@Override
  @NotNull
  public Set<InternalDistributedMember> putOutgoing(@NotNull final DistributionMessage msg) {
    assertTrue(!sentReply, "Trying to reply twice to a message");

    connection.getConduit().getDM().getCancelCriterion().checkCancelInProgress(null);

    if (logger.isTraceEnabled(LogMarker.DM_VERBOSE)) {
      logger.trace(LogMarker.DM_VERBOSE, "Sending a direct reply {} to {}", msg,
          connection.getRemoteAddress());
    }
    final MsgStreamer ms = (MsgStreamer) MsgStreamer.create(getConnections(), msg, false,
        DUMMY_STATS, connection.getBufferPool());
    try {
      ms.writeMessage();
      final ConnectExceptions ce = ms.getConnectExceptions();
      if (ce != null && !ce.getMembers().isEmpty()) {
        assertTrue(ce.getMembers().size() == 1);
        final InternalDistributedMember member = ce.getMembers().get(0);
        logger.warn("Failed sending a direct reply to {}", member);
        return singleton(member);
      }
      sentReply = true;
      return emptySet();
    } catch (NotSerializableException e) {
      throw new InternalGemFireException(e);
    } catch (IOException ex) {
      throw new InternalGemFireException(
          "Unknown error serializing message", ex);
    } finally {
      try {
        ms.close();
      } catch (IOException e) {
        throw new InternalGemFireException("Unknown error serializing message", e);
      }
    }

  }
A reply sender which replies back directly to a dedicated socket socket.
geode-core/src/main/java/org/apache/geode/internal/tcp/DirectReplySender.java