For HSDPA, Apipe and Epipe service termination on the SR where an endpoint-X SAP connects to the mobile RNC (by ATM or Ethernet) and an endpoint Y has a primary spoke-SDP and a secondary SAP on an SR ATM or ASAP MDA (with bridged PDU encapsulation for Epipes). The secondary SAP has the same restrictions as the SAP in endpoint-X for Apipe and Epipe, respectively.
It is sufficient to have a single secondary SAP (without any precedence), which implies that it cannot be mixed with any secondary spoke-SDPs; 1+1 APS and MC-APS is supported on the secondary SAP interface.
Similar to the current pseudowire redundancy implementation, receive should be enabled on both objects even though transmit is only enabled on one.
It is expected that BFD for T-LDP is used in most applications to decrease the fault detection times and minimize the outage times upon failure.