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T1 Crossover Cable

Recently I had to create a T1 Crossover cable in order to connect two Juniper SRX240’s in the lab. A T1 crossover cable is different than an Ethernet crossover cable (but a regular ethernet cable can be used for T1 because both are straight-through).

Anyway, here are the pinouts for a T1 RJ-45 cable:

  • Pin-1 = RX+
  • Pin-2 = RX-
  • Pin-4 = TX+
  • Pin-5 = TX-

Therefore a crossover cable for T1 is:

  • One End Other End
  • Pin-1 === Pin-4
  • Pin-2 === Pin-5
  • Pin-4 === Pin-1
  • Pin-5 === Pin-2

And a loopback connector is:

  • (Same Connector)
  • Pin-1 === Pin-4
  • Pin-2 === Pin-5
  • Pin-4 === Pin-1
  • Pin-5 === Pin-2

See also fonality.com Troubleshooting T1/T1_Cross-over_Cable)

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