Networking Terms
Architecture -- A
design. The term architecture can refer to either hardware or
software, or to a combination of hardware and software. The
architecture of a system always defines its broad outlines, and may
define precise mechanisms as well.
An open
architecture allows the system to be connected easily to devices and
programs made by other manufacturers. Open architectures use
off-the-shelf components and conform to approved standards. A system
with a closed architecture, on the other hand, is one whose
design is proprietary, making it difficult to connect the system to
other systems.
Bus
– (1) A collection of wires through which data is transmitted from
one part of a computer to another. You can think of a bus as a
highway on which data travels within a computer. When used in
reference to personal computers, the term bus usually refers
to internal bus. This is a bus that connects all the internal
computer components to the CPU and main memory. There's also an
expansion bus that enables expansion boards to access the CPU and
memory.
All buses
consist of two parts -- an address bus and a data bus. The data bus
transfers actual data whereas the address bus transfers information
about where the data should go.
The size of a
bus, known as its width, is important because it determines
how much data can be transmitted at one time. For example, a 16-bit
bus can transmit 16 bits of data, whereas a 32-bit bus can transmit
32 bits of data.
Every bus has
a clock speed measured in MHz. A fast bus allows data to be
transferred faster, which makes applications run faster. On PCs, the
old ISA bus is being replaced by faster buses such as PCI.
Nearly all PCs
made today include a local bus for data that requires especially
fast transfer speeds, such as video data. The local bus is a
high-speed pathway that connects directly to the processor.
Several
different types of buses are used on Apple Macintosh computers.
Older Macs use a bus called NuBus, but newer ones use PCI.
(2) In
networking, a bus is a central cable that connects all devices on a
local-area network (LAN). It is also called the backbone.
Client
-- The client part of a client-server architecture. Typically, a
client is an application that runs on a personal computer or
workstation and relies on a server to perform some operations. For
example, an e-mail client is an application that enables you to send
and receive e-mail.
EEPROM
-- Acronym for electrically
erasable programmable
read-only
memory. Pronounced double-ee-prom
or e-e-prom, an EEPROM is a special type of PROM that can be
erased by exposing it to an electrical charge. Like other types of
PROM, EEPROM retains its contents even when the power is turned off.
Also like other types of ROM, EEPROM is not as fast as RAM.
EEPROM is
similar to flash memory (sometimes called flash EEPROM). The
principal difference is that EEPROM requires data to be written or
erased one byte at a time whereas flash memory allows data to be
written or erased in blocks. This makes flash memory faster.
Gateway
-- In networking, a combination of hardware and software that links
two different types of networks. Gateways between e-mail systems,
for example, allow users on different e-mail systems to exchange
messages.
Hardware
-- Refers to objects that you can actually touch, like disks, disk
drives, display screens, keyboards, printers, boards, and chips. In
contrast, software is untouchable. Software exists as ideas,
concepts, and symbols, but it has no substance.
Books provide
a useful analogy. The pages and the ink are the hardware, while the
words, sentences, paragraphs, and the overall meaning are the
software. A computer without software is like a book full of blank
pages -- you need software to make the computer useful just as you
need words to make a book meaningful.
IP address
-- An identifier for a computer or device on a TCP/IP
network. Networks using the TCP/IP
protocol route messages based on the IP address of the destination.
The format of an IP address is a 32-bit numeric address written as
four numbers separated by periods. Each number can be zero to 255.
For example, 1.160.10.240 could be an IP address.
MIB
-- Short for Management
Information
Base,
a database of objects that can be
monitored by a network management system. Both SNMP and RMON use
standardized MIB formats that allows any SNMP and RMON tools to
monitor any device defined by a MIB.
Network
Interface Card
-- Often
abbreviated as NIC, an expansion board you insert into a
computer so the computer can be connected to a network. Most NICs
are designed for a particular type of network, protocol, and media,
although some can serve multiple networks.
Operating
system -- The most
important program that runs on a computer. Every general-purpose
computer must have an operating system to run other programs.
Operating systems perform basic tasks, such as recognizing input
from the keyboard, sending output to the display screen, keeping
track of files and directories on the disk, and controlling
peripheral devices such as disk drives and printers.
For large
systems, the operating system has even greater responsibilities and
powers. It is like a traffic cop -- it makes sure that different
programs and users running at the same time do not interfere with
each other. The operating system is also responsible for security,
ensuring that unauthorized users do not access the system.
Operating
systems can be classified as follows:
·
Multi-user:
Allows two or more users to run programs at the same time. Some
operating systems permit hundreds or even thousands of concurrent
users.
·
Multiprocessing:
Supports running a program on more than one CPU.
·
Multitasking:
Allows more than one program to run concurrently.
·
Multithreading:
Allows different parts
of a single program to run concurrently.
·
Real time:
Responds to input instantly. General-purpose operating systems, such
as DOS and UNIX, are not real-time.
Operating
systems provide a software platform on top of which other programs,
called application programs, can run. The application
programs must be written to run on top of a particular operating
system. Your choice of operating system, therefore, determines to a
great extent the applications you can run. For PCs, the most popular
operating systems are DOS, OS/2, and Windows, but others are
available, such as Linux.
As a user, you
normally interact with the operating system through a set of
commands. For example, the DOS operating system contains commands
such as COPY and RENAME for copying files and changing the names of
files, respectively. The commands are accepted and executed by a
part of the operating system called the command processor or command
line interpreter. Graphical user interfaces allow you to enter
commands by pointing and clicking at objects that appear on the
screen.
PROM
-- Pronounced prom, an acronym for programmable
read-only
memory. A PROM is a memory chip
on which data can be written only once. Once a program has been
written onto a PROM, it remains there forever. Unlike RAM, PROMs
retain their contents when the computer is turned off.
The difference
between a PROM and a ROM (read-only
memory) is
that a PROM is manufactured as blank memory, whereas a ROM is
programmed during the manufacturing process. To write data onto a
PROM chip, you need a special device called a PROM programmer
or PROM burner. The process of programming a PROM is
sometimes called burning the PROM.
An EPROM
(erasable programmable read-only memory) is a special type of PROM
that can be erased by exposing it to ultraviolet light. Once it is
erased, it can be reprogrammed. An EEPROM is similar to a PROM, but
requires only electricity to be erased.
Protocol
-- An agreed-upon format for transmitting data between two devices.
The protocol determines the following:
·
the type of error
checking to be used
·
data compression
method, if any
·
how the sending
device will indicate that it has finished sending a message
·
how the receiving
device will indicate that it has received a message
There are a
variety of standard protocols from which
programmers can choose. Each has particular advantages and
disadvantages; for example, some are simpler than others, some are
more reliable, and some are faster.
From a user's
point of view, the only interesting aspect about protocols is that
your computer or device must support the right ones if you want to
communicate with other computers. The protocol can be implemented
either in hardware or in software.
Ring
network -- A local-area
network (LAN) whose topology is a ring. That is, all of the nodes
are connected in a closed loop. Messages travel around the ring,
with each node reading those messages addressed to it. One of the
advantages of ring networks is that they can span larger distances
than other types of networks, such as bus networks, because each
node regenerates messages as they pass through it.
SNMP
-- Short for Simple Network Management Protocol, a set of
protocols for managing complex networks. The first versions of SNMP
were developed in the early 80s. SNMP works by sending messages,
called protocol data units (PDUs), to different parts of a
network. SNMP-compliant devices, called agents, store data
about themselves in Management Information Bases (MIBs) and return
this data to the SNMP requesters.
SNMP 1 reports
only whether a device is functioning properly. The industry has
attempted to define a new set of protocols called SNMP 2 that
would provide additional information, but the standardization
efforts have not been successful. Instead, network managers have
turned to a related technology called RMON that provides more
detailed information about network usage.
Software
-- Computer instructions or data. Anything that can be stored
electronically is software. The storage devices and display devices
are hardware.
The terms
software and hardware are used as both nouns and
adjectives. For example, you can say: "The problem lies in the
software," meaning that there is a problem with the program or data,
not with the computer itself. You can also say: "It's a software
problem."
The
distinction between software and hardware is sometimes confusing
because they are so integrally linked. Clearly, when you purchase a
program, you are buying software. But to buy the software, you need
to buy the disk (hardware) on which the software is recorded.
Software is
often divided into two categories:
·
Systems software:
Includes the operating system and all the utilities that enable the
computer to function.
·
Applications
software: Includes
programs that do real work for users. For example, word processors,
spreadsheets, and database management systems fall under the
category of applications software.
Subnet
-- A portion of a network that shares a common address component. On
TCP/IP networks, subnets are defined as all devices whose IP
addresses have the same prefix. For example, all devices with IP
addresses that start with 100.100.100. would be part of the same
subnet. Dividing a network into subnets is useful for both security
and performance reasons. IP networks are divided using a subnet
mask.
Subnet Mask
-- A mask used to determine what subnet an IP address belongs to. An
IP address has two components, the network address and the host
address. For example, consider the IP address 150.215.017.009.
Assuming this is part of a Class B network, the first two numbers
(150.215) represent the Class B network address, and the second two
numbers (017.009) identify a particular host on this network.
Subnetting
enables the network administrator to further divide the host part of
the address into two or more subnets. In this case, a part of the
host address is reserved to identify the particular subnet. This is
easier to see if we show the IP address in binary format. The full
address is:
10010110.11010111.00010001.00001001
The Class B
network part is:
10010110.11010111
and the host
address is
00010001.00001001
If this
network is divided into 14 subnets, however, then the first 4 bits
of the host address (0001) are reserved for identifying the subnet.
The subnet
mask is the network address plus the bits reserved for identifying
the subnetwork. (By convention, the bits for the network address are
all set to 1, though it would also work if the bits were set exactly
as in the network address.) In this case, therefore, the subnet mask
would be 11111111.11111111.11110000.00000000. It's called a
mask because it can be used to identify
the subnet to which an IP address belongs by performing a bitwise
AND operation on the mask and the IP address. The result is the
subnetwork address:
Power Management Software
