Can any CCNA or above look at this powerpoint.

headshotheadshot Member Posts: 77 ■■□□□□□□□□
It's a College(cisco networking academy) powerpoint slapped together by instructors. Seems like a lot of misinformation.

Download ccna1_chapter_7 ppt, fast and secure downloading from easy-share.com (sorry about the timer, link is at bottom)

Namely check the part where they say that CSMA/CD can transmit at any time freely. It's maybe 10 slides in. I was under the impression that CSMA/CD has to "listen to the wire" before transmitting.

Also Logical topology vs Physical topology. Here's what they have to say about this.
Physical topology:
Arrangement of the nodes and the physical connections between them..(ok that sounds pretty right, BUT check out what they say about logical topology)
Logical topology:
The way the network transfers frames among nodes. The use of virtual connections between the nodes regardless of the actual physical connection.
-Point-to-Point
-Multiaccess
-Ring
?????
I'm pretty sure logical topology refers to layer 3. Logical addressing, logical topology. Layer 2, physical addressing, physical topology.
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Comments

  • hex_omegahex_omega Member Posts: 183
    I think they are right about CSMA/CD. ANy and every node transmits any time it wants. Only when a collision is detected, all parties involved back off a random amount of time and then try again.
  • powerfoolpowerfool Senior Member Member Posts: 1,647 ■■■■■■■■□□
    CSMA/CD
    Carrier-Sense: Checks for clear media before sending, does this by watching voltage.
    Multiple Access: Self-explanitory
    Collision Detect: Can check if there is a collision and correct, does this by watching voltage.

    Ethernet produces electrical signals at 5v. So, for CS, it makes sure that the media is at 0v before sending. When it puts a signal on the wire, it watches it to make sure it is at 5v, if it is higher, a collision has occurred because multiple hosts have attempted to place a signal on the wire simultaneously. If a collision occurs, the host will wait a random amount of time and attempt the process again.

    Honestly, I don't know why instructors of a Cisco Academy course would make their own materials, the materials provided by Cisco are excellent (I attended the first two semester of the four semester version of the CCNA Academy in 2003 as part of my undergrad).
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  • headshotheadshot Member Posts: 77 ■■□□□□□□□□
    powerfool wrote: »
    CSMA/CD
    Carrier-Sense: Checks for clear media before sending, does this by watching voltage.
    Multiple Access: Self-explanitory
    Collision Detect: Can check if there is a collision and correct, does this by watching voltage.

    Ethernet produces electrical signals at 5v. So, for CS, it makes sure that the media is at 0v before sending. When it puts a signal on the wire, it watches it to make sure it is at 5v, if it is higher, a collision has occurred because multiple hosts have attempted to place a signal on the wire simultaneously. If a collision occurs, the host will wait a random amount of time and attempt the process again.

    Honestly, I don't know why instructors of a Cisco Academy course would make their own materials, the materials provided by Cisco are excellent (I attended the first two semester of the four semester version of the CCNA Academy in 2003 as part of my undergrad).

    I think it's cause they've dumbed it down quite a bit. Comparing that slide show with the one Cisco puts out in their Exploration package, they're in a different league. And the questions on tests reflect this.
  • MickQMickQ Member Posts: 628 ■■■■□□□□□□
    headshot wrote: »
    Namely check the part where they say that CSMA/CD can transmit at any time freely. It's maybe 10 slides in. I was under the impression that CSMA/CD has to "listen to the wire" before transmitting.

    What Powerfool said, with one differentiation.
    CD = collision detection.
    For electrical cabling, it detects collisions by comparing the data sent, with that received on the internal loopback. If it matches, great. If there's a discrepancy, uh oh - collision!


    headshot wrote: »
    Also Logical topology vs Physical topology. Here's what they have to say about this.
    Physical topology:
    Arrangement of the nodes and the physical connections between them..(ok that sounds pretty right, BUT check out what they say about logical topology)

    Do you tell a courier how to send a package, or do you let them decide the route?
    If you want to get from one end of the country to the other, your logical route will basically be the same, but your physical will be different. Do you fly (air), walk (path), cycle (road), drive (motorway), or swim (canal/sea)?

    headshot wrote: »
    Logical topology:
    The way the network transfers frames among nodes. The use of virtual connections between the nodes regardless of the actual physical connection.
    -Point-to-Point, Multiaccess, Ring.
    I'm pretty sure logical topology refers to layer 3. Logical addressing, logical topology. Layer 2, physical addressing, physical topology.
    icon_surprised.gif

    The key to understanding anything is understanding the "how". How does it all work, and why does it do it that way.
    Think about how the computers send messages to each other. Now think of the different types of messages/signals that have to be sent. Break it all down to the basic level and understand these things. The better you can understand them, the better you'll be as a network engineer.

    As for logical topology? Forget the physical layout here. The logical is the way that you tell the network to view and work itself.
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