link vs link up

link is a noun but link up is not a noun.

Word	Noun	Adjective	Verb	Adverb
link	Yes	No	Yes	No
link up	No	No	Yes	No

As verbs, link and link up are synonyms defined as:

Other synonyms of link include associate, colligate, connect, relate, tie in.

As verbs, link and link up are synonyms defined as:

Other synonyms of link include connect, tie.

As verbs, link and link up are synonyms defined as:

Other synonyms of link include connect, join, unite.

link (noun)	link up (noun)
a fastener that serves to join or connect
a two-way radio communication system (usually microwave); part of a more extensive telecommunication network
an interconnecting circuit between two or more locations for the purpose of transmitting and receiving data
a channel for communication between groups
(computing) an instruction that connects one part of a program or an element on a list to another program or list
a unit of length equal to 1/100 of a chain
the means of connection between things linked in series
a connecting shape
the state of being connected

link (verb)	link up (verb)
make a logical or causal connection	make a logical or causal connection
connect, fasten, or put together two or more pieces	connect, fasten, or put together two or more pieces
link with or as with a yoke	be or become joined or united or linked
be or become joined or united or linked