TUTORIAL 1 - Network Topologies & Technologies Flashcards
define topology
describes lay of land
define network topology
describes how network physically laid out & how signals travel from 1 device to another
what are the 2 categories of topologies and why are they categorized
physical and logical
physical layout of devices & cables doesn’t describe how signals travel from 1 device to another
what is a physical topology?
arrangement of cabling & how cables connect 1 device to another in network
what are the different types of physical topologies
bus
star
ring
meshed
point-t-point
what are the strengths of the physical bus topology
Strengths:
simplest & at 1 time most common method for connecting pc
continuous length of cable connecting 1 pc to another in daisy-chain fashion
what are the weaknesses of the physical bus topology
weaknesses:
limit of 30 pc per cable segment
max total length of cabling is 185m
both ends must be terminated if not will over circuit & signal bounce
any break in bus brings down entire network
adding/removing machine brings down entire network temporarily
limited to 10mbps half-duplex
how does data travel in a physical bus
- electrical pulses (signals) travel cable’s length in all directions
- signal travels across medium & from device to device (signal propagation)
- signal continues until weakened/absorbed by terminator
- if not terminated, signal bounces/reflected at end of medium
what is a physical star topology
uses central device for monitoring & managing network
central device is usually hubs & switches which can collects stats about network traffic patterns & detect errors
with cabling & NICs support, star network can be updated by replacing central device of higher speed if needed
Eg. 100mbps to 1gbps
what are the strengths of a physical star topology
faster than bus
centralized monitoring & management of network traffic possible
easier network upgrades
when num of workstations you need exceed num of ports on central device you simply add another central device
what is an extended star topology and what is the other name for it
when num of workstations have exceeded and several central devices are added, extended star is formed
hierarchical star
how does data travel in a physical star
depends on type of central device
central device determines logical topology
hub = logical bus
switch = logical switching
MAU = logical ring
what is a physical ring topology
similar to bus
devices are daisy-chained
no terminator, cabling brought around from last device back to 1st to form ring
most widely used to connect LANs with tech called Fiber Distributed Data Interface (FDDI)
what is a FDDI dual ring
FDDI acts as a high speed backbone to connect LANS (servers, switches) and terminal concentrators (which connects terminals)
uses dual ring which allows data to travel in both directions
1 ring failure doesn’t break network
operates using fiber-optic cable at 100mbps
what is a point-to-point topology (PMP)
it is also known as point-to-multipoint topology
all communication goes through central device
central device can communicate with 2 or more other devices
data travels on a dedicated link.
single connection made from router to switching device that directs traffic to correct branch office
mostly used in WANs where main office has connections to several branch offices via router
can connect 2 LANs separated by highway, river or railway tracks to make a wireless bridge
what is a mesh topology
connects each device to every other device in network
has multiple pt to pt connections for purposes of redundancy & fault tolerance
purpose is to ensure if 1 or more connections fail, there’s still path for reaching all devices on network
expensive due to multiple interfaces & cabling
found in large WANs & internetworks
what is a logical topology
describes how data travels from pc to pc
sometimes may be similar to physical arrangement of cables (bus, star, ring)
in a switched topology, there is always an electrical connection between the computer & switch
but when no data being transferred, there is no logical connection/circuit between devices
what is a network technology, what are some other terms for it and provide some examples
defines frame format & media
a method NIC uses to access the medium & send data frames
(either ethernet, token ring, wireless or a combination)
other terms:
network interface layer technologies
network architectures
data link layer technologies
examples:
LAN
ethernet
802.11 wireless
token ring
WAN
frame relay
FDDI
ATM
what are the 3 types of cables
- Unshielded Twisted Pair (UTP)
most common media type in LANs
consists of 4 pairs of copper wires twisted tgt
comes in numbered categories
sub-categories of UTP:
CAT3, CAT5, CAT6, CAT6a, CAT7
- fiber-optic cabling
uses twin strands of glass to carry pulses of light long distances & at high data rates
- coaxial- cabling
obsolete but used as network medium for Internet access via cable modem
what is baseband and broadband signaling
network technologies can use media to transmit signals in these 2 ways
what is baseband signaling
sends digital signals in each bit of data represented by a pulse of electricity/light
sent at single fixed frequency & no other frames can be sent along with it
no more than 1 frame can be sent at same time
what is broadband signaling
uses analogue techniques to encode binary 1s & 0s across a continuous range of values
signals flow at particular frequency & each frequency represents a channel of data
can have several transmissions occurring at same time
what is an ethernet network and what range of speeds does it have
it is a LAN tech which is easy to install and is also a baseband.
range of speeds: 10 mbps to 10 gbps
operates in physical bus/star and logical bus/switched topology.
has same underlying tech as most NICs and hubs
what is ethernet addressing
every station has a MAC address,
MAC address: 48 bits expressed as 12 hex digits
incoming frames must match NIC’s address/broadcast address (FF-FF-FF-FF-FF-FF)
once processed by NIC, incoming frames sent to network protocol for further processing
what are ethernet frames, give example and frame conditions
there are 4 frame types, depending on network protocol used to send frame
frames must be between 64 & 1518 bytes in order to have pause in between transfers and receive other packets
- destination MAC
- source MAC
- type: network protocol
- data
- FCS: error handling check
example:
ethernet II frame is used by TCP/IP which is a network protocol
what is ethernet media access
media access method:
rules governing how & when medium can be accessed for transmission
Ethernet uses:
Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
this is only used in a hub(switches that have switching tables)
Carrier Sense: listen before send
- must hear silence
Multiple Access: if 2 or more stations hear silence, multiple stations ma transmit at same time
Collision Detection: if 2 or more stations transmit, a collision occurs & is detected by NIC
all stations & servers wait for a random amount of time before retransmitting
all stations must retransmit
what are collisions and collision domains and what are the conditions for it to occur
all devices interconnected by 1 or more hubs hear all signals generated by other devices
usually happens in half-duplex
only during full-duplex mode, (switches) will not have collisions because they have switching tables
collision domain:
extent to which signals in Ethernet bus topology network propagated
all devices in collision domain subject to possibility that whenever a device sends a frame, a collision might occur
more collisions > need retransmit > slower network traffic
what is ethernet error handling, describe how and what ethernet uses to detects errors
ethernet is best-effort delivery system
there will be no acknowledgement whether data gets to destination
network protocols & apps ensure delivery
only collisions will be auto retransmitted
ethernet detects damaged frames using:
error-checking code in frame’s trailer called Cyclic Redundancy Check (CRC)
CRC determines if data is unchanged
if frame detected as damaged, its discarded with no notification
half-duplex VS full-duplex communication
half-duplex
- can talk & listen but not both at the same time (2 way radio)
ethernet on hubs work in half-duplex
full-duplex means NIC/switch can transmit/receive simultaneously
CSMA/CD turned off
most switches operate in full-duplex
define ethernet standards
they are expressed as XBaseY
X: speed
Y: type of media
T = twisted pair
FX = fiber optic
e.g 100BaseFX
100 = speed
Base = baseband(signal) is digital
FX = fiber optic
what are the different types of standards (including obsolete ones)
100BaseT
100BaseTX
100BaseFX
100BaseT ethernet
100GBaseT ethernet
100BaseT4
1000BaseLX
1000BaseSX
1000BaseCX
10 Gigabit ethernet IEEE 802.3ae
40 Gigabit & 100 Gigabit ethernet
decribe 100BaseTX
most common ethernet
category 5/higher UTP (cables)
use 2 of 4 wire pairs
2 types of 100BaseTX hubs
class I - can have >1 hub between devices
class II - can have max 2 hubs
switches can be used to connect many hubs
describe 100BaseFX
runs over 2 strands of fiber optic
usually used as backbone cabling between
hubs/switches
also used when immunity to noise & eavesdroppng required
describe 100BaseT ethernet
AKA Gigabit Ethernet
Category 5/higher UTP
use all 4 wire pairs
describe 1000BaseLX
use fiber-optic media
“L” stands for “long
wavelength” laser
supports max cable length of 5000m
describe 1000BaseSX
use fiber-optic media
“S” stands for “short wavelength” laser
not as long as long-wavelength lasers but less expensive
describe 1000BaseCX
uses specially shielded, balanced, copper jumper cables
AKA “twinax”/”short-haul” copper cables
describe 10 Gigabit Ethernet IEEE 802.3ae
similar to others in frame formats & media access
run only on fiber-optic
max 40km
primarily used for network backbones
varieties
10GBaseSR, 10GBaseLR, 10GBaseER, 10GBaseSW, 10GBaseLW, and 10GBaseEW
describe 40 Gigabit & 100 Gigabit Ethernet
high cost
prohibitive
adoption slow
fiber optic primary medium
though have provisions to use special copper assemblies over short distance
what is WI-FI and what medium does it use
802.11 Wi-Fi
AKA Wireless Fidelity (Wifi)
hotspot - public wifi network
is extension to ethernet
use airwaves instead of cabling as medium
what are the modes of operation for WIFI
there are 2 modes
mostly focus on infrastructure
- infrastructure - u
se central access point (AP) - ad hoc - no central device
data travels from device to device like bus
AKA peer to peer mode
what are the wifi channels and frequencies
operate at 2.4ghz or 5ghz (not fixed)
2.4ghz is actually 2.412 thru 2.484 divided into 14 channels spaced 5mhz apart
work like tv channel - must tune to channel to connect
needs 25mhz to operate spanning 5 channels
choose channels 5 apart from other known APs
5.0ghz actually 4.912 thru 5.825 ghz divided into 42 channels of 10, 20 or 40 mhz each
what are wifi antennas
antennas are both transmitter & receiver
characteristics & placement determine how well device transmits/receives wifi signals
categorised by radiation pattern
- omnidirectional antennas
signal radiate out in equal strengths in all direction
- unidirectional antenna
signals focused in single direction
ideal for long, narrow spaces
what are some access methods and operation
wifi access method
sending station can’t hear if another station begins
transmitting so cannot use CSMA/CD access method that ethernet uses
wifi device use carrier sense multiple access with collision avoidance (CSMA/CA)
use
request-to-send/
clear-to-send (RTS/CTS) packets and acknowledgements
extra handshake avoids collisions
with this extra “chatter” actual throughput cut in half
what are the 9 signal characteristics
- absorption
- solid objects absorb radio signals, causing them to attenuate (weaken)
- refraction
- bending of radio signal as it passes from mediums of diff densities
- diffraction
- altering of wave as it tries to bend around obj
- reflection
- signal hits dense, reflective material resulting in signal loss
- scattering
- signal changes dir in unpredictable ways causing loss in signal strength
- signal-to-noise ratio
- amount of noise compared to signal strength
- noise can come from eq, wireless devices, wireless networks etc
- throughput - actual amt of data transferred
- not counting errors & acknowledgements
- goodput - actual app-to-app data transfer speed
- overhead - packet frame headers, acks & retransmissions
what are non-overlapping channels
Eg. 802.11b & g has 14 channels
1, 6, 11 are non-overlapping
2, 7, 12 are non-overlapping
4, 8, 13 are non-overlapping
describe how wifi security works
signals can travel several hundred feet - wifi devices outside home/office can detect your signals
should be protected by encryption protocol that makes data difficult to interpret
encryption protocols
- wired equivalent privacy (WEP)
- Wifi protected access (WPA)
- WPA2
not all devices support all 3 protocols
older devices might only support WEP or/& WPA
what are some token ring networks
based on IEEE 802.5 standard
token passed along network
only station with token can transmit
frame acknowledged & token released
no collisions
originally operated at 4mbps then increased to 16mbps & later 100mbps
uses category 4 & higher UTP
central device is Multi-Access Unit (MAU)
obsolete
fiber distributed data interface technology
phy and logical ring topology
uses token-passing access method & dual rings for redundancy
transmits at 100mbps & can include up to 500 nodes over dist of 60miles
uses fiber-optic cable only
obsolete on new networks
