What is PDP

To know what is 'PDP', we should know that in order for an MS to be able to send and receive data to and from the PDN, The MS should create a data session between the MS and the GGSN. This data session is called the 'PDP context', which refers to 'Packet Data Protocol' context.

What is 'Attach'

There is one more step before creating a PDP. In order for the MS to be able to create a PDP with the GGSN, it should first make itself visible to the network. Or in other words, the network should know about the presence of the mobile station. In order to achieve this, the MS makes 'Attach' to the network. By making the 'attach' procedure with the core network, the network will know about the presence of the MS.

Procedures implementation

In summary, The MS makes the following procedures in order to be able to send and receive data to and from the PDN,

1. The MS makes an 'attach' procedure to the network. This is done in order for the network to know abut the presence of the MS.
2. The MS creates a 'PDP' with the GGSN.

After those two steps , the MS will be able to send and receive date to and from the PDN.

Mobility Management and Session Management

From previous discussion, there are two independent sub layers identifying the status of every MS in the network.

• The Mobility Management 'MM' sublayer,
• And the Session Management 'SM' sublayer.

Every one of those mentioned sub layers is having different states that identify the state of the MS. 

• The MM sublayer identifies if the network knows about the presence of an MS or not.

• While, the SM sublayer identifies if the MS is having an active data session with the GGSN or not.