Transcript Chapter 5 - YSU Computer Science & Information Systems

Cisco Academy – Chapter 5
Physical Layer
Physical Layer - 1
• defines the electrical, mechanical,
procedural, and functional specifications for
activating, maintaining, and deactivating the
physical link between end systems
• Media
• Devices
• Topologies
• Collision Domains
Media
• STP
• UTP
Shielded Twisted Pair
Unshielded Twisted Pair
» 10-100 Mbps, Inexpensive, 100 meters (333’), 4pairs
• Coaxial Coaxial Cable
» 10-100 Mbps, Inexpensive, 500 meters, Not used
• Fiber
Glass filament
» >100 Mbps, Expensive, 2 km, single and multi-mode
• Wireless Electromagnetic waves
Standards
• Sets of rules or procedures that are either widely
used, or officially specified, and that serve as the
gauge or model of excellence
• ISO International Standards
Organization
• IEEE
Institute of Electrical & Electronic
• TIA/EIA Telecommunications or Electrical
Industry Association
• UL
Underwriters Laboratory
TIA/EIA Standards
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Horizontal cabling
Telecommunications closets
Backbone cabling
Equipment rooms
Work areas
Entrance facilities
LAN Technologies
• Ethernet
– 10-Base T
• Patch Panels, Cables, Jacks, Wiring Closets, Plugs
• Transceivers, repeaters, hubs
• Token Ring
• FDDI
RJ-45 Jack and Connector
• Registered standard
• Reduces noise, reflection and stability
problems
• Layer 1 component
• 8 conductor pins
• Punch down separates wires & forces into
slots (Layer 1 component)
– Rack mounted, 12 or 24 or 48 ports
• Wiring Standard 568A or 568B
Cat 5 Cable
• 4 Twisted Pairs (8 wires)
– Reduces noise problems (crosstalk)
• Inexpensive
• Easy to install
• Layer 1 component
– Carries the bits
Transceiver
• Combines transmitter and receiver
• Convert signals from one form to another
– Converts AUI ports to RJ-45 ports
• Layer 1 devices
• Can be built into NICs
– Called signaling components
• Encode signals onto the physical medium
Repeaters
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Retime and Regenerate Signals
Deal with packets ONLY at bit level
Layer 1 devices
Extend length of network
Extend collision domain
Can’t filter traffic
Hubs
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Multi-port repeaters
Amplify and retime signal
Contain many ports
Layer 1 Device
Extend the collision domain
Provides a central collection point for the
network
Networks
• Shared
– Many hosts have access to same medium
• Extended Shared
– Extends environment for multiple access
• Point to Point (2 units, 1-1 connection)
– Shared, connected to only other other device
• Indirectly connected
– Circuit Switched
Collisions
• When two bits propagate (travel along the same
media) at the same time
• Bits’ are actually packets containing many bits
• Result of too much network traffic (the more
nodes the more work being done the more traffic)
• Domain – area within network where data packets
originated and collided
• All of layer 1 connections are part of collision
domain
Signals and Collisions
• Contention – managing competition for the system
resources
• Collision results in destruction of data packets
– Collision magnifies the signal strength
• A JAM Signal is sent to all nodes
• Algorithm takes over to determine when
retransmission can occur (Back off algorithm)
• Segment is the collision domain
Collision Domain and Devices
• Layer 1 devices that extend the network
result in larger collision domains
– Includes repeaters and hubs
• A network segment includes all wires,
repeaters, and hubs as part of one collision
domain
• Too many collisions result in poor network
performance
Four Repeater Rule
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A.K.A. as 5-4-3-2-1 rule
5 network segments
4 repeaters
3 network segments with hosts
2 link segments
1 collision domain
Segmentation
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At Layer 2 breaks up the collision domains
Use Bridges and Switches (layer 2 devices)
DECREASES the SIZE of the collision domains
INCREASES the NUMBER of collision domains
created
• Both filter the traffic
– Keep local traffic on same segment
– Allow traffic on other segments to pass through
• Segments are still part of the same broadcast
domain
Segmentation cont.
• Try to design the LAN to keep 80% of the traffic
local
• All nodes on a segment before, the bridge/switch
will see and evaluate the datagram
• If the destination node is on the same segment the
nodes processes the datagram
• The bridge/switch will evaluate the datagram but
drop it
• Traffic on the LAN is isolated and reduced
Latency
• All devices add a latency component to the
network
• It takes time for packets to travel through
devices
• Bridges and switches have to take time to
check MAC address to filter the frame
• Router has to take time to check IP address
to route and switch the packet
Network Topology
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The study of location
Two types - Physical and Logical
Physical – describes the wiring schema
Logical – describes how data flows through
the network
• Network can have different physical and
logical topologies
Network Types
• 10-Base T Ethernet
– Logical Topology is a bus
– Physical Topology is a star or extended star
• Token Ring
– Logical Topology is a ring
– Physical Topology is star
• FDDI
– Logical and Physical Ring
Physical Topologies -1
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Bus
Star
Extended Star
Ring
Hierarchical
Mesh
Physical Topologies - 2
• Bus
– Logical – all devices can see all
communications
– Physical – each device is on the same wire
• Ring
– Logical –each station passes data to adjacent
station
– Physical –devices wired in a daisy chain
Physical - 3
• Star
– Physical – all nodes connected to center node
– Logical – all data passes through center node
• Extended Star
– Physical – all center nodes from extensions
connected to center node
– Logical – hierarchical – information
encouraged to stay local
Physical - 4
• Tree
– Logical – hierarchical
– Physical – trunk has several layers or branches
• Mesh
– Logical – depends on exact wiring
– Physical – all nodes connected directly to each
other
Physical - 5
• Cellular
– Physical – geographic cells; electromagnetic
waves
– Logical – communicate within cell or to
adjacent cells