A E said: OK @MikePennington, so what's the "right way"?
Either hire a professional cable installer to check out your cable installation, or get something similar to a Fluke CableIQ. These meters perform detailed tests on the cable that reveal what you're dealing with. GigE has Signal to Noise requirements that simple continuity testers will not check. Cheaper continuity testers are typically what you'll find at lower prices in consumer electronics stores.
After you have satisfied one of the conditions above, test every cable. That's expensive and time-consuming, but it's the only way to be sure you won't deal with flaky connections down the road.
Some might argue that you could merely look at the jacket of the cable and see whether it's at least Cat5e; however, that's still inadequate to truly know whether you can use this for GigabitEthernet because:
- Someone could have used the wrong cable connectors or patch panels
- Someone could have crimped / punched down the correct equipment poorly
- Someone could have made errors pulling the cabling (i.e. used excessive force)
- Someone could have run the cabling across sources of significant electronic noise
- Someone could have violated cable run length requirements
If you're willing to gamble, you can test every cable with a couple of cheap 1GE switches from Wal-Mart, ensure each cable links to 1GE, and hope that those results are repeatable. However, I don't recommend this approach for anyone who cares about whether every cable is done right.
I offer another interpretation: 4 wire cable for 100Mbit/s.
This is basically the same as zac67's answer "Either it's a bad LSA contact, a bad panel insert or a damaged cable.", but probably the situation is intentional, not accidental.
It is compelling that it's exactly pairs 1/2 and 3/6 that are 20m long, while the other pairs are just shown with the length of the patch cable used to connect the tester to the cable.
EDIT:
Actually, the above statement might be wrong.
The cable tester's graphical result is somewhat puzzling. It does show "S" (shielding) as a interrupted link, but the presentation of wire pairs 4&5 and 7&8 is shown as single strech of 1m cable.
If wire pairs 4&5 and 7&8 were discontiguous, i.e. present in the 1m patch cords, but "absent" (probably: "used elsewhere") in the ~20m of fixed-installation cable, they should be shown the same way as the shielding link: with a gap.
Then again, this might be a misinterpretation by the cable tester.
There were days when installed 8-wire cable was used to provide two 8P8C connectors (a.k.a. "RJ45"), but equipped with just 4 wires each (1,2,3,6), to "save some money", and of course because 100Mbit/s Ethernet was a big thing back then and because it ran fine on just two twisted pairs.
Saving money that way has a veeeeery long tail, as we now see. And then there were "Cat5" labelled patch cords too, with just two pairs inside. m-(
You may want to check if you happen to have found one of these old tripwires (pun intended).
Best Answer
First off, you need two of those at each end, one for each direction. Second, it looks more like SC/PC to me, not SC/APC.
If you want to just plug in your replacement cable, then you don't have a choice, because the equipment optics determines multi-mode or single mode, in other words it's not just the cable's physical connector that has to fit where you plug it in, but the fiber's mode also has to correspond to the mode of the optical equipment that you're plugging it in to.
Multi-mode is cheaper (never wondered if it's the fiber or the optics, probably both). For multi-mode the best you'll do over 2000 ft is 100 Mbps.
Be careful, because if this cable plugs in to some equipment that your ISP installed in your building, it is probably NOT active optical equipment, but just a patch into another cable that runs to the ISP's optical equipment in a network room somewhere in your neighborhood. Extending the cable may not be supported by your ISP.
Instead of extending the ISP fiber, you may want to investigate the possibility of leaving your ISP installation as it is, and running cables between your buildings that plug in to your internal network.