Preamble – Synchronization. They give components in the network time to detect the presence of a signal and read the signal
before the frame data arrives.
Start of Frame (SOF) – Start of Frame sequence
Destination and Source Addresses – Physical or MAC addresses. The source address is always a unicast address, the
destination address can be unicast, multicast, broadcast.
Length – Indicates the number of bytes of data that follow this field.
Type – Specifies the upper layer protocol to receive the data.
Data – User or application data. Ethernet II expects a minimum of 46 bytes of data.
If the 802.3 frame does not have a minimum of 64 bytes, padded bytes are added to make 64.
Frame Sequence Check (FCS) – CRC value is used to check for damaged frames. This value is recalculated at the
destination network adapter. If the value is different from what is transmitted, the receiving network adapter assumes that an
error has occurred during transmission and discards the frame.
Ethernet Cabling:
EIA/TIA Horizontal Cabling:
(Using CAT5 cabling in an Ethernet network)
3 Meters – 90 Meters – 6 Meters
Collision Domains - A collision domain is defined as a network segment that shares bandwidth with all other devices on the
same network segment. When two hosts on the same network segment transmit at the same time, the resulting digital signals
will fragment or collide, hence the term collision domain. It's important to know that a collision domain is found only in an
Ethernet half-duplex network
Broadcast Domain - A broadcast domain is defined as all devices on a network segment that hear broadcasts sent on that
segment.
All devices plugged into a hub are in the same collision domain and the same broadcast domain.
All devices plugged into a switch are in separate collision domains but the same broadcast domain. Although, you can buy
special hardware to break up broadcast domains in a switch, or use a switch capable of creating VLANs. VLANs breakup
broadcast domains.
Hubs and Repeaters extend collision and broadcast domains.
Switches, Bridges and Routers break up collision domains.
Routers (and Switches using VLANs) break up broadcast domains.
