A system for managing a data stream between a first network and a second network, the system comprising a node entity in the first network and a gateway entity situated at a boundary between the first network and the second network, wherein the node entity is configured to transmit a data stream addressed to a destination device in the second network, wherein the data stream comprises a first address of the destination device and wherein the first address is an address in the first network, and wherein the gateway entity is configured to: - receive the data stream from the first network; - use a Network Address Translation, NAT, table and allocate a port to at least one device in the second network; - detect at least one device characteristic of the destination device in the second network and store it in such a way that it can be related to the first address and to a port used via the NAT table, - transmit the at least one device characteristic of the destination device to the node entity in the first network in such a way that the at least one device characteristic is relatable to the data stream and to the first address of the destination device, and further wherein the node entity is configured to: - receive the at least one device characteristic of the destination device from the gateway entity, - relate the at least one device characteristic of the destination device to the data stream, - use the at least one device characteristic to make assumptions on user requirements related to delivery of the data stream to a user of the destination device, - perform Quality of Service management on the data stream based on the assumptions. wherein the node entity is configured to transmit a data stream addressed to a destination device in the second network, wherein the data stream comprises a first address of the destination device and wherein the first address is an address in the first network, and wherein the gateway entity is configured to: - receive the data stream from the first network; - use a Network Address Translation, NAT, table and allocate a port to at least one device in the second network; - detect at least one device characteristic of the destination device in the second network and store it in such a way that it can be related to the first address and to a port used via the NAT table, - transmit the at least one device characteristic of the destination device to the node entity in the first network in such a way that the at least one device characteristic is relatable to the data stream and to the first address of the destination device, - receive the data stream from the first network; - use a Network Address Translation, NAT, table and allocate a port to at least one device in the second network; - detect at least one device characteristic of the destination device in the second network and store it in such a way that it can be related to the first address and to a port used via the NAT table, - transmit the at least one device characteristic of the destination device to the node entity in the first network in such a way that the at least one device characteristic is relatable to the data stream and to the first address of the destination device, and further wherein the node entity is configured to: - receive the at least one device characteristic of the destination device from the gateway entity, - relate the at least one device characteristic of the destination device to the data stream, - use the at least one device characteristic to make assumptions on user requirements related to delivery of the data stream to a user of the destination device, - perform Quality of Service management on the data stream based on the assumptions. - receive the at least one device characteristic of the destination device from the gateway entity, - relate the at least one device characteristic of the destination device to the data stream, - use the at least one device characteristic to make assumptions on user requirements related to delivery of the data stream to a user of the destination device, - perform Quality of Service management on the data stream based on the assumptions.