SR OS supports subscriber traffic forwarding over an uplink GTP tunnel toward a GGSN or P-GW. This requires a per-subscriber GTP tunnel based on authentication to be configured. Each subscriber may access only a single APN. Both GTPv1 (Gn) and GTPv2 (S2a/S2b) are supported. A single primary PDP context per subscriber is supported on the Gn interface (3GPP TS 29.060 Release 8) from SR OS to the GGSN. A single default-bearer per subscriber is supported on the S2b interface (3GPPTS 29.274 Release 10), and S2a interface (3GPP TS 29.274 Release 11) from SR OS to the P-GW.