The Carrier Supporting Carrier (CSC) VPRN is a service configured and managed by the backbone (or wholesale) service provider on its Provider Edge routers, known as CSC-PEs. These CSC-PEs connect to the customer carrier's routers, known as CSC-CEs. The CSC VPRN provides an MPLS-based transport service for the customer carrier, effectively acting as a "backbone-as-a-service." The customer carrier's CSC-CE router is a participant in the VPRN service provided by the backbone carrier; it does not host the CSC VPRN service configuration itself.

A. The primary business driver for the CSC model is to enable a customer carrier to offer services over a wide area without the capital expenditure of building its own MPLS core.

B. "Carrier's carrier" and "carrier serving carrier" are widely used industry synonyms that accurately describe the business relationship in a CSC model.

C. The customer carrier leverages the backbone transport provided by the CSC VPRN to connect its own points of presence, from which it delivers its own retail services (like Internet or VPNs) to its end-customers.

1. Nokia 7750 SR OS R21.10.R1 Layer 3 Services Guide: VPRN, Section: "Carrier Supporting Carrier (CSC)".

Reference for Correct Answer (D): The guide states, "A VPRN is created on the backbone provider's PE (CSC-PE) for the carrier customer." This explicitly places the CSC VPRN configuration on the backbone provider's equipment, not the customer carrier's.

Reference for Incorrect Option (A): The guide's introduction to CSC explains that it allows a carrier to "outsource its backbone" to another provider.

Reference for Incorrect Option (C): The guide describes the model: "The customer carrier can then use this backbone to offer its own services to its customers."

2. IETF RFC 4364: BGP/MPLS IP Virtual Private Networks (VPNs), Section 10: "Carrier's Carrier" VPNs.

Reference for Correct Answer (D) & Incorrect Option (B): This section, which provides the foundational standard for the "Carrier's Carrier" (CSC) model, describes the backbone carrier's routers as PEs and the customer carrier's routers as CEs. The VPN service is provided by the PEs to the CEs, confirming the configuration location and the terminology.