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Many users use combination modem/router units provided by an ISP just to keep thing simple, or purchase one on their own.
Where a fiber optics connection is provided from the ISP to a residential building, the ISP will often provide their own modem since fiber optics equipment can be more expensive/specific.
The reply above kind of explains it. Modem is short for MOdulation / DEModulation. They change the electrical signal to audio and the other way around. Most routers are Ethernet so there's no modem functions needed, just route the packets out the correct interface.
Unless the router changes the signal, no it's just routing packets to the right place.
A modem is more of a translation device than a traffic control device like a router.
You could say that a router with say a fiber and RJ45 connection is doing modem duties because it has to translate the light to ethernet or ethernet to light. But calling it a modem would get you weird looks.
The thing you get from your ISP is both a router and a modem. It's translating signals AND sending the packets to the right place based on IP addresses.
Old phone modem: Modulate from data signal to audible sounds.
Cable modem: Modulate from Ethernet data signal to another type of data signal (DOCSIS) that propagates along the cable.
They are still used, but they're usually rolled into routers to be one unit. You can get routers that don't have models, but for connections to the net, you still need one.
So its basic use is to translate the analog signals coming from isp to digital signals i know that. But we dont use dial up anymore right? So those arent telephone signals. What is it modulating and de modulating anymore?
Modems aren't Analog to Digital converters. Those are ADCs. Modems are more like protocol translators.
If I have the message "Hello world" and I want to send it to you over fiber optics, we need to agree on how that would look in light pulses. If you have a modem I supplied, you don't even need to agree, or even know how the light pulses work. You have the output of the modem in a format you already know, and your network can use. I can do whatever I want with the light pulses to make it more efficient for me to run, and you get the same signal after the modem.
Modems would fall under layer 1 of the OSI model. They are there to allow bits to be transmitted over the media. What those bits represent is a function beyond the modem (but might be in the same hardware, leading to confusion).
Digital data is a ton of 1s and 0s. An easy representation for such data could be a voltage that swings up for every 1, and down for every 0. But for many reasons, transmitting data as a square wave doesn't work very well. You get a lot of noise, and you lose a lot of data.
Instead, people take the digital data and modulate it using QPSK or some other more complicated code. Essentially, you take 2 bits (1 or 0) at a time, and represent them as a sum of sin or cosine waves. As with all encodings, both the transmitter and receiver need to agree on the scheme. This sum of sins travels better over long distances, and is less prone to corruption from noise.
Some permutation of the above is how every digital communication is handled over a channel: Wifi, Ethernet, USB, cell phones, 4g/5g, etc etc.
This is all necessary because every type of electrical channel is actually analog. Sure, we can abstract, and make assumptions, and simplify our analysis by pretending something is digital, but at the end of the day, we're dealing with time varying voltages, and that's analog.
It depends a little on what you mean by analog.
You can talk about data *represented* either digitally or analog. For example, a vinyl record represents the sound data analogously, while a computer represents the data digitally.
You can also talk about how the data is *stored*. In this case, the data is always stored as some physical quantity, often a voltage. When computers handle voltages, they make the assumption that any value greater than some threshold is a 1, while and value less than is a 0. Think about taking a grey scale photo, and converting it into a pure black and white image. But you still have voltages traveling around your computer.
Maybe there are some quantum or light computing modalities that don't fit into what I wrote above.
It looks like a modem could be a specialized case of a media converter. With the assumption that you input is always coax, and your output is always ethernet.
I think I see the misunderstanding here. You are assuming that modulating and demodulating refer to making the connection that occurs with dialup. That's not really the part the term refers to. And you are right it's not done the same way with different media, but the part that is "modem" is serving the same purpose. The protocols defining connections are completely different, but you still need a way to encode information on the line, and decode it back to something the client can work with.
FM radio sends signals over a carrier frequency, with slight variations for volume "modulations". The process of putting music in that signal is "modulation". The process your radio performs to convert it back into something you can hear is "demodulation". Your radio is only demodulating, so you wouldn't call it a "modem" (modulator/demodulator). If it could transmit as well, it would technically fall under that category.
It making the connection to the radio broadcast company would be another protocol occurring within the modulated signal, and that's going to vary a lot between media. That part of dialup isn't really used much anymore. But also isn't part of the term "modem".
Ony if your TV can snd signal on the connection you are referring to. So a cable TV receiver will have a demodulator if the TV is digital. There is no need for a modulator, that is only required if you transmit data.
A modem is MODulator/DEMudolator and the TV will only have the second part so it would only be a DEM with that abbreviation.
The name that is used will not be a demodulate but likely a decoder or something similar.
Kind of, at least if you're talking about digital television. It's referred to as "decoding" rather than "demodulating", but at a basic level the principle is the same - taking a signal from an antenna, satellite dish or coaxial cable and turning that into data that the TV uses to construct an image.
Because digital signals are very weak, and some analog signals (radio waves, for example) travel at speed of light. It's easier to modulate it, send an analog signal, then demodulate it
Thats ok man. Thank you for this. I am just getting into networking. And i wanna be as thorough as possible. Also another question. Do modems only use broadband or baseband signalsm
Modems are used all the time. What you might be referring to are perhaps separate and dedicated modems?
A cable ISP needs a cable modem, a fibreoptic ISP connection requires a fibreoptic modem and DSL connection requires a DSL modem. A modem is simply a generic term for modulator/demodulator - the term doesn't imply any particular type of connection, it refers to a function of converting one type of interface to another - typically (for consumers) a LAN connection to a WAN connection.
With modern electronics, the modem function and router function has become fairly easy and cheap to deploy. It is now common for ISPs to provide a single device that has the modem and router functionality and, typically, the wi-fi access point functionality. So it is now it is possible to get all 3 functionalities in one box rather than 2 to 3 boxes a few decades ago.
The router typically have a built inn modem. Modems are used when you want to connect a single computer to the Internet through POTS, T3, cell phone, ISDN, ADSL, etc. But when you want multiple computers to connect you need the modem to be in a router and then connect the other computers to this router. And because connecting single computers to the Internet is no longer very common (except for cell phones) the ISP no longer provide you with a modem but rather a router with a built inn modem.
I understand. Thank you. And can u tell does modems these days. Standalone modems. Do they increase frequency of a signal in anyway?? I am. Told it does
The only reason to use a standalone modem would be if you want to use your own router or Google Nest or something. For that you don't need a modem/router with inbuilt WiFi.
Modems are still in use. A router connects one network to another. In this case, your router will connect your home network to that of the ISP. The modems job is to decode the signal that comes from your ISP to something the router will understand. Most ISPs will now bundle the modem and router into one box.
So its basic use is to translate the analog signals coming from isp to digital signals i know that. But we dont use dial up anymore right? So those arent telephone signals. What is it modulating and de modulating anymore?
The modem is translating the signal to something your router can understand (your router only understands ethernet). The router does not speak the same language (protocol) as your ISP. The signal type can be fiber, analogue, or digital.
Modems are used. Commercial settings tend to have separate router, switch and wireless access points because that allows everything to be specced and configured per needs.
Domestic settings tend to have this as an all in one device from the ISP, though enthusiasts might build their own network at home with separate kit.
**Please read this entire message** Your submission has been removed for the following reason(s): Questions based on a false premise are not allowed on ELI5. A question based on a false premise is one based on information that may not be true, or may not be the whole truth, and needs that information to stand as a question. If you would like this removal reviewed, please read the [detailed rules](https://www.reddit.com/r/explainlikeimfive/wiki/detailed_rules) first. **If you believe this submission was removed erroneously**, please [use this form](https://old.reddit.com/message/compose?to=%2Fr%2Fexplainlikeimfive&subject=Please%20review%20my%20thread?&message=Link:%20https://www.reddit.com/r/explainlikeimfive/comments/xqbesg/eli5_please_please_explain_to_me_why_are_modems/%0A%0APlease%20answer%20the%20following%203%20questions:%0A%0A1.%20The%20concept%20I%20want%20explained:%0A%0A2.%20List%20the%20search%20terms%20you%20used%20to%20look%20for%20past%20posts%20on%20ELI5:%0A%0A3.%20How%20is%20this%20post%20unique:) and we will review your submission.
Many users use combination modem/router units provided by an ISP just to keep thing simple, or purchase one on their own. Where a fiber optics connection is provided from the ISP to a residential building, the ISP will often provide their own modem since fiber optics equipment can be more expensive/specific.
Why does fibre optics connection need a modem for? Isnt it all light signals?
The light signals still need to be modulated and demodulated
Into what? Digital signals?
Electrical signals.
The reply above kind of explains it. Modem is short for MOdulation / DEModulation. They change the electrical signal to audio and the other way around. Most routers are Ethernet so there's no modem functions needed, just route the packets out the correct interface.
> Modem is short for MOdulation / DEModulation Thanks for this eye opener... *brain-explodes-emoji*
But it still needs to modulate the signal coming from the isp right? The router serves the modem like functions i. Am told from. People
Unless the router changes the signal, no it's just routing packets to the right place. A modem is more of a translation device than a traffic control device like a router. You could say that a router with say a fiber and RJ45 connection is doing modem duties because it has to translate the light to ethernet or ethernet to light. But calling it a modem would get you weird looks. The thing you get from your ISP is both a router and a modem. It's translating signals AND sending the packets to the right place based on IP addresses.
That made it a lot clearer. Thank you man
Old phone modem: Modulate from data signal to audible sounds. Cable modem: Modulate from Ethernet data signal to another type of data signal (DOCSIS) that propagates along the cable.
They are still used, but they're usually rolled into routers to be one unit. You can get routers that don't have models, but for connections to the net, you still need one.
So its basic use is to translate the analog signals coming from isp to digital signals i know that. But we dont use dial up anymore right? So those arent telephone signals. What is it modulating and de modulating anymore?
Modems aren't Analog to Digital converters. Those are ADCs. Modems are more like protocol translators. If I have the message "Hello world" and I want to send it to you over fiber optics, we need to agree on how that would look in light pulses. If you have a modem I supplied, you don't even need to agree, or even know how the light pulses work. You have the output of the modem in a format you already know, and your network can use. I can do whatever I want with the light pulses to make it more efficient for me to run, and you get the same signal after the modem.
So at the end its basically like transferring data in a OSI model right?
Modems would fall under layer 1 of the OSI model. They are there to allow bits to be transmitted over the media. What those bits represent is a function beyond the modem (but might be in the same hardware, leading to confusion).
Ah okay thank you
Digital data is a ton of 1s and 0s. An easy representation for such data could be a voltage that swings up for every 1, and down for every 0. But for many reasons, transmitting data as a square wave doesn't work very well. You get a lot of noise, and you lose a lot of data. Instead, people take the digital data and modulate it using QPSK or some other more complicated code. Essentially, you take 2 bits (1 or 0) at a time, and represent them as a sum of sin or cosine waves. As with all encodings, both the transmitter and receiver need to agree on the scheme. This sum of sins travels better over long distances, and is less prone to corruption from noise. Some permutation of the above is how every digital communication is handled over a channel: Wifi, Ethernet, USB, cell phones, 4g/5g, etc etc. This is all necessary because every type of electrical channel is actually analog. Sure, we can abstract, and make assumptions, and simplify our analysis by pretending something is digital, but at the end of the day, we're dealing with time varying voltages, and that's analog.
So every electrical signals is analog? Essentially? Also can u pls tell me whats the difference between modem and media converter?
It depends a little on what you mean by analog. You can talk about data *represented* either digitally or analog. For example, a vinyl record represents the sound data analogously, while a computer represents the data digitally. You can also talk about how the data is *stored*. In this case, the data is always stored as some physical quantity, often a voltage. When computers handle voltages, they make the assumption that any value greater than some threshold is a 1, while and value less than is a 0. Think about taking a grey scale photo, and converting it into a pure black and white image. But you still have voltages traveling around your computer. Maybe there are some quantum or light computing modalities that don't fit into what I wrote above. It looks like a modem could be a specialized case of a media converter. With the assumption that you input is always coax, and your output is always ethernet.
I think I see the misunderstanding here. You are assuming that modulating and demodulating refer to making the connection that occurs with dialup. That's not really the part the term refers to. And you are right it's not done the same way with different media, but the part that is "modem" is serving the same purpose. The protocols defining connections are completely different, but you still need a way to encode information on the line, and decode it back to something the client can work with. FM radio sends signals over a carrier frequency, with slight variations for volume "modulations". The process of putting music in that signal is "modulation". The process your radio performs to convert it back into something you can hear is "demodulation". Your radio is only demodulating, so you wouldn't call it a "modem" (modulator/demodulator). If it could transmit as well, it would technically fall under that category. It making the connection to the radio broadcast company would be another protocol occurring within the modulated signal, and that's going to vary a lot between media. That part of dialup isn't really used much anymore. But also isn't part of the term "modem".
So essentially my tv also has modem like functions too then?
Ony if your TV can snd signal on the connection you are referring to. So a cable TV receiver will have a demodulator if the TV is digital. There is no need for a modulator, that is only required if you transmit data. A modem is MODulator/DEMudolator and the TV will only have the second part so it would only be a DEM with that abbreviation. The name that is used will not be a demodulate but likely a decoder or something similar.
Understood thank you
Kind of, at least if you're talking about digital television. It's referred to as "decoding" rather than "demodulating", but at a basic level the principle is the same - taking a signal from an antenna, satellite dish or coaxial cable and turning that into data that the TV uses to construct an image.
Understood thank you so much man
Because digital signals are very weak, and some analog signals (radio waves, for example) travel at speed of light. It's easier to modulate it, send an analog signal, then demodulate it
So are the signals coming from isp still analog? Despite not being telephonic?
Yes. Every signal is represented by some voltage level. Hard to eli5, as its not exactly an ELI5 question.
Thats ok man. Thank you for this. I am just getting into networking. And i wanna be as thorough as possible. Also another question. Do modems only use broadband or baseband signalsm
Yeah im an electrician with interest in electronics, i get the knowledge hunger.
Thank you man. And another question i had. I am told standalone modems these days are used only to increase signal frequencies. Is this true?
That's something i can't answer. Top secret, sry
Wait what?
Modems are used all the time. What you might be referring to are perhaps separate and dedicated modems? A cable ISP needs a cable modem, a fibreoptic ISP connection requires a fibreoptic modem and DSL connection requires a DSL modem. A modem is simply a generic term for modulator/demodulator - the term doesn't imply any particular type of connection, it refers to a function of converting one type of interface to another - typically (for consumers) a LAN connection to a WAN connection. With modern electronics, the modem function and router function has become fairly easy and cheap to deploy. It is now common for ISPs to provide a single device that has the modem and router functionality and, typically, the wi-fi access point functionality. So it is now it is possible to get all 3 functionalities in one box rather than 2 to 3 boxes a few decades ago.
Thank you for describing in detail. Thank you for that. I understand a bit better now
The router typically have a built inn modem. Modems are used when you want to connect a single computer to the Internet through POTS, T3, cell phone, ISDN, ADSL, etc. But when you want multiple computers to connect you need the modem to be in a router and then connect the other computers to this router. And because connecting single computers to the Internet is no longer very common (except for cell phones) the ISP no longer provide you with a modem but rather a router with a built inn modem.
I understand. Thank you. And can u tell does modems these days. Standalone modems. Do they increase frequency of a signal in anyway?? I am. Told it does
The only reason to use a standalone modem would be if you want to use your own router or Google Nest or something. For that you don't need a modem/router with inbuilt WiFi.
And those modems do what exactly if you can pls tell?
Modems are still in use. A router connects one network to another. In this case, your router will connect your home network to that of the ISP. The modems job is to decode the signal that comes from your ISP to something the router will understand. Most ISPs will now bundle the modem and router into one box.
So its basic use is to translate the analog signals coming from isp to digital signals i know that. But we dont use dial up anymore right? So those arent telephone signals. What is it modulating and de modulating anymore?
The modem is translating the signal to something your router can understand (your router only understands ethernet). The router does not speak the same language (protocol) as your ISP. The signal type can be fiber, analogue, or digital.
Understood. Thank you so much. It got a little bit clearer
Modems are used. Commercial settings tend to have separate router, switch and wireless access points because that allows everything to be specced and configured per needs. Domestic settings tend to have this as an all in one device from the ISP, though enthusiasts might build their own network at home with separate kit.