AAx Networking Glossary

A Reference of Terms used in Networking & Telecommunications






General & Local Area Networks

When most people think of a Network, they are thinking of a LAN (Local Area Network). WAN (Wide Area Network) is the other major category. Most WAN stuff here is down in (Telecom), as transmission over carrier lines is the hallmark of WANs. A LAN is entirely contained within a single location and all its cabling belongs to one owner. Server - First we must deal with the concept of "Server", which confuses some people.
  • A Server is a computer that offers resources to other computers on the network. This server may also be a workstation.
  • A Server is a software process running on a server (computer) or on a workstation (either of which may be running several other servers at the same time) that offers a resource or service to other computers on the network, or to the computer it happens to be running on, or both.
Do you feel better now that you understand this? Good.
NOS - Network Operating System - what most people think of as "the network" These come in many varieties from many vendors, though the active list is being reduced very quickly. protocol - An agreed on set of rules by which two processes interact. There are many, many protocols used in computers and data communications. Some are public standards and others are proprietary.

NetBIOS - Network Basic Input Output System - a network protocol created by IBM for their PC-Net network. It is used by IBM (OS/2 Networking), Artisoft (Lantastic), Microsoft (Microsoft Networking) Samba, and others. NetBEUI (NetBIOS Enhanced User Interface) is includes additional protocols used by OS/2, Microsoft Networking, Samba and others. NetBIOS is not routable and must be encapsulated in TCP/IP to go through routers (NetBIOS over TCP/IP or TCPBEUI)

IPX/SPX - Novell's NetWare networking protocol. Roughly equivalent in purpose to TCP/IP, but designed to be more efficient for smaller networks.

Ethernet - The dominant LAN network transport protocol today. Available in 10-mbs and 100-mbs versions with 1000-mbs (1-gbs) comming soon. An Ethernet card listens to the cable to see if anyone else is transmitting. If the cable is quiet it transmitts its packet. If two transmitt at the same time, then there is a collision and both packets are destroyed. Both cards wait a random length moment and transmit again. If the net is very busy there will be a lot of collisions and performance will suffer. Ethernet is available in various types and speeds. Distances can be increased by running on fiber instead of wire.

  • 10Base5 - Thick Ethernet - Bus topology - 10-mbs on thick coax (about 3/4" and usually bright orange) for 500 meters max. Stations are added using a vampire tap (which pierces the cable to make a connection) above the ceiling, and an AUI drop cable connects it to the 15-pin D AUI connector on the interface board in the station.
  • 10Base2 - Thin Ethernet, "Cheaper Net" - Bus topology - 10-mbs on thin coax for 200 meters max. This is the familiar coax Ethernet where each network card has a "T" connector and a coax cable attaches to each arm of the "T".
  • 10BaseT - UTP Ethernet - Star Topology - 10-mbs on UTP (Unshielded Twisted Pair, Category-3 or better) for 100 meters max. Each station is cabled to a central hub.
  • 100BaseT - Fast Ethernet - Star Topology - 100-mbs on UTP (Category-5) for 100 meters max. Each station is cabled to a central hub.
  • 1000BaseT - Gigabit Ethernet - Star Topology - 1-gbs on UTP (Category-5 or better) for 100 meters max.

Token Ring - IBM's network protocol. Theoretically higher performance under heavy load than Ethernet because it is deterministic (no collisions possible), but it has more overhead. In practice it didn't show enough performance advantage to offset its considerably higher price. Token Ring comes in 4-mbs and 16-mbs versions. Network cards are cabled to a MAU (Media Access Unit). A "token" is passed from card to card around the ring, and only the card holding the token is allowed to send data onto the network cable.

FDDI - Fiber Distributed Data Interface - an ANSI standard for data transmission over optical fiber. Cost of the network cards has restricted FDDI to critical backbone spans.

half duplex, full duplex - bidirectional transmission modes. Half duplex allows transmission in only one direction at a time (like in WWII aviation movies where the pilot says "over" to indicate the other guy can talk now). Full duplex allows both to talk at the same time, as in a telephone conversation.

Broadband - Transmission by modulated carrier - Data over TV cable is broadband, DSL is not. In cable transmission a high frequency carrier signal is modulated by data. In DSL data signals are sent as changes in voltage on the wire. DSL should be called "high data rate", not broadband.

Bandwidth - Network transmission capacity - bandwidth is usually specified in Megabits per second (Mbps) or kilobits per second (kbps) for slow connections and bits per second (bps) for really, really slow connections.

baud (number of signaling elements / second), was once a common term for data transmission rate, but is now almost always misused in place of bps, if it is used at all. Modern high speed encoding allows bps to be much higher than the baud rate of the device.

Typical Bandwidths:

  • 1-gbps - Gigabit Ethernet
  • 100-mbps - Fast Ethernet (100BaseT).
  • 45-mbps - T3, DS-3
  • 16-mbps - 16-megabit Token Ring.
  • 10-mbps - Ethernet: 10Base5 (thick coax) 10Base2 (thin coax) 10BaseT (UTP).
  • 4-mbps - 4-megabit Token Ring
  • 2.048-mbps - E1 (European T1)
  • 1.544-mbps - T1, DS-1
  • 1.544-mbs - ISDN Primary Rate (23 B channels)
  • 128-kbs - ISDN Basic Rate (2 B channels)
  • 64-kbs - DS-0, Digital Data Service
  • 64-kbs - ISDN single B channel
  • 56-kbs - Dedicated data line - Frame Relay, etc.
  • 56-kbs - Modem 56k V.90 - unachievable
  • 42-kbs - Modem 56k V.90 - about the fastest you're going to actually get
  • 33.6-kbs - Modem 33.6 - theoretical maximum for modems.
  • 300-bps - Modem - the original Hayes modem speed.

Switched, Connectionless - Network transmission behavior - The telephone system is a switched system. An actual circuit is established between two points and remains devoted to that connection until it is broken - easy to understand. IP (Internet Protocol) and similar data networks are connectionless. Data transactions are made up into addressed packets (think letter in an addressed envelope). Let's say your computer wants to send a request to a Web site for a page. The request is made up into a packet, addressed and passed to the nearest router. Routers read the address and pass the packet on towards its destination. The Web site recieves the packet, reads it, makes up the page into packets, addresses them according to the return address in the recieved packet, and sends them off to the nearest router. Then it forgets about you entirely until it recieves another request packet.

ISO 7-layer Stack - The International Standard Organisation's design for a networking protocol in 7 well defined layers. It was to replace interim protocol TCP/IP and all other network protocols. Unfortunately ISO met TCP/IP in a dark alley and hasn't been heard from since. Today the ISO 7-layer Stack is used only as a teaching tool to explain protocol stacks.

Timeshare - Sharing a large computer - generally among a number of companies. A large computer in a centralized location slices its processing time among a number of customers who have terminals at their sites. Timeshare was wiped out by the PC, which could put similar computing power on the individuals desktop with no need for a large central computer and communications wiring.

RPC - Remote Procedure Call - the heart of Client- Server networking. Allows a client to initiate a procedure on a remote server, running it on the server instead of on the client as with normal networking.

MHS - Message Handling System - an ISO standard in development for a complete e-mail system. X.400 and X.500 are parts of MHS.

X.25 - a telecommunications protocol for transmission over certain types of leased lines. Popular in Europe.

X.400 - CCITT/ISO standard for a mail transfer protocol similar in purpose to SMTP which is replacing it due to the popularity of the Internet and it's protocols. X.400 standards have been absorbed into other e-mail systems like Microsof Exchange. Some components of X.400 are UA (User Agent), MTA (Message Transfer Agent (moves mail among servers an mailboxes)) and MS (Message Store (maintains message databases)).

X.500 - ITU/ISO standard for e-mail directory services. It is large and complex and has not been widely adopted. LDAP (Lightweight Directory Access Protocol) is a simplified Internet standard based on X.500 that is gaining popularity.

CMC - Common Messaging Calls - an XAPIA specification for an e-mail API. It currently supports X.400 and SMTP/ MIME e-mail protocols. There are two varieties: Simple CMC, for e-mail enabled applications, and Full CMC for entire e-mail systems. Full CMC has been selected for Lotus Notes 4.0 and Novell's GroupWise XTD. "The World against Microsoft" - see MAPI.

Internet, The Internet - an internet is any network of networks. The Internet is a specific worldwide network of networks covered here in its own pages.

Exchange Server - Microsoft proprietary e-mail system - a key part of Microsoft's "Back Office" server suite. It is a large, very complex e-mail system most people wish they had never gotten involved with. Runs only on Windows NT/2000 servers.

MAPI - Messaging API - Microsoft's messaging protocol for Exchange Server. "Microsoft against the World" - see CMC. There are two versions, Simple MAPI, nearly identical to Simple CMC, and Extended MAPI, almost completely unrelated to CMC but providing tight integration into the Windows NT operating System.

DUN - Dial-Up Networking - a Microsoft method for connecting to a remote system by modem. Supports SLIP, PPP and X.25 connections.

RAS - Remote Access Services - Microsoft dial-in service for remote access.

Replication - Making a copy of a directory, database or message store from one server to another to make them identical.

Synchronization - Justifying two or more directories, databases or message stores that have been independently updated to make them identical without losing data from either or any of them.

Outlook - Client software (running on individual workstations) for access to Exchange Server e-mail and calendaring.

Policy Based Network Management - Yet another attempt to make large networks manageable. In theory, the manager sets up a system of rules (policies) which are followed by all the devices controlling data flow over the network.

SNMP - Simple Network Management Protocol - Yet another Unix derived protocol. SNMP is a system where all conformant devices controlling data flow and system health on the network can be polled for status from a central management console. Remote configuration is also sometimes supported.

LDAP - Lightweight Directory Access Protocol - A subset of the ISO X.500 network directory protocol which has proven too complex for anyone to actually use. LDAP maintains a directory tree of all the subnets, servers, users, printers and other objects on the network. Other directory protocols (Microsoft's Active Directory; Netscape's Directory Server; Novell's NDS (NetWare Directory Services)) are based on, partially based on, claim to be somewhat compatible with, or offer an interface to LDAP directories.

Telnet - Terminal emulation over a network - Terminals are traditionally connected to host computers by serial data cables or coax cable (IBM) - one cable from each terminal all the way back to the computer or to a terminal server. With telnet, a PC running terminal emulation software attaches to the host computer through the same network cable it uses for normal network services.

Telnet is often used as the management interface for routers and other network devices. You log in as if to a normal Unix computer and run the configuration and statistics programs.

WAP - Wireless Application Protocol - a set of protocols based on Internet protocols but modified for use with wireless devices that have long latency, imperfect access coverage, small screens and low power processors. It uses a cut-down version of XML called WML (Wireless Markup Language).


E-mail messages are sent to an e-mail address which is composed in strict conformance to the rules of the particular e-mail system in use. The most well known is the Internet e-mail address which is in the form of "joeblow@squid.nitnet.com", where "joeblow" is the mailbox, "squid" is the server, "nitnet" is the network and ".com" is the top level domain. Note that "joeblow" may not actually be the real mailbox name on the server, but an "alias" for the real mailbox name.

E-mail messages are delivered to a mailbox on a mail server. A mailbox is a "container" for messages addressed to a particular person or entity.

For Internet mail, the usual setup is to receive your mail on a POP (Post Office Protocol) server and send it out through an SMTP server. Rarely, the SMTP server is also used to recieve mail.

The Microsoft Exchange Server insists on receiving Internet mail from an SMTP server, with special protocols, so only a few ISPs support Exchange Server and that makes it a real hassle.


The Internet glossary is on its own separate page.

Telecom & Wide Area Networks (WAN)

The Telecom & WAN glossary has it's own separate page.

Wire, Cable & Fiber

Category-3, Category-4, Category-5 - Grades of UTP (Unshielded Twisted Pair) cable used for telecommunications and networking.
Category-3 is suitable for transmission speeds to 10-Mbs (Ethernet 10BaseT) for distances to 100 meters. Cat-3 is common as a 4-pair cable, but is available in 25-pair, 50-pair, and even larger cables
Category-4 was created for 16-Mbs Token Ring networking, and has been completely replaced by Category-5.
Category-5 is designed for transmission speeds to 100-Mbs (Fast Ethernet) for distances to 100 meters. Some faster services can also run on Category-5. Cat-5 cable is always 4-pair.
Category cable comes in plenum and non-plenum versions.

Plenum Cable - Cable that meets code for use in air passages. In many office buildings the space between an accoustic drop ceiling and the real ceiling is a plenum area and requires plenum cable. Plenum cable gives off little smoke when burned.

Hardware for Networking

DSU, DSU/CSU - Digital Services Unit / Channel Services Unit A unit that provides connection between a computer or computer network and digital communications lines. The DSU side talks to the computer, the CSU side talks to the line.

Modem - Modulator Demodulator - A device that turns digital data into sound for transmission over voice phone lines (modulator) and turns such sounds back into digital data (demodulator) at the other end. Modems have evolved rapidly until now, at 56.6-kbps, there is no longer any evolution left. Modem standards are:

To Be Determined

No topic paragraph available yet.

©:Andrew Grygus - Automation Access
Velocity Networks: Network Consulting Service - Internet Service Provider - Web Page Design and Hosting
All trademarks and trade names are recognized as property of their owners