<P> Once a bridge learns the addresses of its connected nodes, it forwards data link layer frames using a layer 2 forwarding method . There are four forwarding methods a bridge can use, of which the second through fourth methods were performance - increasing methods when used on "switch" products with the same input and output port bandwidths: </P> <Ol> <Li> Store and forward: the switch buffers and verifies each frame before forwarding it; a frame is received in its entirety before it is forwarded . </Li> <Li> Cut through: the switch starts forwarding after the frame's destination address is received . There is no error checking with this method . When the outgoing port is busy at the time, the switch falls back to store - and - forward operation . Also, when the egress port is running at a faster data rate than the ingress port, store - and - forward is usually used . </Li> <Li> Fragment free: a method that attempts to retain the benefits of both store and forward and cut through . Fragment free checks the first 64 bytes of the frame, where addressing information is stored . According to Ethernet specifications, collisions should be detected during the first 64 bytes of the frame, so frames that are in error because of a collision will not be forwarded . This way the frame will always reach its intended destination . Error checking of the actual data in the packet is left for the end device . </Li> <Li> Adaptive switching: a method of automatically selecting between the other three modes . </Li> </Ol> <Li> Store and forward: the switch buffers and verifies each frame before forwarding it; a frame is received in its entirety before it is forwarded . </Li> <Li> Cut through: the switch starts forwarding after the frame's destination address is received . There is no error checking with this method . When the outgoing port is busy at the time, the switch falls back to store - and - forward operation . Also, when the egress port is running at a faster data rate than the ingress port, store - and - forward is usually used . </Li>

What is the characteristics of store and forward switches
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