[Day 9] 2. Switching

Switching refers to the process of forwarding data packets from one device to another within the same network. A switch uses MAC (Media Access Control) addresses to direct the data frames to the correct destination port. It operates at Layer 2 (Data Link Layer) of the OSI model.

Store-and-Forward Switching:

• How it works: The switch receives the entire data frame (i.e., 1518 bytes), checks it for errors using CRC (Cyclic Redundancy Check), and then forwards it if no errors are detected.
• Pros: More reliable as it checks for errors.
• Cons: Higher latency, as the entire frame must be received before forwarding.

Cut-Through Switching:

• How it works: The switch reads only the destination MAC address from the frame(i.e., 6 Bytes) and forwards it immediately without waiting for the entire frame.
• Pros: Lower latency since it starts forwarding earlier.
• Cons: Less reliable, as it forwards corrupted frames since no error-checking occurs.

Modified Cut-Through

• How it works: Combines elements of both store-and-forward and cut-through. The switch may perform a minimal check (e.g., reading the first 64 bytes) to ensure that the frame is not corrupt before forwarding it.
• Pros: Balances speed and reliability, offering lower latency than store-and-forward while still providing some error checking.
• Cons: Slightly more complex implementation compared to pure cut-through.

These mechanisms help determine how switches manage data traffic and influence network performance.

Note: Latency depends on frame size.

When a frame is received:

• If the destination MAC address is a broadcast address, the switch will flood the frame to all its ports.
• If the destination MAC address is unknown, the switch will also flood the frame to all ports.
• If the destination MAC address is recognized / known, the switch will forward the frame only to the specific port associated with that address.