code: public ExecutionVertex getVertexByChannelID(final ChannelID id) {
  
  		final ExecutionEdge edge = this.edgeMap.get(id);
  		if (edge == null) {
  			return null;
  		}
  
  		if (id.equals(edge.getOutputChannelID())) {
  			return edge.getOutputGate().getVertex();
  		}
  
  		return edge.getInputGate().getVertex();
  	}
docs: Identifies an execution by the specified channel ID and returns it.
  
  @param id
  the channel ID to identify the vertex with
  @return the execution vertex which has a channel with ID <code>id</code> or <code>null</code> if no such vertex
  exists in the execution graph