It's in protocol.c
static void CompressStart(descriptor_t *apDescriptor)
{
/* If your mud uses MCCP (Mud Client Compression Protocol), you need to
* call whatever function normally starts compression from here - the
* ReportBug() call should then be deleted.
*
* Otherwise you can just ignore this function.
*/
ReportBug("CompressStart() in protocol.c is being called, but it doesn't do anything!\n");
}