Basic Glossary on Campus Networks

Basic Glossary on Campus Networks


Author
John Wobus, jmwobus@syr.edu (corrections welcome)
Date
3/12/97
This file
http://web.syr.edu/~jmwobus/comfaqs/lan-glossary.html
Related information
http://web.syr.edu/~jmwobus/lans/

Other Similar Glossaries


Glossary

100BASE-FX
A variant of IEEE 802.3 for a 100Mbps Ethernet-like network. Borrows the physical characteristics of FDDI's multimode fiber PMD, but uses Ethernet framing & CSMA/CD. One of three flavors of "100BASE-T" proposed by the Fast Ethernet Alliance. Came from the 100BASE-X proposal.
100BASE-T
Generic name for the 100Mbps vairants of IEEE 802.3, especially the twisted-pair based ones. The three variants are called 100BASE-TX, 100BASE-FX, and 100BASE-T4. A medium-independent interface and an adaptor is define (to be used like the AUI and MAU of 10Mbps 802.3). When a device is said to support 100BASE-T, usually 100BASE-TX is meant.
100BASE-T4
A variant of IEEE 802.3 for a 100Mbps Ethernet-like network. One of the flavors of "100BASE-T". Uses 8B6T encoding and 25MHZ clocking, and in addition to the two pairs traditionally used in the manner of 10BASE-T, also has two pair used in bidirectional half-duplex fashion. Among other things, this means that this particular kind of Ethernet cannot be made full duplex without the use of more pair. Came from the 4T+ proposal.
100BASE-TX
A variant of IEEE 802.3 for a 100Mbps Ethernet-like network. Borrows the physical characteristics of FDDI's TP-PMD, TP-PMD, but uses Ethernet framing & CSMA/CD. One of three flavors of "100BASE-T" proposed by the Fast Ethernet Alliance. Came from the 100BASE-X proposal.
100BASE-X
Old name for 100BASE-FX and 100BASE-TX.
100Mbps Copper UNI
ATM Forum UNI specification for 100Mbps over some sort of copper cable. I believe it is just 100MbpsUNI making use of FDDI's TP-PMD rather than the older fiber PMD.
100Mbps UNI
ATM Forum 100Mbps multimode fiber private UNI. Same as Fore's TAXI. Borrows optical characteristics & basic encoding of FDDI.
100VG-AnyLAN
"100VG-AnyLAN": Originally a proposal to IEEE 802.3 for a 100Mbps Ethernet-like network, later relegated to IEEE 802.12. Formerly known as 100BASE-VG. Uses Demand Priority media access method and Quartet Signaling. I've also seen reference to its ability to use Category 4 UTP, Category 5 UTP, and STP, but I don't know how many pairs.
100VG-AnyLAN Forum
Group of vendors trying to accelerate 100VG-AnyLAN acceptance & interoperability.
10BASE2
IEEE 802.3 10BASE2: IEEE's standardized version of Digital Equipment Corporation's ThinWire Ethernet, which runs over a thinner coaxial cable than the original 10BASE5. Another old nickname for it was "CheaperNet". The coaxial cable is specific to 10BASE2, but two variants of off-the-shelf RG cable are sometimes used. The cable looks very similar to the cable used for IBM 3270-style terminals or that used for home cable TV, but has different electrical characteristics. The "2" in the name refers to the 200 meter (or more precisely, 185 meter) limit on the cable length. Like 10BASE5, computers are attached along the length of the cable. See "IEEE 802.3".
10BASE5
IEEE 802.3 10BASE5: "Ethernet" or "ThickWire Ethernet", IEEE's standarized version of the original 10Mbps Ethernet which runs over a rather thick Ethernet-specific type of coaxial cable. The "5" in the name refers to the 500 meter maximum cable length. Computers are attached along the length of the cable. See "IEEE 802.3".
10BASE-F
Three variants of IEEE 802.3 which runs over multimode fiber. See 10BASE-FB, 10BASE-FP, and 10BASE-FL and "IEEE 802.3".
10BASE-FB
IEEE 802.3 10BASE-FB: "Synchronous Ethernet" which is a special-purpose multimode fiber link for linking repeaters that allows the repeaters to communicate more efficiently, thus enlarging the count of repeaters that can be placed in series above the traditional 4. Described in IEEE 802.3 Section 17.
10BASE-FL
IEEE 802.3 10BASE-FL: multimode fiber Ethernet used to attach a pair of devices (each being either a host or a repeater) as a "Link Segment"--a lot like 10BASE-T except that it uses fiber. It makes FOIRL obsolete. 10BASE-FL transceivers can interoperate with FOIRL transceivers. It is described in IEEE 802.3 Section 18.
10BASE-FP
IEEE 802.3 10BASE-FP: passive star fiber Ethernet. Attaches a number of Ethernet devices together with a passive star hub (i.e., the hub is not electronic--it just splits the light travelling through each incoming fiber to go out all the outgoing fibers). It is described in IEEE 802.3 Section 16.
10BASE-T
A variant of IEEE 802.3 which allows stations to be attached via twisted-pair cable.
155Mbps UNI
ATM Forum 155Mbps private UNI. In two flavors: multimode and shielded twisted-pair. The multimode version is incompatible with STS3cUNI. This version is for private networks only and presumably will be less expensive. I heard that a C5 version has been proposed.
25Mbps UNI
IBM proposed copper interface for ATM that so far as been rejected by the ATM Forum. IBM's proposal that borrows some of Token Ring's signaling characteristics. I've read the statement that the ATM Forum doesn't support this proposal.
4T+
Old name for 100BASE-T4.
51Mbps UNI
I don't know the actual name. ATM Forum 51Mbps UNI for Category 3 UTP. Uses AT&T's 16-CAP (a 16 constellation modem-type modulation scheme) line coding to transmit the signal. The transmission convergence layer (framing) conforms to the STS-1 SONET standard.
802, 802.x
see IEEE 802, IEEE 802.x.
AAL "ATM Adaption Layer"
(ATM term) the layer between ATM cells and the (typically packetized) data that they carry. For example, if you send IP packets over an ATM network, some sort of ATM Adaption Layer will be used.
ABR "Available Bit Rate"
(ATM term) one of several quality-of-service traffic classes used in ATM. ABR basically means "use whatever is available", i.e. don't offer any special quality of service.
ADSL "Asymmetric Digital Subscriber Line"
Remote access method that makes use of a faster channel for local-to-remote communications than remote-to-local.
ANSI "American National Standards Institute"
A definer of standards of all kinds, including FDDI.
ANSI X3
ANSI group developing standards for information processing.
ANSI X3T9
ANSI group within X3 developing standards for I/O interfaces.
ANSI X3T9.3 Committee
ANSI group within X3T9 standardizing HiPPI.
ANSI X3T9.5 Committee
ANSI group within X3T9 that standardized FDDI, PMD, SMF-PMD, and is standardizing TP-PMD and LCF-PMD.
AppleTalk
A protocol family developed by Apple Computer to implement LANs serving Macintoshes.
ATM "Asynchronous Transfer Mode"
a method for switching little fixed-size packets (cells) around. Like T1 and DS3, digitized voice was a major consideration in its design, but it can be used for data. It can be run at different speeds over different media including T1 and DS3 as well as 51Mbps, 100Mbps, 155Mbps and 622Mbps standards (see SONET & TAXI). The fixed cell size is 53 bytes. Though ATM is really designed for voice and WANs, there are schemes to use it in LANs. ATM is a big buzzword these days but it is still very new.
ATM Forum
Non-profit international industry consortium chartered to accelerate ATM acceptance & interoperability.
AUI "Attachment Unit Interface"
the Ethernet/IEEE 802.3 term for the interface between a MAU and a station. A special kind of cable known as an "AUI Cable" can attach a MAU to a station at a distance (up to 50 meters).
Backbone
a fairly nebulous term for a part of the network that interconnects other parts of the network. For example, a campus might have an FDDI ring that interconnects a number of Ethernets. The FDDI ring could be called the network's backbone.
BNC Connector "Bayonet Neill-Concelman connector"
a type of connector used for attaching coax cable to electronic equipment which can be attached or detached quicker than connectors that screw. ThinWire Ethernet (IEEE 802.3 10BASE2) uses BNC connectors.
Bridge
A network "relay" which reads, buffers, and sends data to relay it from one data link to another, but makes the two data links appear as one to levels higher than the data link layer.
Broadcast
A message (e.g. packet or frame) sent to all the nodes on a network.
Broadcast Address
An address which can be used as the destination of a communication that indicates the packet/message is a broadcast. IP has broadcast addresses as does IEEE 802.
Broadcast Domain
That part of a network which receives the same broadcasts.
Bus
A term used for a kind of electronic device in which a number of elements are wired together with a single wire in such way that all the elements can use the same wire to transmit information to other devices on it. Buses are used internally in computers and used to attach computers to peripherals. For the purposes of LANs, bus is a term for a LAN topology which has the same characteristic: the same wire is attached to a number of devices which all share that wire to transmit to other devices on the LAN. ThickWire and ThinWire Ethernet, Localtalk, and ARCnet are examples of LAN technologies with a bus topology.
Category 3 Unshielded Twisted Pair
standardization of unshielded twisted pair cable for voice use. Some data communications standards such as 10BASE-T can utilize it.
Category 4 Unshielded Twisted Pair
standardization of unshielded twisted pair cable.
Category 5 Unshielded Twisted Pair
standardization of unshielded twisted pair cable for data use. TP-PMD requires Category 5 cable rather than Category 3.
Category 6
Name people and organizations often associate with their various proposals for yet another gradee of twisted pair media. At the time of this writing, 9/27/96, there is no official "Category 6".
CBR "Constant Bit Rate"
(ATM term) one of several quality-of-service traffic classes used in ATM. See also "ABR".
CCITT "Consultative Committee for International Telegraph and Telephone"
An international telecommunications standards organization, now subsumed by the ITU.
CDDI "Copper Data Distribution Interface"
Commonly used term for TP-PMD, but actually a trade name of Crescendo.
Cell
An ATM 53-byte cell. Note: there are various proposals for how typical packets will be broken into cells and restored.
Cell Switching
a term for ATM-style networks. See "ATM".
CMIP "Common Management Information Protocol"
An OSI protocol for management of network equipment. Not widely implemented. See SNMP.
CMOT "CMIP over TCP/IP"
A protocol consisting of CMIP running under TCP/IP. An alternative to SNMP.
Coaxial Cable
any of a number of kinds of electrical communications cable designed so one conductor is in the center and the second conductor forms a ring around it. Depending upon who you talk to, someone might have a specific kind of coaxial cable in mind. Some well known kinds are various Cable TV cables, cables used by IBM 327x terminals and ARCNet, and cables used by Ethernet & IEEE 802.3.
Collapsed Backbone
a network backbone that is located in a single room. It might be a single router or multiport bridge, or a small LAN of some sort. A typical collapsed-backbone- style campus LAN might consist of Ethernets in a number of buildings, each with a repeated fiber link into a single room at a central point where a router interconnects them. An example of the opposite would be putting a router in each building and interconnecting them all with a big FDDI ring.
Concentrator
a device which allows a number of stations to be connected to a LAN. In the case of Ethernet, it is simply a multi-port repeater. In the case of ring networks like Token Ring and FDDI, it acts as a switch which keeps the ring intact even if individual devices are unplugged.
Counterrotating Ring
(see Ring, FDDI, Token Ring) a method of using two ring networks going in opposite directions to provide redundancy. The network interfaces can change the path of the ring that the data flows around, thereby preserving the ring (thus the operation of the LAN) even if some of the cable is uplugged or cut, or if a device on the ring fails in such a way that it can't transmit data around the ring.
CRC "Cyclic Redundancy Check"
An error checking technique: a way in which a frame or packet can be created in such a way that the receiver can determine whether an error is likely to have occurred in the transmission.
CSMA/CD "Carrier Sense Multiple Access with Collision Detection"
The method by which nodes on an Ethernet/IEEE 802.3 LAN gain access to the network, i.e. one of several techniques that have been built into different LAN technologies to allow multiple nodes to share the same wires/electronics to send their data.
Cut-Through Switching
A method of switching (bridging) where the beginning of the packet/frame is being sent on one LAN while the end of it is still being received from another LAN. The method allows quicker transmission of the data in the best case, but defeats some of the error checking that would be available in standard bridging.
DAS "Dual Attachment Station"
A type of FDDI node that attaches to both rings of a counter-rotating ring to provide some fallback capability. The other type is SAS (Single Attachment Station). Typically, more vital FDDI nodes are DAS, e.g. routers, servers, links between hubs, and invividual client stations are SAS.
DECNet
Trade name of Digital Equipment Corporation for some of their networking products. It is a kind of network built out of Digital Equipment Corporations own networking protocols (with some standard protocols also used).
Dialup Modem
Modem used over ordinary dial-up telephone lines as opposed to private or leased lines.
DS3 UNI
ATM Forum DS3 UNI, 44.236Mbps.
DXI
ATM Forum "Data Exchange Interface".
ELAN "Emulated LAN"
Essentially, a fairly simple kind of VLAN defined in the ATM Forum's LANE specification. Unlike many VLAN schemes, the ELAN scheme is agreed upon by multiple vendors, i.e., the members of the ATM Forum.
Ethernet
LAN data-link protocol developed by a consortium of vendors; later standardized as IEEE 802.3 with a few modifications. For many applications, users have not adopted all the IEEE 802.3 differences. Ethernet/802.3 now can be run on two types of coaxial cable as well as multi-mode fiber and unshielded twisted-pair. "Raw" rate of data transmission is 10 megabits/second.
Fast Ethernet
A nickname for the 100Mbps version of IEEE 802.3.
Fast Ethernet Alliance
Group of vendors working on a 100Mbps version of IEEE 802.3. They intend to submit their proposals for approval by the IEEE for a new set of 802.3 standards called 100BASE-T.
FDDI "Fiber Data Distribution Interface"
LAN data-link protocol. Designed to run on multi-mode fiber. "Raw" rate of data transmission is 100 megabits/second. Developed by the American National Standards Institute.
FDDI-2
Same speed, same fiber, same basic protocol as FDDI. FDDI-2 adds a layer which allows you to allocate fixed bandwidth to applications of your choice, making it more like broadband. FDDI-2 is still rather new.
FDSE
Full Duplex Ethernet: a variant of Switched Ethernet which does not use CSMA/CD, but uses slightly-modified network interface cards to send & receive packets simultaneously. Presumably based on 10BASE-T for most clients, and cannot be based on ThinWire or ThickWire Ethernet.
Fiber
optical fiber: a very long, narrow, flexible piece of glass. Used for high-speed communications.
Fibre Channel
an ANSI standard to replace HiPPI. It uses optical fiber instead of copper cables. Speeds are up to roughly 1Gbps.
Fibre Channel Systems Initiative
Group of vendors trying to accelerate Fiber Channel acceptance & interoperability. Members include: HP, IBM, Sun.
Firewall Router
a router which blocks traffic according to various criteria for security--for example a router which allows no telnet to any host through one of its interfaces but allows ftp to a list of authorized hosts through the same interface.
FOIRL "Fiber Optic Inter-Repeater Link"
a standard for running IEEE 802.3 over fiber, linking two devices (each either a host or a repeater) as a "Link Segment". It has been replaced by 10BASE-FL.
Fragment
A portion of a packet/frame. In Ethernet terminology, Fragment (or "Runt") often means a part of an Ethernet frame left over from a collision. In IP terminology, Fragment means a packet which is the result of splitting a larger packet into smaller ones.
Frame
A term for the unit of data transferred on a LAN; it is something larger than a cell, i.e. depending on the type of LAN, hundreds or thousands of bytes long (any particular type of LAN will have a limit on the frame size, e.g. Ethernet's 1500 byte/octet limit). Roughly equivalent to the term packet, but "frame" is a LAN term whereas "packet" is a term used for higher level protocols such TCP/IP, IPX, and AppleTalk.
Frame Switching
A term used in contrast to "Cell Switching". Frame Switching means a switch which forwards entire frames, e.g. Ethernet or FDDI frames.
FTP
Protocol in the "TCP/IP" family for copying files from one computer to another. Stands for "File Transfer Protocol".
Full Duplex
A possible property of a data-communications line: that data can be transferred in both directions, simultaneously. The alternatives are Half Duplex and Simplex.
Full Duplex Switched Ethernet Consortium
Group of vendors that are working out the details of FDSE. Cabletron is a member.
Full Duplex Token Ring
IBM scheme to add switching to token-ring hubs that would allow full-duplex linking to individual computers using modified token-ring adaptors. Has the same wiring characteristics as token ring.
GAE
Gigabit Ethernet Alliance.
Gateway
A type of "network relay" that attaches two networks to build a larger network. Modern "narrow" usage is that it is one that translates an entire stack of protocols, e.g., translates TCP/IP-style mail to ISO-style mail. Older usage used it for other types of relays--in particular, in the "TCP/IP" world, it has been used to refer to what many now insist is a "router".
Gigabit Ethernet
High-speed version of Ethernet (a billion bits per second) under development by the IEEE.
Gigabit Ethernet Alliance
Group of vendors working together to help drive the standarization of Ethernet at 1Gbps data rates.
GOSIP "Government Open Systems Interconnect Profile"
A subset of OSI standards specific to US Government procurements, designed to maximize interoperability in areas where plain OSI standards are ambiguous or allow options. Theoretically, required of all US Government networking procurements since mid-1990.
Half Duplex
A possible property of a data-communications line: that data can be transferred in either direction, but only in one direction at a time. If the line is sufficiently high-speed, then to a human, it may appear that data transfer is simultaneous in both directions if the two ends quickly take turns transferring. The alternatives are Half Duplex and Simplex.
Hardware Address
Often used phrase for MAC Layer address or Ethernet address.
HDLC "High-level Data Link Control"
A low-level protocol used on synchronous WAN lines.
HDSL "High-bit-rate Digital Subscriber Line"
Remote access line above basic ISDN speed.
Header
A portion of a message (cell, packet, frame, etc) at the front with control information such as the destination address.
Heartbeat
In Ethernet (Version 2), a test of the collision functionality of the transciever. The term "Heartbeat" is often (wrongly) used interchangeably with "SQE" which is a similar function of IEEE 802.3. See Question on SQE/Heartbeat below.
HiPPI
"High Performance Parallel Interface", ANSI draft standard X3T9.3.
HSSI "High Speed Serial Interface"
A physical layer interface for serial communications between a DTE (e.g. a router) and a DCE (e.g. a DSU/CSU) that supports up to 52Mbps. Serves the same purpose as RS-232, but at a higher range of communication speeds. Used mostly for DS3 WAN links.
Hub
a nebulous term, typically applied to a multiport repeater or concentrator consisting of a chassis with slots to be populated by cards, allowing it to be configured with various numbers and combinations of LAN ports. Vendors of networking equipment often also have other types of devices that can be inserted in the slots such as terminal servers, bridges, routers, gateways, etc.
ICMP "Internet Control Message Protocol"
(TCP/IP term) An IP-related protocol used to carry out some control functions such as "ping". Documented in RFC792.
IEEE
Institute of Electrical & Electronic Engineers
IEEE 802
The set of IEEE standards for the definition of LAN protocols. A story goes that a long time ago, IEEE and ANSI decided that IEEE would get the slow protocols and ANSI would get the fast ones, thus IEEE defined the 802 protocols and ANSI defined FDDI. Presumably IEEE saw limited application for FDDI at the time. Also, the IEEE standards-making committees associated with these standards.
IEEE 802.1
The IEEE 802 standard for Network Management and Network Bridging of IEEE 802 networks.
IEEE 802.11
Proposed IEEE 802 group for wireless Ethernet.
IEEE 802.12
Group within IEEE 802 working on 100VG-AnyLAN.
IEEE 802.2
An IEEE standard for the portion of LAN data-link protocols that is the same for all flavors of IEEE LAN protocols, e.g. 802.3 and 802.5. Sometimes not used.
IEEE 802.3
An IEEE standard for LANs--their "improved" version of Ethernet. See Ethernet.
IEEE 802.3u
The portion of IEEE 802.3 which defines the 100Mbps version, i.e. Fast Ethernet or 100BASE-T.
IEEE 802.4
An IEEE standard for LANs: Token Bus networks. Basically, standardizes MAP, a protocol that operates a Token Bus protocol on broadband.
IEEE 802.5
An IEEE standard for Token-Ring-based LANs. There are two types: 4Mbps and 16Mbps. See also "Token Ring".
IEEE 802.6
An IEEE standard for Metropolitan Area Networks. Also known as DQDB.
IEEE 802.7
IEEE 802 technical advisory group on Broadband.
IEEE 802.8
IEEE 802 technical advisory group on FDDI & fiber optics.
IEEE 802.9
IEEE 802 group on integrated data & voice networks.
IETF "Internet Engineering Task Force" A group responsible for defining protocols in the TCP/IP family for use on the Internet.
IMAP "Internet Mail Access Protocol"
TCP/IP-based protocol similar to POP, but with additional function designed to handle storage of mail on the server rather than the client. There are two versions in common use: IMAP2 and IMAP4.
IP "Internet Protocol" The basic protocol of TCP/IP and the Internet.
IPX
Novell's protocol used by Netware. Utilizes part of XNS. A router with "IPX routing" purports to interconnect LANs so that Novell Netware clients & servers can talk through the router.
ISDN "Integrated Services Digital Network"
A recent development in telephone/data communications that offers the subscriber digitized voice service and/or 64Kbps data service.
LAN Switching
Term for bridging or cut-through switching, usually referring to a device with more than two ports.
LANE
ATM Forum's method of using an ATM switch or switches to emulate an Ethernet or Token Ring LAN. The resulting "Emulated LAN" is called an ELAN, which can be thought of as a kind of fairly simple VLAN.
Latency
The amount delay in the delivery of data through a network or network device.
LCF-PMD
FDDI "Low-Cost Fiber" PMD. Less expensive than PMD. I don't believe it is common nor is it finished as a standard.
MAU "Media Adaptor Unit"
an IEEE 802.3 or Ethernet device which attaches a station to the cable. Popularly called a "transceiver". Can be attached by cable to the station or built into the station.
MAC "Media Access Control" A layer within the OSI Data Link Layer.
MIB "Management Information Base"
the set of parameters an SNMP management station can query or set in an SNMP agent (e.g. router). Standard, minimal MIBs have been defined (MIB I, MIB II), and vendors often have custom entries. In theory, any SNMP manager can talk to any SNMP agent with a properly defined MIB.
MII "Media Independent Interface"
An Interface much like the 10Mbps Ethernet "AUI" Interface only for 100Mbps Ethernet (100BASE-T, etc).
MPOA "Multiprotocol Over ATM"
ATM Forum's method of using an ATM switch or switches to take the place of routing. The protocol/method is currently in development. As its name implies, it is intended to handle more than just TCP/IP, but TCP/IP support is what is being developed to begin with.
Multimode fiber
A type of fiber mostly used for shorter, e.g. campus distances. It can carry 100 megabits/second for typical campus distances, the actual maximum speed (given the right electronics) depending upon the actual distance. It is easier to connect to than Single Mode Fiber, but its limit on speed x distance is lower.
NIC "Network Interface Card"
A term used for the card you put in a PC to allow it to be attached to a network. The term and acronym is most often used with respect to IBM compatibles, and LANs such as Ethernet and Token Ring.
NFS "Network File System"
an IP-based protocol originally developed by Sun Microsystems which provides file services.
Octet
A networking term which is basically equivalent to the term "byte", i.e. 8 bits.
OCx
(e.g. OC1, OC3) variants of SONET.
OSI "Open System Interconnect"
A standard put forth by the ISO for communication between computer equipment and networks.
OSI Reference Model
A model put forth by the ISO for communication between computer equipment and networks, which maps out 7 protocol layers.

Top layer:    layer number 7: application layer

              layer number 6: presentation layer

              layer number 5: session layer

              layer number 4: transport layer

              layer number 3: network layer

              layer number 2: data-link layer (e.g. IEEE 802.x)

Bottom layer: layer number 1: physical layer (wire & electricity)

This model explains what each layer does. The model is often used to explain anyones protocols (not just OSI) to the point where many people seem to believe that true data-communications requires these 7 layers.
PMD
FDDI "Physical Layer Medium Dependent" part. When "PMD" is used by itself, it may refer to the usual kind of FDDI physical layer that uses multimode fiber. Note that FDDI terminology also uses it as a more generic term, referring to different FDDI PMD's such as TP-PMD and SMF-PMD.
POP "Post Office Protocol"
A TCP/IP-based protocol designed to allow client-stations (e.g. micros) to read mail from a server. There are three versions under the name "POP": POP, POP2, and POP3. Latter versions are NOT compatible with earlier versions.
Protocol
The "rules" by which two network elements trade information in order to communicate. Must include rules about a lot of mundane detail as well as rules about how to recover from a lot of unusual communication problems. Thus they can be quite complicated.
Relay
One terminology uses the term "relay" as a device that interconnects LANs, different kinds of relays being repeaters, bridges, routers, and gateways.
Repeater
In the "Ethernet" world, a "relay" that regenerates and cleans up signals, but does no buffering of data packets. It can extend an Ethernet by strengthening signals, but timing limitations on Ethernets still limit their size.
RFC "Request For Comments"
The name is a real red herring when it comes to Internet RFCs. Some really are "Requests For Comments" but all Internet protocol documents are stamped with an RFC number that they never shake, so the acronym RFC generally refers to documents that describe protocols in the TCP/IP family.
RG numbers (E.g. RG62; sometimes there are qualifiers, e.g. RG 58 A/U)
a shorthand designation for military cable. RG58 & RG62 designate two different types of cable used by the military. Some data-communications equipment was designed to work with a particular military standard, e.g. IBM 3270-type terminals use RG62. In other cases, people use an RG-numbered cable that is close to what they need: for example ThinWire Ethernet & IEEE 802.3 10BASE2 define the type of cable they need and people sometimes substitute flavors of RG58, which are "close". One can't recommend this practice because you can get yourself in trouble. I think "RG" originally stood for "Radio Guide", presumably reflecting the fact that the series of cables was designed to handle radio frequencies. The IEEE 802.3 10BASE2 specifications define two RG numbered cables (RG58 A/U and RG58 C/U) as meeting the cable requirements for thin Ethernet. However, cable vendors may list a range of cables under these same RG numbers, and some of the cables listed may not meet the 802.3 specs. You need to check the cable specifications closely, and beware of relying on the RG number alone when ordering network cables.
Ring
A classification of network technology (known as its topology) exemplified by Token Ring and FDDI. The interconnected devices are connected one-to-another in the shape of a ring and data flows around it in one direction. See also "Counterrotating Ring".
RJ numbers ("Regestered Jack" numbers, e.g. RJ11, RJ45)
numbers applied to types of connectors often used in UTP wiring. Borrowed from voice telecommunications industry.
Router
A network "relay" that uses a protocol beyond the data-link protocol to route traffic between LANs and other network links.
Routing Protocol
a protocol sent between routers by which routers exchange information own how to route to various parts of the network. The TCP/IP family of protocols has a bunch, such as RIP, EGP, BGP, OSPF, and dual IS-IS.
RSVP "Resource Reservation Protocol"
A method being developed by the IETF to assist in providing quality-of-service characteristics to communications over an IP network. The name refers to the fact that it allows the end-stations to reserve bandwidth on the network.
SDH "Synchronous Digital Hierarchy"
Similar to SONET, but used outside North America. Some of the SDH and SONET standards are identical. Standardized by the CCITT.
SDLC "Serial Data Link Control"
A low-level protocol used on synchronous WAN lines.
Shielded Twisted Pair
a type of twisted-pair cable with a metallic shield around the twisted conductors. The shield reduces the noise from the cable and reduces the effects of noise on the communications in the cable, but changes the electrical characteristics of the cable so some equipment optimized to non-shielded cable runs worse on shielded cable.
Single Mode fiber
a type of fiber optic cable used for longer distances and higher speeds, e.g. for long-distance telephone lines. See also "Multimode Fiber".
SMF-PMD
FDDI "Single-Mode Fiber" PMD. Runs further than PMD.
SMTP "Simple Mail Transfer Protocol"
the protocol in the TCP/IP family used to transfer electronic mail between computers. It is not oriented towards a client/server system so other protocols (see "POP") are often used in that context. However, servers will use SMTP if they need to transfer a message to another server.
SNMP "Simple Network Management Protocol"
Originally developed to manage IP based network equipment like routers and bridges, now extended to wiring hubs, workstations, toasters, jukeboxes, etc. SNMP for IPX and AppleTalk under development. Widely implemented. See CMIP.
SONET "Synchronous Optical Network"
A set of standard fiber-optic-based serial standards planned for use with ATM in North America. Developed by Bellcore. Different types of SONET run at different speeds (OC1 runs at 51Mbps, OC3 runs at 155Mbps, OC12 runs at about 600Mbps, OC48 runs at over 2Gbps), and use different types of fiber (OC3 has several variants for use with different fibers & different distances; there are versions for both single mode and multimode fiber).
SQE Test "Signal Quality Error Test"
an IEEE 802.3 function that tests the transceiver. The term "SQE" is often (wrongly) used interchangeably with "Heartbeat" which is a similar function of Ethernet Version 2. See Question on SQE/Heartbeat below.
Star
A classification of network technology (known as its topology) defined by a network which consists of a central element attached to its client computers via wires leading out from the central element. A LAN that consists of a number of computers each directly attached to an ATM switch is a good example of a star-topology LAN.
STP
Shielded Twisted Pair
STS-3c UNI
ATM Forum SONET STS-3c UNI, 155.52Mbps.
Switched Ethernet
really the same as Ethernet as far as standards go: acts like a very fast multiport Ethernet bridge giving an Ethernet to each station. Presumably based on 10BASE-T for most stations.
Switched FDDI
really the same as FDDI as far as standards go: acts like a very fast multiport FDDI bridge. Basically the DEC GigaSwitch.
T1
A phone-company standard for running 24 digitized voice circuits through one 1.5megabit/second digital channel. Since phone companies run lots of T1, and will run T1 between customer sites, the standard is often used for data communications, either to provide 24 low-speed circuits, or to provide 1 high-speed circuit, or to be divided other ways.
TAXI
"Transparent Asynchronous Transmitter-Receiver Interface" Two ATM UNI specifications developed by Fore. The slower one ran at 100Mbps and borrowed the physical characteristics of FDDI and has been adopted by the ATM Forum as its 100Mbps UNI specification. The faster one ran at 140Mbps.
TCP/IP "Transmission Control Protocol/Internet Protocol"
literally, two protocols developed for the Defense Data Network to allow their ARPANET to attach to other networks relatively transparently. The name also designates the entire family of protocols built out of IP and TCP. The Internet is based upon TCP/IP.
TELNET
a protocol in the TCP/IP family that is used for "remote login". The name is also often used as the name of the client program that utilizes the TELNET protocol.
Terminal Server
a network device that allows a number of terminals to attach to a LAN, and do remote logins across the LAN.
ThickWire
"ThickWire" Ethernet or IEEE 802.3 10BASE5.
ThinWire
ThinWire Ethernet or IEEE 802.3 10BASE2.
TN3270
A variant of the TELNET program that allows one to attach to IBM mainframes and use the mainframe as if you had a 3270 or similar terminal.
Token Ring
People often use the term "Token Ring" to designate IEEE 802.5 (see above). In the more general sense of the phrase, a token ring is a type of LAN that has stations wired in a ring, where each station constantly passes a special message (a "token") on to the next. Whoever has the token can send a message.
Topology
Term used to describe a general characteristic of a LAN technology which more or less describes the shape of the necessary wiring. Three examples are bus, ring, and star.
TP
"Twisted Pair".
TP-PMD
FDDI "Twisted Pair Physical Layer Medium". ANSI specification for FDDI-like service over UTP. Being standardized by ANSI X3T9.5. Was X3T9/93-130 X3T9.5/93-022 TP-PMD/306 Rev 2.0, now there is a Rev 2.1. Uses MLT-3 encoding instead of CDDI's NRZI encoding.
Tunneling
An important concept in the design of many kinds of networks: taking some protocol-family's ability to move packets from user to user, or to open virtual-circuits between users, and use this as if it were a data-link protocol to run another protocol family's upper layers (or even the same protocol family's upper layers). Examples: running TCP/IP over AppleTalk instead of something like Ethernet; running AppleTalk over DECNet instead of something like Localtalk or Ethernet.
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 not shielded (see "Shielded twisted Pair").
Type1
IBM Type 1 STP. The most usual type of Shielded Twisted Pair in LAN communications.
UNI
ATM Forum "User to Network Interface". See ATM.
UTP (Unshielded Twisted-Pair)
See "Twisted-Pair" and "Shielded Twisted-Pair".
Virtual LAN (VLAN)
A portion of one or more LAN switches which delivers packets as if it were a physical LAN; actually like a switched LAN. It is a feature planned or included in numerous LAN switches. VLAN is a well-known industry buzzword as of 1995 and 1996 and is not used consistently throughout the industry. The most primitive VLAN facility that a switch can have allows the switch to be partitioned into two or more groups of ports (VLANs) within which communication is possible, but between which communication is blocked. More complex is a feature which allows each VLAN to reside on two or more switches (e.g. some of VLAN A's ports are on switch 1 and some of its ports are on switch 2; and the same for VLAN B) even though the two switches are connected through a single physical interface. The most complex is provision for VLANs that overlap, i.e. port 1 of a switch is on VLAN A and VLAN B, while port 2 is on VLAN A but not VLAN B, etc. The term "Virtual Network" is also used.
Virtual Network
See "Virtual LAN".
WAN "Wide Area Network"
A term for state/country/world-wide networks developed to parallel the term LAN for "Local Area Network".
X.25
Protocol used for inter-computer communications over WANs.
X.400, X.500
OSI protocols for mail and directory services.