A method performed by a first access network node for determining a time synchronisation inaccuracy value between the first access network node and a second access network node , wherein the time synchronization inaccuracy is a time difference between internal clocks of the first access network node and the second access network node, the first access network node being communicatively connected to the second access network node , the method comprising: • receiving a Precision Time Protocol, PTP, packet including node identifications, Node IDs, representing respective transport network nodes along a first path extending between a grandmaster entity and the first access network node , • from the second access network node , obtaining Node IDs representing respective transport network nodes along a second path extending between the grandmaster entity and the second access network node , • determining a first common transport network node of the first path and the second path, by comparing received Node IDs of transport network nodes along the first path with obtained Node IDs of transport network nodes along the second path, • calculating the time synchronisation inaccuracy value between the first access network node and the second access network node , based on: the number of transport network nodes of the first path between the first common transport network node and the first access network node ; and the number of transport network nodes of the second path between the first common transport network node and the second access network node , the calculating being further based on respective time inaccuracy values of: the transport network nodes of the first path between the first common transport network node and the first access network node ; and the transport network nodes of the second path between the first common transport network node and the second access network node . • receiving a Precision Time Protocol, PTP, packet including node identifications, Node IDs, representing respective transport network nodes along a first path extending between a grandmaster entity and the first access network node , • from the second access network node , obtaining Node IDs representing respective transport network nodes along a second path extending between the grandmaster entity and the second access network node , • determining a first common transport network node of the first path and the second path, by comparing received Node IDs of transport network nodes along the first path with obtained Node IDs of transport network nodes along the second path, • calculating the time synchronisation inaccuracy value between the first access network node and the second access network node , based on: the number of transport network nodes of the first path between the first common transport network node and the first access network node ; and the number of transport network nodes of the second path between the first common transport network node and the second access network node , the calculating being further based on respective time inaccuracy values of: the transport network nodes of the first path between the first common transport network node and the first access network node ; and the transport network nodes of the second path between the first common transport network node and the second access network node . <EOS>