Ethernet linked access point appears sensitive to cable length well below specified limits.

Ethernet linked access point appears sensitive to cable length well below specified limits.

I?m seeking to locate a wireless access point remote from my main router, a D-Link DI-524 whose wireless function has been turned off. The wireless access point is being implemented with a nearly identical D-Link DI-524 wireless router whose DHCP function has been turned off. The IP address of the second D-Link DI-524 wireless router has been altered so as not to conflict with the IP address of the first router. One of the LAN outputs of the first router is connected to one of the LAN outputs of the second router so that it acts like a switch.

I have tested the above configuration at three locations linked by three different CAT5 cables.

Location #1 ? WORKS fine when linked by commercially constructed 10? long CAT5 cable.

Location #2 ? WORKS fine when linked by home built 40? long CAT5 cable.

Location #3 ? DOES NOT WORK when linked by home built 100? long CAT5 cable. ? Not only is there no communication over the link, but the lights on both routers do not even indicate a connection. YET, if at this same location #3, the 100? long cable is plugged into any one of several computers, the connection indicator lights come on immediately, and full normal network access is quickly obtained.

As the cable length is well under the 100 meter (300 feet) maximum length for Ethernet, at first I thought that maybe the third cable is somehow wired differently, perhaps as a ?Cross over cable? rather than as a ?straight through? cable. I understand that some interfaces can cross and un-cross a cable automatically as needed. I am uncertain whether or not the LAN ports of the DI-524 have that feature, but an examination of all of my cables, both home made and commercially assembled, and all appear to be wired ?straight through.?

I?ve also sought to confirm that the problem is not associated with the RJ45 connector at the end of the cable. The symptoms are unchanged when a short (10 foot long) Ethernet extender (female to male) cable is used, so the connector at the end of the 100? cable is not disturbed as I switch between the D-Link DI-524 and my lap-top computer..

Any Suggestions?

Reply to
windsurferLA
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added cabling & ethernet newsgroups - Wonder if a small ethernet cable tester has been used to verify proper pairs ?

Reply to
ps56k

These homebuilt cables, which wiring pattern did you use? T-568A or -B ? If you don't know what I'm talking about, it is highly likely you split a pair.

Please do not complain "but the other comp works". Difference NICs and drivers are more error-tolerant and have more robust fall-backs.

Electrons may be color blind, but they _do_ know who their dance [twist] partners are.

-- Robert

Reply to
Robert Redelmeier

Huh? Unless he did something really disgusting, like EIA-568A on one end and EIA-568B on the other, either wiring standard will work. The color codes are different, but the pairing is identical.

Drivel: I once had some hired help in wiring a medical office. I did

568B while my hired help did 568A wiring. Nothing worked when we were done. Never ignore the obvious.

True. I recently demonstrated that I can run 10baseT-HDX (half duplex) through 2,000 ft of CAT5e (two rolls in series), without any data degradation. If I had a 3rd roll, I would have added it. The catch is that it would only work between my Cisco 1900 ethernet switch, and a desktop with an Intel Pro100 card. It would function to other devices (several laptops, assorted junk around the office), but these showed various errors in the switch SNMP logs.

Perhaps a matchmaker would be appropriate?

See item #6:

Reply to
Jeff Liebermann

In comp.dcom.cabling Jeff Liebermann wrote in part:

Oh yes, fully agreed. But I think it relatively unlikely the OP would have followed either without some awareness. I'm testing for that awareness.

The intuitive wiring patterns (SBS and USOC) will split a pair. All the correct ones are somewhat counter-intuitive.

Easier to notice and fix with jacks.

Nice data point.

-- Robert

Reply to
Robert Redelmeier

Robert ... thanks for the hint.. the likely cause has been identified.

When you asked about T-568A or T-568B, it triggered a memory. I then recalled that the connectors were not assembled at the same time; one end was rebuilt because of intermittent connection problems. The intermittent end had been the very first RJ45 connector that I had ever assembled. I further recalled being uncertain at the time I was rebuilding the connector whether to use the "A" or "B" configuration.

Now doubting my wiring skills, I got out my jeweler's eye loop to very carefully look at both ends to make sure one had not be wired "A" and the other "B." The result was not what I expected. A careful examination of the newer end appears to reveal that the blue-white (#5) and the green white (#3) were inadvertently interchanged at that end and only that end.

I expect that repairing the cable will solve the problem. WHAT I FIND SURPRISING is that the cable has worked with so many (guest's) computers for so long that it was not until the A - B question was raised that I thought to check the colors of the inner wires - a not so easy a task for old eyes like mine. Obviously, there is enough cross talk between the pairs to effect a connection with most, but not all, hardware.

Although I feel rather stupid for not spotting the wiring error earlier, I never suspected a wiring error would be the problem. When ever I assemble a connector, I keep a multi-colored wiring chart right in front of me. Obviously, it was not enough to preclude the error.

Thanks for everyone's help.. Tomorrow, we try a rebuild.

Reply to
windsurferLA

I enjoy asking the original questions backwards. In this case, it's "what would I have to do, to CREATE the problem"? Creative wiring and connector terminations are the probable culprits as the terminating equipment is obviously working.

I'll do the newsgroup(s) a favor and not rant on how Ma Bell, the old TIA and the EIA created this mess.

At the time (about 1998), if you purchased any manner of pre-wired ethernet jumpers, you got EIA-568B wiring. Never mind that EIA-568A is the real standard. Well, my accomplice was working on his BICSI certification, and they were preaching EIA-568A. Never mind that I told him that I wanted the color coding to be consistent throughout the entire building, all of which was EIA-568B. He decided that BICSI must be correct and was fully prepared to have me (not him) re-terminate the entire building (about 400 wall jacks) to insure compliance. I paid him his fee and hired a day worker from the local lumber yard. He didn't speak much English, but he undid the damage in amazingly little time, and finished the job in about half the time I had expected. The cable certifier found two wiring errors out of perhaps 60 wall jacks. I was going to pay him a bonus, but that was before I noticed some of my tools had evaporated. Sigh.

Careful here. That's not an endorsement for installing 2,000ft CAT5e runs. I once calculated the maximum cable length at about 1,200ft for

10baseT-HDX before timing becomes an issue. Why 2,000ft worked is still a mystery to me. It shouldn't have unless the timing on the ethernet devices is more relaxed than required. Also, note that I was using 10baseT-HDX (half-duplex). Full duplex and/or 100baseT will not work due to collision domain issues and cable near end crosstalk. You also have to use an ethernet switch. Hubs (repeaters) will not work.

I do have several 900ft runs in service (one of which goes under some railroad tracks). No problems. I do have a 500ft run that is giving me problems. I haven't had time to troubleshoot (due access issues), but am guessing that I have some induced interference from rotating machinery, transformers, ballasts, or something similar.

As for stretching the technology, I done my part:

  1. DSL over barbed wired. 1Mbit/sec SDSL. Distance is about 3,500ft of barbed wire, with 100ft of CAT5e at each end. However, the multiple splices tend to be noisy so it was replaced with a wireless link about 2 years ago.
  2. 10base2 (cheapernet) over CATV 75 ohm RG-6/u coax. Distance was about 1500ft at one location. The other location was a radio station that was stuffed full of RG-6/u coax runs. Terminated with 50 ohms at both ends (because 10base2 uses DC levels for busy detection). Only two transceivers (no taps or T connectors). With such high losses, the far end reflections just disappear and never become a problem.
  3. FTTS (fiber through the sewer). Actually it's drain under the road that dumps into the river, but it looks much like a sewer. About
800ft. I keep waiting for it to fail as some water propelled rock cuts the outer jacket, but it's been up for 8 years and shows no change in fiber attenuation. I've lost two transceivers, but the fiber is holding it's own.
  1. In the miscellaneous category, I've done ethernet through the sewers (in order to cross the LATA boundaries), ethernet over 25 pair telco bundles, ethernet over two 117VAC extension cords (I was desperate), DSL over zip cord, and adapters made primarily from clip leads. 900MHz data over G-Line. I won't mention any of my other wireless atrocities.

One of these days, I'll follow the standards and rules, but not this week.

Reply to
Jeff Liebermann

Starlan 1 Mbps?

Michael

Reply to
msg
  1. In the miscellaneous category...ethernet over 25 pair

...or perhaps LatticeNet?

Reply to
msg

wow - StarLan - That really takes me back... We creating the video training and marketing materials...

Reply to
ps56k

Nope. 10Mbits/sec half-duplex ethernet over 25 pair telco bundles. Works fine up to about 100ft. It might work farther, but I haven't tried it.

Gaaak. Starlan brings back not very fond memories of doing battle with 3B2-400 clunkers using Ma Bell 258A wiring on CAT3 shared with Pre-Merlin phone systems. I had no idea what I was doing, so it's little wonder that I could never make it all work quite right.

Sorry, no LatticeNet. Some Token Ring (4Mbit/sec), Moses Networks Promise LAN, DECNet, Novell Netware, 3com something pure ISO stack, Microsoft LAN Manager, Lantastic, and probably a few more that I'm successfully forgotten about. Add a bunch of TCP/IP implimentations for Windoze 3.x that never quite worked right, and a mess of non-802.11 schemes and protocols, that went nowhere.

Reply to
Jeff Liebermann

The propagation velocity of UTP is about 5.1 ns/meter, or roughly

1.5 ns/foot. Your 2,000 foot run has a round-trip delay of around 6 us, which is far less than the 48 us allowance in half-duplex 10 Mb/s Ethernet (i.e., 51.2 us less the 3.2 us "jam" time). As long as the *signal characteristics* were still acceptable to the line receiver, it should work, as there are no protocol timing violations in this arrangement.

Much of the timing allowance in ordinary networks is allocated to the repeaters; I suspect that your setup was a two-station back-to-back connection, which has LOTS of timing margin.

Backwards. The collision domain (timing) issues are related only to

*half* duplex Ethernet, not full duplex. You can (and we often do) run full-duplex Ethernet over tens or hundreds of kilometers (using fiber) with no timing concerns.

-- Rich Seifert Networks and Communications Consulting 21885 Bear Creek Way (408) 395-5700 Los Gatos, CA 95033 (408) 228-0803 FAX

Send replies to: usenet at richseifert dot com

Reply to
Rich Seifert

3B2 - ahhhhhh - We also did the training video & product intro for the "Unix PC" - along with the IBM 3270 replacement..... can't recall the number, maybe 6500 ? Lastly - we did the AT&T PC product materials & launch -

ahhhhhh -

Reply to
ps56k

I knew some of the developers there, and just *loved* the product name. In the end, it was more of a promise than a LAN, however.

My all-time favorite communications product name was from a company (whose name I forget) up in Marin county who built a very simple device. "Back in the day", terminals connected to computers using modems, which had a "DCE flavor" (modem-to-host computer) and a "DTE flavor" (modem-to-terminal) for the wiring. If you wanted to connect a terminal directly to a computer, you could eliminate the modem, but needed to cross-connect the transmit/receive pairs in the cable. Today we all know this as a "null modem" cable, and it is fairly ubiquitous, but it hasn't always been so.

This small company marketed a "null modem" device; a small box that had the transmit/receive cross-wiring, with connectors that would allow the use of ordinary, uncrossed-wiring modem cables to the DTE and DCE. Simple, but useful if you don't have a null modem cable.

No technological genius here, but great marketing savvy. Instead of calling it a "cable crossover" or some such, they called the device a "QuasiModem"--the box had a picture of a bent-over Quasimodo carrying the device under his arm, with the slogan "We've got a *hunch* you'll like it!"

Believe it or not, between the last two sentences I just went outside my office and shot a bobcat who was chasing my house cat, whose name happens to be "Cat 3"(he is my third cat). No, I am not planning to upgrade him to Cat 5.

-- Rich Seifert Networks and Communications Consulting 21885 Bear Creek Way (408) 395-5700 Los Gatos, CA 95033 (408) 228-0803 FAX

Send replies to: usenet at richseifert dot com

Reply to
Rich Seifert

In comp.dcom.cabling windsurferLA wrote in part:

That's the idea.

This is the most common newbie wiring mistake. Swapping the whites turns the layout into side-by-side and splits the green and blue pairs.

It is hard for everybody, and impossible with some cable mrfs where the whites are unmarked (some plenum).

Crosstalk is not really required. rememeber the signal is differential and also present full-strength on the green. Still, a bit surprising it ran as well as it did. Of course, it never needed to carry more than 1 MBps, so retransmits would go largely unnoticed.

Many years of experience have led to to _ALWAYS_ check the cabling first. Especially if there is any indication it is home-made. It is incredibly difficult to crimp connectors correctly.

-- Robert

Reply to
Robert Redelmeier

Rich Seifert wrote: (snip)

Shouldn't that be gato tres?

What do they call the wiring in Spain and Mexico?

(snip)

-- glen

Reply to
glen herrmannsfeldt

TIA/EIA 583-Ã

Reply to
DTC

In comp.dcom.cabling Jeff Liebermann wrote in part:

A good diagnostic method.

Probably because the US government requires -A

While US industry historically has been -B

10basedT has such relaxed timing because of the cascading permitted. It became 100baseTX by tightening the circle. Timing is mostly relevant for collision situations. If you are isolated by a switch, how can it matter?

Keeping crosstalk out is probably the main benefit.

I hope these installations have adequate lightening protection!

That's fine when expertise is available for troubleshooting and the reliability is acceptable.

-- Robert

Reply to
Robert Redelmeier

Which is why I like the Leviton Quick port for the part time do it yourself crowd. You can buy the jacks at Home Depot on Saturday afternoon and they have the wire colors on the sides of the jacks.

David

Reply to
DLR

In comp.dcom.cabling DLR wrote in part:

Agreed. The key is _JACKS_ . They're much easier to get right than _PLUGS_ .

-- Robert

Reply to
Robert Redelmeier

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