Accronyms and Glossary - the quest for meaning

Every industry has a lexicon all its own, and computing (and business) are no exception.

  1. Authentication
    1. NIS (yp)
    2. Kerberos
    3. LDAP
  2. NTP

The process of determining that the entity is in fact what or who the entity claims to be.  A government issued ID card with a photograph can be used to authenticate somebody.  Kerberos provides a strong authentication service.  NIS provides a weak authentication service (it's rather easily faked and intercepted).  Posession of my secret password authenticates me, but that's not very strong anymore and other authenticators are being developed and deployed.  Compare with Authorization and identification.
The process of determining that the entity is authorized to do what they want to do.  A drivers license authorizes the bearer to drive, and it has positive endorsements (e.g. motorcycles, trucks) and negative endorsements (must wear corrective lenses, must not carry passengers).  An American social security card is a better example: it authorizes the bearer to work in the United States and to collect social security benefits. However, it doesn't have a picture of the bearer, so it cannot be used to authenticate that the bearer is who they claim to be. The /etc/passwd and /etc/group files are repositories of authorization information. Compare with authentication and identification.
Data Flow Diagram
A hierarchy of diagrams that show the flow of data with a system in greater and greater detail.   Design.
Data Flow Diagram  write more here.  See also Structured Analysis and Structured Design.  More references: How to draw data flow diagrams (not open source)
Distributed Name Server.  A network service that translates computer names, such as into IP addresses such as
When a system fails, there is a mechanism to switch to an alternate system. This is usually implemented by a load
A system has failed if it is unable to deliver correct answers to legitimate requests for any reason, or it delivers correct answers to illegitimate requests, for any reason.
Internet Assigned Numbers Authority
The process of uniquely describing an entity or person.  For example, I am one of at least three Jeff Silvermans, but I am the only one with my social security number.  My name does not uniquely identify me (if you don't believe me, ask Bill Jones or John Smith).   My username uniquely identifies me in the space of my computer systems.  Compare with authentication and Authorization
Internet Engineering Task Force.
Load Balancing

Refer also to "Load Balancing" and Fail Over.

Mean Time between Failures
Mean Time To Repair.  Also known in the literature as MTTF (Mean Time To Fix).
Network Address Translation
Network Address Translation
A mechanism for translating network addresses into private addresses.  This is discussed in gory detail in RFC 1918.  The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space for private internets: - (10/8 prefix), - (172.16/12 prefix), amd - (192.168/16 prefix)
Network Information Service (NIS)
A reliable network service that provides a mapping from keys in maps to values. Some common maps include NIS has lots of other possible uses, such as telephone books and any other data that is read-mostly and changes slowly.
Network Time Protocol
A network service which is capable of keeping the clocks of ordinary PCs synchronized to within a millisecond of the correct time.
Network Information service
Network Time protocol

Reliability is (MTBF-MTTR)/MTBF = 1-MTTR/MTBF.  Since typical values for reliability are on the order of .9, .99, or .999, it is common to simply count 9s.  So, example, a system with 1 hour of downtime (MTTR = 1 hour) in a thousand hours of operation  (MTBF=1000 hours) would be .999 or 3 nines.  There are about 9000 hours in a year, so a system running 24x7 with 3 nines reliability should fail about  9 times a year.
OSI Model or the OSI stack
A conceptual model of how networks work.  The model consists of layers, each layer uses functionality of the layer below it.  The layers, their functions, and  how TCP/IP fits into the model is:
OSI layer
TCP/IP equivalent
7 Application
The application
The application
6 Presentation
Data translation, encryption
TLS, SSL (when used)
5 Session
Creating and destroying sessions
4 Transport
Reliable delivery of data
3 Network
Routing packets
2 Data link
Delivering datagrams, controlling the connections
Ethernet, SLIP, PPP, similar
1 Physical
Moving data on and off the media
Ethernet, RS-232, Wireless, similar

Return on investment.  The basic measure of the value of a given investment.  See management.
Virtual IP
Short for Virtual Router Redundancy Protocol. An election protocol that dynamically assigns responsibility for one or more virtual router(s) to the VRRP router(s) on a LAN, allowing several routers on a multiaccess link to utilize the same virtual IP address. A VRRP router is configured to run the VRRP protocol in conjunction with one or more other routers attached to a LAN. See the IETF VRRP charter , webopedia, and Cisco's page on VRRP.
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Revision 1.1 2006/01/05 06:02:19 jeffs
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