Procotols vs. Treaties: according to the United Nations ref. guide

Definition of key terms used in the UN Treaty Collection

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What are Protocols:

The term "protocol" is used for agreements less formal than those
entitled "treaty" or "convention". The term could be used to cover the
following kinds of instruments:

(a) A Protocol of Signature is an instrument subsidiary to a treaty,
and drawn up by the same parties. Such a Protocol deals with ancillary
matters such as the interpretation of particular clauses of the
treaty, those formal clauses not inserted in the treaty, or the
regulation of technical matters. Ratification of the treaty will
normally ipso facto involve ratification of such a Protocol.

(b) An Optional Protocol to a Treaty is an instrument that establishes
additional rights and obligations to a treaty. It is usually adopted
on the same day, but is of independent character and subject to
independent ratification. Such protocols enable certain parties of the
treaty to establish among themselves a framework of obligations which
reach further than the general treaty and to which not all parties of
the general treaty consent, creating a "two-tier system". The Optional
Protocol to the International Covenant on Civil and Political Rights
of 1966 is a well-known example.

(c) A Protocol based on a Framework Treaty is an instrument with
specific substantive obligations that implements the general
objectives of a previous framework or umbrella convention. Such
protocols ensure a more simplified and accelerated treaty-making
process and have been used particularly in the field of international
environmental law. An example is the 1987 Montreal Protocol on
Substances that Deplete the Ozone Layer adopted on the basis of Arts.2
and 8 of the 1985 Vienna Convention for the Protection of the Ozone
Layer.

(d) A Protocol to amend is an instrument that contains provisions that
amend one or various former treaties, such as the Protocol of 1946
amending the Agreements, Conventions and Protocols on Narcotic Drugs.

(e) A Protocol as a supplementary treaty is an instrument which
contains supplementary provisions to a previous treaty, e.g. the 1967
Protocol relating to the Status of Refugees to the 1951 Convention
relating to the Status of Refugees.

(f) A Proces-Verbal is an instrument that contains a record of certain
understandings arrived at by the contracting parties.

What are Treaties:

The term "treaty" can be used as a common generic term or as a
particular term which indicates an instrument with certain
characteristics.

(a) Treaty as a generic term: The term "treaty" has regularly been
used as a generic term embracing all instruments binding at
international law concluded between international entities, regardless
of their formal designation. Both the 1969 Vienna Convention and the
1986 Vienna Convention confirm this generic use of the term
"treaty". The 1969 Vienna Convention defines a treaty as "an
international agreement concluded between States in written form and
governed by international law, whether embodied in a single instrument
or in two or more related instruments and whatever its particular
designation". The 1986 Vienna Convention extends the definition of
treaties to include international agreements involving international
organizations as parties. In order to speak of a "treaty" in the
generic sense, an instrument has to meet various criteria. First of
all, it has to be a binding instrument, which means that the
contracting parties intended to create legal rights and
duties. Secondly, the instrument must be concluded by states or
international organizations with treaty-making power. Thirdly, it has
to be governed by international law. Finally the engagement has to be
in writing. Even before the 1969 Vienna Convention on the Law of
Treaties, the word "treaty" in its generic sense had been generally
reserved for engagements concluded in written form.

(b) Treaty as a specific term: There are no consistent rules when
state practice employs the terms "treaty" as a title for an
international instrument. Usually the term "treaty" is reserved for
matters of some gravity that require more solemn agreements. Their
signatures are usually sealed and they normally require
ratification. Typical examples of international instruments designated
as "treaties" are Peace Treaties, Border Treaties, Delimitation
Treaties, Extradition Treaties and Treaties of Friendship, Commerce
and Cooperation. The use of the term "treaty" for international
instruments has considerably declined in the last decades in favor of
other terms.

http://untreaty.un.org/English/guide.a