What dramatic function does the conversation between Montano and the two gentlemen serve? ( Othello, Act II, Scene i)

In addition to shakespeareguru's points, I might add that
the discourse between Montano and the two gentlemen helps to establish Othello as a
respected general.  The men are obviously concerned for Othello's safety, as Othello has
travelled through the same waters that shipwrecked the Turkish fleet.  Further, Montano
describes Othello as "a worthy governor," "Brave Othello," and says, "I have served him,
and the man commands/ Like a full soldier." 

In including
these descriptions of Othello, Shakespeare helps readers understand how respected he is;
this, along with the descriptions of his honorable role as a General in Act 1, makes his
behavior in Act 3-5 even more shocking. 

Also, Montano and
the gentlemen discuss briefly note that Cassio, who has already arrived in Cyprus, is
genuinely worried about Othello's safety:

readability="14">

But this same Cassio, though he speak of
comfort

Touching the Turkish loss, yet he looks
sadly

And prays the Moor be safe, for they were
parted

With foul and violent
tempest.

Here, Shakespeare
establishes Cassio's loyalty to Othello by pointing out that while Cassio is happy that
there won't be a war, he is upset because Othello's ship hasn't yet arrived.  Again, as
audiences realize that Cassio genuinely loves and respects Othello, they are later able
to realize Othello's gross flaw in judgment (his misplaced trust in Iago, whom Othello
didn't feel was worthy of the lieutenancy) and the ridiculousness of Othello's
willingness to believe Iago's lies.