Network Computing Glossary [by Sound Visions]

Glossary Index:


Terms commonly used in the Lab's Networked World:


ATM, "Asyncronous Transfer Mode" - A type of data-link protocol built on a switched physical architecture. Sonet/ATM OC3 is designed to run at 155 megabits/second, with OC12 rated at 622 mb/s. ATM standards are still evolving, making ATM equipment availability low and and costs relatively high for end-user applications.

AUI, "Attachment Unit Interface" - the Ethernet term for the interface between a MAUand a Station. Also known as "DIX" (for Digital, Intel, Xerox) connector. An "AUI Cable" can attach a MAU to a station at a distance (up to 50 meters), or a "micro" MAU may be plugged directly into a computer/station's AUI port. Occasionally (and erroneously) called "Thick-Net".


BNC - A Bayonet-type locking connector used for Thin-Net cabling. Also used for instrumentation and video cabling. WARNING: Network (RG-58) and Video (RG-59) cabling are NOT INTEROPERABLE. Bridge - A Bridge is a (ethernet level-2) gateway between 2 Local Area Networks or network segments. Bridges transfer MAC-layer packets from one network to another, performing frame-level format conversion if needed. Commonly, bridges auto-configure, building mapping tables for stations on opposite sides of the bridge from each other.

Bridge - A Bridge is a (ethernet level-2) gateway between 2 Local Area Networks or network segments. Bridges transfer MAC-layer packets from one network to another, performing frame-level format conversion if needed. Commonly, bridges auto-configure, building mapping tables for stations on opposite sides of the bridge from each other.

Bus Network - A type of network configuration where multiple nodes share access at the physical level. Each node must therefore wait until the medium (the wire or bus) is free before sending its data packet. Also known as a Daisy-Chained network. thin-net is an example of a daisy-chained network.


Concentrator - An active hub which interconnects multiple network nodes (computers, printers, etc.) on a shared access medium such as ethernet. Typically, we use Raylan brand Ethernet concentrators, to which each host attaches via fiber to a Fiber Drop Card. A concentrator provides communication between all hosts on that network segment. One port of the concentrator will connect to the building Router, which acts as a Gateway, connecting to hosts on other segments in the Lab and the Internet in general.

Coupler, ST Fiber Coupler - A coupler is a device used to splice (or couple) two optical fibers together. The Lab uses ST style couplers. [ picture ] Couplers are typically found in distribution frames ( LDFs, IDFs, and the MDF).


Daisy-Chain - A daisy chain is typically a bus which is made up of separate sections, each of which connects two machines together. Each machine typically uses pass-through connectors, so all the cables form one long wire with machines distributed along it. thin-net is a daisy-chained network, for example. Other examples of daisy-chains are SCSI and LocalTalk.

Advantages of daisy-chaining are that custom networks can be assembled using simple compnents, and that individual stations or nodes may typically be added or removed from anywhere on the chain. The incremental cost is low--usually adding just one interconnect cable (and tranceiver, if need be). Disadvantages of daisy-chaining can be subtle, but far-reaching. The bus is a shared medium; only one of the many stations can be transmitting at any given time. The entire network can often be disrupted when any station is added or removed. One station may fail, jamming the entire bus with noise. Even correctly working stations decrease signal quality slightly, so care must be taken not to exceed length and node density guidelines. Also, most daisy-chins are transmission lines, and therefore need correct termination in order to work at all.

Drop Box - The common term for our portable fiber termination outlets. Drop boxes are used in the laboratory areas of the Media Lab, typically open areas where tables and machines move fairly often.

Each drop box has from 3 to 6 ports and a label indicating the port-IDs and location of the fiber patch panel which all the ports are connected to. A host is connected to the drop box using a fiber patch cable".

Drop-Cable - The term used for the cable which connects a computer or MAU to its network drop or wall outlet. Typically, a drop cable would be a short ST-to-ST fiber (for a 10baseFL drop), but it actually applies to whatever cable is appropriate for the medium and protocol being used.

A fiber optic cable is typically1 to 5 meters in length and terminates with an ST connector [picture] at each end. These attach a fiber NIC or tranceiver to a drop box or wall box. It's usually equivalent to a fiber patch cable. NOTE: in some cases the drop cable uses a different connector to fit a non-ST device, e.g., an ST-to-SMC (typical for ATM) or ST-toFSD (for FDDI devices).


E15-040, aka 040,'The Machine Room' - This is the primary Network Computing Systems machine room. It houses the building routers, telecom interfaces and primary fileservers. It is located on the lower level, right across from the frieght elevator; it has a key-code door, and wizards from the various groups as well as NeCSys staff have 24-hour access to it.

ETHERNET - A LAN data-link protocol developed by a consortium of vendors; later standardized as IEEE 802.3 with a few modifications. Most of the Media-Labs hosts are networked via Ethernet.

"Raw" data rate for Ethernet/802.3 is 10 megabits/second, hence the term "10base" used in describing Ethernet running over various media:

                        "10base2" = Thinnet
                        "10baseT" = Twisted-Pair
                        "10baseFL" = Multi-Mode Fiber
                        "10base5" = ThickNet

There also exists an extended version of ethernet which runs at 100 mbits per second, called 100baseT (AKA 'fast ethernet'), and connections which auto-switch, 10/100baseT.


FDC, Fiber Drop Card (RayLan) - A small 10baseFL ethernet interface card which resides in a Raylan model 1600 Concentrator and connects to a particular host. Each host is connected to its own Fiber Drop Card.
An indicator LED on the FDC indicates the Link Status of that fiber connection: Green = Carrier received. Yellow = No Carrier. Red = FAULT. A red FAULT light indicates that the SNMP management card has locked out that particular concentrator slot.

FDDI, Fiber Distributed Data Interface - A LAN data-link protocol with a nominal 100 megabit/second data rate. FDDI is a point-to-point protocol, but is usually used in a token-ring arrangement (SAS) or dual token ring (DAS) configuration.

FTP, File Transport Protocol - An application-level communications protocol that allows the user to move files and navigate directories on remote machines, typically called "FTP hosts". FTP allows for both anonymous and user-specific permissions, as well as file-drop and batch moves. See the Unix command ftp.

Fetch - A shareware application, most commonly used on Macintoshes, to allow File Transport Protocol access to files on other systems or sites.

Fileserver - A computer which exports some of its disk drives over its network connection to other computers, which use these disks as if they were 'local' disks. Fileservers typically have high I/O bandwidth, fast network interfaces, and many Gigabytes of storage. The main Lab fileservers are hub, campbell, cga, garden, heathrow, mc, spinach, and vlw.


Gateway - A Gateway is a network device that connects multiple networks together. Gateways are classified depending on what Network Layer they operate at: A level-1 Gateway is a Repeater; A level-2 Gateway is a Bridge; A level-3 Gateway is a Router; A level-4 Gateway is a Transport Layer Gateway.

See Network Layers for more info on the different network layer definitions.


HTTP, Hyper-Text Transport Protocol - An application-level communications protocol that allows supports World Wide Web (WWW) browsers on remote machines. This protocol is the base language of the WWW clients (browsers) and WWW servers.

Home Page - The starting location of a particular person, company or organization's World Wide Web site. A site is typically composed of HTTP documents, image files, sound files, executable scripts, and other resources.

Home Run - A cabling configuration for office areas, in which each node (typically, wall-boxes) are cabled directly back to the IDF or MDF instead of connecting to a more local LDF. Home runs are used primarily in our office suites, because there is no central space for an IDF, and usually a lower density and dynamicism of machines.

Hub - The generic name for a device at which several or many connections meet, such as a repeater, concentrator, switch, or router. The center of a star-type network is called a hub.


IDF, Intermediate Distribution Frame - The IDF is a set of racks containing fiber patch panels and shared network hardware for an entire floor. This is where network feeds from the MDF ('vertical' runs) are patched through to the various LDFs (via 'horzontal' runs), and also where home-run hosts patch into their conentrators. Vertical trunks from each IDF run to the MDF in E15-040.

IP, Internet Protocol - The Internet Protocol, usually referred to as the TCP/IP protocol stack, allows computers residing on different networks to connect across gateways on wide-area networks. Each node on an IP network is assigned an IP address, typically expressed as 'xx.xx.xx.xx' All IP addresses at the Media Lab begin with 'XX.XX.'
See network layers.

The INTERNET We use the term Internet to indicate the collection of all "public" networks interconnected across the world accessible via TCP/IP protocol. It is comprised of thousands of colleges and universities, tens of thousands of businesses, and millions of personal computers worldwide.




LAN, Local Area Network - The extent of network which connects computers that are physically close together, typically within a single room or building. Ethernet,ATM, and FDDI are protocols typically used in LANs. (Compare with WAN)

LDF, Local Distribution Frame - The LDF is a rack cabinet containing fiber patch panels and network hardware for a workgroup area. Typically, it consists of one or two 19" racks, from 4 to 8 feet tall. The LDF is where most ethernet concentrators are installed, and is logically one step up from wall-boxes and drop-boxes. Horizontal trunks from each LDF run to the IDF on that floor.

LocalTalk Localtalk was the original network standard developed by Apple Computer for the Macintosh. It was optimized for ease of use and low cost. It uses either PhoneNet (TP ) or LocalTalk Cable (STP) cabling, is a daisy-chained, shared-access medium that is connected to a MAc's printer or modem serial port.


MAU, "Media Access Unit" - Also known as Transceiver. An Ethernet device which attaches a networked station to the network media. These may be attached by an AUI "drop" cable, or plug directly onto the station (typically a "micro-mau", or be built into the station's Network Interface Card). Some of our commonly-used tranceivers are pictured here.

MDF, Master Distribution Frame - The MDF is the hub of the entire Media Laboratory. It is located in 6 rack cabinets in E15-040, with over 1400 vertical trunk fibers running to the 3 IDFs. The MDF contains our main routers, switches, and communications hardware, as well as 'building-wide' concentrators.

Multimode Fiber - A type of fiber mostly used for shorter, e.g. campus distances. It can easily carry 100 megabits/second for typical campus distances, with the maximum speed dependent upon the protocol used. The entire Media Lab is cabled with multimode fiber.


Network Drop - The term applied to the network run from the local concentrator or hub to the office wall box, drop cable, and network interface hardware. Typically, this includes the Fiber Drop Card (or concentrator port), LDF Patch, premise (permanent) office run, wall box and drop cable. Depending on the host's built-in hardware, one also needs a tranceiver or Network Interface Card.

Network Layers - A network is implemented by dividing the various functions it performs into a number of layers, in order to simplify and streamline its design and interoperability. It is built from the physical layer (layer 1) on up, with each layer supporting all the layers above it. Separation into such layers allows the substitution of one implementation of that layer for another without requiring a redesign of other layers, for example, TCP/IP runs the same over thin-net or 10baseT, with no need to reconfigure the upper layers.


   ISO Layer   

   OSI Layer   

----------------------- Description -----------------------

7 Application Application Application-specific data formatting, encoding, decoding and end-use.
6 Presentation Presentation  
5 Session Session Ports and Sockets
4 Transport Transport Provides network-independent transport service between systems; TCP, UDP, and ICMP protocols
3c Internet Network IP/Internet Protocol layer
3b Enhancement Network  
3a Subnetwork
Network Controls the path of a logical connection through the network
2b Logical Link Data Link Formatting of data bytes and frames, block synchronization, error detection
2a Medium Access
Control (MAC)
Data Link Medium-independent MAC Layer shared-access protocols - CSMACD, ethernet, fast-ethernet, FDDI, OC3-ATM
1 Physical Physical The Physical MEDIUM which carries signal: Thin-net, twisted-pair, fiber or AUI connections; Modulated of electrical or optical signal levels.

NIC, Network Interface Card - A card containing the circuitry necessary to connect a computer to a particular network media. Typically, the NIC plugs into the computer's accessory bus, (PCI, turbochannel, nuBus, etc.) and provides a network connection such as 10baseFL (fiber ethernet), thin-net, AUI, etc. See Choosing a NIC.



Patch Cable (Fiber Patch Cable) - A fiber optic cable, typically from 1 to 5 meters in length and terminated with an ST connector at each end. Patch cables are used in fiber patch panels to interconnect devices or cables. See also drop cable.

Patch Panel (Fiber Patch Panel) - A small cabinet containing fiber optic couplers, used to allow easy interconnection of different fiber optic cables or devices. The Lab's patch panels all use ST connectors, so one may patch any fiber in a panel to any other fiber with a fiber patch cable; patches may also connect to nearby network devices such as concentrators or switches; typically several patch panels and concentrators are located in each LDF.

Port-ID -- [Definition removed for security reasons]



Repeater - A simple network hub that serves as an ethernet level 1 (Physical Layer) gateway between different subnetork segments. Typically, a repeater merely amplifies and passes through all information to all of its ports. More sophisticated repeaters sense physical-layer subnet faults and deactivate those ports.

Router - A sophisticated network hub which serves as an ethernet level 3 (Network Layer) gateway between different segments and networks. Our routers connect via several protocols-- ethernet, FDDI, ATM--and can perform bridging and certain filtering operations. Our building routers live in E15-040.


SMTP, Simple Mail Transport Protocol - A communications protocol used for implementing electronic mail over the Internet. It operates using sockets on the Session Layer.

SNMP, Simple Network Management Protocol - A communications protocols used at the intermediate Network Layers to debug and manage network devices and connectivity.

ST Connector - The type of fiber-optic connector most commonly used at the Media Lab. An ST connector is has a 2.5mm shaft and bayonet locking ring, and allows quick connect and disconnect of our 125 micron multi-mode fiber. All LDFs, IDFs, and the MDF use ST connectors and couplers.. [ picture ]

Station - A node on a network; archaic. Stations are now called network nodes.

STP, "Shielded Twisted Pair" - A type of cable containing two twisted wires with a foil or braid shield wrapped around them. Apple's LocalTalk is uses STP media, for example. STP is not as common as UTP, "Unshielded Twisted Pair".

Shared Access Medium A type of network or protocol where multiple interconnections all send their signals over the same physical medium. In 10base2, copper-based thin-net for example, many network nodes are daisy-chained onto a single wire. The single wire carries at most one packet at a time, and all other nodes must wait until that packet ends before transmitting their own packet onto the medium. The nodes share the available bandwidth by using the medium one at a time; this method is called Time Domain Multiplexing.

Single-Mode Fiber A type of fiber optic cable in which there is only one mode for the light to follow, thereby minimizing dispersion (smearing in the time domain). Single Mode is mainly used for long runs (>10km) and fed with lasers. It is more difficult to splice and patch than Multimode Fiber, but its limit on (speed x distance) is higher.

Star, Star Network - The descriptive name of any network which is configured with many branches attaching to a common point. The common point, also known as the parent node, is the hub of the star, and the outer, or child, nodes are the branches, or leaves.
10baseT is an example of a physical star network, while thinnet is, instead, a bus-based network.

Switch - Generically, a switch is a device that turns current on and off. In the networking world, it's data connections that are being made and broken. A switch is a network hub device which, instead of putting packets onto a shared 'backbone' bus, creates a direct connection to the destination port.


TCP/IP, Transport Control Protocol / Internet Protocol - TCP and IP are communications protocols, that is, structured languages in which data is communicated between one process and another, and between one network and another. TCP/IP is implmented in a multi-level layered structure.

TCP/IP is the 'glue' that that ties together the many heterogeneous networks that make up the Internet.

TP, "Twisted Pair" - The type of wire used by the phone company to wire telephones -- at least over distances like between your house and the central office. It has two conductors, which are twisted. The twists are important: they give it electrical characteristics which allow some kinds of communications otherwise not possible. Ordinary telephone cables are UTP (unshielded twisted pair) (see also STP, "Shielded Twisted-Pair".).

Termination - The "proper end" of a network segment which operates as a transmission line. Proper termination simulates an ideal transmission line by exactly matching the impedance of the medium. Improper termination, such as a complete open circuit, a complete short, or non-matching resistance, causes signals on the medium to bounce off the impedance discontinuity. Such reflections usually result in lowered Signal-to-Noise ratio, slower data rates, and eventual data loss.

Thick-Net - An archaic form of ethernet, using a 5/8" diameter coax cable, and either N-type screw connectors or "vampire taps". Also known as 10base5, and useful for runs up to 500 meters in length. A station would connect to Thick-Net via a "MAU" and an "AUI" cable.

Thin-Net - Coaxial cable with BNC connectors used for ethernet network cabling. Also known as 10base2. NOTE: Ethernet cable is 50-ohm impedance, usually marked as "RG-58" or "IEEE 802.3 compliant". It looks similar to 75-ohm video cable, but is NOT. NEVER use video cabling in place of network cabling--it breaks the network and is difficult to track down.

Tranceiver - Also known as an Media Access Unit. An Ethernet device which attaches a networked station to the network. May be attached by an AUI cable, or plug directly onto the station (a "micro-mau"), or be built into the station. Some of our commonly-used tranceivers are pictured here.

Transmission Line - A theoretical model of a how electrical signals propagate down a wire. In the simplest model, the wire has constant impedance and extends infinitely in both directions; the wire has no loss, so the signal does not deteriorate or change. Transmission Line Theory also contains other models for predicting what the effects of line loss, changing impedance, capacitance, inductance, and improper termination would have on the signal.


UTP, "Unshielded Twisted-Pair" - See "Twisted-Pair" and STP, "Shielded Twisted-Pair"



WAN, Wide Area Network - A network that connects computers in different cities or countries, also known as long-haul-networks. WANs often use telephone company equipment such as leased lines or fiber connections to hook up to distant net nodes or gateways.

Wall Box - The common term for our wall mounted fiber outlet devices (AMP-brand Surface Mount Outlets). Wall boxes are the typical network terminations in every room of the Media Lab. Each wall box has from 3 to 6 ports and a label indicating the port-IDs and location of the fiber patch panel which all the ports are connected to. A host is connected to the wall box using a fiber patch cable.

Wizards - The working title for the collection of students and staff folk who are members of the individual research groups at the Lab who help out with technical support. Wizards are approved by Lab faculty and help make technical and policy decisions; they are also granted access to some of the centralized NeCSys systems to aid with off-hours emergencies.

World Wide Web, WWW- The catch-all name for the massive conglomeration of Hypertext, HTTP, FTP, and other servers on the Internet which provide a rich variety of publishing and services, including on-line magazines, personal and corporate home-pages , catalogs, customer service interfaces, search engines, software updates, and so on. The WWW is distributed across tens of thousands of servers across the world, and millions of client machines as well.


X-modem - A serial-line protocol used to transmit binary files over modem lines before SLIP and PPP. See the Unix commands sx, sy, sz, rx, ry, rz. Modern alternatives are Fetch and FTP.

XCVR - Common abbreviation for Transceiver.


Y-modem - A serial-line protocol used to transmit binary files over modem lines before SLIP and PPP. See the Unix commands sx, sy, sz, rx, ry, rz. Modern alternatives are Fetch and FTP.


Z-modem - A serial-line protocol used to batch-transmit multiple binary files over modem lines before SLIP and PPP. See the Unix commands sx, sy, sz, rx, ry, rz. Modern alternatives are Fetch and FTP.

Glossary Index: