A packet data protocol (PDP) context provides a packet data connection over which a mobile device and a data network can exchange Internet protocol (IP) packets. A PDP context has a record of parameters that consists of all the required information for establishing an end-to-end connection with the data network. These parameters include a PDP type, a PDP address type, a quality of service (QoS) profile request (e.g., QoS parameters requested by a user), a QoS profile negotiated by the data network, an authentication type, and a domain name system (DNS) type (e.g., dynamic DNS or static DNS).
The PDP context is mainly designed to provide two specific functions for the mobile device. The PDP context is designed to allocate a PDP address, such as an IP version 4 or an IP version 6 type address, to the mobile device. The PDP context is also used to make a logical connection with QoS profiles, the set of QoS attributes negotiated for and utilized by a single PDP context, through the data network.
Current, high-end mobile devices are capable of establishing multiple PDP contexts to serve applications operating in parallel. These PDP contexts can differ in their QoS parameters and/or the target data network to which they provide a data connection. By way of example, a mobile device can establish a first PDP context to access the Internet through a web browser and a second PDP context to access an application provided by an application server.
Generally speaking, there are two types of PDP contexts—a primary PDP context and a secondary PDP context. A primary PDP context has a unique associated IP address. Primary PDP contexts can be activated or deactivated independently from one another. A secondary PDP context is created based upon a primary PDP context, and shares an IP address and access point (AP) with the primary PDP context on which it is based. Thus, the primary and the associated secondary PDP context provide connection to the same packet data network with different guaranteed QoS.
One primary PDP context might have multiple secondary contexts associated with it. Each PDP context has its own radio access bearer (RAB) and tunnel to transfer user plane data. The primary PDP context has to be active prior to activating an associated secondary PDP context. Any secondary PDP context can be deactivated while keeping the associated primary PDP context and any eventual other secondary PDP contexts active. If a primary PDP context is deactivated, this will also deactivate all of the associated secondary PDP contexts. In 3GPP (3rd Generation Partnership Project) networks, a total of eleven PDP contexts, including any combination of primary and secondary PDP contexts, may coexist simultaneously in connection with a single mobile device, although certain limitations of the mobile device may limit the number of PDP contexts the mobile device may maintain simultaneously.
Each of multiple PDP contexts can have different QoS profiles. A primary PDP context is a normal PDP context with default QoS profile attributes and it is always activated first. For the multiple primary PDP contexts, each context has a different PDP address and is used to attach to a different packet data network (PDN) identified by a different access point name (APN).
An APN is used in 3GPP data access networks (e.g., General Packet Radio Service (GPRS) or Evolved Packet Core (EPC) networks) to identify a PDN with which a mobile device communicates, and to define a type of service provided by the PDN. For example, an APN may identify a connection to an IP Multimedia Subsystem (IMS), a messaging service center (e.g., a Multimedia Messaging Service Center (MMSC)), a wireless application protocol (WAP) server, the Internet, an application server, or another device, node, network, or service.
In a PDN, an operator's packet domain network is responsible for providing data connectivity to the mobile user. The user accesses one or more PDNs provided by the operator or an external network provided by another operator. Exemplary PDNs include, but are not limited to, networks providing IMS services, MMS services, WAP services, Internet services, and visual voicemail (WM) services, A Gateway GPRS Support Node (GGSN) provides connectivity between one or more PDNs and the operator's packet domain network. In general, a user accesses a PDN via a GGSN, which may be located in a visited operator's network, or may be located in the user's home operator network. In some circumstances, inter-operator networks provide IP connectivity between operators' packet domain networks.
An APN is also used to identify the PDN from which to provide the user's IP address and to select a GGSN from which the PDN is accessible. APN resolution is the process of DNS look-up to determine the IP address of the GGSN that provides connectivity to the PDN identified by the APN. When a GPRS mobile device activates a PDP context, the mobile device provides the APN to which the mobile device wants to connect. The APN is resolved to identify and to select the appropriate GGSN, and to provide an IP address to the mobile device. The AP identified by the APN is then used in a DNS query to a private DNS network. This process gives the IP address of the GGSN which should serve the access point. At this point the PDP context can be activated.
APNs can be either shared or dedicated. Shared APNs allow a mobile device to share the PDP context with other applications. Shared APNs compromise performance for service availability. On the other hand, dedicated APNs use a dedicated PDP context without sharing with other applications to meet high performance requirements of some applications (e.g., real-time applications such as visual voicemail).
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