QoS fundamentals for the case where multiple PWs are multiplexed over a single cross-connect are shown in Figure: QoS on FPE-based PW-port.
Egress QoS may be applied on both sides of the cross-connect (PXC sub-ports .a and .b) to control congestion on the cross-connect itself. This can be accomplished via an Egress Port Scheduler (EPS) applied to each sub-port.
EPS applied to pxc-1.a (transit side) manages congestion on the cross-connect for traffic coming from the external PWs. A single set of queues is shared by all PWs utilizing this cross-connect in this direction.
EPS applied to the pxc-1.b (terminating side) is used to manage congestion on the cross-connect for traffic going toward the PWs (leaving the SR OS node). A set of queues is dedicated to each PW-port SAP.
QoS on PXC sub-ports is described in the 7450 ESS, 7750 SR, 7950 XRS, and VSR Interface Configuration Guide, "PXC".