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.
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.
In summary, The MS makes the following procedures in order to be able to send and receive data to and from the PDN,
After those two steps , the MS will be able to send and receive date to and from the PDN.
Later, we will go deeper into 'PDP context' activation procedure, and 'Attach' procedure.
From previous discussion, there are two independent sub layers identifying the status of every MS in the network.
Every one of those mentioned sub layers is having different states that identify the state of the MS.
Later, we will go deeper into MM and SM sublayers.