$5.[$Network Address Translation, $15$ pt$]$ Consider the scenario below in which three hosts, with private IP addresses $10\mathrm{.}0\mathrm{.}1\mathrm{.}10,10\mathrm{.}0\mathrm{.}1\mathrm{.}15,10\mathrm{.}0\mathrm{.}1\mathrm{.}22$ are in a local network behind a NAT'd router that sits between these three hosts and the larger Internet. IP datagrams being sent from, or destined to$,$ these three hosts must pass through this NAT router. The router's interface on the LAN side has IP address $10\mathrm{.}0\mathrm{.}1\mathrm{.}28,$ while the router's address on the Internet side has IP address $135\mathrm{.}122\mathrm{.}201\mathrm{.}212.$

Suppose that the host with IP address $10\mathrm{.}0\mathrm{.}1\mathrm{.}15$ sends an IP datagram destined to host $128\mathrm{.}119\mathrm{.}173\mathrm{.}184.$ The source port is $3443,$ and the destination port is $80.($a$)$ Describe IP address and port number of source and destination at each of the $4$ steps. $($b$)$ Now suppose the host with IP address $10\mathrm{.}0\mathrm{.}1\mathrm{.}22$ send an IP datagram to the same destination, with source port $=2567$ and destination port $\backslash (=80\backslash ).$ Describe the updated NAT translation table after a new entry is added to the table.