PDN address stands for Packet Data Network address is an IP address. when the UE initially attaches to the LTE network an IP address (PDN address) is allocated to UE by it so UE can connect to a PDN (i.e an IP network). These IP addresses are used to identify the UE to/from which an IP packet is sent when the IP packet is forwarded from an LTE network to a PDN, or received from a PDN. An IP address is allocated to an UE either permanently or dynamically for the UE to connect to the PDN. These two types of allocation are called static IP address allocation and dynamic IP address allocation, respectively. A static IP address is allocated by the operator at the time of subscription of UE and provisions the UE’s IP address to an HSS so in that way, the UE is assigned the same IP address every time it initially attaches to the PDN regardless of the time and location of such attach. A dynamic IP address is assigned by a PGW. The PGW has an IP pool from which PGW dynamically assigns an available IP address from the pool every time a UE performs initial attach to an LTE network. So in that way, a different IP address is assigned to a UE upon each initial attach of the UE to the network.
An UE can have more than one IP addresses because an UE can be connected to more than one PDN through an LTE network depending on the services, the LTE network allocates each UE a different IP address per each PDN the UE is connected to e.g. two IP addresses for a UE with two connected PDNs.