Problem $4(10$ points$)$:

Consider the Internet over cable and the corresponding spectrum allocation. Refer to Textbook

Figure $52$ on Textbook page $182.$

a$)(2$ points$)$ Specify the bandwidth allocated for upstream data and that for downstream data.

b$)(4$ points$)$ Assume $1$ symbol per Hz $,$ what is maximum upstream bit rate and maximum

downstream bit rate?

c$)(4$ points$)$ In light of the cable system, explain very briefly the "ranging" process.

Problem $5(10$ points$)$:

A source is sending a file of size $F$ bits to a destination node. The traversed path consists of $10$

consecutive identical links, where the transmission rate $Rk\frac{b}{s}$ and the propagation time $T_{\text{p}\text{r}\text{o}\text{p}}$

seconds for each link. The source fragments the file into packets of size $P$ bits per packet. The last

packet may be padded with dummy data such that the final size of the payload is $P$ bits. In addition,

the source adds a header of size $H$ bits per packet for each packet. Packets are sent sequentially on

the consecutive links and the file is reassembled in the destination node. A router can be receiving a

packet on one link and transmitting another on the other link. It is required to compute the total file

transfer time, denoted by $T_{\text{f}\text{i}\text{l}\text{e}},$ from source to destination. Account for transmission and propagation

times only, and ignore any processing times.

a$)(2$ points$)$ Assume $P=1$ bit per packet. Compute $T_{\text{f}\text{i}\text{l}\text{e}}.$

b$)(2$ points$)$ Assume $P=F$ bit per packet. Compute $T_{\text{f}\text{i}\text{l}\text{e}}.$

c$)(6$ points$)$ What $P^{*}$ value will result in minimum total file transfer time, denoted by $T_{\text{f}\text{i}\text{l}\text{e}}^{*}.$ What is the

corresponding $T_{\text{f}\text{i}\text{l}\text{e}}^{*}?$

Assume $F=2{10}^6$ bits, $R=56k\frac{b}{s},T_{\text{p}\text{r}\text{o}\text{p}}=3sec,$ and $H=20$ bytes.

Hint: $T_{\text{f}\text{i}\text{l}\text{e}}=N(T_p+T_{\text{p}\text{r}\text{o}\text{p}})+(K-1)T_p-$where $N$ is the number of links, $T_p=\frac{P+H}{R}$ time to transmit the

packet, $K=[\frac{F}{P}]$ is the number of packets resulting from dividing the file of $F$ bits into $P-$bit packets.