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

Topologies Tree –Cable TV –Single wire, bidirectional, can be broadband –Need Taps (jaws) –One break it all goes down –Shared Bus 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 bus 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 1Computer 2Computer 3 HUB B Computer 4Computer 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 talk Computer 1 Computer 2

Token Ring 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 (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