GPRS: A new opportunity for the development of wireless internet

GPRS provides a seamless, direct Internet connection. GPRS supports X.25 protocols and IP protocols that have far-reaching implications for the Internet. GPRS is a supplement rather than a substitute for the existing circuit-switched data Service (CSD) and short Message Service (SMS) in GSM network. GPRS can dynamically allocate wireless resources according to users ' needs, so as to realize multi-user sharing and improve frequency utilization. At the same time, the billing will be changed from the traditional time to the transmission of user data.

Logically speaking, we can add two new network nodes in the GSM network structure to realize GPRS. These two nodes are: GPRS service support node (serving GPRS support NODE,SGSN), GPRS Gateway support node (Gateway GPRS support NODE,GGSN).

In GPRS architecture, Base station (BSS) and SGSN devices are generally connected by frame relay (called GB interface), SGSN and GGSN devices are connected via IP network (called GN Interface). GGSN can be used by routers with NAT (Network address translation) to assume the conversion of internal IP address and external network IP address. MS (Mobile station) can access the network within the GPRS, or access the external PDN (packet data network) or the Internet via APN (access point name). (Computer science)

When users access the Internet, intranet or ISP through the GPRS network, the access mode can be summarized as transparent access and non-transparent access. If the user's IP address is the public address assigned by the operator (dynamic or static), then GGSN does not participate in the user authentication and authorization process, the user can access the GPRS internal network or the Internet through GGSN transparently, this way is called the transparent way. When the IP address of the user's MS is a private address (dynamic or static) assigned by the corporate network or ISP, when a user accesses the corporate network or ISP, GGSN requires that the user be authenticated or certified by a dedicated server in the corporate network or ISP, in a non-transparent manner.

The performance evaluation of GPRS system mainly includes three aspects:

The first is the system capacity. The system capacity of GPRS includes GSN network capacity and RF (RF) capacity. In GSM system, the capacity of the system is the number of users that the system can support. In GPRS system, because of the use of packet switching technology, a number of users can share the wireless channel, so in describing the capacity of GPRS switching system, in addition to the user's habit of users, but also the number of stored maximum PDP context, user attachment number, simultaneous activation of the PDP context number, Data throughput and other indicators.

The second is the data rate. The data rate provided by GPRS depends on the encoding scheme adopted, and there are four kinds of encoding data rate in the standard, respectively, 9 per channel. 05KBIT/S, 13. 4KBIT/S, 15. 6KBIT/S and 21. 4kbit/s. With all 8 business channels available on a single frequency, the maximum data throughput can be as high as 171kbit/s per user. However, due to the overhead of channel coding and multi-slot allocation, the more realistic maximum throughput is 115kbit/s. The transfer rate of most applications can be much lower under the condition that the quality of service is acceptable.

GPRS can predict a series of new applications on GSM network because it provides data connection at variable data transmission rate and has high bandwidth efficiency. By using the same packet transfer technology, GGSN can provide a gateway to other public data networks (PDN) that are connected to GPRS to provide seamless service across different networks.

In the GPRS system, the user's call establishment time is greatly shortened, and any call only needs to be established once. Once the call is established through a process called "attachment," the user becomes the service object of the network and is only required to network resources when sending and receiving data. If the last block of data in a data stream has been sent out and confirmed, or if the timer reaches the timing limit, the resources it uses will be freed and reassigned. When you want to send and receive new data blocks, GPRS calls are still open and can be built again. Compared with the current circuit switching service, its re-access delay is very short, thus increasing the utilization of network resources.

In addition to system capacity, data rate, PCU, SGSN, GGSN, billing system performance is also an important factor to evaluate the performance of GPRS. The performance of these devices is mainly described by reliability (such as device failure rate, interrupt recovery service time), throughput and system capacity (such as processing capacity and billing capacity), interface metrics with external networks, and so on.

At present, the development of GPRS faces four difficult problems. One is the lack of GPRS mobile phone, the current mobile phone needs to be upgraded to high-speed data transmission and support packet data Exchange services to access the GPRS network. The second is the rate and billing issues, rates and billing methods for the development of new mobile data market is particularly important, so the GPRS charging method should also be based on market development of prudent research, in order to facilitate the market. The third is the application of mobile data card, the early launch of the card, you can easily insert the handheld computer, so that it and GPRS network connection. Four is the development of various application software, GPRS business promotion of a lot of applications in need of software, at present this has yet to be developed.