code: private void connectBacklink(final AbstractJobVertex vertex, final ChannelType channelType,
  			final int indexOfOutputGate, final int indexOfInputGate,
  			DistributionPattern distributionPattern) {
  
  		// Make sure the array is big enough
  		for (int i = this.backwardEdges.size(); i <= indexOfInputGate; i++) {
  			this.backwardEdges.add(null);
  		}
  
  		this.backwardEdges.set(indexOfInputGate, new JobEdge(vertex, channelType, indexOfOutputGate,
  			distributionPattern));
  	}
docs: Creates a backward link from a connected job vertex.
  
  @param vertex
  the job vertex to connect to
  @param channelType
  the channel type the two vertices should be connected by at runtime
  @param compressionLevel
  the compression level the corresponding channel should have at runtime
  @param indexOfOutputGate
  index of the producing task's output gate to be used
  @param indexOfInputGate
  index of the consuming task's input gate to be used