Average rate to browsers:
\[\begin{aligned} 100\text{ K } \cdot 15/\text{ sec } = 1.5 \text{ MBps } \end{aligned}\]So our LAN utilization is:
\[\begin{aligned} \frac{1.5 \text{ Mbps }}{10 \text{ Mbps}} = 15\% \end{aligned}\]And the access link utilization is:
\[\begin{aligned} \frac{1.5 \text{ Mbps }}{1.54 \text{ Mbps}} = 99\% \end{aligned}\]
Access link utilization:
\[\begin{aligned} 99\% \cdot 0.6 = 58\% \end{aligned}\]Total delay:
\[\begin{aligned} 0.6 \cdot (\text{delay from origin}) + 0.4 \cdot (\text{delay when satisfied from cache}) \end{aligned}\]
FTP uses port: 21
SMTP uses port: 25
The servers will play both roles, i.e. Gmail server will play the client and the Yahoo server will play the server. If they do the opposite then their roles will swap.
