LOGICAL TOPOLOGY
def
how data is transmitted
BUS
a common tranmission medium
Ethernet
TOKEN RING
data received from one neighbour
pass onto another neighbor
Token Ring
TRAFFIC CONTROL
def
ACCESS METHOD
how computer places data into media access
BUS
physical topology
STAR
BUS
Multiple Access
Carrier Sense
if the wire is used by other devices
wait
COLLISION HANDLING
CSMA/CA
used in wireless system
use for BUS
"clear to send" signal
acknowledged to proceed
wait until it is allowed to go
next time, double the time
CSMA/CD
used in ethernet
threshold bandwidth
lower, keep requesting
higher, stop requesting
pros
simple software
little overheat
complete control of the media
as long as no other hv access
cons
access times r not predictable
can't give faster access
chance of collisions increase, when new device join network
TOKEN RING
used for RING topology
very high performance system
TOKEN
sent around the ring
1 direction
Sent data
1
"grab" token
attach data to "token"
address "token" to sender
2
target picks up packet
target release token back to the ring
3
sender receive the token
sender knows token has arrived
4
token is marked free
token released to the ring again
PROS
deterministic
predictable load/delay
prioritise for faster transmission
eliminate collision
CONS
requires interactive software
Polling
used for mainframe
MAC ADDRESSING
MAC address
aka Ethernet address
unique ID for NIC
3 char manufacturers - 3 char serial number
Physical passing
Ethernet frames
procedure
slide 22/23
Subnet
hub
switch
bridge
repeater
separate traffic
Multiple subnet
LAYER 2 PROTOCAL
MICROSOFT
NET BUI protocol
VPN
security purpose
adds a protective layer
LOGICAL LINK CONTROL
TRANMISSION SYNCRONISATION
Asynchronous
2 devices dont sync
only send/receive
uncomplicated
no separate control signals
overhead packet
detect errors
Synchronous
faster transmission
more reliable
improved error detection
Isochronous
fastest
hybrid of Asynchronous & Synchronous
CONNECTION SERVICES
LLC - Level Flow Control
Error control
STANDARDS
802
802.11
cable standards
10base
base T