The TCP receiver "advertises" free buffer space by including rwnd $($receive window$)$ value in every segment. The TCP receive window $($rwnd$)$ is expressed as:O rwnd $=$ RcvBuffer $-[$LastByteRcvd $-$ LastByteACKed$]$O rwnd $=$ RcvBuffer $-[$LastByteRcvd $-$ LastByteRead$]$O rwnd $=$ RcvBuffer $-[$LastByteRcvd $-$ LastByteSent$]$O rwnd $=$ RcvBuffer $-[$LastByteRead $-$ LastByteRcvd$]$