( ATM ( ( ( ( ( is ( ( a form ) ( of cell ) ) ) relay ) , ) ( where ( ( all ( transmitted data ) ) ( ( is ( fragmented ( into ( ( -LRB- ( small -RRB- ) ) ( fixed-size data ) ) ) ) ) ( units ( called cells ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP ATM)) (VP (VBZ is) (NP (NP (DT a) (NN form)) (PP (IN of) (NP (NN cell)))) (ADVP (RB relay)) (, ,) (SBAR (WHADVP (WRB where)) (S (NP (DT all) (JJ transmitted) (NNS data)) (VP (VBZ is) (ADJP (JJ fragmented) (PP (IN into) (NP (PRN (-LRB- -LRB-) (ADJP (JJ small)) (-RRB- -RRB-)) (JJ fixed-size) (NNS data)))) (SBAR (S (NP (NNS units)) (VP (VBD called) (NP (NNS cells))))))))) (. .)))
ATM is a form of cell relay,  where all transmitted data is fragmented into (small) fixed-size data units called cells .
(ROOT (S (NP (DT All) (NNS cells)) (VP (VBP have) (NP (NP (DT the) (JJ small) (NN size)) (PP (IN in) (NP (JJ common))))) (. .)))