From Introduction to Networks by Cisco Press, 2014
Chapter 4
Wireless -
-range limitations
-easily mobile
-performance directly related to distance
-performance degraded by other wireless
wired
-won't degrade in performance based on distance
-hard to move
-static positioning
-as many devices with no degredation
Physical layer
types of media
-copper
-fiber optic
-wireless
Functional Areas
Physical components - electronic hardware, media, connectors, interfaces
encoding - convert a stream of data bits into predefined code
common network encoding schemes
-manchester - 0 is high to low transition
1 is low to high transition
-non-return to zero - two states meaning 0 and 1, and no neutral/rest position
signaling - method of representing bits
asynchronous - transmitted without clock signal. frames require start/stop indicator flags
synchronous - data signal sent with clock signal
ways to transmit
frequency modulation - carrier frequency varies
amplitude modulation - carrier amplitude varies
pulse code modulation - analog signal is converted to digital by sampling the signals amplitude and expressing as binary
data transfer speeds (in bits)
know your metric
throughput - measure of bits across media in a given time
-varies by...
-amount of traffic
-type of traffic
-latency - amount of time, including delays, to travel from one point to another
throughput can't be faster than the slowest link
Copper cabling
-inexpensive
-easy to install
-limited by distance
-limited by signal interference
data transmitted as electrical pulses
attenuation - the longer a signal travels, the weaker it gets
electromagnetic interference (EMI) and/or radio frequency interference (RFI)
-capable of distorting signal or corrupting signal
-produced by florescent lights and electrical motors
crosstalk - electrical or magnetic signal on one wire distorts the signal on another wire
-canceled by twisting pairs together
main types of copper media
-shielded twisted pair (STP)
-unshielded twisted pair (UTP)
-coaxial
UTP - most common
- 4 pairs of color coded wires
STP - not as common
-provides better noise protection
-more expensive
-difficult to work with
-if improperly grounded shield can act as antenna and pick up signals
-4 pairs of color coded wires
coax - 2 conductors sharing the same axis
-traditionally used in cable tv, early Ethernet
-still used for
-wireless
-cable internet
all copper susceptible to fire/electrical hazards
-toxic gas released when burned
-lightning strikes
-over voltage fries ports
prevent problems by....
-separate data and electrical
-connect cables correctly
-inspect for damage
-most be grounded correctly
UTP cabling
-cancelation - pair wires in a circuit, then magnetic fields are cancelled
-vary twists per wire enhances cancellation effect
standards defined by EIA/TIA
-cable types
-cable lengths
-connectors
-cable termination
-methods of testing
categorized by IEEE by transmission speed
- terminated with ISO 8877 RJ45 jack
termination options
-Ethernet straight through
-crossover
-rollover
Fiber Optic Cable
-higher data rate
-longer distance
Fiber is used
-Enterprise networks as the backbone
-fiber to the home (FTTH), access networks
-long haul networks
-submarine networks
fiber design/layout
-core - pure glass - transmission medium
-cladding - surrounds core, acts as a mirror
-jacket -surrounds and protects core and cladding
-susceptible to sharp bends
transmitted using...
-lasers
-LED
-laser light through the fiber could damage the human eye
single mode fiber - small core and lasers
-long distance
multimode fiber
-large core and LED
-cheaper
-up to 550 meters
terminated with optical fiber connector
-70 different connector types
most popular
-straight tip (ST) - older, bayonet style
-subscriber connector (SC) square or standard connector
-LC (lucent connector) little or local connector, growing in popularity due to small size
All fiber connectors have light travel in one direction at a time (half duplex)
Need 2 cables to send/receive at the same time (full duplex)
terminating fiber requires special training and equipment
common failures
-misalignment- not joined correctly
-end gap - media does not correctly touch the splice or connection
-end finish - dirt, not properly polished at termination
use a tester or bright flash light
tester
optical time domain reflector
Advantages for fiber over UTP
-fiber immune to EMI/RFI
-greater lengths
-fiber more expensive over the same distance
-different skills to terminate/splice fiber
-requires careful handling
wireless media
-carry electromagnetic signals that represent binary digits
-not restricted to connectors or pathways
-greatest mobility
-number of devices expanding
concerns -
-coverage area - work well in open areas, but are blocked by certain obstructions
-interference - can be obstructed by common household devices
-security - requires no physical access, so it is easy to gain unauthorized access
-security a major failing
standards
IEEE 802.11 (WLAN) - wifi uses a contention or non-deterministic system with system CSMA-CA
IEEE 802.15 (wireless PAN or Bluetooth)
IEEE 802.16 Wi-Max point to point microwave
physical layer standards apply to
-data to radio signal encoding
-frequency and power of transmission
-signal reception and decoding
-antenna design and construction
common implementation is to use a WAP connected to a LAN
-lots of wired standards. check and make sure they interoperate
-stringent policy following
various 802.11 standards
-a
-b
-g
-n
-ac
-ad
data link layer
purpose - responsible for the exchange of frames between nodes over a physical medium
node - network devices connected to a common medium
2 services
-accepts L3 packets and package them into frames
-controls media access control and performs error detection
data link layer divided into 2 layers
------------------------------------------------------------------------
network
-------------------------------------------------------------------------
data link | llc sublayer
----------------------------------------------------------
| mac sublayer | | | |
-----------------------------------------802.3 - 802.11 | 802.15 |
physical | | | | |
--------------------------------------------------------------------------
LLC (logical link control)
-defines software process that provide service to network layer protocols
MAC (media access control)
-MAC processes defined by hardware; data link layer addressing and delimiting of data according to physical media connected
MAC method - gets frame on and off the media
at each step, data goes up to layer 3 and is re-encapsulated as it gets back out
-encapsulation in header and trailer to create a frame
contains
-header - control and addressing
-data - information. IP header, transport layer header and data
-trailer - control info and error dection
framing breaks stream of 0s and 1s into decipherable groupings
-frame start/stop indicator flags
-addressing
-type - used by LLC to identify L3 protocol
-control - special flow control services
-data - frame payload
-error detection
Layer 2 standards
Topologies
MAC provides traffic rules
topology - how the connection between the nodes appears to the data link layer
media sharing - how the nodes share the media
physical topologies - where in the building
logical topologies - how network frames transfer frames from node to node
IP address map
WAN topologies
point to point
hub and spoke
mesh - every system connected to every other
virtual circuit
logical connection between two nodes
half duplex - one sends, everyone listens
full duplex - send and receive at the same time
physical topologies - star end devices
-connected to intermediate device
-extended star
-bus
-ring
contention-based access - all nodes compete for use of the media, but have a plan during collision
controlled access - each node has its own time to use the media
CSMA/CD - monitor traffic, send if silent
CSMA/CA -
data link frames
fragile environment requires more control
-think media transmission through clouds, space, space, brick walls, hills...
protected environment requires fewer control
-think hardwired lines that go short distances
------------------------------------------------
header
------------------------------------------------
start frame | address | type/length
------------------------------------------------
different data link protocol use
-priority/QoS
-logical connection control field
-physical link control
-flow control - to start/stop traffic
-congestion control - indicates congestion
data link provides addressing that is used in transmitting across shared media
called physical address
physical address specific to device
-non-hierarchal
-can't be used to find device on the internet
-only used for local delivery
if you want to cross networks, an intermediate device is necessary
trailer used to determine if frame arrived without errors
create a CRC and places it in the FCS field
at destination, check FCS. if error, discard
-not a perfect method
all layer 2 use depends on topology
common data link protocols
-ethernet
-PPP
-802.11 wireless
-HLDC
-frame relay
Ethernet
-dominant LAN technology
-802.2 and 802.3 standards
-provides unacknowledged connectionless service using CSMA/CA as media access
-MAC is 48 bits, represented in hex
Point to point protocol
-deliver frames between nodes
-developed by RFC
-layered architecture
-establishes logical connections (sessions)
-PPP session hides physical media from upper PPP protocol
802.11 wireless
-same LLC and 48 bit addressing scheme as ethernet
-more controls based on media
-uses CSMA/CA
-uses acknowledgements to confirm successful delivery
-supports authentication, encryption, privacy, association
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