Subj : Mpost To : Tobias Ernst From : Gord Hannah Date : Mon Jan 06 2003 11:40 am Following up a message from Gord Hannah to All About [1 of 12] Comm Echo Primer: As you requested. From the commandline: [H:\mpost]mpostp -Th:\echomaint\commp.txt -Ch:\mpost\mpost.cfg MPost/2 v2.0a-stable - the Fidonet/Squish/Jam Message Base Writer (C) Copyright 1992 by CodeLand, All Rights Reserved Reading H:\Echomaint\Commp.Txt Writing $H:\Echo\Comm 12/12 Done! (exit 0) Message base is squish. Squish flatly refuses to toss to the world. GH> @MSGID: 1:17/23.1 004d2063 GH> @SPLIT: 06 Jan 03 11:38:25 @17/23 18631 01/12 +++++++++++ GH> * Copied (from: COMM) by Gord Hannah using timEd/2 1.10.y2k+. GH> Fidonet COMM Echo Primer GH> Revision 1.3.6 12/1/2000 GH> | = Revised Entry + = New Entry GH> (1) (2) GH> For newcomers to this, the FidoNet International echo COMM, there GH> follows a discussion of terms which will be encountered frequently GH> in the messages herein. A firm grounding in these will add GH> considerable to understanding the messages in this echo. GH> +========+ +========+ GH> |Computer| DTE- DCE- DTE- |Computer| GH> | A | Rate +--A--+ Rate +--B--+ Rate | B | GH> | |~~~~~~~~~~|Modem|~~~~~~~~~~~~~|Modem|~~~~~~~~~~| | GH> +========+ +=====+ +=====+ +========+ GH> Pictured above is a brief sketch of a complete signal circuit, GH> consisting of two computers (A & B) interconnected thru their GH> Modems. GH> DEFINITIONS: GH> 56Kbps Modems [Pre-V.90] - Rockwell, USR, Lucent Technologies, and GH> Motorola marketed incompatible chipsets/modems that operated in a GH> server/client format at up to 56Kbps over standard telephone lines GH> prior to the adoption of ITU-T V.90. USR implemented a protocol GH> dubbed X2, and the remainder combined efforts to implement a GH> protocol dubbed K56Flex (a combination of Rockwell's K56Plus and GH> Lucent's VFlex/2 protocols). The X2 and K56Flex protocols do not GH> interoperate. GH> ADSL (Asymmetric Digital Subscriber Line) - a modem technology that GH> converts existing twisted-pair telephone lines into access paths for GH> multimedia and high speed data communications. ADSL transmits more GH> than 6Mbps to a subscriber, and as much as 640 kbps more in both GH> directions. GH> An ADSL circuit connects an ADSL modem on each end of a twisted-pair GH> phone line, creating three information channels; a high speed GH> downstream channel, a medium speed duplex channel, and a POTS (Plain GH> Old Telephone Service) channel. The POTS channel is split off from GH> the digital modem by filters, thus guaranteeing uninterrupted POTS, GH> even if ADSL fails. The high speed channel ranges from 1.5 to 6.1 GH> Mbps, while duplex rates range from 16 to 640 kbps. Each channel can GH> be sub-multiplexed to form multiple, lower rate channels. GH> ARQ - (A)utomatic (R)epeat Re(Q)uest - a general term which GH> describes detection and retransmission of defective blocks of data. GH> When appended to a CONNECT string (eg. CONNECT 28800/ARQ) it GH> indicates that the modems have negotiated some manner of error GH> control for the link. GH> ASCII - (A)merican (S)tandard (C)ode for (I)nformation GH> (I)nterchange. A standard for defining codes for information GH> exchange between equipment produced by different manufacturers. GH> ASYNCHRONOUS - Describes data transmission technique in which the GH> length of time between transmitted characters may vary. Because the GH> time lapses between transmitted characters may vary, a receiving GH> modem must be signaled as to when the data bits of a character begin GH> and when they end. The addition of Start and Stop bits serves this GH> purpose. GH> ATM - An international ISDN high-speed, high-volume, GH> packet-switching transmission protocol standard. ATM uses short, GH> uniform, 53-byte cells to divide data into efficient, manageable GH> packets for ultrafast switching through a high-performance GH> communications network. The 53-byte cells contain 5-byte destination GH> address headers and 48 data bytes. ATM is the first packet-switched GH> technology designed from the ground up to support integrated voice, GH> video, and data communication applications. It is well-suited to GH> high-speed WAN transmission bursts. ATM currently accommodates GH> transmission speeds from 64 Kbps to 622 Mbps. ATM may support GH> gigabit speeds in the future. GH> BANDWIDTH - The frequency range available for use by modems on an GH> ordinary two-wire dial-up telephone line. This corresponds to the GH> frequency range required to reproduce the human voice, or GH> approximately 3500Hz (200-3700hZ). GH> BAUD - Perhaps the most mis-used term in all of the discussions GH> posted in this forum. It actually refers to the unit of measure for GH> the number of discrete changes of state which occur in a GH> communication channel per second (ie. the number of times per second GH> that carrier frequencies are modulated). It is an old term from the GH> days of Frequency Shift Keyed modems. The name honors Jean Maurice GH> Emile Baudot, who invented a bit encoding scheme for characters (it GH> is/was not the same as that presently used for encoding ASCII GH> characters however). GH> Relative to FSK modems, the use of Baud referred to the rate that GH> you could shift from one FSK Tone to another. The tones directly GH> represented the ones and zeros of data being transmitted. In the GH> early days they were generally referred to as the Mark Frequency and GH> the Space Frequency. Accordingly, with this direct correlation of GH> tones to 1s and 0s, the Baud Rate was the same as the Bit Rate. GH> [Note: The FSK transmission schemes referenced above are to GH> bi-frequency implementations such as V.21 and the Bell 103 protocol. GH> Multi-frequency FSK schemes also exist, but they have not been GH> widely implemented over the PSTN]. GH> As more complex ways of transmission were devised it was natural to GH> try to extrapolate this concise definition to define their GH> operation. An early extrapolation was to Phase Shift Keyed (PSK) GH> modems such as the V.26 Series of modems. This was unfortunate, but GH> it did actually occur. The extrapolation went like this: The PSK GH> modem generated a signal with 4 possible phase states and thus 4 GH> possible phase changes. The states were 0, 90, 180 and 270 degrees GH> of the carrier. The possible changes were the same. GH> ___ MPost/2 v2.0a GH> - Origin: Marsh BBS (c), Dawson Creek, BC Canada (1:17/23.1) Hope this helps. Keep us posted. We are a fine board trying to make it better. http://www.pris.bc.ca/ghannah ghannah@pris.bc.ca Cheers! Gord -=Team OS/2=- --- timEd/2 1.10.y2k+ * Origin: Marsh BBS (c), Dawson Creek, BC Canada (1:17/23.1) .