In the poem, "Mother to Son," where does Hughes use onomatopoeia and assonance?

Langston Hughes' poignant poem, "Mother to Son," tells the
story of a mother giving some hard-life-experience advice to her son. The
onomatopoeia (the formation or use of words--such as
hiss or murmur--that imitate the sounds
associated with the objects or actions they refer to) is not as definitive as most
examples, but the closest wording to fit this literary device would be the colloquial
"I'se been a climin' ", which attempts to imitate the act of the hard and
never-ending climb up the steep stairs of life. The closest example of
assonance (also called vowel rhyme,
in which the same vowel sounds are used with different consonants in the
stressed syllables of the rhyming words) would be the line "Where there ain't been no
light"; the first three words use the hard "eh" sound. The examples of "I'se" and
"climbin'" would also fit the definition of the term. Perhaps a better used literary
device is the personification, where Hughes gives "life"
the attributes given to stairs (tacks, splinters, boards, no
carpet).