docs: private void removeOldChannels()
      {
          Iterator<AsteriskChannelImpl> i;
  
          synchronized (channels)
          {
              i = channels.values().iterator();
              while (i.hasNext())
              {
                  final AsteriskChannel channel = i.next();
                  final Date dateOfRemoval = channel.getDateOfRemoval();
                  if (channel.getState() == ChannelState.HUNGUP && dateOfRemoval != null)
                  {
                      final long diff = DateUtil.getDate().getTime() - dateOfRemoval.getTime();
                      if (diff >= REMOVAL_THRESHOLD)
                      {
                          i.remove();
                      }
                  }
              }
          }
      }