Accronyms and Glossary - the quest for meaning
Every industry has a lexicon all its own, and computing (and
business) are no exception.
- NIS (yp)
- 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
- 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 project-web01.load.finao.com into IP addresses
such as 172.20.1.256
- 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
- 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: 10.0.0.0
- 10.255.255.255 (10/8 prefix), 172.16.0.0 -172.31.255.255
(172.16/12 prefix), amd 192.168.0.0 - 192.168.255.255 (192.168/16
- Network Information
- 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.
- passwd for identifying and authenticating users,
- groups for authorizing users to access certain
resources on machines,
- names for converting computer names to IP addresses
(not commonly used, DNS is more common)
- 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
|Data translation, encryption
|TLS, SSL (when used)
|Creating and destroying
|Reliable delivery of data
|2 Data link
controlling the connections
SLIP, PPP, similar
|Moving data on and off the
|Ethernet, RS-232, Wireless,
- 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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Initial checkin to CVS
Revision 1.1 2006/01/05 06:02:19 jeffs