Explicit Congestion Notification

Explicit Congestion Notification (ECN ) is an extension of the network protocol TCP / IP overload control and is described in RFC (2001) described 3168. Using ECN can tell a router by a simple marking a bit in the IP header of an impending overload. ECN is defined on both the IP level and at the TCP layer of the network layer model and requires two bits in the former the TOS byte in the IP header and in the TCP header. In the TCP header, two bits are used for a 6 -bit block which is reserved for future use.

Are all routers on the path between source and sink ECN -capable, can be combined with this method, the number of due to overload dropped packets reduced by the sink displayed by the router overload danger of source reports back, whereupon this reduces the data rate.

Those who use the ECN should be aware that some administrators have not yet realized the abolition of the TOS byte. Also go routers and firewalls even well-known companies partially unpredictable with the ECN bits to. There is therefore a risk that a compound with activated ECN is not concluded.

ECN, however, can be used only if both hosts declare their willingness to do so. The method uses an ECN bit to (explicit) indicate the jam, place the packets from the network scheduler with RED algorithm only to discard (implicit notification choke packet). The sending station can then restrict its data stream aware. Through the dedicated information ( ECN bit ) line quality is not artificially deteriorated, as is the case with RED / WRED, but not dominate all network nodes, the ECN process and therefore drop the packets which have set the ECN bit. Since the correct behavior for the case of non- ECN -enabled components would be ignoring the ECN bits, these devices are considered to be faulty.

A similar method is the DEC bit.

• TCP / IP