Punching down a keystone

[Oberon.Smite]

When using a punchdown tool to get a CAT5e cable into a keystone jack, do I use standard A or B?

[jj9987]

If you want a straight cable, then both ends need to be same - either both A or both B.

If you want crossover cable, then one end needs to be A and another end needs to be B.

 

[ARikozuM]

5 minutes ago, jj9987 said:

If you want a straight cable, then both ends need to be same - either both A or both B.

If you want crossover cable, then one end needs to be A and another end needs to be B.

It doesn't matter much these days as the switch can do it by itself as long as you adhere to the order on both ends.

 

@Oberon.Smite The standard doesn't matter as long as you're consistent with each cable. Personally I use all straight cables in my house.

[jj9987]

1 hour ago, ARikozuM said:

It doesn't matter much these days as the switch can do it by itself as long as you adhere to the order on both ends.

 

@Oberon.Smite The standard doesn't matter as long as you're consistent with each cable. Personally I use all straight cables in my house.

Depending on the devices, it may be relevant. For standard home network, yes, it does not matter as Auto-MDIX can make use of both type of cables.

 

For example, on some devices (older Cisco routers/switches for example) the console cable must be straight one.

[brwainer]

1 hour ago, jj9987 said:

If you want a straight cable, then both ends need to be same - either both A or both B.

If you want crossover cable, then one end needs to be A and another end needs to be B.

 

this is wrong. If you make a cable that is A on one end and B on the other, you only end up crossing over 2 of the 4 pairs - the other 2 pairs end up being not crossed. When you plug a cable like this into devices, they may take a long time to connect, and when they do they will end up with either 100Mb straight, or 100Mb crossover. You can't get 1Gb crossover out of it, even if both ends were Auto-MDIX - because Auto-MDIX only swaps all the TXs and RXs at the same time, it can't swap individual pairs around. To make a true crossover cable that works at gigabit speed, you have to be sure that every pair is crossed. But with Auto-MDIX on most devices, it mostly only matters if you are connecting two old switches together - and in that case it's easier just to buy premade crossover patch cables.

[brwainer]

11 minutes ago, jj9987 said:

Depending on the devices, it may be relevant. For standard home network, yes, it does not matter as Auto-MDIX can make use of both type of cables.

 

For example, on some devices (older Cisco routers/switches for example) the console cable must be straight one.

most Cisco (and HP and Dell and Mikrotik and....) require rollover cables for the console cable, which is an entirely different thing from straight or crossover.

[brwainer]

2 hours ago, Oberon.Smite said:

When using a punchdown tool to get a CAT5e cable into a keystone jack, do I use standard A or B?

if there are already lines in the building that are A or B, you should follow that for consistency. For brand new installs (the first time ethernet is being punched down in a building) B is recommended.

[dendryganarren]

In my experience B is more common in data, and if I don't remember wrong B is actually slightly better for data - but nothing that you would notice.

I think A is more common in telephony.

Gigabit devices is requireed to have Auto-MDIX, so most devices will cross over automagically. If you have very old 100Mbit devices they can require a crossover cale, i e A -> B

[ARikozuM]

@Electronics Wizardy

[brwainer]

4 hours ago, dendryganarren said:

In my experience B is more common in data, and if I don't remember wrong B is actually slightly better for data - but nothing that you would notice.

I think A is more common in telephony.

Gigabit devices is requireed to have Auto-MDIX, so most devices will cross over automagically. If you have very old 100Mbit devices they can require a crossover cale, i e A -> B

There is an exception that it is not required in switches and routers - it's only required on end devices so that they can be plugged into each other directly. Most switches have it, but not all.

[Brightglaive]

Dendryganarren, jj9987 and ARikozuM are correct. As long as you DON't mix 568A with 568B (In otherwords use 568A on both ends or 568B on both ends), you will get a straight through cable. Although that means less and less as most switches sold today implement auto-MDIx which negates the crossover vs. straight-through cable argument.  568A is mostly used because the punchdown can be used for residential telephony or data. (It complies with USOC - Universal Service Order Codes and is required for federal government contracts) . Allegedly 568B does give a minor improvement, due to a very small amount less of crosstalk for data. The wiring scheme was mostly used in commercial installations primarily by AT&T for the Merlin Bell Phone systems (if you remember or were born that far back) and in some cases continues to be used out of pure corporate inertia.