It started with an IM, if the person was listed as being in a meeting or had their DND status on, you couldn't IM them. If they were available, you had to ask, "Do you have a minute." and they were free to answer "no" and then set up a time to IM you back later.
If an IM was unsuccessful, or if the person was not on IM for some reason, you could then email them and you had to wait for a response before doing anything else. This was of course after you had gone through the IM process.
If the person wasn't on IM or didn't answer your email (the person had an hour to respond to your email), then and only then were you allowed to go to their desk. If they were at their desk, you still had to ask if they had time to talk. They could still say "no" and you had to accept whatever time frame they set to talk later.
If all of these were unsuccessful, then you had the final option to go to your manager. The only advantage was your manager started with an email and had 30 minutes to answer any emails with "911" In the message title.
The rules seemed pretty archaic, but if you followed them, you'd find they were pretty efficient in promoting a very quiet office, with little or no distractions. There were periods were I could go hours without needing my headphones - it was pretty amazing.