Solved

Collisions

Posted on 2004-10-17
5
862 Views
Last Modified: 2013-12-07
Ok, is it true collisions are impossible to come by in Full duplex ethernet? If its true, why? (my Cisco press book said its impossible)

Is it also true that collisions cannot occur in half duplex as well because only one host transmits at a time?

When DO collisions occur and why?
thanks
0
Comment
Question by:dissolved
5 Comments
 
LVL 7

Assisted Solution

by:NicBrey
NicBrey earned 100 total points
ID: 12335899
Theoreticaly collisions cannot occur in full duplex mode. But with damaged cabling and hardware problems on ports they do. Also, bad packets can casue it.
Collisions will occur when you use a hub. All the ports on a hub is in one collision domain. So only one host can transmit at any givin time. When 2 or more hosts transmit, you get a collision, because a hub broadcasts a packet received on one port out of all the other ports.
Every port in a swtich is in it's own collision domain. The switch builds a forwarding table, and only transmits a packet received on one port out on the port where it is destined to go. If the switch does not know a destination port for a packet, it will broadcast, learn the destination and adds it to the table.
0
 
LVL 16

Assisted Solution

by:The--Captain
The--Captain earned 150 total points
ID: 12336318
Googling for:

full duplex hub

yields this nugget:
http://www.cormantech.com/news.asp?SpecificNewsID=77

Cheers,
-Jon

0
 
LVL 3

Accepted Solution

by:
Felix2000 earned 200 total points
ID: 12336834
A Collision happens when 2 hosts try to send onto the network at the same time.
Collision cannot happen on Full duplex links because Transmit and Receive are on difference phyical wires.  If frames are bad or have errors this is not considered a collision this results in Framing Error, CRC Errors.  

Half Duplex those same physical wires are now shared between host and switch or hosts on a hub. Before sending they check the line see if it's free and send away. If 2 hosts both check the line at the same time and it's clear and then send this is where collisions occur.

Think of your wire as a highway, in Full everybody has their own lane and can't hurt anyone else.  In half duplex the highway is shared and now packets can collide with each other on that same link.

Hope it helps
-= Felix =-
0
 

Author Comment

by:dissolved
ID: 12338534
Thanks guys! So CDMA collision detection is NOT used on full duplex I'm assuming?. Since collisions arent possible ?
Thanks!
0
 
LVL 1

Assisted Solution

by:forrestd
forrestd earned 50 total points
ID: 12341670
That's correct CSMA/CD comed from the days of shared ethernet segments (& later hubs & switched runnign at half duplex).  In a full duplex environment no collision detection takes place i.e. a NIC can transmit & receive at the same time (i.e. FULL Duplex) as opposed to only being able to do one or the other.

This comes from the days of Ethernet when Ethernet was a single shared cable (collision domain) sometimes bridged with other cables.
0

Featured Post

Netscaler Common Configuration How To guides

If you use NetScaler you will want to see these guides. The NetScaler How To Guides show administrators how to get NetScaler up and configured by providing instructions for common scenarios and some not so common ones.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Let’s list some of the technologies that enable smooth teleworking. 
Even if you have implemented a Mobile Device Management solution company wide, it is a good idea to make sure you are taking into account all of the major risks to your electronic protected health information (ePHI).
Get a first impression of how PRTG looks and learn how it works.   This video is a short introduction to PRTG, as an initial overview or as a quick start for new PRTG users.
Here's a very brief overview of the methods PRTG Network Monitor (https://www.paessler.com/prtg) offers for monitoring bandwidth, to help you decide which methods you´d like to investigate in more detail.  The methods are covered in more detail in o…

803 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question