i saw the name Ascelin and thought it looked like Asselink (a Dutch surname). Asselink has the same origin as Esselink, which is like Hesselink, which is like Hessels and Hessels means 'son of Hessel'.
i'm sorry but this isnt all:
Hessel is a Dutch male name, with variants like Hasse and Hesling (notable!, looks like Aisling). It's meaning is unclear, but there are six possibilities given:
1) from the Germanic hasan which means 'beautiful' or 'smooth' 2) it's taken from the Hessian people, living in Germany 3) nickname of names beginning with hart- like Hartmann 4) nickname of names beginning with hade like Hedwig 5) nickname of names beginning with her- like Herman 6) nickname of Hendrik (Hezelo is a nn of Heinrich)
...time to rest now...
let's go on:
personally i think the derivation from the germanic adal is not true. this above makes more sense, because it all knits the web together (Hesling and Aisling; Ashlyn being derived from Aisling, as BtN says; Ascelin, Asselink and Ashlyn all like each other)
It seems pretty clear that Asselink and Ashlyn are from the same origin. so i think it's safe to say that the same is applied for Ascelin.