Ethernet has two basic protocals. One being TCP/IP and the other being UDP.
TCP/IP is basically a guaranteed delivery. The receiver re-assembles the packets n the correct order even if they arrive out of order. There is error checking in this protocol.
That protocal isn't good for video and audio. In this protocol, packets might not make it. QOS or Quality Of Service was introduced to prioritize traffic.
Hubs just mix everything together. Everything connected sees all the traffic.
Switches on the othe rhand if you had 3 computers, A, B and C and one printer if A was printing B and C would not see that traffic.
Businesses will use a managed switch. They are classified as L1, L2 and L3 or Layer 1, 2 and 3. The Levels, basically define what they can do.
as the Internet matured, the role of the router, switch, hub, bridge etc has morphed a bit, Switches can perform router functions and VLAN's or Virtual LANS were created.
So, an IP phone would have a separate VLAN associated with that network. Traffic destined for a printer wouldn;t collide with voice traffic at all.
There is something called multicasting and unicasting. If you were "televising" (delivering a live performace via the Internet), it makes sense to have one source and many destinations. Unicasting, sets up a link between two devices,
So, there is a lot of stuff going on,
A simple bridge would be when traffic say travels via fiber.
In a home with a DSL modem, router, switch and Wireless. They can all be combined together, The wireless in generally used in Bridge mode, but Access point devices have a few different modes taht it can use. Bridge or Access Point mode. They can even set up ethernet to wireless to ethernet bridge. e.g. A printer could pass traffic via Ethernet-wireless-Ethernet to the printer and that wireless network is separate.
The router portion gets you out of subnet. Home routers use NAT to make all of your computers effectively routeable to the Internet if you allow. The public I address has services or PORTS associated with it. HTTP is port 80. If a request came in for port 80 of the public IP address, the router says, that goes to my http server on addresss 10.0.1.200.
DSL in bridge mode is quite unique, When traffic leaves the WAN port of the router, it travels via a DSL bridge to the DSLAM (A DSL telco thing). From there is travels using an ATM protocol ( a telco thing) and eventually to a router via ethernet. So, when you ping the IP address of your public IP from inside your netowork, the packet travels through the telco lines and ATM until the router at the end point responds. For me that router is located about 40 miles from me.
A ping packet sent from outside the network, wouldn't even see the telephone line or the ATM network.
So, there's lots of stuff going on,
What makes a lot of this possible is that every interface gets a unique MAC address. Unique makes it easier. The only thing that matters is that the MAC address is unique in the routeable segment. Thus you can CLONE MAC addresses of cable modems. With cable, everyone is on the same wire, so the cable company uses the MAC address to know it's you. If you change your cable modem, you either have to have the cable company re-authenticate you or just make the MAC address the same as your old cable modem.
DSL doesn't need that, since it's a different physical wire.
You create routeable segments with an IP address. some are public (visible to the Internet) and some are private (non-routeable to the Internet, just the local LAN).