Troy's Reference Page
Proxy server-A server that sits between a client application, such as a Web browser, and a real server. It intercepts all requests to the real server to see if it can fulfill the requests itself. If not, it forwards the request to the real server. Proxy servers have two main purposes Improve Performance, Filter Requests
NAT Network Address Translation, an Internet standard
that enables a local-area network (LAN) to use one set of IP addresses for
internal traffic and a second set of addresses for external traffic. A NAT box
located where the LAN meets the Internet makes all necessary IP address
translations. NAT serves three main purposes:
Provides a type of firewall by hiding internal IP addresses Enables a company to
use more internal IP addresses. Since they're used internally only, there's no
possibility of conflict with IP addresses used by other companies and
organizations. Allows a company to combine multiple ISDN connections into a
single Internet connection
VPN virtual private network, a network that is constructed by using public wires to connect nodes. For example, there are a number of systems that enable you to create networks using the Internet as the medium for transporting data. These systems use encryption and other security mechanisms to ensure that only authorized users can access the network and that the data cannot be intercepted.
L2 tunneling A technology that enables one network to send its data via another network's connections. Tunneling works by encapsulating a network protocol within packets carried by the second network. For example, Microsoft's PPTP technology enables organizations to use the Internet to transmit data across a virtual private network (VPN). It does this by embedding its own network protocol within the TCP/IP packets carried by the Internet.
LIFO last in first out
Frame Relay A packet-switching protocol for connecting devices on a Wide Area Network (WAN). Frame Relay networks in the U.S. support data transfer rates at T-1 (1.544 Mbps) and T-3 (45 Mbps) speeds. In fact, you can think of Frame Relay as a way of utilizing existing T-1 and T-3 lines owned by a service provider. Most telephone companies now provide Frame Relay service for customers who want connections at 56 Kbps to T-1 speeds. (In Europe, Frame Relay speeds vary from 64 Kbps to 2 Mbps. In the U.S., Frame Relay is quite popular because it is relatively inexpensive. However, it is being replaced in some areas by faster technologies, such as ATM.
IP6v
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.
IP4
ICMP Internet Control Message Protocol, an extension to the Internet Protocol (IP) defined by RFC 792. ICMP supports packets containing error, control, and informational messages. The PING command, for example, uses ICMP to test an Internet connection.
T1 A dedicated phone connection supporting data rates of 1.544Mbits per second. A T-1 line actually consists of 24 individual channels, each of which supports 64Kbits per second. Each 64Kbit/second channel can be configured to carry voice or data traffic. Most telephone companies allow you to buy just some of these individual channels, known as fractional T-1 access. T-1 lines are a popular leased line option for businesses connecting to the Internet and for Internet Service Providers (ISPs) connecting to the Internet backbone. The Internet backbone itself consists of faster T-3 connections. T-1 lines are sometimes referred to as DS1 lines.
E1 Similar to the North American T-1, E1 is the European format for digital transmission. E1 carries signals at 2 Mbps (32 channels at 64Kbps), versus the T1, which carries signals at 1.544 Mbps (24 channels at 64Kbps). E1 and T1 lines may be interconnected for international use.
ISDN integrated services digital network, an international communications standard for sending voice, video, and data over digital telephone lines or normal telephone wires. ISDN supports data transfer rates of 64 Kbps (64,000 bits per second). There are two types of ISDN: Basic Rate (BRI) ISDN -- consists of two 64-Kbps B-channels and one D-channel for transmitting control information. Primary Rate ISDN -- consists of 23 B-channels and one D-channel (U.S.) or 30 B-channels and one D-channel (Europe). The original version of ISDN employs baseband transmission. Another version, called B-ISDN, uses broadband transmission and is able to support transmission rates of 1.5 Mbps. B-ISDN requires fiber optic cables and is not widely available
DDS Digital Data Storage, the industry standard for
digital audio tape (DAT) formats.
There are currently four kinds of DDS.
DDS-1
DDS-2
DDS-3
DDS-4
PPP Point-to-Point Protocol, a method of connecting a computer to the
Internet. PPP is more stable than the older SLIP protocol and provides error
checking features. Working in the data link layer of the OSI model, PPP sends
the computer's TCP/IP packets to a server that puts them onto the Internet.
HDLC High-level Data Link Control, a transmission protocol used at the data link layer (layer 2) of the OSI seven layer model for data communications. The HDLC protocol embeds information in a data frame that allows devices to control data flow and correct errors. HDLC is an ISO standard developed from the Synchronous Data Link Control (SDLC) standard proposed by IBM in the 1970's. For any HDLC communications session, one station is designated primary and the other secondary. A session can use one of the following connection modes, which determine how the primary and secondary stations interact. Normal unbalanced: The secondary station responds only to the primary station. Asynchronous: The secondary station can initiate a message. Asynchronous balanced: Both stations send and receive over its part of a duplex line. This mode is used for X.25 packet-switching networks.
RFC 1490
CSU/DSU Channel Service Unit/Data Service Unit. The CSU is a device that connects a terminal to a digital line. Typically, the two devices are packaged as a single unit. The DSU is a device that performs protective and diagnostic functions for a telecommunications line. You can think of it as a very high-powered and expensive modem. Such a device is required for both ends of a T-1 or T-3 connection, and the units at both ends must be set to the same communications standard.
Router A device that forwards data packets along networks. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP’s network. Routers are located at gateways, the places where two or more networks connect. Routers use headers and forwarding tables to determine the best path for forwarding the packets, and they use protocols such as ICMP to communicate with each other and configure the best route between any two hosts. Very little filtering of data is done through routers.
Edge Router Also called an "access router," it is a router that sits at the periphery (edge) of a network, in contrast with a core router that is in the middle of a network. Edge routers and core routers are relative terms. They are all just routers, but of different size and capacity. One tier's core router is another tier's edge router
Backbone router/Core router router that resides within the middle or backbone of the network rather than at its periphery. See
Switch In networks, a device that filters and forwards packets between LAN segments. Switches operate at the data link layer (layer 2) and sometimes the network layer (layer 3) of the OSI Reference Model and therefore support any packet protocol. LANs that use switches to join segments are called switched LANs or, in the case of Ethernet networks, switched Ethernet LANs.
ATM Asynchronous Transfer Mode) A network technology for both local and wide area networks (LANs and WANs) that supports real-time voice and video as well as data. The topology uses switches that establish a logical circuit from end to end, which guarantees quality of service (QoS). However, unlike telephone switches that dedicate circuits end to end, unused bandwidth in ATM's logical circuits can be appropriated when needed. For example, idle bandwidth in a videoconference circuit can be used to transfer data.
ATM is widely used as a backbone technology in carrier networks and large
enterprises, but never became popular as a local network (LAN) topology (see
below). ATM is highly scalable and supports transmission speeds of 1.5, 25, 100,
155, 622, 2488 and 9953 Mbps (see
OC).
ATM is also running as slow as 9.6 Kbps between ships at sea. An ATM switch can
be added into the middle of a switch fabric to enhance total capacity, and the
new switch is automatically updated using ATM's PNNI routing protocol.
Quality of Service (Qos) The ability to
specify a quality of service is one of ATM's most important features, allowing
voice and video to be transmitted smoothly. The following levels of service are
available: Constant Bit Rate (CBR) guarantees bandwidth for real-time voice and
video. Real-time variable Bit Rate (rt-VBR) supports interactive multimedia that
requires minimal delays, and non-real-time variable bit rate (nrt-VBR) is used
for bursty transaction traffic. Available Bit Rate (ABR) adjusts bandwidth
according to congestion levels for LAN traffic. Unspecified Bit Rate (UBR)
provides a best effort for non-critical data such as file transfers.
PBX Private Branch eXchange) An in
house telephone switching system that interconnects telephone extensions to each
other as well as to the outside telephone network (PSTN). A PBX enables a
single-line telephone set to gain access to one of a group of pooled (shared)
trunks by dialing an 8 or 9 prefix. PBXs also include functions such as least
cost routing for outside calls, call forwarding, conference calling and call
accounting. Modern PBXs use all-digital methods for switching, but may support
both analog and digital telephones and telephone lines. See
IP PBX
and WPBX.
DSL (Digital Subscriber Line) A technology that dramatically increases the digital capacity of ordinary telephone lines (the local loops) into the home or office. DSL speeds are tied to the distance between the customer and the telco central office. DSL is geared to two types of usage. Asymmetric DSL (ADSL) is for Internet access, where fast downstream is required, but slow upstream is acceptable. Symmetric DSL (SDSL, HDSL, etc.) is designed for short haul connections that require high speed in both directions.
Unlike ISDN, which is also digital but travels through the switched telephone network, DSL provides "always-on" operation. At the telco central office, DSL traffic is aggregated in a unit called the DSL Access Multiplexor (DSLAM) and forwarded to the appropriate ISP or data network.
Internet Internet) "The" Internet is made up of computers in more than 100 countries covering commercial, academic and government endeavors. Originally developed for the U.S. military, the Internet became widely used for academic and commercial research. Users had access to unpublished data and journals on a huge variety of subjects. Today, the Internet has become commercialized into a worldwide information highway, providing information on every subject known to humankind
Internet2 high-speed network for government, academic and research use administered by UCAID, and developed by more than 100 universities with assistance from private companies and the U.S. government. It is not intended for commercial use or to replace the Internet, but is, in fact, the reincarnation of it. However, whereas the first Internet was designed to primarily exchange text, Internet2 is being developed to exchange real-time, multimedia data at high speed, something today's commercial Internet does not do well. Resulting technological advancements should eventually migrate to the global Internet.
last updated 03/13/2003
All definitions on this page were taking from other websites see reference page for links.
