It is useful if the receiver has some method for determining if the message is correct, before sending it on. This is called error checking . If messages are to be kept secret, they can be encoded using cryptography. This process is called encryption . Relay stations on major roads.
Messages travel by relay courier from one station to the next.
Fire beacons introduced to permit signaling from one station to the next without the need for human runners. They say, moreover, that sometimes this express does not stop all night, but the night-messengers succeed the day messengers in relays, and when this is the case, this express, some say, gets over ground faster than the cranes. You must know that the city of Khan-balik is a centre from which many roads radiate to many provinces, one to each, and every road bears the name of the province to which it runs. The whole system is admirably contrived. Here the messengers find no less than 400 horses, stationed here by the Great Khan's orders and always kept in readiness for his messengers when they are sent on any mission.