If this is a lack of bandwidth at the player end then you will need to lower he bitrate of the stream as adding a sortbuffer will only fix the stream for the duration of the buffer.
A buffer can be added on the player side specifically JW player and Flowplayer have a buffer which is configurable.
If it's a problem from the source and the packets are out of order and this is effecting the stream then you can add a buffer in Wowza which will allow time to manage packets before the client plays them.
To do this, In the Application.xml file add the following Property blocks to the Streams/Properties section:
The "sortBufferSize" value is in milliseconds.