Carrier Supporting Carrier (CSC) is a solution for the 7750 SR and 7950 XRS that allows one service provider (the Customer Carrier) to use the IP VPN service of another service provider (the Super Carrier) for some or all of its backbone transport. RFC 4364 defines a Carrier Supporting Carrier solution for BGP/MPLS IP VPNs that uses MPLS on the interconnections between the two service providers to provide a scalable and secure solution.
CSC support in SR OS allows a 7750 SR or 7950 XRS to be deployed as any of the following devices shown in Figure: Carrier Supporting Carrier reference diagram:
PE1 (service provider PE)
CSC-CE1, CSC-CE2 and CSC-CE3 (CE device from the point of view of the backbone service provider)
CSC-PE1, CSC-PE2 and CSC-PE3 (PE device of the backbone service provider)
ASBR1 and ASBR2 (ASBR of the backbone service provider)
Figure: Carrier Supporting Carrier reference diagram