Unit 3: MAC Sublayer and IP Addressing - Practice Quiz

1 What is the main purpose of a multiple access protocol?

2 Which layer commonly handles multiple access protocols in a local area network?

3 In Pure ALOHA, when may a station transmit a frame?

4 How does Slotted ALOHA differ from Pure ALOHA?

5 What does a station normally do after a collision in ALOHA?

6 What does a station do before transmitting in CSMA?

7 What does the abbreviation CSMA stand for?

8 What does the CD in CSMA/CD represent?

9 What does a station do when it detects a collision in CSMA/CD?

10 Which type of address is carried in an Ethernet frame header?

11 What is the standard length of an Ethernet MAC address?

12 Which field allows an Ethernet receiver to check whether a frame was corrupted?

13 Which classful IPv4 class uses the default subnet mask 255.0.0.0?

14 Which class does the IPv4 address 172.16.5.10 belong to under classful addressing?

15 What is the default prefix length of a Class C IPv4 network?

16 What does CIDR stand for?

17 What does /24 indicate in the CIDR address 192.168.1.0/24?

18 Which subnet mask is equivalent to the CIDR prefix /16?

19 What is the network address of host 192.168.1.25/24?

20 How many usable host addresses are available in an IPv4 /30 subnet?

21 A shared broadcast channel has many stations, but collisions occur only occasionally because traffic is light. Which protocol category allows stations to transmit without a central controller and resolves contention when it occurs?

22 A channel of bandwidth Mbps is divided equally among four continuously active stations using FDMA. Ignoring guard bands, what bandwidth is assigned to each station?

23 In Pure ALOHA, each frame requires ms for transmission. What is the vulnerable period during which another transmission can cause a collision?

24 A Slotted ALOHA network generates an average offered load of frame per slot. Using , what is the approximate normalized throughput?

25 Why does Slotted ALOHA achieve a higher maximum throughput than Pure ALOHA?

26 A station using nonpersistent CSMA senses that the channel is busy. What should the station do next?

27 Two stations using 1-persistent CSMA are waiting while the channel is busy. What is most likely to happen when the current transmission ends?

28 In a Mbps CSMA/CD network, the maximum one-way propagation delay is microseconds. What minimum frame size is required for reliable collision detection?

29 After the third collision, Ethernet's binary exponential backoff selects an integer from which range?

30 Why is CSMA/CD generally unnecessary on a modern switched Ethernet link operating in full-duplex mode?

31 An Ethernet switch receives a frame whose destination MAC address is not present in its forwarding table. What does the switch normally do?

32 An Ethernet frame carries bytes of upper-layer data. How many padding bytes are required to meet the standard minimum payload size?

33 A switch learns that MAC address 00:1A:2B:3C:4D:5E is reachable through port 4. Which frame field did the switch examine to learn this mapping?

34 Under classful addressing, what are the network address and default mask for the host address 172.20.14.8?

35 A Class C network uses its default subnet mask. How many usable host addresses are available in that network?

36 Which CIDR block contains the address 192.168.10.77/26?

37 A router has routes 10.0.0.0/8, 10.20.0.0/16, and 10.20.30.0/24. Which route is selected for destination 10.20.30.45?

38 What is the smallest CIDR prefix that provides at least usable IPv4 host addresses?

39 The network 192.168.50.0/24 must be divided into at least six equal-size subnets. Which new prefix provides enough subnets while retaining the most host addresses per subnet?

40 For the subnet 10.1.8.0/21, which pair gives the valid host range?

41 A bit-map reservation protocol serves 64 stations. Each reservation cycle contains one reservation bit per station, followed by one 1000-bit data frame from every station that reserved a slot. If exactly 8 stations transmit in each cycle and guard times and acknowledgments are ignored, what is the channel efficiency?

42 In a pure ALOHA network, frames have a fixed transmission time of ms. Including retransmissions, attempts form a Poisson process at 1000 frames per second. Approximately how many frames per second are successfully delivered?

43 A slotted ALOHA system is measured to have normalized throughput . Assuming Poisson attempts and , which pair gives the two possible approximate offered loads?

44 Stations A and B are at opposite ends of a bus with one-way propagation delay . Under 1-persistent CSMA, A begins transmitting at , while B senses the channel idle and begins at . Ignoring collision-detection circuitry delay, when do B and A first detect the collision, respectively?

45 Five stations are ready at the beginning of the same idle slot in a -persistent CSMA system. Assuming independent decisions, which value of maximizes the probability that exactly one station transmits, and what is that maximum probability?

46 A custom Gbit/s CSMA/CD LAN has a maximum station separation of 500 m. Signal propagation speed is m/s, and repeaters add a total one-way delay of . What minimum frame length is required so that a sender is still transmitting when a worst-case collision returns?

47 After its tenth collision, an Ethernet station applies binary exponential backoff and chooses uniformly from through . What is the probability that its selected backoff is at least 512 slot times?

48 A full-duplex Ethernet link continuously sends maximum-size untagged frames with 1500-byte payloads. Count the 18-byte MAC header/FCS overhead, 8-byte preamble/SFD, and 12-byte interframe gap. What fraction of link capacity carries payload?

49 On a 100 Mbit/s Ethernet link, what time elapses from the first bit of a frame's preamble until the earliest legal start of the next frame if the MAC frame is the minimum 64 bytes? Include the 8-byte preamble/SFD and 12-byte interframe gap.

50 Under classful IPv4 addressing, which tuple correctly describes the address 191.255.1.1?

51 The Class B network 150.40.0.0 is subnetted by borrowing 6 host bits. Under modern rules that permit subnet zero and the all-ones subnet, which result is correct?

52 A router has routes 203.0.113.0/24 via A, 203.0.113.64/26 via B, 203.0.113.128/25 via C, and 203.0.113.192/27 via D. Which next hop is selected for destination 203.0.113.207?

53 A router has eight routes covering every /24 network from 10.44.32.0/24 through 10.44.39.0/24, with no gaps. What is the most specific single CIDR aggregate that represents exactly these routes?

54 An organization needs one CIDR block containing at least 3000 IPv4 addresses, and the block must begin exactly at 172.20.48.0. What is the smallest valid block?

55 A CIDR block has prefix length /20. How many distinct /27 subnets can it contain, and how many conventional usable host addresses does each /27 provide?

56 Using VLSM, 192.168.50.0/24 is allocated in descending requirement order: 100 hosts, 50 hosts, and 25 hosts. Each subnet is assigned the lowest available aligned block. What is the largest remaining aligned subnet?

57 For host address 203.0.113.77/27, which network, usable-host range, and directed-broadcast address are correct?

58 The network 10.0.0.0/20 must be divided into equal-size subnets. At least 10 subnets are required, and each must support at least 100 conventional usable hosts. Which prefix maximizes hosts per subnet while meeting both constraints?

59 A point-to-point router link is assigned 192.0.2.10/31 and follows RFC 3021. Which statement is correct?

60 An administrator proposes assigning 192.168.10.64/26 to one LAN and 192.168.10.96/27 to another LAN. What is the exact relationship between these subnets?