I came across an article on the economist magazine about skype.
"Although all of Skype’s data are encrypted, the chunks that encode silence are smaller than those which encode speech, which allows them to be detected reliably."
Could you help me understand the above grammar, what does the second "which" ( which allows them to be detected reliably) describe? what is to be detected reliably? " those which encode speech" or "Skype’s data"? thank you.