fitz said:
And if you to go more deeper into it, you could go into the idea of bridges (which is technically what most cable/DSL "Modems" are.. but let's stay away from that right now.
Actually, I believe the word you are looking for is a Gateway, not a bridge.
A router is in fact, a layer three device that
routes information from one network to another network (or subnetwork) based upon IP addresses. SOHO routers (or routers that are used in homes and small offices) are technically
not routers at all, but are mearly gateways. Most SOHO routers include a switch (some include a wireless access point).
A gateway is a device that forwards information from one location to another location. It is your access point out of your network. Routers (commercial) are gateway devices, but are not consider gateways because they dynamically forward information to a destination based upon IP address where as gateways simply forward information to its next hop (which may be a router or some other device). A commercial router that statically forwards information to another point (just as with SOHO routers) would be technically considered to be a gateway.
Modems are also gateways. The purpose of a modem is to convert signals from one format to the next and transmit that information to its next location. Since a modem does not dynamically forward anything, rather is simply sends it to your ISP, it is considered a gateway.
Bridges are layer two devices that forward information based upon MAC addresses. Bridges do one of two things with a packet that enters it:
1. Sends the packet through another port if the destination MAC address is listed in the bridge's known MAC table.
2. Send the packet through an uplink port if the MAC address is NOT listed in the bridge's known MAC table.
Now, you are probably saying, "That sounds just like a switch." You would be partially correct. See, bridges and switches are the exact same thing, the only difference is in function. Bridges
DO NOT contain multiple ports. Rather, the contain an in port and an out port. The purpose of a bridge is to prevent broadcast traffic from a segment on your network from flooding traffic that does not need the information. For example, if I work in the accounting department and I'm sending information to our server which is also located in the accounting department, I can use a bridge to prevent the data from my computer from going to say, the marketing department since the bridge would notice that the destination MAC address is listed in its table and would not forward it through its out port. Switches, on the other hand, have multiple ports. They can be used to accomplish the exact same thing as bridges, but the purpose that is generally given to switches is to:
1. Prevent Broadcast Traffic off the switch and
2. Speed up the network since bandwidth between the ports are
NOT shared just as fitz said.
Repeaters are layer one devices that simply reamplify and retransmit a data single. A repeater can be used to extend your cabling beyond the limit of you cable. Repeaters (as with bridges) contain an in port and an out port. Now, you are probably saying, "Why do I care about repeaters." The reason is because a hubs is the
EXACT same thing as a repeater. The only difference here is that, just as with a switch to a bridge, a hub is a repeater with multiple ports. A hubs main job is to split a connection comming into it into several connections, amplify those connections, then send them out of the ports. Because a hub does nothing more than transmit data through its ports, the bandwidth through the ports are shared. This is also why you do not see "Gigabit Hubs."
Now, if you want the benefits of a hub (increase network distance) with the bandwidth control of a switch, you may consider a "Smart Hub." These devices do come in gigabit and are slightly more expensive than a switch.
But, if all you need is Gigabit ethernet, a switch is all you need.