Which feature prevents oversubscription of WAN links?

• A. QoS policing
• B. Bandwidth reservation
• C. Load balancing
• D. CAC

Answer: (D)

Preventing oversubscription of WAN links is handled by Call Admission Control, which gates new sessions based on available bandwidth. When a new call or session is requested, CAC checks how much bandwidth is already in use and how much is reserved for guaranteed QoS. If there is enough capacity to meet the required QoS for the new session, the admission proceeds; if not, the request is blocked or delayed to protect the performance of existing traffic. This ensures that the WAN link isn’t overwhelmed and voice/video quality remains acceptable.

QoS policing enforces traffic rates after admission, not before, so it doesn’t prevent new sessions from consuming capacity. Load balancing distributes traffic across multiple links but can still allow overall demand to exceed total capacity. Bandwidth reservation can set aside capacity, but it’s not as dynamic or universally applied for admission control as CAC.