in the augmented control state information for the connection that the atm cell is in is set to 1 if so 1276 yes the ingress line card is the loopback location therefore the cell is looped back at the ingress line card using the procedure described in 1 a above and the corresponding processing steps 1218 1228 of fig1 otherwise the cell is dropped if the card_id of the ingress line card does not match llid 706 of the atm cell 1274 no the llid is masked with the node_id of the line card and it is compared to the card_id of the line card masked with this node_id mask if the two masked fields match 1278 yes and remote_endpoint_indication 1104 of the augmented circuit state of the connection that the atm cell is in is set 1280 yes the cell must be looped back at the node at a remote card accordingly the procedure is the same as that described in 1 b above and steps 1242 1262 of fig1 in this latter case the remote slot_id is obtained by masking the llid with the 1 39 s complement of the node_id_mask alternatively a slot_id mask could be stored as well and used to mask the llid the slot_id extracted from the cell must match the egress slot_id in the circuit state if there is no match.