange encryption group monitoring method, which does not reduce the security level of the encryption group on the wireless interface of the base station and the terminal. During the encrypted group call, the encrypted voice initiated by terminal 1 is decrypted, and the encrypted voice and the decrypted non-encrypted voice are sent to the upper-level exchange. The upper-level exchange sends the high-level encrypted voice stream to terminal 2, and the non-encrypted voice is sent to the command and dispatch terminal. In this way, the high-level encrypted voice stream is always transmitted on the wireless interface of the base station and the terminal, and the command and dispatch terminal of the upper-level exchange obtains the non-encrypted voice and can monitor normally. The non-encrypted voice is transmitted in the IP private network, and the security can be guaranteed, eliminating the potential safety hazards. The present embodiment provides a PDT digital cluster cross-exchange encryption group monitoring method, which follows the overall architecture of the PDT exchange system interconnection, is simple to implement, and can meet the business needs of the upper-level exchange command and dispatch terminal to temporarily monitor the call group of the lower-level exchange, while also ensuring the encryption level of the calls within the encryption group members.

[0028] The technical scheme and technical effects of the present invention will be further described below through specific examples. The following examples are explanations of the present invention and the present invention is not limited to the following examples.

[0029] The traditional encrypted group call monitoring process is as follows Figure 2As shown in the figure, it can be seen that the traditional processing method of encryption group monitoring is that when the command and dispatch terminal of the lower-level switching system initiates a monitoring request, the lower-level switching system finds that the monitoring is not in the local area code, and then reduces the encryption level of the encryption group, and all subsequent calls are calls with low encryption levels. This reduces the security level of the entire encrypted call group, and the wireless interfaces of all base stations and terminals participating in the call group are in danger.

[0030] The processing method of the encryption group in this application is as follows Figure 3 As shown, the security level of the encryption group is not reduced on the wireless interface of the base station and the terminal, eliminating security risks. The following steps are included: Step 1: The lower-level exchange records non-local area code monitoring.

[0031] After the lower-level exchange receives the monitoring request from the command and dispatch terminal of the upper-level exchange, it records that there are users with non-local area codes participating in the call in the current encryption group.

[0032] Step 2: The lower-level switch initiates a call request, which includes a high-level encrypted voice stream and a non-encrypted voice stream.

[0033] When terminal 1 of the lower-level exchange initiates an encrypted group call, the encrypted call request is transmitted to the lower-level exchange through the base station. The lower-level exchange finds that the encryption group has the participation of the command and dispatch terminal user of the upper-level exchange with a non-local area code. At the same time, it also finds that the member terminal 2 of the encryption group has roamed to the upper-level exchange. Therefore, the lower-level exchange initiates a call request to the upper-level exchange and indicates in the message body of the call request that the current call provides two voice streams (high-level encrypted voice stream and non-encrypted voice stream) at the same time.

[0034] Step 3: The superior exchange transfers the high-level encrypted voice stream to the encryption group member terminal 2 roaming to the superior exchange, and transfers the non-encrypted voice stream to the command and dispatch terminal to enter the encryption group monitoring.

[0035] After receiving the call request, the upper-level switch forwards the call request to the upper-level base station (high-level encrypted voice stream) and the command and dispatch terminal (non-encrypted voice stream).

[0036] The upper-level base station initiates an encrypted group call request to terminal 2 via the air interface, and terminal 2 enters the encrypted group call.

[0037] At the same time, after receiving a non-encrypted call, the command and dispatch terminal also enters the encryption group call.

[0038] Step 4: Decrypt the encrypted voice initiated by terminal 1 of the lower-level switch, and the lower-level switch forwards the encrypted voice and non-encrypted voice to the upper-level switch.

[0039] The encrypted voice initiated by terminal 1 is transmitted to the lower-level switch after passing through the lower-level base station. The lower-level switch sends the encrypted voice to the local encryption and decryption server to obtain the decrypted unencrypted voice. The lower-level switch forwards the encrypted voice of the lower-level base station and the decrypted unencrypted voice to the upper-level switch.

[0040] Step 5: The upper-level exchange transfers the encrypted voice to the terminal 2 and transfers the unencrypted voice to the command and dispatch terminal to realize encryption group monitoring.

[0041] The upper-level exchange receives the encrypted and decrypted non-encrypted mixed voice stream, strips out the encrypted voice stream, and forwards the encrypted voice stream to terminal 2 through the upper-level base station. The stripped non-encrypted voice stream is directly forwarded to the command and dispatch terminal.

[0042] In this way, the wireless interface between the base station and the terminal always transmits a high-level encrypted voice stream, while the command and dispatch seat of the upper exchange receives unencrypted voice and can monitor it normally. The unencrypted voice is transmitted in the IP private network, and the security can be guaranteed.

[0043] This embodiment also provides a method for reducing the time of establishing a group call and the time of handover between PDT digital trunking switches, which mainly includes: 1. Multiple switches in the PDT digital trunking system manage their own base stations and handle their own mobility management and other services.

[0044] 2. Multiple switches in the PDT digital trunking system share mobile user information and device network topology information through a database, which means that each switch can perceive all base station information and user mobile data in the entire network through data interaction.

[0045] 3. Compared with the common mode that the group call controller can only be assumed by one interconnected switch, in this application, multiple switches of the PDT digital trunking system can play the role of the group call controller.

[0046] 4. The rules stipulate that the exchange to which the base station initiating each group call belongs is the temporary group call controller.

[0047] 5. The temporary group call controller searches the entire network for base stations to which users registered in the current call group belong, and directly forwards the call to all base stations that need to participate.

[0048] According to the above, only one exchange in the current group participates in the group call service processing, but the group call service is established normally. Due to the lack of participation of multiple exchanges, the service processing delay of the exchange participation and the network delay through multiple exchanges are reduced, achieving the purpose of shortening the group call establishment time.

[0049] Similarly, voice and handoff during a call also reduces the extra processing and network delays caused by the involvement of multiple switches, thereby achieving a time-saving method.

[0050] Embodiment 2: The present embodiment provides a PDT digital cluster cross-exchange encryption group monitoring method, and its operation process is as follows: step 1, the lower-level exchange records the non-local area code for monitoring; step 2, the lower-level exchange initiates a call request, and the call request includes a high-level encrypted voice stream and a non-encrypted voice stream; step 3, the upper-level exchange transfers the high-level encrypted voice stream to the encryption group member terminal 2 roaming to the upper-level exchange, and transfers the non-encrypted voice stream to the command and dispatch terminal to enter the encryption group monitoring; step 4, the encrypted voice initiated by the terminal 1 of the lower-level exchange is decrypted, and the lower-level exchange forwards the encrypted voice and the non-encrypted voice to the upper-level exchange; step 5, the upper-level exchange transfers the encrypted voice to the terminal 2, and transfers the non-encrypted voice to the command and dispatch terminal to realize the encryption group monitoring.

[0051] Specifically, the present embodiment provides a PDT digital trunking cross-switch encryption group monitoring method, comprising the following steps: 1. The command and dispatch terminal of the upper-level exchange initiates call monitoring of the encryption group of the lower-level exchange.

[0052] 2. The lower-level exchange finds that the command and dispatch terminal of the upper-level exchange is monitoring and the number area code is not local, so it records that the upper-level exchange is monitoring on the encryption group.

[0053] 3. Terminal 1 of the lower-level switch initiates an encrypted group call and sends an encrypted call request to the lower-level base station.

[0054] 4. The lower-level base station then forwards the encrypted call request to the lower-level exchange. The lower-level exchange finds that the upper-level exchange has a command and dispatch terminal with a non-local area code monitoring, and a member terminal 2 of the encryption group roams to the upper-level base station of the upper-level exchange.

[0055] 5. The lower-level switch constructs a call request and sends it to the upper-level switch, and indicates in the request message body that the local call includes both high-level encrypted voice streams and non-encrypted voice streams.

[0056] 6. After receiving the call request, the upper-level exchange sends the encrypted call request to the upper-level base station 2 and sends the unencrypted call request to the command and dispatch terminal.

[0057] 7. The upper-level base station transfers the encryption request (channel allocation) to terminal 2, and terminal 2 enters the encrypted call; at the same time, the dispatch command terminal also enters the monitoring state.

[0058] 8. Terminal 1 initiates encrypted voice, which is then transferred to the lower-level switch after passing through the base station of the lower-level switch.

[0059] When terminal 1 sends encrypted voice, it writes the original voice header and voice frame into the encryption card respectively, obtains ciphertext data after encryption processing, encapsulates the ciphertext data, and then sends it to the base station of the lower-level exchange by terminal 1, and the base station of the lower-level exchange forwards it to the lower-level exchange.

[0060] 9. The lower-level exchange sends the encrypted voice to the encryption and decryption server for decryption, obtains the unencrypted voice, and forwards the encrypted voice and the decrypted unencrypted voice to the upper-level exchange.

[0061] The process of the encryption and decryption server decrypting the encrypted voice is to write the voice frame into the encryption card, and the encryption card decrypts it to obtain the original voice data and obtain the non-encrypted voice.

[0062] 10. The upper-level switch strips out the encrypted voice and forwards it to the upper-level base station, and then forwards it to terminal 2 through the air interface to realize encrypted calls. The upper-level switch strips out the non-encrypted voice and forwards it to the command and dispatch terminal, which can also monitor the voice of the encrypted call group normally.

[0063] The present embodiment provides a PDT digital cluster cross-exchange encryption group monitoring method, which does not reduce the security level of the encryption group on the wireless interface of the base station and the terminal. During the encrypted group call, the encrypted voice initiated by terminal 1 is decrypted, and the encrypted voice and the decrypted non-encrypted voice are sent to the upper-level exchange. The upper-level exchange sends the high-level encrypted voice stream to terminal 2, and the non-encrypted voice is sent to the command and dispatch terminal. In this way, the high-level encrypted voice stream is always transmitted on the wireless interface of the base station and the terminal, and the command and dispatch terminal of the upper-level exchange obtains the non-encrypted voice and can monitor normally. The non-encrypted voice is transmitted in the IP private network, and the security can be guaranteed, eliminating the potential safety hazards. The present embodiment provides a PDT digital cluster cross-exchange encryption group monitoring method, which follows the overall architecture of the PDT exchange system interconnection, is simple to implement, and can meet the business needs of the upper-level exchange command and dispatch terminal to temporarily monitor the call group of the lower-level exchange, while also ensuring the encryption level of the calls within the encryption group members.

[0064] This embodiment also provides a method for terminal 1 to initiate encrypted voice and encryption and decryption server to decrypt the encrypted voice, mainly comprising: terminal 1 inserts a synchronization control frame in the form of a PI header before the voice frame sent. In order to prevent the synchronization control frame from being damaged due to channel bit errors, multiple synchronization control frames can be inserted according to actual conditions to ensure that the encryption and decryption server obtains the correct synchronization control frame before decrypting the encrypted voice.

[0065] In order to ensure that the encryption and decryption server that enters late during the group call can correctly decrypt the voice stream, in the subsequent call process, Terminal 1 needs to periodically send synchronization control frames through embedded FLC signaling. If the encryption and decryption server does not receive a legitimate synchronization control frame, it needs to continue waiting and remain silent. When the encryption and decryption server receives a legitimate synchronization control frame, it will use the initial vector carried in the synchronization control frame to decrypt the encrypted voice stream starting from the next voice frame and start playing the voice.

[0066] Specifically: Terminal 1 first encodes 60ms of plaintext speech into 129 bits of speech data; then, the 129 bits of speech data are XORed with the 129bit key stream; further, the XOR result is concatenated with the 15bis speech frame sequence number, and then FEC encoding is performed to output 216bis ciphertext speech data.

[0067] After receiving the encrypted voice data sent by terminal 1, the encryption and decryption server first performs FEC decoding to obtain 144 bits of data; then, it extracts the 15 bits of voice frame sequence number from the 144 bits of data; finally, it performs XOR with the remaining 129 bis data and the key stream, decrypts it and restores it to plain text voice to obtain non-encrypted voice.

[0068] Alternatively, terminal 1 determines the key TEK used in the communication based on the key index (KD), group call / single call identification (G / D), called party identification (TMSD) and calling party identification (SMSD). TEK, G / I, TMSI and SMSI are subjected to a key derivation algorithm to generate the encryption key CK used to calculate the key stream. The random number generator generates an initial vector (IV) for each encrypted voice call, and internally maintains a counter used as a voice frame sequence number (FN). Each time a key stream is generated, the counter automatically increases by 1. Terminal 1 uses CK, FN and IV as inputs to the key stream generator to generate a continuous key stream, which is XORed with the voice data stream output by the voice encoder Vocoder and then concatenated with FN to obtain encrypted voice.

[0069] The encrypted voice reaches the lower-level exchange through the base station of the lower-level exchange, and the lower-level exchange sends the encrypted voice to the encryption and decryption server for decryption: the encryption and decryption server obtains the basic information of this call through call control signaling such as GRANT, Grp_ V_ ch_ Usr, U_V_ Ch_Usr, etc.: G / I (group call / individual call), TMSI (called mobile user identity code), SMSI (calling mobile user identity code). After receiving the legal synchronization control frame, the called party determines the TEK (Traffic EncryptionKey) used for communication through the basic call information (G / I, TMSI, SMSI) and the KI (key index) in the synchronization control frame. TEK and G / I, TMSI, SMSI are then subjected to the key derivation algorithm to generate the encryption key CK used to calculate the key stream. When decrypting, first extract the frame number from each voice frame, and use the same algorithm as terminal 1 by CK, FN and IV to obtain the same key stream as terminal 1, and obtain the decrypted non-encrypted voice after XOR with the ciphertext stream.

[0070] Embodiment three: This embodiment also provides a PDT digital cluster cross-switch encryption group monitoring device, including a memory, at least one processor, a computer program stored in the memory and executable on the at least one processor, and at least one communication bus.

[0071] The memory is used to store computer programs and encryption group monitoring data. The computer programs include a decryption program for decrypting the encrypted voice initiated by terminal 1, a separation program for stripping the encrypted and non-encrypted mixed voice streams received by the upper-level exchange, and other programs involved in the PDT digital cluster cross-exchange encryption group monitoring method (such as using the Get PiHeader function to obtain the encryption header, using the Voice Encode Encrypt function to perform voice encryption processing, and using the VoiceDecode Decrypt function to perform voice decryption processing). The processor realizes the decryption of the encrypted voice initiated by terminal 1 and the separation of the encrypted and non-encrypted mixed voice streams by running or executing the computer program stored in the memory and calling the data stored in the memory, and finally realizes the steps of the PDT digital cluster cross-exchange encryption group monitoring method mentioned in Example 1 and Example 2.

[0072] The memory mainly includes a program storage area and a data storage area. The program storage area can store an operating system, an application required for at least one function (such as a sound playback function, an image playback function, etc.), etc.; the data storage area can store data created according to the use of the monitoring device (such as audio data), etc. In addition, the memory can include a non-volatile memory, such as a hard disk, a memory, a plug-in hard disk, a smart memory card (Smart Media Card, SMC), a secure digital (Secure Digital, SD) card, a flash card (Flash Card), at least one disk storage device, a flash memory device, or other non-volatile solid-state storage devices.

[0073] At least one processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

[0074] The processor may be a microprocessor or any conventional processor, etc. The processor is the control center of the monitoring device, and uses various interfaces and lines to connect various parts of the entire monitoring device.

[0075] The above-described embodiment is only a preferred solution of the present invention and does not limit the present invention in any form. There are other variations and modifications without exceeding the technical solution described in the claims.

Claims

1. A PDT digital trunking cross-switch encryption group monitoring method, characterized in that: The following steps are involved: S1: Subordinate exchange records are not monitored by local area codes; S2: The lower-level switch initiates an encryption group call request, which includes a high-level encrypted voice stream and a non-encrypted voice stream; S3: The upper switch transfers the high-level encrypted voice stream to the encryption group member terminal 2 roaming to the upper switch, and transfers the unencrypted voice stream to the command and dispatch terminal to enter the encryption group monitoring; S4: decrypt the encrypted voice initiated by terminal 1 of the lower-level switch, and the lower-level switch forwards the encrypted voice and the unencrypted voice to the upper-level switch; S5: The upper level switch transfers the encrypted voice to the terminal 2 and transfers the unencrypted voice to the command and dispatch terminal to implement encryption group monitoring.

2. A PDT digital trunking cross-switch encryption group monitoring method according to claim 1, characterized in that: The decryption of the encrypted voice initiated by the terminal 1 of the lower-level switch includes: the encrypted voice initiated by the terminal 1 is transmitted to the lower-level switch after passing through the lower-level base station, and the lower-level switch hands the encrypted voice to the local encryption and decryption server to obtain non-encrypted voice.

3. A PDT digital trunking cross-switch encryption group monitoring method according to claim 1 or 2, characterized in that: The step S3 also includes that the upper-level switch forwards the high-level encrypted voice stream to the upper-level base station, the upper-level base station initiates an encrypted group call request to the terminal 2, and the terminal 2 enters the encrypted group call; After receiving the non-encrypted voice stream, the command and dispatch terminal also enters the encryption group call.

4. A PDT digital trunking cross-switch encryption group monitoring method according to claim 1 or 2, characterized in that: In step S2, terminal 1 of the lower-level exchange initiates an encrypted group call, and transmits the encrypted call request to the lower-level exchange through the base station. If the lower-level exchange finds that the encryption group has the participation of the command and dispatch terminal user of the upper-level exchange with a non-local area code, and the member terminal 2 of the encryption group roams to the upper-level exchange, a call request is initiated to the upper-level exchange.

5. A PDT digital trunking cross-switch encryption group monitoring method according to claim 1, characterized in that: The switch to which the base station initiating each group call belongs is the temporary group call controller.

6. A PDT digital trunking cross-switch encryption group monitoring method according to claim 5, characterized in that: The temporary group call controller searches for base stations to which users registered in the current call group belong in the entire network, and directly forwards the call to all base stations that need to participate.

7. A PDT digital trunking cross-switch encryption group monitoring method according to claim 1, 5 or 6, characterized in that: Multiple switches in the PDT digital trunking system manage their own base stations and handle their own mobility management services.

8. A PDT digital trunking cross-switch encryption group monitoring method according to claim 1, 5 or 6, characterized in that: Multiple switches in the PDT digital trunking system all serve as group call controllers.

9. A PDT digital trunking cross-switch encryption group monitoring method according to claim 1, 5 or 6, characterized in that: Multiple switches in the PDT digital trunking system share mobile user information and device network topology information through a database.

10. A PDT digital trunking cross-switch encryption group monitoring method according to claim 1 or 2 or 5 or 6, characterized in that: In the step S1, after receiving the monitoring request of the scheduling terminal from the upper-level switch, the lower-level switch records the event of the user with a non-local area code in the current encryption group participating in the call.

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