CONFIGURATION UTILITY PROGRAM
Need Defined
DHCP MODE
DHCP SERVER - A server in the network or a service within a
server that assigns IP addresses.
DYNAMIC - versus Static
Refers to operations performed "on the fly," which are based on
decisions made while the program is running rather than beforehand.
The expression, "buffers are dynamically created," means that space
is created when actually needed, not reserved ahead of time. The
expression, "data is compressed onto the disk dynamically" means
that the compression algorithms are being applied when the data is
being written rather than before. Contrast with static.
DYNAMIC IP ADDRESS
An IP address that is automatically assigned to a client station
in a TCP/IP network, typically by a DHCP server. Network devices
that serve multiple users, such as servers and printers, are usually
assigned static IP addresses. See static IP address, IP address and
DHCP.
DVR - Digital Video Recorder or see PVR
ETHERNET
The most widely used local area network (LAN) access method, defined
by the IEEE as the 802.3 standard. Ethernet has become so popular
that a specification for "LAN connection" or "network card"
generally implies Ethernet without saying so. All Macs and many PCs
come with 10/100 Ethernet ports for home use, not just to create a
small home network, but to connect to the Internet via a DSL or
cable modem, which requires it. A 10/100 port means that it supports
both 10BaseT at 10 megabits per second (Mbps) and 100BaseT at 100
Mbps.
Ethernet is normally a shared media LAN. All stations on the segment
share the total bandwidth, which is either 10 Mbps (Ethernet), 100
Mbps (Fast Ethernet) or 1000 Mbps (Gigabit Ethernet). With switched
Ethernet, each sender and receiver pair have the full bandwidth.
Twisted pair Ethernet (10BaseT) uses economical telephone
wiring and standard RJ-45 connectors, often taking advantage of
installed wires in a building. It is wired in a star configuration
and requires a hub or switch. Fast Ethernet (100BaseT) is similar,
but uses two different twisted pair configurations (see 100BaseT).
Today's Ethernet network adapters, hubs and switches generally
support both 10BaseT and 100BaseT (10/100) and automatically sense
and adapt to the transmitted speed. The earlier versions of 10 Mbps
Ethernet used coaxial cable (see 10Base5 and 10Base2).
Fiber-optic Ethernet (10BaseF and 100BaseFX) is impervious to
external radiation and is often used to extend Ethernet segments up
to 1.2 miles. Specifications exist for complete fiber-optic networks
as well as backbone implementations. FOIRL (Fiber-Optic Repeater
Link) was an earlier standard that is limited to .6 miles distance.
Ethernet transmits variable length frames from 72 to 1518 bytes in
length, each containing a header with the addresses of the source
and destination stations and a trailer that contains error
correction data. Higher-level protocols, such as IP and IPX,
fragment long messages into the frame size required by the Ethernet
network being employed (see MTU).
Ethernet uses the CSMA/CD technology to broadcast each frame onto
the physical medium (wire, fiber, etc.). All stations attached to
the Ethernet are "listening," and the station with the matching
destination address accepts the frame and checks for errors.
Ethernet is a data link protocol (MAC layer protocol) and functions
at layers 1 and 2 of the OSI model.
Ethernet was invented by Robert Metcalfe and David Boggs at Xerox
PARC in 1973, which first ran at 2.94 Mbps. Metcalfe later joined
Digital where he facilitated a joint venture between Digital, Intel
and Xerox to collaborate further on Ethernet. Version 1 was
finalized in 1980, and products shipped in the following year. In
1983, the IEEE approved the Ethernet 802.3 standard. See 100BaseT,
Gigabit Ethernet, 10 Gigabit Ethernet and switched Ethernet.
10 Mbps AND 100 Mbps
ETHERNET LIMITATIONS
Maximum Maximum
Type Segment length Devices
TWISTED PAIR (star topology)
10BaseT 328 ft. (100 m) 1
100BaseT 328 ft. (100 m) 1
COAX (bus topology)
10Base5 "thick" 1640 ft. (500 m) 100
10Base2 "thin" 607 ft. (185 m) 30
FIBER (star topology)
FOIRL .6 mi. (1 km) 1
10BaseF 1.2 mi. (2 km) 1
100BaseFX multimode 1.2 mi. (2 km) 1
100BaseFX single-mode 6 mi. (10 km) 1
10BASET.WMF
Twisted Pair Ethernet
Most Ethernets use twisted pair wiring. All cables use RJ-45
connectors between the network adapters in the PC and a central hub
or switch.
Ethernet Switch
This 10/100 switch from Omnitron has 16 ports and automatically
senses the transmission rate of the line and adjusts accordingly.
10BASE5.WMF
The Original Ethernet
The first Ethernet (10Base5) used a bus topology and a thick coaxial
cable. Transceivers connect the network adapters to the cable via a
vampire tap that "bites" into the coax.
10BASE2.WMF
Thin Ethernet
10Base2 Ethernet was a later variation of the original 10Base5. It
used a thinner coaxial cable attached to each node using BNC
T-connectors.
FIREWIRE
A high-speed serial bus developed by Apple and Texas Instruments
that allows for the connection of up to 63 devices. Also known as
the IEEE 1394 standard, the i.Link connector and the High
Performance Serial Bus (HPSB), the original spec calls for 100, 200
and 400 Mbits/sec transfer rates. IEEE 1394b provides 800, 1600 and
3200 Mbits/sec speeds.
FireWire supports hot swapping, multiple speeds on the same bus and
isochronous data transfer, which guarantees bandwidth for multimedia
operations. It is expected to be widely used for attaching digital
cameras and other video devices to the computer.
IP ADDRESS -
(Internet Protocol address) The address of a computer attached to a
TCP/IP network. Every client and server station must have a unique
IP address. Client workstations have either a permanent address or
one that is dynamically assigned to them each dial-up session. IP
addresses are written as four sets of numbers separated by periods;
for example, 204.171.64.2.
PVR - (Personal Video
Recorder) Also known as a "digital video recorder" or "DVR," it is a
consumer device that digitizes broadcast TV onto a hard disk and
plays it back immediately, allowing the viewer to pause at any time
and return later. Using hardware-based MPEG-2 compression like DVD
movies, it also records programs for later viewing just like a VCR.
Using a phone line, the PVR can call a service provider and download
the channel guide updates as well as software updates for the unit
itself. The PVR can also be set to periodically record favorite
shows whenever they are broadcast. Also built into satellite
receivers and set-top boxes, ReplayTV (
www.replaytv.com ) and TiVo (
www.tivo.com ) were the first to
introduce products in 1999.
RELOAD
To download again the same Web page that is on screen to see if it
has changed since the last time it was downloaded. See refresh.
REFRESH
To download again (reload) the same Web page that is on screen
to see if it has changed since the last time it was downloaded. See
reload.
SERVER
A computer in a network shared by multiple users. The term may refer
to both the hardware and software or just the software that performs
the service. For example, Web server may refer to the Web server
software in a computer that also runs other applications, or, it may
refer to a computer system dedicated only to the Web server
application. There would be several dedicated Web servers in a large
Web site.
STATIC IP ADDRESS
A permanent IP address that is assigned to a node in a TCP/IP
network. Servers and routers are usually assigned static IP
addresses, while client stations are often assigned dynamic IP
addresses from a DHCP server each time they come online. Users
connected to the Internet via cable modems and DSL either in the
office or at home are also assigned long term (static) IP addresses,
which makes them more vulnerable to hacker attacks than IP addresses
that are dynamically assigned. See dynamic IP address, IP address
and DHCP.
streaming video
Video transmission over a data network. It is widely used on the Web
to deliver video on demand or a video broadcast at a set time. In
streaming video, both the client and server software cooperate for
uninterrupted motion. The client side buffers a few seconds of video
data before it starts sending it to the screen, which compensates
for momentary delays in packet delivery. Streaming video implies a
one-way transmission and tolerates erratic networks. Contrast with
videoconferencing, which requires realtime, two-way transmission
without delays. See streaming audio.
WEBCAST
(A) To send live audio or video programming over the Web. It is
the Internet counterpart to traditional radio and TV broadcasting.
(B) To send selected Web-based information (text, graphics, audio,
video, etc.) to Internet users based on individual requirements. See
push technology.
WEB SERVER
A computer that provides World Wide Web services on the Internet. It
includes the hardware, operating system, Web server software, TCP/IP
protocols and the Web site content (Web pages). If the Web server is
used internally and not by the public, it may be known as an
"intranet server."
The term may refer to just the software and not the entire computer
system. In such cases, it refers to the HTTP server that manages Web
page requests from the browser and delivers HTML documents (Web
pages) in response. The Web server also executes server-side scripts
(CGI scripts, JSPs, ASPs, etc.) that provide functions such as
database searching and e-commerce.
A single computer system used to provide all the Internet services
for a department or a small company would include the HTTP server
(Web pages), FTP server (file downloads), NNTP server (newsgroups)
and SMTP server (mail service). This system with all its services
could be called a Web server.
Web servers are also often used for vertical applications. Any
network device, such as the print server in the example below, can
contain an internal Web server (HTTP server) as the means for
configuring the unit. Contrast with Web client. See application
server and embedded Web server.
