[windows2000] Re: Need some basic instruction in networking
- From: "Timothy Mangan" <tmangan@xxxxxxxxxxxx>
- To: <windows2000@xxxxxxxxxxxxx>
- Date: Sat, 8 Nov 2003 14:37:48 -0500
[NOTE: Long Response]
1) What is a CSU/DSU?
A CSU/DSU is a layer 1 conversion device. It takes a serial interface cable
(coming out of the router) and converts it to a synchronized 1.544Mhz
digital signal which is used to send to the telco CO. The CSU/DSU will
always have information about the quality of the line between the CSU/DSU
and the CO (often called "the local loop"). If you call the CO they will
test out the local loop remotely. They can either read the registers
remotely or run a "CSU loopback test". If you complained and they said they
tested the line, this has been done and the line is OK. Pin-outs for T1
cables are different. If you want to replace those cables, get a T1
replacement. Belden makes them, as do others.
2) Where else can the problem be?
In logical order: In-house LAN, Router, Router to CSU/DSU, Local loop, the
backbone (Internet?), and repeat at the far end. You want to isolate out
portions of the problem. For example, that CSU loopback I mentioned
earlier.
- To eliminate the "in-house LAN", work from router to router (the router
closest to the T1 at each site). You are probably using Cisco Routers.
Find someone with a password and log in (you can usually telnet in,
otherwise there will be a console port). You can ping the ip address of the
router at the far end (as well as traceroute, although that is blocked in
the internet backbone much today). If the round trip delay between routers
is reasonable (eg under 300ms), then the WAN is OK and the problem will be
in-house.
Often, the problem is in the local loop or the backbone, and the following
applies if that is the case. You should be able to ping your ISP gateway
and watch delay time there. Most of the delay should occur in the local
loop (as the speeds are slower). Sometimes it happens between carriers in
the backbone. You might have Quest as the ISP at both ends, but typically
the traffic will be carried over someone else in-between (companies like
Global Crossing). The interfaces between carriers will clog up sometimes
when they need to add a new interface to handle increased capacity. When
this happens, the local ISP might say "my network is OK". If you are in
this situation -- especially if you use the same ISP at each end -- you want
to ask them to measure the delay between the two gateway routers (the first
router in the ISP attached to each site). Ask them for a round trip delay
number.
- You can turn on a "DSU loopback" in the CSU/DSU as well. This is a
loopback that sends data sent by the router back to itself. If that
loopback is enabled and the router sees itself (you have to be logged into
the router to see this), you have proved out the serial cable between the
two.
Hopefully this can help.
Timothy R. Mangan - Founder, TMurgent Technologies
tmangan@xxxxxxxxxxxx www.tmurgent.com (+1)781.492.0403
-----Original Message-----
From: windows2000-bounce@xxxxxxxxxxxxx
[mailto:windows2000-bounce@xxxxxxxxxxxxx] On Behalf Of Rod Falanga
Sent: Friday, November 07, 2003 3:13 PM
To: windows2000@xxxxxxxxxxxxx
Subject: [windows2000] Need some basic instruction in networking
For about 6 weeks now we have been experiencing really horrible connectivity
problems. We have a T1 line, but our network speeds to the Internet have
been abysmal at best. I have run some tests using DSLReports.com and have
found speeds as low as 14 kbps!!!
I've contacted Qwest and they have run some tests on our line from our
office to the ISP. They have informed me that everything is fine.
So, the problem, as I see it, is either here in our building, somewhere
(server, router, cables, something), or at the other end. I've tried
replacing cables, and have done what I could to replace all of the CAT-5
cables I could fine, but sometimes some cables are connected to things I
don't understand. For example, we've got something called a T1 CSU/DSU. I
don't have the foggiest idea what that is. And replacing CAT-5 cables on
that this just makes us loose our Internet connectivity completely.
So, what are things like CSU/DSU? Or, let's put it differently, starting at
the ISP who supplies us with T1 access, what "things" are in between that
and the NIC card in my edge server?
Rod
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Enabling User & Group Level Oversight & Access Policies
Fully Functional in a Thick or Thin Client Environment
http://www.pearlsw.com
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