I want an idea for my Masters in Computer Science and communication thesis. I am confused between to categories, networking or web/android development. Please help me and tell me what is the appropriate idea.
Thank you very much.

If this is your advanced degree and you don't yet have a topic my best suggestion is to get thinking. Have you consulted with your academic advisor on the subject?

This is not necessarily the best question to be asking an online forum if you desire an advanced degree.

What L7Sqr said, with emphasis! You are working for an advanced degree and have no idea what problems you are interested in solving? Good luck is all I can say! If the two subjects you mention (network and web/android development) are both of interest to you, then flip a coin. FWIW, web/android are not necessarily mutually inclusive subjects. Web coding is used on all mobile devices. Android is a "mostly" mobile computing environment, but in reality, it is Linux for smaller devices. So, as far as I can tell, you are interested in three subjects: networking, web development, and android/mobile. So, figure out what is most interesting to you, and go there.

actually am also looking for a suitable topic for my thesis .you can include hybrid apps if you are going to do mobile application