Method for transmitting a data stream containing first data packets and second data packets and a reservation request in a packet-switched communication network along a communication connection from a transmitter (2, T) to a receiver (2, L) through at least one switch (2, Sx), wherein the method comprises: (a) transmitting the first data packets without a guaranteed transmission time of the first data packets, and (b) transmitting the second data packets with a guaranteed maximum transmission time of the second data packets, wherein the packet-switched communication network is designed, (i) when transmitting the second data packets with a guaranteed transmission time from the transmitter (2, T) to the receiver (2, L), - to reserve a certain quality of service for this data transmission by way of the reservation request sent by the transmitter (2, T) and - to start the data transmission of the second data packets with a guaranteed transmission time only after receiving confirmation of the sent reservation request by the transmitter (2, T), and (ii) to send selected data of the data stream immediately without previous sending of the reservation request and awaiting confirmation thereof as first data packets without a guaranteed transmission time by the receiver (2, T), even though the selected data are data that are supposed to be transmitted in a guaranteed transmission time, and to forward the reservation request only after the start of the sending of the first data packets, wherein, following reception of confirmation of the forwarded reservation request, data packets of the data stream that have not yet been transmitted are redeclared by the transmitter (2, T) as data packets with a guaranteed transmission time, characterized in that, following reception of confirmation of the forwarded reservation request, first data packets of the data stream, which have already been transmitted without a guaranteed transmission time and have not yet reached the receiver, are redeclared, on their journey along the communication connection in the at least one switch (2, Sx) that receives the data packets (7, 8) and sends them again, as data packets with a guaranteed transmission time. (a) transmitting the first data packets without a guaranteed transmission time of the first data packets, and (b) transmitting the second data packets with a guaranteed maximum transmission time of the second data packets, wherein the packet-switched communication network is designed, (i) when transmitting the second data packets with a guaranteed transmission time from the transmitter (2, T) to the receiver (2, L), - to reserve a certain quality of service for this data transmission by way of the reservation request sent by the transmitter (2, T) and - to start the data transmission of the second data packets with a guaranteed transmission time only after receiving confirmation of the sent reservation request by the transmitter (2, T), and (ii) to send selected data of the data stream immediately without previous sending of the reservation request and awaiting confirmation thereof as first data packets without a guaranteed transmission time by the receiver (2, T), even though the selected data are data that are supposed to be transmitted in a guaranteed transmission time, and to forward the reservation request only after the start of the sending of the first data packets, wherein, following reception of confirmation of the forwarded reservation request, data packets of the data stream that have not yet been transmitted are redeclared by the transmitter (2, T) as data packets with a guaranteed transmission time, characterized in that, following reception of confirmation of the forwarded reservation request, first data packets of the data stream, which have already been transmitted without a guaranteed transmission time and have not yet reached the receiver, are redeclared, on their journey along the communication connection in the at least one switch (2, Sx) that receives the data packets (7, 8) and sends them again, as data packets with a guaranteed transmission time. (i) when transmitting the second data packets with a guaranteed transmission time from the transmitter (2, T) to the receiver (2, L), - to reserve a certain quality of service for this data transmission by way of the reservation request sent by the transmitter (2, T) and - to start the data transmission of the second data packets with a guaranteed transmission time only after receiving confirmation of the sent reservation request by the transmitter (2, T), and - to reserve a certain quality of service for this data transmission by way of the reservation request sent by the transmitter (2, T) and - to start the data transmission of the second data packets with a guaranteed transmission time only after receiving confirmation of the sent reservation request by the transmitter (2, T), and (ii) to send selected data of the data stream immediately without previous sending of the reservation request and awaiting confirmation thereof as first data packets without a guaranteed transmission time by the receiver (2, T), even though the selected data are data that are supposed to be transmitted in a guaranteed transmission time, and