When you make a IMPS transfer, your sender mobile first sends this information to the sender bank , which checks the data; whether your MMID is correct or not and if it matches with what it has in its system. If it's all correct, it debits the money from your bank account and transfers this to the NCPI server, which then transfers it back to the receiver's bank. The receiver bank goes about checking everything again and then sends the status of the whole transaction to NCPI, which passes it back to Sender's bank. Both Receiver and Sender are then updated about the transaction through SMS. All this normally takes just about 15-30 seconds for everything to happen and the money gets transferred near instantaneously.
If receive a message saying that "IMPS transfer pending at bank's end", it states that the transaction is pending in between Sender's bank and Receiver's bank as shown in the image below. This process can take up to 15-30 minutes be patience.