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Network Terminology / Ethernet Jargon



ADSL
Asymmetric Digital Subscriber Line. This broadband technology allows high-speed internet access, ranging from 200kb/sec up to 2 Mbit/sec. It is called asymmetric because upload speeds are only a fraction of the download speed. This provides a cheap and efficient method for home broadband, as the upload speed isn't that important.
Bridge
A bridge will connect to distinct segments (usually referring to a physical length of wire) and transmit traffic between them. This allows you to extend the maximum size of the network while still not breaking the maximum wire length, attached device count, or number of repeaters for a network segment.
Category 3, 4, 5, 5a
Category 5 is a class of cable and connector that is capable of supporting 100 Mbit Ethernet (100BaseT). Cat 4 is hardly used; it's data transmission rate is somewhere between Cat 5 and Cat3. Cat 3 is only for 10Mbit Ethernet (10BaseT) and phone lines. Cat 3 is a lot cheaper for connectors and cable, so if you are even thinking about using 100BaseT in the future, make sure you use Cat 5 and not Cat 3. Cat 5a is the newest specification, theoretically allowing speeds up to 350Mbit/sec.
Coax
Coaxial cable (coax) is a metallic electrical cable used for RF (radio frequency) and certain data communications transmission.
Collision
A collision is a condition where two devices detect that the network is idle and end up trying to send packets at exactly the same time (within 1 round-trip delay). Since only one device can transmit at a time, both devices must back off and attempt to retransmit again.
Crossover Cable
An Ethernet Crossover cable is specially wired to allow you to directly connect two Ethernet devices without a hub or switch. These cables differ from standard Ethernet cables in that the transmit and receive wire pairs are reversed. For example, the send pair becomes the receive pair on the other end.
EIA/TIA568
This is the color-code connection standard for an RJ-45 (8 conductor) connector. There are two wiring standards: 568A and 568B. The only difference between the two is that two pairs of colors are swapped. The 568B is an older standard defined by AT&T. All new installations are supposed to use 568A. What really is important is that everything be consistent in all your wiring. Otherwise, you'll get yourself confused. Note that the difference is only in what color is used for what pin, not what signal is on what pin, so in a patch cable with both ends pre-wired, it doesn't matter.
Homerun
A cable run that goes directly from a jack in a wall plate to a centralized position (patch panel). There are no stops or interruptions between the two.
Hub
Hubs act as the center of a "star" topology. They have between 4 and 20+ ports. Internally, hubs are "dumb" devices that just resend information they receive. All devices attached utilize a part of the rated speed, be it 10 or 100Mbit/sec. Hubs know nothing about a packet's destination. Therefore, hubs are generally the cheapest connecting device in a star topography, although for a busier network, switches are more robust. Hubs have one collision domain and one broadcast domain.
LAN
Local Area Network. This term describes a network that is contained within a local area, for example a single building.
NIC
Network Interface Card. This peripheral card plugs into an ISA or PCI slot and allows a computer to access the network. NICs are also available in USB format so a network card can be added without opening the computer.
Plenum
A type of network cable used thorough air ducts. The sheathing surrounding the cable is made from polymers that do not give off toxic or carcinogenic fumes when burned. Plenum-rated cable is intended to prevent the spread of hazardous fumes, not to prevent the spread of a fire itself. Plenum cable costs about 4 times that of regular CAT5 cable.
Port
A jack on a hub. Each patch cable connects to its own port.
Repeater
A repeater acts on a purely electrical level to connect two segments. All it does is amplify and reshape (and, depending on the type, possibly retime) the analog waveform to extend network segment distances. It does not know anything about addresses or forwarding.
Router
Like hubs and switches, a router is the center of a "star" network topology. Routers are even more efficient than switches because a router can breakup broadcast domains in addition to collision domains. Having multiple broadcast domains allows a router to connect two separate network, and they are often found as the connection between a LAN and WAN, and internet. Routers have multiple collision domains (one for each switch port) and multiple broadcast domains (up to the number allowed by the router manufacturer).
RJ-11
RJ-11 is standard modular phone connector. There are 3 different types: 2, 4, and 6 conductor connectors. They're all the same, except that contacts or wires are missing. Ordinary phone connectors are 4-conductor (2 pairs = 2 phone lines). Sometimes you get a phone wire that only has 2 conductors in it; this will screw you up if you're trying to run more than 1 phone line. There's also a little-bitty version of this connector that only has 2 conductors on it. It will fit in the same socket.
RJ-45
RJ-45 is the 8-conductor version of an RJ-11. It looks like a regular modular phone connector, only it's wider. You need to use RJ-45 for Ethernet, because the connection standard puts the Ethernet on some of the outer connectors not in RJ-11. RJ-11 plugs will fit into an RJ-45 socket, but because the plastic plug is smaller, some of the contacts will get bend back a little.
Segment
A segment is a piece of network wire bounded by bridges, routers, repeaters or terminators.
Switch
Switches act as the center of a "star" topology, much like hubs. They have between 4 and 20+ ports. Internally, switches are different that hubs due to their intelligent design. Switches"remember" what device is attached to what port, and will relay packets only to the proper destination port. Because of this, all devices attached are able to utilize their maximum rated speed, be it 10 or 100Mbit/sec/port. This cleaver design makes switches more expensive, but in a busy network, switches can keep the traffic flowing. Switches have multiple collision domains (one for each switch port) and one broadcast domain.
STP
STP is for SHIELDED, twisted pair. STP is typically used for Token-Ring networks, not Ethernet.
UTP
UTP is for Unshielded, twisted pair. This is usually what phone companies install. 10BaseT also runs on this. UTP is graded according to its data carrying ability (e.g., Category 3, Category 4, Category 5). 10BaseT Ethernet requires at least Category 3 cable.
WAN
Wide Area Network. This term describes a network that connects LANs. It usually consists of leasing an "always-on" connection (ISDN, T1) from a telecommunication company.
 

 

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