Maximum number of messages allowed to be sent for a specific channel instance.
As defined by RFC 3080 every channel created cannot repeat message number sent. Every message sent have an unique identifier used to reply to it and to differentiate them from each other.
A channel cannot sent more messages that the number defined for MAX_MSG_NO. Once a channel reach that number it cannot be used for any new message. This doesn't mean this channel must be closed. The channel still have pending to receive all replies generated for every message created.