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Dial-up |
| Dial-up pertains to a telephone connection in a system of many
lines shared by many users. A dial-up connection is established and maintained for a
limited time duration. The alternative is a dedicated connection, which is continuously in
place. Dial-up lines are sometimes called switched lines and dedicated lines are called
nonswitched lines. A dedicated line is often a leased line that is rented from a telephone
company. A dial-up connection can be initiated manually or automatically by your computer's modem or other device.
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K56 flex |
| K56flex is a trademarked modem and transmission
technology from the Rockwell Corporation for sending data downstream on ordinary phone lines at 56 Kbps (thousand bits per second). K56flex is similar in capability to US Robotics' x2 modem and transmission technology. The 56 Kbps speed is achieved in the downstream direction only (to your home or business). Upstream speed is at the regular maximum speed of 33.6 Kbps. 56 Kbps transmission technologies exploit the fact that most telephone company offices are interconnected with digital lines. Assuming your Internet connection provider has a digital connection to its telephone company office, the downstream traffic from your local Internet access provider can use a new transmission technique on your regular twisted-pair phone line that bypasses the usual digital-to-analog conversion. Your K56flex modem doesn't need to demodulate the downstream data. Instead, it decodes a stream of multi-bit voltage pulses generated as though the line was equipped for digital information. (Upstream data still requiresdigital-to-analog modulation.) Unlike ISDN, the 56 Kbps technologies do not require any additional installation or extra charges from your local phone company. On the other hand, the maximum transmission speed of ISDN is twice that of x2/K56flex at 128 Kbps. You also have the flexibility of combining digital and voice transmission on the same line.
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V.90 |
| The V Series Recommendations from the ITU-T are summarized in
the table below. They include the most commonly used modem standards and other telephone
network standards. Prior to the ITU-T standards, the American Telephone and Telegraph
Company and the Bell System offered its own standards (Bell 103 and Bell 212A) at very low
transfer rates. Another set of standards, the Microcom Networking Protocol, or MNP Class 1
through Class 10 (there is no Class 8), has gained some currency, but the development of
an international set of standards means these will most likely prevail and continue to be
extended. (Some modems offer both MNP and ITU-T standards.) In general, when modems "handshake," they agree on the highest standard transfer rate that both can achieve. Beginning with V.22bis, ITU-T transfer rates increase in 2400 bps multiples. (bis stands for "second version." terbo stands for "third version.")
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PPP |
| PPP (Point-to-Point Protocol) is a protocol for communication
between two computers using a serial interface, typically a personal computer connected by
phone line to a server. For example, your Internet server provider may provide you with a
PPP connection so that the provider's server can respond to your requests, pass them on to
the Internet, and forward your requested Internet responses back to you. PPP uses the
Internet protocol (IP) (and is designed to handle others). It is sometimes considered a member of the TCP/IP suite of protocols. Relative to the Open Systems Interconnection (OSI) reference model, PPP provides layer 2 (data-link layer) service. PPP is a full-duplex protocol that can be used on various physical media, including twisted pair or fiber optic lines or satellite transmission. It uses a variation of High Speed Data Link Control (HDLC) for packet encapsulation. PPP is usually preferred over the earlier de facto standard Serial Line Internet Protocol (SLIP) because it can handle synchronous as well as asynchronous communication. PPP can share a line with other users and it has error detection that SLIP lacks. Where a choice is possible, PPP should be preferred.
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News Groups |
| A newsgroup is a discussion about a particular subject
consisting of notes written to a central Internet site and redistributed through Usenet, a worldwide network of news discussion groups. Usenet uses the Network News Transfer Protocol (NNTP). Newsgroups are organized into subject hierarchies, with the first few letters of the newsgroup name indicating the major subject category and sub-categories represented by a subtopic name. Many subjects have multiple levels of subtopics. Some major subject categories are: news, rec (recreation), soc (society), sci (science), comp (computers), and so forth (there are many more). Users can post to existing newsgroups, respond to previous posts, and create new newsgroups. Newcomers to newsgroups are requested to learn basic Usenet "netiquette" and to get familiar with a newsgroup before posting to it. A FAQ is provided. The rules can be found when you start to enter the Usenet through your browser or an online service. You can subscribe to the postings on a particular newsgroup. Some newsgroups are moderated by a designated person who decides which postings to allow or to remove. Most newsgroups are unmoderated. |
