Ethernet Tutorial
LANs
Networks are collections of separate computers that communicate with each other over a common cable or radio medium. Local area networks (LANs) tend to be confined to one geographical location, while wide area networks (WANs) tend to span many physical locations.
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Ethernet
Ethernet is the most popular LAN technology currently in use. Other popular LAN types include Token Ring, Fast Ethernet, Fiber Distributed Data Interface (FDDI), Localtalk, Ethertalk, and Arcnet. Ethernet is popular due to it's low cost, multitude of wiring types, and market acceptance.
The Ethernet standard is defined by the Institute for Electrical and Electronic Engineers (IEEE). The IEEE Standard 802.3 defines the rules for configuring Ethernet as well as the protocol that allow the computers to communicate.
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Protocols
Network protocols are standards that allow computers to communicate with each other. A protocol defines how the computers should identify each other on the network, the form that the data should take in transit, and how the information should be reconstructed once it reaches its final destination. Protocols also define how to handle damaged transmissions. IPX, TCP/IP, DECnet, AppleTalk, LAT, SMB, DLC, and NetBEUI are examples of network protocols.
Although each protocol is different, they all use the physical cabling in the same manner, which allows them to peacefully coexist. This concept is known as "protocol independence", which means that the physical network and the protocols are not directly connected.
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Media and Topologies
One of the most important parts of designing and installing a network is deciding on which cabling medium and wiring topology to use. There are four major types of media in use today: Thickwire, thin coax, unshielded twisted pair (UTP), and fiber optic.
Ethernet media are used in two basic topologies called "bus" and "star". The topology defines how a node (which is any device such as a computer, printer, or hub) is connected to the network.
A bus topology consists of nodes connected together by a single long cable. Each node "taps" into the bus and directly communicates with all other nodes on the bus. The major advantage of this topology is the easy expansion, by adding extra "taps", and the lack a hub. The major disadvantage is that any break in the cable will cause all nodes on the cable to loose connection to the network.
A star topology links exactly two nodes together on the network. A hub is used to collection point where many of the connections come together. The major advantage is any single break only disables one host. The major disadvantage is the added cost of a hub.
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Thickwire Ethernet
Thickwire, or 10BASE5 ethernet, was generally used to create large "backbones". A network backbone joins many smaller network segments into one large LAN. Thickwire made an excellent backbone because it can support many nodes in a bus topology and the segment can be quite long. It can be run from workgroup to workgroup where smaller networks can then be attached to the backbone. A thickwire segment can be up to 500 meters long and have as many as 100 nodes attached. New nodes are connected to the cable by drilling into the media with a device known as a "vampire tap". Nodes must be spaced exactly 2.5 meters apart to prevent signals from interfering with one another.
Thickwire is being replaced by thin coax and fiber optic cabling in most cases. The expense of the cable, coupled along with the expense of the vampire taps, has begun to eliminate this form of cabling.
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Thin Coax Ethernet
Thin coax, or 10BASE2 ethernet, offer the advantages of thicknet's bus topology, with reduced cost and easier installation. Thin coaxial cable is thinner and more flexible than thickwire, but it can support only 30 nodes per segment, and each node must be at least 1.5 meters apart.
A thin coax cable has BNC type connectors on both ends. You then connect the segments of cable together with a "T" connector, and connect the third connection of the "T" to the node. Each end of the long segment must be terminated with a 50 ohm resistor and grounded.
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Twisted Pair Ethernet
Unshielded twisted pair (UTP), or 10BASE-T ethernet, cable is a 4 pair cable which is very similar to telephone cable in both appearance and end connector appearance. It comes in a variety of grades, with level 1 being the lowest quality and level 5 being the best.
Level 1 and 2 cabling should only be used for voice and low speed transmissions (less than 5 Mbps). Level 3 may be used for data speeds up to 16Mbps, while level 4 can handle speeds up to 20Mbps. The finest cable avaliable, level 5, can handle speeds up to 100Mbps.
A 10BASE-T ethernet network uses a star topology, with each node being connected directly to a hub. The major limitation to this cable is a maximum calbe length of 100 meters, and that each node must have its own connection to the hub.
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Fiber Optic Ethernet
Fiber-optic, or 10BASE-FL ethernet, is similar to twisted pair. Fiber-optic cable can handle 100Mbps transmission speeds, but is not affected by electrical emissions or electro-magnetic interference . Lighting strikes, which can be transmitted by other cabling types, is not transmitted by Fiber-optic cable. The major advantage of fiber-optic cable is the 2 kilometer maximum length. The disadvantage being the higher cost of cable and equipment.
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Fast Ethernet
With the addition of large data steams such as real time video and audio, networks have begun to require high transmission speeds. The new ethernet standard established to handle this requirement is called Fast Ethernet, or 100BASE-T. It is defined by IEEE standard 802.3u, which raises the maximum speed from 10 megabits per second to 100 megabits per second. There are three types of Fast Ethernet currently avaliable:
100BASE-TX for use with level 5 UTP cable
100BASE-FX for use with fiber-optic cable
100BASE-T4 which has an extra two wires for use with level 3 UTP cable
Currently the 100BASE-TX standard has become the most popular due to its close compatilibity with the 10BASE-T ethernet standard.
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Hubs
A hub is a central point where multiple cables come together. A hub usually allows 8, 16, or 64 node connections to communicate. If any single connection disconnects or is having problems the hub can partition (remove from the network) it and allow all other nodes to continue to communicate.
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Tranceivers
Transceivers, also known as Media Attachment Units (MAUs), are used to connect nodes to the various ethernet media. Generally the transceiver allows the attachment of 10BASE-T or 10BASE-2 cable on one side, and the connection via a 15 pin D-shell connector, known as an Application User Interface (AUI), on the other.
The user would connect the AUI connection to the computer and the 10BASE-T or 10BASE-2 connection to the network media.
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Repeaters
Repeaters are used to connect two or more ethernet segments of any media type. They can be used to extend a segment beyond its maximum length or maximum number of nodes by restoring signal quality and timing. Repeaters can also be used to connect segments consisting of different media types together into one larger segment.
It must be noted that a repeater counts as a node on every segment to which it is attached.
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Bridges
The function of a bridge is to connect separate ethernets together. Bridges map the ethernet addresses of the nodes residing on each network segment and then allow only the necessary traffic to pass through the bridge. A bridge can also filter out certain traffic and prevent it from passing through.
When a packet is received by the bridge, the bridge determines the destination and source segments. If the segments are the same, the packet is dropped("filtered"); if the segments are different, the packet is forwarded to the proper segment. Additionally, bridges prevent all bad or misaligned packets from spreading by not forwarding them.
Bridges are called "store-and-forward" devices because they look at the whole ethernet packet before making their filtering or forwarding decisions.
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Switches
An ethernet switch is a bridge which can connect more than two segments together. The idea behind a switch is that it removes all unneeded traffic from each segment by only forwarding the traffic needed on that segment, which provides better performance on the network.
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Routers
Routers work in a manner similar to switches and bridges in that they filter out network traffic. Rather than doing so by packet addresses they filter by specific protocol.
An IP router can divide a network into various subnets so that only traffic destined for particular IP addresses can pass between segments. The price paid for this type of intelligent forwarding and filtering is usually calculated in speed of the network, because this protocol filtering usually takes more time than packet filtering.
Networks are collections of separate computers that communicate with each other over a common cable or radio medium. Local area networks (LANs) tend to be confined to one geographical location, while wide area networks (WANs) tend to span many physical locations.
--------------------------------------------------------------------------------
Ethernet
Ethernet is the most popular LAN technology currently in use. Other popular LAN types include Token Ring, Fast Ethernet, Fiber Distributed Data Interface (FDDI), Localtalk, Ethertalk, and Arcnet. Ethernet is popular due to it's low cost, multitude of wiring types, and market acceptance.
The Ethernet standard is defined by the Institute for Electrical and Electronic Engineers (IEEE). The IEEE Standard 802.3 defines the rules for configuring Ethernet as well as the protocol that allow the computers to communicate.
--------------------------------------------------------------------------------
Protocols
Network protocols are standards that allow computers to communicate with each other. A protocol defines how the computers should identify each other on the network, the form that the data should take in transit, and how the information should be reconstructed once it reaches its final destination. Protocols also define how to handle damaged transmissions. IPX, TCP/IP, DECnet, AppleTalk, LAT, SMB, DLC, and NetBEUI are examples of network protocols.
Although each protocol is different, they all use the physical cabling in the same manner, which allows them to peacefully coexist. This concept is known as "protocol independence", which means that the physical network and the protocols are not directly connected.
--------------------------------------------------------------------------------
Media and Topologies
One of the most important parts of designing and installing a network is deciding on which cabling medium and wiring topology to use. There are four major types of media in use today: Thickwire, thin coax, unshielded twisted pair (UTP), and fiber optic.
Ethernet media are used in two basic topologies called "bus" and "star". The topology defines how a node (which is any device such as a computer, printer, or hub) is connected to the network.
A bus topology consists of nodes connected together by a single long cable. Each node "taps" into the bus and directly communicates with all other nodes on the bus. The major advantage of this topology is the easy expansion, by adding extra "taps", and the lack a hub. The major disadvantage is that any break in the cable will cause all nodes on the cable to loose connection to the network.
A star topology links exactly two nodes together on the network. A hub is used to collection point where many of the connections come together. The major advantage is any single break only disables one host. The major disadvantage is the added cost of a hub.
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Thickwire Ethernet
Thickwire, or 10BASE5 ethernet, was generally used to create large "backbones". A network backbone joins many smaller network segments into one large LAN. Thickwire made an excellent backbone because it can support many nodes in a bus topology and the segment can be quite long. It can be run from workgroup to workgroup where smaller networks can then be attached to the backbone. A thickwire segment can be up to 500 meters long and have as many as 100 nodes attached. New nodes are connected to the cable by drilling into the media with a device known as a "vampire tap". Nodes must be spaced exactly 2.5 meters apart to prevent signals from interfering with one another.
Thickwire is being replaced by thin coax and fiber optic cabling in most cases. The expense of the cable, coupled along with the expense of the vampire taps, has begun to eliminate this form of cabling.
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Thin Coax Ethernet
Thin coax, or 10BASE2 ethernet, offer the advantages of thicknet's bus topology, with reduced cost and easier installation. Thin coaxial cable is thinner and more flexible than thickwire, but it can support only 30 nodes per segment, and each node must be at least 1.5 meters apart.
A thin coax cable has BNC type connectors on both ends. You then connect the segments of cable together with a "T" connector, and connect the third connection of the "T" to the node. Each end of the long segment must be terminated with a 50 ohm resistor and grounded.
--------------------------------------------------------------------------------
Twisted Pair Ethernet
Unshielded twisted pair (UTP), or 10BASE-T ethernet, cable is a 4 pair cable which is very similar to telephone cable in both appearance and end connector appearance. It comes in a variety of grades, with level 1 being the lowest quality and level 5 being the best.
Level 1 and 2 cabling should only be used for voice and low speed transmissions (less than 5 Mbps). Level 3 may be used for data speeds up to 16Mbps, while level 4 can handle speeds up to 20Mbps. The finest cable avaliable, level 5, can handle speeds up to 100Mbps.
A 10BASE-T ethernet network uses a star topology, with each node being connected directly to a hub. The major limitation to this cable is a maximum calbe length of 100 meters, and that each node must have its own connection to the hub.
--------------------------------------------------------------------------------
Fiber Optic Ethernet
Fiber-optic, or 10BASE-FL ethernet, is similar to twisted pair. Fiber-optic cable can handle 100Mbps transmission speeds, but is not affected by electrical emissions or electro-magnetic interference . Lighting strikes, which can be transmitted by other cabling types, is not transmitted by Fiber-optic cable. The major advantage of fiber-optic cable is the 2 kilometer maximum length. The disadvantage being the higher cost of cable and equipment.
--------------------------------------------------------------------------------
Fast Ethernet
With the addition of large data steams such as real time video and audio, networks have begun to require high transmission speeds. The new ethernet standard established to handle this requirement is called Fast Ethernet, or 100BASE-T. It is defined by IEEE standard 802.3u, which raises the maximum speed from 10 megabits per second to 100 megabits per second. There are three types of Fast Ethernet currently avaliable:
100BASE-TX for use with level 5 UTP cable
100BASE-FX for use with fiber-optic cable
100BASE-T4 which has an extra two wires for use with level 3 UTP cable
Currently the 100BASE-TX standard has become the most popular due to its close compatilibity with the 10BASE-T ethernet standard.
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Hubs
A hub is a central point where multiple cables come together. A hub usually allows 8, 16, or 64 node connections to communicate. If any single connection disconnects or is having problems the hub can partition (remove from the network) it and allow all other nodes to continue to communicate.
--------------------------------------------------------------------------------
Tranceivers
Transceivers, also known as Media Attachment Units (MAUs), are used to connect nodes to the various ethernet media. Generally the transceiver allows the attachment of 10BASE-T or 10BASE-2 cable on one side, and the connection via a 15 pin D-shell connector, known as an Application User Interface (AUI), on the other.
The user would connect the AUI connection to the computer and the 10BASE-T or 10BASE-2 connection to the network media.
--------------------------------------------------------------------------------
Repeaters
Repeaters are used to connect two or more ethernet segments of any media type. They can be used to extend a segment beyond its maximum length or maximum number of nodes by restoring signal quality and timing. Repeaters can also be used to connect segments consisting of different media types together into one larger segment.
It must be noted that a repeater counts as a node on every segment to which it is attached.
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Bridges
The function of a bridge is to connect separate ethernets together. Bridges map the ethernet addresses of the nodes residing on each network segment and then allow only the necessary traffic to pass through the bridge. A bridge can also filter out certain traffic and prevent it from passing through.
When a packet is received by the bridge, the bridge determines the destination and source segments. If the segments are the same, the packet is dropped("filtered"); if the segments are different, the packet is forwarded to the proper segment. Additionally, bridges prevent all bad or misaligned packets from spreading by not forwarding them.
Bridges are called "store-and-forward" devices because they look at the whole ethernet packet before making their filtering or forwarding decisions.
--------------------------------------------------------------------------------
Switches
An ethernet switch is a bridge which can connect more than two segments together. The idea behind a switch is that it removes all unneeded traffic from each segment by only forwarding the traffic needed on that segment, which provides better performance on the network.
--------------------------------------------------------------------------------
Routers
Routers work in a manner similar to switches and bridges in that they filter out network traffic. Rather than doing so by packet addresses they filter by specific protocol.
An IP router can divide a network into various subnets so that only traffic destined for particular IP addresses can pass between segments. The price paid for this type of intelligent forwarding and filtering is usually calculated in speed of the network, because this protocol filtering usually takes more time than packet filtering.
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