A method of transmitting audio data from a first node to a second node in a communication network comprising: receiving a signal; dividing the signal into frames arranged in a first data stream comprising active and inactive frames wherein the active frames are frames containing information containing voice activity and the inactive frames are frames containing periods of voice inactivity; analysing at least one characteristic of the signal to determine if the signal is stable over a plurality of frames; selecting at least one active frame to be dropped from the plurality of frames of the first data stream on a condition that it is determined that the signal remains stable over a plural number of frames; dropping the selected at least one frame; inputting the frames that are not dropped from the first data stream into a core stream; and transmitting the core stream from the first node to the second node, wherein the frames are inserted into packets in the core stream before transmitting the packets; characterized in that: the method comprises classifying the active frames as containing either a stable voiced sound, a stable unvoiced sound, or an unstable transient sound; the selected at least one frame is selected from the active frames classified as containing either a stable voiced sound or a stable unvoiced sound; and said number of frames that should remain stable according to said condition is reduced if conditions of the communication network are good. receiving a signal; dividing the signal into frames arranged in a first data stream comprising active and inactive frames wherein the active frames are frames containing information containing voice activity and the inactive frames are frames containing periods of voice inactivity; analysing at least one characteristic of the signal to determine if the signal is stable over a plurality of frames; selecting at least one active frame to be dropped from the plurality of frames of the first data stream on a condition that it is determined that the signal remains stable over a plural number of frames; dropping the selected at least one frame; inputting the frames that are not dropped from the first data stream into a core stream; and transmitting the core stream from the first node to the second node, wherein the frames are inserted into packets in the core stream before transmitting the packets; characterized in that: the method comprises classifying the active frames as containing either a stable voiced sound, a stable unvoiced sound, or an unstable transient sound; the selected at least one frame is selected from the active frames classified as containing either a stable voiced sound or a stable unvoiced sound; and said number of frames that should remain stable according to said condition is reduced if conditions of the communication network are good. the method comprises classifying the active frames as containing either a stable voiced sound, a stable unvoiced sound, or an unstable transient sound; the selected at least one frame is selected from the active frames classified as containing either a stable voiced sound or a stable unvoiced sound; and said number of frames that should remain stable according to said condition is reduced if conditions of the communication network are good.