What is a collision in a LAN?

[ArmenK]

Hi all, i noticed that the collision light on my hub lights up once in a while, and sometimes it lights up alot, like when im doing mass file transfers. Well i wanted to know what a collision is on a lan and if it is bad or not too bad... thanks
Armen

 

[mk52]

its bad

it means that a packet didnt reach its destination and got dropped

-MeliK

 

[sohcrates]

and unfortunately, when a packet gets lost, your NIC doesn't realize that it got lost, and continues sending as if everything is ok....therefore corrupting your transfer.

EDIT: sorry, i meant to say "sometimes a packet gets lost"

 

[mk52]

<< and unfortunately, when a packet gets lost, your NIC doesn't realize that it got lost, and continues sending as if everything is ok....therefore corrupting your transfer. >>



no its simply resends the dropped packet
you only get corrupted files if there are extremely many collisions and pc A cant keep up resending.

 

[ArmenK]

damn, i was just transfering about 800 megs and the collision light was on the whole time, does this mean the files are all corrupted?

 

[mk52]

nope as I said if a packet is dropped it gets send again.
you should be fine if the copy process went without errors.

-MeliK

 

[Doctorweir]

How many other Rigs are on this LAN (active)?
The Collision light just indicates, that the line is busy and the sending PC has to keep resending...but even if it flashes all the time, enough data will pass through perfectly...

 

[ArmenK]

ok, cool, thanks alot.

its amazing how fast u get answers around here hehe

 

[Paulson]

It takes longer though

It gets there fine I'm sure, but ufta, takes a while. Having a switch is really nice

 

[Bozo Galora]

Actually, Paulson is correct. (Gag, GAG, GAAAAAAAGKK!!!!)

A switch would filter your traffic, reducing collision domain.
Sounds like you need a Gigabit hub (1000BaseT) or &quot;M&quot; version (managed) or disconnect other hosts when doing a large transfer

There is a four bit CRC check in the Ethernet frame, and handshaking/windowing going on to prevent corruption.

&quot;shortly after the 1980 IEEE 802.3 specification, Digital Equipment
Corporation, Intel Corporation, and Xerox Corporation jointly developed and released an Ethernet specification, Version 2.0, that was substantially compatible with IEEE 802.3. Together, Ethernet and IEEE 802.3 currently maintain the greatest market share of any LAN protocol. Today, the term Ethernet is often used to refer to all carrier sense multiple access/collision detection (CSMA/CD) LAN?s that generally conform to Ethernet specifications, including IEEE 802.3.

Ethernet and IEEE 802.3 specify similar technologies; both are CSMA/CD LANs. Stations on a CSMA/CD LAN can access the network at any time. Before sending data, CSMA/CD stations listen to the network to determine if it is already in use. If it is, then they wait. If the network is not in use, the stations transmit. A collision occurs when two stations listen for network traffic, hear none, and transmit
simultaneously. In this case, both transmissions are damaged, and the
stations must retransmit at some later time. Backoff algorithms determine when the colliding stations can retransmit. CSMA/CD stations can detect collisions, so they know when they must retransmit.&quot;