Figure 1.2 Ethernet frame as defined by IEEE 802.3 standard
< 1526
Consists a cyclic redundancy check value that is used to
validate that the frames were not damaged
4
Frame Check Sequence
(FCS)
Actual data being carried 46??“1500 Data
Identifies number of data bytes or Frame ID (type of frame) 2 Length/Type
Identifies the sending device (station) 6 Source Address (SA)
Identifies the devices (stations) to receive the frame 6 Destination Address (DA)
Tells where the frame begins 1 Start-of-Frame Delimiter
Indicates a frame is coming 7 Preamble
Description Bytes Field
Preamble SOF DA SA
Length/
Type
Data FCS
7 6 6 2 4 46??“1500 Bytes 1
8 Chapter 1
?– Connectivity mechanism Different media are employed for connectivity (the
???Ether,??? in the Ethernet). This medium physically connects the DCEs and the
DTEs; Unshielded Twisted Pair (UTP) or (multimode) fiber optic cables are commonly
used in enterprise LANs.
As depicted in the Figure 1.3, the devices in the LAN are usually connected in a star
topology with a switch or router acting as a hub and the DTEs connected using a physical
media (CAT 5, as shown in Figure 1.3, is commonly used).
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