Diplomacy was, even in the 14th Century, an ancient calling. Indeed, diplomacy can justifiably called one of the oldest professions, as our ancestors no doubt attempted to talk their opponents into making concessions before the more expensive and riskier armed force was applied. By the Medieval period, diplomacy was a well developed aspect of state craft. The diplomats were often the most able men (and sometimes women) in the realm. Because communications were so slow (no faster than a speedy horse or swift boat), the diplomats were expected to be able to operate independently without getting themselves, or their masters, into trouble. The diplomat had to be able to think like his master and be well aware of all aspects of his own nation and the one he was visiting. Everyone recognized the value of diplomats and, as a result, they were generally granted immunity from harm. It was considered a grave insult, not to mention being in extremely bad taste, to molest diplomats. Harming diplomats was commonly considered equivalent to a declaration of war. If nothing else, this encouraged the diplomats to keep everyone in a peaceful frame of mind.
There were three ranks of diplomats; ambassadors, emissaries and heralds.
The ambassadors were only used for dealing with the most exhalted rulers, the Pope and the Holy Roman Emperor. The emperor would send an ambassador to someone and have the other party send an ambassador back. Kings sent emmisaries to each other. An ambassador was usually himself a high ranking noble and was treated as such.
Emissaries were used for every other sort of relationship between feudal rulers. They varied in noble rank (and many were able commoners) depending on the rank (or importance) of the people they had to deal with. It was not unusual for distinguished clergy and poets to serve as emissaries, as, for rexample, did St. Catherine of Siena, Petrarch, and Chaucer
Lastly, we have the heralds, who were used for sundry minor diplomatic tasks. Heralds were often clergy, educated men who were literate and already had a degree of immunity from harm because of their religious affilliation. Heralds would be used, for example, to carry diplomatic messages. Often these messages would not be written down, but rather would be memorized by the Herald and recited to the recipient. Although heralds had diplomatic immunity, they usually travelled alone or in small groups and were thus liable to attack by brigands. Heralds were almost always present at battles and sieges, the heralds of both sides cooperating to keep a diplomatic channel open and to decide what a battle would be named and to record the details for posterity. Among their other functions, Heralds maintained the official records of coats-of-arms, and important duty in Medieval society.
Ambassadors outrank emissaries, who are then ranked by the rank of the lord to whom they are sent. They report to the Lord High Chancellor in England and the Chancellor in France.
There were no permanent embassies as there are now. The ambassadors and emmisaries were expected to travel back and forth to maintain communication between their master and the great lord on the other end. There were permanent arrangements in some cases, and these "embassies" were put in charge of a minister of the government. Even these ministers often travelled back to consult with their master. But out of this arrangement came the current system of ambassadors and embassys.