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As I understand it, all devices capable of connecting to the internet these days either come with their own modem already inside them (like a modem in the motherboard of a PC, or the internal modem that comes with game consoles) or can have a small, external modem plugged into them via USB. That being said, what's the purpose of the modem inside of a hybrid modem/router, which seems to be pretty standard fare nowadays? And what's the purpose of having a modem connected between the router and the ISP? After all, don't the modems in the individual devices already do all the work?

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closed as too broad by Ƭᴇcʜιᴇ007, Tog, Moses, Carl B, Mokubai Nov 25 '13 at 22:20

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Its simply design for people who don't want 2 devices where one has the capability of both. There is no advantage of having a just a modem and a separate device working as a router instead of a modem + gateway built into the same device. –  Ramhound Nov 23 '13 at 19:30
    
Perhaps some ISPs will only permit their own modems to connect their network, and the available choice of combined wireless routers is crappy or expensive, or both? –  Joseph Quinsey Nov 23 '13 at 19:48
    
I have a slight feeling you're mistaking Ethernet ports with actual Internet access. But both previous comments seem right. –  Doktoro Reichard Nov 23 '13 at 19:49
    
@JosephQuinsey - Even if that was the case. In either you need either a DSL/Cable Modem or a DSL/Cable Gateway. In both cases you can use a router. –  Ramhound Nov 23 '13 at 19:52
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@Ramhound There are certainly benefits to two device. Expense of replacement and upgrade for one. With the rate wireless specs have evolved vs DSL or DOCSIS I would much rather spend $40 each upgrade cycle than the $80 - 150 of most gateways. There are also things like online support and flexibility, where the gateway is generally proprietary and hard to get support from anyone besides the ISP while it is under warranty. –  AthomSfere Nov 23 '13 at 20:14

3 Answers 3

Short answer to your last question: no.

Your title question should probably be turned around - "What is the purpose of a modem with a built-in router?", since the modem is the critical piece, while the router is just a very good enhancement.

Your devices have a network interface, not a modem. The modem connects you with your Internet Service Provider (ISP). It is programmed with all of the handshakes, login, password, anything the ISP requires to let you into their network.

Taking one device as an example: In the case of a PC, the network interface is often a separate card, or a "NIC", connected to the motherboard. Once the modem arranges the connection with the ISP, the simplest connection is to run an Ethernet cable directly from your PC's NIC to the modem. There are other options, to include wireless (which also requires a card, extra capability on the motherboard, or USB adapter).

The direct connection is also the least secure. This is where the router comes in.

For security, a hardware router is a very good idea... but it doesn't have to be a separate box. To help keep their customers more secure, many ISPs have begun providing modems with a router built in, especially when it's capable of wireless transmission. Or you can buy them retail.

I like having a separate router, because I'm old-school, with machines running cables to the four ports typically offered. Modems, whether equipped with a router or not, typically only have one port.

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None of those devices have a modem. They have Ethernet ports.

Ethernet ports, cables, switches, etc create a local area network (LAN). Wireless devices create a wireless local area network (WLAN). A router is commonly used configure and tie a LAN and WLAN together as well as to share an internet connection amongst them. The internet connection is commonly provided by a cable or DSL/ADSL/etc modem.

A combined router and modem reduces the the number of boxes / power supplies etc.

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The other is talking about the Cable/DSL gateways which are indeed modems with multiple lan ports instead of a single lan port. –  Ramhound Nov 24 '13 at 6:20

Actually most computers these days don't have modems in them, they have ethernet. Now ethernet Is a great choice for local area networks (after all that is what it was designed for) but standard ethernet has the range of a couple good football passes. If you want to run longer distances, you need another technology such as fiber, long range ethernet, dsl, or 'broadband cable'. these technologies need adapters to work with standard ethernet, and if you are going to spend the money for an expensive link, why don't you share it with all your computers, thus the popularity of routers.

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