In DBMS first thing that any one should know is Client Server Architecture. This is not only true for DBMS but for anyone in IT should have basic knowledge of networking.
You can read about basics of networking from the links below.
www.unt.edu/zlot/survey/client_server_krm_01may2002.ppt
http://www.indiabix.com/technical/networking/3
http://www.mhprofessional.com/downloads/products/0071615385/0071615385_chap01.pdf
http://en.wikipedia.org/wiki/OSI_model
http://en.wikipedia.org/wiki/TCP/IP_model
Enjoy your reading.
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