Conference netcad::hub_mgnt

    Let me update this note.  My customer says that any STP cable will do,
    not just type 9.  If we support a different variant of STP, they will
    buy it from us.
            
    So, I know that the PORTswitch 900TP supports STP (as does the
    DECrepeater 900TM).  I just do not know what variant to tell them to
    use.
    
    Now the question is, will the following products support STP:
    
    	DECconcentrator 900MX
    
    	DECswitch 900EF
    
    	PEswitch 900TX
    
    Thanks,
    
    Mark
    
                                                                         
    Thanks,
                                                                         
    Mark
    

    The PORTswitch is compatible with any 100-ohm cable, shielded or
    unshielded.

STP cable is nominally 150 ohm impedance so you may need some
type of UTP-STP converter.

-tom

    What about STP support by the following units:
    
            DECconcentrator 900MX
        
            DECswitch 900EF
        
            PEswitch 900TX
        
    Thanks,
    
    Mark
    

    Whoa! Mark D. you've got Ethernet and FDDI devices mixed into
    one, and are asking about STP cables. I also noticed that you
    cross-posted this question in the FDDI notes conference.
    So are you asking about Ethernet STP or asking about FDDI *and*
    Ethernet STP cable applications?
    
    As far as Ethernet goes, for the switches, they will work on both
    UTP and STP with a differential impedance between 85-111 ohms.
    
    Bob

    My customer wants to use STP for both FDDI and Ethernet connections.
    
    I have asked this in the FDDI and GIGAswitch conferences also.
    
    Ok, so the DS900EF, PEswitch 900TX and PORTswitch 900TP all support 100
    ohm STP.  This is good news.
    
    Yes, I have the DECconcentrator 900MX in this conference.  It is a hub
    module and there are many other questions concerning the DC900MX in
    this conference.  WHere would you suggest that I place this question?
    The DS900EF and PEswitch 90TX are Ethernet devices, but all questions
    are in this conference...
    
    Thanks,
    
    Mark
    

    Mark, my only concern is if your customer is going to use the
    same raw STP cable, that's fine (including the DC900MX with TP
    ModPMD's), but your customer has to be careful in how the ends
    of these cables are wired. The copper FDDI ModPMDs at each end of
    an FDDI STP link require that there be a crossover.
    The DECswitch 900EF (workgroup bridge) TP ports don't have an internal
    crossover, so a single crossover STP cable will be fine here.
    The PEswitch 900TX (desktop bridge) has an internal crossover on its
    TP ports, so a straight through cable would be desired it it connects
    to a device at the other end without an internal crossover. Connecting
    to another PEswitch, you'd need a crossover cable.
    The PORTswitch 900TP has internal crossover on its ports. So the
    scenario of what it gets connected to at the other end dictates whether
    the cable in between is to be a crossover cable or not.
    So your customer is going to have to be careful with how he instructs
    the cable installer to terminate the ends of the STP cable with RJ45
    connectors.
    Then there is the concern of getting FDDI STP cables mixed up with
    10BASE-T cables and plugging the ends in the wrong product.
    
    Bob

    Thanks for the concerns.  I have noted them.  I just wanted to make
    sure it was possible and then supported.
    
    I will discuss the STP issues with them.
    
    Thanks,
    
    Mark
    

    WHAT ?
    
    Please look into the OPEN DECconnect Applications Guide.  Digital sells
    a whole line of wonderful SHIELDED 100 ohm CAT 5 punchdowns, and patch
    cables and giblets.   It is VERY popular in Europe, and has tie-downs
    for the shielding, and metal covers over the punch-downs, etc.
    
    There are pre-manufactured jumpers with the metal tabs on the RJ45 to
    continue the sheilding throughout the cable plant.   You do not have to
    make this up yourself.
    
    The OPEN DECconnect sheilded 100 ohm TP product set is tested, and fully
    supported by Digital for 10BaseT, or FDDI.  The hardware is all there
    and available from Digital.
    
      

    Thanks.  We noticed this ScTP 100ohm cable today, and the shielded
    RJ54s, etc.
    
    But, we have heard that it isn't recommended to use shielded cables as 
    it can cause the chassis of the two devices to be connected together 
    and that can cause problems when the devices are widely spaced.  A 
    large network of nodes with chassis interconnected by cable shields is 
    doomed to be problematic.
    
    What are your feelings on this?
    
    Thanks,
    
    Mark