Convert RJ11 to ethernet cable?

Question

Can I convert this funny cable with 4 wires into an ethernet cable for connecting my laptop to the internet?

The cable currently has a white/yellow banded wire, a white/blue banded wire, an orange wire and a blue wire.

One of the ends is a BT connector and the other end is an RJ11 head with only 2 pins.

Solution

First of all: Yes you can, but it won't make you happy.

10Mbit/s Ethernet uses 2 pairs and works quite well over short distances with the kind of cable shown, you just need to crimp an RJ45 plug on it (using the pairs 1/2 and 3/6).

Now 10Mbit/s is not very fast, so you might want to go alternative routes. Assuming The idea behind using this cable is avoiding a recabling, you might want to consider Ethernet over powerlines, this works amazingly well in many home settings, the adapters (Devolo and TP-Link have worked for me) are cheap as chips.

EDIT

As requested in the comments, a few more details about the needed plugs:

Ethernet typically uses RJ45 plugs with 8 pins (1..8) carrying 4 pairs of wires. For historical reasons, these pairs are assigned to the pins this way: 1&2, 3&6, 4&5, 7&8. Older Ethernet connections use only the pairs 1&2 and 3&6.

So for a straight-through cable you need to connect pin 1 of one end with pin 1 on the other side, same with pins 2,3 and 6 and for a cross-over cable you need to connect 1-3, 2-6, 3-1, 6-2.

If the wires in the cable are paired (i.e. always two are twisted together inside the cable's protective mantle) honor this pairing when connecting the cables.

The mechanical process of putting the plug on the cable is called "crimping" and it is easily done with cheap "crimp pliers". If you don't have one, I recommend you just cut a cheap Ethernet patch cable in the middle and solder the two resulting "pigtail" half-cables to the ends of the old cable, using the orange/orange-white and the green/green-white pairs.

Comments

[theonlygusti]

My internet DLoad speed is only 5Mbps at best, but would having 10Mbit/s connection to router really damage that?

[Eugen Rieck]

Not at all! Routers are typically either 10/100 oer 10/100/1000 compatible

[user1686]

You can successfully run 100 Mbps over this, can't you?

[wysiwyg]

@theonlygusti Yes, see this Wikipedia article or this

[theonlygusti]

Do you mind explaining/linking to something which explains what "crimp an RJ45 plug on it (using the pairs 1/2 and 3/6)" means?

[theonlygusti]

I don't understand; what do you think I should do?

[Eugen Rieck]

Done, see edit.

[Eugen Rieck]

@grawity Most likely you can't: While 100Mbit/s uses only 2 pairs as well, the quality of the cable (i.e. its electric, inductive and capacitive properties) will not be good enough.

[user1686]

@EugenRieck: On an unrelated note, are crossover cables even permitted by GigE? Won't they confuse the auto-crossover negotiation already performed by LAN cards?

[Eugen Rieck]

@grawity All switches, NICs and Routers I know of will happily accept (but of course not need) them. Since most Gbit equipment is downward compatible to 100Mbit, where crossover cables are a usefull concept, this doesn't surprise me.

[user1686]

@EugenRieck: Does that apply both to partial crossover cables (where the 100Mbit pairs are crossed and the rest straight) and to full crossover (as you described)?

[Eugen Rieck]

@grawity The cable I described has only the 2 pairs. There is no crossover (I know of) of pairs 4/5 and 7/8

[user1686]

@EugenRieck: Ah, well, I meant this kind which keeps coming up in my googles.

[Eugen Rieck]

@grawity Ah - that's a "double crossover" ... in times, when a 4pair wall socket was sometimes used to transport 2x 100Mbit/s (with adapters), such a cable would create a crossover for both of those. When used with a "normal" single 100M, the second crossing would be meaningless, as the pairs are unused.

[Gene]

Talk to your Internet company first and find out what you need, see if they will provide it or go to a electronics shop to get it. Somehow simply patching a four wire line to an Ethernet plug to go into your computer doesn't sound like it will work.

[theonlygusti]

Sounds like it will work to me...

[Gene]

Ok, let us know how it went.

[ivan_pozdeev]

According to en.wikipedia.org/wiki/Fast_Ethernet#100BASE-TX, en.wikipedia.org/wiki/Gigabit_Ethernet#1000BASE-T and en.wikipedia.org/wiki/Category_3_cable, Cat3 has insufficient pass band for 100BASE-TX meaning if you use it, you'll get significant data loss and delays from transmission errors (which may or may not be tolerable depending on your definition of "decent"). 1000BASE-T also uses Cat5+ but achieves this by using all 4 pairs and much more complex (thus less interference-resistant) signal encoding.