Computer Networks Quiz 2: 23 November 2025 (September 2025 term)

During the fast recovery, a TCP connection has:

$CWND = 8 \text{ MSS}$

$\text{Inflight} = 4 \text{ MSS}$

Each duplicate ACK increases CWND by 1 MSS.

If 4 duplicate ACKs are received before a new ACK arrives, what will be the value of CWND just before the new ACK, and what will it be value after the new ACK arrives (when CWND and inflight realign)?

A packet with destination IP 128.20.15.7 arrives at a router. The router's forwarding table has the following entries:

Which output port will the router select?

A TCP receiver has a buffer size of 30 KB. The sender transmits data at 10 KB/s, while the receiver’s application reads data from the buffer at 6 KB/s. Assuming the buffer is initially empty, after how many seconds will the receiver buffer become full ?
Note: Give your answer to two decimal places.

A TCP connection has an advertised window size of 32 KB and a Round Trip Time (RTT) of 80 ms. Ignoring congestion effects, compute the maximum achievable through-put based solely on flow control.
Note: Write the answer in KB/s.

An organization has been assigned an address block of 10.25.4.0/26. How many usable host addresses can be assigned to devices in this network?

An organization has 1,800 devices connected in a private network. Each NAT router can handle up to 80,000 simultaneous connections and can serve 300 devices comfortably. If the organization uses NAT (one public IP address per NAT router), how many public IP addresses are required?

An administrator is given the private IP block 192.168.0.0/16. They need to create subnets that can each support at least 500 hosts. What is the smallest subnet mask prefix they can use, in CIDR notation?

At the start of an RTT, the congestion window (CWND) is 15 MSS where the Maximum Segment Size (MSS) is 1200 bytes. TCP is operating in the congestion avoidance phase, and there is one ACK per segment. What will be the new value of CWND (in bytes) after receiving 15 ACKs (i.e., one RTT worth of ACKs)?

A TCP connection has a round-trip time (RTT) of 80 ms and a maximum segment size (MSS) of 1200 bytes. If the steady-state congestion window is 50 MSS, what is the maximum achievable throughput (in Mbps)? Note: Give your answer to two decimal places.

Given IP address A = 172.25.50.22 and B = 172.25.63.10 with netmask 255.255.240.0, compute the network address of A (iexpressed in dotted-decimal form).

Given the following weighted graph of routers:

Using Dijkstra's Algorithm, compute the total cost of the shortest path from $U$ to $Z$.