Difference between Store and Forward Switch and Cut Through Switch

This page compares Store and Forward Switch vs Cut Through Switch and mentions difference between Store and Forward Switch and Cut Through Switch or switching.

The switches operate at layer-2 (i.e. data link) and layer-3 (i.e. network layer) of OSI protocol stack.

Figure depicts entire L2 frame contents (i.e. FCS, L3/L4 data, ethernet type, source and destination MAC addresses) on which switches operate.

Store and Forward Switch or Switching

Store and Forward Switch

Definition: The switch which forward the frame only after receiving the entire frame contents is known as Store and Forward Switch. The process followed by this switch is known as Store and Forward Switching.

Following are the functional features of store and forward switch.
• Do error checking (using FCS) on each frame after the entire frame has arrived into the switch. This switch calculates FCS from received frame frame and compare it with received FCS value to determine validity of frame.
• If the error checking algorithm determines there is no error, the switch looks in its MAC address table for the port to which to forward the destination device.
• Store and Forward Switches are highly reliable because does not forward bad frames.
• Slower than other types of switches because it holds on to each frame until it is completely received to check for errors before forwarding.

Cut Through Switch or Switching

Definition: The switch which forward the frame after just examining the frame's destination MAC address to appropriate port is known as Cut Through Switch. The process followed by this switch is known as Cut Through Switching. This switch directly operates on destination MAC address embedded in L2 frame as shown.

Following are the functional features of Cut Through Switch.
• Faster than store and forward because does not perform error checking on frames.
• Reads address information for each frame as the frames enter the switch.
• After looking up the port of the destination device, frame is forwarded.
• Cut Through Switch forwards bad frames. This leads to performance penalty because bad frames can not be used and replacement frames must be sent which creates additional traffic.

Fragment free cut through switch

Following are the features of this Fragment free cut through switch type:
• Combines speed of cut through switch with error checking functionality.
• Forwards all frames initially, but determines that if a particular port is receiving too many bad frames, it reconfigures the port to store and forward mode.
• This switch is considered to be preferred switching solution.

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