Module 2.3.3 Data Link Layer Quiz Answers
Network Addressing and Basic Troubleshooting – Module 2.3.3 Data Link Layer Quiz Answers
1. A school is adding 10 computers to a classroom. What is the most common physical network topology that is used in a classroom?
- extended star
Explanation: The star physical topology is common in smaller networks. It is easy to troubleshoot, and connection issues are limited to the cable and host affected. Bus and ring topologies are harder to troubleshoot. Extended star topologies are more suitable for larger, more complex networks.
2. Which media access method requires that an end device send a notification across the media before sending data?
- token passing
Explanation: Using CSMA/CA as the media access control method, a device will examine the network media. If there is no carrier, the device sends a notification and, if no other device uses the media, it begins to send its data. This method differs from CSMA/CD, where a device will send data once it senses that the media is free, without sending a notification.
3. An enterprise has four branches. The headquarters needs full connectivity to all branches. The branches do not need to be connected directly to each other. Which WAN topology is most suitable?
- full mesh
- hub and spoke
Explanation: A point-to-point topology only connects two nodes. A bus is a legacy topology for LANs. Mesh and full mesh topologies have more connectivity than needed (all or most of the branches will be connected to each other).A hub and spoke design will connect the headquarters to all of its branches, as desired.
4. What is a characteristic of CSMA/CA that differs from CSMA/CD?
- CSMA/CA is suitable for networks with token ring topology.
- An end device sends a notification across the media before it sends a data frame.
- No collisions can exist within a local CSMA/CA network.
- CSMA/CA is a deterministic access method that controls use of the network.
Explanation: Both CSMA/CD and CSMA/CA are contention-based access control methods. With CSMA/CD, each end device monitors the media for the presence of a data signal. If the media is free, the device transmits data. With CSMA/CA, each end device also examines the media for the presence of a data signal. If the media is free, the device sends a notification across the media of its intent to use it. The device then sends data. With this method, CSMA/CA avoids possible collisions but does not completely stop them.
5. Which statement correctly describes the operation of CSMA/CD?
- The end device waits until it receives a token then transmits the data.
- The end device waits until there is no carrier signal, transmits a token, then transmits the data.
- The end device waits until there are no data signals then transmits the data while listening for collisions.
- The end device waits until there are no data signals, sends a notification that it is going to use the media, then transmits the data.
Explanation: Nodes using carrier sense multiple access with collision detection (CSMA/CD) wait until the media is not being used before sending data. They will then listen for signals from other nodes that may indicate that a collision has occurred. If a node is using collision avoidance (CSMA/CA), it will notify the other nodes of its intent to transmit data to prevent a collision. Controlled access techniques, such as token passing, do not experience collisions.
6. Which topology type describes the process that hosts use to access and communicate on a network?
Explanation: A physical topology defines the way in which computers, printers, and other devices are connected to a network. A star topology is a type of physical topology and has a central connection point, which is a device such as a hub, switch, or router. A bus topology is another type of physical topology where each computer connects to a common cable.
7. How does a device use CSMA/CA technology to avoid collisions?
- It monitors the media and only begins to transmit when the media is free.
- It sends a notification before transmitting when the media is free.
- It uses a full-duplex channel for communication.
- It waits for a token before transmitting.
Explanation: In CSMA/CA, the device examines the media for the presence of a data signal. If the media is free, the device sends a notification across the media of its intent to use it. The device then sends the data. This method is used by 802.11 wireless networking technologies.
8. On a point-to-point network, which communication type is used when two devices can both transmit and receive but not at the same time?
- controlled access
Explanation: Half-duplex communication occurs when both devices can both transmit and receive on the medium but cannot do so simultaneously. Full-duplex communication occurs when both devices can transmit and receive on the medium at the same time. Half-duplex communication is typically contention-based, whereas controlled (deterministic) access is applied in technologies where devices take turns to access the medium.
9. A dental office provides a WLAN in the waiting area for patients to access the Internet. The WLAN is equipped with a wireless router that connects to the Internet through a cable connection. Which data transmission mode is used by wireless devices?
Explanation: WLAN standards use carrier sense multiple access with collision avoidance (CSMA/CA). Each wireless device that transmits data includes in the frame the time duration that it needs for the transmission. All other wireless devices receive this information and know how long the medium will be unavailable. Therefore, wireless devices operate in half-duplex mode.
10. Which LAN topology requires a central intermediate device to connect end devices?
Explanation: In a star network topology end devices are connected to a central intermediate device such as a hub or a switch.
11. What is used on WLANs to avoid packet collisions?
Explanation: WLANs are half-duplex networks which means that only one client can transmit or receive at any given moment. WLANs use carrier sense multiple access with collision avoidance (CSMA/CA) to determine when to send data on the network to avoid packet collisions.
12. What is the first step in the CSMA/CA process when a wireless client is attempting to communicate on the wireless network?
- The client listens for traffic on the channel.
- The client sends an RTS message to the AP.
- The AP sends a CTS message to the client.
- The client sends a test frame onto the channel.
Explanation: When a wireless client is attempting to communicate on the network, it will first listen to the channel to be sure it is idle. Next, the client sends an request to send (RTS) message to the access point (AP) to request dedicated access to the network. The access point (AP) will then send a clear to send (CTS) message granting access to the client. The client will then transmit data.