An optical connection path surveillance device for a transparent optical
network includes analysis means (80, 81) adapted to detect node
signatures carried by an optical signal in transit at a point of said
network, each node signature including information uniquely associated
with a switching node of the network. The analysis means include
calculation means (81) adapted to determine a number of hops from said
detected node signatures and error detection means (81) adapted to
compare said number of hops to a predetermined threshold in order to
detect a routing error in relation to said optical signal if said
threshold is exceeded. In one embodiment, a surveillance device detects
looped paths on the basis of the detected node signatures.