code: protected int decodeMandatoryParameters(ISUPParameterFactory parameterFactory, byte[] b, int index)
              throws ParameterException {
          int localIndex = index;
          index += super.decodeMandatoryParameters(parameterFactory, b, index);
          if (b.length - index > 1) {
              CircuitGroupSuperVisionMessageType cgsvmt = parameterFactory.createCircuitGroupSuperVisionMessageType();
              ((AbstractISUPParameter) cgsvmt).decode(new byte[] { b[index] });
              this.setSupervisionType(cgsvmt);
              index++;
              return index - localIndex;
          } else {
              throw new IllegalArgumentException("byte[] must have atleast four octets");
          }
      }
docs: /*
  (non-Javadoc)
  
  @see org.restcomm.protocols.ss7.isup.ISUPMessageImpl#decodeMandatoryParameters(byte[], int)