Link technologies

Link technologies tend to be designed for either point to point transmission or for resolving contention in broadcast transmissions. Explain why basic Ethernet and wireless LANs are a half duplex technology and how the CSMA algorithm is able to resolve contention. How is switched Ethernet able to work full duplex mode and make the CSMA algorithm redundant.

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Roguetadhg

http://www.techexams.net/forums/ccna-ccent/9622-do-switches-need-use-csma-cd.html
CompTIA Network+ Plus Certification Tutorial CSMA/CD Switches

Roguetadhg

the links worked for you, Mallow?

MallowGirl12

Roguetadhg wrote: »

the links worked for you, Mallow?

Thank You, the links defo worked

MrXpert

Switches don't use CSMA/CD (Carrier Sense Multiple Access with collision detection) CSMA/CD is basically the way a device might talk on ethernet and how it deals with a shared electrical bus such as ethernet and it usually is mentioned when talking about Hubs. Hubs use CSMA/CD and operate in half duplex. This means that when you have clients plugged into a hub they create their own broadcast domain but more significantly they are also one big collision domain. As a result of this if two or more clients try to send frames at the same time, a collision would occur and the frames would be dropped. To avoid this situation CSMA/CD is used in hubs.
Carrier=network signal
Sense=the ability to detect
MA=all devices have equal access

There's a few steps in CSMA/CD
1. A PC with a frame to send listens to the traffic on the network (electrical signals)
2.When network not busy it sends
3.Frame reaches the hub, the hub then broadcasts it out all other ports except the one it came in on
4.The PCs who the frame is not for will ignore it
Now if CSMA/CD is invoked then its the same from steps 1-2 but this time another PC also sends at the same time.
A collision occurs and both PCs send out a jamming signal to tell everyone not to send because a collision has occurred.
After the jam signal stops both PCs set their random backoff timer and when that expires they resend their data.
As a result of this contention based method, there will be alot of conjestion where you have lots of hubs. It is not ideal.

Switches provide us with microsegmentation which basically means each port is its own collision domain. A client PC can send/receive at same time.Switches are intelligent and work out which PCs are connected to which ports by the use of the MAC table.

802.11 wireless LANS are half duplex because they are contention based. I think they operate on layer 1 and 2 of OSI layer. The more wireless clients attached to a AP, the slower will the data rates be. Instead of using CSMA/CD they use CSMA/CA (Collision Avoidance)and it involves a lot of listening, waiting and ACK packets being sent to confirm.Given how complex wireless stuff is i'm always amazed how fast the data rates can be

Roguetadhg

Given the complexity of sending anything across the internet, i'm surprised how fast I can download cat videos from Youtube.

Once i got into how a video is wrapped and sent to A to B. It's amazing. Just thinking about it is pretty darn cool. It makes me appreciate download/upload speeds much more.

MallowGirl12

Roguetadhg wrote: »

Given the complexity of sending anything across the internet, i'm surprised how fast I can download cat videos from Youtube.

Once i got into how a video is wrapped and sent to A to B. It's amazing. Just thinking about it is pretty darn cool. It makes me appreciate download/upload speeds much more.

Thank You all so much, once i pass this exam, i'll be so thankful to you all and am already grateful to u guys for answering to my questions

if you guys were taking this exam, you all would have passed it with 100% heehee

killuminati1987

A switch may not use CSMA/CD media access method, but its logical topology is still considered a bus, especially to higher layer protocols, no? That still confuses me a lil'.

MrXpert

killuminati1987 wrote: »

A switch may not use CSMA/CD media access method, but its logical topology is still considered a bus, especially to higher layer protocols, no? That still confuses me a lil'.

Yes a switch doesn't use CSMA/CD because of "microsegmentation".Each switch port is its own collission domain therefore a host plugged into a port can only collide with itself rendering CSMA/CD useless on switches.