What is the industry standard for Network Up-Time

I work in a small office with a handful of other people.  We have have no real internal network except a phone system and a network printer.  We've outsourced our networking and storage to a firm who has set us up on a Citrix server.  So, we all have a virtual desktop we use as well as shared storage space within the server.
Occasionally, the system will go down and I have to call and generate a ticket with their tech support department.  Generally, the system is only down for 10-15 minutes max but often times less. By far, the majority of the time, they system works fine.
I've worked with technology for most of my life and understand that occasionally there will be issues so I'm pretty patient with the system.  
Other users in the office thing the system is poor and expect 0 downtime.  I've tried telling them that occasionally things happen but it doesn't get me far.  I've even tried relating it to Trucks breaking down (we're a trucking company), but it doesn't seem to help.  
Is there an industry standard measure concerning the amount of down time that is acceptable for a system.  If so, I'd like to use it rate the firm I deal with to determine if we're receiving an acceptable product.  Thanks.