WS parameters & return values data integrity

[Strider]

Hello All,

I have built a web service that accepts and sends binary data encoded as base64 strings.
What I need to know is if the .NET framework infrastructure checks the integrity of the data
being passed arround or do I need to do it in the application layer?

I must point out that the web service clients are PDAs running on the .NET CF and communicating
via GPRS with the Web Service. So the big question is do I rely upon the underlying network layers or
do I do the integrity checks myself adding checksums and stuff like that?

Thanks in advance