Some years ago we have been told by more than one vendor, that we would need twice the number of boxes to support the SIP over TCP to achieve the same performan

Some years ago we have been told by more than one vendor, that we would need twice the number of boxes to support the SIP over TCP to achieve the same performance as SIP over UDP. And given the limited IP competence of telco vendors, SIP over UDP causes less trouble. One artificially limited the TCP transmission window to 6k (turned out he used an old FreeBSD version that did this to optimize modem dialup connections(!)) One asked us to choose between SACK and the ability to handle re-ordered segments, as his stack couldn't handle both.