Day10 LAN. Why? Allow more than one machine to share –Resources –Internet connectivity...
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Transcript of Day10 LAN. Why? Allow more than one machine to share –Resources –Internet connectivity...
Day10
LAN
Why?• Allow more than one machine to
share– Resources– Internet connectivity– Information
Good• LANs are abstract from the
hardware– HP printer will work with an IBM PC or
a MAC or Linux– You usually don’t know what type of
machine you are connecting to, it’s irrelevant since you both talk the same protocols.
• More web servers run on Linux (apache) than windows (IIS), but you can access them all from windows.
Shared Bus• Anytime we see a network where
everyone shares a single wire (either physically or logically) – Traffic from any host to any host goes
to all hosts– Everyone is supposed to ignore it
unless it is addressed to them
Computer Computer Computer Computer
Topologies• Tree
– Cable TV– Single wire, bidirectional, can be
broadband– Need Taps (jaws)– One break it all goes down– Shared Bus
Computer
Computer
ComputerComputer
Computer Computer
Star Wired Bus• Works like a bus (single wire)• Looks like a star (each
workstation connects to central point)
• Most networks use this today– Ethernet– Token Ring
• Shared busComputer Computer Computer
Hubs• Workstations connect to hubs
– Dumb repeaters– Take data in one port, broadcast it to
all ports
• Can be connected to other hubs via a crossover cable
• Mostly obsolete
HUB A
Computer 1 Computer 2 Computer 3
HUB B
Computer 4 Computer 5
Media Access Control Protocol• Carrier Sense Multiple Access
(CSMA)• Collision Detection (CD)
– CSMA/CD– E.g. Ethernet
• Listen for Carrier• Transmit and listen for collision• Wait and retransmit
• 100Mbps Ethernet has max speed of 40Mbps because of collisions
CSMA/CA• Collision Avoidance:
– a station that intends to transmit sends a jam signal
– after waiting a sufficient time for all stations to receive the jam signal, the data station transmits a frame
– while transmitting, if the data station detects a jam signal from another station, it stops transmitting for a random time and then tries again.
,
Star-Wired Ring• Token ring is the most common
example– Every workstation connects to a Hub
like device (MAU).– MAU creates a circle between
workstations• Empty ports are shorted
– Workstation adds data to ring, and removes it when it gets back.
– Token decides who can talkComputer 1Computer 2
Token Ring 802.5• Round Robin Protocol
– Single token– No collisions– More efficient– More expensive – Slower speeds– Basically dead
Wireless• Access point
– Converts from wireless to wired– Can be more than one used to blanket
a larger area
Computer
IEEE 802.3 (Ethernet) Frame
Ethernet– [speed][base/broad][distance (in 100
meters)• 10Base2
– 10Mbps baseband signal for 200 meters
• 10BaseT– 10Mbps baseband signal for 100 meters
• 100baseT– 100Mbps baseband for 100 meters
• 1000baseT• 1000BaseFx – 1000m, SX/LX – 100m, LX• 10Gbase-fiber/T