关于PDP context

关于PDP Context

2008-11-15 16:08

PDP Context，即Packet Data Protocol Context，意思是“分组数据协议上下文”，简称“PDP上下文”。     用户开通GPRS功能首先要在HLR给用户加载签约信息，即给用户添加PDP上下文索引，索引包括了接入点名称APN，分组数据用户的附着过程类似于位置更新过程，在这里简单说说PDP上下文激活过程：     1、MS发起PDP 上下文激活请求，激活消息中携带了APN名称，如CUNET。     2、SGSN接收到PDP 上下文激活请求，向DNS Server发起域名解析请求，需要解析的域名为完整的APN。     3、DNS Server将解析结果返回给SGSN，解析结果为GGSN 信令面的IP地址，如10.161.234.254。     4、SGSN根据解析结果，发送激活请求给目的GGSN，消息中携带了APN。     5、GGSN接收到激活请求后，根据APN为MS分配IP地址，并将分配的IP地址返回给SGSN。     6、SGSN将GGSN分配的IP地址发送给MS，激活成功。     7、激活成功后，MS可以使用分配的IP地址与外部网络进行通信。       PDP Context     The PDP (Packet Data Protocol, e.g. IP, X.25, FrameRelay) context is a data structure present on both the SGSN and the GGSN which contains the subscriber's session information when the subscriber has an active session. When a mobile wants to use GPRS, it must first attach and then activate a PDP context. This allocates a PDP context data structure in the SGSN that the subscriber is currently visiting and the GGSN serving the subscribers access point. The data recorded includes:          1、Subscriber's IP address     2、Subscriber's IMSI     3、Subscriber's     4、Tunnel Endpoint ID (TEID) at the GGSN     5、Tunnel Endpoint ID (TEID) at the SGSN           The Tunnel Endpoint ID (TEID) is a number allocated by the GSN which identifies the tunnelled data related to a particular PDP context.         There are two kinds of PDP contexts:       1、Primary PDP Context     Has a unique IP address associated with it     2、Secondary PDP Context     Shares an IP address with another PDP context     Is created based on an existing PDP context (to share the IP address)     Secondary PDP contexts may have different Quality Of Service settings     A total of 11 PDP contexts (with any combination of Primary and Secondary) can co-exist.