A method for a call control node (MSC-S2) for setting up transmission of voice data from a calling party towards a called party via at least one media gateway node (MGW-1, MGW-2), said call control node (MSC-S2) acting as a terminating call control node being adapted for communicating with the at least one media gateway node (MGW-1, MGW-2) and with an originating call control node (MSC-S1), wherein each media gateway node (MGW-1, MGW-2) comprises at least a context (C1, C2) and wherein each context (C1, C2) comprises at least two terminations (T1, T2, T3, T4) towards a calling party or a called party or towards a termination (T1, T2, T3, T4) of another context (C1, C2), the method comprising: receiving first information from the originating call control node (MSC-S1) indicative of at least one media gateway node (MGW-1, MGW-2) usable for transmitting the voice data; receiving second information from the originating call control node (MSC-S1) indicative of a codec to be used from the calling party towards the at least one media gateway node (MGW-1, MGW-2) usable for transmitting the voice data; determining whether the voice data is transmittable by the at least one media gateway node (MGW-1, MGW-2) towards the called party encoded by said codec; determining whether a common media gateway node (MGW-1) is usable by both the originating call control node (MSC-S1) and the terminating call control node (MSC-S2), wherein the common media gateway node (MGW-1) comprises at least two contexts (C1, C2) and wherein a termination (T2, T3) of one context (C1, C2) is connected to a termination (T2, T3) of the other context (C1, C2); sending first backward information to the originating call control node (MSC-S1) indicative of said codec; sending second backward information to the originating call control node (MSC-S1) indicative of the common media gateway node (MGW-1); and enforcing, based on the determination of a common media gateway node (MGW-1), said codec on the connected terminations (T2, T3) between the contexts (C1, C2). receiving first information from the originating call control node (MSC-S1) indicative of at least one media gateway node (MGW-1, MGW-2) usable for transmitting the voice data; receiving second information from the originating call control node (MSC-S1) indicative of a codec to be used from the calling party towards the at least one media gateway node (MGW-1, MGW-2) usable for transmitting the voice data; determining whether the voice data is transmittable by the at least one media gateway node (MGW-1, MGW-2) towards the called party encoded by said codec; determining whether a common media gateway node (MGW-1) is usable by both the originating call control node (MSC-S1) and the terminating call control node (MSC-S2), wherein the common media gateway node (MGW-1) comprises at least two contexts (C1, C2) and wherein a termination (T2, T3) of one context (C1, C2) is connected to a termination (T2, T3) of the other context (C1, C2); sending first backward information to the originating call control node (MSC-S1) indicative of said codec; sending second backward information to the originating call control node (MSC-S1) indicative of the common media gateway node (MGW-1); and enforcing, based on the determination of a common media gateway node (MGW-1), said codec on the connected terminations (T2, T3) between the contexts (C1, C2).