Why does CPU utilization of various unrelated tasks increase in presence of network traffic?

["Vijay R" <vjr.work@xxxxxxxxx>]

I do not whether this is the right pace to ask this question. Please forgive me and direct me, if it is not.
I am using "top" command to check the CPU utilization of various tasks in presence and absence of network traffic. 
It shows that even the processes which have nothing to do with networking have their utilization increased in presence of network traffic.
Can anybody throw light on this?

Thank you,
VJ