Hi Megabyzus,

- From the licensing point of view the sendmessage functionality is not considered as an extra option and therefore is included in the base license of the server and in each client option.
For further info please refer here: https://lightstreamer.com/ls-features

- In most cases the communication between client and server in Lightstreamer is based on a websocket transport; therefore a bidirectional channel always active.
This offers many advantages in the case of a bidirectional communication, in particular you will save the round trip for each request but just send the message on the already open channel with benefits in terms of performance, reliability and even server scalability.

Regards,
Giuseppe