Re: (PM) PRI - CRC Errors

Muditha Gunatilake (muditha@seychelles.net)
Mon, 15 Mar 1999 14:18:43 +0400

I noticed alot CRC errors on my router...we have a E1 line connecting us
to via satellite to the UK. The problem was C & W (my PTT) were using
an external clock an now they are using the first time slot as the
clock and the problem has been sorted

May be this might help...

regards

> Hello Jake
> How do you suppose that when a CRC occurs, the frame is retransmitted.
>
> You are receiving frames at E1 speeds, there are no redundent frames,
> so how
> are these frames retransmitted.
> One frame on an E1 link contains 1 byte from each timeslot.
> As far as I know, all that happens is that the frame with the CRC
> error is
> dropped, and a signal is sent back to the remote end to tell it that
> an CRC
> error occured.
>
> > -----Original Message-----
> > From: owner-portmaster-users@livingston.com
> > [mailto:owner-portmaster-users@livingston.com]On Behalf Of Jake
> > Messinger
> > Sent: Friday, March 12, 1999 04:54
> > To: Robert Blayzor
> > Cc: portmaster-users@livingston.com
> > Subject: Re: (PM) PRI - CRC Errors
> >
> >
> > On Thu, 11 Mar 1999, Robert Blayzor wrote:
> >
> > :I'm curious as to how CRC errors effect a PRI. I currently have a
> PRI
> > :that is taking a few CRC hits every hour... not many, about 1-20
> CRC
> > :errors per hour, possibly just a bit more.
> >
> > How it affects a pri? Well it reduces your transmission efficiency.
> CRC
> > errors are caused when a packet of data didnt pass the error check
> and the
> > data had to be sent again. I believe ISDN uses continuous ARQ but I
> can
> > check tomorrow.
> >
> > What is causing the errors? They are pretty random? Could be
> attenuation,
> > could be rf interference, could be poor connections on either end.
> 20 per
> > houris not too many IMO. You are talking about a retransmission
> > of a maximum
> > of 20*1500=30000 extra bytes per hour versus a total thruput of a
> PRI in 1
> > hour (1.54 mbits/sec max thruput). This ratio of errors to data
> would be
> > tiny.. This is unless of course, the errors referred to
> > are the uncorectable CRC errors where the receiver requested
> > retransmission
> > from the sender and either never got it or never got a good
> retransmission
> > after X amount of times. I would tend to think that the portmaster
> is
> > reporting the former and not the latter.
> >
> > ~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*
> > -,._.,-*~
> > Jake Messinger, VP. ph:713-772-6690 Lucent Dealer
> > AMS, Inc. fx:713-774-3498 Medical
> Billing
> > 8300 Bissonnet #400 jake@ams.com , ICQ# 4403734 Internet
> Services
> > Houston, Texas 77074 www.ams.com/~jake and Hardware
> >
> > Adjunct Professor University of Houston, CBA jake@uh.edu
> > ~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*
> > -,._.,-*~
> >
> > INVENTOR OF the _.,-*~''~*-,._ SQUIGGLES (c) 1978
> >
>

--
 --
 ---------------------
 Muditha Gunatilake
 Atlas Seychelles Ltd


 Phone:304060
 email: muditha@seychelles.net
        mbh3gpa@afs.mcc.ac.uk
        muditha@creole.seychelles.net
 :-)




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