Which two functions are performed at the LLC sublayer of the OSI Data Link Layer to facilitate Ethernet communication? (Choose two.)

The LLC (Logical Link Control) sublayer of the OSI Data Link Layer performs several functions to facilitate Ethernet communication. Among the options you’ve listed, the two functions performed at the LLC sublayer are:

1. Places information in the Ethernet frame that identifies which network layer protocol is being encapsulated by the frame. The LLC sublayer adds control information in the Ethernet frame to identify the network layer protocol (like IPv4 or IPv6) being used. This is crucial for the receiving system to understand how to interpret the encapsulated data.
2. Enables IPv4 and IPv6 to utilize the same physical medium. By providing multiplexing capabilities and specifying the network layer protocol in use, the LLC allows different network protocols (like IPv4 and IPv6) to share the same physical network medium, such as Ethernet.

The other functions you mentioned are not specifically performed by the LLC sublayer:

• Integrates Layer 2 flows between 10 Gigabit Ethernet over fiber and 1 Gigabit Ethernet over copper: This is more related to the physical layer and its interfaces, rather than the LLC sublayer.
• Implements trailer with frame check sequence for error detection: This is generally a function of the MAC (Media Access Control) sublayer of the Data Link Layer, which deals with physical addressing and error detection.
• Applies source and destination MAC addresses to Ethernet frame: Again, this is a function of the MAC sublayer, not the LLC sublayer. The MAC sublayer handles the framing of data packets, including the addition of source and destination MAC addresses.

In the context of the OSI model’s Data Link Layer, particularly the Logical Link Control (LLC) sublayer, two functions relevant to Ethernet communication are:

1. Places information in the Ethernet frame that identifies which network layer protocol is being encapsulated by the frame: The LLC sublayer is responsible for identifying and encapsulating network layer protocols within the Ethernet frame. This involves adding information to the frame which indicates the type of payload it is carrying, whether it’s an IP packet, an ARP request, etc. This function is crucial for the proper delivery and interpretation of the data at the receiving end.
2. Adds Ethernet control information to network protocol data: The LLC sublayer adds control information to the network protocol data, which is essential for managing and controlling the communication process. This includes frame synchronization, error checking, and flow control. This function ensures that the data transmitted over the Ethernet network is reliable and synchronized.

The other functions mentioned, such as applying source and destination MAC addresses, integrating Layer 2 flows between different Ethernet types, and implementing CSMA/CD over legacy half-duplex media, are typically associated with the Media Access Control (MAC) sublayer of the Data Link Layer, not the LLC sublayer. The MAC sublayer is responsible for the physical addressing and media access control mechanisms in Ethernet communication.