State of PPP connection when the Physical Layer goes down - PPP

This is a discussion on State of PPP connection when the Physical Layer goes down - PPP ; Hi All, I am running PPP on a satellite link. And my satellite modem looses lock often. In that case if i havent enabled the PPP keepalive and if the physical layer goes down and comes back the PPP session ...

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Thread: State of PPP connection when the Physical Layer goes down

  1. State of PPP connection when the Physical Layer goes down

    Hi All,
    I am running PPP on a satellite link. And my satellite modem looses
    lock often. In that case if i havent enabled the PPP keepalive and if
    the physical layer goes down and comes back the PPP session should be
    UP again right.?

    Do we need to provide any lowerlayer UP/DOWN notification to PPP when
    the link goes down/UP.?

    How is this normally handled.? I'm running the linux PPPD application.

    Thanks
    Vanitha


  2. Re: State of PPP connection when the Physical Layer goes down

    vanitha@agilis.st.com.sg writes:

    >Hi All,
    >I am running PPP on a satellite link. And my satellite modem looses
    >lock often. In that case if i havent enabled the PPP keepalive and if
    >the physical layer goes down and comes back the PPP session should be
    >UP again right.?


    There is nothing in the ppp protocol that says how long it should take to
    transmit a byte. It could be 10000 years. Now, you might not want the
    system waiting there that long, and ppp has techniques for testing a link
    to see if it is acting reasonable (eg LCP echo) but if you have a different
    definition of reasonable, who is ppp to argue.

    >Do we need to provide any lowerlayer UP/DOWN notification to PPP when
    >the link goes down/UP.?


    >How is this normally handled.? I'm running the linux PPPD application.


    "Normally", the modem detects if the link is up and send a hardware message
    to the computer if it goes down (DTE or whatever?) and ppp tears down the
    link. Altenatively, LCP echo is used and if a sufficient number of echos
    are not responded to, then again ppp tears down the link as being useless.
    "Normally" one does not want to have one's computer sitting there trying to
    send stuff over a dead line. But if you do, go ahead.

    >Thanks
    >Vanitha



  3. Re: State of PPP connection when the Physical Layer goes down

    vanitha@agilis.st.com.sg writes:
    > I am running PPP on a satellite link. And my satellite modem looses
    > lock often. In that case if i havent enabled the PPP keepalive and if
    > the physical layer goes down and comes back the PPP session should be
    > UP again right.?


    If the physical layer you're using properly signals up/down
    indications into PPP (as expected by RFC 1661), then when the
    satellite link goes down, the PPP link and all of the network layers
    will go down. When the link goes back up, PPP *may* come back up,
    depending on how it was configured.

    If the physical layer is "broken" (meaning that it doesn't bother with
    up/down notifications into PPP), then the interface will just sit
    there forever, acting as a black hole in your network.

    > Do we need to provide any lowerlayer UP/DOWN notification to PPP when
    > the link goes down/UP.?


    You should. Failing to do so usually means that the link is
    operationally difficult to use.

    > How is this normally handled.? I'm running the linux PPPD application.


    Link down is typically signaled by sending SIGHUP to the controlling
    terminal. Link up is typically handled by having an open(2) call
    without the O_NDELAY flag block in the kernel until carrier is
    detected.

    Your mileage might vary. It depends on exactly how this thing is
    connected to pppd. (Pppd generally assumes the use of modem control
    signals.)

    --
    James Carlson, KISS Network
    Sun Microsystems / 1 Network Drive 71.234W Vox +1 781 442 2084
    MS UBUR02-212 / Burlington MA 01803-2757 42.497N Fax +1 781 442 1677

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