# Ubiswitch pairs swapped (port 3)?

**URL:** <https://forum.botblox.org/t/ubiswitch-pairs-swapped-port-3/121>\
**Category:** BotBlox Hardware\
**Tags:** ubiswitch\
**Created:** [December 26, 2023, 1:22pm UTC](https://forum.botblox.org/t/ubiswitch-pairs-swapped-port-3/121 "2023-12-26T13:22:49Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![PeterMaes](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.botblox.org/petermaes/32/231_2.png) [@PeterMaes](https://forum.botblox.org/u/PeterMaes)\
**Post date:** [December 26, 2023, 1:22pm UTC](https://forum.botblox.org/t/ubiswitch-pairs-swapped-port-3/121/1 "2023-12-26T13:22:49Z")

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It seems for port 3 the pairs A and B are swapped. Also pair C and D are swapped. Can you confirm this ?  
I double checked my pcb design and cables for crossings, but only port 3 is reporting swapped pairs in my test setup. As this will not affect the correct functioning of the port it is no problem, but documentation/datasheets should be correct.  
 ![Screenshot 2023-12-26 at 14.23.23](https://canada1.discourse-cdn.com/flex027/uploads/botblox1/original/1X/28f0f28ae4af09c57d7fa72f6dc22cbdc70f8dd6.png)

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**Author:** ![josh\_elijah](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.botblox.org/josh_elijah/32/568_2.png) [@josh\_elijah](https://forum.botblox.org/u/josh_elijah)\
**Post date:** [December 31, 2023, 3:12pm UTC](https://forum.botblox.org/t/ubiswitch-pairs-swapped-port-3/121/2 "2023-12-31T15:12:56Z")

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There is no difference in the routing of port 3 in comparison to any of the other ports.

They are all mapped as:

 ![image](https://canada1.discourse-cdn.com/flex027/uploads/botblox1/original/1X/aa639ed8966352f6d61e9b6820e744049e116f20.png)

Pin 1: C-  
Pin 2: C+  
Pin 3: D+  
Pin 4: D-  
Pin 5: B+  
Pin 6: B-  
Pin 7: A+  
Pin 8: A-

Then, using the supplied cables, this maps to the RJ-45 connector as below.

 ![image](https://canada1.discourse-cdn.com/flex027/uploads/botblox1/original/1X/cd6afae399ed665b6d7a25e0c30a1ed8336b4a1a.jpeg)

This is the standard mapping for RJ-45 straight cables (see below), and is how all of our gigabit ethernet boards are mapped.

 ![image](https://canada1.discourse-cdn.com/flex027/uploads/botblox1/original/1X/cb551f0c33f96777e4b7fa342a6059340a142eda.jpeg)

What device are you using to check cable mapping, and is that device expecting a straight or crossover cable?

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<div class="post-metadata">

**Author:** ![PeterMaes](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.botblox.org/petermaes/32/231_2.png) [@PeterMaes](https://forum.botblox.org/u/PeterMaes)\
**Post date:** [January 5, 2024, 9:31am UTC](https://forum.botblox.org/t/ubiswitch-pairs-swapped-port-3/121/3 "2024-01-05T09:31:15Z")

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We use the Copper Test available in Cisco SG3xx -series to verify cable mapping, but I have found that this test is very unreliable. Successive tests show different results and after repeating the test a few times it ends with a fault message.  
So I guess there is no issue at all with swapped pairs.

test is described here :

> **[How to Copper Test a Port on a Switch](https://www.cisco.com/c/en/us/support/docs/smb/switches/cisco-small-business-200-series-smart-switches/smb3317-how-to-copper-test-a-port-on-a-switch.html)**
>
> This article explains the performance of the copper ports test done by the VCT on Gigabit Ethernet (GE) ports.