here: http://www.tech-archive.net/Archive/DotNet/microsoft.public.dotnet.framework.adonet/2006-10/msg00064.html
You can read also that Thomas Weingartner wrote:
Timeout: SqlException.Number == -2 (This is an ADO.NET error code)
General Network Error: SqlException.Number == 11
Deadlock: SqlException.Number == 1205 (This is an SQL Server error code)
...
We handle the "General Network Error" as a timeout exception too. It only occurs under rare circumstances e.g. when your update/insert/delete query will raise a long running trigger.