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Store-and-Forward Switching
With Store-and-Forward switching, the switch copies the entire frame into its buffer and computes the
CRC.
The frame is discarded if a CRC error is detected or if the frame is a runt (less than 64 bytes including
the CRC) or a giant (more than 1518 bytes including the CRC). The LAN switch then looks up the
destination address in its switching table and determines the outgoing interface. The frame is then sent
to the interface.
Store-and-Forward switching is standard on Cisco Catalyst 5000 switches.
Latency using Store-and-Forward switching is dependant upon the frame size and is slower than Cut-
through switching.
Cut-Through Switching
With Cut-Through switching, the switch copies only the Destination Address which is the first 6 bytes
after the frame preamble into its buffer. The LAN switch then looks up the destination address in its
switching table and determines the outgoing interface. The frame is then sent to the interface. A cut-
through switch provides reduced latency because it begins to forward the frame as soon as it reads the
destination address and determines the outgoing interface.
Modified Version
Cisco also uses a modified version of switching which is a hybrid of the other two. It works like cut-
through switching, but the packet does not get forwarded until entire packet header is received.
Frame tagging - A Unique User ID placed in the header of each frame as it travels the switch fabric
with a user-assigned ID defined in each frame.
*Keypoints:Know the difference between "Store-and-Forward" and "Cut-Through" switching.Know that Store-and-Forward switching receives the complete frame and checks the CRC beforeforwarding the frame.Know that a Catalyst switch uses a Spanning-Tree Protocol to ensure data flows properly through asingle network path.Know that switches use 3 basic methods to increase available bandwidth 1) loop avoidance, 2)broadcast filtering, and 3) packet forwarding and filtering.Know that the Modified Version of switching does not forward the packet until the data portion isreceived.Know that the latency of Store-and-Forward switching varies with the size of the frames.Know the above definition of Frame Tagging.Know that switches enable high-speed data exchange.Know that a switch cannot translate from one media type to another.Fast Ethernet
Fast Ethernet is based on the Ethernet's CSMA/CD contention method but is ten times faster. Because
of the slot time used in CSMA/CD networks the total segment distance must also be reduced.
Fast Ethernet Specifications
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100BaseTX - 100BaseTX uses a two-pair Category 5 UTP cable with an RJ45 connector and
the same pin out as in 10BaseT. 100BaseTX supports full duplex operation. For 100BaseTX
using Cat5 UTP with a max distance is 100 Meters