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There are three main frame transmission modes:
- Fast-forward –
With this transmission mode, the switch reads the destination
address before receiving the entire frame. The frame is then
forwarded before the entire frame arrives. This mode decreases the
latency of the transmission but has poor LAN switching error
detection. Fast-forward is the term used to indicate a switch is in
cut-through mode.
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Store-and-forward –
The entire frame is received
before any forwarding takes place. The destination and source
addresses are read and filters are applied before the frame is
forwarded. Latency occurs while the frame is being received. Latency
is greater with larger frames because the entire frame must be
received before the switching process begins. The switch has time
available to check for errors, which allows more error detection.
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Fragment-free –
This mode of switching reads the first 64 bytes of an Ethernet frame
and then begins forwarding it to the appropriate port or ports.
Fragment-free is a term used to indicate the switch is using
modified cut-through switching.
Another transmission mode is a
combination of cut-through and store-and-forward. This hybrid mode is
called adaptive cut-through. In this mode, the switch uses cut-through
until it detects a given number of errors. Once the error threshold is
reached, the switch changes to store-and-forward mode.
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Interactive Media Activity
Drag and Drop: Switching Method Trigger Points
When the student has completed this activity, the student
will be able to understand the different methods of switching.
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