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  1. Hi Zaman,

    Error correction before transmission doesn’t make much sense to me. TCP uses a sequence number and acknowledgment number, these can be used for retransmissions if something doesn’t make it to the other side.

    The other thing that TCP does is calculating a checksum for the header. This allows the receiver to check if the TCP segment is OK or not.

    Rene

  2. Durga,
    The Internet would break :slight_smile:

    Seriously, it would, and here’s why: Let’s say we tried to use MAC addresses as a layer 3 identity for communicating between devices at a distance (not on the same local network). MAC addresses are burned into the network cards by the manufacturer, and each card has a unique MAC (in theory). The problem comes when you are trying to keep track of who is where. The reason that the Internet is able to function now is primary due to a protocol called BGP that figures out the best way to get from one IP address to another.

    Even t

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  3. Hi Sreejith,

    I would say SONET/SDH belongs to layer 1. It specifies the physical layer and you can run different L2 protocols (including Ethernet) on top of it. It’s not like frame-relay which has a clear specification of L1 + L2.

    The main difference is that the physical layer is different between SONET on one end and Ethernet on a LAN on the other side. When you receive something from the SONET side, it goes from the physical layer to the data link layer and you end up with an Ethernet frame. The outgoing interface is selected, the frame goes from the data lin

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  4. When I learned the OSI Model years ago. I’ve always like this saying.

    Please, Don’t, Never, Throw, Sausage, Pizza, Away

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