A method comprising: generating a Session Description Protocol, SDP, construct, the SDP construct being arranged to be included in a first signaling flow, the first signaling flow being a Session Initiation Protocol, SIP, signaling flow; providing an attribute in the SDP construct, the attribute being provided in a body of a payload of the SDP construct, the attribute being arranged to identify an application type associated with a first traffic flow, the first traffic flow being a real-time transport protocol, RTP, traffic flow; forwarding the SDP construct on the first signaling flow from a first element in a first administrative domain to a second element in a second administrative domain, wherein the attribute further comprises a directional tag arranged to enable the second administrative domain to process the first traffic flow by indicating whether the traffic is to be sent only, received only, or both sent and received; wherein the method further comprises, after forwarding the SDP construct on the first signaling flow: determining that the application type associated with the first traffic flow has changed; generating an updated SDP construct, the SDP construct being arranged to be included in a second signaling flow, the second signaling flow being a SIP signaling flow between the first and second elements (160a, 160b); providing an updated attribute in the updated SDP construct, the updated attribute being arranged to identify the changed application type; and forwarding the updated SDP construct on the second signaling flow. generating a Session Description Protocol, SDP, construct, the SDP construct being arranged to be included in a first signaling flow, the first signaling flow being a Session Initiation Protocol, SIP, signaling flow; providing an attribute in the SDP construct, the attribute being provided in a body of a payload of the SDP construct, the attribute being arranged to identify an application type associated with a first traffic flow, the first traffic flow being a real-time transport protocol, RTP, traffic flow; forwarding the SDP construct on the first signaling flow from a first element in a first administrative domain to a second element in a second administrative domain, wherein the attribute further comprises a directional tag arranged to enable the second administrative domain to process the first traffic flow by indicating whether the traffic is to be sent only, received only, or both sent and received; wherein the method further comprises, after forwarding the SDP construct on the first signaling flow: determining that the application type associated with the first traffic flow has changed; generating an updated SDP construct, the SDP construct being arranged to be included in a second signaling flow, the second signaling flow being a SIP signaling flow between the first and second elements (160a, 160b); providing an updated attribute in the updated SDP construct, the updated attribute being arranged to identify the changed application type; and forwarding the updated SDP construct on the second signaling flow. determining that the application type associated with the first traffic flow has changed; generating an updated SDP construct, the SDP construct being arranged to be included in a second signaling flow, the second signaling flow being a SIP signaling flow between the first and second elements (160a, 160b); providing an updated attribute in the updated SDP construct, the updated attribute being arranged to identify the changed application type; and forwarding the updated SDP construct on the second signaling flow.