GPRS is an abbreviation of General Packet Radio System, which is a technology between the second generation and the third generation, usually called 2.5G. GPRS uses the same frequency band, bandwidth, burst structure, wireless modulation standard, frequency hopping rules and the same TDMA frame structure as GSM. Therefore, when building a GPRS system based on the GSM system, most of the components in the GSM system do not need hardware changes, only software upgrades are required. With GPRS, the user's call setup time is greatly reduced, and almost "always on". In addition, GPRS is billed based on the amount of data transmitted by the operator rather than the connection time, thus making each user's service cost lower.
The main features of GPRS:Compared with the original GSM circuit-switched data transmission method, GPRS adopts packet switching technology. Due to the use of "grouping" technology, users can avoid the trouble of dropping the Internet. In addition, the method of using GPRS to access the Internet is different from WAP. If you use WAP to access the Internet, you can go online at home, first "dial-up connection", and you can't use the phone line at the same time after surfing the Internet, but GPRS is superior, downloading data and calling can be carried out simultaneously. .
Technically speaking, the transmission of voice (ie, call) continues to use GSM, and the transmission of data uses GPRS, which raises the application of mobile phones to a higher level and does not require re-networking, which is very economical. GPRS is widely used, including sending and receiving e-mails via mobile phones, and browsing on the Internet. With GPRS, data can be sent and received in packets, which means that users are always online and on a per-flow basis, reducing service costs.
The biggest advantage of GPRS is that the data transmission speed is not comparable to that of WAP. The current GSM mobile communication network has a transmission speed of 9.6K bytes per second. The GPRS mobile phone has reached a transmission speed of 56Kbps when it was introduced at the beginning of this year, and now it has reached 115Kbps (this speed is twice the ideal rate of the commonly used 56k modem). ). In addition to the speed advantage, GPRS also has the feature of "always on", that is, users keep in touch with the network at any time. For example, when a user accesses the Internet, clicking a hyperlink causes the mobile phone to send and receive data on the wireless channel. After the home page is downloaded to the local area, there is no data transmission, and the mobile phone enters a “pre-sleep stateâ€, and the mobile phone is released. The wireless channel is used by other users. At this time, the network maintains a logical connection with the user. When the user clicks again, the mobile phone immediately requests the wireless channel to transmit data to the network, instead of disconnecting the line like ordinary dial-up. You have to redial to get online.
Basic working principle of GPRS communicationGPRS introduces two new network nodes on the original circuit-switched (CSD)-based GSM network: GPRS Service Support Node (SGSN) and Gateway Support Node (GGSN). The SGSN and the MSC are at the same level, and the storage unit of a single MS is tracked to implement security functions and access control, and is connected to the base station system through frame relay. The GGSN supports interworking with external packet switched networks and is connected to the SGSN via an IP based GPRS backbone. Figure 1 shows the block diagram of the GPRS and Internet connection.
The GPRS terminal obtains data from the client system through the interface, and the processed GPRS packet data is transmitted to the GSM base station. After the packet data is encapsulated by the SGSN, the SGSN communicates with the gateway support contact GGSN through the GPRS backbone network. The GGSN processes the packet data and sends it to the destination network, such as the Internet or X.25 network.
If the packet data is sent to another GPRS terminal, the data is sent by the GPRS backbone network to the SGSN and then sent to the GPRS terminal via the BSS.
Protocol model of PRSThe Um interface is the air interface of GSM. The communication protocol on the Um interface has five layers, and the bottom layer is the physical layer, the MAC (Media Access Control) layer, the LLG (Logical Link Control) layer, the SNDC layer, and the network layer. The physical layer of the Um interface is the radio interface part, while the physical link layer is responsible for providing various logical channels of the air interface. The carrier frequency bandwidth of the GSM air interface is 200 kHz, and one carrier frequency is divided into 8 physical channels. If 8 physical channels are allocated to transmit GPRS data, the original data rate can be up to 200 Kbps. Considering the overhead of the forward error correction code, the final data rate can reach about 164 kbps; the MAC is the medium access control layer. The main role of the MAC is to define and allocate GPRS logical channels for the air interface so that these channels can be shared by different mobile terminals; the LLG layer is the logical link control layer. It is a wireless link protocol based on the high-speed data link protocol HDLG; SNDC is called a sub-network dependency layer. Its main role is to complete the packetization and packing of the transmitted data, determine the TCP/IP address and encryption mode; the network layer protocol is currently mainly the TCP/IP and L25 protocols provided by the Phasel phase. The TCP/IP and X.25 protocols are transparent to traditional GSM network devices (eg, BSS, NSS, etc.).
GPRS application rangeGPRS is a new type of packet data transmission service opened on the existing GSM network. Based on the standardized network protocol supported by the GPRS bearer service, GPRS can provide a series of interactive service services:
1. Point-to-point connection-oriented data services. To send multi-packet services between two users or multiple users, the service requires work procedures such as establishing a connection, transferring data, and releasing the connection.
2. Single-point to multi-point business. Send a single message to multiple users based on the requirements of a business requester. The service can be further divided into point-to-multipoint multi-channel broadcasting service, point-to-multipoint group call service and IP multicast service.
3. Point-to-point connectionless network services. Each data packet is independent of each other, the information transmission between users does not require an end-to-end call setup procedure, the packet transmission has no logical connection, and the delivery of the packet is not acknowledged and protected, and is a service supported by the IP protocol. In addition to providing point-to-point and point-to-multipoint data services, GPRS can also support user terminal services, supplementary services, GSM short message services, and various GPRS telecommunications services.
In-car 5G can make in-car infotainment systems as versatile as smartphones or tablets, supporting advanced in-car games such as virtual reality (VR), high-resolution video streaming, and a large number of App options that can create value-creating experiences. In addition, the software update of the vehicle no longer needs to be returned to the dealer, and the OTA method can be adopted like a smart phone or NB.
5G is also expected to vigorously promote the cellular Internet of Vehicles (C-V2X) to become a killer application. For example, the decentralized data processing method of Edge Computing has great potential, which can greatly reduce the need to transmit to the central database. The amount of data, for example, when a road is congested, when updating a road condition map, only need to transmit the data to all vehicles within a radius of about 2 miles, instead of transmitting to the United States or the world and occupying bandwidth, which can reduce transmission costs and time.
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