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Introduction to the Ethernet (CSMA/CD (cs - carrier sense (is there a…
Introduction to the Ethernet
The MAC address
Ethernet Media Access Control address
The "physical" address of a network adapter
unique to a device
48 bits / 6 bytes long
displayed in hexadecimal
8c:2d:aa:4b:98:a7
a mac address is seperated into 2 pieces
8c:2d:aa:
OUI Organizationally Unique Identifier
"The manufacturer"
4b:98:a7
Network Interface Controller-Specific
"The serial number"
Duplex
Half-duplex
a device cannot send and receive simultaneously
all lan hubs are half-duplex devices
switch interfaces can be configured as half-duplex
but usually when connecting to other half-duplex device
Full-duplex
data can be sent and received at the same time
a properly configured switch interface will be set to full-duplex
Half duplex ethernet
traffic received on one interface is repeated to all other interfaces
CSMA/CD
cs - carrier sense
is there a carrier
is there a signal available that we can use to send some data?
ma - multiple access
more than one device on the network
cd - collsision detect
collision - two stations talking at onece
identify when data gets garbled
half-duplex ethernet
not used any longer
CSMA/CD operation
listen for opening
dont send if network is already busy
send a frame of data
send data whenever you can
theres no queue or prioritization
if a collision occurs
transmit a jam signal to let everyone know a collision has occured
wait a random amount of time
retry the transmission
Full-duplex ethernet
full-duplex
send and receive simultaneously
CSMA/CA
ca -collision avoidance
common on wireless networks
collision detection isnt possible
a sending station cant hear other stations
use rts/cts
im ready to send
youre clear to send
solves the hidden node problem
station a can hear the access point
station b can hear the access point
stationa cant hear station b
Preamble
SFD
Destination MAC address
Source MAC address
EtherType
Payload
FCS