Managing Core SQL Server 2008 R2 Technologies - Microsoft SQL Server 2008 R2 Administration - page 190

The connectivity to the SQL Azure database is managed by Tabular Data Stream (TDS)
protocol having limited support. However, the majority of SQL Server client APIs support
TDS protocol, so the supported features by SQL Azure work with existing client APIs. The
following screenshot is a reference to the SQL Azure network topology . The SQL Azure Network
topology diagram (in the next screenshot) is reproduced with permission from the Microsoft
Corpo ration: http://social.technet.microsoft.com/wiki/contents/articles/
sql-azure-connection-management-in-sql-azu re.aspx ).
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For best performance, the code-far connectivity patterns will benefit your application
because of direct connectivity to the database in the cloud. The only restriction here is
that all the client applications must use the TDS protocol for the data access. Hence, it is
essential to develop the client applications using SQL Server client APIs, such as ADO.NET,
ODBC, and SQLNCLI.