Router’s Four Core Components | Generated by AI

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Question: From the perspective of functional structure, a router includes input ports, output ports, routing processor, and which of the following components?

A. Routing control
B. Interface
C. Switching fabric
D. A/D conversion

Answer:

The correct answer is C. Switching fabric

Detailed Explanation:

A modern router’s functional architecture (also called its internal structure or building blocks) is typically composed of four main parts:

1. Input ports (输入端口)
   • Physical interfaces that receive incoming packets from the network.
   • Perform Layer 1–2 functions (physical reception, link-layer processing).
   • Often include line cards with PHY, MAC, and initial packet lookup/processing.
2. Output ports (输出端口)
   • Physical interfaces that transmit outgoing packets to the next hop.
   • Handle queuing, scheduling, and transmission.
3. Routing processor (路由处理器 / 路由引擎 / control plane)
   • Runs the routing protocols (OSPF, BGP, RIP, etc.).
   • Maintains the routing table (RIB – Routing Information Base).
   • Computes the forwarding table (FIB – Forwarding Information Base).
   • Distributes forwarding decisions to the line cards / ports.
4. Switching fabric (交换结构 / 交换矩阵 / switching fabric / backplane / interconnect)
   • The internal high-speed interconnect that moves packets from input ports to output ports.
   • This is the data plane forwarding engine — the actual hardware path that packets take inside the router after the forwarding decision is made.
   • Common types: shared memory, crossbar switch, multistage interconnection network (e.g., Clos network), etc.
   • Without the switching fabric, packets cannot be transferred from input to output at high speed.

Why the other options are incorrect:

• A. Routing control
  → Vague term. Routing control is part of the routing processor (control plane), not a separate structural component. This is not one of the standard four blocks of a router.

• B. Interface
  → Interfaces are already covered by input ports and output ports. “Interface” is too general and not listed as a distinct fourth component in standard router architecture.

• D. A/D conversion (Analog-to-Digital conversion)
  → This belongs to physical layer hardware (e.g., in modems or optical transceivers), not a functional block of a router’s packet-forwarding architecture.

Standard textbook / exam model of router structure (very frequently tested):

Router =

• Input ports
• Output ports
• Switching fabric (交换结构)
• Routing processor (路由处理器)

Your answer A was incorrect because “路由控制” is not a standard separate component — it is a function performed inside the routing processor.

Correct answer: C. Switching fabric (交换结构)

References:

• None (standard router architecture from “Computer Networking: A Top-Down Approach” by Kurose & Ross, Cisco CCNA/CCNP materials, and common Chinese network engineering certification textbooks)

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