# Cable topology



## balanga (Jan 16, 2018)

I'm moving to a cable ISP from fibre optics and am a bit confused as to how I can make the most of it... Basically the property has a single cable coming into the property and has a splitter feeding cables into two rooms. One has a TV decoder, the other has a cable router supplied by the ISP. I'm not sure if I can do anything with that router - I don't have login details and am not sure if I would break something if I tried resetting it. I would like to have a wired network in the room with the TV but don't know if that is achievable. I see that the TV decoder has been assigned an IP address so it has Internet access and I'm wondering what would happen if I added my own cable router... would it get an IP address from the ISP? Is there any way I can connect up the two rooms?


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## SirDice (Jan 16, 2018)

The TV signal is usually out-of-band, i.e. it's not on the same network as your internet connection.

Most of the time you get a normal ethernet cable connection. Plug that into a router or a FreeBSD machine. Then on the other side of that router you can build a LAN just like normal. There's really nothing different compared to a cable modem/router except the way you're actually connected (fibre instead of cable).


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## balanga (Jan 16, 2018)

I guess I didn't express myself clearly... I have a cable from the ISP coming into the house to which there are cables to two rooms connected via a splitter. An ISP supplied cable router is connected to one of the cables in one room. Apart from using a Cat 5 cable how can I get connected a wired connection in the other room. If I installed my own cable modem would that connect to the ISP and auto configure itself?


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## SirDice (Jan 16, 2018)

For starters, you don't use a _cable_ modem (or router). It's specifically for cable networks (DOCSIS). Fibre networks don't use DOCSIS so a _cable_ modem is useless.


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## PacketMan (Jan 16, 2018)

The signals on the coax cable are in different frequency bands, no different than radio stations in the air.  So you cannot mess your TV by screwing with modems.  The splitter simply puts all of the signals on multiple cables; there is no difference in the signals except the power level will be lower. Split too many times and the signals will be too low to use.

To use the ISP supplied modem/router simply put into the LAN port, and you should be able to use DHCP. NOTE: if its a modem and not a router you will get a public IP address, and you will need to supply your own NAT/firewall based router.  If indeed its a router (both functions can co-exist inside the same device) then you should see that you have a private IP address.

Regarding having a 'LAN' in your place, over the coax wires, the only real way to achieve this is by using what is called a MoCA modem.  I have three of these in my house and they work great.  I use existing coax and attached three MoCA modems. The coax cables from units #2 and #3 go back to #1. At the #1 unit there is a splitter.  I get approx 600Mbps of Ethernet throughput over the coax; not to shabby. Now for some important notes:  I used coax that did not have TV signals on them, but I understand MoCA will work fine co-existing with TV signals because it uses different RF band.  Also you can't assume the signals flowing in your house / apartment.  As well, for the benefit of others, if you are in an apartment building, you have to be sure any and all cables are inside your place and in your control otherwise you have a security issue.  Assuming you are good to go there, then generally speaking your topology should look like this:

Cable ISP modem >> NAT router >> Ethernet connections >> MoCA modem#1 >> coax cable >> MoCA modem#2 >> Ethernet connection.
To use a 3rd MoCA modem: MoCA modem #1 >> coax splitter >> MoCA modem #3 >> Ethernet connection.

This is really the only way you can use existing coax cable to build you own home LAN.  Using additional cable modems will not work, unless the ISP offers such a service where they have their modems configured in such a way. I do know newer version of DOCSIS does provide L2 bridging services/functionality to modems, but I have yet to hear of an ISP providing LAN services inside a house using multiple modems.

Hope this helps.


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## balanga (Jan 16, 2018)

Thanks PacketMan - far more information than I can handle, but I'll keep reading it over - some of it may sink it ....

This is the supplied ISP modem:-

http://www.normann-engineering.com/products/product_pdf/premise_equipment//technicolor/tc7230.pdf

I'm unable to log into it and was wondering what would happen if I did a reset, but maybe I would be unable to reconfigure it.
I guess my best option of having a wired network in the other room would be to use a powerline extender, if you don't think I can install my own router


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## ronaldlees (Jan 16, 2018)

balanga said:


> Thanks PacketMan - far more information than I can handle, but I'll keep reading it over - some of it may sink it ....
> 
> This is the supplied ISP modem:-
> 
> ...



Moca devices are really expensive.  So, if you're on a budget, there's the passive devices.  I've never tried them, and don't know if they really work - but do a search for "Passive Ethernet Extender for Coax" and you should find some of them, which are about the price of a WiFi dongle.


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## usdmatt (Jan 16, 2018)

I would save the hassle and just run ethernet over powerline.

I know nothing about cable but would there be any possibility of removing the splitter, directly joining the incoming cable with the cable to the tv room (ideally using a junction box made for the purpose), then just re-using the splitter in the tv room to give you both tv & modem/router in that room?


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## PacketMan (Jan 16, 2018)

Why not call the ISP, ask them what that devices does (i.e modem and/or router)? Why try to sneak around them? And ask them if there is a user interface that you can have access to? I know lots of ISPs that provide a router will provide access to the 'user' menus.

I tried powerline extenders, and generally speaking it sucks and I don't use them. Low bandwidth capabilities, and generally low performance / stability.  Depending on where you live will affect the wiring in your building.  In North America, our homes are wired twice. There are two 'hot wires', not one.  Each hot wire is 120VAC, but each is opposite in the sine-wave cycle (some say 180 degrees out of phase but that is not technically correct) thus giving you the 220VAC for your stove, clothes dryer, and other heavy load appliances.  What does this mean to powerline extenders? What this means is if you plug one extender into an outlet on "side A" and another extender into an outlet on "side B" there is no way for them to communicate directly, since the two sides two not touch each other directly. Thus there are only two 'paths' for the powerline signals to reach each other: (1) through the power company transformer that feeds your (and your neighbor) house, and (b) through the appliances I just mention. The transformers is a huge inductive/magnetic device, and the the appliances in your house have huge resistance currents going through them, so very harsh and 'unfriendly' to powerline signals.  Unless your two outlets are on the same 'side' and wired on short runs, the performance is generally disappointing.


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## balanga (Jan 16, 2018)

ronaldlees said:


> Moca devices are really expensive.  So, if you're on a budget, there's the passive devices.  I've never tried them, and don't know if they really work - but do a search for "Passive Ethernet Extender for Coax" and you should find some of them, which are about the price of a WiFi dongle.



Thanks for pointing them out - I didn't know such things existed, but they did not see as cheap as you suggested.

Is this what you mean?


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## ronaldlees (Jan 16, 2018)

balanga said:


> Thanks for pointing them out - I didn't know such things existed, but they did not see as cheap as you suggested.
> 
> Is this what you mean?



I've never seen those, but they're not passive.  They require a power supply.  But - they're somewhat interesting I think. Thanks for the link!

I have no idea how they're set up - maybe they use a MC10EL89 "differential fan-out to coax" chip, or something like that, which is probably a lot cheaper than what the MoCA devices use ...

Would like to know.


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## balanga (Jan 16, 2018)

usdmatt said:


> I would save the hassle and just run ethernet over powerline.
> 
> I know nothing about cable but would there be any possibility of removing the splitter, directly joining the incoming cable with the cable to the tv room (ideally using a junction box made for the purpose), then just re-using the splitter in the tv room to give you both tv & modem/router in that room?


er 
What I wanted was wired Internet access in both rooms. Ethernet over powerline is probably my best option....

One thing which puzzles me is that these devises are rated at, say 500Mpbs, but if you have a computer with a 1Gb NIC and it connects to a router over a powerline connector the link speed will only be 100Mbps... or have I got that wrong?


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## usdmatt (Jan 16, 2018)

Sorry, I wasn't sure whether you specifically needed Ethernet in both rooms, or had a need for Ethernet in the same room as the TV but could get away with wifi where the router currently is.

The speed you get is heavily dependent on the quality of the wiring and distance between the units. Just like the speeds quoted for WiFi it's usually impossible to get the full speed, unless you literally just connect the transceiver chips in each unit directly with a dedicated cable and get their absolute maximum rated performance. I also suspect many of them, again like Wifi, have a tendency to quote overall capacity (both ways added together) rather than actual link speed. (For instance you can buy wireless gear that says 1200Mbps!!, but really it tops out at 600Mbps if you actually want to use it full duplex.)


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## balanga (Jan 16, 2018)

ronaldlees said:


> I've never seen those, but they're not passive.  They require a power supply.  But - they're somewhat interesting I think. Thanks for the link!
> 
> I have no idea how they're set up - maybe they use a MC10EL89 "differential fan-out to coax" chip, or something like that, which is probably a lot cheaper than what the MoCA devices use ...
> 
> Would like to know.



I'm even more confused because this looks very similar to the above but is described as a MoCA adapter


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## ronaldlees (Jan 16, 2018)

balanga said:


> I'm even more confused because this looks very similar to the above but is described as a MoCA adapter



Yes, that's a little less money than what I've seen published for devces that use MoCA technology ... but still it's 100+ each, and you need at least two.


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## ronaldlees (Jan 16, 2018)

balanga said:


> Thanks for pointing them out - I didn't know such things existed, but they did not see as cheap as you suggested.
> 
> Is this what you mean?



It's been awhile since I looked for these, but this link may be what I've seen before.  Again, I don't know if they work, but they're cheap:

https://www.amazon.com/NE-SE01-020Q-Seco-Larm-Passive-Ethernet-Extender/dp/B01718U2KQ

It's cheap dongle priced for a pair of them. I think I read in the reviews that they're not very good when there's a TV signal on the same coax.


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## PacketMan (Jan 16, 2018)

balanga said:


> One thing which puzzles me is that these devises are rated at, say 500Mpbs



Assuming the vendor is not too slimy that means (a) the ethernet port will run at 1Gbps, and (b) the bandwidth throughput will be up to 500mbps through the powerlines in your house.  Mine are rated the same, and at best I get around 5 to 6 Mbps if I remember right.

It really depends on your requirements, as I've said before "what is the problem you are trying to fix".  If its getting unsecure low bandwidth ethernet access in a room where there are no other options then powerline just might be the ticket.  If you require more secure higher bandwidth access then Wifi, MoCA, or running your own CAT5/6 cable will be your options.


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## PacketMan (Jan 16, 2018)

...and this thread should probably be moved to Off Topic since its not directly about networking with FreeBSD.


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## usdmatt (Jan 16, 2018)

The passive adaptors seem to basically just be media converters. It doesn't look like you'd be able to use the cable for Ethernet, but still pass the TV signal over it as well? The other ones have cable in/out which suggest it can be put "inline"; I know nothing about this stuff though and can't seem to find anything that blatantly says "This device lets you send Ethernet and TV/Cable Internet signal over the same coax".


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## ronaldlees (Jan 16, 2018)

usdmatt said:


> The passive adaptors seem to basically just be media converters. It doesn't look like you'd be able to use the cable for Ethernet, but still pass the TV signal over it as well? The other ones have cable in/out which suggest it can be put "inline"; I know nothing about this stuff though and can't seem to find anything that blatantly says "This device lets you send Ethernet and TV/Cable Internet signal over the same coax".



I really don't know anything about them either.  But, sometimes the simple/cheap stuff works "well enough."  This is definitely not my endorsement  - because "too good to be true" has been a discovery made often.  But hey - maybe they'd work OK.  I don't want to lend any weight either way ...

But, one of the reviews states:

   "I purchased these to extend my internet data line to a room where I had a coax cable but no Cat5/6 ..." 

The reviewer indicated that he was successful, FWIW.


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## usdmatt (Jan 16, 2018)

> "I purchased these to extend my internet data line to a room where I had a coax cable but no Cat5/6 ..."



Yeah I can find a lot of examples of using existing coax cable in a house to create an ethernet network using this stuff. This should work great and is an obvious solution if you have existing unused coax cabling but no cat5/6. I'm happy to be corrected here by someone that actually has cable experience, but I just can't find anything that clearly states you can use them on coax that is also handling tv or cable Internet service. (assuming OP is actually using TV service coming in over the coax).


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## ronaldlees (Jan 16, 2018)

usdmatt said:


> Yeah I can find a lot of examples of using existing coax cable in a house to create an ethernet network using this stuff. This should work great and is an obvious solution if you have existing unused coax cabling but no cat5/6. I'm happy to be corrected here by someone that actually has cable experience, but I just can't find anything that clearly states you can use them on coax that is also handling tv or cable Internet service. (assuming OP is actually using TV service coming in over the coax).



For my sources, I have only the reviews from the link ...

And one of them agrees with you:  you can't use it simultaneously for ethernet and TV.

So, like you said, it's just a media converter, and has no protocol knowledge.  Being passive, that's reasonable.  Of course the OP could unplug the TV source, or switch it with a little coax switch to do internet, but that would be a hassle.  Sometimes cheap is a hassle  - and sometimes it doesn't work at all.  Sorry if you thought you were being corrected.  I don't know any more than you about these things.


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## aragats (Jan 16, 2018)

balanga said:


> If I installed my own cable modem would that connect to the ISP and auto configure itself?


Most ISPs register the modem's MAC address, and without that it will not be autoconfigured or allowed to get outside of the ISP's network. Most likely they will refuse to register another one for the same customer.


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## SirDice (Jan 17, 2018)

usdmatt said:


> Yeah I can find a lot of examples of using existing coax cable in a house to create an ethernet network using this stuff.


Before UTP there was coax (10BASE2 and 10BASE5). In theory you could use it but it's only 10Mbit. And there's an impedance issue with the cable too, TV coax cable is 75 ohm, network coax cable is 50 ohm. You're going to have a hard time finding a network card that supports 10BASE2 though, they've become quite rare. I think I may have an old ISA 3COM card stashed in a drawer somewhere that has MAU, BNC and RJ-45 connectors.  

But perhaps someone created a specific network adapter to piggy-back on the TV cable but I've never seen one.


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## usdmatt (Jan 17, 2018)

Yeah I remember the old coax networking and daisy chained connectors. I'm not talking about actually using that stuff directly, but using these MoCA devices to send Ethernet over coax, breaking it out to standard cat[56]/rj45 for the actual devices to connect to. I expect these things can easily pass more than 10Mbps (in fact they specify 1Gbps for MoCA 2 although I expect that's total capacity if you have multiple of these on the same coax run).

My question is whether it's possible to plug a coax carrying TV signal, and Ethernet into one of these devices, pass both signals over a single coax, then break out into Ethernet and TV at the other end. I suspect not which means in OP's case he could use the existing coax to get a decent network connection between the rooms, but not have the cable TV service in there as well.


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## Snurg (Jan 17, 2018)

I would strongly advise against using powerline.
At least if you have no detailed knowledge about your electric configuration topology. For example, there are still some 127V networks in some regions of Europe. The 220V you get from these are not true 220V to ground, instead this is the differential of two phases shifted 120 degrees, as PacketMan described. These have no real ground connection because the currents flow between two floating phases, and powerline will perform poorly because it has to go through the transformer and side channels like appliances. This will result in poor and inconstant performance, if it works at all.

Another possible problem results in that if your house is supplied with three phases, they could be distributed differently for load balancing. For example, if L1 supplies room A and L2 supplies room B, you won't get a powerline connection working (except maybe poor connection via side channels like three-phase appliances, heaters and the like ).

But the worst thing is that it can make heavy radio interferences, and if somebody complains about, say, bad radio reception, the local authorities can find where this comes from.
And if they find it's your powerline ethernet, you are responsible, and will have not only to pay a fine, but also get prohibited to use that again, possibly even getting your equipment confiscated.
Your local jusrisdiction might be slightly different, but afaik it's the same all over the world. If you are responsible, you have to pay.

This is the reason why there exist no such things which insert an additional networking band into a broadband cable. It would cause many issues, as it would inevitably distort the whole cable segment, causing much anger with people still using analog TV etc. This would be as punishable as causing distortions via RF emissions using powerline, as described above.

As SirDice said, coaxial ethernet is history, 10Base2, using RG58 or the like with 50 ohms impedance.
I had to maintain a big network of a German newspaper a quarter of a century ago. Total length of cabling was about a kilometer, with about 100 computers connected.
It was horrible task. So many possibilities for things to go wrong. And things went wrong often.
Bad terminations, weak connections, damages in the cables, defective network cards or MAUs. A single of these problems could put a whole segment of the network out of operation.
Luckily I had a specialized ethernet tester, showing problems like this, open connections, shorts, bad terminations etc and indicating the cable distance where the problem was.

When a problem occurred, I had to rush, as often dozens of journalists were waiting for me to find and fix the problem asap. This was quite stressy, as the premises were quite big.
For example, one day some plumbers drilled holes in the walls, and drilled into a cable. I had to hurriedly lay almost 100m temporary cabling through the stairways, connecting the remote floor to the servers again.

This I'd really suggest to lay an additional twisted pair ethernet cable. But, make sure to cut the grounding of the cable if your electric installation has no separate ground connection, which is often the case with older installations which have floating grounds.


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## SirDice (Jan 17, 2018)

One way you could try is to replace the existing 'old' coax cable. You tie a new coax cable _and_ an UTP cable to one end of the existing coax cable. Then from the other side pull out the old cable. If done properly the attached UTP and new coax cable will be pulled into and through the piping. Not to be taken lightly, and it definitely helps if you've done this before. It takes a bit of fiddling to attach the new cables to the old in such a way they won't come off or get snagged somewhere half-way through.


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## Snurg (Jan 17, 2018)

You could ask your local electrician. Pulling cables through cabling tubes as SirDice mentioned above is usually being done using glass fiber strings made exclusively for this purpose.
The electrician also can tell you whether it is advisable to cut the grounding from your ethernet cable (i.e. if you have floating ground).


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## SirDice (Jan 17, 2018)

Snurg said:


> Pulling cables through cabling tubes as SirDice mentioned above is usually being done using glass fiber strings made exclusively for this purpose.


Fibre usually gets "blown" into piping, it's called cable jetting. But both coax and UTP are usually sturdy enough to be pulled the traditional way.


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## usdmatt (Jan 17, 2018)

We pull cables with pull wires (sometimes an existing or spare bit of cable) all the time. Gets a bit frustrating when you use enough tape an elephant couldn't pull it off, and yet the second the cable goes out of sight it slips free with the slighted tug.

If you're pulling multiple cables it helps to attach them staggered so that you're not trying to get all the cable through together. (attach one cable to the existing one, then attach the second to the new cable further down so there's no point with all 3 cables together) Another trick is to strip the cables back 6 inches, fold a couple of the inner conductors over each other and back on themselves, then twist the excess. You end up with a link that is pretty strong, and also get the benefit that the join is actually slimmer than the original cable. (The most common issue is that you usually have a bump where the new cable is attached to the existing, which gets caught on everything).



> cut the grounding from your ethernet cable



Not sure what you're referring to here?


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## Snurg (Jan 17, 2018)

usdmatt said:


> Not sure what you're referring to here?


What I was referring to here is when the electric wiring is done with 2 wires only (one live, one ground), where the ground wire also gets connected to the earth connector in the wallplug.
In these cases you have sort of "floating earth".
Depending on the current, there is always a voltage drop along the wires.

For example, if there is a, say, 10amps load from an electric heater, then the earth connector on a 2-wire electric connection can get quite high voltage relative to actual ground level.
This is due to the wiring resistance causing voltage drop.
And now imagine a, say, ethernet cable connecting to another computer on another electric line, which has less load.
This is like a parallel circuit of resistances. The ethernet cable shielding will then serve as secondary ground wire, supplying a part of this load current.
Which it is neither intended nor rated for. Imagine that thin foil shielding and the thin ground wire of the CatX cables having to bear a current of, say, 5 amps...  ...this is a serious fire hazard.

And, sadly these two-wire electric installations are not that rare.
Thus especially in buildings with older electric installations one should check this out to be on the safe side.

To make sure there is no fire hazard, it is advisable in such cases to strip off a segment of the cable screening, cutting the ground connection between both ends of the cable while maintaining most of the RF shielding.
The data lines are fed through insulation transformers usually rated to at least 1kV, so they will not serve as conductors (unless the cable is defective due to internal shorts).

(The above applies *only* to ethernet patch cables! The situation and the necessary protective measures are different with other kinds of interface.)

BTW, usdmatt, great collection of tricks for pulling cables. I even sometimes soldered the wires being pulled out with these to be pulled in, results in a quite strong connection without bump.

Edit: Regarding the ground issue, I found a detailed article covering other aspects of that topic, too.


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## ronaldlees (Jan 17, 2018)

I remember pulling a 100' fish tape reel line through an outdoor conduit at 18 deg F, dragging a thick bundle of telco. The conduit was 175' in the air, on the side of a tower. It was "back and forth, back and forth" until our fingers were frozen. The run wasn't a straight shot either. Then we hoped there was no chafing, shorts, cursing, and redo (would have been the next day, for dang sure). House wiring?  No prob.


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## balanga (Jan 19, 2018)

Whilst on the topic of cable, can anyone tell me if I can add my own TV decoder in another room or does it have to be one provided by my cable provider? I notice that the decoder I have does have an IP address so maybe they can block devices which do not have known MAC addresses...


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## usdmatt (Jan 19, 2018)

Does the decoder have a private or real IP address? I'd expect the decoder to just use the Internet via the router rather than having its own connection. Your router appears to be a modem/router/firewall/ap so there's quite a few settings there you as an end user may want to change, so I'd be surprised if you aren't allowed access to it. There may be a section in the web interface showing connected devices which will tell you if the TV decoder is connected to it or not.

To be honest within 5 minutes of getting it, I'd have looked up the internal address of the router (default gateway in `ipconfig`/`netstat -rn`), and be trying default logins in the browser to see what I can do (or looking on the router itself for a label with the login details).

Of course depending on how clever the ISP network is, they could be identifying the modem in the TV decoder and attaching that to a dedicated VLAN with a NAT gateway. I wouldn't want to put the TV boxes on real addresses. Seems over complicated to provide two connections when the decoder could just use WiFi though.


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## SirDice (Jan 19, 2018)

balanga said:


> can anyone tell me if I can add my own TV decoder in another room or does it have to be one provided by my cable provider?


Your cable provider will be able to answer that. Some allow third-party decoders, some don't. And some will charge extra for each additional decoder.


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## SirDice (Jan 19, 2018)

usdmatt said:


> I'd expect the decoder to just use the Internet via the router rather than having its own connection.


With Ziggo (Dutch digital cable provider) the decoder has an IP address but it's connected to a separate network, it does not 'share' the internet connection.


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## balanga (Jan 19, 2018)

usdmatt said:


> Does the decoder have a private or real IP address? I'd expect the decoder to just use the Internet via the router rather than having its own connection. Your router appears to be a modem/router/firewall/ap so there's quite a few settings there you as an end user may want to change, so I'd be surprised if you aren't allowed access to it. There may be a section in the web interface showing connected devices which will tell you if the TV decoder is connected to it or not.



Unfortunately access to the router is not available. No login details are provided. This is the ISPs policy.


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