error rate

I think I might have seen this question before, so please excuse me if
this is not appropriate and just ignore it.

Could someone let me know what would be an acceptable error rates on
a leased line, especially international (transoceanic) links?
This would break down to transmission error on the fiber/satelite,
electronic error on end equipments (includes DACS, DSU/CSU, routers etc).

If any references could be provided, that would be even better!