PDP context and PDP address

MS to access the external pdn,ms should also have the corresponding address with the PDN, called PDP address, PDP address is used for the outside part of the group data network to identify MS in the PDP context when the address used. If you use a mobile phone on GPRS, you will be assigned to the PDP message, you can understand that the PDP context to get the IP address of the Internet, it is to save a data transmission route related to all the parameters, it contains parameters with the location of the wireless network is different.
PDP address like the opening of a landline telephone, the opening of the phone number on the list, and PDP context is this phone open work list, not only has the phone number assigned to you, as well as the corresponding other attributes of the phone, other functions of information; PDP contexts (PDP context) is a structure, and IP ADR is only a member of the structure, others include QOS,APN, which are the PDP context (PDP contexts) content.

1. If it is the principal and subordinate PDP, there are only 1 addresses (the same PDP context). If all are the main PDP, then there are multiple addresses. (Multiple PDP contexts)
2.PDP Context Standard explanation is not very clear, popular point is to say you want to use mobile phone website, then you will use CMWAP this PDP context, and when you use the mobile phone when the cat to connect the Internet, using is cmnet. The idea is that in order to meet different needs, you will be assigned different IP addresses to connect to different businesses. TFT (traffic flow Template) refers to the business stream 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 points that are used with PDP addresses in SGSN/GGSN to identify a PDP context .
The two-activated PDP context differs from the activated PDP context with only the QoS profile, with each PDP context having a unique Ti (Transaction Identifier) and NSAPI. In many PDP contexts, only one PDP context is allowed without TFT, When the downlink N-pdus is transmitted, the GGSN will select the appropriate PDP context according to the TFT matching, and the different PDP contexts should be chosen by QoS when the data is sent.
MS sends two activation requests to SGSN activate secondary PDP context request (linked Ti, Nsapi,ti, QoS requested, TFT) contains linked Ti, indicating assigned to any activated PD P-context (with the same PDP address and APN) the TI value.

GPRS mobile phone and network attachment, request an IP address to the network, the address can be static and dynamic PDP address
PDP address indicates user network layer address PDP address can be assigned to MS in the following four ways
HPLMN operator assigned to MS a permanent PDP address (static PDP address)
When the PDP context is activated, the HPLMN operator temporarily assigns a PDP address to MS (dynamic HPLMN PDP address)
When the PDP context is activated, the VPLMN operator temporarily assigns a PDP address to MS (dynamic VPLMN PDP address)
When using HPLMN or VPLMN dynamic addresses, the GGSN is responsible for assigning or releasing the dynamic address. Only if the PDP address is static can the network initiate request PDP context activation. VPLMN refers to the access to PLMN. The use of dynamic HPLMN PDP or dynamic VPLMN PDP address, by the HPLMN operator in the contract with the user stipulated. When using dynamic addresses, the dynamic PDP addresses are allocated and released by GGSN. If the PDP Mobile Association activation is a network request, only the static PDP address can be used. PDP address is a GPRS user's network layer address, and the standard network layer address (such as: IPv4 address, IPv6 address, X. 121 address) established a temporary or permanent association. PDP addresses can be assigned to MS in 3 ways:
Static PDP address: HPLMN assigns a PDP address permanently to MS;
Dynamic HPLMN PDP address: When a PDP context is activated, HPLMN assigns a PDP address temporarily to MS;
Dynamic VPLMN PDP address: When a PDP context is activated, VPLMN temporarily assigns a PDP address to Ms.
Selection rules and mappings of APN
In the GPRS core network, APN is the reference name of the GGSN used, and is used to identify the external network that is connected. During PDP context activation, when MS sends an activation PDP context request to SGSN, SGSN selects a APN based on the APN selection rule. The rule is a complex decision tree. SGSN according to the 3 request parameters of MS (PDP type, PDP address, APN) and the corresponding 3 reservation parameters in HLR.
SGSN queries the DNS server with the selected APN, obtains the GGSN IP address by DNS mapping, and SGSN sends the PDP context request message to the GGSN to establish a tunnel between SGSN and GGSN.