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