Transmit / Receive Assignments on fibe duplex connectors

Thanks for the response Dmitri, As to why I wanted to know - We have a large inter-floor / inter-building plant with ST connectors (we are shifing to LC). As such we do the following:

1. We light check the duplex patch cables we receive to make sure we have continuity on both leads.
2. We then tag the transmit lead with a small cable tie.
3. For the ST-ST patch cables, we put the cable tie on the fiber that has the length marking printed on it.
4. We designate the electronics of the network to be the "head end". If it is a network to network patch, the electronics that is closer to the core network is designated as the "head end"
5. We then start patching making sure the cable tie (transmit of the network electronics) is the first of the pair.
6. The last patch cable feeding to the "tail end" has the cable swapped, the cable tie would be on the second half of the patch.

This does two things: first we're not installing a dead patch cable (yes I know it could a lousy termination, we find that later after tearing out our hair). Second thing is the we reduce the problem of swapped cables in the path. This method has worked well for us.

As I stated in my original post, I scoured the web looking for a standard but found none. But I note the following:

We use Allied Telesyn, Cisco and SMC equipment. On all of those I have noted that when you view the electronics (with the key UP) the transmit is on the left. The fun part here is that CISCO mounts the SC GBIC with the key down, thus putting the transmit on the right. Cisco mounts the LC and MTRJ with the key up.

I have even noted that on Allied Telesyn equipment with ST electronics, they put the transmit on the left (as you stare into electronics with your other good eye) and they make the ST connectors different shades of gray, with the light gray being transmit.

Long winded reply, but the goal was just find out if there was a designated standard rather than a defacto standard.

Jay

Never heard of a standard that specifies the exact location of the transmit and receive fibers in a pair (which does not mean such standard does not exist). In my mind that is a proprietary spec by the actual transceiver module manufacturer

However: why do you even need to know?

Most likely you will be able to solve any pair reversing problem by having a single patch cord with separable connectors. That is, get a cord in which the connectors are not a single unit, but two separate connectors, clipped together with a little plastic clip. This way you can turn it around if you have to. This does not work for MT-RJ though. You'd have to simply carry extra MT-RJ crossover. But you need at least one crossover in the link (if you are using equipment by the same manufacturer) anyways, so it's a very handy item to have.

Hi Jay,

Kudos for taking great care of your fiber plant! Most customers NEVER do a SINGLE item from your 6-item list, especially the most obvious #1 ;-) With that said, I think you should disregard the actual location of the transmitting and receiving fibers. As long as you keep track of polarity of the patch cords, it absolutely does not matter which fiber carries light in which direction (well, assuming losses are generally the same). Besides, with ST connectors which aren't paired, you can always swap the ends if you encounter a different piece of equipment. This actually should be the very first step in troubleshooting any fiber problem.

BTW, if the standard you are looking for would be established, what would you do in case your fiber ports are vertical? ;-)

If a standard were established (and IF is the biggest word in the english dictionary) the the key of the connector is the KEY - Pun intended. If the key is located on top, xmit is on the left. Rotate the GBIC 90 degrees to the right, the key is on the right, and now xmit is on top. Conversely, rotatate the GBIC to the left 90 degrees, the key of the connector is on the left and xmit is now on the bottom.

Jay

Dmitri(Cabl> Hi Jay,

Google "fiber polarity" First link is a good guide

Anothere reference: TSB125-2001 Guidelines for Maintaining Optical Fiber Polarity Through Reverse-Pair Positioning

Systimax has a similarly titled document that I found to be the most clear in the descriptions (says almost the exact same thing as the RCDD). The official title is Duplex Fiber Polarity Guidelines. It might be a little hard to find on the Systimax web site, though Commscope is making things easier. If you can't find it email me off board and I'll send it too you. Take out the spaces before the @ and take out the extra "dot" after yahoo. Post here that you did send because that is not an oft used address.

Thanks Cableguy, I had seen the Systimax white paper in my googleing, which reinforced my idea that the electronics has the transmit on the left, with the key way "up". The white paper did not point to a standard that I could discern, but the eyes are old and tired.

Thanks for the tip on the TSB125, back to google.

Jay

TheCabl>

Makes sense ;-)