Peterson Davie 3.26

Question

Suppose a workstation has an $I/O$ bus speed of $800$ Mbps and memory bandwidth of $2$ Gbps. Assuming direct memory access (DMA) is used to move data in and out of main memory, how many interfaces to $100$-Mbps Ethernet links could a switch based on this workstation handle?

Answer 1

I/O bus speed = 800Mbps

Memory bandwidth = 2Gbps

I/O bus speed < Memory Bandwidth it is bottleneck.

Effective bandwidth that the I/O bus can provide is 800/2 =400Mbps because each packet crosses the I/O bus twice.

Therefore, the number of interfaces is ⌊400/100⌋ = 4

(Definitions of the terms used in the solution are available at https://gateoverflow.in/43611/peterson-davie-3-27 )