Sharing single user identity among multiple devices : single IMPU to multiple IMPI

In IMS between IMPU and IMPI many to many relationship is possible. so lets see how this is possible and what are the use cases.

Lets have an example in which we have 3 UE.
UE1 : only audio call capable.
UE2 : Video call capable.
UE3 : Gaming console.

so having same IMPU shared among these three IMPIs we how we can come to know to which IMPI call will be terminated.

This decision making can be done by S-CSCF by knowing the type of service and capability of devices.
And same can be achieved by forking as well.
There are two types of forking:
1. Sequential forking :
    Sequential forking means that different items of UE are contacted one by one.  Timeout has been maintained for contacting devices.
2. Parallel forking
    Parallel forking means that different items of UE are contacted at the same time. Only one session will be established.