In standard German (of Germany and Austria) we use the spelling difference between ss and ß to signal whether the preceding vowel is short or long. A short vowel is followed by ss, a long vowel is followed by ß.
In Swiss standard German (N.B. I really mean Swiss standard German here, and not Swiss German), there is no ß letter, and words which would include it in Germany and Austria are always spelt with ss.
Is this just an orthographic fact, or does it also mean that the vowel before ss is always short? In other words, in Swiss standard German, would you read Strasse with a long or short a?