looped RJ45

[Biosylum]

I recently found an RJ45 connector with pins 1&2 looped back into pins 7&8 repectively. Just that, a pair of wires, 6", looped back into itself. Just curious if anyone would know why someone would create this thing.

 

[TheStu]

Port Testing maybe? But i'm not really sure how. Throughout my entire time of my CCNA Cert. Course, I never once saw anythign like that.

 

[futuristicmonkey]

Hook one of those up to a Windows box and it might think you're connected to a network. This is 3rd hand info, so take it as you will.

I don't know why it wouldn't work on a n*x box, either.

 

[Uhtrinity]

Loopback tester, they used to be part of computer repair tool kits. Like stated above they are used in conjunction with diagnostic software to diagnose parallel or serial ports.

 

[stevf]

that is not an ethernet loopback tester though - you would need to hook up pin 1 to 3 and 2 to 6 (I think that is corrrect, unless i need to reverse 3 and 6) to make a loopback tester

did find reference to a rocketport serial interface that uses rj45 and could be a loopback tester for that as it uses:

Pin Name/Description
1 Request To Send
2 Data Terminal Ready
3 Ground
4 Transmit Data
5 Receive Data
6 Data Carrier Detect
7 Data Set Ready
8 Clear To Send

other than that, not sure what it could be other than a failed attempt at a loopback connecter for ethernet

 

[LightninTrip]

sounds like maybe somebody was screwing around with a piece of cable and some connectors...I do it all the time at work..haha...

 

[ScottMac]

I loop for 1&2 --> 7&8 would be for DDS (56K), ATM over copper, possible audio / video (would depend on the BALUN/Adapter).

That would be considered a "hard loop." With a T1/DS1, there's a NIU/"SmartJack that terminates and provides a demarcation point on the line at the customer premises. The NIU/SJ can be commanded to loop at either side (customer side or provider side).

A DDS/56 line doesn't have a "smartjack" ... it's just copper that terminates at a biscuit block ... to put up a loop (for testing), the CSU/DSU can be commanded to loop, or a loopback plug can be put into the jack.

Once the loop is established, the provider / telco can send bit patterns down the line, and get 'em back to compare in order to judge the quality of the connection.

FWIW

Scott

 

[m1ldslide1]

Without having the energy to google my T1 and ethernet pinouts I'd say it's either a T1 loopback plug or an ethernet loopback plug. For ethernet it doesn't do much good, as I made one once and spanning-tree err-disables the port instantly (at least in cisco land) but for T1's they're an important troubleshooting tool.

 

[Fallen Kell]

Lots of interfaces can be converted to a RJ45 connection. This could be anything from a custom connection, to a terminator of a chain, to bad wiring job.

But it is most likely a 99-7912-043-1 RJ-48S 4W 56K loopback connector, used to test a 56K connection.

 

[ScottMac]

Originally posted by: m1ldslide1
Without having the energy to google my T1 and ethernet pinouts I'd say it's either a T1 loopback plug or an ethernet loopback plug. For ethernet it doesn't do much good, as I made one once and spanning-tree err-disables the port instantly (at least in cisco land) but for T1's they're an important troubleshooting tool.

10/100 Ethernet uses pins 1&2, 3&6 (loopback 1-->3, 2-->6)
GigE uses all four pair (both directions at the same time on all pair). The loopback would be 1->3, 2->6, 4-7, 5->8.

T1 is 1&2, 4&5 (1-->4, 2-->5)

FWIW

Scott

 

[grant2]

Just an idea...

Sometimes our telecomm equipment would go dead for a few hours (software crash etc., it was a test environment) and the telephone company would termate our ds1 service because the equipment didn't respond for so long.

So we would plug a device like you describe onto the wire for a few seconds to have the telephone co's equipment reactivate the line.

When we plugged it onto a wire connected to our ds1 switch, it would loop back the "active" signal so that our switch though it was properly connected to another piece of equipment.

 

[Rastus]

You use that kind of loopback plug where a rollover cable (1>8, 2>7, 3>6, 4>5) is used.