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"G" Networking Definitions & Concepts...

G, or Giga .. to .. Guidelines for the Definition of Managed Objedcts (GDMO)

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G, or Giga:

An abbreviation for the prefix giga, as in GHz (gigahertz) or Gbps (gigabits per second). This order of magnitude corresponds to 230, which is roughly 109, or billions (in the United States counting system). Also see Orders of Magnitude.

Gain:

In electrical signaling, an increase in a signal's voltage, power, or current. This type of increase can occure only through amplification. Noise caused by a monentary increase in signal amplitude is called a gain hit.

Gatedaemon:

In the Internet environment, a program that can be used for routing packets. Gatedaemon, or gated (pronounced "gate dee"), as it is called, supports multiple rounting protocols, and protocol familes.

Gateway:

A gateway is a communication processor (hardware and/or software package) between different computer networks whose job it is to transmit messages from one network to another network. For example, a gateway can be used to connect a PC-based network and an IBM mainframe, or a Token Ring network and an AppleTalk network. One important aspect is protocol conversion. A gateway is usually realized using a special-purpose computer. Protocol conversion (protocol translation) usually takes place at the line and transport protocol levels.

The table below "Context and Properties of Gateways" summarizes the characteristics of this type of internetwork link.

CONTEXT AND PROPERTIES OF GATEWAYS:

Context


Internetwork Links:
Bridge
Gateway
Router


Gateway Properties

Connects dissimilar networks, such as different architectures, LAN to mainframe or WAN,...

Some provide access to special services, such as e-mail or fax,

Operates at upper layers of the OSI Reference Model,

Takes transmission capabilities for granted in order to focus on content and format,

Often does data translation or conversion,

Needs a network interface card for each architecuter supported.



Gateways are like "relay stations" which link together two different protocols or protocol hierarchies and thus execute a conversion of the protocol. Examples of commercial gateways are the special-purpose computers through which Macintoshes on the Apple LocalTalk LAN communicate with UNIX processors and NFS as file server.

More generally, the term can refer to any device or software package that connects two different environments, regardless of whether networks are involved. As such a gatway can slso be considered a communications server or, in some cases, an access server.

There are also special purpose, dedicated computers that are attached to two or more networks that route packets from one to the other. In particular, an IP gateway routes IP datagrams among the networks to which it connects. Gateways route packets to other gateways until they can be delivered to the final destination directly across one physical network. The term is loosely applied to any machine that transfers information from one network to another, as in mail gateway. Although the original literature used the term gateway, venders often call them IP routers.

Therefore:

Gateways route packets among networks, not among machines/devices

In the Internet community, the term gateway has been used to refer to anything that connects networks. The connecting device is generally a router, and this term has replaced gateway in Internet contexts.

Gateways in Networks

A gateway provides a LAN with access to a different type of network, an internetwork, a mainframe computer, or a particular type of operating environment. A gateway serves to connect networks with very different architectures, for example, an Ethenet LAN and an SNA network, or a LAN and an X.25 packet-switching service. Gateways are also used to provide access to special services, such as e-mail (electronic mail), fax, and Telex.

Gateways can operate at serveral of the higher OSI Reference Model levels, most notabley at the session, presentation, and application layers. Gateways usually operate above the communications subnet (which comprises the bottom three layers in the OSI Reference Model). This means that gateways take transmission capabilities for granted and concentrate on the content of the transmission.

In the course of doing their work, gateways may very likely change the representaton of data before passing it on. For example, a gateway may convert from ASCII to EBCDIC on the way to an IBM mainframe, encrypting or decrypting data between the source and destination environments. Gateways also must do protocol conversion, since the different environments connected by a gateway will generally use different protocol families.

The multilayer operation of gateways is in contrast to repeaters, bridges, and routers, which each operate at a single level (the physical, data-link, and network layers, respectively), and which do not change the data in any way.

Gateway IP address:

See IP (Internet Protocol) address.

Gauge:

A measure of electrical wire diameter. Under the American Wire Gauge (AWA) standards, higher gauge numbers indicate a thinner cable. See the AWG Article for a table of some sample gauge values.

Gaussian Noise:

In electrical signaling, noise resulting from the vibration of atoms or molecules. This noise occurs over all frequencies, and it increases with temperture.

General Format Identifier (GFI):

In an X.25 packet, a field that indicates packet formats and several other features.

Generalized Data Stream (GDS):

The format for mapped data in the APPC (Advanced Program-to-Program Communications) extension of IBM's SNA (Systems Network Architecture). Data from highlevel applications is converted to GDS format before transmission. This helps protect from format differences, such as when one application uses the ASCII character format and the other uses EBCDIC.

Generic Flow Control (GFC):

In the ATM networking model, a protocol that is used to make sure all nodes get access to the transmission medium. This service is provided at the ATM (Asynchronous Transfer Mode) layer in the model.

Geosynchronous Orbit:

An orbit around the earth, such as the orbit of a communications satellite. A satellite in geosynchronous orbit is known as a geosynchronous or geostationary satellite. The orbit is "synchronous" becouse the satellite makes a revolution in about 24 hours. The satellites are about 36,000 kilometers (22,350 miles) above the earth, and they appear to be statioinary over a location.

Ghosting:

A term used to describe the intermittent appearance and disappearance of network devices. This is also known as bouncing on the net.

Gigabit Ethernet:

Gigabit Ethernet is a term describing various technologies for implementing Ethernet networking at a nominal speed of one gigabit per second.

Gigabit Ethernet is supported over both optical fiber and twisted pair cable. Physical layer standards include 1000BASE-T, 1Gbps over cat-5e copper cabling and 1000BASE-SX for short to medium distances over fibre.

Whilst it is currently (as of 2002) deployed in high-capacity backbone network links (for instance, on a high-capacity campus network) its speed is largely not yet required for small network installations.

It is no longer the fastest Ethernet standard, with the ratification of 10 Gigabit Ethernet in 2002.

Global Conceptual Schema: (DBMS & DDBMS)

The global conceptual schema is a logical description (ERD) of the whole database, as if it were not distributed. This level corresponds to the conceptual level of the ANSI-SPARC architecture and contains definitions of entities, relationships, constraints, security, and integrity information. It provides physical data independence from the distributed environment. The global external schemas provide logical data independence. In a DDBMS, the GCS is the union (U) of all local conceptual schemas.

Granularity (Data Warehouse):

The level of detail contained in a unit of data. The more detail there is, the lower the level of granularity. The less detail there is, the higher the level of granularity.

The single most important aspect of design of a data warehouse is the issue of granularity. Indeed, the issue of granularity permeates the entire architecture that surrounds the data warehouse environment. Granularity refers to the level of detail or summarization of the units of data in the data warehouse. The more detail there is, the lower the level of granularity. The less detail is, the higher the level of granularity.

For example, a simple transaction would be at a low level of granularity. A summary of all transactions for the month would be at a high level of granularity.

Granularity of data has always been a major design issue. In early operational systems, granularity was taken for granted. When detailed data is being updated, it is almost a given that data be stored at the lowest level of granularity. In the data warehouse environment, though, granularity is not assumed.

Granularity is the major design issue in the data warehouse environment because it profoundly affects the volume of data that resides in the data warehouse and the type of query that can be answered. The volume of data in a warehouse is traded off against the level of detail of a query.

In almost all cases, data comes into the data warehouse at too high a level of granularity. This means that the developer must spend a lot of resources breaking the data apart. Occasionally, though, data enters the warehouse at too low level of granularity. An example of data at too low a level of granularity is the Web log data generated by the Web-based e-business environment. Web log clickstream data must be edited, filtered, and summarized before its granularity is fit for the data warehouse.

Graphical User Interface (GUI):

A graphically based interface, used on systems such as the Macintosh, Motif, or Microsoft Windows. In GUIs (pronounced "gooeys"), information and commands are presented through metaphors such as icons, a desktop, pulldown menus, and the user gives commands by pointing to or manipulating the icons. GUIs are in contrast to character-based inferfaces, such as the default interfaces for DOS or UNIX.

Groupware:

Also called collaborative computing. Groupware includes programs designed to handle group-related tasks such as scheduling meetings, sending messages and other information, and coauthoring documents. Other programs include networked bulletin board systems and group decision support systems.

Guaranteed Bandwidth:

In networking or telecommunications, the capability for transmitting continuously and reliably at a specified transmission speed. The guarantee makes it possible to send time-dependent data (such as voice, video, or multimedia) over the line.

Guard Band:

In telecommunications and electrical transmissions, a guard band (sometimes written guardband) is a thin frequency band used to separte bands (channels) above and below the guard band. By providing a gap between the two channels, the guard band helps prevent interference and signal leakage.

In cellular communications, a guard band is a 3 megahertz (MHz) band that separates two voice channels in order to keep the channels from interfering with each other.

In the never-ending quest to transmit more and more quickly, some vendors have developed products that transmit data along these guard bands.

Guard Time:

In time division multiplexed (TDM) signaling, a brief interval of "silence" between transmissions. This period can be used for synchronization and compensating for signal distortion. This is the temporal analog to a guard band.

Guest:

In many networks, Guest is a special account or user name. This account is for the use of anyone who needs to log into the network or a particular system for public information. The access must be temporary, and the account is afforded only restricted access rights.

Guided Media:

Transmission media that constrain the electromagnetic, acoustic, or optical signal because of physical properties of the medium. For example, in fiber-optic transmissions, the cladding reflects the signal back into the core. Similarly, coaxial or twisted-pair cable constrains the electrical signal, and telephone lines constrain an acoustic signal.

Guidelines for the Definition of Managed Objedcts (GDMO):

An ISO (International Standardization Organization) specification that provides notation for describing managed objects and actions involving such objects.




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Networking "G" Definition and Concepts

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