Source Quench is an ICMP based mechanism used by network devices to inform data sender that the packets can not be forwarded due to buffers overload. When the message is received by a TCP sender, that sender should decrease its send window to the respective destination in order to limit outgoing traffic.
Source Squench has been not consider now a days any more becoz of some reason: i.e
1. Source Squench message can lost in the way to sender.
2. Source Squencs carry very little information per packect say it only sense basci information regarding congestion.
3. Source Quench messages, like all ICMP messages, are expensive for a router to generate. This is bad because the congestion control mechanism could contribute additional congestion, if router processing resources become a bottleneck.
4. Source Squench can also cause Denial of Service.
In effect, ICMP Source Quench messages are almost never generated on the Internet today, and would be ignored almost everywhere if they still existed.