RE: (PM) PRI - CRC Errors

James Courtier-Dutton (dutton@livingston-ent.co.uk)
Fri, 12 Mar 1999 09:57:59 -0000

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.
>
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