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Topologies
• The structure of the network– Physical topology
• Actual layout of the media
– Logical topology• How the hosts access the media
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Physical Topologies
• Bus– Uses a single
backbone cable– All hosts
connect directly to backbone
• Ring– Connects each
host to the next, and the last to the first
– Physical ring of cable
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Physical Topologies
• Star– Connects all
cables to a central point of concentration
– Usually a hub or switch at center
• Extended Star– Links stars by
linking hubs or switches
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Physical Topologies
• Hierarchical– Similar to
extended star– Links star
LANs to a computer that controls network traffic
• Mesh– Each host is
connected to all other hosts
– No breaks, ever!
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Logical Topologies
• Broadcast– Each host sends its data to all other
hosts
– First come, first served to use the network
– Ethernet
• Token Passing– Controls access by passing token
– Host can send when it has the token
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LAN Devices
• Devices that connect to a LAN are called hosts
• Hosts are not part of any layer
• Operate at all layers
• Symbols not standardized– Bear a
resemblance to device
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Network Interface Cards
• Network adapter– printed circuit board or PCMCIA
board
• Adapts the host device to the network medium
• Each has a unique MAC address– Media Access Control
• No standard symbol– Implied on each host
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Transceivers
• Converts one type of signal or connector to another– AUI to RJ-45 on router
• Attachment Unit Interface
• Layer 1– only looks at bits
• Found on routers
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Media
• Carries a flow of information– Bits and bytes
• Layer 1• Media selection
is based on:– Cable length
– Cost
– Ease of installation
– Total number of computers on the media
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Repeaters
• Regenerate and retime signals at the bit level
• Allows data to travel further• Single-port “in”• Single-port “out”• Layer 1
– bits
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5-4-3 Rule for Repeaters
• Five Repeater Rule– You can connect 5 segments with 4
repeaters, but only 3 cable segments can have hosts on them
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Hubs
• Regenerate & retime network signals– done at bit level for many hosts
• “Multi-port Repeater”• Create a central connection point• Increases reliability• Layer 1
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Active Hubs
• Use energy from a power supply to regenerate signals
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Passive Hubs
• Simply split signal to multiple users– Like a Y cable
• Do not regenerate bits
• Do not extend cable length
• Only allow two or more hosts to connect to same cable segment
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Intelligent Hubs
• Console ports
• Can be programmed to manage network traffic
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Dumb Hubs
• Take an incoming network signal and repeat it to every port
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Hubs in other topologies
• Token Ring– MAU– Media Access Unit
• FDDI– MAU is called a concentrator
• All Layer 1
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Bridges
• Layer 2 device• Connects two LAN segments• Filters traffic based on MAC
address– local traffic is kept local
– other traffic is directed out
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Switches
• Layer 2 device• “Multi-port bridge”• Decisions based on MAC
addresses• Switch data out of the port
where the receiving host is connected
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Switches
• Looks outwardly like a hub• Makes data transmission more
efficient• Combines connectivity of hub
with the traffic regulation of a bridge on each port
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Routers
• Layer 3• Can make decisions based on
groups/ classes of addresses• Can connect different layer 2
technologies– Ethernet, FDDI, Token-Ring
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Routers
• Backbone of the Internet• Examines incoming packets,
switches to correct outgoing port• Most important regulating devices
on large networks
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Clouds
• Suggests another network (perhaps Internet)
• Does not supply details• Really a collection of devices• Layer 1-7
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Segments
• Common path for data transmission• Each time a device is used to extend
cable length or manage data flow, a new segment is created
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Segments
• Function of a segment is to act as an efficient local LAN that is part of a larger network
• Segment, as applied to LANs, is completely different from the Layer 4 PDU known as a segment