The endpoints of an N-to-1 mode VLL on a 7750 SR can be:
ATM VCs — VPI/VCI translation is supported (that is, the VPI/VCI at each endpoint does not need to be the same).
ATM VPs — VPI translation is supported (that is, the VPI at each endpoint need not be the same, but the original VCI is maintained).
ATM VTs (a VP range) — No VPI translation is supported (that is, the VPI/VCI of each cell is maintained across the network).
ATM ports — No translation is supported (that is, the VPI/VCI of each cell is maintained across the network).
For N-to-1 mode VLLs, cell concatenation is supported. Cells are packed on ingress to the VLL and unpacked on egress. As cells are being packed, the concatenation process may be terminated by:
Reaching a maximum number of cells per packet.
Expiry of a timer.
(Optionally) change of the CLP bit.
(Optionally) change of the PTI bits indicating the end of the AAL5 packet.
In N-to-1 mode, OAM cells are transported through the VLL as any other cell. The PTI and CLP bits are untouched, even if VPI/VCI translation is carried out.