Transcript Topologies

Topologies
• The structure of the network
– Physical topology
• Actual layout of the media
– Logical topology
• How the hosts access the media
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
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
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!
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
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
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
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
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
Repeaters
• Regenerate and retime signals at
the bit level
• Allows data to travel further
• Single-port “in”
• Single-port “out”
• Layer 1
– bits
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
Hubs
• Regenerate & retime network
signals
– done at bit level for many hosts
•
•
•
•
“Multi-port Repeater”
Create a central connection point
Increases reliability
Layer 1
Active Hubs
• Use energy from a power supply
to regenerate signals
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
Intelligent Hubs
• Console ports
• Can be programmed to manage
network traffic
Dumb Hubs
• Take an incoming network
signal and repeat it to every port
Hubs in other topologies
• Token Ring
– MAU
– Media Access Unit
• FDDI
– MAU is called a concentrator
• All Layer 1
Bridges
• Layer 2 device
• Connects two LAN segments
• Filters traffic based on MAC
address
– local traffic is kept local
– other traffic is directed out
Switches
• Layer 2 device
• “Multi-port bridge”
• Decisions based on MAC
addresses
• Switch data out of the port
where the receiving host is
connected
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
Routers
• Layer 3
• Can make decisions based on
groups/ classes of addresses
• Can connect different layer 2
technologies
– Ethernet, FDDI, Token-Ring
Routers
• Backbone of the Internet
• Examines incoming packets,
switches to correct outgoing port
• Most important regulating devices
on large networks
Clouds
• Suggests another network (perhaps
Internet)
• Does not supply details
• Really a collection of devices
• Layer 1-7
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
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