When a new congestion control algorithm is proposed, TCP friendliness needed to be satisfied.
TCP friendliness means that the average throughput of application using the new congestion control algorithm should NOT exceed that of traditional TCP congestion control.
reference:
S.Floyd, M.Handley, J.Padhye, J.Widmer, "Equation-Based Congestion Control for Unicast Applications", ACM SIGCOMM Computer Communication Review, vol. 30, no. 4, pp. 43-56, Oct. 2000.