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Thread: again, how?

  1. #1
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    again, how?

    how is it possible for millions of clients to be able to communicate across the pond on only a handful of cables?

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    Senior Member Ronald Roe's Avatar
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    Multiple signals can be sent on a single cable if they're on different carrier frequencies, provided there's a receiver-transmitter capable of multiplexing (handling multiple frequencies at once). Data can even be sent in sidebands of existing data frequencies. That's how radios in modern cars receive RDS data.

    Not to mention, data is sent in small, usually sequentially numbered packets. They're held in a queue until they can be sent. There's a whole big management scheme that's part of the TCP/IP stack, and it all happens in terms of micro seconds. Packets take different routes to their destination, and are reassembled on the receiving end. There's a lot to it, and it all works together at almost the speed of light.
    busso likes this.
    Ron Roe
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    WDF Staff mlseim's Avatar
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    Cable map as of 2015.

    http://submarine-cable-map-2015.telegeography.com/

    Note, there are a lot of fiber optic cables now.
    Fiber optics is the magical part about transferring lots of data across small cables..
    busso likes this.


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    when I think about sessions and established connections I imagine something similar to an old switchboard for telecoms. once a connection is established part of that cable is dedicated to maintaining a connection between client server and is also somehow encrypted. I know this is wrong I just cant understand or grasp how connections are actually held

  6. #5
    Senior Member Ronald Roe's Avatar
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    If y ou sen d a me ssag e, it' s bro ken i nto p iece s tha t are reass embl ed on the o ther end.


    Imagine it like this: you want to send a message to your friend. You write it on a piece of paper. The mail man can't carry the entire paper at once, because it's too big. So, you tear it into sections that make sense and number them so they can be reassembled easily. Unfortunately, the mail man can't carry all of the pieces himself either. So, you send some pieces with him, some via UPS, some via FedEx and some via DHL. Your friend receives the messages on the other end, one at a time. Then he reassembles them in order and reads your message.
    Ron Roe
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    "If every app were designed using the same design template, oh wait...Bootstrap."

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    i understand the packet creation process, I'm guessing a connection between two comeputers just means that the ports on the receiving and sending ends are dedicated to receiving packets? there isn't a direct physical connection?

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    Senior Member Ronald Roe's Avatar
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    Nope. That's just virtual. A connection has up to 32K ports available. I forget the range, but a few thousand of the lower end ports are dedicated to certain protocols, but the rest are open for use. The port being used is sent along in the packet, which will only be accepted if the receiving end has opened that port for communication. Which port that is will be sent as part of the initial response from the receiving device.
    Ron Roe
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    "If every app were designed using the same design template, oh wait...Bootstrap."

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    So a packet sent from the client could actually take a different route so long as it ends up at the right port? After the initial request for port 80 what is responsible for deciding which port to continue comma?

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    Senior Member Ronald Roe's Avatar
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    After the request comes in, the receiving server opens a port and sends that port number to the sending host. The request is then sent and marked to be accepted only on that open port.
    Ron Roe
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    "If every app were designed using the same design template, oh wait...Bootstrap."

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    that's why I was so confused by switches etc... thanks Ron


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