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Short for Asynchronous Transfer Mode, a network technology based on transferring data in cells or packets of a fixed size. The cell used with ATM is relatively small compared to units used with older technologies. The small, constant cell size allows ATM equipment to transmit video, audio, and computer data over the same network, and assure that no single type of data hogs the line.
Some people think
that ATM holds the answer to the
Internet
bandwidth problem, but others are skeptical. ATM creates a fixed
channel, or
route, between two points whenever data transfer begins. This differs from
TCP/IP, in
which messages are divided into
packets and
each packet can take a different route from source to destination. This
difference makes it easier to track and bill data usage across an ATM network,
but it makes it less adaptable to sudden surges in network
traffic.
When purchasing ATM service, you generally have a choice of four different types of service:
Constant bit rate (CBR): specifies a fixed bit rate so that data is sent in a steady stream. This is analogous to a leased line.
Variable bit rate (VBR): provides a specified throughput capacity but data is not sent evenly. This is a popular choice for voice and videoconferencing data.
Available bit rate (ABR): provides a guaranteed minimum capacity but allows data to be bursted at higher capacities when the network is free.
Unspecified bit rate (UBR): does not guarantee any throughput levels. This is used for applications, such as file transfer, that can tolerate delays.
Another term for bus, the main wire that connects nodes. The term is often used to describe the main network connections composing the Internet.
The amount of data that can be transmitted in a fixed amount of time. For digital devices, the bandwidth is usually expressed in bits per second bytes per second. For analog devices, the bandwidth is expressed in cycles per second, or Hertz (Hz).
Short for Border Gateway Protocol, an exterior gateway routing protocol that enables groups of routers (called autonomous systems) to share routing information so that efficient, loop-free routes can be established. BGP is commonly used within and between Internet Service Providers (ISPs). The protocol is defined in RFC 1771.
Short for Basic-Rate Interface, the basic ISDN configuration, which consists of two B-channels that can carry voice or data at rate of 64 Kbps, and one D-channel, which carries call-control information. Another type of ISDN configuration is called Primary-Rate Interface (PRI), which consists of 23 B-channels (30 in Europe) and one D-channel.
Pronounced see-lek. A Competitive Local Exchange Carrier is a telephone company that competes with an Incumbent Local Exchange Carrier (ILEC) such as a Regional Bell Operating Company (RBOC), GTE, ALLNET, etc.
With the passage of the Telecommunications Act of 1996, there has been an explosion in the number of CLECs. The Act allows companies with CLEC status to use ILEC infrastructure in two ways:
1) Access to UNEs
Important to CLEC telecommunications networking is the availability of unbundled network elements or UNEs (through a collocation arrangement). UNEs are defined by the Act as any "facility or equipment used in the provision of a telecommunications service," as well as "features, functions, and capabilities that are provided by means of such facility or equipment." For CLECs the most important UNE available to them is the local loop, which connects the ILEC switches to the ILEC's present customers. With the local loop, CLECs will be able to connect their switches with the ILEC's switches, thus giving them access to ILEC customers.
2) Resale
Another option open to CLECs is the resale strategy. The Act states that any telecommunications services ILECs offer at retail, must be offered to CLECs at a wholesale discount. This saves the CLEC from having to invest in switches, fiber optic transmission facilities, or collocation arrangements.
In any case, a CLEC may decide on one or the other or even both. So, you can see why obtaining CLEC status is very beneficial, especially for ISPs, who may easily get access to the copper loops and other switching elements necessary to provide xDSL services.
Recently courts, in response to the growth of cable Internet access, have also required cable companies to follow the same guidelines as ILECs.
Applying for CLEC status is a very tedious and complex process that involves a Regulatory Attorney or Consultant, the State Public Utilities Commission, and about 50 other steps. But remember, it will be worth it, and now is a good time, because the courts continually are trying to force ILEC costs to CLECs down and are making access to UNEs easier in the name of fair competition. So, get in before regulators begin to re-regulate the other way.
Short for central office exchange service, a type of PBX service in which switching occurs at a local telephone station instead of at the company premises. Typically, the telephone company owns and manages all the communications equipment necessary to implement the PBX and then sells various services to the company.
Short for central office. In telephony, a CO is a telecommunications office centralized in a specific locality to handle the telephone service for that locality. Telephone lines are connected to the CO on a local loop. The CO switches calls between local service and long-distance service. ISDN and DSL signals also channel through the CO.
A server, usually a Web server, that is located at a dedicated facility designed with resources which include a secured cage or cabinet, regulated power, dedicated Internet connection, security and support.
These co-location facilities offer the customer a secure place to physically house their hardware and equipment as opposed to locating it in their offices or warehouse where the potential for fire, theft or vandalism is much greater.
Most co-location facilities offer high-security, including cameras, fire detection and extinguishing devices, multiple connection feeds, filtered power, backup power generators and other items to ensure high-availability which is mandatory for all Web-based, virtual businesses.
Co-location sites are being erected at various points around the world to provide services to the rapidly expanding Web hosting and e-commerce marketplace. The term co-location is also known as colo.
Short for 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.
Short for Data Encryption Standard, a popular symmetric-key encryption method developed in 1975 and standardized by ANSI in 1981 as ANSI X.3.92. DES uses a 56-bit key and is illegal to export out of the U.S. or Canada if you don't meet the BXA requirements.
(1) Short for Domain Name System (or Service), an Internet service that translates domain names into IP addresses. Because domain names are alphabetic, they're easier to remember. The Internet however, is really based on IP addresses. Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address. For example, the domain name www.example.com might translate to 198.105.232.4.
The DNS system is, in fact, its own network. If one DNS server doesn't know how to translate a particular domain name, it asks another one, and so on, until the correct IP address is returned.
(2) Short for digital nervous system, a term coined by Bill Gates to describe a network of personal computers that make it easier to obtain and understand information.
Refers collectively to all types of digital subscriber lines, the two main categories being ADSL and SDSL. Two other types of xDSL technologies are High-data-rate DSL (HDSL) and Very high DSL (VDSL).
DSL technologies use sophisticated modulation schemes to pack data onto copper wires. They are sometimes referred to as last-mile technologies because they are used only for connections from a telephone switching station to a home or office, not between switching stations.
xDSL is similar to ISDN inasmuch as both operate over existing copper telephone lines (POTS) and both require the short runs to a central telephone office (usually less than 20,000 feet). However, xDSL offers much higher speeds - up to 32 Mbps for upstream traffic, and from 32 Kbps to over 1 Mbps for downstream traffic.
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, with 2 channels reserved for signaling and controlling), versus the T1, which carries signals at 1.544 Mbps (24 channels at 64Kbps). E1 and T1 lines may be interconnected for international use.
Short for Electronic Data Interchange, the transfer of data between different companies using networks, such as the Internet. As more and more companies get connected to the Internet, EDI is becoming increasingly important as an easy mechanism for companies to buy, sell, and trade information. ANSI has approved a set of EDI standards known as the X12 standards.
Short for electronic mail, the transmission of messages over communications networks. The messages can be notes entered from the keyboard or electronic files stored on disk. Most mainframes, minicomputers, and computer networks have an e-mail system. Some electronic-mail systems are confined to a single computer system or network, but others have gateways to other computer systems, enabling users to send electronic mail anywhere in the world. Companies that are fully computerized make extensive use of e-mail because it is fast, flexible, and reliable.
Most e-mail systems include a rudimentary text editor for composing messages, but many allow you to edit your messages using any editor you want. You then send the message to the recipient by specifying the recipient's address. You can also send the same message to several users at once. This is called broadcasting.
Sent messages are stored in electronic mailboxes until the recipient fetches them. To see if you have any mail, you may have to check your electronic mailbox periodically, although many systems alert you when mail is received. After reading your mail, you can store it in a text file, forward it to other users, or delete it. Copies of memos can be printed out on a printer if you want a paper copy.
All online services and Internet Service Providers (ISPs) offer e-mail and most also support gateways so that you can exchange mail with users of other systems. Usually, it takes only a few seconds or minutes for mail to arrive at its destination. This is a particularly effective way to communicate with a group because you can broadcast a message or document to everyone in the group at once.
Although different e-mail systems use different formats, there are some emerging standards that are making it possible for users on all systems to exchange messages. In the PC world, an important e-mail standard is MAPI. The CCITT standards organization has developed the X.400 standard, which attempts to provide a universal way of addressing messages. To date, though, the de facto addressing standard is the one used by the Internet system because almost all e-mail systems have an Internet gateway.
Another common spelling for e-mail is email.
The translation of data into a secret code. Encryption is the most effective way to achieve data security. To read an encrypted file, you must have access to a secret key or password that enables you to decrypt it. Unencrypted data is called plain text ; encrypted data is referred to as cipher text.
There are two main types of encryption: asymmetric encryption (also called public-key encryption) and symmetric encryption.
A system designed to prevent unauthorized access to or from a private network. Firewalls can be implemented in both hardware and software, or a combination of both. Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet the specified security criteria.
There are several types of firewall techniques:
Packet filters: Looks at each packet entering or leaving the network and accepts or rejects it based on user-defined rules. Packet filtering is fairly effective and transparent to users, but it is difficult to configure. In addition, it is susceptible to IP spoofing.
Application gateway: Applies security mechanisms to specific applications, such as FTP and Telnet servers. This is very effective, but can impose performance degradation.
Circuit-level gateway: Applies security mechanisms when a TCP or UDP connection is established. Once the connection has been made, packets can flow between the hosts without further checking.
Proxy server: Intercepts all messages entering and leaving the network. The proxy server effectively hides the true network addresses.
In practice, many firewalls use two or more of these techniques in concert.
A firewall is considered a first line of defense in protecting private information. For greater security, data can be encrypted.
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.
Abbreviation of File Transfer Protocol, the protocol used on the Internet for sending files.
(1) A node on a network that serves as an entrance to another network. In enterprises, the gateway is the computer that routes the traffic from a workstation to the outside network that is serving the Web pages. In homes, the gateway is the ISP that connects the user to the internet.
In enterprises, the gateway node often acts as a proxy server and a firewall. The gateway is also associated with both a router, which use headers and forwarding tables to determine where packets are sent, and a switch, which provides the actual path for the packet in and out of the gateway.
(2) A computer system located on earth that switches data signals and voice signals between satellites and terrestrial networks.
(3) An earlier term for router, though now obsolete in this sense as router is commonly used.
(n) (1) A computer system that is accessed by a user working at a remote location. Typically, the term is used when there are two computer systems connected by modems and telephone lines. The system that contains the data is called the host, while the computer at which the user sits is called the remote terminal.
(2) A computer that is connected to a TCP/IP network, including the Internet. Each host has a unique IP address.
(v) To provide the infrastructure for a computer service. For example, there are many companies that host Web servers. This means that they provide the hardware, software, and communications lines required by the server, but the content on the server may be controlled by someone else.
A Hosting Services Provider (HSP) is an application service provider dedicated to providing hosting services. Typically operates a Web server farm, either at a data center or collocation facility.
Short for HyperText Markup Language, the authoring language used to create documents on the World Wide Web. HTML is similar to SGML, although it is not a strict subset.
HTML defines the structure and layout of a Web document by using a variety of tags and attributes. The correct structure for an HTML document starts with (enter here what document is about) and ends with . All the information you'd like to include in your Web page fits in between the and tags.
There are hundreds of other tags used to format and layout the information in a Web page. Tags are also used to specify hypertext links. These allow Web developers to direct users to other Web pages with only a click of the mouse on either an image or word(s). For a more complete list of tags, check out some of the URLs below.
Short for Hypertext Transfer Protocol, the underlying protocol used by the World Wide Web. HTTP defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands. For example, when you enter a URL in your browser, this actually sends an HTTP command to the Web server directing it to fetch and transmit the requested Web page.
The other main standard that controls how the World Wide Web works is HTML, which covers how Web pages are formatted and displayed.
HTTP is called a stateless protocol because each command is executed independently, without any knowledge of the commands that came before it. This is the main reason that it is difficult to implement Web sites that react intelligently to user input. This shortcoming of HTTP is being addressed in a number of new technologies, including ActiveX, Java, JavaScript and cookies.
Short for incumbent local exchange carrier. An ILEC is a telephone company that was providing local service when the Telecommunications Act of 1996 was enacted. Compare with CLEC, a company that competes with the already established local telephone business.
A global network connecting millions of computers. More than 100 countries are linked into exchanges of data, news and opinions.
Unlike online services, which are centrally controlled, the Internet is decentralized by design. Each Internet computer, called a host, is independent. Its operators can choose which Internet services to use and which local services to make available to the global Internet community. Remarkably, this anarchy by design works exceedingly well.
There are a variety of ways to access the Internet. Most online services, such as America Online, offer access to some Internet services. It is also possible to gain access through a commercial Internet Service Provider (ISP).
The Internet is not synonymous with World Wide Web.
An intrusion detection system (IDS) inspects all inbound and outbound network activity and identifies suspicious patterns that may indicate a network or system attack from someone attempting to break into or compromise a system.
There are several ways to categorize IDS:
Misuse detection vs. anomaly detection: in misuse detection, the IDS analyzes the information it gathers and compares it to large databases of attack signatures. Essentially, the IDS looks for a specific attack that has already been documented. Like a virus detection system, misuse detection software is only as good as the database of attack signatures that it uses to compare packets against. In anomaly detection, the system administrator defines the baseline, or normal, state of the network’s traffic load, breakdown, protocol, and typical packet size. The anomaly detector monitors network segments to compare their state to the normal baseline and look for anomalies.
Network-based vs. host-based systems: in a network-based system, or NIDS, the individual packets flowing through a network are analyzed. The NIDS can detect malicious packets that are designed to be overlooked by a firewall’s simplistic filtering rules. In a host-based system, the IDS examines at the activity on each individual computer or host.
Passive system vs. reactive system: in a passive system, the IDS detects a potential security breach, logs the information and signals an alert. In a reactive system, the IDS responds to the suspicious activity by logging off a user or by reprogramming the firewall to block network traffic from the suspected malicious source.
Though they both relate to network security, an IDS differs from a firewall in that a firewall looks out for intrusions in order to stop them from happening. The firewall limits the access between networks in order to prevent intrusion and does not signal an attack from inside the network. An IDS evaluates a suspected intrusion once it has taken place and signals an alarm. An IDS also watches for attacks that originate from within a system.
Abbreviation of Internet Protocol, pronounced as two separate letters. IP specifies the format of packets, also called data grams, and the addressing scheme. Most networks combine IP with a higher-level protocol called Transmission Control Protocol (TCP), which establishes a virtual connection between a destination and a source.
IP by itself is something like the postal system. It allows you to address a package and drop it in the system, but there's no direct link between you and the recipient. TCP/IP, on the other hand, establishes a connection between two hosts so that they can send messages back and forth for a period of time.
The current version of IP is IPv4. A new version, called IPv6 or IPng, is under development.
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.
Within an isolated network, you can assign IP addresses at random as long as each one is unique. However, connecting a private network to the Internet requires using registered IP addresses (called Internet addresses) to avoid duplicates.
The four numbers in an IP address are used in different ways to identify a particular network and a host on that network. Three regional Internet registries -- ARIN, RIPE NCC and APNIC -- assign Internet addresses from the following three classes.
Class A - supports 16 million hosts on each of 127 networks
Class B - supports 65,000 hosts on each of 16,000 networks
Class C - supports 254 hosts on each of 2 million networks
The number of unassigned Internet addresses is running out, so a new classless scheme called CIDR is gradually replacing the system based on classes A, B, and C and is tied to adoption of IPv6.
Short for IP Security, a set of protocols developed by the IETF to support secure exchange of packets at the IP layer. IPsec has been deployed widely to implement Virtual Private Networks (VPNs).
IPsec supports two encryption modes: Transport and Tunnel. Transport mode encrypts only the data portion (payload) of each packet, but leaves the header untouched. The more secure Tunnel mode encrypts both the header and the payload. On the receiving side, an IPSec-compliant device decrypts each packet.
For IPsec to work, the sending and receiving devices must share a public key. This is accomplished through a protocol known as Internet Security Association and Key Management Protocol/Oakley (ISAKMP/Oakley), which allows the receiver to obtain a public key and authenticate the sender using digital certificates.
Abbreviation of 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.
Short for Internet Service Provider, a company that provides access to the Internet. For a monthly fee, the service provider gives you a software package, username, password and access phone number. Equipped with a modem, you can then log on to the Internet and browse the World Wide Web and USENET, and send and receive e-mail.
In addition to serving individuals, ISPs also serve large companies, providing a direct connection from the company's networks to the Internet. ISPs themselves are connected to one another through Network Access Points (NAPs).
ISPs are also called IAPs (Internet Access Providers).
In networking, the amount of time it takes a packet to travel from source to destination. Together, latency and bandwidth define the speed and capacity of a network.
(A.K.A. Private Line, Point-To-Point)
A permanent telephone connection between two points set up by a telecommunications common carrier. Typically, leased lines are used by businesses to connect geographically distant offices. Unlike normal dial-up connections, a leased line is always active. The fee for the connection is a fixed monthly rate. The primary factors affecting the monthly fee are distance between end points and the speed of the circuit. Because the connection doesn't carry anybody else's communications, the carrier can assure a given level of quality.
For example, a T-1 channel is a type of leased line that provides a maximum transmission speed of 1.544 Mbps. You can divide the connection into different lines for data and voice communication or use the channel for one high speed data circuit. Dividing the connection is called multiplexing.
Increasingly, leased lines are being used by companies, and even individuals, for Internet access because they afford faster data transfer rates and are cost-effective if the Internet is used heavily.
In telephony, a local loop refers to the connection between a telecommunication company's CO to the lines in the service subscriber's home or office. Originally, local loop service carried only telephone service to subscribers. But today, with the use of modems, ISDN and DSL signals are transmitted to subscribers as well through the local loop.
Short for Metropolitan Area Network, a data network designed for a town or city. In terms of geographic breadth, MANs are larger than local-area networks (LANs), but smaller than wide-area networks (WANs). MANs are usually characterized by very high-speed connections using fiber optical cable or other digital media.
Short for Network Access Point, a public network exchange facility where Internet Service Providers (ISPs) can connect with one another in peering arrangements. The NAPs are a key component of the Internet backbone because the connections within them determine how traffic is routed. They are also the points of most Internet congestion.
Short for 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.
(1) In networks, a processing location. A node can be a computer or some other device, such as a printer. Every node has a unique network address, sometimes called a Data Link Control (DLC) address or Media Access Control (MAC) address.
Short for Optical Carrier, used to specify the speed of fiber optic networks conforming to the SONET standard. The table shows the speeds for common OC levels.
OC = Speed
OC-1 = 51.85 Mbps
OC-3 = 155.52 Mbps
OC-12 = 622.08 Mbps
OC-24 = 1.244 Gbps
OC-48 = 2.488 Gbps
OC-192=9.952 Gbps
A piece of a message transmitted over a packet-switching network. See under packet switching. One of the key features of a packet is that it contains the destination address in addition to the data. In IP networks, packets are often called datagrams.
Short for port address translation, a type of network address translation. During PAT, each computer on LAN is translated to the same IP address, but with a different port number assignment.
PAT is also referred to as overloading, port mapping, port-level multiplexed NAT or single address NAT.
Short for public key infrastructure, a system of digital certificates, Certificate Authorities, and other registration authorities that verify and authenticate the validity of each party involved in an Internet transaction. PKIs are currently evolving and there is no single PKI nor even a single agreed-upon standard for setting up a PKI. However, nearly everyone agrees that reliable PKIs are necessary before electronic commerce can become widespread.
A PKI is also called a trust hierarchy.
(1) Short for Post Office Protocol, a protocol used to retrieve e-mail from a mail server. Most e-mail applications (sometimes called an e-mail client) use the POP protocol, although some can use the newer IMAP (Internet Message Access Protocol).
There are two versions of POP. The first, called POP2, became a standard in the mid-80's and requires SMTP to send messages. The newer version, POP3, can be used with or without SMTP.
(2) Short for point of presence, an access point to the Internet. ISPs have typically multiple POPs. A point of presence is a physical location, either part of the facilities of a telecommunications provider that the ISP rents or a separate location from the telecommunications provider, that houses servers, routers, ATM switches and digital/analog call aggregators.
Short for plain old telephone service, which refers to the standard telephone service that most homes use. In contrast, telephone services based on high-speed, digital communications lines, such as ISDN and FDDI, are not POTS. The main distinctions between POTS and non-POTS services are speed and bandwidth. POTS is generally restricted to about 52 Kbps (52,000 bits per second).
The POTS network is also called the public switched telephone network (PSTN).
Short for Primary-Rate Interface, a type of ISDN service designed for larger organizations. PRI includes 23 B-channels (30 in Europe) and one D-Channel. In contrast, BRI (Basic-Rate Interface), which is designed for individuals and small businesses, contains just two B-channels and one D-channel.
PRI service is generally transmitted through a T-1 line (or an E1 line in Europe).
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.
A Service Level Agreement (SLA) is a contract between an ASP and the end user which stipulates and commits the ASP to a required level of service. An SLA should contain a specified level of service, support options, enforcement or penalty provisions for services not provided, a guaranteed level of system performance as relates to downtime or uptime, a specified level of customer support and what software or hardware will be provided and for what fee.
Short for Simple Mail Transfer Protocol, a protocol for sending e-mail messages between servers. Most e-mail systems that send mail over the Internet use SMTP to send messages from one server to another; the messages can then be retrieved with an e-mail client using either POP or IMAP. In addition, SMTP is generally used to send messages from a mail client to a mail server. This is why you need to specify both the POP or IMAP server and the SMTP server when you configure your e-mail application.
Short for Synchronous Optical Network, a standard for connecting fiber-optic transmission systems. SONET was proposed by Bellcore in the middle 1980s and is now an ANSI standard.
SONET defines interface standards at the physical layer of the OSI seven-layer model. The standard defines a hierarchy of interface rates that allow data streams at different rates to be multiplexed. SONET establishes Optical Carrier (OC) levels from 51.8 Mbps (about the same as a T-3 line) to 2.48 Gbps. Prior rate standards used by different countries specified rates that were not compatible for multiplexing. With the implementation of SONET, communication carriers throughout the world can interconnect their existing digital carrier and fiber optic systems.
The international equivalent of SONET, standardized by the ITU, is called SDH.
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.
A dedicated phone connection supporting data rates of about 43 Mbps. A T-3 line actually consists of 672 individual channels, each of which supports 64 Kbps.
T-3 lines are used mainly by Internet Service Providers (ISPs) connecting to the Internet backbone and for the backbone itself.
T-3 lines are sometimes referred to as DS3 lines.
Abbreviation of Transmission Control Protocol, and pronounced as separate letters. TCP is one of the main protocols in TCP/IP networks. Whereas the IP protocol deals only with packets, TCP enables two hosts to establish a connection and exchange streams of data. TCP guarantees delivery of data and also guarantees that packets will be delivered in the same order in which they were sent.
Short for unbundled network element, parts of a network that ILECs are required to offer to their customers on an unbundled basis. Important to CLEC telecommunications networking is the availability of UNEs (through a collocation arrangement). UNEs are defined by the Telecommunications Act of 1996 as any "facility or equipment used in the provision of a telecommunications service," as well as "features, functions, and capabilities that are provided by means of such facility or equipment." For CLECs the most important UNE available to them is the local loop, which connects the ILEC switches to the ILEC's present customers. With the local loop, CLECs will be able to connect their switches with the ILEC's switches, thus giving them access to ILEC customers.
Short for 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.
A computer network that spans a relatively large geographical area. Typically, a WAN consists of two or more local-area networks (LANs).
Computers connected to a wide-area network are often connected through public networks, such as the telephone system. They can also be connected through leased lines or satellites. The largest WAN in existence is the Internet.
Short for wireless fidelity and is meant to be used generically when referring of any type of 802.11 network, whether 802.11b, 802.11a, dual-band, etc. The term is promulgated by the Wi-Fi Alliance.
Any products tested and approved as "Wi-Fi Certified" (a registered trademark) by the Wi-Fi Alliance are certified as interoperable with each other, even if they are from different manufacturers. A user with a "Wi-Fi Certified" product can use any brand of access point with any other brand of client hardware that also is certified. Typically, however, any Wi-Fi product using the same radio frequency (for example, 2.4GHz for 802.11b or 11g, 5GHz for 802.11a) will work with any other, even if not "Wi-Fi Certified."
Formerly, the term "Wi-Fi" was used only in place of the 2.4GHz 802.11b standard, in the same way that "Ethernet" is used in place of IEEE 802.3. The Alliance expanded the generic use of the term in an attempt to stop confusion about wireless LAN interoperability.
A system of Internet servers that support specially formatted documents. The documents are formatted in a script called HTML (Hypertext Markup Language) that supports links to other documents, as well as graphics, audio, and video files. This means you can jump from one document to another simply by clicking on hot spots. Not all Internet servers are part of the World Wide Web.
There are several applications called Web browsers that make it easy to access the World Wide Web; Two of the most popular being Netscape Navigator and Microsoft's Internet Explorer.
A popular standard for packet-switching networks. The X.25 standard was approved by the CCITT (now the ITU) in 1976. It defines layers 1, 2, and 3 in the OSI Reference Model.