GPRS technology

1.GPRS technology embodied
General Packet Radio Service GPRS, GSM-based system is a wireless packet switching technology, to provide end-to-end, wide-area wireless IP connection. Tongsudejiang, GPRS is a high-speed data-processing technology, methods of "division" in the form of transmitting information to the hands of the user. Although GPRS is available as a GSM network to the 3G mobile communications technology evolution of the transition, but in many ways, has a significant advantage. At present, Hong Kong's status as the first testing ground for GPRS areas, have achieved good results.
Due to the use of a "group" of technology, Internet users can be disconnected from the suffering of the (situation about the use of just a software download NetAnts almost). In addition, the use of GPRS and WAP access to the Internet and in different ways, such as WAP access on the Internet at home, the first "dial-up connection" and then the Internet can not use the telephone line, but on more favorable GPRS, download information and can call At the same time. Technically, the transmission of voice (that call) to continue to use GSM, and data can be transmitted using GPRS, this is the case, put mobile phone applications to a higher level. GPRS technology development and also the "economy", because only the existing GSM network to develop. GPRS uses the wide range of issues, including the adoption of mobile phones to send and receive e-mail, browse the Internet, and so on.
Internet phones are now the slogan is "always online", "IP in hand", using GPRS, the realization of the data packet to send and receive, at the same time this means that the user is always online and by billing traffic, to quickly lower the costs of the services. The continued state of dystocia in China Mobile / Unicom WAP tariff policy, if the CSD (circuit-switched data, that is usually said that the dial-up data, WAP European and Asian business methods used by the bearer) carrying changed to achieve the GPRS, it means that Dozens of people from a common commitment to one of the original cost.
And GPRS the greatest advantage: its data transfer speed is not WAP can be compared. The current GSM mobile communications network for the transmission speed of 9.6K bytes per second, GPRS mobile phones launched in the beginning of this year have reached a speed of 56Kbps, up to now is to achieve a 115Kbps (this is the speed of common ideals 56Kmodem twice the rate) . Therefore, we cherish you in the hands of Nokia7110 and MotorolaL2000, I believe that the introduction of GPRS handsets, they have to give way.
2. Packet (Packet) technology
The so-called packet (Packet) is the Date package into a number of separate packets, and then these packets to send out one by one, a bit similar in form to send parcels, the advantages of using packet-switched only when there is a need to send information when Will take up bandwidth, but also to transfer the amount of data pricing, which the user is a more reasonable way of accounting, because the Internet such as data transmission bandwidth is most of the time between the home. In addition, GSM phase 2, the standard, GPRS offers four different coding methods, the encoding also provide different protection error (Error Protection) capability. The use of four different encoding every time slot available for transfer rate of CS-1 (9.05K), CS-2 (13.4K), CS-3 (15.6K) and CS-4 (21.4K), which CS-1 to protect the most rigorous, CS-4, it is absolutely not be any protection. At the same time, each user can use a maximum of eight hours slot, so-called GPRS for a maximum transfer rate of 171.2K.
3.GPRS network structure
GPRS network is based on the existing GSM network to achieve. In the existing GSM networks need to increase the number of nodes, such as GGSN (Gateway GPRSSupporting Node, Gateway GPRS support node) and SGSN (Serving GSN, to support the GPRS service node).
GPRS network reference model as shown in Figure 1. GSN is the GPRS network, the most important nodes of the network. GSN with a mobile routing management functions, which can connect various types of data networks and can be connected to the GPRS register. GSN to be completed and a variety of mobile data network between the data and format conversion. GSN can be a similar independent of routers and prepared, in the GSM and can also be integrated with the MSC.
GSN There are two types: one for the SGSN (Serving GSN, services GSN), the other for the GGSN (GatewayGSN, Gateway GSN), SGSN main role is to record the mobile station from its current location information and mobile station and GGSN Between the completion of the mobile division to send and receive data. GGSN is the main gateway from the role it can be a wide range of data and network connections such as ISDN, PSPDN and LAN, and so on. Some of the literature, the GGSN called GPRS router. GGSN can GSM network in the GPRS packet data protocol conversion package that will allow these groups to send packets to the remote TCP / IP or X.25 network.
In addition, some manufacturers raised GR (GSMRegister, GPRS data) concept. GR similar to the GSM in the HLR, is a GPRS business database. It can stand on its own, and can co-exist HLR by the server or the realization of program-controlled switches. GR in the name of the ETSI's proposal does not specifically mentioned.
GPRS network also introduced a new network interface of the following:
Gn, GSN backbone interface for a variety of between GSN
Gb, BSS and the interface between the sGsN.
Gr, SGSN and the interface between the HLR.
Gp, different GSM networks (different PLMN) interface between.
Gs, SGSN and the interface between the MSC.
4.GPRS agreement model
Um is the interface of the GSM air interface. Um interface communication protocol layer 5, bottom-up followed by the physical layer, MAC Mdium AccessControl) layer, LLC (Logical Link Control) layer, SNDC (Subnetwork DependantConvergence) layer and network layer.
Um interface of the physical layer for the radio frequency interface, and the physical link layer is responsible for providing a variety of air interface logical channel. GSM air interface to the carrier frequency bandwidth 20OkHz, a carrier frequency is divided into 8 physical channels.
8 If you have physical distribution channel for the transmission of GPRS data, the raw data rate of up to 20Okb / s. Forward Error Correction Code to consider the costs, the final data rate of up to 164kb / s or so.
MAC for media access control layer. MAC's main role is to define the distribution of air interface and the GPRS logical channel, so that these channels will be different mobile sharing. GPRS logical channel of a total of 3 categories, namely, the Public Channel, channel and business groups GPRS radio channel. Public Channel used to transmit data communications control signaling, is subdivided into specific responses, such as paging and channel. Business groups to channel packet data transmission. Radio channel is used to the mobile network to send information.
LLC Logical Link Control layer to layer. It is a high-speed data link based on the order of the HDLC protocol wireless link. LLC layer is responsible for the high-level SNDC layer SNDC data unit formed LLC address field frame in order to generate full-frame LLC. In addition, LLC can be a point-to-multipoint addressing the frame and the re-issued control.
LLR in the BSS layer is a logical link layer transmission. This layer is responsible for MS and SGSN transfer between the frame LLC. LLR layer SNDC for the data unit is transparent, that is not responsible for SNDC data.
SNDC known as the combination dependence on sub-layer. Its main role is to complete the transfer of data packet, packing, determine the TCP / IP address and encryption methods. SNDC in the layer, mobile and data transmission between the SGSN has been divided into one or more packets SNDC unit. SNDC packet generation unit was placed intra LLC.
Network layer protocol of the current stage of Phase 1 is provided by the TCP / IP protocol and L25. TCP / IP and X.25 protocol to the traditional GSM network equipment (such as equipment such as the NSS and BSS) is transparent.
5.GPRS routing management
GPRS is the management of the routing GPRS networks and addressing how to set up a data transmission route. GPRS routing management in the following 3 areas: mobile station to send data to establish the route; mobile station set up to receive data routing; and mobile roaming at the time of the establishment of routing data.
In the first case, in Figure 3 shown in a path. When the mobile station have had a PDU (packet data unit), the PDU after SNDC layer processing, called SNDC data unit. LLC layer and then, after dealing with LLC for CHENG through the air interface to the GSM mobile network in Taiwan's SGSN. SGSN the data sent to the GGSN. GGSN to receive the news of solutions for dealing with equipment, can be converted into a public data transmission network in the format (such as PSPDN the PDU), a public data network to the end user. In order to improve the efficiency of the transmission, data transmission and to ensure the safety of air interface can be done on data compression and encryption.
In the second case, a public data network users send data to mobile station. First of all, the data network through the establishment of a standard agreement between the GGSN and data network routing. Data issued by the network user data unit (for example, PSPDN in the PDU), through the establishment of good data routing unit PDU to GGSN. GGSN and then to the PDU mobile station where the SGSN on GSN into the PDU package SNDC data unit, another layer to deal with LLC to LLC unit frame and eventually through the air interface to the mobile station.
The third is a data network to transmit data to a user is roaming of mobile users. The data must go through attribution to the GGSN, and then sent to the mobile user A. In the air by the mouth of the channel constitutes a GPRS air interface channel as follows:
PDTCH (Pachet Data Traffic Channe1), packet data channel. This channel used to send the air interface GPRS packet data.
PPCH (Packet Paging Channe1), group paging channel for paging PPCH called GPRS users.
PRACH (Packet Randem Access Channel), grouping random access channel. GPRS users PRACH to the base station to issue a request channel.
PAGCH (Packet Access Grant Channel), Packet Access response channel. PAGCH is a response channel, the response to PRACH.
PACCH (Packet Asscrchted ControlChannel), with the sub-Channel routes. This channel used to send the realization of GPRS data services signaling.
6. GPRS technology services
GPRS packet data billing functions, that is, according to billing data.
7. GPRS and IP
The introduction of GPRS technology, telecommunications networks and computer networks, organically linked to North Korea in the future all-IP network platform for development.
GPRS can be seen from the structure, the base station and the connection between the SGSN prepared through the general frame relay connection, SGSN and GGSN equipment between the IP network.
GGSN may be replaced by an NAT (network address translation) routers to assume the function of internal and external IP address of the IP network address translation, MS may be accessed within the GPRS network can also be APN (external network access by name) to visit the external PDN / Internet network.
Logo in the GPRS devices such as mobile phones MS logo in addition to the GSM used in the IMSI, MSISDN number, and so on, but also need the distribution of IP addresses. Network element equipment SGSN, GGSN logo of the existing SS7 address, and the IP address of the GGSN data, GSN (SGSN or GGSN) communications between the use of IP addresses, and GSN with the MSC, HLR, and other entities use of communication 7 Signaling its address. GPRS in the system, there are two important records database information. First, the user mobility management context for the management of the mobile user location information, and the other is the user context of the PDP (Packet Data context of the agreement) for the management of MS from the phone to Gateway GGSN and the ISP (Internet Service Provider ) Between the data routing information. When MS access GPRS network internal or external PDN / Internet network, MS to activate PDP fat SGSN context of a request message, MS may choose to contract with the operator of fixed service GGSN. According to the rules of APN or choose from SGSN choice GGSN, SGSN made GGSN to the establishment of information PDP context request. GGSN allocated an IP address of the MS (static or dynamic, public or private), set up in the context of the PDP, the need for the user's identity, the need for quality of service for authentication and verification in the successful establishment and activation after the PDP context, MS , SGSN and GGSN are stored PDP context of the user's information. With the user's location information and data routing information, MS will be able to access the network resources. Second-generation GPRS and a half of the products available in the development and deployment of GPRS business encountered some new concepts.