Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What Problem did the Invention of Hubs, Switches & Routers Solve?

  1. Sep 18, 2010 #1
    Hey guys, I just started a networking course and I'm pretty bogged down with information that I'm trying to put into a rational context.

    From my understanding, networking first began with the telephone line, which is pretty straightforward. You have the sender and the receiver. Then there was the problem of sending text information, so from that demand, came the modem, which worked on the telephone line, and so that was also straightforward.

    What I can't quite wrap my head around yet is hubs, switches and routers.

    I think my difficulty stems from not having a clear understanding of the problem that hubs, switches and routers solve. What exactly was the limitation of merely a modem based network? Why was there a demand for further technologies like hubs, switches and routers?

    My understanding is that hubs are a simpler and less intelligent technology.

    The next step up would be switches

    And then the next step in evolution was routers.

    But I'm not clear on the difference between hubs, switches and routers. I did google this info, and I found the explanations difficult because like I've been emphasizing, none of the explanations focus on the problems that these technologies solve.

    So that's where I need you guys.
  2. jcsd
  3. Sep 18, 2010 #2


    User Avatar
    Science Advisor

    The key point you're missing was the transition from a circuit-switched network to a packet-switched network. In the old modem days, when two users were connected by a modem, they tied up a line whenever they were connected. Not only did they tie up the line whether they were communicating or not, but the available capacity of the line was far higher than what they were actually using. Also, there are only so many wires, and there are far more potential users than wires (hence those annoying busy signals). Imagine if when you were using the highway, nobody else could use it until you were done. With a packet-switched network (using hubs, routers and switches), everybody can share the same lines, and they send information in packets, where each packet has an address that tells the routers and switches where to send it. The bandwidth available to everyone goes way up, and the busy signals pretty much go away.

    Try reading this:
  4. Sep 18, 2010 #3
    Keep in mind that ethernet is just one type of network topology. Networking is constantly evolving. There are various types of networks, though ethernet and tcp/ip is king. Back in the old days when pc networks were young, there were several standards and each had its own pros and cons.

    You need to learn them just to understand networking and if you are taking a course, you will have to learn them. The various issues with each type of network technology impact how you plan and implement your network.

    Before you learn hubs, routers, and switches you need to understand the basics. And that is what is a broadcast domain and a collision domain. This concept is the why a hub, switch and router exist. ( well it is a bit deeper, but it is the why ).

    You also need to learn the layers of TCP/IP. The layers are a key to all of this as well.

    So study collision domains, broadcast domains, and the tcp/ip layers. Understand each layer. ( understand what occurs and what protocols operate at each level ).

    Once you do that, post and I will take you down the path.
  5. Sep 18, 2010 #4
    also post any questions you have while studying those concepts and I will clarify them.
  6. Sep 18, 2010 #5
    Hi phyzguy and Aireborne18,

    Alright, that was great, thanks for that. Still unsure about some things, but I feel I've progressed.

    Ok, I will focus on those subjects, thanks.

    Very nice of you, thanks. Look out for this thread or other network related threads by me in the near future then! I will post some more, no doubt.
  7. Sep 18, 2010 #6
    Alright Airborne, or anyone else, question for you:

    I was thinking about the difference between hubs and switches. What I understand about hubs is that they indiscriminately give (to every computer they are connected to) whatever they receive. However, what I don't understand is the situation where you would need to set up a hub.

    My understanding of sending info to people is that everything exists on a server outside of your home. So if I'm living in my parents basement, sending my Dad an email upstairs is not about the email traveling from my computer to his computer upstairs, but rather, the email travels from my computer, outside of my home, all the way to a server which is possibly in another state, and then once the email is stored on that server, then the email makes it's way back to my house and into my fathers gmail or outlook account.

    So I can't quite wrap my head around what hubs do. Does it have anything to do with shared folders? For instance, if I want to share a folder of pictures on my hard drive with my Dad's computer upstairs, does a hub connect our hard drives together so that what exists on my hard drive can be duplicated, sent and stored on his hard drive?
  8. Sep 18, 2010 #7
    Also do not think about the internet at this point. Start with you have 2 computers and you connect them with a crossover network cable. Then add another computer. You then will start introducing a need for various networking components and various devices.

    You are thinking about this the right way. Really you are.

    At the core of this there is always the common issue of connecting computer A and B. It is easy when you only have two computers. When you add a hundred computers to the network you are still interested in being able to connect computer A and B, but also computers A to 100.

    Always think back to the basic two computers connected. It is basically two wires, send and receive. That is what it boils down to.
  9. Sep 18, 2010 #8
    Okay I was posting while you were posting..

    Forget the internet.

    Okay think about all of this as the send and receive wires in my previous post. In your house you have more than one computer, so you cannot just connect one network cable between two computers? So that is where a hub comes in. It basically is a way to share the send/receive wires across more than 2 computers. All the computers on the hub are all operating on the same set of send/recieve wires.

    The issue is that the hub does nothing more than just share the send/receive wire. It does not process any packets. Whenever a computer wants to send information, all of the computers must negotiate on their own. ( okay there is half and full duplex, but more on that later ).

    So what is happening with a hub is that you have one circuit with all of the computers on that circuit. And only one computer can transmit on the circuit at a time. If that happens you get errors. As you can see the more computers on this hub, the slower it will be, because there will be alot of overhead incurred each time a computer wants to transmit over the circuit.

    That is where switches come into the picture. Hubs are just simply a device create one large circuit. A switch is smarter. A switch basically pretends like it is a bunch of circuits. So each computer only has to negotiate with the switch, so each computer has its own circuit with the switch, and it does not have to worry about negoiating with every computer on the hub to get attenction.
    The switch handles it. Each port on the switch is its own little circuit.

    Let me know if I confused you
  10. Sep 18, 2010 #9
  11. Sep 18, 2010 #10
    Hi Airbonre,

    Can you actually send information to another computer with just a crossover cable? Don't you need some kind of device to generate transfer speed of some kind?

    How can I add a third computer to two computers connected with a cable. We need a device of some kind, don't we?

    Do you mean that adding a third computer requires some kind of device, but only two computers can be networked without a device?

    Here's the thing, the only experience I have with networking is using servers to access info that is stored on that server. I also know that when I send an email, it goes to the server and is stored on the server before it's sent to the intended destination.

    What you're talking about is eliminating the server as a factor, which I find confusing, because I don't have any experience with server-excluded networking. In my experience, a server is always the intermediary, the middle man. All things come and go through the server. To talk about networking in any other context is confusing for me, so I was hoping maybe you could give me some practical examples, some instances of where one might actually want to link two computers together with a crossover network cable. Is it for sharing a hard drive or folder between two computers in the same house?

    I always thought though that sending and receiving involves some kind of device, such as a modem, that somehow creates a transfer speed. Can a simple crossover network cable send coherent signals across to another computer? I am not familiar with this.
  12. Sep 18, 2010 #11
    If you are connecting two computers, you can use the network port and buy what is called a crossover network cable.

    Yes you need a device to add computers. That is the hub.

    But what you need to really grasp is that there are levels to the network. You have physical, logical, and eventually software layers. When you learn networking you need to start at the bottom and work up the layers.

    In its basic form the network is a pair of wires connecting one computer to another. The more computers that must talk over the pair of wires, the more networking equipment you need.

    And when you start connecting to other networks ( like the internet ), then you need devices for that.

    But since you are learning, you need to understand the basics here. And that is the TCP/IP stack and the concept of broadcast domains, and collision domains.

    As you work up the layers in the TCP/IP stack you add more functionality and protocols.
  13. Sep 18, 2010 #12
    You asked what problem was solved.. Well you learned a hub solved the problem of connecting more than two computers. It also has issues ( collision and broadcast domains will explain those issues ).

    The issue is that it extends the two wires to alot of computers. Only one computer can talk on the two wires at a time.

    ( Forget the how they talk to each other, you need to work up to that level ) The more you understand of the two wires connecting a bunch of computers, the easier it is to understand the more complex issues and devices. They are all designed to solve the performance and distance limitations of the two wire concept. And they also help the packets negotiate the maze created.
  14. Sep 18, 2010 #13

    Math Is Hard

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I don't know if it is helpful to mention, but my teacher sometimes called hubs "repeaters". It basically reinforced the idea that hubs are pretty stupid, they just take incoming information and repeat it across the channel, with no involvement in determining a destination for the data.
  15. Sep 18, 2010 #14
    I made a jpeg of a hub connecting three computers:


    Based on the model in the image above, can you give practical examples of the very lowest level send/receive functions? Perhaps if I understand those lower level functions, and the needs that create the demand for those functions, I would see new problems based on new demands created by new desires which create new problems to be solved.
  16. Sep 18, 2010 #15
    The issue is that the hub is not really a discrete device like you have pictured, and you need to understand that each connection is a twisted pair. And in your drawing, there is only one twisted pair that all of the three computers share..

    They are all on the same segment, or circuit. Or one common shared piece of wire. So what is the issue with that? Only one can use the wire at a time.

    The repeater comment above is correct.

    So if any computer wants to talk to another, they must fight each other for exclusive use of the shared piece of wire.

    Have you studied the TCP/IP stack? Do you know what layer 1, 2, and 3 are?

    Did you read up on a collision domain? Well you have drawn one. The 3 computers are constantly fighting for the one piece of wire.
  17. Sep 18, 2010 #16
    Before any of the file sharing or other higher level function can occur, like computer 1 sharing a file to computer 3, they must be able to negotiate for usage of that common piece of wire. Only one can be sending, and only one can be receiving.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook