How Does the Switch Buffer and Forward?

About this interactive

From the lesson: - **Port-based memory:** every port has a fixed amount of memory. Its queue can fill and drop frames, and a frame waiting there can hold up the frames behind it. Needs more memory overall. - **Shared memory:** one pool, allocated to ports as they need it. The preferred design, and it can get by with less memory. - **Store-and-forward:** takes in the whole frame and checks the frame check sequence in its trailer before sending it on. Slower, but a bad frame is dropped. - **Cut-through** sends sooner, without checking the whole frame: - **Fast-forward:** starts forwarding as soon as it has read the destination MAC address. The fastest, but bad frames go on to the next hop. - **Fragment-free:** reads the first 64 bytes first, since collision damage shows up there. In between on speed.

What you'll learn

Tell port-based memory buffering (a fixed share for each port) from shared memory buffering (one pool, given out as needed)
Tell store-and-forward (the whole frame, checked before sending) from the two cut-through methods: fast-forward (sends once the destination MAC is read) and fragment-free (reads the first 64 bytes first)

Aligned to

Cisco CCNA

1.13 Describe switching concepts

CompTIA Network+

1.2 Compare and contrast networking appliances, applications, and functions.

Key terms

Buffering: The temporary storage of a frame in switch memory while the switch determines the correct outgoing port for forwarding.
Port-Based Memory Buffering: A buffering method that pre-allocates a fixed amount of memory to each switch port, storing incoming frames until the destination port is determined.
Shared Memory Buffering: A buffering method that dynamically allocates a common pool of memory across all switch ports, adjusting to the current traffic demands of each port.
Store-and-Forward Switching: A switching method that receives and stores the entire frame, performs an error check, and only forwards the frame if it passes validation.
Fast-Forward Switching: A cut-through switching method that reads only the destination MAC address and immediately begins forwarding the frame, offering the lowest latency but no error checking.
Fragment-Free Switching: A cut-through switching method that reads the first 64 bytes of a frame to check for collision fragments before forwarding, balancing speed and minimal error detection.
Latency: The time delay between sending a request and receiving a response over a network.
Frame Check Sequence: A cyclic redundancy check value appended to the end of a data link frame that allows the receiver to detect transmission errors. The sending device calculates the FCS from the frame contents, and the receiving device recalculates it; a mismatch means the frame was corrupted and should be discarded.

Topics

Switch Buffering Store And Forward Cut Through Fast Forward Fragment Free Interactive Categorize

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