Part IV:  Hubs and Switches
Hubs first gained popularity as the 10baseT standard was developed.  To describe what hub is, another name might fit better, and that is repeater.  A hub takes a signal from a node connected to it, boosts the signal’s strength and broadcasts it to all other nodes also connected to the hub.  The downside of this becomes that the CSMA/CD protocol still has to be used as collisions will frequently occur.  This is what the collision light on all hubs symbolizes in case you were ever wondering.  10Mbit and 100Mbit hubs have been developed, however there are currently no 1000Mbit hubs.  Also, hubs only allow for half duplex operation.  That is to say traffic can only flow at 10 or 100Mbit/s one way and not at these speeds simultaneously both ways.  The figure below shows a common setup with hubs:

A hub based network topology

Notice the inefficiency of this setup.  As the node on the right sends traffic into the network it will reach the first hub where it will then be transferred into all outgoing channels including the channel to the 2nd hub, where the signal will once again be strengthened and broadcast further on all outgoing channels.  This can lead to a major amount of broadcast traffic as well as numerous collisions.

A switch is similar to a hub, but it does not broadcast the traffic received from one connected node to all the other connected nodes.  Rather, the traffic only goes to the node for which it is intended.  The advantage of this is that each node is now on its own collision segment and does not have to worry about running the CSMA/CD protocol.

A switch based network topology

Since the traffic can now also be full duplex (full speed send and receive at the same time) collisions can really only occur inside the switch.  Thus the switch itself handles all of the collisions and also has buffers for incoming and outgoing traffic for each of the nodes.  Furthermore, a switch has the ability to filter traffic.  That is to say if the traffic is not meant to go through this particular switch it will not be passed on.  To pass or forward data on, a switch builds a table with MAC addresses and the corresponding port on the switch the data traffic would need to go through to reach that corresponding MAC address.  At the end, all these novel improvements over hubs present a more efficient network topology that offers better overall performance.

Summary & Conclusion
The table below gives a quick summary of past and current Ethernet standards and their length and cable requirements:

* denotes capability of full duplex transmission

This article’s attempt has been to demystify the workings of Ethernet and provide an insight of how far this networking technology that millions use daily has come from its conception in the 1970′s.  What does the future hold in store for Ethernet?  10 gigabit is on the horizon, but will copper be able to provide the necessary signal rate?  There’s no doubt in my mind that speeds will continue to ramp up as computers become more powerful and the Internet continues to grow with multimedia content

I hope this discussion has been insightful (perhaps also helpful) to some of you.  If you are interested in learning about Ethernet in greater detail, I strongly encourage you to check out the sources below.  Please leave your questions/comments on this article using the comment system found at the bottom of this page.

Sources:

Computer Networking:  A Top-Down Approach Featuring the Internet, third edition.  James F. Kurose and Keith W. Ross

Computer Networking, fourth edition.  Andrew S. Tanenbaum

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