help needed debugging DDS 56kb prob

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2 total messages Started by Steve Dyer Sat, 08 Sep 1990 04:14

#642

Author: Steve Dyer
Date: Sat, 08 Sep 1990 04:14

23 lines
1535 bytes

This isn't specifically Cisco-related, but I thought that the readers
here might be familiar with this kind of scenario.

I've just installed a 56kb DDS circuit with DSU/CSUs on each end and a
Cisco CGS/2 on my end (there's a larger Cisco on the other end.)  The
line itself came up with only a little difficulty, but I am having
regular trouble with the serial line staying up for any length of time
without the Cisco dropping DTR and resetting the line.  The number of
carrier transitions reported by "show interface" is almost mindboggling--
after 10 minutes from powerup, it reports 817 carrier transitions and
8 interface resets.  Naturally, this is wreaking havoc with applications
getting ICMP unreachables and prematurely closing.

I had the telco run loopback tests on both ends of the line for as long
as 15 minutes and they reported that it looked as clean as a whistle,
with no data or clocking errors.

I'm really at a loss for where to look next.  Anyone have any pointers?

-- 
Steve Dyer
dyer@ursa-major.spdcc.com aka {ima,harvard,rayssd,linus,m2c}!spdcc!dyer
dyer@arktouros.mit.edu, dyer@hstbme.mit.edu

Re: help needed debugging DDS 56kb prob

#645

Author: Steve Dyer
Date: Sun, 09 Sep 1990 03:20

28 lines
1993 bytes

In article <3951@ursa-major.SPDCC.COM> dyer@ursa-major.spdcc.COM (Steve Dyer) writes:
>[problems of hundreds of carrier transitions and serial line resets]

The problem has disappeared, and the superficial solution was simple
(if that was in fact the source of the problem.)  I'd specified the
high-speed serial interface on my CGS/2 even though I was planning to
run at 56kb so that I could upgrade simply to fractional T1 speeds if my
downstream link ever upgraded also.  During the initial configuration
of the serial interface, we neglected to specify the line bandwidth as 56kb
(since that was what had been assumed for other CGS/2 models, and was
the default for the Cisco on the other end of the DDS line.  Apparently
though, the default for the high-speed serial interface is T1 rate.
Once I reset this to 56kb, things settled down within minutes, and
I've had only a few carrier transitions and no interface resets since.

I suppose that the "bandwidth" field is used for the initial values
of the HDLC timers, and having such a mismatch between the two sides
(not to mention the actual bandwidth) could cause problems, no? 

By the way, I really have to say that I'm impressed how easily it
is to install one of these gateways and have it all work--it's
practically a "turnkey" operation.  Things have come a long way
since the original LSI-11 gateways when I was at BBN... :-)

-- 
Steve Dyer
dyer@ursa-major.spdcc.com aka {ima,harvard,rayssd,linus,m2c}!spdcc!dyer
dyer@arktouros.mit.edu, dyer@hstbme.mit.edu

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