T1 drops because of DS3 trouble?

Discussion in 'Cisco' started by admin too, Feb 23, 2004.

  1. admin too

    admin too Guest

    One of our T1's is with MCI and for two weeks my Cisco router with internal
    CSU/DSU has been sending me syslog messages every couple hours or so saying
    my serial interface is going up and down. The down time is usually just a
    few seconds, sometimes longer which causes our ISDN dial-backup to kick in.
    We have telnet users and of course their sessions drop.

    MCI has been pointing to SBC and SBC keeps finding something wrong,
    (repeaters, etc), but the problem never goes away and the symptoms I've
    explained never go away.

    Today I called MCI and asked and they said SBC detected trouble with a MCI
    DS3 and they are working on it.

    So can a DS3 way up stream (beyond SBC and outside my local loop) really
    cause a serial interface to bounce like this? A tech I talked to at MCI said
    'that's exactly what it would look like at your end'. But it doesn't sound
    right to me.
     
    admin too, Feb 23, 2004
    #1
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  2. On Mon, 23 Feb 2004 14:05:33 -0800, "admin too"
    <> wrote:

    >One of our T1's is with MCI and for two weeks my Cisco router with internal
    >CSU/DSU has been sending me syslog messages every couple hours or so saying
    >my serial interface is going up and down. The down time is usually just a
    >few seconds, sometimes longer which causes our ISDN dial-backup to kick in.
    >We have telnet users and of course their sessions drop.
    >
    >MCI has been pointing to SBC and SBC keeps finding something wrong,
    >(repeaters, etc), but the problem never goes away and the symptoms I've
    >explained never go away.
    >
    >Today I called MCI and asked and they said SBC detected trouble with a MCI
    >DS3 and they are working on it.
    >
    >So can a DS3 way up stream (beyond SBC and outside my local loop) really
    >cause a serial interface to bounce like this? A tech I talked to at MCI said
    >'that's exactly what it would look like at your end'. But it doesn't sound
    >right to me.


    I would imagine that if the T3 sits between your router and the MCI
    neighbor router, problems with it could indeed cause the state of your
    interface to drop. IIRC, the "line protocol" state is essentially the
    layer 2 state, which usually means HDLC or PPP or FR between you and
    the neighbor router. So that state should change if there's a problem
    in between; I don't know about the physical interface state, however
    -- that may just refer to whether or not you're getting a signal from
    the (first) upstream switch.

    -Terry
     
    Terry Baranski, Feb 24, 2004
    #2
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  3. On Mon, 23 Feb 2004 14:05:33 -0800, "admin too" <> wrote:

    ~ One of our T1's is with MCI and for two weeks my Cisco router with internal
    ~ CSU/DSU has been sending me syslog messages every couple hours or so saying
    ~ my serial interface is going up and down. The down time is usually just a
    ~ few seconds, sometimes longer which causes our ISDN dial-backup to kick in.
    ~ We have telnet users and of course their sessions drop.
    ~
    ~ MCI has been pointing to SBC and SBC keeps finding something wrong,
    ~ (repeaters, etc), but the problem never goes away and the symptoms I've
    ~ explained never go away.
    ~
    ~ Today I called MCI and asked and they said SBC detected trouble with a MCI
    ~ DS3 and they are working on it.
    ~
    ~ So can a DS3 way up stream (beyond SBC and outside my local loop) really
    ~ cause a serial interface to bounce like this? A tech I talked to at MCI said
    ~ 'that's exactly what it would look like at your end'. But it doesn't sound
    ~ right to me.

    Sure, your T1 circuit has to ride on top of some physical carrier.
    Your circuit is presumably 2 copper pairs coming into your premises,
    but the T1 may be muxed onto a DS3 carrier (or OC12, or whatever)
    for some of its legs.
     
    Aaron Leonard, Feb 24, 2004
    #3
  4. admin too

    CCIE8122 Guest

    > One of our T1's is with MCI and for two weeks my Cisco router with internal
    > CSU/DSU has been sending me syslog messages every couple hours or so saying
    > my serial interface is going up and down. The down time is usually just a
    > few seconds, sometimes longer which causes our ISDN dial-backup to kick in.
    > We have telnet users and of course their sessions drop.
    >
    > MCI has been pointing to SBC and SBC keeps finding something wrong,
    > (repeaters, etc), but the problem never goes away and the symptoms I've
    > explained never go away.
    >
    > Today I called MCI and asked and they said SBC detected trouble with a MCI
    > DS3 and they are working on it.
    >
    > So can a DS3 way up stream (beyond SBC and outside my local loop) really
    > cause a serial interface to bounce like this? A tech I talked to at MCI said
    > 'that's exactly what it would look like at your end'. But it doesn't sound
    > right to me.


    He is absolutely correct, but I would still have SBC recard and recable
    your T-1 interface on their MUXed DS-3 that serves your loop. It could
    be an MCI issue, but this is almost always a LEC issue.

    If the local loop was ordered through MCI--which is most likely as most
    people do not order their own loop from the LEC and do a cross-connect
    to the IXC--meaning you ordered the total service from MCI, and never
    even talked to SBC, then what has happened is MCI has leased the your
    T-1 loop from SBC and then MCI has cross-connected to SBC in their
    (MCI's) POP.

    In this case, MCI--not you--is known as the "customer of record" for
    that T-1 loop. Even though you are the end-customer for the T-1, you
    cannot call SBC to have it serviced. You must call MCI, and have them
    call SBC, since SBC will only recognize MCI as the customer (after all,
    again, they leased it from MCI, not you).

    This is where telco troubleshooting can get nasty, because you get the
    LEC and the IXC finger-pointing, and you can only get the story from one
    side.

    What I do here is I call MCI, reference the trouble ticket that you have
    opened, ask to speak to a manager or tier-3 person, and ask them to get
    SBC on with you on the line. You ask MCI to ask SBC to recard the
    interface and recable everything--they will do this if asked, especially
    when explained that this is a chronic problem. You probably should also
    have MCI recard their interface on their MUXed DS-3.

    I know that Fujitsu has issued a recall on a ton of T-1 cards with
    problems like the one you are describing. Since a lot of the LECs use
    Fujis (I am not sure about SBC), this is most likely the culprit.

    The upshot is that they really cant replace all the recalled cards
    because they are most of them in service, so they wait till one has
    issues and recard it then.

    HTH

    kr
     
    CCIE8122, Feb 29, 2004
    #4
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