Hello Sathish
Yes, initially, however the OSPF RFC gives some leeway to vendors to choose how they want to implement it. Take a look at this NetworkLessons note.
These are indeed unicast. They provide summaries of the router’s LSDB (Link-State Database).
LSR (Link-State Request) — These are unicast, not multicast. They are used to request more information about a particular LSA.
LSU (Link-State Update) — These are unicast in response to LSR, and multicast for flooding LSAs. They are used to send updates of a router’s LSDB.
LSAck (Link-State Acknowledgment) — These are unicast for received LSAs and Multicast for grouped LSAcks
I hope this has been helpful!
Laz