There is provided a method comprising: receiving, by a first network node, data packets transmitted by a second network node; if at least one data packet of the data packets is noticed not being available to the first network node, sending an indication to the second network node that the at least one data packet of the data packets is not available to the first network node, and repeating sending the indication until a confirmation message is received, wherein the confirmation message comprises confirmation that the indication is received by the second network node.