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LAYERS

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  • #52621 Reply
    MKT
    Guest

    Hi all..

    Does the layer 3 messages on air interface refers to the OSI layer3.

    exchange of layer 3 messages is between MS-BTS or MS-MSC?

    What is there in layer2 messages.?

    #52622 Reply
    pix
    Guest

    yes, the term “layer 3” refers to the OSI model, which says what functions should be handled by the layer 3. But OSI doesn’t say exactly what messages or what mechanisms should be implemented.

    the layer 3 for GSM is very particular, because it handles mobility, call management, etc.

    The layer 3 is conveyed on SACCH, FACCH and SDCCH, and usually it contains information that are useful for the BSC (LapD protocol) and the MSC (DTAP protocol).

    The layer 2… mmm… it contains some information, you can see them during drive tests, but i forgot what it is.

    Why don’t you google it ?? it’s really easy to find good documents about this !
    http://www.pulsewan.com/data101/gsm_basics.htm

    etc etc..

    “Layer 2
    Layer 1 multiplexes the physical access to the radio channel and provides a number of logical channels
    which can be used for signalling. Layer 2 is responsible for establishing a data link on these logical channels
    to allow reliable transmission of Layer 3 signalling messages. It corresponds to the Data Link layer (layer 2)
    in the OS1 model.
    Layer 2 can operate in two modes.
    0 Unacknowledged mode – used for broadcast data where acknowledgement is not possible and
    measurement reports where acknowledgement is not essential.
    0 Acknowledged mode – used for all connections where reliable transmission of Layer 3 messages is
    important (e.g. call set-up).”

    #52623 Reply
    pix
    Guest

    sorry, the LAPD protocol is in layer 2.

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