Preamble, SFD, or Interpacket Gap?

About this interactive

The lesson's Layer 1 Ethernet packet: the frame (64 to 1,522 bytes) plus 8 more bytes, so 72 to 1,530 bytes on the wire. - **Preamble:** 7 octets of alternating 1s and 0s (10101010). It synchronizes the clocks of the two devices, so the receiver can tell where each bit starts and does not misread the signal. - **Start frame delimiter (SFD):** 1 octet, 10101011. The final 11 breaks the pattern and says: sync is done, the frame comes next, starting with the destination MAC address. - **Interpacket gap:** after the frame, the NIC must wait the time of 12 octets (96 bit times) before it may send the next frame.

What you'll learn

Identify the preamble (7 octets of alternating 1s and 0s that synchronize the receiver's clock), the start frame delimiter (1 octet, 10101011, that marks where the frame begins) and the interpacket gap (12 octets' worth of idle time between frames) from what each does
Place each around the Ethernet frame: the preamble and SFD before it, the gap after it

Aligned to

CompTIA Network+

1.1 Explain concepts related to the Open Systems Interconnection (OSI) reference model.

Cisco CCST Networking

1.1 Identify the fundamental conceptual building blocks of networks

Key terms

Preamble: A 7-octet sequence of alternating 1s and 0s transmitted at the start of an Ethernet packet to synchronize the clock timing between communicating devices.
Start Frame Delimiter: A 1-octet field following the preamble that signals the end of synchronization and the beginning of the Ethernet frame data.
Interpacket Gap: A mandatory idle period equivalent to 12 octets that a network interface card must wait after transmitting a frame before sending the next one.
Physical Layer: Layer 1 of the OSI model, responsible for the transmission of raw bits over a physical medium.
Ethernet Frame: The Layer 2 data unit used on Ethernet networks, containing a preamble, source and destination MAC addresses, an EtherType field identifying the Layer 3 protocol, a payload (typically an IP packet), and a 4-byte FCS for error detection. Switches use the MAC addresses in Ethernet frames to make forwarding decisions.

Topics

Ethernet Physical Layer Preamble Start Frame Delimiter Interpacket Gap Interactive Categorize

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