When a router connects to a Frame Relay wide area network using a serial DTE interface, how is the clock rate or timing for that link determined?

Introduction / Context:
On serial WAN links, only one side provides clocking or timing, while the other side synchronizes to that clock. Understanding which device is responsible for clocking on a Frame Relay connection is essential for correct configuration and troubleshooting of DTE and DCE roles.

Given Data / Assumptions:

• The router is connected to a Frame Relay network using a serial interface configured as a DTE.
• DTE stands for data terminal equipment, typically customer premises equipment such as routers.
• The service provider supplies a CSU or DSU that connects to the Frame Relay cloud.
• The question asks how the clock rate is determined on this type of link.

Concept / Approach:
In synchronous serial communication, the DCE device provides clocking, and the DTE device synchronizes to it. For a typical Frame Relay deployment, the service provider or carrier supplies the DCE role through a CSU or DSU, or through a provider managed device at the local loop. The customer router acts as the DTE and does not generate the line clock when connected to a real service provider. Therefore, the router does not configure a clock rate on such live links because timing comes from the CSU or DSU.

Step-by-Step Solution:
1. Identify the router role: it is described as having a serial DTE interface, which implies it is the customer side device.2. Recall that in DCE and DTE pairings, the DCE device provides the clock rate for the synchronous link.3. In a Frame Relay deployment, the CSU or DSU provided by the service provider acts as the DCE and connects toward the Frame Relay network.4. The router, as DTE, simply receives the timing from the CSU or DSU and does not configure a clock rate for that live circuit.5. Therefore, the correct statement is that the clock rate is supplied by the CSU or DSU device, not by the router.

Verification / Alternative check:
In a lab environment where two routers are directly connected back to back, one router is configured as DCE and requires a clock rate command, while the other is DTE. However, when connected to an actual provider network, the customer router is always DTE and no clock rate is configured. Provider documentation and Cisco training materials emphasize this distinction.

Why Other Options Are Wrong:
Option B incorrectly suggests that the far end router provides the clock, which is not how service provider circuits are designed. Option C describes the lab scenario where a router with a DCE cable uses the clock rate command, but the question explicitly states that the interface is DTE on a Frame Relay WAN link. Option D is vague and incorrect because clocking is not derived from higher layer protocols; it is a Physical layer function provided by the DCE device.

Common Pitfalls:
A typical mistake is to memorize the clock rate command without remembering that it applies only to DCE interfaces, commonly used in labs. In real world provider connections, the customer router rarely sets the clock; it simply synchronizes to the service provider equipment. Understanding this difference will help you correctly answer questions about DTE and DCE roles in WAN technologies.

Final Answer:
The clock rate is supplied by the attached CSU or DSU device owned by the service provider.