local area networks n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Local Area Networks PowerPoint Presentation
Download Presentation
Local Area Networks

Loading in 2 Seconds...

play fullscreen
1 / 23

Local Area Networks - PowerPoint PPT Presentation


  • 112 Views
  • Uploaded on

Local Area Networks. LAN. Why LANs?. Provide a means of DIRECT connection to other machines Manage access Provide reasonable performance Hopefully allow for interconnection with other LANs. LAN criteria. Resolve access Fair access Quick access Fast transmission Security Robustness.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Local Area Networks' - nanji


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
why lans
Why LANs?
  • Provide a means of DIRECT connection to other machines
  • Manage access
  • Provide reasonable performance
  • Hopefully allow for interconnection with other LANs
lan criteria
LAN criteria
  • Resolve access
  • Fair access
  • Quick access
  • Fast transmission
  • Security
  • Robustness
do lans meet these criteria
Do LANs meet these criteria?
  • There are a huge number of network designs which have been proposed
  • Few are actually in operation
  • Most LAN designs excel in a few of the previous areas but not all
  • OSI allows for integration of newer technologies as they evolve.
  • For now-> price & performance drive us to ethernet.
ethernet

Ethernet

What you are likely to see

ethernet1
Ethernet
  • Broadcast medium
    • Everyone sees all transmissions*
  • Orderly free-for-all to determine access
  • Cheap
  • High performance (few Mbps to Gbps)
  • Many standards
    • Speed
    • Medium
basic principles
Basic Principles
  • Access strategies vary significantly.
  • Centralized
    • Some main controlling unit deciding
    • Less Robust
  • Decentralized
    • Group decisions
    • Controlled behavior
  • Moving centralized control
other classifications
Other classifications
  • Reserved vs non-reserved
  • Static versus dynamic
  • Broadband (FDM) vs baseband (TDM-ethernet)
  • LAN, MAN, WAN
  • Optical vs electrical
what strategy does ethernet use
What strategy does ethernet use?
  • Less time required to decide access means faster access and less delay.
  • Simple algorithm like using a “party-line” in a telephone system
  • Pick up the phone and see if it’s in use
  • If not send
    • checking to make sure no one else did the same
slide10

Assume each at extreme ends

A begins transmission (a<<1)

A

B

A message almost reaches B and B starts

A

B

B sees the collision

A

B

A sees the collision

A

B

After “2a”, either collision or not

and what does that tell us
And what does that tell us?
  • Within “2a” frame transmission times, the initiator will
    • See a collision and stop transmitting
    • See NO collision and proceed with the assurance that NO ONE ELSE will transmit as others will look before beginning.
  • But what happens after a collision?
    • No central organizer
    • Wait a random amount of time and try again
    • If another collision -> WAIT LONGER!
how many collisions can occur
How many collisions can occur?
  • Eventually the physical layer responds that it can’t deliver and the (OSI) layer above decides what to do next
  • There is NO UPPER BOUND on how long it will take to get access
  • Can’t service some types of traffic well
    • Video and voice
how does it work so well
How does it work so well?
  • If “a” is small enough, a number of contention cycles (“2a”) can occur for each transmission.
  • E.g. if 2a= .002 and it takes 5 collision cycles, the overhead is 5x.002=.01 of the time and 1/(1+.01) is still very good.
  • Capacity typically far exceeds demand which means most of the time the network is free and no collisions occur.
  • Degrades in a heavily loaded environment!
what does it look like
What does it look like?
  • Originally a bus architecture
  • Now a logical bus but a physical star

HUB

computer

computer

computer

computer

slide15

SWITCH

computer

computer

computer

computer

SWITCH

computer

computer

computer

computer

What impact does that have on performance?

What impact does that have on network security?

queueing revisited offered load versus throughput
Queueing Revisited Offered Load Versus Throughput

Throughput

ideal

more typical

100%

ethernet

100%

200%

Offered Load

token rings

Token Rings

An alternative

slide18

token

In order to use the net, you must seize the token

slide19

message

token

slide20

message

token

slide21

message

message

token

what is the improvement
What is the improvement?
  • A little delay in getting access
  • An upper bound on access as long as all behave well (and they do .. Same program)
  • Used in environments where upper bound is required like in automated manufacturing.
  • Previous queueing graph is more like the ideal, does not degrade to zero.