Is VWIC 2MFT E1 able to do G.703 64 kbps co-directional?

Discussion in 'Cisco' started by Roberto Kodama, Oct 30, 2003.

  1. Hi!

    We were using Cisco 2611 with 1 WIC 2A/S + Rad's Converter G.703
    64kbps codirectional/V.35 + 3Com 16-port hub.

    Now we are in acquisition of additional router to expand our network
    and our Cisco reseller is suggesting Cisco 2651XM + 1 VWIC 2MFT E1 +
    NM-16ESW as a one-box solution.

    Can VWIC 2MFT E1 replace Rad's Converter? I'm feeling not, since it is
    designed for 2MB links full or fractioned, not for G.703 codirectional
    64 link alone...

    Am I right?

    Thanks in advance

    Roberto Kodama
     
    Roberto Kodama, Oct 30, 2003
    #1
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  2. Roberto Kodama

    Andre Beck Guest

    That sounds like a V.35 to G.703 Terminal Adapter that indeed operates
    G.703 at 64kbps.
    I don't see how the VWIC should replace the *real* 64kbps TA. But then
    again, I'm not sure what "G.703 64kbps codirectional" actually means.
    It reads like just 64k, but it might as well be a 64kbps bearer channel
    within a T1 or E1 compound.
    I feel the same. You can use just one B-channel of the whole E1 to get
    just 64kbps payload off the 1984kbps available in a G.704/G.703 E1
    line. But that is sure not the same as a pure 64kbps line.

    The cheapest way to get two times 64kbps out of a router is actually
    a BRI. A real 64kbps line is not unlikely to be provisioned based on
    ISDN anyway (dunno about .br, but at least here in .de its typical),
    so the best way is to get the telco to strip their provisioning down
    to the naked I.430 circuit and then connect to it using a BRI in leased
    line configuration.
     
    Andre Beck, Nov 1, 2003
    #2
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  3. Hi! Thanks for answers.

    Below some additional info:

    RAD'Converter is SPD-703-1 model
    (http://www.rad.com/Article/0,6583,16470,00.html). Does this clarify
    something for you?
    As I understand is possible to get a 64kbps slot time from a 2MB E1
    with VWIC, but not from a 64 kbps link alone... Think this 64 kbps
    link as a PCM Digital line...

    In fact we are linking SDH or PDH radios where there is a 64kbps
    digital service channel and its provided interface is 64kbps G.703
    standard.

    Best Regards
    Roberto Kodama
     
    Roberto Kodama, Nov 3, 2003
    #3
  4. Roberto Kodama

    Andre Beck Guest

    Well, it makes me quite sure about the adapter beeing a pure 64kbps G.703
    device. It's not feeding some single time slot in a G.703 E1, it is native
    64kbps. If it needs to be muxed upwards the hierarchy, a "channel bank"
    is required. This will probably mux up to 30 (or 31) such lines into a
    PCM30 (which is a E1).
    I've been using PCM lines to some extend, some years ago. These were,
    however, interfaced using ISDN (S0 compliant BRI) and looked just like
    normal Basic Rate NTs. Plug them into a router's BRI, make it leased
    and establish either 128kbps/144kbps L1 bundle (the two B-channels
    aka timeslots they provide are octet synchronous) or use MP to bundle
    the Bs on L2. Pretty robust stuff, came from ke/Quante. I realize, however,
    that focusing that much on ISDN style interfaces is a german specialty
    (yet a neat one, BRI *is* cheap, though not that cheap in Cisco world
    if you need to buy a WIC-1B...).
    If it's a service channel that drops out some hierarchy mux/demux, there
    is no easy way to get it as a BRI. 64kbps G.703 is probably one of the
    simplest interfaces you can get for something like that - just two
    twisted pairs and a trivial signaling. The drawback is that this inter-
    face is not really common with routers, it's pure telco world - so you
    have two options:

    a) Use a TA (like the RAD one) that turns the 64kbps G.703 into something
    serial you can terminate on a Cisco (you do that already), or
    b) If you need a multitude of these, try to get telco equipment that can
    mux a bunch of such 64kbps G.703 into one E1. It should allow for 30
    or even 31 lines to be muxed into the E1, some just exclude time slot
    16 for bizarre reasons (in PRI applications, 16 is used as the D-channel,
    but this doesn't make it any special timeslot on a leased/muxed one).

    To get b) into a router, just use the appropriate PRI interface in leased
    line mode. We are doing this with E1s on PA-MC-8E1s, the german Telco
    is providing us 64kbps and 128kbps leased lines (PCM) to a bunch of
    customers muxed onto E1 lines this way. If they can buy that PCM stuff
    somewhere, you sure can, too. On a 26xx, you'd need a PRI NM, though -
    the VWICs cannot interface more than two channel groups, but you could
    aggregate as much as 31. This, of course, only pays if you need more but
    a handful of them, but then it's getting really chic.
     
    Andre Beck, Nov 6, 2003
    #4
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