Modems and Routers - Computing and Networks

chiller15 · 29-11-2009, 15:20

Don't worry, this isn't a general query about what router and that, it's a more specific one.

I'm pretty computer literate, but there's been something about modems and routers that's been bugging me.

I know that the modem converts the signal coming down the line, such as analogue into signals that the router/network/computer can understand.

Now, DSL modems will only work with DSL routers, and cable modems only work with cable routers.

But if the modem does the job of converting the data...why aren't routers universal?

I really ought to know this stuff.

ForestChav · 29-11-2009, 15:33

Because all a router does is connect two networks together. Cable routers don't include a modem because here, the ISP (Virgin Media) provide this and they don't allow other modems on their network. With ADSL you can use any ADSL modem and the router often has a modem inside the box. That means if you can find an ADSL modem with no routing and an ethernet port, then you can use that with a "cable" router - the cable router is just a router, as opposed to a router/modem which won't work with a cable connection because the input is a phone line (RJ11) not an Ethernet port (RJ45).

chiller15 · 29-11-2009, 15:40

Ahh, so that's the only real difference, one has an RJ11 connection and the other is RJ45?

I know all about how routers work, and their purpose and what not, but it's just bugged me.

The senario I'm about to list, both places have seperate routers and modems...none of them are 'two in one' devices.

I only asked, because at my parents house, they're on Virgin Media, and using a Linksys WRT54G that I bought and setup for them. But now I'm living with my girl friend, she's on BT. I just wondered why I couldn't bring my Linksys here, and have it work. But evidentially, it wont.

RobAnt · 29-11-2009, 16:12

Essentially, yes.

Cable services are interfaced via a router which doesn't have a modem built in. ADSL and Dial-Up routers do, generally speaking, have a modem.

In fact, I know of very few dial-up routers, though, and they're expensive for the limited service they offer.

You can, of course, buy ADSL modems, which provide an RJ45 output so they can be used with cable routers. But I don't know of an ISP which provides such a modem. And those that do actually provide a single port combined ADSL modem/router, so it can be connected either directly to a single PC, or to a network hub or switch.

Strictly speaking, again, cable routers can be used without modems to merge networks together, which aren't on the Internet - but are in, say, a large corporate environment.

Read my tutorial at the top of this subject for a more detailed look at this subject.

TheBigM · 29-11-2009, 16:14

Technically they are called gateways not routers. Being pedantic routers let one network flow into another whereas a gateway joins up a LAN and a WAN.

Just think of ADSL routers like "cable routers" except that they have decided to put the ADSL modem inside of the router box for convenience rather than have to link them by network cable as one does on Virgin.

If you were to buy an ADSL modem (they come with a single ethernet port) that could plug into the WRT54G but life is simpler for everyone by having a combined modem/router where possible.

RobAnt · 29-11-2009, 16:19

Quote:

Originally Posted by TheBigM

Technically they are called gateways not routers. Being pedantic routers let one network flow into another whereas a gateway joins up a LAN and a WAN.

Just think of ADSL routers like "cable routers" except that they have decided to put the ADSL modem inside of the router box for convenience rather than have to link them by network cable as one does on Virgin.

If you were to buy an ADSL modem (they come with a single ethernet port) that could plug into the WRT54G but life is simpler for everyone by having a combined modem/router where possible.

Gateways/Routers semantics. They aren't different, just a different way of expressing the same thing. They're usually sold as routers.

What is a WAN but a network of networks?

It could be argued, I suppose, that a Router includes services that most gateways don't - such as a DHCP server.

Rowdy · 29-11-2009, 16:48

From pedants corner: strictly speaking, a modem is what we now call a dial-up modem, i.e., it converts a data stream into sound waves and vice-versa (modulates/demodulates). A "DSL modem" is not a modem at all, though we still use the word.

Orbitalzone · 29-11-2009, 17:47

Quote:

Originally Posted by Rowdy

From pedants corner: strictly speaking, a modem is what we now call a dial-up modem, i.e., it converts a data stream into sound waves and vice-versa (modulates/demodulates). A "DSL modem" is not a modem at all, though we still use the word.

hehe, I thought I was going to be smart and state this and found you beat me to it

TheBigM · 29-11-2009, 19:44

Quote:

Originally Posted by Rowdy

From pedants corner: strictly speaking, a modem is what we now call a dial-up modem, i.e., it converts a data stream into sound waves and vice-versa (modulates/demodulates). A "DSL modem" is not a modem at all, though we still use the word.

You realise we don't have sound waves travelling down telephone lines - never have done. It has always been electrical signals. Sound waves are only between handset and mouth/ear.

It is still acceptable to call them modems because they are converting the networking signal to one that can travel down either phone lines or co-axial depending on whether you have xDSL or cable.

chiller15 · 29-11-2009, 19:54

How, for example, on a telephone line that doesn't have a modem. Say I have a phone, but no Internet access, did the analogue transmissions get converted into electrical signals?

Loobster · 29-11-2009, 20:04

Quote:

Originally Posted by chiller15

Now, DSL modems will only work with DSL routers, and cable modems only work with cable routers.

Incorrect. A DSL modem presents as ethernet, just as a cable modem does.

A DSL router has an integrated modem, so you don't see it as a seperate device.

But if you had a seperate DSL modem, you can use the same ethernet router (inaccurately sometimes called a 'cable' router) as you would with a cable modem.

Loobster · 29-11-2009, 20:10

Also I don't really subscribe to the term 'gateway' because it's a made up marketing term designed to make a given device sound more grandiose.

All gateways are routers, by defenition. Granted some devices do more than simply route packets, but they still route packets, just the same.

Rowdy · 29-11-2009, 20:31

Quote:

Originally Posted by TheBigM

You realise we don't have sound waves travelling down telephone lines - never have done. It has always been electrical signals. Sound waves are only between handset and mouth/ear.

Well, OK, but the signal produced by a modem is an exact replica of the sound wave - so, same thing, really. (Let's not get into digital v. analogue phone lines lol.)

Quote:

It is still acceptable to call them modems because they are converting the networking signal to one that can travel down either phone lines or co-axial depending on whether you have xDSL or cable.

Of course it is - just like it's acceptable to say "drive a car". "Drive" is something you do to an animal, not an inanimate object like a car. But, because we're doing essentially the same thing, we still use the same word.

Quote:

Originally Posted by Loobster

Also I don't really subscribe to the term 'gateway' because it's a made up marketing term designed to make a given device sound more grandiose.

All gateways are routers, by defenition. Granted some devices do more than simply route packets, but they still route packets, just the same.

How about "switch" then? Or more precisely, "level 3 switch"?

Loobster · 29-11-2009, 20:38

Quote:

Originally Posted by Rowdy

How about "switch" then? Or more precisely, "level 3 switch"?

Huh? Switches and routers are distinct and different devices.

Rowdy · 29-11-2009, 20:53

Quote:

Originally Posted by Loobster

Huh? Switches and routers are distinct and different devices.

But the differences are getting a little.........well, fuzzy. Quite a good PDF about it here.

Loobster · 29-11-2009, 20:58

Although managed switches (i.e. something you can create a VLAN on) are more sophisticated than unmanaged switches, they still only restrict traffic within a LAN, rather than connecting two LANs or LAN and WAN together.

ForestChav · 29-11-2009, 22:07

Quote:

Originally Posted by Loobster

Incorrect. A DSL modem presents as ethernet, just as a cable modem does.

A DSL router has an integrated modem, so you don't see it as a seperate device.

But if you had a seperate DSL modem, you can use the same ethernet router (inaccurately sometimes called a 'cable' router) as you would with a cable modem.

So basically what I said then

29-11-2009, 15:20	#1
chiller15 Forum Member Join Date: Oct 2009 Gender: Male Location: Liverpool Services: Sky+, VM 10Mb, Q6600, 4GB DDR2, 74GB Raptor, 8800GTX, X-FI Posts: 1,065	Modems and Routers Don't worry, this isn't a general query about what router and that, it's a more specific one. I'm pretty computer literate, but there's been something about modems and routers that's been bugging me. I know that the modem converts the signal coming down the line, such as analogue into signals that the router/network/computer can understand. Now, DSL modems will only work with DSL routers, and cable modems only work with cable routers. But if the modem does the job of converting the data...why aren't routers universal? I really ought to know this stuff.

29-11-2009, 15:33	#2
ForestChav Forum Member Join Date: Jul 2006 Gender: Male Location: Nottingham - Chavland :s Services: VM 10Mb, Sky+, WinHomeServer, Win7, N95, PSP, Squeezebox Duet LOSE THE GAME Posts: 22,932 Blog Entries: 8	Because all a router does is connect two networks together. Cable routers don't include a modem because here, the ISP (Virgin Media) provide this and they don't allow other modems on their network. With ADSL you can use any ADSL modem and the router often has a modem inside the box. That means if you can find an ADSL modem with no routing and an ethernet port, then you can use that with a "cable" router - the cable router is just a router, as opposed to a router/modem which won't work with a cable connection because the input is a phone line (RJ11) not an Ethernet port (RJ45).

29-11-2009, 15:40	#3
chiller15 Forum Member Join Date: Oct 2009 Gender: Male Location: Liverpool Services: Sky+, VM 10Mb, Q6600, 4GB DDR2, 74GB Raptor, 8800GTX, X-FI Posts: 1,065	Ahh, so that's the only real difference, one has an RJ11 connection and the other is RJ45? I know all about how routers work, and their purpose and what not, but it's just bugged me. The senario I'm about to list, both places have seperate routers and modems...none of them are 'two in one' devices. I only asked, because at my parents house, they're on Virgin Media, and using a Linksys WRT54G that I bought and setup for them. But now I'm living with my girl friend, she's on BT. I just wondered why I couldn't bring my Linksys here, and have it work. But evidentially, it wont.

29-11-2009, 16:12	#4
RobAnt Forum Member Join Date: Jun 2003 Location: South West Services: Virgin Broadband, TV, Phone Posts: 8,867	Essentially, yes. Cable services are interfaced via a router which doesn't have a modem built in. ADSL and Dial-Up routers do, generally speaking, have a modem. In fact, I know of very few dial-up routers, though, and they're expensive for the limited service they offer. You can, of course, buy ADSL modems, which provide an RJ45 output so they can be used with cable routers. But I don't know of an ISP which provides such a modem. And those that do actually provide a single port combined ADSL modem/router, so it can be connected either directly to a single PC, or to a network hub or switch. Strictly speaking, again, cable routers can be used without modems to merge networks together, which aren't on the Internet - but are in, say, a large corporate environment. Read my tutorial at the top of this subject for a more detailed look at this subject.

29-11-2009, 16:14	#5
TheBigM Forum Member Join Date: Aug 2004 Location: moon Posts: 7,055	Technically they are called gateways not routers. Being pedantic routers let one network flow into another whereas a gateway joins up a LAN and a WAN. Just think of ADSL routers like "cable routers" except that they have decided to put the ADSL modem inside of the router box for convenience rather than have to link them by network cable as one does on Virgin. If you were to buy an ADSL modem (they come with a single ethernet port) that could plug into the WRT54G but life is simpler for everyone by having a combined modem/router where possible.

29-11-2009, 16:48	#7
Rowdy Forum Member Join Date: Mar 2007 Gender: Male Location: At the bottom of the garden Services: Freeview, O2 Broadband Posts: 3,236	From pedants corner: strictly speaking, a modem is what we now call a dial-up modem, i.e., it converts a data stream into sound waves and vice-versa (modulates/demodulates). A "DSL modem" is not a modem at all, though we still use the word.

29-11-2009, 19:54	#10
chiller15 Forum Member Join Date: Oct 2009 Gender: Male Location: Liverpool Services: Sky+, VM 10Mb, Q6600, 4GB DDR2, 74GB Raptor, 8800GTX, X-FI Posts: 1,065	How, for example, on a telephone line that doesn't have a modem. Say I have a phone, but no Internet access, did the analogue transmissions get converted into electrical signals?

29-11-2009, 20:10	#12
Loobster Forum Member Join Date: Mar 2003 Services: Windows 7 x64, Q6700, 8GB DDR2, 1TB Spinpoint, GeForce 8600GTS Posts: 10,063	Also I don't really subscribe to the term 'gateway' because it's a made up marketing term designed to make a given device sound more grandiose. All gateways are routers, by defenition. Granted some devices do more than simply route packets, but they still route packets, just the same.

29-11-2009, 20:58	#16
Loobster Forum Member Join Date: Mar 2003 Services: Windows 7 x64, Q6700, 8GB DDR2, 1TB Spinpoint, GeForce 8600GTS Posts: 10,063	Although managed switches (i.e. something you can create a VLAN on) are more sophisticated than unmanaged switches, they still only restrict traffic within a LAN, rather than connecting two LANs or LAN and WAN together.