Hi,

L3 is the last line of support and usually comprises of a developer team which addresses the technical issues. Sometimes the issues reported by customers cannot be solved by L1 & L2 . In that case, the L3 team analyses the issue and fixes it. The issues which the L3 team gets involves code/development related fixes.

A software  engineer applies mathematical analysis and the principles of computer cience in order to design and develop computer software.  When working with a client, a software engineer will typically analyze the client's needs, then design, test, and develop the computer software in order to meet those needs.

Hope this helps.