CN101237603B - A method and system for realizing IP interface between GSM wireless network and core network - Google Patents

Abstract

The embodiment of the invention discloses a method for realizing IP-based interface between the GSM wireless network and the core network. Including: A. The mobile switching center MSC server receives the call request sent by the mobile station MS and carries its own supported code pattern, the MSC server establishes a code pattern priority table according to the call request message, and sends an add endpoint message to the media gateway MGW wireless side; B. The MSC server receives the response message returned by the MGW wireless side, including the IP address and port number allocated by the MGW for the call, and sends an assignment message to the BSC. The BSC receives the assignment message, and the corresponding IP bearer is established and code pattern negotiation is performed. The embodiment of the invention also discloses a system for realizing IP-based interface between the GSM wireless network and the core network. The application of the present invention can avoid quality degradation and transmission delay caused by multiple code conversions of voice, and save TC resources and transmission resources.

Description

A method and system for realizing IP-based interface between GSM wireless network and core network

technical field

The invention relates to the GSM network interface technology, in particular to a method and system for realizing the interface between the GSM wireless network and the core network to be IP-based.

Background technique

GSM system (GSM, Global System for Mobile Communication), also known as Global System for Mobile Communication (Global Communications), is a GSM system defined by the third generation collaboration project (3GPP, Third Generation Partnership Project) standard organization, mainly composed of mobile switching subsystems (MSS, Mobile Switching Subsystem), Base Station Subsystem (BSS, Base Station Subsystem) and mobile station (MS, Mobile Station) are composed of three parts. Figure 1 is a schematic diagram of the existing GSM network system structure, as shown in Figure 1. The system includes: MSS , BSS and MS, among them, MSS completes the main switching function of GSM, manages user data and database required for mobility at the same time, manages the communication between GSM mobile users and the communication between GSM mobile users and other communication network users, including Mobile switching center (MSC, Mobile Switching Center) server and media gateway (MGW, Media GateWay), BSS includes base station controller (BSC, BaseStation Controller) and base station transceiver (BTS, Base Transceiver Station), BSC is oriented to wireless network, It is mainly responsible for wireless network, wireless resource management and the establishment, connection and release management of the wireless connection between the calling and called MS and the calling and called side BTS, and provides functions such as voice coding, code conversion and rate adaptation. The BTS completes the conversion between the BSC and the wireless channel, realizes the wireless transmission and related control functions between the BTS and the MS through the air interface.

The interface between the BTS and the BSC is the Abis interface, which uses time-division multiplexing (TDM, Time-DivisionMultiplexing) coding and rate adjustment (TRAU, Transcoder and Rate Adaptation Unit) protocol frames to transmit GSM voice and data messages, and each TRAU channel , Occupying 16K bandwidth, voice encoding formats include half rate (HR, Half Rate), full rate (FR, Full Rate) and enhanced full rate (EFR, Enhanced Full Rate) encoding. The interface between BSS and MSC server is A interface, and the A interface between BSC and MGW adopts the G.711 protocol of TDM to transmit voice and data, and the encoding method is G.711. Each call occupies a bandwidth of 64Kbps.

On the MSS side, the MSC server and MGW adopt the bearer control separation method of 3GPP R4. All signaling control parts are handled by the MSC server, and all bearer parts are handled by the MGW. The Nb interface is used between the MGW and the MGW. The method is generally Adaptive Multi-Rate (AMR, Adaptive Multi-Rate) encoding, and the Internet Protocol (IP, Internet Protocol) transmission method is used to improve transmission efficiency and save bandwidth. The Nc interface is used between the MSC server and the MGW, and the A interface is used between the MSC server and the BSC. By transmitting the BSSAP (Base Station Subsystem Application Part) signaling, it is used to carry the user's connection request, cut off the connection and other messages , sent to the BTS after being processed by the BSC, and the BSSAP message is defined by the specification GSM08.08. The Nc interface is used between the MSC server and the MSC server, and the problem of separation of call control and bearer control is solved by Bearer Independent Call Control protocol (BICC, Bearer Independent Call Control protocol), so that call control signaling can be carried on various networks, which is a direct Proposed for the application of telephone services, it can provide good transparency for implementing services in the existing circuit-switched telephone network in NGN.

It can be seen from the above that in the existing GSM network system, the BSC side needs to complete the conversion of the voice compression coding (such as HR/FR/EFR coding) on the radio side to the G.711 non-compression coding, and the MGW on the core network side needs to complete the non-compression coding The conversion of compression coding G.711 to AMR compression coding, and, on both sides of the MGW, the conversion of the bearer mode (TDM bearer on the MGW side, and IP bearer on the other side) is required. In order to achieve the above conversion, usually in the GSM The BSC of the network system is inserted into the TRAU or a code converter (TC, TranScodec), and the TC is inserted into the MGW to perform the corresponding conversion of speech coding and bearer mode, which reduces the speech quality and wastes a lot of expensive TC resources, resulting in equipment high cost. At the same time, since the A interface adopts G.711 encoding, each call needs to occupy 64K of bandwidth, resulting in a waste of long-distance transmission resources from the BSC to the MGW.

In order to save TDM transmission resources between BSC and MGW, the improved method currently proposed is to transfer the TRAU on the BSC side to the MGW side and place it together with the MGW, as shown in Figure 2, which shows the improved calling and called side Schematic diagram of the GSM network structure. The Ater interface is used between the BSC and TRAU, and voice and data are transmitted in the form of TRAU frames. Between TRAU and MGW, keep the original interface and bearer mode, because each call on the Ater interface only occupies 16K bandwidth, and 4 calls can be multiplexed into one TDM time slot, thus saving BSC and MGW Valuable long-distance transmission resources between them.

Although the above improved method solves the problem of long-distance transmission resource waste between BSC and MGW, it still needs to insert TC on both TRAU and MGW to convert the voice coding format and bearer mode, and there is also voice quality caused by multiple code conversions. Decrease and waste of TC resources.

Contents of the invention

In view of this, the main purpose of the embodiments of the present invention is to provide a method for realizing the IP-based interface between the GSM wireless network and the core network, so as to improve the voice quality.

Another object of the embodiments of the present invention is to provide a system for realizing the IP-based interface between the GSM wireless network and the core network, so as to improve the voice quality.

In order to achieve the above purpose, the technical solutions of the embodiments of the present invention are specifically implemented as follows:

A method for realizing the IP-based interface between the GSM wireless network and the core network, the method comprising the following steps:

A. The mobile switching center MSC server receives the call request message carrying its own supported code pattern sent by the mobile station MS, and the MSC server establishes a code pattern priority table according to the call request message, and sends an add endpoint message to the media gateway MGW wireless side ;

B. The MSC server receives the response message returned by the MGW wireless side that includes the IP address and port number assigned by the MGW for the call, and sends an assignment message to the BSC, the assignment message carrying the IP assigned by the MGW for the call address and port number and the server pattern priority table, the BSC receives the assignment message, the corresponding IP bearer is established and pattern negotiation is performed;

Wherein, after step B, it further includes: the BSC modifying code pattern,

When it is determined that the pattern converter TC is set on the BSC side, the BSC modifies the selected pattern and reports it to the MSC server, and the MSC server initiates pattern renegotiation; or, the TC is set on the MGW side, When the BSC modifies or switches the code pattern, it initiates a code pattern change request, and after the MSC server modifies the code pattern of the corresponding endpoint of the MGW, it sends a change response code pattern information to the BSC, and the BSC receives the code pattern change information , to modify the pattern.

A system for realizing the IP-based interface between the GSM wireless network and the core network, including a BSC, an MSC server, and an MGW, and the MSC server is further used to realize an IP-based interface with the BSC and the MGW, wherein,

The MSC server is used for signaling control, receives a call request message carrying a code pattern supported by the MS itself, establishes a code pattern priority table, sends an add endpoint message to the MGW wireless side, and receives the message returned by the MGW wireless side containing the MGW: A response message of the assigned IP address and port number for the call, and sending an assignment message to the BSC, where the assignment message carries the IP address and port number assigned by the MGW for the call and the pattern priority list;

The MGW receives the add endpoint message sent by the MSC server, and returns to the MSC server a response message containing the IP address and port number allocated by the MGW for the call;

The BSC transparently transmits the call request message to the MSC server, receives the assignment message sent by the MSC server, and establishes IP bearer and pattern negotiation corresponding to the MGW according to the received assignment message ;

Wherein, when the pattern converter TC is set on the BSC side, the BSC modifies the selected pattern and reports it to the MSC server, and the MSC server initiates pattern renegotiation; or, the TC is set on the MGW side , when the BSC modifies or switches the code pattern, it initiates a code pattern change request, and after the MSC server modifies the code pattern of the corresponding endpoint of the MGW, it sends a change response code pattern information to the BSC, and the BSC receives the change pattern information, modify code pattern.

It can be seen from the above technical solutions that the method and system for realizing the IP-based interface between the GSM wireless network and the core network in the embodiment of the present invention adopts IP bearer on the A interface between the BSC and the MGW, and directly transmits HR/FR/EFR compressed voice on the A interface Encoding can effectively reduce the waste of TC resources, and realize the full-path codec-free operation (TrFO, Transcoder-FreeOperation) or half-way TrFO of the call path between the BSC on the calling side and the called side. Further, by adopting IP bearer on the Ater interface and/or the Abis interface to directly transmit HR/FR/EFR compressed voice coding, the waste of TC resources is reduced, and TrFO is realized in the whole or half way of the network. At the same time, the waste of long-distance transmission resources can be effectively reduced.

Description of drawings

FIG. 1 is a schematic structural diagram of an existing GSM network system.

Fig. 2 is a schematic diagram of the improved GSM network structure on the calling and called sides.

FIG. 3 is a schematic diagram of the system structure of the interface between the GSM wireless network and the core network in an IP-based embodiment of the present invention.

FIG. 4 is a schematic structural diagram of a system for implementing IP-based A interface between the GSM wireless network and the core network in Embodiment 1 of the present invention.

FIG. 5 is a schematic diagram of the layered structure of the protocol stack of the signaling plane and bearer plane of the system A interface shown in FIG. 4 according to an embodiment of the present invention.

FIG. 6 is a schematic diagram of a system structure for implementing IP-based A interface between the GSM wireless network and the core network in Embodiment 2 of the present invention.

FIG. 7 is a schematic structural diagram of a system for implementing an IP-based Ater interface between a GSM wireless network and a core network in Embodiment 3 of the present invention.

FIG. 8 is a schematic structural diagram of a system for implementing IP between a GSM wireless network and a core network in Embodiment 4 of the present invention.

FIG. 9 is a schematic structural diagram of a system for implementing IP between a GSM wireless network and a core network in Embodiment 5 of the present invention.

FIG. 10 is a schematic diagram of a signaling processing flow in which the TC is set on the BSC side according to an embodiment of the present invention.

FIG. 11 is a schematic diagram of a signaling processing flow in which the TC is set on the MGW side according to an embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and examples.

The embodiment of the present invention can effectively reduce the waste of TC resources by realizing the IP-based A interface between the BSC and the MGW, and directly transmit compressed voice codes such as HR/FR/EFR on the wireless side, and realize TrFO with full or half-way voice channels .

In order to realize the idea above, the present invention proposes a system for realizing the interface between the GSM wireless network and the core network to be IP-based. The IP-based interface between the GSM wireless network and the core network includes establishing an IP bearer and implementing code pattern negotiation: media services are transmitted over IP, signaling is transmitted over IP, and at the same time, the problem of voice quality degradation caused by the introduction of coding TC is solved. FIG. 3 is a schematic diagram of the system structure of the interface between the GSM wireless network and the core network in an IP-based embodiment of the present invention. Referring to Fig. 3, the system includes: MS, BTS, BSC, MSC server and MGW.

Among them, the MS is used to send a call request message carrying its own supported code pattern to the BSC, and receive the call processing message returned by the MSC server;

The BTS is used to transparently transmit the call request message sent by the MS and the call processing message sent by the MSC server;

BSC is used to establish IP bearer with MGW and implement code conversion, receive call request message sent by MS, transparently transmit to MSC server, receive call processing message sent by MSC server, and forward it; receive assignment message sent by MSC server , if it is determined that the interface between the BSC and the MGW is the A interface, obtain the MGW wireless side IP address and port number, allocate its own IP address and port number for the call, and establish an IP bearer;

If it is determined that the interface between the BSC and the MGW is the Ater interface, use the in-band signaling method on the bearer plane (the in-band signaling between the BSC and the MGW can be established in advance), and establish the Ater interface channel between the BSC and the MGW through TRAU signaling negotiation, Establish IP bearer; Or, simulate the Ater interface between BSC and MGW as A interface, BSC receives the assignment message, obtains the IP address and port number of the wireless side of MGW, assigns the IP address and port number of its own Ater interface side for the call, and establishes IP bearer;

Receive the assignment message sent by the MSC server, select the code pattern according to the code pattern priority table information or its own strategy, and feed back the code pattern selected by the BSC to the MSC server through the assignment response message; if the selected code pattern and the code pattern priority table The code pattern with the highest priority among them is the same, realizing the TrFO of this section, and completing the transparent transmission of the media stream; otherwise, receiving the code pattern modification message from the MSC server, and completing the code pattern between the code pattern selected by the BSC and the code pattern required by the MSC server convert.

The MSC server adopts the bearer control separation method of 3GPP R4, which is used to process the signaling control part, and transmits the IP bearer-related information such as IP address and port number through the extended BSSAP signaling, receives the call request message sent by the MS, and extracts the code in it type, take the intersection with the code types supported by itself, establish a code type priority table, and send a call processing message to the MS; send an add endpoint message to the MGW wireless side, and receive a response message returned by the MGW; send or receive a code type priority table information, complete the code type negotiation to implement TrFO; send an assignment message to the BSC, receive the assignment response message containing the selected code type sent by the BSC, and send it to the MGW; if the code type conversion function is completed at the BSC, it is necessary At this time, a pattern modification message can be sent to the BSC or MGW.

MGW is used to establish an IP bearer with the BSC and implement code conversion, receive the add endpoint message sent by the MSC server, send a response message including the IP address and port number allocated for the call to the MSC server, and receive the bearer and message sent by the MSC server Change the pattern message, obtain the IP address and port number assigned by the BSC for the call, and establish an IP bearer; and modify the pattern of the corresponding endpoint according to the message instruction.

In the system shown in Figure 3, the MGW may or may not be the same MGW; when the MGW is not the same MGW, the establishment of an IP bearer connection on the A interface between the BSC and the MGW on the other side is similar to the system shown in Figure 3. I won't repeat them here.

Moreover, the MSC servers may or may not be the same MSC server; when the MSC servers are not the same MSC server, the Nc interface is used between the MSC server and the MSC server, and the Nb interface is used between the MGW and the MGW. The MSC server sends initialization (IAM) information to the MSC server on the called side, and the MSC server on the called side returns IP bearer related information to establish an IP bearer between the Nb interface side of the calling side MGW and the Nb interface side of the called side MGW. You can refer to BICC and IP Bearer Control Protocol (IPBCP, IP Bearer Control Protocol). Establishing an IP bearer connection between the MGW wireless side and the BSC on the calling and called sides is similar to establishing an IP bearer connection between the calling or called side MGW wireless side and the BSC. It is necessary to perform code pattern negotiation to realize the establishment of TrFO and IP Bearer establishment. The difference is that both sides are carried by IP, and the TrFO negotiation of all channels is required. However, only one side is IP bearer, and only a half-way TrFO can establish a session.

In Figure 3, the assignment response message should include information such as the code pattern selected by the BSC, the IP address and port number allocated by the BSC for the call.

Based on the system shown in FIG. 3 , seven embodiments are given below to describe in detail the implementation of the present invention in the process of implementing the IP bearer of the GSM network interface. In the system structural diagrams of the seven embodiments of the present invention, the dotted line shows signaling information, and the solid line shows bearer information.

Embodiment one:

FIG. 4 is a schematic structural diagram of a system for implementing IP-based A interface between the GSM wireless network and the core network in Embodiment 1 of the present invention. In this embodiment, the BTS, BSC, MSC server and MGW included on the calling side are taken as an example. When the code conversion TC is set on the BSC side, the A interface implements IP bearer for description. The IP-based implementation of the A interface on the called side is similar to that on the calling side, and will not be repeated here. Referring to Fig. 4, the interface between the BTS and the BSC is the Abis interface, the interface between the BSC and the MGW is the A interface, and the interface between the MGW and the MSC server is the Mc interface.

The A interface control plane adopts the signaling transmission (Sigtran, Signal Transport) protocol specified in the standard to carry the bearer. In this embodiment, in order to realize the function of the A interface IP bearer, it is necessary to expand the management function of the A interface control plane voice IP mode bearer resource, and Extend the necessary BSSAP information, for example, the extended BSSAP message has the ability to transmit IP bearer related information such as IP address and port number.

The MS initiates a call and carries the supported code pattern information, which is transparently transmitted by the BTS. The BSC receives the call request message and sends it to the MSC server through the BSSAP signaling. The MSC server obtains the code pattern supported by the calling party and intersects with the code pattern supported by itself , form a code pattern priority table, send an add endpoint message to the MGW wireless side through the Mc interface, the MGW receives the add endpoint message, allocate an IP address and port number for the call, and return the IP address and port allocated by the MGW to the MSC server through the Mc interface The MSC server receives the response message from the MGW, and the MSC server sends to the BSC an assignment message carrying the IP address, port number and MSC server code type priority list allocated by the MGW for this call through the BSSAP signaling, and the BSC receives the assignment message. message, assigning the own IP address and port number for the call, and initiating the establishment of an IP bearer. At the same time, the BSC selects the code pattern according to the code pattern priority table information or its own strategy, and returns to the MSC server including the code pattern selected by the BSC, and the BSC as the call Assignment response message for assigned IP address and port number. The MSC server receives the assignment response message, obtains the IP address and port number assigned by the BSC for the call, and sends it to the MGW wireless end point. The MGW wireless end point obtains the IP address and port number assigned by the BSC for the call, and then establishes a connection with the BSC. At the same time, the MSC server receives the assignment response message, obtains the BSC selection code pattern from it, puts the selection code pattern of the BSC on the calling side into the first position of the code pattern priority table, and then transmits it to the MSC server on the called side. In the process of backward transmission, indicate or modify the code pattern of the MGW-related endpoints in the path to be the optimal code pattern, and the MSC server at the called side sends the acquired code pattern priority table to the BSC at the called side. If the BSC at the called side supports the The BSC on the calling side selects the code pattern and selects the optimal code pattern, then realizes TrFO in all channels of the conversation; otherwise, the BSC on the called side feeds back the selected code pattern to the MSC server on the called side through an assignment response message, and the called The MSC server on the calling side sends the modified code pattern to the BSC on the called side or the endpoint on the wireless side of the MGW on the called side, or sends the code pattern change to the BSC on the calling side or the endpoint on the Nb side of the MGW on the calling side through the MSC server on the calling side command, after the called side BSC or the called side MGW wireless side endpoint or the calling side BSC or the calling side MGW Nb side endpoint receives the code pattern change command, complete the selection of the calling code pattern and the called selection pattern conversion between.

If there is a TDM bearer between the MGW on the called side and the BSC on the called side, if the BSC on the called side supports the code pattern selected by the BSC on the calling side and selects the optimal code pattern, the MSC server on the called side sends a message to the called side The MGW sends a code pattern modification message to complete the bearer format conversion from IP to TDM on the MGW at the called side, and implement TrFO at the called side; otherwise, if the BSC at the called side does not support the code pattern selected by the BSC at the calling side, the called The MSC server on the calling side sends a code pattern modification message to the MGW on the called side, and the code pattern conversion and bearer format conversion from IP to TDM are simultaneously completed on the called side MGW. If the bearer between the calling side MGW and the calling side BSC is TDM, similar to this, code conversion and IP to TDM bearer format conversion are completed on the calling side MGW at the same time, but the code type negotiation between MSC servers The process is different. The MSC server on the calling side indicates in the message to the MSC server on the called side that it needs to return the code pattern selected by the BSC on the called side, so the MSC server on the called side passes the code pattern selected by the BSC on the called side to the calling side. The MSC server on the calling side modifies the code pattern of the MGW-related endpoints in the path to the code pattern selected by the called BSC, and then the MSC server on the calling side sends the code pattern selected by the BSC on the calling side to the MGW on the calling side Nb interface endpoint. In this way, it is ensured that all the code patterns of the IP bearer parts are consistent, and only the TDM-to-IP conversion point is inserted into the TC.

Fig. 5 is a schematic diagram of the layered structure of the protocol stack of the system A interface signaling plane and bearer plane shown in Fig. 4 according to the embodiment of the present invention. Referring to Fig. 5, the bottom layer of the A interface signaling plane protocol stack is Media Access Control (MAC, Media Access Control) layer, if the physical layer is not 100M or Gigabit Ethernet, but POS (Packet Over SONET/SDH/GE, Gigabit Ethernet) or IP OVER E1, the bottom layer is Point-to-Point Protocol (PPP, Point-to -Point Protocol) layer, upwards in turn, the second layer IP layer, the third layer Stream Control Transmission Protocol (SCTP, Stream Control Transmission Protocol) layer, the fourth layer M3 User Adaptation (M3UA, M3User application) layer, the fifth layer client Terminal Control Protocol (SCCP, Skinny Client Control Protocol) layer, the top layer is the BSSAP layer, and signaling is transmitted between each layer in turn. In this embodiment, it is necessary to carry out the management functions of the BSSAP layer BSSAP protocol and voice IP mode bearer resources Corresponding extensions.

If the IP interface is 100M or Gigabit Ethernet, the bottom layer of the protocol stack on the bearer plane of the A interface is the MAC layer. If it is a POS interface or IP OVER E1 interface, the lowest layer is the PPP layer, and the second layer is the IP layer. The third layer is the User Datagram Protocol (UDP, User Data Protocol) layer, and the fourth layer is the Real-time Transmission Protocol (RTP, Real-time Transmission Protocol) layer, and the bearer information is transmitted between each layer in sequence.

In practical applications, the original TDM bearer of the Abis interface between the BTS and the BSC can also be used as an IP bearer, which can further reduce the time delay caused by the conversion of the network bearer mode and improve the utilization rate of transmission resources.

And, among the embodiment, the MSC server can be the same MSC server, also can be different MSC servers, when the MSC server is not the same MSC server, after one side MSC server obtains the code pattern selected by the corresponding BSC, and the other side MSC server Carry out code negotiation. If both sides cannot obtain a consistent code pattern, only insert a TC on the BSC on one side for code conversion.

It can be seen from the foregoing embodiments that the present invention establishes an IP bearer on the A interface between the BSC and the MGW through the MSC server, which effectively reduces the conversion of the voice encoding format, and even does not need to perform the conversion of the voice encoding format, reducing the voice transmission delay , which improves the quality of voice transmission and saves TC resources. At the same time, due to the adoption of IP bearer mode, it saves precious long-distance transmission resources between BSC and MGW. For example, in the original GSM network system, up to four TCs are required between the BSCs on the calling and called sides to convert different code patterns and bearer modes. There is no need or only one TC to convert the code type and the bearer mode. If the Abis interface is also adopted in the IP bearer mode, the entire call path between the calling and called MSs does not need to be converted in the bearer mode.

In the first embodiment above, the TC is set on the BSC side. In practical applications, the TC may also be set on the MGW side, and the A interface implements IP bearer. As for the TC is set on the MGW side, the TRAU frame can be terminated on the BSC side or on the MGW side. The specific implementation methods will be described through Embodiment 2 and Embodiment 3 respectively below.

Embodiment two:

FIG. 6 is a schematic diagram of a system structure for implementing IP-based A interface between the GSM wireless network and the core network in Embodiment 2 of the present invention. This embodiment takes the BTS, BSC, MSC server and MGW included in the calling side as an example, and the MSC server and MGW on the calling and called side can be the same MSC server and MGW, the TC is set on the MGW side, and the TRAU frame is terminated on the BSC side. That is, there is an A interface between the BSC and the MGW, and the A interface implements IP bearer.

The control plane of the A interface is carried by the standard Sigtran protocol. It is necessary to expand the resource management function of the IP voice bearer mode and expand the BSSAP information so that the expanded BSSAP information has the ability to transmit IP bearer-related information such as IP address and port number; The service plane of the A interface adopts IP bearer.

The system A interface shown in Figure 6 establishes an IP bearer connection similar to that in Figure 4, the difference is that code conversion is required to be completed on the MGW, not on the BSC; after the BSC selects the code, the BSC sends the BSSAP signaling to the The assignment response message of the MSC server carries the pattern information selected by the BSC, and the MSC server is responsible for pattern negotiation; if the BSC on the called side supports the pattern selected by the BSC on the calling side and selects the optimal Otherwise, the called side MSC server receives the assignment response message from the called side BSC, and the called side MSC server sends the code pattern selected by the called side BSC to the called side through the code pattern change command of the Mc interface. The calling side MGW wireless side endpoint; or the called side MSC server forwards the code pattern selected by the called side BSC to the calling side MSC server, and the calling side MSC server passes the code pattern change command to the called side BSC The code pattern is selected and sent to the Nb endpoint of the MGW on the calling side. After receiving the command, the MGW compares whether the code patterns of the endpoints on both sides of the call are consistent. If not, insert a TC. The protocol stack hierarchy structure of the signaling plane and bearer plane of the A/Ater interface is also the same as that in FIG. 5 .

If only one side of the calling and called A interface is IP and the other side is TDM, the code conversion is always on the MGW whose A interface is TDM. The specific implementation is similar to the first embodiment.

Similarly, the original TDM bearer of the Abis interface between the BTS and the BSC can also be used as an IP bearer to further reduce the time delay caused by the conversion of the network bearer mode and improve the utilization rate of transmission resources.

Embodiment three:

FIG. 7 is a schematic structural diagram of a system for implementing an IP-based Ater interface between a GSM wireless network and a core network in Embodiment 3 of the present invention. The difference from Figure 6 is that the TRAU frame transmitted by the system shown in Figure 7 is terminated at the MGW side, that is, the interface between the BSC and the MGW is equivalent to the Ater interface in the original GSM system.

Since the TRAU frame is terminated at the MGW side, the interface between the BSC and the MGW is an Ater interface. However, the A interface in the original GSM system is shrunk to the inside of the MGW. The A interface signaling is carried by Sigtran, and the Ater interface signaling is carried by IP. The signaling between the BSC and the MSC server can be directly communicated through IP, or can be forwarded through IP through the MGW; the MSC server controls the circuit establishment of the IP bearer plane of the Ater interface, and there are two methods:

1). The MSC server does not control the establishment of the circuit on the IP bearer plane of the Ater interface: using the in-band signaling method on the bearer plane, the MGW and the BSC negotiate to establish the Ater interface channel through TRAU signaling. The MGW obtains the voice code pattern of the BSC by analyzing the TRAU frame of the Ater interface and judges whether the code patterns on both sides are consistent. If not, the MGW inserts the TC to convert the voice code.

2). The MSC server controls the circuit establishment of the Ater interface IP bearer plane: expands the resource management function of the IP voice bearer mode and the relevant information of the BSSAP protocol IP bearer, and simulates the Ater interface into the A interface in the original system. The circuit establishment of the IP bearer plane of the Ater interface is similar to that shown in Figure 4. The difference is that after the MGW and the BSC establish the IP bearer, the MSC server obtains the selected code pattern of the BSC and sends it to the endpoint corresponding to the BSC side of the MGW, thus ensuring The code pattern on the BSC side is consistent with the code pattern on the MGW corresponding to the end point on the BSC side. The MGW then compares whether the code patterns on both sides are consistent. If they are consistent, the TrFO of the session is implemented; otherwise, a TC is inserted for code conversion.

Compared with FIG. 5 , the A/Ater interface bearer plane protocol stack of the system shown in FIG. 7 adds a fifth layer, the TRAU layer.

It can be seen from the above embodiments that the BSC does not need to perform TRAU frame processing, nor does it need to perform voice coding conversion, but only transparently transmit the TRAU frames.

In the above embodiments 1, 2, and 3, the transmitted TRAU frames are terminated by the BSC or MGW. Further, the TRAU frames can also be canceled in the whole network, that is, the voice frames based on IP bearer are directly output at the BTS.

The specific implementations thereof will be described below through Embodiment 4 and Embodiment 5 respectively.

Embodiment four:

FIG. 8 is a schematic structural diagram of a system for implementing IP between a GSM wireless network and a core network in Embodiment 4 of the present invention. As shown in Figure 8, the establishment method of the IP bearer connection between the BSC and the MGW is similar to that shown in Figure 4. It is necessary to extend the BSSAP protocol to transmit information related to the IP bearer such as the IP address and port number. The code pattern of the BSC on the calling side near the MGW is inconsistent with that on the side of the called BSC on the called side. A TC is inserted on the MGW side for code conversion. After the IP bearer connection is established, the BTS outputs IP-based voice frames, for example, IP/UDP /RTP/VOICE message, the BSC receives the voice frame and forwards it to the MGW.

In the above embodiment, since there is no need to convert the bearer mode, the transmission delay is reduced and the quality of voice transmission is improved.

Moreover, the BSC in the above embodiment may not participate in the forwarding of voice frames after the IP bearer connection is established, and the BTS and the MGW directly interact with the voice frames, further reducing the time delay caused by forwarding voice frames on the BSC and saving the BSC processing capacity.

Embodiment five:

FIG. 9 is a schematic structural diagram of a system for implementing IP between a GSM wireless network and a core network in Embodiment 5 of the present invention. The BSC performs signaling transmission control (LAPD, Link Access Procedure on the D channel) through the public channel D and the BSSAP performs signaling interactions with the BTS and the MSC server respectively, and does not participate in the forwarding of voice frames on the bearer plane. In this embodiment, in order to establish For the bearer connection between the BTS and the MGW, the IP bearer-related information needs to be extended for the BSSAP protocol and the LAPD protocol. The establishment of the bearer connection is similar to that in Figure 4. The difference is that the BSC receives the assignment message and obtains the IP bearer information and then sends it to the BTS through LAPD signaling. The IP address and port number of the local BTS, and the IP bearer information (IP address and port number) allocated by the BTS for the call are reported to the BSC, and the BSC sends the IP address and port number allocated by the BTS to the MSC server through an assignment response message. The MSC server then instructs the MGW. Both the BTS and the MGW know the IP address and port number of the opposite end, so they can establish the bearer. The pattern adopted by the BTS is completely controlled by the BSC, that is, the selected pattern carried by the BSC in the assignment response message. The MSC server sends the BTS code pattern selected by the wireless side to the MGW to ensure that the code pattern of the endpoint of the MGW close to the wireless side is always consistent with the code pattern used by the BTS. The MSC server conducts code pattern negotiation on all channels of the session, and if the negotiation is consistent, TrFO is realized. If not consistent, select the MGW at the calling side or the MGW at the called side to insert into the TC for code conversion.

In practical applications, the MS may also switch between different BTSs. The BSC sends a notification to the MSC server, notifying the MSC server of the IP address and port number information of the new BTS. The MSC server receives the notification information and issues the bearer information to the MGW. Notification of modification and completion of bearer switching.

Embodiment 6 and Embodiment 7 are given again below to illustrate the signaling control flow of the present invention.

Embodiment six:

FIG. 10 is a schematic diagram of a signaling processing flow in which the TC is set on the BSC side according to an embodiment of the present invention. In this embodiment, the TC is set at the BSC, and the BSC completes the voice coding conversion, and establishes an IP bearer connection at the calling party. Referring to FIG. 10, the process includes:

Step 101, the MS initiates a call, and forwards it to the MSC server via the BTS and the BSC;

Step 102, the MSC server returns a call request message being processed to the MS;

Step 103, the MSC server sends an add endpoint message to the MGW;

In steps 101-103, the call request message received by the MSC server carries code patterns supported by the MS itself, and intersects with the code patterns supported by the MSC server to form a code pattern priority table, and adds an endpoint on the MGW wireless side through the Mc interface;

Step 104, the MGW wireless side receives the add endpoint message, and returns a response message;

In this step, the MGW wireless side receives the add endpoint message, assigns an IP address and port number for the call, and the response message includes the IP address and port number assigned by the MGW for this call;

Step 105, the MSC server receives the response message, and sends an assignment message to the BSC, carrying the IP address, port number and MSC server pattern priority list allocated by the MGW for this call;

Step 106, the BSC receives the assignment message, and returns an assignment response message carrying the assigned IP bearer information and the selected pattern;

In this step, the BSC receives the response message, obtains the IP address and port number allocated by the MGW for the call, and allocates its own IP address and port number for the call, and at the same time initiates the establishment of an IP bearer. The BSC selects the code pattern used by itself, and can The pattern is selected according to the priority order in the pattern priority table provided by the MSC server, or the pattern can be selected according to its own strategy, and the BSC returns to the MSC server an instruction including the selected pattern of the BSC and the IP address and port number allocated by the BSC for the call. Match the response message. The MSC server initiates code pattern negotiation for all-session calls, and the steps are as follows:

The BSC selects the code pattern and sends the code pattern information to the MSC server. The MSC server forwards the code pattern selected by the BSC and puts the code pattern selected by the BSC on the calling side in the first position of the code pattern priority table and sends it to the called side. BSC; if the BSC at the called side supports and selects the code pattern selected by the BSC at the calling side, TrFO of the full-channel approach is implemented; otherwise, the code pattern selected by the BSC at the called side is inconsistent with the priority order in the code pattern priority table of the MSC server , the code conversion needs to be completed on the BSC at the called side. For example, the calling party assigns FR/EFR, the BSC on the calling side selects FR, the MSC server on the calling side forwards the FR, the MS on the called side supports HR/FR/EFR, and the MSC server on the called side sends the FR/HR/EFR, if the BSC on the called side selects FR, the code pattern selected by the BSC on the calling side is consistent with the preferred code pattern recommended by the MSC server on the calling side, and there is no need to insert a TC for code pattern conversion, and the full-channel approach can be realized TrFO; if the BSC on the called side selects HR, it will feed back to the MSC server on the called side through an assignment response message. After analyzing and judging, the MSC server on the called side finds that TrFO cannot be implemented in this section, it will issue a modification code to the BSC on the called side type message, so that the BSC on the called side completes the code type conversion between FR and HR.

In practical applications, after the IP bearer connection is established, if the BSC needs to modify the selected code pattern due to reasons such as wireless network capacity, the BSC will modify the selected code pattern by itself and report it to the MSC server, and the MSC server will discover the code pattern. type renegotiation. The process is similar to the code pattern negotiation of call establishment, except that the MSC server on the called side may transfer the preferred code pattern to the MSC server on the calling side. After the BSC pattern of one side changes, the TrFO of the whole session may be broken; however, it is also possible to make the original non-TrFO call negotiated as a TrFO call through renegotiation.

Embodiment seven:

Fig. 11 is a schematic diagram of a signaling processing flow in which the TC is set on the MGW side according to an embodiment of the present invention. Referring to Fig. 11 , the flow includes:

Step 111, the MS initiates a call, and forwards it to the MSC server via the BTS and the BSC;

Step 112, the MSC server returns a call request message being processed to the MS;

Step 113, the MSC server sends an add endpoint message to the MGW wireless side;

In steps 111-113, the call request message received by the MSC server carries the code patterns supported by the MS itself, and intersects with the code patterns supported by the MSC server to form a code pattern priority table, and adds an endpoint on the MGW wireless side through the Mc interface

Step 114, the MGW wireless side receives the add endpoint message, and returns a response message;

In this step, in this step, the MGW wireless side receives the add endpoint message, and allocates an IP address and port number for the call, and the response message includes the IP address and port number allocated by the MGW for this call.

Step 115, the MSC server receives the response message, and sends an assignment message to the BSC, carrying the IP address, port number and MSC server pattern priority list allocated by the MGW for this call;

Step 116, the BSC receives the assignment message and returns an assignment response message;

In this step, the BSC receives the assignment message, obtains the IP address and port number assigned by the MGW for the call, assigns its own IP address and port number for the call, and establishes an IP bearer. The BSC selects the code pattern used by itself, which can be based on The pattern priority table provided by the MSC server selects the pattern in priority order, or selects the pattern according to its own strategy, and sends an assignment response including the selected pattern of the BSC and the IP address and port number assigned by the BSC to the MSC server. information.

Step 117, the MSC server receives the assignment response message, and sends the IP bearer information and code change message contained in it to the MGW wireless side;

In step 118, the MGW wireless side endpoint receives the IP bearer information and the code change message, performs corresponding processing, and returns a response message.

In this step, the MGW obtains the IP bearer information on the wireless side designated by the BSC, and the MGW can initiate bearer establishment to the BSC/BTS on the wireless side. The endpoint on the MGW wireless side receives the change code pattern message, modifies the code pattern of the endpoint according to the code pattern indicated therein, and returns a response message to the MSC server.

The signaling process of the called party is similar to that of the calling party. The code pattern of the end point on the side of the BSC near the wireless network is guaranteed to be consistent with the code pattern of the end point of the MGW on the side of the BSC through the code type change message. The MGW only needs to compare the Nb interface with the Whether the code patterns of the A/Ater interface are consistent, if the code patterns are not consistent, insert a code pattern conversion TC; otherwise, do not insert a code pattern conversion TC, and realize the TrFO of the full or half path of the voice channel.

After the IP bearer connection is established, the BSC initiates a code change request when modifying or switching the code type according to the needs. After the MSC server has modified all the code types of the corresponding endpoints of the MGW, it sends a change response code type information to the BSC, and the BSC receives Change code pattern message, modify code pattern.

The present invention adopts IP transmission between BSS and MSS, utilizes the packet multiplexing feature of IP to achieve the purpose of saving transmission. In practical applications, real-time compression protocol (CRTP, Compressed Real-Time Protocol), real-time protocol multiplexing Use (RTP Multiplex), point-to-point protocol multiplexing (PPPMUX, Point to Point Protocol Multiplex), IP header multiplexing and other related technologies to further improve transmission efficiency. The preferred embodiments above are used to further describe the purpose, technical solutions and advantages of the present invention in detail. It should be understood that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Within the spirit and principles of the present invention, any modifications, equivalent replacements, improvements, etc., shall be included within the protection scope of the present invention.

Claims (16)

1. a method for realizing the interface IP between GSM wireless network and core network, is characterized in that, the method comprises: A. The mobile switching center MSC server receives the call request message carrying its own supported code pattern sent by the mobile station MS, and the MSC server establishes a code pattern priority table according to the call request message, and sends an add endpoint message to the media gateway MGW wireless side ; B. The MSC server receives the response message returned by the MGW wireless side that includes the IP address and port number assigned by the MGW for the call, and sends an assignment message to the BSC, the assignment message carrying the IP assigned by the MGW for the call address and port number and the server pattern priority table, the BSC receives the assignment message, the corresponding IP bearer is established and pattern negotiation is performed; Wherein, after step B, it further includes: the BSC modifying code pattern, When it is determined that the pattern converter TC is set on the BSC side, the BSC modifies the selected pattern and reports it to the MSC server, and the MSC server initiates pattern renegotiation; or, the TC is set on the MGW side, When the BSC modifies or switches the code pattern, it initiates a code pattern change request, and after the MSC server modifies the code pattern of the corresponding endpoint of the MGW, it sends a change response code pattern information to the BSC, and the BSC receives the code pattern change information , to modify the pattern. 2. The method according to claim 1, wherein the mobile switching center MSC server in step A receives the call request message carrying the self-support code pattern sent by the mobile station MS comprising: the MS initiates a call request message carrying self-support The coded call request message is transmitted to the MSC server through the transparent transmission of the base transceiver station BTS and the BSC. 3. method according to claim 1, it is characterized in that, the described MSC server of step A sets up code pattern prioritization list according to call request message and comprises: described MSC server receives described call request message, and the code pattern that self supports and The received code patterns supported by the MS are intersected, and the code pattern priority table is established. 4. The method according to claim 1, wherein the step B, wherein the MSC server receives the response message returned by the MGW and includes the IP address and port number assigned by the MGW wireless side for the call, comprises: the MGW wireless side receives the Add an endpoint message, assign an IP address and port number for the call, and return to the MSC server a response message carrying the MGW wireless side to assign an IP address and port number for the call; the assignment message sent to the BSC includes the MGW wireless side The IP address and port number allocated for the call and the pattern priority table information. 5. The method according to claim 1, wherein the BSC in step B receives the assignment message, and the establishment of the corresponding IP bearer comprises: The BSC receives the assignment message, if it is determined that the interface between the BSC and the MGW is an A interface, obtains the IP address and port number assigned by the MGW for the call, assigns the IP address and port number to the call, and initiates IP bearer establishment, sending an assignment response message including the IP address and port number allocated by the BSC for the call to the MSC server, and the MSC server sends the received assignment response message to the MGW wireless side An endpoint, the MGW wireless side endpoint obtains the IP address and port number allocated by the BSC for the call, and establishes the IP bearer with the BSC; or The BSC receives the assignment message, and if it is determined that the interface between the BSC and the MGW includes an Ater interface, establishes an Ater interface between the BSC and the MGW through TRAU signaling negotiation using in-band signaling on the bearer plane. An interface channel, establishing the IP bearer; or, simulating the Ater interface between the BSC and the MGW as an A interface, the BSC receives the assignment message, and obtains the IP address and port number allocated by the MGW for the call , assigning the IP address and port number on the Ater interface side of the call, initiating the establishment of an IP bearer, and sending an assignment response message including the IP address and port number assigned by the BSC to the MSC server to the MSC server, and the MSC The server sends the assignment response message to the MGW wireless side, and the MGW wireless side acquires the IP address and port number allocated by the BSC for the call, and establishes the IP bearer. 6. The method according to claim 1, wherein when the interface between the MGW and the BSC does not include an Ater interface, the BSC receiving the assignment message in step B, and performing pattern negotiation includes: receiving the assignment message by the BSC After configuring the message, select the code type according to the priority code type in the code type priority table, or select the code type according to the BSC's own strategy, and return the code type selected by the BSC to the MSC server through the assignment response message, and the MSC server receives the assignment response message , to perform code type negotiation, if the negotiation is consistent, the code type negotiation is successful, otherwise, the corresponding code type is converted according to the code type negotiation result. 7. The method according to claim 1, wherein when the interface between the MGW and the BSC includes an Ater interface, the BSC receiving the assignment message in step B, and performing code pattern negotiation include: The BSC receives the assignment message, selects the code pattern, and adopts the in-band signaling method on the bearer plane. The MGW obtains the voice code pattern of the BSC by analyzing the TRAU frame of the Ater interface and judges whether the code patterns on both sides are consistent. If not, insert the TC perform a speech coding conversion; or, The Ater interface between the BSC and MGW is simulated as an A interface. The BSC receives the assignment message, selects the code pattern, and returns the assignment response information including the code pattern selected by the BSC to the MSC server. After the MSC server obtains the code pattern selected by the BSC, it sends The MGW corresponds to the endpoint on the BSC side, and the MGW compares whether the code patterns of the endpoints on both sides of the MGW are consistent. If they are consistent, implement the TrFO of the session, otherwise, insert a TC for code conversion. 8. The method according to claim 6, characterized in that, when an IP bearer is used between the calling side MGW and the calling side BSC and between the called side MGW and the called side BSC, the pattern negotiation is performed, If the negotiation is consistent, the code type negotiation is successful; otherwise, the steps of converting the corresponding code type according to the code type negotiation result include: If it is determined that the interface between the MGW and the BSC is the A interface, the MSC server receives the assignment response message to obtain the selected code pattern of the BSC, and puts the selected code pattern of the BSC on the calling side into the first position of the code pattern priority table and transmits it backward To the MSC server on the called side, the MSC server on the called side sends the acquired pattern priority list to the BSC on the called side; If the BSC on the called side supports the code pattern selected by the BSC on the calling side and selects the optimal pattern, the code pattern negotiation is successful; otherwise, the BSC on the called side feeds back the selected code pattern to the MSC on the called side through an assignment response message Server, the MSC server on the called side sends the modified code pattern to the BSC on the called side or the endpoint on the wireless side of the MGW on the called side, or sends the code to the endpoint on the Nb side of the BSC on the calling side or the MGW on the calling side through the MSC server on the calling side Type change command, after the called side BSC or the called side MGW wireless side endpoint or the calling side BSC or the calling side MGW Nb side endpoint receives the code pattern changing command, complete the selection of the calling side BSC code pattern and the called It is called the conversion between the selected patterns of the side BSC. 9. The method according to claim 6, characterized in that, when the called side MGW and the called side BSC are time division multiplexed TDM bearers, the code type negotiation is performed, and if the negotiation is consistent, the code type negotiation is successful, Otherwise, the steps of converting the corresponding code type according to the code type negotiation result include: The MSC server receives the assignment response message, obtains the selected code pattern of the BSC from it, puts the selected code pattern of the BSC on the calling side in the first position of the code pattern priority table, and then transmits it to the MSC server on the called side, and the MSC server on the called side will The obtained code pattern priority list is sent to the BSC on the called side; If the BSC at the called side supports the code pattern selected by the BSC at the calling side, and selects the optimal pattern, the code pattern negotiation succeeds, and the MSC server at the called side sends a code pattern modification message to the MGW at the called side, and the MGW at the called side The bearer format conversion from IP to TDM can be completed on the called side, and TrFO can be implemented on the called side; otherwise, the MSC server on the called side sends a modification code message to the MGW on the called side, and the code type conversion and IP Bearer format conversion to TDM. 10. The method according to claim 6, characterized in that, when the calling side MGW and the calling side BSC are time division multiplexed TDM bearers, the code type negotiation is performed, and if the negotiation is consistent, the code type negotiation is successful, Otherwise, the steps of converting the corresponding code type according to the code type negotiation result include: The MSC server receives the assignment response message, obtains the selected code pattern of the BSC from it, puts the selected code pattern of the BSC on the calling side in the first position of the code pattern priority table, and then transmits it to the MSC server on the called side, and carries it back to the called side For the selected code pattern information of the BSC, the MSC server at the called side transmits the selected code pattern of the BSC at the called side to the MSC server at the calling side, and the MSC server at the calling side sends the selected code pattern of the BSC at the called side to the MGW at the calling side On the end point of the Nb interface of the Nb interface, make the code pattern of the IP bearer part consistent, and complete the code pattern conversion and the bearer format conversion from IP to TDM on the calling side MGW. 11. The method according to claim 1, characterized in that, after step B, further comprising: BSC modifying code pattern; When it is determined that the TC is set on the BSC side, the BSC modifies the selected pattern and reports it to the MSC server, and the MSC server initiates pattern renegotiation; Or, the TC is set on the MGW side. When the BSC modifies or switches the code, it initiates a code change request. After the MSC server modifies the code of the corresponding endpoint of the MGW, it sends a change response code information to the BSC, and the BSC receives the code change information. , to modify the pattern. 12. The method according to claim 1, wherein when the BSC and the BTS are TDM bearers, when establishing the IP bearer between the BSC and the BTS, the Abis interface between the BSC and the BTS is set as an IP interface, and the transmission is based on IP Protocol voice frames. 13. The method according to claim 1, wherein said step B further comprises: MGW receives the add endpoint message, allocates an IP address and port number for the call, and returns a response message carrying the IP address and port number allocated by the MGW for the call to the MSC server, and the MSC server receives the response message, sends an assignment message to the BSC, and obtains the IP bearer information Then send it to the BTS through LAPD signaling. The BTS obtains the IP address and port number allocated by the MGW wireless side for the call, and allocates its own IP address and port number for the call. The BTS reports the IP bearer information allocated for the call to the BSC, and the BSC Then send the IP address and port number assigned by the BTS to the MSC server through an assignment response message, and then the MSC server instructs the MGW. BTS and MGW obtain the IP address and port number of the opposite end, and establish IP bearer; The BSC receives the assignment message, selects the pattern, sends the selected pattern to the BTS through LAPD signaling, and returns an assignment response message containing the BTS pattern to the MSC server, and the MSC server sends the BTS pattern selected by the BSC to the MGW. The code pattern of the end point on the wireless side of the MGW is consistent with the code pattern of the BTS; initiate code pattern negotiation again, and implement TrFO if the negotiation is consistent; otherwise, insert a TC into the MGW at the calling side or the MGW at the called side to perform code pattern conversion. 14. The method according to claim 1, further comprising: switching the MS between different BTSs; The BSC obtains the IP address and port number of the BTS of the switched party, initiates a notification event to the MSC server, and notifies the MSC server of the IP address and port number of the BTS of the switched party, and the MSC server modifies the bearer of the MGW. 15. A system for realizing IP-based interface between GSM wireless network and core network, including BSC, MSC server and MGW, characterized in that, said MSC server is further used to realize IP-based interface with said BSC and MGW, wherein , The MSC server is used for signaling control, receives a call request message carrying a code pattern supported by the MS itself, establishes a code pattern priority table, sends an add endpoint message to the MGW wireless side, and receives the message returned by the MGW wireless side containing the MGW: A response message of the assigned IP address and port number for the call, and sending an assignment message to the BSC, where the assignment message carries the IP address and port number assigned by the MGW for the call and the pattern priority table; The MGW receives the add endpoint message sent by the MSC server, and returns to the MSC server a response message containing the IP address and port number allocated by the MGW for the call; The BSC transparently transmits the call request message to the MSC server, receives the assignment message sent by the MSC server, and establishes IP bearer and pattern negotiation corresponding to the MGW according to the received assignment message ; Wherein, when the pattern converter TC is set on the BSC side, the BSC modifies the selected pattern and reports it to the MSC server, and the MSC server initiates pattern renegotiation; or, the TC is set on the MGW side , when the BSC modifies or switches the code pattern, it initiates a code pattern change request, and after the MSC server modifies the code pattern of the corresponding endpoint of the MGW, it sends a change response code pattern information to the BSC, and the BSC receives the change pattern information, modify the pattern. 16. The system according to claim 15, characterized in that the Abis interface between the BSC and the BTS is set as an IP interface for transmitting voice frames based on the IP protocol.

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