This video crochet tutorial will help you learn how to crochet the ridged string network stitch.
Foundation Chain: Multiples of 4 + 1 (add 1 for base chain)
Row 1: (right side) 1 sc into 2nd ch from hook, *3ch, skip 3ch, 1 sc into next ch, rep from * to end, turn.
Row 2: 1 ch, working into back loop only of each st work 1sc into first st, *3ch, skip 3ch, 1sc into next sc; rep from * to end, skip tch, turn.
Repeat row 2 until you have reached your desired length.
After a few repeats your pattern should look like this: