A method, being performed by a SIP server, comprising: initiating a Session Initiation Protocol, SIP, communication session between a line side User Agent, UA, and a far side UA, in which the line side UA sets an initial Differentiated Services Code Point, DSCP, value in a protocol session field for the SIP communication session, receiving a SIP INVITE message, including the initial DSCP value, from the line side UA and forwarding it to the far side UA; receiving, from the far side UA, a SIP response message and forwarding it to the line side UA; transmitting, to the far side UA, a SIP acknowledgement message, received from the line side UA, thereby starting the SIP communication session; in response to a change in condition of the SIP communication session: generating a new DSCP value; replacing the initial DSCP value by the new DSCP value in the protocol session field or adding the new DSCP value to a second protocol session field of the existing SIP communication session, such that there are at least two DSCP values for the protocol session; and transmitting a SIP INFO method request message having the new DSCP value to the line side UA informing it to mark all future Real-Time Transport Protocol, RTP, packets for the current SIP communication session with the new DSCP value, wherein the new DSCP value is different to the initial DSCP value. initiating a Session Initiation Protocol, SIP, communication session between a line side User Agent, UA, and a far side UA, in which the line side UA sets an initial Differentiated Services Code Point, DSCP, value in a protocol session field for the SIP communication session, receiving a SIP INVITE message, including the initial DSCP value, from the line side UA and forwarding it to the far side UA; receiving, from the far side UA, a SIP response message and forwarding it to the line side UA; transmitting, to the far side UA, a SIP acknowledgement message, received from the line side UA, thereby starting the SIP communication session; in response to a change in condition of the SIP communication session: generating a new DSCP value; replacing the initial DSCP value by the new DSCP value in the protocol session field or adding the new DSCP value to a second protocol session field of the existing SIP communication session, such that there are at least two DSCP values for the protocol session; and transmitting a SIP INFO method request message having the new DSCP value to the line side UA informing it to mark all future Real-Time Transport Protocol, RTP, packets for the current SIP communication session with the new DSCP value, wherein the new DSCP value is different to the initial DSCP value. generating a new DSCP value; replacing the initial DSCP value by the new DSCP value in the protocol session field or adding the new DSCP value to a second protocol session field of the existing SIP communication session, such that there are at least two DSCP values for the protocol session; and transmitting a SIP INFO method request message having the new DSCP value to the line side UA informing it to mark all future Real-Time Transport Protocol, RTP, packets for the current SIP communication session with the new DSCP value, wherein the new DSCP value is different to the initial DSCP value.