[c-nsp] PA-T3 vs. PA-T3+

[Bill Wichers]

>On Sun, Sep 19, 2004 at 02:05:40PM +0200, Daniel Roesen wrote:
> > > Thanks for your data.  Have you talked to your Carrier about this?  Maybe
> > > they can reduce the output signal of their T3 port?  (I certainly plan
> > > to do this, instead of putting addition 50m of cabling into this
> > > already-crowded edge router rack...)
> >
> > Isn't there a cable length parameter on T3 interfaces too?
>
>There is ("cablelength 1-450"), but it does not seem to have a noticeable
>effect.  At least not on this specific line.
>
>gert

Your carrier should be able to change the LBO (Line Build Out) parameter on 
their mux/switch/etc. I had this issue with a circuit about a year ago 
(although our problem was that we were at the edge of the absolute max 
reach on 734A cabling -- about 900 feet -- and had to MAXIMIZE the signal). 
In this particular case we had a cross-connect between Level3 and SBC where 
each carrier had fiber facilities in our building, but they were at 
opposite ends of the place... Anyway, the solution was to request that each 
carrier set their LBO to max on the transmit side and to max sensitivity on 
the receivers (some equipment can pad the input a bit to reduce 
sensitivity). Level3 was using Alcatel equipment, SBC was using a Fujitsu 
FLM2400.

In your case you might be overdriving the input on one side or the other of 
your DS3 circuit. Check which direction you see more errors in, then either 
reduce the LBO or pad the input of the receiver seeing errors. The carriers 
usually only have a few levels (in our case Level3 had 3 steps and SBC had 
2) to choose from, so they are limited too like the other post that 
mentioned Cisco having only 2 actual levels available.

Worst case try using a longer patch cord. 735 cabling (the smaller DS3 
cable) will have greater loss than the larger 734 cabling, so try using a 
25'-50' 735 patch cord. The 450' limit is for 734A cabling, for 735 the 
limit is 230'. 735 cable is also a lot easier to handle than 734 in 
confined spaces such as busy equipment racks.

      -Bill



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Waveform Technology
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