Switching Fabrics
💡 The Core Idea
The switching fabric is the hardware interconnect that moves data from the input port to the output port. Its capacity determines the total throughput of the router.
🧠 Types of Fabrics
1. Memory (Generation 1)
- Mechanism: Packet is copied into the CPU’s RAM, then copied out.
- Limit: Limited by memory bandwidth and bus speed. Behaves like a standard PC.
2. Shared Bus (Generation 2)
- Mechanism: All input ports share a single communication bus. Only one packet can cross at a time.
- Limit: Bus bandwidth.
3. Crossbar Switch (Generation 3/Modern)
- Mechanism: A grid of horizontal and vertical buses. Multiple packets can cross simultaneously (e.g., A->Y and B->X) as long as they don’t share an output.
- Challenge: Head-of-Line (HOL) Blocking (if the first packet in the queue is blocked, subsequent packets are stuck).