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Networking: Hub, Switch, Modem, Router?
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Old 16-02-2008, 14:03   #1
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Networking: Hub, Switch, Modem, Router?

We see a number of posts where users are venturing into the world of wanting multiple computers, gaming consoles, and the like to all be able to connect to their boradband service. Trouble is the world of networking can be a daunting place, especially if you wander into that high street store and get bamboozled by the salesman who might not be that sure of what you are saying either. Let's try and get some clarity:

Modems

In the UK there are two main systems of residential broadband supply, via a cable connection with Virgin Media, or a BT type phone line (ADSL). To connect to the broadband system the user requires a modem (or in a few cases on cable a Set Top Box) to pass the signal between the phone or cable connection and the local computer. Modems work quite differently between cable and ADSL, and thus you can't swap your cable modem onto ADSL or vice versa. ADSL users can generally use and replace their own modems. Cable users cannot replace their modem, and must use the one provided by Virgin Media.

A modem is intended to only speak to one device (computer, game console or router) at a time. Some ADSL modems, will recognise that the connected device has been changed, cable modems will not. If a device connection is changed, simply reboot (power off for a few seconds then power up) the modem.

When a device is connected to a modem, the connected device is usually allocated an IP address by the modem. This IP address, is a numbered code which helps the connection to decide where to pass the various electronic signals. A modem can only allocate this single IP address.

Hubs & Switches

A hub is essentially a junction box for ethernet. Every signal it receives from one wire, will be passed to all the other connected wires and thus the devices at the end of them. This is old technology superceded by switches.

A switch is a smart junction box. It is capable of receiving a signal and realising that it only needs to go to one single device rather than all of the network, based on the mac addresses that it can see. The mac address is a hardware identifier for a networking component, such as an ethernet card. Switches are great for extending the capacity of a wired LAN so you can plug in more and more computers, with different port capacity and connection speeds widely available.

A hub or switch cannot be placed as the first connected item next to your modem. Switches and hubs cannot allocate IP addresses, nor masquerade multiple devices into the single IP the modem required, not deal with NAT (Network Address Translation) thus your modem would get confused. Expecting to see only one computer, the modem would instead see past the hub or switch trying to communicate with all the devices connected yet not knowing which is the one device that it can support.

Routers

The answer to connecting more than one computer or consoles to the same modem, lies in using a router. This is a clever box of tricks which will sit between your broadband line, and the various devices.

In simple terms, the modem sees the WAN (Wide Area Network or internet) side of the router and speaks to it, allocating the WAN port of the router the IP address. The modem does not need to know that there is stuff connected on the LAN (Local Area Network) side of the router. Indeed, as far as the modem is concerned there is only one device connected, the router as the modem does not communicate past it inot the LAN. It is the router's job to make the connection to the home computers, consoles or whatever. Routers are capable of speaking to multiple devices, and can allocate each of them their own local IP addresses. Thus the router will receive a signal from a device, and can decide if that signal goes to the internet presenting the computer(s) to the modem as if it were just the one device, performing NAT as required for the modem communications, or simply sending the signals to another computer on the LAN for file sharing.

There are two main classes of router, ADSL or Cable. An ADSL based router will often integrate a modem for use with the BT type connection. This means an ADSL router cannot be used on Cable Networks. However the cable router, having no inbuilt modem, can be used with cable or ADSL since it must connect, to a modem. Make sure you are getting the right type!

Router functions

Routers offer additional advantages, depending on the model. These features are usually controlled via a browser (internet explorer) type screen accessed from your LAN computer.

Basic wired routers will usually have an inbuilt LAN side switch of four LAN ethernet ports. This allows you to wire up 4 computers or consoles. If you want more connections, simply add a another switch to one of those LAN ports (I've seen networks of 30 computers set up this way, with switches daisy chained one after another). You can also add a wireless access Point to one of these wired ports, or indeed elsewhere on your LAN side network, or alternatively you can connect it to the homeplug to system (networking over your power socket wires).

Today, most domestic grade routers will include a Wireless Access Point, in addition to the wired ports. This simplifies the number of boxes you need. However, make sure that the wireless will run at the speeds and have the connectivity and security features you want. That's a separate topic. Most routers with wireless inbuilt can have this feature disabled.

Routers will frequently include a firewall. This helps to protect your network against intruders, however you may need to adjust the firewall to allow special applications to pass their traffic. Typically this is necesary for people home hosting web servers. using torrents and the like. You can disable the firewall completely, but why loose this protection?

Some routers allow parental type controls. This means certain computers can be prevented from connecting at all to the internet at certain times of day. Alternatively, by subscription, access might be blocked to unsuitable web sites.

Routers may have a QoS (Quality of Service) function. In other words traffic shaping for your home network. If one person is hogging all the bandwidth with their continuous downloads, you can limit that capacity so everyone else can have a share.

Typical Network Setup

The attached example diagram indicates how all these networking components could be used. Note that terms of use of many ISPs may not allow you to connect more than 3 or 4 devices to a single home connection.

Virgin Media's SuperHub

Please do not confuse the "Virgin Media Hub" or "Virgin Media Superhub" with the traditional computer network hub. The Virgin Media product is arguably misnamed. It is in fact a combined cable modem and wired / wireless enabled router.
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