A system has an n-layer protocol hierarchy. Applications generate messages of length M bytes. At each of the layers, an h-byte header is added. What fraction of the network bandwidth is filled with headers? Please explain the answer to me.
You have n layers of protocol, and at each layer h bytes are added, so the total number of header bytes is nh.
Your payload is M bytes, so the total packet size is M + nh.
The fraction of each packet used by protocol headers is therefore
nh
------
M + nh
This is actually a gross over-simplification, since each layer will have different protocol headers, with each likely to be of a different size. Further, the size of the protocol headers might be adjusted by routers along the way.