cast on 108 stitches with long tail cast-on on 3.5mm kneedles using circulars in magic loop. 2x2 rib for about 6 rows then change to 4mm kneedles,

purl 12 knit 6 round for 6 rows
7th row purl 12 cable 3 back round
purl 12 knit 6 round for 7 rows
15th row purl 12 then cable 3 f
purl 12 knit 6 round for 7 rows
then purl 12 cable 3 f
and carry on until 7 inches deep then dec 12 by k2tog in first two stitches of the purl section and last two stitches of the purl sections x 6
do not decrease on alternate rows but carry on the cable pattern
decrease until only 1 purl stitch remains between cable then decrease twice in each of the cable 6 knit stiches.