I use polypropylene string using the same technique that Andyww2013 has described (how much you will need depends on how close your poles are and how densely your peas have been sown, because they do support each other to some extent.)
A rather appealing idea is to use jute string and then throw the whole lot on the compost heap after cropping, although not having tried that you'll need someone else to advise you whether the string rots down in a timely fashion...