PDP context and PDP address

Ms must connect to the external pdn. Ms must also have the address corresponding to the pdn, which is called the PDP address. The PDP address is used for the external grouping data network to identify the PDP context of Ms. If you use GPRS on your mobile phone, you will be assigned a PDP message. It can be understood that the IP address obtained from PDP context is connected to the Internet. It stores all the parameters related to a data transmission route, the parameter varies with the location in the wireless network.
The PDP address is like the phone number on the activation ticket when you activate a Wired phone. The PDP context is the opening ticket for this phone. Not only is there a phone number assigned to you, there are other properties related to this phone. Information about other functions; PDP context is a structure, and ip adr is only a member of The structure. Others include QoS, APN, etc, these are the content of PDP context.

1. If it is a master-slave PDP, there is only one address (the same PDP context ). If both are primary PDP, there will be multiple addresses. (Multiple PDP contexts)
2. the definition of PDP context standards is not very clear. Generally, for example, if you want to use a mobile phone to access a website, you will use the PDP context of cmwap, when you use a mobile phone to connect to the Internet, you use cmnet. Generally, different IP addresses are allocated to access different services to meet different needs.
TFT (Traffic Flow template) refers to the business flow Template
Nsapi (Network Layer Service Access Point identifier) is used for network layer routing. In ms, nsapi is used to identify a PDP business access point, and together with the PDP address in sgsn/ggsn, it is used to identify a PDP context.
The context of the secondary activation PDP is different from that of the Activated PDP. Each PDP context has a unique Ti (transaction identifier) and nsapi. in many PDP contexts, only one PDP context is allowed without TFT. When the downstream N-PDUS is transmitted, the ggsn selects the appropriate PDP context based on TFT matching, the MS selects different PDP contexts based on QoS when sending data.
The MS sends a secondary activation request to sgsn activate secondary PDP context request (linked Ti, nsapi, Ti, QoS requested, TFT) containing linked Ti, indicates the Ti value allocated to any Activated PDP context (with the same PDP address and APN.

After the GPRS mobile phone is attached to the network, it requests an IP address from the network, which can be a static or dynamic PDP address.
The PDP Address indicates that the user's network layer address PDP address can be allocated to ms in the following four ways:
A permanent PDP address (static PDP address) is assigned to Ms by the e-hpc operator)
When the PDP context is activated, the hpcmn operator temporarily allocates a PDP address to the MS (Dynamic hzmn PDP address)
When the PDP context is activated, the vplmn operator temporarily assigns a PDP address to MS (Dynamic vplmn PDP address)
When you use a Dynamic Address of either Either either of them, ggsn is responsible for allocating or releasing the dynamic address. Only when the PDP address is static can the network initiate a request to activate the PDP context.
Vplmn refers to accessing plmn. The dynamic vplmn PDP address or dynamic vplmn PDP address is used, which is specified by the e-hpc operator in the contract with the user. When a dynamic address is used, the ggsn allocates and releases the dynamic PDP address. If the activation of the PDP Mobile Association is a network request, the static PDP address can only be used.
The PDP address is the network layer address of the GPRS user and is temporarily or permanently associated with the standard network layer address (such as IPv4 address, IPv6 address, and X. 121 address. The PDP address can be allocated to MS in three ways:
Static PDP address: a PDP address is permanently allocated to Ms;
Dynamic maid address: When a PDP context is activated, it is only then temporarily allocated to Ms by the maid address;
Dynamic vplmn PDP address: When a PDP context is activated, vplmn temporarily assigns a PDP address to Ms.
 
Selection rules and ing of APN
In the GPRS core network, APN is the reference name of the ggsn used and used to identify the accessed external network. During PDP context activation, when MS sends an activation PDP context request to sgsn, sgsn selects an APN according to the selection rule of APN. This rule is a complex decision tree. Sgsn compares the three request parameters (PDP type, PDP address, and APN) in MS with the three reservation parameters in HLR.
Sgsn asks the DNS server with the selected APN, And the IP address of ggsn is obtained by DNS ing. At the same time, sgsn sends a message for creating the PDP context request to the ggsn to establish a tunnel between sgsn and ggsn.

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