You must be very strong in analytical tools and mathematics with proven records. Required analytic tools are probability theory, measure theory, optimization, stochastic process, to name a few.
You should have basic understanding of current literature in networking; You are encouraged to read articles in journals and IEEE magazine, and conference proceedings. Example includes IEEE Network magazine, IEEE/ACM Transactions on Networking, IEEE INFOCOM, ACM MobiCoom, MobiHoc, Sigcomm, Sigmetrics, among others.
I usually work with PhD students. Under "very rare" circumstance I will hire MS students.
Experience with network simulator (such as ns-2, opnet) are strongly preferred, if you already have strong analytical backgrounds as stated in item 1 above
I hire students only after I work with the student at least for a semester, if the student is already at NCSU.
Updated: Oct. 2009