too many table fragmentation

My database is 10.2.0.5 and 2 node RAC.

One of tables is copied by using dblink at another database(CTAS).

two table's space is not same.  I think the reason is a fragmentation. But Fragmentation block is too much.

This table is many DML (update , insert).

Quation> I want to know why happen too much fragmentation and How can I fix it?

1. source table information

select bytes,EXTENTS  ,INITIAL_EXTENT, NEXT_EXTENT

from dba_segments

WHERE segment_name='PT_VO_BUY' and owner='VODUSER';

bytes               EXTENTS   INITIAL_EXTENT  NEXT_EXTENT

--------------       --------         ------------------------  -----------------------

8,3886,080     7637            20,971,520              20,971,520

SELECT TABLE_NAME,ROUND((BLOCKS*8),2) "SIZE(KB)",

       ROUND((NUM_ROWS*AVG_ROW_LEN/1024),2) "ACTUAL_DATA(KB)",