Determining a time synchronization inaccuracy value between a first node and a second node. A PTP packet is received including Node IDs representing respective transport nodes along a first path, and from the second node Node IDs are obtained representing respective transport nodes along a second path. Furthermore, a first common node of the first path and the second path is determined. The time synchronization inaccuracy value between the first node and the second node is calculated. By including Node IDs in received PTP packets before forwarding them to a node, the node is enabled to determine a first common node. Thereby, the node may calculate relative time inaccuracy values with respect to the other access network nodes, which may be used to decrease inaccuracy time synchronization for co-ordination functions.