CompTIA Network+ Practice Test 2025 – All-in-One Guide to Master Your Certification!

The beginning of an Ethernet frame is identified by the preamble and the Start Frame Delimiter (SFD). The preamble serves as a synchronization pattern that prepares the receiving device for the arrival of the frame. It consists of a series of alternating ones and zeros, allowing the devices on the network to establish timing and synchronization before processing the actual data.

Following the preamble, the Start Frame Delimiter signals the start of the frame data. It is a unique sequence that indicates the end of the preamble and the start of the actual frame information. This combination of the preamble and SFD is essential for properly delineating the beginning of the frame during transmission, ensuring that the receiving devices can correctly interpret the Ethernet frame contents.

Other options refer to components that are important within the frame but do not signify the start. For example, the Destination MAC Address is part of the frame header that follows the SFD, while the Source MAC Address and Type identify the sender and the frame type, respectively, but are not involved in marking the beginning of the frame. The Payload and Frame Check Sequence are also part of the frame structure but come after the initial identifiers.