Hello everyone

IAM INTO LECTURE 41 

VLAN :: Review Questions


YOU EXPLAIN INTO THIS LECTURE INTO REVISION  THAT EACH BRIGE OR SWITCH HAVE MEMORY INTO EACH PORTS, AND THAT MEMORY IF TWO FRAMES SENT AND RECIEVED AT SAME TIME VIA DIFFERENT PORTS WILL NEVER HAVE COLLISSIONS BECAUSE  THESE FRAMES ARE STORED INTO SEPARATE SECTIONS OF MEMORY AND WHEN SENDING FRAMES FINISHED THE RECIEVED FRAMES WILL HAPPENED 


IS THAT MEANS THIS SWITCH OR BRIDGE IS HALF-DUPLEX NOT FULL DUPLEX?

AND WE SAY FULL-DUPLEX IS SEND AND RECIEVE DATA AT SAME TIME , NOT STORED INTO MEMORY


I CANNOT UNDERSTANDING THIS POINT

I HOPE TO EXPLAINING THIS POINT AGAIN LITTLE EASY

 

THANKS ALOT

Comments

  • Hopefully I can clarify for you:

    IS THAT MEANS THIS SWITCH OR BRIDGE IS HALF-DUPLEX NOT FULL DUPLEX?

    Ports that are 10/100 will auto negotiate to half-duplex. This is the default behavior. If the end station (computer) negotiates to 100/full then the port on the switch will also be 100/full. If the negotiation is 10/half or 100/half, this could be caused by a misnegotiation, which does happen. You can hard code "duplex full/speed 100" to get the desired speed/duplex. 

    AND WE SAY FULL-DUPLEX IS SEND AND RECIEVE DATA AT SAME TIME , NOT STORED INTO MEMORY

    Full duplex is as you state, sending and receiving data at the same time. Because there are L2 checks for forwarding traffic in the L2 environment, depending on how the L2 forwarding is implemented will determine how the memory is used. Examples of this are Store and Forward and cut through.

     
     
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    If store and forward are used, then more memory will be used to process the frame. If cut through is used then less memory will be used. 

    Hopefully that answers your question. If not, please advise what you are not understanding.

    Rob



    On Tuesday, December 8, 2015 2:00 PM, major133 <[email protected]> wrote:


    IAM INTO LECTURE 41 


    VLAN :: Review Questions



    YOU EXPLAIN INTO THIS LECTURE INTO REVISION  THAT EACH BRIGE OR SWITCH HAVE MEMORY INTO EACH PORTS, AND THAT MEMORY IF TWO FRAMES SENT AND RECIEVED AT SAME TIME VIA DIFFERENT PORTS WILL NEVER HAVE COLLISSIONS BECAUSE  THESE FRAMES ARE STORED INTO SEPARATE SECTIONS OF MEMORY AND WHEN SENDING FRAMES FINISHED THE RECIEVED FRAMES WILL HAPPENED 



    IS THAT MEANS THIS SWITCH OR BRIDGE IS HALF-DUPLEX NOT FULL DUPLEX?

    AND WE SAY FULL-DUPLEX IS SEND AND RECIEVE DATA AT SAME TIME , NOT STORED INTO MEMORY



    I CANNOT UNDERSTANDING THIS POINT

    I HOPE TO EXPLAINING THIS POINT AGAIN LITTLE EASY

     

    THANKS ALOT



    Internetwork Expert - The Industry Leader in CCIE Preparation

    http://www.internetworkexpert.com




  • mr rob

    thank you very very much for your reply for me and your attention

    iam mohamed atallah from egypt 30 years old , and i hope to be your friend


    what does this word means "10/half or 100/half " ?


    thanks alot

  • They mean 10/half and 100/half, this refers to speed of 10Mbps and half duplex, the same for the 100/half, speed of 100Mbps and half duplex.  



    On Wednesday, December 9, 2015 2:18 AM, major133 <[email protected]> wrote:


    mr rob

    thank you very very much for your reply for me and your attention

    iam mohamed atallah from egypt 30 years old , and i hope to be your friend



    what does this word means "10/half or 100/half " ?



    thanks alot



    Internetwork Expert - The Industry Leader in CCIE Preparation

    http://www.internetworkexpert.com




  • good[*]

    now you know one friend from egypt.  hope to be good friend

  • peetypeety ✭✭✭

    IS THAT MEANS THIS SWITCH OR BRIDGE IS HALF-DUPLEX NOT FULL DUPLEX?

    AND WE SAY FULL-DUPLEX IS SEND AND RECIEVE DATA AT SAME TIME , NOT STORED INTO MEMORY

     

    If a device is capable of full-duplex, you must realize that full or half duplex is decided on a per-port basis. Just because ports 1,2, and 3 are full duplex doesn't mean that port 4 is full duplex.

    Regardless of whether a port is full or half duplex, memory is still essential in the packet forwarding process. There are two main switching modes, "store and forward" or "cut-through". In store and forward, the entire packet is received into the switch so the checksum can be validated. Once validated, the packet is forwarded. This can happen while still preserving full-duplex. In cut-through, once the packet header is received and a forwarding decision can be made, the packet can begin being transmitted to the recipient, but if a checksum error is detected, the bridge/switch would have to abort the packet.

    There's also a need for packet memory whenever there's a speed difference between two ports involved in a particular packet flow. If one port is running at 10Mbps and the other is running at 100Mbps, the bridge/switch would have to receive essentially the entire packet (i.e. at least 90% of it) from the 10Mbps side before it started transmitting it out the 100Mbps port, otherwise it'd run out of data to send before the packet got finished.

  • With regards to the video you mention...my discussion about switches/bridges and memory really wasn't concerned with the duplex (or speed) of an individual port or whether frames could collide on an individual cable.

    My main point in that video was to demonstrate the concept of "collision domains", and that while every port on a hub is collectively in a single collision domain...each individual port on a switch/bridge is in its own, unique collision domain. This is because hubs have no memory for storing received frames.  They are simply electrical repeaters of bits.  So an Ethernet frame (which could be composed of up to 12,144-bits) is received-and-transmitted one-bit-at-a-time by a hub.  There is nothing to prevent two (or three or four, etc) frames from being sent to the hub at exactly the same time from different devices on different ports.  If that happens the individual bits from each frame will "run into each other" causing collisions. A hub is like a traffic intersection without any stop signs or traffic lights.  There is nothing in that intersection to prevent the cars from running into each other.

    But switches and bridges have memory that hubs don't have.  Switches these days are mostly designed as "store-and-forward".  Well, in order to "store" something you must have memory somewhere inside the switch to hold all those bits until bit number 12,144 is received (the last bit of an Ethernet frame, if we're assuming a maximum-sized Ethernet frame).  The way that memory is allocated inside switches is that each individual port receives its own portion of memory, so if multiple frames are received FROM DIFFERENT PORTS at the same time...they will all be held/stored in their own memory partitions and will not run into each other (no collisions).

    In my previous analogy, the memory inside a switch is like a police officer directing traffic at that same intersection.  Even if multiple cars arrive at the same time, only one will be allowed to go through the intersection.  The others have to wait their turn.

    This is no different than your laptop.  Imagine that you have an Ethernet cable connected to your laptop and...at the same time...you also have your WiFI NIC connected on that laptop to a WiFi network.  Your laptop could be receiving Wi-Fi frames at exactly the same time as it is receiving wired Ethernet frames.  Do they conflict with each other or cause collisions?  No.  Because your laptop has some memory allocated for receiving WiFI frames and other memory (probably on the same chip) allocated for receiving wired Ethernet frames. Even if a WiFi and wired Ethernet frame are received by your laptop simultaneously, they will both be held in memory and can only be processed one-at-a-time by your CPU.

    That was the message I was trying to convey in that video.

    Keith

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