LTE: what is the use of SN and HFN at PDCP layer and why it is required ?

Question

I came through these terms like seamless and lossless handover, what is the significance's in these type of handovers and when these thing happens?

Answer 1

It is an overflow counter mechanism used in the eNB and UE in order to limit the actual number of sequence number bits that is needed to be sent over the radio. The HFN needs to be synchronized between the UE and eNB, i.e. when the PDCP SN has reach its maximum value (which in turn depends on number of bits used for PDCP SN (5, 7 or 12 bits), PDCP SN will be restarted from 0 AND HFN will be increased by one. COUNT (32 bits) is made up of PDCP SN together with HFN, and is used in the security process.

Comments

Nice explanation

Answer 2

so can we say that if we set 12 bits instead 7 bits then it is easier for UE to decode packets correctly ? what is the advantage and disadvantage of setting 12 bits instead of 7 bits?