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Data link, Bluetooth - Coggle Diagram
Data link
PDU
Flag
RX discards bit after11111
TX inserts a 0 after 011111 always
bit stuffing
byte stuffing
tx inserts 01111101 after 01111101
RX discards first 01111101
escape byte
ADDRESS
Control
DATA
CRC
FLAG
LAN
small area
Problems shared use
bursty traffic
need for address
WIFI -> star topology
Originally BUS topology
connection
Multiplexing
Distributed
Multiple sources or receivers
like cellular network
Centralized
Static channel not good for bursty use
Dynamic assignment?
Complex
Moderator gives permissions
Reservations
Protocols
Random access
No order
Wifi
Free access
No collision prevent
Recover
Mac defined
Detect and reduce
Hystory
Aloha
Two channels (master - slaves)
Master gives feedback
Master channel no risk of collision
No sync needed
ASAP approach
Stop and wait
Exponential backoff time for retry
Different retransmission time for node
Performance
Peak where throughput = f(traffic)
20% max throughput
No control on traffic
Slotted aloha
Node knows when slot start
No partial collision
after collision
Next try with p probability
40% max
No priorities
CSMA (carrier sense)
Politeness
1 persistent
Retry when sensed free
no persistent
random time before sensing
p persistent
Collission
if two sources start contemporary
propagation time dependant
vulnerability periof
0.01 persistent (best)
CSMA CD
Collision detection
Lost packet but free channel earlier
Not easy for radio
No ack need
if Frame time > 2*(propagation delay)
Performance
transmission time / propagation delay
Performs well in small areas
1 persistant preferred (atlow load)
exponential backoff
no priority
ethernet until born of swithces
CSMA CA
Radio avoidance not detection
Collision domain
portion of network where collision occurs easy
non persitent CSMA
need for ack due to no collision detection
ack after SIFS< DIFS
Collisions
same backoff period
DIF expires while backoff expires
Ordered access
Token to send data
Token passed
Evaluate performance
Delay
Throughput
Fairness
Scalability
History
IBM SDLC
ANSi standard
ADCPP
CCITT
ITU-T
LANs
MAC sublayer
ISDN
phone
ATM
layer 2 protocols
LLC (logical link control)
Medium access control (MAC)
Second sublayer
First sublayer
ISO 8802/2
NO error control
SNAP PDU (access protocol)
Extension
sub network
to include IP
ATM (async tranfer mode)
48+5 byte data/header
High speed
DSL + multiplexing DSLAM
IP established as a new
Point to point protocol
no error correction
only detection
PDU
protocol
info
check
state
establishment
dead
Auth
NCP (network control)
configure
Data compression
MAC
6 byte
unicast or multicast
ETHERNET
802.3
differences on packet format
CSMA CD
Collision aborted
jamming sequence (make aware)
No ack used
Frame format
preamble (sync)
MAC (dest + source)
DATA (46-1000 B)
silent GAP
LENGTH (<1500)
Design Parameters
min 64 byte packet
not LENGTH but HIGHEr LAYER >1500
WIFI
802.11
no sensing
CSMA/CA
gain connection to transmitt
half duplex
tx or Rx
ACK for collision detection
Tx
DIFS channel free time
DFC
exponential backoff if busy
ACK (for fail)
Receives a reservation period
ISSUES
Hidden terminal
two distant terminal don t sense each other
overlapping tranmsission
AP must decide who transmit
DFC with handshaking
RTS exchange info
Tx to AP
CTS aftr SIFS
AP to everyone
DATA
ACK
RX
SIFS time before ACK sent
SIFS < DIFS
Bit rate
Slowest node slows channel
your time divided by time waited
slower than the slowest node
Bluetooth
Layers
Physical
Radio
frequecy hopping spread
spectrum modulation
79 possible frequencies
2.45 GHz
Frame
access code
header
payload
increase bit rate for it
channels
SCO
never retransmitted
voice
ACL
no data lost
sharing
LInk control baseband
access to medium
Link manger
energy
Energy
40 channels
3 for signalling
reduced frames
reduced bit rates
history
PIconet
scatternet
Bridge between piconets
Profiles based architecture
eg. headsets
5.3 version
short range
SIG group