The construction of GPRS network

GPRS as the transition of GSM network to the third generation system, its network formation has its own characteristics. From the network structure, GPRS can be seen as an increase in the existing GSM network based on a grouping domain. First of all, it should use the existing GSM wireless resources, can expand the new frequency point or support GPRS service on the original frequency point, second, the network requirements to add new network entities such as SGSN, GGSN, CG and so on, and request the establishment of GPRS backbone network.

GPRS BSS Group Network

In order to support GPRS, the existing GSM BSS must be upgraded. Because of different manufacturers of BSS devices, some manufacturers of BSS equipment need hardware upgrades, but some manufacturers can do only software upgrades. Because the investment of BSS accounts for a large proportion of the whole GSM system investment, it is directly related to the operator's investment strategy whether the BSS equipment needs hardware upgrading.

In order to support GPRS, it is usually necessary to introduce PCU unit into GSM BSc, which is generally used in two ways: one is to use PCU as a logical unit of BSC, the other is to use PCU as a physical entity. From the perspective of not affecting the existing GSM system architecture and network flexibility, PCU as an independent physical entity is a better solution. In this case, PCU can be configured flexibly according to the operator's choice, which can be shared with BSC, can be set independently, and can be placed on the SGSN side. PCU and BSC can correspond to each other, or a PCU can correspond to multiple BSC. Because GPRS and GSM share wireless resources that is common GSM community, it is necessary to increase the packet channel PDCH on the basis of GSM's existing wireless channel. In the GSM/GPRS system, in order to ensure the service quality of voice services, the service quality of packet data services should be improved as far as possible, and the PDCH dynamic provisioning and dynamic transformation of coding methods are usually used to achieve this goal.

(1) PDCH dynamic deployment

According to the actual situation of the network, a certain number of business channels are set up as packet channels, including a subset of fixed packet channels. When the voice service is less, some tch channels can be converted to PDCH (mainly Pdtch channel), and some pdch should be converted to tch in order to ensure the priority of voice service when the voice service is busy. Dynamic prediction, real-time provisioning and a series of resource allocation strategies can be used in PDCH channel dynamic provisioning. (Computer science)

(2) Dynamic transformation of codec mode

GPRS support CS-1, CS-2, CS-3 and CS-4 four kinds of codec, the corresponding rate is 9.02kbps, 13.4kbps, 15.6kbps, 21.4kbps, they have different requirements for wireless environment. The dynamic transformation of codec mode is to adjust the coding and decoding mode dynamically according to the different wireless environment, so as to achieve higher access rate without the change of wireless resources. PCU according to the BTS Measurement report (including receiving quality, uplink power, etc.), RLC retransmission times and other parameters to determine the encoding and decoding mode transformation strategy.

GPRS Network side Group Network

(1) Problems to be considered in GPRS network side networking planning

Network size

The original GSM network scale is basically the carrier number/number of users to measure, and GPRS due to the GSM network based on the introduction of the packet technology, taking into account the GPRS and GSM shared wireless resources, the pure carrier number/user number measurement network scale will be not comprehensive. The size of the GPRS network can be measured by the following metrics:

Number of packet channels supported (Pdtch quantity);

Maximum number of users attached;

Simultaneously activating the PDP context quantity;

Throughput.

The above indicators are based on a certain traffic model, including user average throughput, packet (mainly IP packet), average Baochang and other indicators.

APN

GPRS introduces the concept of APN, when the user PDP is activated, the APN is usually used as the parameter, which corresponds to the service provider of the external network. There is a specific correspondence between a GGSN,APN and a business provider. When a user accesses an external network, if the user does not specify a specific APN, the network side will assign the user a default APN, and the user can specify the specific APN.

GPRS Network side Equipment

GPRS network side equipment including SGSN, GGSN, CG, DNS, RADIUS Server, BG and other components, and the original GSM equipment such as HLR, MSC, Gmsc and other corresponding upgrades. In the GPRS network, SGSN, GGSN is the main equipment, SGSN, GGSN and MSc, HLR in the capacity and data, there is no specific corresponding relationship, operators can be flexible according to the actual situation of the network configuration.

(2) The establishment of GPRS backbone network

GPRS backbone network is GPRS network side node SGSN, GGSN, CG, DNS (corresponding to GPRS backbone network), such as the bearer networks, support roaming and have fixed IP address of the user business needs GPRS backbone network support. GPRS backbone network method and the existing Internet network completely consistent, you can adopt a mature ATM/IP technology.

Because GPRS backbone network is a whole network concept, the network scale is big, if specially for the GPRS backbone network to form a network is not economical, the most feasible way is in the general IP network to carry GPRS backbone network, namely GPRS backbone network as a VPN of IP network. The cmnet, which is being set up by China Mobile, basically employs this idea, cmnet business is positioned to provide all the services provided by IP network, highlighting mobile features and providing mobile internet services. At the same time, to ensure the quality of business services, the premise of providing real-time telecommunications services, especially mobile telecommunications services. Cmnet will be China's mobile GPRS backbone network, the provinces of the GPRS nodes (such as SGSN, GGSN, CG, etc.) access to the province's mobile internet, through the GGSN access to mobile Internet backbone of the provincial network connection nodes.

(3) 3G factors in GPRS network side networking planning

GPRS can provide mobile users with superior performance, rich and diverse business, it is a GSM to 3G evolution solution of an important part, so in the establishment of GPRS network must fully consider the evolution to 3G. The 3G factors involved in the planning of GPRS network side networking include equipment characteristics, backbone network formation, business provision and so on.

Device characteristics

The 3G R99 network includes a grouping domain and a circuit domain, in which the grouping domain consists of nodes of SGSN and GGSN, and the circuit domain is composed of MSC which supports 3G protocol. The grouping domain in 3G R99 core network is basically consistent with GSM/GPRS from function and business node. From the idea of the network, the existing GSM to 3G R99 Transition has the following several ideas:

3G Core network and GSM/GPRS network are independent of each other;

Existing GSM/GPRS network upgrades support 3G services, 3G RNs can be connected to the upgraded GSM/GPRS network;

The 3G core network also supports GSM/GPRS BSS and 3G RNS access.

The first of the above three ideas is not advisable, this idea for the network interoperability disadvantage, but also not conducive to the protection of operators in the 2G network investment. For the use of the latter two types of ideas, the operator according to the network status of the selection. For the large-scale network operators, if the whole network of existing equipment on the hardware and software upgrades, its operability is limited, and for the new network equipment requirements at the same time support Gsm/gprs BSS and 3G RNs Access is a very feasible solution.

GPRS, as a grouping domain in the GSM/GPRS network and 3G Core network, is more able to embody this idea in the network because of its consistency in the entity and function. If GPRS main node SGSN, GGSN can support GPRS and 3G characteristic at the same time, can protect the investment of the operator fully, and can introduce 3G business quickly.

Backbone Network Formation

From the above discussion can be seen, GPRS backbone network of large scale, while GPRS and 3G core network packet domain in the network structure has strong consistency. In the 3G core network, there is also a backbone network similar to the GPRS backbone network, so in the construction of GPRS backbone network, it is necessary to consider the future as a 3G core network of the feasibility of carrying network.