Download Media, Connections, and Collisions

Media, Connections,
and Collisions
Honolulu Community College
Cisco Academy Training Center
Semester 1
Version 2.1.1
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Overview
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Network foundation is the physical layer, Layer 1
of the OSI Reference Model.
Physical layer defines the electrical, mechanical,
procedural, and functional specifications for
activating, maintaining, and deactivating the
physical link between end systems.
Different types of networking media.
How network devices, cable specifications,
network topologies, collisions and collision
domains affect how much data can travel across
the network and how fast.
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F Speed and throughput: 10-100 Mbps
F Average $ per node: Moderately Expensive
F Media and connector size: Medium to Large
F Maximum cable length: 100m (short)
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Shielded Twisted Pair - STP
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Combines the techniques of shielding,
cancellation, and twisting of wires.
STP gives greater protection from all types of
external interference, but is more expensive than
UTP (unshielded twisted-pair cable).
Shielding must be properly grounded.
 If
improperly grounded, shielding to act like an
antenna (noise pickup).
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F Speed and throughput: 10-100 Mbps
F Average $ per node: Least Expensive
F Media and connector size: Small
F Maximum cable length: 100m (short)
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UTP - Unshielded Twisted Pair
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Least expensive networking media, and most
common.
 Small
size (.43 cm diameter)
 easy to install, and more cables in wiring ducts.
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Relies on cancellation to minimize interference.
 prone
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to electrical noise and interference
To reduce crosstalk, the number of twists in the
wire pairs varies.
Uses solid RJ-45 connection.
Fastest copper media.
Disadvantage is short unboosted runs - 100m.
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Coaxial Cable (coax)
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Longer unboosted distances than other copper
media.
Two sizes:
 Thinnet
-10Base2
- 185m.
 Thicknet
-10Base5
- 500m.
F Speed and throughput: 10-100 Mbps
F Average $ per node: Inexpensive
F Media and connector size: Medium
F Maximum cable length: 500m (medium)
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Problems with Coax
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Difficult to work with - thicker diameter.
Requires proper grounding at both ends.
Improper grounding can give more
interference.
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Fiber Optic Cable
F Speed and throughput: 100+ Mbps
F Average $ per node: Most Expensive
F Media and connector size: Small
F Maximum cable length: Up to 2km
F Single mode: One stream of laser-generated light
F Multimode: Multiple streams of LED-generated
light
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Fiber Optic Cable
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Uses modulated light transmissions.
Most expensive networking media, in materials
and installation.
Not susceptible to EMI and RFI.
Does not conduct electricity (advantage for use
between buildings, floors, etc).
Fastest speeds of all networking media.
Long unboosted distances - up to 2 km.
Used primarily for backbone cabling.
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Wireless Communications
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Wireless signals are electromagnetic waves,
which can travel through a vacuum or air.
 no
physical medium is necessary.
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Purpose of LAN Media Specifications
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Mid-1980s, no standards, networking media were
largely proprietary, networks used different specs
and implementations.
OSI model was created;
provided a set of standards.
 Standards
are sets of rules
or procedures that are either
widely used, or officially specified.
 Ensured compatibility and
interoperability between various
types of network technologies.
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Standards
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Many groups joined the movement to specify the
types of cable that could be used for specific
purposes or functions.
 IEEE
- Institute of Electrical and Electronics
Engineers
 UL - Underwriters Laboratories
 EIA - Electrical Industries Association
 TIA - Telecommunications Industry Association
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Standards (cont.)
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IEEE
 cabling
requirements in 802.3 (Ethernet) and
802.5 (Token Ring) specifications.
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UL
 identification
program that lists markings for
shielded and unshielded twisted-pair media.
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TIA/EIA
 568-A cabling
standards, 569 wiring closets.
 greatest impact on networking media standards.
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TIA/EIA 568-A
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Focuses on standards for horizontal cabling.
 horizontal
cabling includes the networking media
that extends from wiring closet to workstation.
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Maximum distance for cable runs in horizontal
cabling is 90 m (CAT 5 UTP ).
Patch cords or cross-connect jumpers located at
the horizontal cross-connect cannot exceed 6 m.
Patch cords to connect equipment at the work
area - 3m.
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UTP - Category Ratings
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Cat 1 - not rated for data.
Cat 2 - for voice/PBX (private branch exchange).
 Low
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performance UTP, for voice, low speed data.
Cat 3 - use for 10BaseT networks.
Cat 4 - low loss, 10baseT, up to 16 Mbps.
Cat 5 - low-loss extended frequency, for
100baseX systems - Fast Ethernet.
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Ethernet 10BaseT
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Layer 1 Components and Devices
 Passive
F patch
 Active
F
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(no energy to operate) components:
panels, plugs, cabling, jacks.
devices:
transceivers, repeaters, hubs.
Connectors & Jacks: RJ-45
8
wire connector, terminates UTP.
 Jacks require punch-down tool.
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Cabling: standard is Cat 5 UTP.
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Ethernet Layer 1 Components
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Patch panel: convenient groupings of RJ-45
jacks.
8
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wire jacks, require punch-down tool.
Transceiver: a combination of transmitter and
receiver.
 Connects
to AUI port to give a particular type of
connection.
 Transmit from one pin configuration and/or media
to another.
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Ethernet Layer 1 Components (2)
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Repeaters: regenerate, and retime
signals, which enables cables to
reach longer distances.
 cannot
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filter network traffic.
Hubs: multiport repeaters.
 serve
as the center of a
star topology.
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Layer 1 components create or act on the bits.
 They
recognize no information patterns in the bits,
no addresses, and no data.
 Their function is simply to move bits around.
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Types of Networks
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Shared media - occurs when multiple hosts
have access to the same medium.
 Ethernet
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is a shared media environment.
Point-to-point - one device is connected to only
one other device via a link.
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Circuit vs Packet Switched
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Circuit-switched - indirectly-connected network
in which actual electrical connection is ‘switched
on’ for the duration of the communication.
 Telephone
service is circuit-switched.
 ISDN.
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Packet-switched - link connection between two
communicating hosts, where the source sends
messages in packets.
 Advantage:
many hosts can share same link.
 Frame Relay is an example of packet-switched.
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Collisions & Collision Domains
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Ethernet allows only one data packet to access
the media at any one time.
 If
two or more nodes transmits at the same time, a
collision occurs, and the data is damaged.
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Collision domain - area in the network, where the
data packets originate and collide.
When a collision occurs, the data packets that
collide are destroyed, bit by bit.
CSMA/CD is the method Ethernet uses to handle
media contention.
 Developed
at the University of Hawaii in 1960s.
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Repeaters and Collision Domain
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Repeater extends the collision domain, therefore,
the network on both sides of the repeater is one
larger collision domain.
One Large Collision Domain
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Hubs and Collision Domain
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Hubs, like repeaters, extend the collision domain.
One Large Collision Domain
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5-4-3-2-1 Rule of Thumb
 Five
sections of the network,
 Four repeaters or hubs,
 Three sections of the network have hosts,
 Two sections are link segments (for link purposes),
 One large collision domain.
One Collision Domain
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Segmentation
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Purpose is to reduce size of collision domains.
Can segment with bridges, switches or routers.
One Collision Domain
One Collision Domain
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Physical Topology
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Topology defines the structure of the network.
Physical topology is the actual layout of the wire
(media).
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Logical Topology
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Logical topology is how information flows through
a network.
A network’s physical topology may be completely
different from its logical topology.
 Ethernet
10Base-T uses an extended-star physical
topology, but acts like a logical bus topology.
 Token Ring uses a physical star, and a logical ring.
 FDDI uses a physical and a logical ring.
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Linear Bus Topology
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Bus topology has all nodes
connected directly to one link.
Physical perspective:
 all
hosts are connected to each other, and can
communicate directly.
 a break in the cable disconnects hosts from each
other.
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Logical perspective:
 enables
all devices to see all signals from all other
devices.
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Ring Topology
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Ring topology has each node
connected directly to only the
two adjacent nodes.
Physical perspective:
 all
devices are directly connected to two adjacent
devices in a daisy-chain.
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Logical perspective:
 each
station passes the data to its adjacent station.
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Dual Ring Topology
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Dual ring topology has
two concentric rings.
Physical perspective:
 same
as a ring topology,
except there is a second,
redundant ring, that connects the same devices.
 each device is part of two independent ring
topologies.
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Logical perspective:
 acts
like two independent rings, of which, only one
at a time is used.
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Star Topology
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Star topology has a central
node with all links to other
nodes radiating from it.
Physical perspective:
 all
nodes communicate with each other, through
central node.
 central node is a single point of failure.
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Logical perspective:
 all
information goes through one device.
 desirable for security or restricted access reasons.
 but network is susceptible to any problems in the
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star's central node.
Extended Star Topology
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Each node that links to center
node is also the center of
another star.
Physical perspective:
a
core star topology, with each of the end nodes
acting as the center of its own star topology.
 advantage is shorter wiring runs.
 limits number of devices that interconnect to any
one central node.
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Logical perspective:
 extended
star topology is very hierarchical.
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Tree Topology
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Tree topology uses a trunk
node from which it branches
to other nodes.
Physical perspective:
 trunk
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is a wire that has several layers of branches.
Logical perspective:
 flow
of information is hierarchical.
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Irregular Topology
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Irregular network topology
has no obvious pattern to
the links and nodes.
Physical perspective:
 wiring
is inconsistent; the nodes have varying
numbers of wires leading from them.
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Logical perspective:
 no
obvious pattern.
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Mesh Topology
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In a mesh topology every
node is linked directly to
every other node.
Physical perspective:
 every
node is physically connected to every other
node, creating a redundant connection.
 requires large amount of media and connections.
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Logical perspective:
 behavior
of a mesh topology depends greatly on
the devices used.
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Cellular Topology
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Cellular topology consists of
circular or hexagonal areas,
each of which has an individual
node at its center.
Physical perspective:
a
geographic area that’s divided into regions (cells)
for the purposes of wireless technology.
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Logical perspective:
 communication
is directly between nodes or only
with adjacent cells (distance limitations and
interference affect operations).
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Summary
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Function of the physical layer is to transmit data.
Networking media:
 Coax,
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STP, UTP, fiber.
TIA/EIA-568-A & TIA/EIA-569 - most widely used
standards for networking media.
Collisions and collision domains.
Physical topology vs logical topology.
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