TCP uses only cumulative acknowledgements.
sender seqno=100--------------------------receiver ack=101
sender seq no=150(instead of 101)------------------receiver ack=101
sender seq no=200--------------------receiver ack=101
sender seq no=101------------------------receiver ack=201
Receivers sends only cumulative instead of independent seq no for every segment.
http://www.cs.newpaltz.edu/~easwaran/CCN/Week6/tcpACK.pdf