Ethernet, Token Ring, and FDDI

There are 5 common parts that every network generally contain.  They are the Nodes, the cables, the connectors, the Network Operating System, and the Network Interface Card, or NIC.  NICs are the device that transfer the signals from the cables to the nodes, and are one of the more important aspects of networking you must understand.

Ethernet

Up until two years ago, Ethernet networks were the most common networks on the planet.  With the boom of the Internet, other network types have grown rapidly, but Ethernet still remains the easiest and most cost-effective networking topology.

Ethernet is usually installed as a bus or star architecture.  The bus architecture is the easiest to set up, as the wire runs from computer to computer and is terminated at each end.  The star architecture requires more cable and more work, but is easier to troubleshoot.  If a break occurs in the cable of a bus architecture, the network fails.  If a break occurs in the cable of a star architecture, only the network segment that contains that break fails.

Ethernet is a passive network.  All network traffic is delivered node-to-node.  That means the computers themselves transfer all the data, not hubs or routers.  They are also called CSMA/CD networkds, or Carrier Sense Multiple Access with Collision Detection.  That means that two nodes can not transmit at the same time.  If two nodes transmit data at the same time, the data collides and fails to transfer.  Therefore, Ethernet networks require the node to check for network activity before sending data.

IEEE 802.3

In order to standardize Ethernet, it is broken down into speed and cable types by the IEEE Standard number 802.3.  The standards within 802.3 are;

• 10Base2 - Can transmit at up to 10Mbps (Megabit Per Second) at distances up to 185 meters.  This connection method requires that a cable from another node connect to a T-Connector attached to the NIC, which in turn connects to another node or a 50ohm terminator.  (It is a bus topology.)  It is often called Thinnet or ThinEthernet, and uses coaxial cable to connect.

• 10Base5 - Also transmits at 10Mbps, but can send signals up to 500 meters.  It is referred to as Thicknet or ThickEthernet, and requires special connections between the cable and the NIC.  It is also a bus architecture, as the cable runs between nodes in a straight line.

• 10BaseT - Transmits at 10Mbps, but uses Unshielded Twisted pair cables.  It has a maximum of 100 meters of transmission distance, and can run in either a bus or start topology.

• 100BaseT - Transmits at 100Mbps the same distances as 10BaseT, but uses Sheilded Twisted Pair cables to transmit at faster speeds.

• 10/100/1000BaseF  - Uses Fiber-Optic cable to transmit upwards of 1 Gbps over several kilometers.  Fiber-Optic cabling is generally used as a backbone between networks, not a network itself.  It is expensive, and it's speed isn't needed for intra-network communication.  Therefore, you will most often see this topology used for high-speed inter-network connections.  

Token Ring

Token Ring is an IBM-created network topology.  It arranges nodes and network cables in order to form a ring or a loop.  As opposed to CSMA/CD where nodes check the network for activity before sending, Token Ring networks use a token to determine when a node can transmit.

The nodes in a Token Ring network actually don't physically look like a ring.  In fact, central units referred to as MAU's (Multistation Access Units).  That means that Token Ring is logically a Ring but physically a star topology.  Because it's physically a star, a single break in the ring doesn't take down the whole network.

The token is passed from node to node around the network in a particular direction.  When a node wished to transmit, it waits for the token to arrive, transmits it's data with the token, and then waits for the token to arrive again to transmit again.  This is called Token Passing.

Token Ring is also a guaranteed delivery networking system.  When a node transmits data with the token, it sends a special message inside the token.  When the token arrives at the destination, it reverses this special message and re-transmits the token.  When the token reaches the original sending computer, it can then tell if the data was sent properly.  If the token does not contain the changed message, the sending computer knows it must re-send the data.

FDDI

Fiber Distributed Data Interface is also a Ring topology, but uses two rings rather than one single ring.  It can transmit up to 1Gbps, and can send data up to 2 kilometers.  The reason for the second ring is for fault tolerance, and in other adaptations of FDDI to allow multiple tokens to pass at the same time.  

You should be aware of the basics.  Expect to see limited information on Fiber optics, FDDI, and token passing, but study more for the 802.3 standards and how Token Ring networks work.