code: private void updateRingingAgents(String channelCalling, AsteriskAgentImpl agent)
      {
          synchronized (ringingAgents)
          {
              if (ringingAgents.containsKey(channelCalling))
              {
                  updateAgentState(ringingAgents.get(channelCalling), AgentState.AGENT_IDLE);
              }
              ringingAgents.put(channelCalling, agent);
          }
      }
docs: Updates state of agent, if the call in a queue was redirect to the next
  agent because the ringed agent doesn't answer the call. After reset
  state, put the next agent in charge.
  
  @param channelCalling
  @param agent