GPRS部件名词与Core Network工作原理解读

GPRS tunnelling protocol (GTP):

GPRS Tunnelling Protocol is the defining IP-based protocol of the GPRS core network. Primarily it is the protocol which allows end users of a GSM or WCDMA network to move from place to place while continuing to connect to the Internet as if from one location at the Gateway GPRS support node (GGSN). It does this by carrying the subscriber’s data from the subscriber’s current serving GPRS support node (SGSN) to the GGSN which is handling the subscriber’s session. Three forms of GTP are used by the GPRS core network.


PDP Context作为GTP的组成部分,记录着用户数据,包括IMSI, IP, 以及SGSN和GGSN的连接ID号。

Gateway GPRS support node (GGSN):

From an external network’s (Internet) point of view, the GGSN is a router to a “sub-network”, because the GGSN ‘hides’ the GPRS infrastructure from the external network. When the GGSN receives data addressed to a specific user, it checks if the user is active. If it is, the GGSN forwards the data to the SGSN serving the mobile user, but if the mobile user is inactive, the data is discarded. On the other hand, mobile-originated packets are routed to the right network by the GGSN.



Serving GPRS support node (SGSN)

A serving GPRS support node (SGSN) is responsible for the delivery of data packets from and to the mobile stations within its geographical service area. Its tasks include packet routing and transfer, mobility management (attach/detach and location management), logical link management, and authentication and charging functions. The location register of the SGSN stores location information (e.g., current cell, current VLR) and user profiles (e.g., IMSI, address(es) used in the packet data network) of all GPRS users registered with it.



Traffic Flow:

EU->Tower->RNC->SGSN->HLR(Authentication)->SGSN->EU->SGSN->GGSN(DHCP)->SGSN->EU(IP Assigned)->SGSN->GGSN->Internet.


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