CN116155870A - VoIP telephone message transmission method of high-speed magnetic levitation train-ground communication system - Google Patents

Abstract

The invention discloses a VoIP telephone message transmission method of a high-speed maglev vehicle-ground communication system, using a high-speed maglev train or a ground control center as a signal sender, and the other as a signal receiver; including the following steps: S1, sending a VoIP telephone message The text is transmitted to the communication device of the signal sender through the TCP/IP protocol; S2, analyze the VoIP telephony message, and assign the IP address; S3, process the application layer content of the VoIP telephony message; S4, pass non-TCP The /IP protocol transmits the signal after the framing to the signal receiver base station; S5, analyzes the received framing signal to determine whether it is RTP/RTCP or SIP: if it is the RTP/RTCP protocol, then directly carry out VoIP packaging; if it is the SIP protocol Then decapsulate and package, and then perform VoIP packaging; S6, transmit the message to the corresponding device according to the destination port or signaling requirements. The invention unpacks and packs based on the data structure of different protocols, and realizes the transmission of the VoIP dispatching telephone in the communication system of the high-speed maglev vehicle without the TCP/IP protocol.

Description

VoIP telephony message transmission method for high-speed maglev vehicle-ground communication system

technical field

The invention belongs to the technical field of communication, and in particular relates to a VoIP telephone message transmission method of a communication system of a high-speed magnetic levitation vehicle.

Background technique

An IP dispatching telephone is installed on the high-speed maglev train, and its function is mainly a special telephone set for the train dispatcher to direct the train operation. The train dispatching communication methods mainly include: communication at different positions on the same train, communication between the train and the ground control center, communication between different trains, etc. Wherein the conversation on different positions on the same train, because it is under the same network segment, is the same as the message transmission based on VoIP (Voice of IP) commonly used, directly adopts the TCP/IP message transmission based on VoIP. In the other two cases, in addition to using the VoIP-based protocol, it also needs to be realized through the vehicle-ground communication system of the high-speed maglev train.

At present, the commonly used VoIP telephony message transmission is completed in the network based on the TCP/IP protocol. The application layer is mainly based on SIP/RTP (RTCP) to complete the signaling control and voice media stream transmission, and the transport layer is based on The UDP protocol, the network layer is the IP protocol, and finally the data link layer is completed by the HDLC protocol.

The communication process of the VoIP dispatch phone is shown in Figure 1. The specific transmission process is as follows: the VoIP protocol first needs to use SIP to establish a connection. SIP is a signaling protocol at the application layer, and usually consists of a start line, a message header, and an optional message body. To establish a call between two IP phones, a series of operations such as request, answer, and ringing are required to be completed by the call initiator, the server, and the call receiver. At the same time, based on SIP message transmission, the number of bytes sent each time is not Fixed frame length. The call process is based on the RTP and RTCP protocols, and the language signal that has been compressed through analog-to-digital conversion and language coding is packaged at the application layer. Among them, RTP is mainly responsible for the data transmission of the media stream, and RTCP completes the transmission control of the media stream. The data format and size based on RTP and RTCP are relatively fixed. After the encapsulation of the application layer is completed, it is sent to the transport layer and the network transport layer in turn for UDP grouping and IP grouping, and can be transmitted in the network after being framed by a simple HDLC protocol. On the contrary, the telephone receiver or server will process the received signal corresponding to each layer to complete the unpacking data processing, until the SIP or RTP protocol format of the application layer, and complete the decoding to recover the signaling or voice signal.

The communication system of the high-speed maglev vehicle has a special service interface for IP dispatching telephones. However, due to the limited capacity of the service interface and the transmission of messages belonging to non-traditional TCP/IP protocols, it cannot be directly connected to VoIP messages. Therefore, it is necessary to VoIP messages are repackaged and framed and address managed to complete message transmission in the vehicle-to-ground communication system. And because RTP/RTCP and SIP belong to the application layer protocol, the VoIP voice phone based on NAT technology needs to complete the leap from RTP, SIP to NAT, that is, the internal network first transmits to the public network, and then transmits to the target in the public network. After the public network, the target public network is transmitted to its internal network. Similar management and allocation of IP addresses is required on the existing high-speed maglev vehicle communication system to realize message transmission of IP telephone services in the non-TCP/IP high-speed maglev vehicle communication system.

The present invention is aimed at the VoIP scheduling telephone message transmission of the communication system of the high-speed maglev vehicle, realizes the compatibility between the IP telephone message and the communication system of the vehicle, and solves the inconsistent protocol when the VoIP telephone service is transmitted in the communication system of the maglev vehicle , the frame length is not fixed, and address management and other issues have important application value and engineering significance in the field of high-speed maglev vehicle-to-ground communication.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art, to provide a frame structure of the service interface of the vehicle-ground communication system by aiming at the signaling data and call data of the VoIP phone, unpacking and grouping based on the data structure of different protocols , realizing the VoIP telephony message transmission method of the high-speed maglev vehicle-ground communication system for the VoIP dispatching telephone to be transmitted in the non-TCP/IP protocol high-speed maglev vehicle-ground communication system.

The purpose of the present invention is achieved by the following technical solutions: the VoIP telephone message transmission method of the high-speed magnetic levitation vehicle-ground communication system communicates between the high-speed magnetic levitation train and the ground control center, and uses the high-speed magnetic levitation train or the ground control center as the signal sender, the other party is the signal receiver; including the following steps:

S1, transmitting the VoIP telephone message of the signal sender to the communication device of the signal sender through the TCP/IP protocol;

S2. The communication device of the signal sender analyzes the VoIP telephony message, and allocates the IP address;

S3. Processing the application layer content of the parsed VoIP telephony message, including the following sub-steps:

S31. Determine the space size of the VoIP service interface;

S32. Determine the protocol type, and process according to the different protocol types:

If the application layer of the VoIP telephone message is an RTP/RTCP media stream data packet, it does not need to be unpacked, and the data packet is directly sent to the framing part of the VoIP service interface in the vehicle-ground communication system for framing;

If the application layer of the VoIP telephone message is a SIP signaling packet, first determine whether the length of the packet exceeds the size of the VoIP service interface in the vehicle-to-ground communication system, if it exceeds, the packet is unpacked according to the size of the service interface; Then frame the VoIP service interface framing part sent to the vehicle-ground communication system;

S4. The base station of the signal sender transmits the framed signal to the base station of the signal receiver through a non-TCP/IP protocol;

S5. The VoIP service interface deframing part of the signal receiver base station analyzes the received framing signal to determine whether it is RTP/RTCP or SIP: if it is the RTP/RTCP protocol, it will directly perform VoIP packaging and recompose the VoIP phone message; if it is The SIP protocol decapsulates the received message and packs the decapsulated message, and then performs VoIP packaging to recompose the VoIP telephone message;

S6. Transmit the packet to the corresponding device according to the destination port or signaling requirements.

The VoIP telephony message is composed of voice media stream or signaling, encapsulated by RTP/RTCP or SIP at the application layer, then encapsulated and framed by UDP at the transport layer, encapsulated by IP at the network layer, and finally encapsulated at the data link layer Encapsulation, through OSI four-layer encapsulation to form VoIP data packets.

In step S2, the method for allocating the IP address is as follows: from the IP phone of the signal sender to the communication device of the signal sender, the target IP address is the IP address of the signal sender’s communication device, and the source IP address is the IP address of the signal sender Set the source IP address of the message based on SIP or RTP/RTCP in the application layer as the intranet address of the IP phone of the information sender, and set the destination IP address as the scheduling server of the information receiver or the IP phone of the information receiver Intranet address; when transmitting, it is necessary to convert the IP address of the IP phone or server into the address of the vehicle communication device or ground communication device, and complete the conversion of the TCP/IP network transmission address and the non-TCP/IP network transmission address.

The specific implementation method of the step S31 is: determine the length of the VoIP service interface in the vehicle-to-ground communication system based on the size after the RTP protocol completes the encapsulation of the application layer; then determine the length of its identifier according to the design of the frame structure; then the entire service The size of the interface is the sum of the length of the VoIP service interface and the length of the identifier.

In the step S32, the signal after the framing of the VoIP service interface framing part includes a header, a data content part and a tail;

The header includes the frame header, function type, destination address, source address and the size of the data content, with special characters as the frame header; the second part is the function type, indicating whether the data is based on RTP, RTCP or SIP protocol; at the same time, the header needs to be determined Device destination address and source address, its source address and destination address are determined by looking up the table according to the source IP address and destination IP address of its application layer;

The data content part includes the frame header, the total number of slices, the slice number, the effective data length and the first CRC check;

The tail includes a frame check and a frame tail composed of special characters.

The beneficial effects of the present invention are: the present invention designs the frame structure of the service interface of the vehicle-ground communication system by aiming at the signaling data and call data of the VoIP phone, so that the VoIP message with variable frame length becomes a message with fixed frame length. The text is transmitted. Based on the data structure unpacking and grouping of different protocols, the transmission of VoIP dispatching calls in the non-TCP/IP protocol high-speed maglev vehicle ground communication system is realized, and the service interface of VoIP dispatching telephones in the current high-speed maglev vehicle ground communication system is solved. Due to the byte is too long, the purpose is uncertain, and the IP address management leads to incompatibility. By using the method of the invention, the VoIP dispatching phone can be used normally and stably on the train.

Description of drawings

Fig. 1 is the VoIP transmission process;

Figure 2 is a high-speed maglev service interface;

Fig. 3 is a flowchart of VoIP packet transmission;

Fig. 4 is the processing of VoIP message, (1) is the frame structure of VoIP message, (2) is the analysis of VoIP message, (3) is the packet splitting and reorganization to SIP agreement, (4) is dispatching telephone Business interface frame structure;

Figure 5 shows VoIP packet address management.

Detailed ways

In the high-speed maglev train, the special telephone set for the train dispatcher to direct the train operation is an IP telephone based on the VoIP (Voice of IP) network model. Figure 1 shows the VoIP telephone transmission process, which is composed of users and proxy servers. To talk between users, the SIP signaling protocol needs to be used: first, a connection is established through the proxy server, that is, user 1 initiates a request to the proxy server, and the server then Turning to user 2, after completing a series of processes such as ringing and responding, user 1 and user 2 start to establish a call. The call transmission process is to carry out AD sampling and compression coding on the voice information, and then send it after RTP encapsulation and IP protocol encapsulation, and the receiving part is to process IP encapsulation and RTP data packets. Finally, through decoding, decompression and DA conversion, it becomes voice information. The above data transmission is based on the network of TCP/IP protocol for transmission.

The high-speed maglev vehicle-ground communication system has different service interfaces for different services. As shown in Figure 2, service interface 1 is train diagnosis, service 2 interface is dispatching telephone, and service interface n. Each service interface specifies different frame structures and byte sizes according to different needs.

The present invention mainly completes unpacking and grouping of relevant protocols, design of business interface frame structure, and IP address management based on the structural characteristics of protocols such as RTP (RTCP) and SIP in VoIP, the VoIP transmission framework, and the characteristics of the communication service interface of the maglev vehicle. distribution process. The present invention is in the communication system business of high-speed maglev vehicle, based on RTP (RTCP)/SIP protocol message frame structure as shown in Figure 4 (1), its VoIP transmission all adopts TCP/IP network transmission in the vehicle or on the ground, and Vehicle-to-ground or vehicle-to-vehicle communication is based on the service interface under the wireless communication system. As for the size of the space allocated by the VoIP service interface, since the size of the message composed of the SIP protocol is variable and generally much larger than the space of the service interface of the system, it is necessary to unpack the message based on the SIP protocol to send and receive the package. The size of RTP and RTCP protocol packets is relatively fixed, but since there are multiple protocols in the transmission process, it is necessary to design a special frame structure for the service interface so that the receiving end can recognize the function of the service interface and perform subsequent processing. And because the VoIP phone transmission process also needs to complete the IP address spanning in the vehicle-to-ground communication, a special design is required. The technical solution of the present invention will be further described below in conjunction with the accompanying drawings.

As shown in Figure 3, the VoIP telephone message transmission method of the high-speed maglev vehicle-ground communication system of the present invention communicates between the high-speed maglev train and the ground control center, and uses the high-speed maglev train or the ground control center as the signal sender, then The other party is the signal receiver, and the present embodiment uses the train as the signal sender; including the following steps:

S1. Transmit the VoIP telephony message of the in-vehicle IP telephone to the in-vehicle communication device through the TCP/IP protocol; the dispatching telephone also needs to design the frame structure and space size according to its requirements. Firstly, determine the size of the scheduling phone space: the VoIP-based phone message transmission method is based on the RTP (RTCP) protocol in the call media stream, and the RTCP protocol controls the media stream information, while the signaling part is based on the SIP protocol. As shown in Figure 4 (1), the VoIP telephony message is composed of voice media streams or signaling, encapsulated using RTP/RTCP or SIP at the application layer, and then encapsulated and framed using UDP at the transport layer, and used at the network layer IP is encapsulated, the data link layer is finally encapsulated, and VoIP data packets are formed through OSI four-layer encapsulation.

S2. The in-vehicle communication device parses the VoIP telephony message and assigns an IP address; because the IP telephony is based on the RTP or SIP protocol at the application layer, which contains its target IP address and source address. However, the air interface signals of the vehicle-mounted base station and the ground base station of the high-speed maglev vehicle-ground communication system are non-TCP/IP-transmitted communication signals, and cannot directly transmit IP-encapsulated network messages based on VoIP. Therefore, it is impossible to directly set the source IP address and target IP address of each layer as the source IP phone and target IP phone, so the IP address needs to be allocated; the network transmission process, the addressing method is mainly through the IP address of the transport layer and the network layer, Therefore, the destination IP address and source IP address of the transport layer and the network layer are determined by the transmission path. The method of assigning the IP address is as follows: since it is a two-way communication, the IP address assignment methods of the sending and receiving ends are the same, and the train is used as the signal sender. , from the vehicle-mounted IP phone to the vehicle-mounted communication device, the target IP address is the IP address of the vehicle-mounted communication device, and the source IP address is the IP phone in the vehicle; the source IP address of the message based on SIP or RTP/RTCP in the application layer Set as the internal network address of the IP phone in the vehicle, and set the target IP address as the internal network address of the ground dispatching server or the ground dispatching IP phone; when transmitting, it is necessary to convert the IP address of the phone or server to the vehicle communication device or ground communication The address of the device completes the conversion between the TCP/IP network transmission address and the non-TCP/IP network transmission address. The receiving end is the communication equipment on the ground. After the ground communication equipment completes the message analysis and repackages, it completes the TCP/IP network protocol message transmission according to its content. As shown in Figure 5, when the on-board IP phone B in car A talks to the ground IP phone E in D, it is necessary to use signaling based on the SIP protocol to communicate between the on-board phone B in A, the server F in D, and the IP phone in D. G. Complete the connection between two IP phones through a series of handshakes, and then complete the call through the media stream of the RTP protocol. First of all, the vehicle-mounted IP phone needs to use the network TCP/IP protocol to transmit messages. The source IP address of the network layer and the transport layer is 192.168.23.4 (1004), which is the actual IP address of the IP phone in network transmission, and the destination IP address The address 192.168.23.5 (1005) is the IP address used for the actual transmission of the vehicle communication device. On the vehicle communication device, there are two ways of VOIP message transmission, one is based on TCP/IP message transmission, the transmission direction is from the vehicle communication device to the IP phone, so the source address is the actual IP address of the vehicle communication device , and the target IP is the IP address of the car phone; the second is the message transmission based on the non-TPC/IP protocol of the vehicle-ground communication system, the transmission content is based on the VOIP application layer, and its address is the physical device address specified in advance. For example, the source address of the vehicle communication device is 0x010001, and the target device address is 0x0f000f, which is the physical address of the ground communication device. The ground communication equipment is similar to the vehicle communication equipment, and there are two different message transmission methods. Then complete the TCP/IP message transmission of the server and IP phone according to the function and type of VOIP. After the message processing is completed, the on-vehicle communication equipment and the ground communication equipment continue to build and analyze the service interface. In the actual transmission process, the IP address of the application layer does not need to be considered, but the function of the service interface is determined according to the source IP address of the application layer. Dispatch calls and source addresses. Thus, the VOIP message transmission can be completed without considering the destination IP address and source address in the application layer.

S3. Processing the application layer content of the parsed VoIP telephony message, including the following sub-steps:

S31, determine the space size of VoIP service interface; VoIP telephony message transmission is the transmission under different protocols, because its follow-up transport layer of RTP (RTCP) agreement, the number of bytes such as network layer is all fixed size, and can not revise The content of the application layer, so the length of the VoIP service interface in the vehicle-to-ground communication system is determined by the size after the application layer is encapsulated based on the RTP protocol; then the length of the identifier is determined according to the design of the frame structure; the entire service interface The size is the sum of the length of the VoIP service interface and the length of the identifier. Since the number of bytes increased due to encapsulation on the transport layer, network layer, and data link layer is fixed, it is generally 50 bytes. At the application layer, if it is a media stream data packet based on the RTP protocol, the number of bytes is also a fixed number of bytes, generally 214 bytes. The bytes of RTCP packets are smaller, generally only half the size of RTP. The number of bytes of the signaling data packet based on the SIP protocol is different according to its content, and the number of bytes is long and not fixed, generally between 400 and 1200 bytes. Since the data transmitted by the service interface is mainly the application layer of VoIP, the size of the data space of the VoIP service interface in the high-speed maglev vehicle communication system is determined by the size after the application layer is encapsulated based on the RTP protocol, that is, the size of the service interface is set. The size is: 214 bytes, and the design identifier has a total of 11 bytes, so the frame size corresponding to the VoIP service in the communication system of the high-speed maglev vehicle is: 225 bytes.

S32. Determine the protocol type, and process according to the different protocol types:

After setting the size of the service interface, the media stream data based on the RTP and RTCP protocols can be transmitted at one time. Therefore, if the application layer of the VoIP phone message contains RTP/RTCP media stream data packets, there is no need to unpack the packets, and the data packets can be directly Send it to the framing part of the VoIP service interface in the vehicle-ground communication system for framing;

The signaling data based on the SIP protocol may not be transmitted at one time, so if the space size of the service interface is exceeded, it is necessary to fragment the signaling data based on the SIP protocol. Therefore, if the application layer of the VoIP telephony message is a SIP signaling packet, because it involves splitting data, it redesigns the VoIP service interface according to the 4-byte identifier and 210-byte data content. First determine whether the length of the data packet exceeds the size (210 bytes) allocated to the SIP signaling data packet by the VoIP service interface in the vehicle-to-ground communication system. If it exceeds, the data packet will be unpacked; then it will be sent to the vehicle-to-ground communication system The framing part of the VoIP service interface performs framing. After unpacking, each piece of data is disassembled into a fixed and appropriate size. If the number of the last piece does not meet the size requirements, it will also be sealed into one piece for processing. After unpacking the signaling data packet based on the SIP protocol, an identifier needs to be added so that the original message can be restored when receiving the group packet subsequently. The specific unpacking method is shown in Figure 3 and Figure 4 (2) and (3). After completing the SIP protocol and packaging the signaling data packets to the network layer, the size of each piece of bytes is 210 bytes. If the size of the last piece of bytes is less than 210 bytes, fill the bytes with 0. Among them, the 4-byte identifier design is: the frame header occupies 8 bits, and the design is: 0x80 (1000_0000), and the total packet width occupies 4 bits, that is, there may be 0 to 15 subpackages in total, and the subpackage sequence number also occupies 4bit, each serial number represents which subpackage it is; for example, 0101_0100, that is, a total of 5 subpackets are divided into one transmission, and this subpackage is the fourth subpackage. The bit width of the effective signaling length is 8 bits, which represents the length of the effective signaling data in the signaling. Except for the last packet, the value is 1101_0010. The last packet is assigned according to its actual effective signaling data length, for example 0_1011_1110, which means that the last packet valid data is 190 bytes. The last bit is the 7-bit header CRC check code, and the 1-bit 0 indicates the last bit of the identifier.

The design of the identifier is as follows: 1. The highest bit is the frame header, generally with special characters as its frame header; 2. The total number of subpackages, and the subpackage sequence number of each package; 3. Give each subpackage effective data length. In general, except that the effective length of the last subpacket data is not necessarily the maximum value, each other subpacket data will be filled to a fixed maximum value, and the number of the last subpacket may not be enough, depending on the length of the effective data. Determine the valid data of the last packet. In addition, the checksum of the header is added to determine whether there is an error in the frame data transmission process, and if there is an error, retransmit.

The service interface needs to repackage the data into frames to adapt to the high-speed maglev communication system. The signal after framing in the framing part of the VoIP service interface includes a header, a data content part and a tail, as shown in FIG. 4(4). The header includes the frame header, function type, destination address, source address and the size of the data content, with special characters as the frame header; the second part is the function type, indicating whether the data is based on RTP, RTCP or SIP protocol; at the same time, the header needs to be determined The destination address and source address of the device, its source address and destination address are determined according to the source IP address and destination IP address of the application layer and by looking up the table, so that the subsequent transmission process can know the source and purpose of the data;

The data content part includes the frame header, the total number of slices, the slice number, the effective data length and the first CRC check;

The tail includes a frame check and a frame tail composed of special characters.

In this embodiment, the data content is a packet of data sub-packetized by RTP (RTCP) or SIP, plus a header and a tail to form the entire service interface. The header and the tail occupy 11 bytes in total. The header is designed to use 16bit special characters as the frame header, for example: 0x5a5a. Then determine the function type with a length of 2 bits, that is, 00 (default), 01 represents the adopted RTP protocol, 10 represents the sampled RTCP protocol, and 11 represents the adopted SIP protocol. Both the destination address and the source address occupy 24 bits, and the number of each dispatching phone or server on each train or each base station is tabulated in advance, and the source and destination of the call are determined according to the address of the application layer, and through table lookup filling. The tail is mainly determined by the 7bit CRC checksum and the 6bit frame end, and the frame end also uses special characters: 0b00_0000, which represents the end of the entire frame.

S4. The vehicle-mounted base station transmits the framed signal to the ground base station through a non-TCP/IP protocol; the vehicle-mounted communication device determines whether the service interface is a dispatching phone according to the source IP, and determines the target of the service interface according to the target IP of the original VoIP application layer. ground communication equipment. Then determine whether the protocol type of the service interface is RTP or SIP according to the content of the application layer, and express it in the service interface through an identifier. The data part of the business interface is based on the application layer of the RTP/SIP protocol, and the data after corresponding unpacking and redesign.

S5. The process of ground processing is opposite to the process of sending messages in the vehicle. The VoIP service interface deframing part of the ground base station analyzes the received framing signal and parses the received frame structure. Function to determine the subsequent network layer and transport layer target IP, determine the source IP of the transport layer/network layer according to its transmission path, and determine whether its type is RTP or SIP according to the identifier; if it is the RTP protocol, directly carry out VoIP packaging, and repackage Form the VoIP telephone message; if it is the SIP protocol, the received message will be decapsulated and the decapsulated message will be packaged, and then VoIP packaging will be carried out to recompose the VoIP telephone message; the message of the ground equipment will be transmitted to The process of the IP phone in the car is the same. Finally, the connection is established according to the signaling through the overall process, and the media stream completes the voice data interaction, and then the normal call of the VoIP dispatching phone can be completed.

S6. Transmitting the message to the ground IP phone or the ground server according to the destination port or signaling requirements.

Those skilled in the art will appreciate that the embodiments described here are to help readers understand the principles of the present invention, and it should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical revelations disclosed in the present invention without departing from the essence of the present invention, and these modifications and combinations are still within the protection scope of the present invention.

Claims (5)

1. The VoIP telephone message transmission method of the high-speed maglev train-ground communication system is characterized in that communication is carried out between the high-speed maglev train and a ground control center, the high-speed maglev train or the ground control center is used as a signal sender, and the other party is used as a signal receiver; the method is characterized by comprising the following steps of:

s1, transmitting a VoIP phone message of a signal sender to communication equipment of the signal sender through a TCP/IP protocol;

s2, the communication equipment of the signal sender analyzes the VoIP phone message and distributes the IP address;

s3, processing the application layer content of the parsed VoIP phone message, which comprises the following sub-steps:

s31, determining the space size of a VoIP service interface;

s32, judging the protocol type, and processing according to the different protocol types:

if the application layer of the VoIP phone message is an RTP/RTCP media stream data packet, directly sending the data packet into a VoIP service interface framing part in a train-ground communication system for framing without unpacking;

if the application layer of the VoIP phone message is a SIP signaling data packet, firstly determining whether the length of the data packet exceeds the size of a VoIP service interface in the train-ground communication system, and unpacking the data packet according to the size of the service interface if the length of the data packet exceeds the size of the VoIP service interface; then framing the VoIP service interface framing part sent into the train-ground communication system;

s4, the base station of the signal sender transmits the signals after framing to the base station of the signal receiver through a non-TCP/IP protocol;

s5, the VoIP service interface frame de-framing part of the base station of the signal receiver analyzes the received framing signals and determines whether RTP/RTCP or SIP: if the RTP/RTCP protocol is adopted, voIP packaging is directly carried out, and VoIP phone messages are recombined; if the SIP protocol is adopted, the received message is unpacked, the unpacked message is packed, and then VoIP packaging is carried out, so that a VoIP telephone message is recombined;

s6, transmitting the message to the corresponding equipment according to the destination port or the signaling requirement.

2. The method for transmitting VoIP packets in a high-speed maglev train-ground communication system according to claim 1, wherein the VoIP packets consist of voice media streams or signaling, encapsulated by RTP/RTCP or SIP at the application layer, encapsulated by UDP at the transport layer for framing, encapsulated by IP at the network layer, encapsulated by data link layer, and encapsulated by OSI four layers to form VoIP packets.

3. The method for transmitting VoIP messages in a high-speed maglev train-ground communication system according to claim 1, wherein in step S2, the method for assigning IP addresses comprises: the IP telephone of the signal sender is transmitted to the communication equipment of the signal sender, the target IP address is the IP address of the communication equipment of the signal sender, and the source IP address is the IP telephone of the signal sender; setting a source IP address of a message based on SIP or RTP/RTCP in an application layer as an intranet address of an IP telephone of an information sender, and setting a target IP address as an intranet address of an information receiver scheduling server or an information receiver IP telephone; when in transmission, the IP address of the IP telephone or the server needs to be converted into the address of the vehicle-mounted communication equipment or the ground communication equipment, so that the conversion of the TCP/IP network transmission address and the non-TCP/IP network transmission address is completed.

4. The method for transmitting VoIP messages in a high-speed maglev train-ground communication system according to claim 1, wherein the specific implementation method of step S31 is as follows: determining the length of a VoIP service interface in the train-ground communication system based on the size of the RTP after the encapsulation of the application layer is completed; determining the length of the identifier according to the design of the frame structure; the size of the entire service interface is the sum of the length of the VoIP service interface and the length of the identifier.

5. The method for transmitting VoIP messages in a high-speed maglev train-ground communication system according to claim 1, wherein the signal after framing by the VoIP service interface framing portion in step S32 includes a header portion, a data content portion and a tail portion;

the header comprises a frame header, a function type, a destination address, a source address and the size of data content, and special characters are used as the frame header; the second part is a function type, indicating whether the data is based on RTP, RTCP or SIP protocol; meanwhile, the header also needs to determine the destination address and the source address of the equipment, and the source address and the destination address are determined according to the source IP address and the destination IP address of the application layer and by looking up a table;

the data content part comprises a frame header, a total number of slices, a slice sequence number, an effective data length and a header CRC check;

the trailer includes a frame check and a frame trailer consisting of special characters.

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