Collision Detection and Carrier Sensing in Network Interface Ports | Cisco 200-125 Exam

Network Interface Port

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A network interface port has collision detection and carrier sensing enabled on a shared twisted pair network. From this statement, what is known about the network interface port?



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A. B. C. D. E.


Modern Ethernet networks built with switches and full-duplex connections no longer utilize CSMA/CD. CSMA/CD is only used in obsolete shared media Ethernet

(which uses repeater or hub).

The given statement implies that the network interface port has collision detection and carrier sensing enabled. Let's examine what this means:

  1. Collision detection: This is a mechanism used in shared Ethernet networks to detect if two or more devices are transmitting data simultaneously, which results in data collisions and data loss. In Ethernet networks that use CSMA/CD (Carrier Sense Multiple Access with Collision Detection) protocol, the transmitting device listens for any signals on the network while it is transmitting data. If it detects any signal, it stops transmitting and sends a jam signal to all devices on the network, indicating that a collision has occurred.

  2. Carrier sensing: This is another mechanism used in Ethernet networks to detect the presence of a carrier signal on the network. Before a device starts transmitting data, it checks to ensure that there is no other device transmitting on the network. If the network is idle, the device transmits its data. However, if the network is busy, the device waits for a random amount of time before trying again.

From the above discussion, it is clear that the given network interface port is using the CSMA/CD protocol, which is used in half-duplex Ethernet networks. In half-duplex Ethernet networks, devices cannot transmit and receive data simultaneously; they have to take turns. When a device is transmitting data, it cannot receive any data, and vice versa. This means that the network interface port is not operating at full-duplex.

Now, we need to determine the speed of the network interface port. The given statement does not provide any information about the speed of the port. However, we can make an educated guess based on the fact that collision detection and carrier sensing are enabled.

In Ethernet networks, the maximum cable length is determined by the collision domain. The collision domain is the network segment in which collisions can occur. In half-duplex Ethernet networks that use the CSMA/CD protocol, collisions can occur when two or more devices transmit data simultaneously. The larger the collision domain, the higher the likelihood of collisions.

For twisted-pair Ethernet networks, the maximum length of the collision domain is 100 meters. Therefore, if the network interface port is using twisted-pair cable, it is most likely operating at 10 Mb/s or 100 Mb/s.

However, we cannot determine the exact speed of the port based on the given information. Therefore, we cannot conclude whether the network interface port is a 10 Mb/s or a 100 Mb/s port.

In conclusion, the correct answer to the question is C. This is an Ethernet port operating at half duplex.