Computer Networks · Full Mock 1

How many named root server identities (a.root-servers.net to m.root-servers.net) are there?

Same page (9 objects of 100 KB, 10 Mbps, RTT 20 ms) with non-persistent HTTP and no parallelism. Total time in ms?

With even parity, what parity bit is added to the data 1011001?

Encode the 8 data bits 10011010 with even-parity Hamming code (parity at positions 1, 2, 4, 8). Which 12-bit codeword results?

Go-Back-N uses a sender window of 7. What is the minimum number of sequence-number bits?

For the same transfer (window 5, frames 1–20, frames 4 and 13 lost once), how many fewer transmissions does Selective Repeat need than Go-Back-N?

How many bits are in an IPv4 address?

Using the five-entry table, which destinations are forwarded out of eth0?

What is the maximum throughput of slotted ALOHA (three decimals)?

In slotted ALOHA, 5 stations each transmit in a slot with probability 0.1, independently. What is the probability that a slot carries exactly one frame (a success)? (four decimals)

How many milliseconds does it take to transmit (push onto the link) a 1000-byte packet on a 1 Mbps link?

A geostationary satellite orbits 36,000 km above the equator. A request goes ground → satellite → ground and the reply returns the same way, at 3 × 10⁸ m/s. Minimum RTT in ms?

What is the minimum size of an IPv4 header in bytes?

A 4000-byte datagram is fragmented for an MTU-1500 link; later every fragment meets an MTU-576 link and is fragmented again. How many fragments arrive at the destination?

RIP uses hop count as its metric. Which hop count does it treat as "infinity" (unreachable)?

For which destinations does u use x as its first hop?

How many hexadecimal characters long is a SHA-256 digest?

RSA with p = 17, q = 11 and e = 7. What is d?

How many bytes is the UDP header?

A long-lived Reno flow oscillates between W/2 and W, with W = 40 segments of 1500 bytes and RTT 100 ms. Its average throughput is about 0.75 W per RTT. What is that in Mbps?

A browser has a cached copy and sends If-Modified-Since. The page has not changed. What does the server send?

Why do many standard CRC generators include the factor (x + 1)?

Why must a Selective Repeat window be at most half the sequence-number space?

What was the default (classful) mask of a class B network such as 172.16.0.0?

Why is CSMA/CD effectively unused in modern Gigabit Ethernet LANs?

Which components make up the delay a packet experiences at one router hop?

An attacker on a café Wi-Fi sends unsolicited ARP replies claiming the gateway's IP belongs to its own MAC. What does this achieve, and what protects users?

Why is RIP slow to recover from link failures compared with OSPF?

How does a browser decide to trust a server's certificate?

What triggers TCP fast retransmit?