How to connect CAT 5 or 6 to a modular telephone jack

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How to connect CAT 5 or 6 to a modular telephone jack?

I need to connect an 8C8P jack to a 4-conductor telephone-style jack, at
both ends of the cable..  

Two basic questions:  

A) Terminology,   Does RJ45 just refer to 4-conductor modular telephone
line connectors, that are on the ends of the cord from the phone to

Or does it refer to the connectors on the ends of ethernet cables, too?
like  8C8P.

If the latter, is there a name that means only the 4-conductor
connectors two paragraphs up?  

B) Functionality.   A while back nice people in another group suggested
in order to shut my window more**, that I replace the wire which goes
from my telephone NID, network interface device, outside my house, up
the wall and in the window straight to a Y-connector and then to my
phone and my DSL modem, that I replace it with a flat or superflat
ethernet cable.**   But it suddenly dawned on me that my DSL modem
expects a 4-conductor RJ45 plug/  And I just checked and so does the
NID.  They are not wide enough for 8C8P.

So I need some kind of adapter.  But I can't find an adapter yet.  If I
get what is described as an in-line coupler,
or even
( product link shortened)
will I be able to plug a piece of 4-conductor phone-style modular cable
into the 8-conductor jack, with good electrical contact?

Or could I take a piece of CAT5E or CAT6, cut off the end, and put a
4-conductor RJ45 telephone-style connector on the middle 4 wires?   No,
right, because they are shielded.  

And if I take off t he shielding, won't the wire underneath be thinner
than what is normally used with the 4-conductor RJ45 plugs?  

Or could I take a short piece of 4-conductor wire with an RJ-45 on both
ends, cut off one of them and connect an 8C8P plug in place of it.  That
would work, I think, but I don't think my connecting tool can handle
8-pin connectors.  I have to check on that.  

What can I do?  


**Details:   (The phone wiring inside my house is screwed up -- I've
spent hours trying to find the problem. Sometimes it works and sometimes
it doesn't, so I've stopped using it --- and even if it were good, it
comes in through  the basement, but the DSL modem is on the 2nd floor
and I wanted the wire to go straight to the DSL modem (orignally a
phone-line modem for dial-up),   So it goes up the front of the house
and through the window, but the wire I'm using is so thick that the
window and storm window won't shut all the way -- This is fine in the
summer but not the winter --  and if it did shut all the way, the
aluminum frame of both the window and the window frame would likely
weaken the signal using regular, unshielded, untwisted modular phone
wire*** or round 4-conductor white wire, the kind used inside interior
walls for extension phones., so that's why I was urged to switch to
CAT5E flat or superflat. )

***When I did use regular modular wire like what goes from the wall to a
phone, my download speed was consistently 1/3 of what it is consistently
now.  The window shut okay, however.  

Re: How to connect CAT 5 or 6 to a modular telephone jack

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In my (limited) experience, the RJ45 8-position 8-conductor connector is
used for network connections and the RJ11 6-position 2-conductor
connector is used for residential single-line telephone connections.  

If you have a multi-line telephone, you need connectors with more
conductors, like the RJ14 and RJ25, although they still have 6

--    St. Paul, MN

Re: How to connect CAT 5 or 6 to a modular telephone jack

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Ah, that's one term I needed to know, RJ11.    Thanks.  

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No I just have a single line phone**.  Maybe a 6P2C connector will fit
in the jacks at the NID and the the DSL modem.  I'll look again, and I
may have an RJ11 with which to check.  

But even if it fits, I still need a way to get from RJ45 to RJ11 at each

 ** although the NID itself is wired with two plugs, each with 2 wires.
And then there is a cable going to the basement that has at least 8
colors, that goes to an easy-connection device,  I don't know where the
4 extra colors come from, but that's just a curiosity anyhow.   I didn't
pay much attention to all this when the wires worked, because I only had
one line, but now that they don't work, I've unpllugged one of those
4P2C plugs and plugged in my own wire.  

Re: How to connect CAT 5 or 6 to a modular telephone jack

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Using this, I wikied for 3 of the connectors and found out they are
called   "registered jacks", RJ.   I guess all the other jacks are not
registered and will be deported as soon as the rules are set.    I got
redirected to

It lists: "modular connectors:

    eight-contact 8P8C plug (used for RJ45, RJ49, RJ61 and others)
    six-contact 6P6C plug used for RJ25
    four-contact 6P4C plug used for RJ14 (often also used instead of
6P2C for RJ11)
    four-contact 4P4C handset plug (also popularly, though incorrectly,
called "RJ9", "RJ10", or "RJ22")

RJ11, RJ14, and RJ25 can be plugged into the same six-pin 6P6C jack,
pictured."  [That's what I t hought, but it says nothing similar for

So I just have to find an RJ45 female to RJ25 male adapter.   I see
there is a bunch of stuff.  I'll find one I'm sure.  

Thanks again.  

Re: How to connect CAT 5 or 6 to a modular telephone jack

micky wrote:
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I see a splitter device here.

Ethernet 8 wire cable is arranged in 4 pairs and supports
communications at 125MB/sec using GbE.

If you use the splitter idea, it reserves four pins (1,2,3,6)
for 10/100BT Ethernet (no more GbE), and of the remaining four wires,
it arranges two of the wires for the RJ11 phone line. On the RJ11
(like, with six pins), the middle two pins might be "line 1".
You don't have to use the RJ45 jack of course, and could
use a splitter like this, as a RJ45 to RJ11 adapter.

You would need to purchase such a splitter, as intended for
your own country. I would not buy a "BT splitter" for usage
in Canada or US, because there might be some subtle difference
in how they wire stuff there. And vice versa. It might be
which pins on the RJ11 they use, which could differ. I think
mine, the center two pins would be the ones I use.

Since the wires are arranged in pairs, if you have excess wires
to work with, you have the choice of routing Tip and Ring over
a single twisted pair. Or putting Tip on a wire in one pair,
and Ring on a wire in the other pair. I don't know which of those
choices is most appropriate. If you buy the splitter concept,
someone has made this decision for you (as to which wires
of 4,5,7,8 have Tip and Ring).


When I rewired my phone wiring here (due to low data rates),
at that time I could buy four wire untwisted cable at the store.
I drilled a hole in a closet in the room I'm in, and routed
the wire from the basement, through a drop ceiling area, then
up through the hole in the floor. I didn't get creative, and
just stuck with the wire colors as I found them. (Preserved
wire colors on both ends.) By disconnecting the old phone wire
network at the demarc in the basement, things worked a lot
better. In the room I'm in, I used one of those square RJ11 boxes
with the four screw terminals on the back. The screw terminations
accept solid wire provided by the cable I bought. Mine doesn't
look exactly like this, but this illustrates the screw termination

                                  4 wire
    TelcoWire --- Basement(demarc) ----- computer room -+- filter --- phone
                                   X                    +-- ADSL --- router ...
                                   +-- all other house jacks (dead)

That's how I fixed mine up. The "All other house jacks" have
a corrosion problem, and getting the jacks off the wall, some
of which are painted down, is a non-starter. The old jacks
were just left sitting there, like decorations.

My phone company used to provide a multi-page primer on the web,
for doing your own phone wiring. The phone company charges $99
to step inside your house, to correct errors. (The $99 is for
the "truck roll".) But if you make no wiring errors, you're
allowed to do your own house wiring here.


Re: How to connect CAT 5 or 6 to a modular telephone jack

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This is very interesting, and I have a new CCTV system to install. The
old one with coax cable is obsolete and the new one uses IP cable of
the Cat5 or Cat6 variety.   I am laying the cable myself but there are
so many types available that I am confused about the right type.
The cable length will be 50 metres (170ft) from the PVR to each camera
and most cabling will be indoors.  The DC or AC cable is already there
so The IP cable will not carry any voltage.   Which cable to use?
There are so many grades available.    The cameras are

Re: How to connect CAT 5 or 6 to a modular telephone jack

Peter Jason wrote:

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    250 MHz and is suitable for 10BASE-T, 100BASE-TX (Fast Ethernet),
    1000BASE-T/1000BASE-TX (Gigabit Ethernet)...

    100 MHz and is suitable for 10BASE-T, 100BASE-TX (Fast Ethernet),
    and 1000BASE-T (Gigabit Ethernet).

    1000BASE-T uses all four cable pairs for simultaneous transmission
    in both directions through the use of adaptive equalization and a
    five-level pulse amplitude modulation (PAM-5) technique. The
    symbol rate is identical to that of 100BASE-TX (125 Mbaud)

That tells you (maybe), that the cables are all backward compatible
with regard to 10/100/1000 networking. One difference, is what
happens when you bundle the Ethernet cables together. For example,
installers at work would take huge trunks of cables, and put
nylon wraps around them. This is bad from a crosstalk perspective,
and if there is enough crosstalk, it might require retransmission
of a TCP/IP packet.

So if you go Cat6, the difference would be visible to instrumentation,
when fat bundles of Cat6 are assembled. Cat6 also has headroom for
potential higher rate transmission (but with an attendant reduction
in max cable length).


In this article, you can see that again, the Cat5-Cat5e-Cat6 comparison
is like "Good-Better-Best" in towels at Sears.

    "For this measurement the filter is a fifth-order Butterworth
     with a 3-dB cutoff at 100 MHz."  [That suggests the PAM-5 is carried
                                       in 100MHz of bandwidth...]

Based on what I read there, I would select *either Cat5e or Cat6* .

The Cat6 would be for the purpose of putting in a real estate brochure
for the house, that it has been "upgraded to Cat6". In other words,
it's a nice to have, for the day you're running some 10GBE protocol
over shorter cable lengths. But the Cat5e will likely solve the
IP camera wiring problem of today. People generally don't
recommend going cheap on cables, because once they're in the
walls, there's nothing you can do with them. Sure, you could run
conduit, to support pulling them or something, but in a lot of
cases these cables will just be (carefully) stapled down. If
you're doing that, use an appropriate fastener that won't
cut the cable.

And when I suggest Cat5e or Cat6, I'm trying to put GbE cabling
in your walls, suited to all GbE applications. Some day, a high
resolution camera might need more than 12.5MB/sec transfer rate,
at which time you want GbE. The low-resolution cameras now, might
well be 100BT with MPEG compression, and able to keep the data rate
in the 3-5MB/sec range.


This is not an IP camera. It's coaxial.

It uses HDCVI transmission, and I couldn't find any documents
which didn't just waffle about it. Like this one. Apparently
HDCVI is bidirectional, with most of the bandwidth in the
recording direction, but there's some capability in
the other direction for control. One forum, some users
compared recorded quality, and the HDCVI is a little soft.
Implying as you would expect, some sort of compression
and signal conditioning at the camera end. No idea what
kind of signal is present on the cable. There's no reason
an IP camera could not do better, as the IP camera is
working with a shorter cable length, and not solving the
same problem this one is (extreme reach).

You can see the back of the camera here, with coaxial connector
and female input power connections.

Maybe you had some other IP camera in mind ? With an IP
camera, you can use PoE for powering, if you need the
entire solution to be carried by one cable.


Re: How to connect CAT 5 or 6 to a modular telephone jack

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Thanks Paul, I'll order the Cat5 from my old CCTV installer because
it's the one they use all the time.   I'm going to buy all the
hardware from them and do the installation, buy a packet of 4 IP
addresses, and then have them commission the system of two cameras
upgradable to four.   This will save much money.

Yes the camera brochure they supplied was for the old coax system, and
now they suggest this IP one...
or at least something very similar.

Re: How to connect CAT 5 or 6 to a modular telephone jack

Peter Jason wrote:

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Draw me a diagram of your intended networking setup.


This is what I'd do. I don't know what software you'd
use on the Public side, while using your remote computing device.

                     LAN                 WAN
   Cam#1 ---| POE capable   |--- Cable Modem --- remote viewing app
   Cam#2 ---| router box ?  |   (Port forward
   Cam#3 ---|               |   to port on NVR)
   Cam#4 ---|               |
                        |               |
        NVR computer ---|               |

The idea would be, the NVR computer records the content
of the four video feeds. The four video cameras could
connect at 100BT rates. The NVR computer has a GbE connection
(so I need a GbE router box with POE). The POE is so
the cameras don't need a separate power feed (optional).
The NVR needs enough bandwidth for four feeds in and
one feed out (5X camera bandwidth), which I'm guessing
gets pretty close to needing to use GbE. 1X camera
bandwidth goes to the WAN side, while viewing.

Once the video is stored on the NVR, the remote viewing application
logs into the NVR. This requires port forwarding a particular
port, so that an external attempt to connect, gets forwarded
to the serving software running on the NVR.

Using the remote viewing app, you select one of the four cameras
for viewing.

The idea behind this setup, is only one public IP address is needed.

If you want to do it the following way, you'll need deep pockets.
No router at all. This would be a way of using four public IP addresses
in the routable range (not 192.168). The remote viewing application would
connect by issuing the correct Dynamic DNS address like or, where DDNS
maps the symbolic address to the numeric one. So now we have
four Cable Modems and four coax cables running to the
pole on the street. And four Cable Modem connection bills
to pay each month.

   Cam#1 --- Cable Modem#1 --- remote viewing app

   Cam#2 --- Cable Modem#2 ---

   Cam#3 --- Cable Modem#3 ---

   Cam#4 --- Cable Modem#4 ---

The NVR idea does some multiplexing and concentration of a sort,
inside the home, and reduces the externally facing stuff to
just one connection.


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