PRCA (Proportional Rate Control Algorithm) cont.

Problems with PRCA:
- originally only negative polarity feedback used therefore if RM cell to reduce rate lost, source continues to increase rate -fixed by introducing “positive” polarity feedback too.
- Fairness problem: Long path VC have large probability of EFCI bit being set; the switches on congestion set EFCI on all VC’s - fixed by using selective feedback or intelligent marking