It is possible to transport services over GRE-MPLS tunnels when the service MTU is larger than the cellular interface MTU. This requires the GRE-MPLS packets to be fragmented and reassembled using GRE SDP fragmentation and reassembly operations. See "GRE SDP tunnel fragmentation and reassembly" in the 7450 ESS, 7750 SR, 7950 XRS, and VSR Services Overview Guide.