Sure! Let’s dive deeper into what’s inside a router based on Computer Networking: A Top-Down Approach by Jim Kurose & Keith Ross (Chapter 4: The Network Layer).
🔍 Inside a Router: A Detailed Breakdown
A router is a specialized packet-switching device that connects different networks and forwards packets based on IP addresses. It has four main components, each playing a crucial role in packet forwarding.
🏗 1. Input Ports (Ingress)
This is where packets arrive from incoming links. The input port handles:
- Physical-layer functions → Converting signals from wires (Ethernet, fiber, etc.)
- Link-layer functions → Processing Ethernet frames, detecting MAC addresses
- Lookup & Forwarding → Determines the outgoing port using a forwarding table
🔹 Key Subcomponents:
- Line Termination – Converts signals from electrical/optical form to digital
- Link-layer Processing – Extracts IP packets from frames (removes Ethernet headers)
- Lookup & Forwarding Control – Queries the forwarding table to find the correct output port
⚡ Speed Optimization:
- Some routers store forwarding tables in TCAM (Ternary Content Addressable Memory) for fast lookups.
- Direct Memory Access (DMA) is used to transfer packets efficiently from input to output.
🔀 2. Switching Fabric
The switching fabric is the "backbone" of a router, responsible for moving packets from the correct input port to the correct output port.