Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!hplabs!pyramid!lstowell
From: lstowell@pyrnova.pyramid.com (Lon Stowell)
Newsgroups: comp.dcom.lans
Subject: Re: More questions regarding the LAN
Message-ID: <146308@pyramid.pyramid.com>
Date: 26 Feb 91 19:31:34 GMT
Sender: daemon@pyramid.pyramid.com
Reply-To: lstowell@pyrnova.pyramid.com (Lon Stowell)
Organization: Pyramid Technology Corp., Mountain View, CA
Lines: 44

In article <31710003@hpctdlb.HP.COM> chw@hpctdlb.HP.COM (Charlie Whiteside) writes:
>
> These are very interesting discussions! I don't understand something
>here though:
>
>
>>     This is where I must differ on the use of the AR and FCI
>>     bits fairly strongly....they are part of the fundamental
>>     ring mechanisms for finding Active Monitors, noting whether
>>     or not the destination is present and has or has not
>>     "copied" a xmitted frame.  Without these two bits you would
>>     have needed an Ack sequence at the MAC layer....overhead
>>     these two avoid.
>
>I thought the FCI (I'm assuming this means the Frame Copy bits in
>the Frame Status Byte) had nothing to do with the Active Monitory
>present. Isn't the AC (Access Control xxxTMxxx) byte the one which
>sets the Monitor bit to alert of two active monitors?
>
    This is what I get for an incomplete posting.   The
    processes i referred to are for discovering whether or not
    there is ANYONE else on the ring...and therefore YOU must
    become the Active Monitor whether or not your local system
    has told you not to.   

    The process is actually part of the Insert, Ring Poll, and
    Neighbor Notification...all of which use the Active Monitor
    Present and Standby Monitor Present frames.....the xmitting
    station just makes a quick check of the AR, FCI bits to see
    whether or not there is other intelligent life on the LAN,
    and if so, who is there.   

    The Access Control field is used only by the Active
    Monitor...it sets the bit the first time the frame passes.
    If any Active Monitor sees this bit set in a passing frame
    it knows that either the xmitter of the frame is unable to
    strip properly OR that there is another Active Monitor...and
    that either an error (can't strip) or monitor contention is
    required.   

    The flags are used in different portions of monitor
    detection and selection.  Active Monitors tend to become
    upset when seeing AMP frames on the ring without THEIR
    address as source.