blume@netmbx.UUCP (Heiko Blume) (10/02/88)
as far as i remember the baud rate tells you how many changes of the
discrete signal levels are possible. since more than two levels are
possible you can code more than two bits with one baud.
for instance the USR HST modem uses a 2400 baud line with 4 bits per
baud to achive a 9600 bps rate.
--
Heiko Blume | lazy : blume@netmbx.UUCP
Seekorso 29 | crazy : ...!{pyramid,unido,altger}!tmpmbx!netmbx!blume
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WestGermany | telex : 183008 intro d | fax : (+49 30) 882 50 65dave@arnold.UUCP (Dave Arnold) (10/03/88)
In article <1464@netmbx.UUCP>, blume@netmbx.UUCP (Heiko Blume) writes: > as far as i remember the baud rate tells you how many changes of the > discrete signal levels are possible. since more than two levels are > possible you can code more than two bits with one baud. Yes. However, most people I know say "baud" when referring to "bps". I am aware of the difference, but say "baud" anyway. In the future, this is going to be a confusion. I think we should all get this right now. Saying "baud" is really pointless unless you are intimate with the signaling details. -- Dave Arnold dave@arnold.UUCP {cci632|uunet}!ccicpg!arnold!dave
dave@arnold.UUCP (Dave Arnold) (10/03/88)
In article <202@arnold.UUCP>, dave@arnold.UUCP (Dave Arnold) writes: > [...] signaling details. i mean: unless you are intimate with the modulation details. -- Dave Arnold dave@arnold.UUCP {cci632|uunet}!ccicpg!arnold!dave
chris@mimsy.UUCP (Chris Torek) (10/04/88)
>In article <1464@netmbx.UUCP> blume@netmbx.UUCP (Heiko Blume) writes: >>as far as i remember the baud rate tells you how many changes of the >>discrete signal levels are possible. Not exactly. `Baud rate' means `number of channel symbols per unit time'; multiplying this by `number of bits per channel system' gives the more familiar bits per unit time, typically bits per second. In article <202@arnold.UUCP> dave@arnold.UUCP (Dave Arnold) writes: >Yes. However, most people I know say "baud" when referring to >"bps". I am aware of the difference, but say "baud" anyway. >In the future, this is going to be a confusion. I think we >should all get this right now. Saying "baud" is really pointless >unless you are intimate with the signaling details. It may be best to stick with `bps'. After all, I use a Telebit TB+ modem at 19200 *baud* ... between the serial port on the TB+ and that on the Vax! That part of the link runs at 19200 channel symbols per second, with each channel symbol conveying one bit. The modem-to- modem link uses something else entirely, but I never said which link was `19200 baud'. -- In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163) Domain: chris@mimsy.umd.edu Path: uunet!mimsy!chris
wes@obie.UUCP (Barnacle Wes) (10/07/88)
In article <1464@netmbx.UUCP> blume@netmbx.UUCP (Heiko Blume) writes: > as far as i remember the baud rate tells you how many changes of the > discrete signal levels are possible. In article <13842@mimsy.UUCP>, chris@mimsy.UUCP (Chris Torek) writes: > Not exactly. `Baud rate' means `number of channel symbols per unit > time'; multiplying this by `number of bits per channel system' gives > the more familiar bits per unit time, typically bits per second. Nope, Heiko was right. Baud refers to the number of state changes the carrier makes per unit time. How this relates to the bit rate depends on the modulation scheme you are using (NRZ, NRZ1, diphase, etc.). > It may be best to stick with `bps'. After all, I use a Telebit TB+ > modem at 19200 *baud* ... between the serial port on the TB+ and that > on the Vax! That part of the link runs at 19200 channel symbols per > second, with each channel symbol conveying one bit. The modem-to- > modem link uses something else entirely, but I never said which link > was `19200 baud'. Actually, it is highly likely that you are using the TB+ at *19200 bps* since that is probably what your computer is sending out. With the way RS232 signals are encoded, the actual baud rate is somewhat slower than the bit rate, since adjacent bits of the same type do not cause a state change. In other words, if you send out an ASCII NUL character, you will only get two state changes in the entire byte - one for the start bit, and one for the stop bit. If you are transmitting at 19,200 bps, this give you an effective baud rate of 3840! -- {hpda, uwmcsd1}!sp7040!obie!wes "How do you make the boat go when there's no wind?" -- Me --
chris@mimsy.UUCP (Chris Torek) (10/10/88)
>>In article <1464@netmbx.UUCP> blume@netmbx.UUCP (Heiko Blume) wrote: >>>as far as i remember the baud rate tells you how many changes of the >>>discrete signal levels are possible. >In article <13842@mimsy.UUCP> I answered: >>Not exactly. `Baud rate' means `number of channel symbols per unit >>time'; multiplying this by `number of bits per channel system' gives >>the more familiar bits per unit time, typically bits per second. In article <210@obie.UUCP> wes@obie.UUCP (Barnacle Wes) replies: >Nope, Heiko was right. Baud refers to the number of state changes the >carrier makes per unit time. How this relates to the bit rate depends >on the modulation scheme you are using (NRZ, NRZ1, diphase, etc.). All three of these definitions are different. While it is not my field, I must say that, from an information-theoretic point of view, my definition makes the most sense to me (no surprise here :-) ). Heiko's definition is `how many changes are possible'; your is `how many are made per time'. It is easy to convert from `possible changes *per* *time*'---which is no doubt what Heiko *meant*---into `amount of information per time', but knowing the actual number of changes (your definition, unless you reword it) tells very little. Imagine a 300 baud FSK modem that is in the spacing state, and remains that way for .02667 seconds. It is making *no* state changes per unit time, yet a machine connected to it infers from this a NUL character---eight bits of information! With my definition, this 300 baud modem is sending 300 channel symbols per second. Each channel symbol is one bit of information. A 1200 `baud' 212A modem sends 600 channel symbols per second, but, since it uses quadrature modulation, carries two bits of information per symbol, for a total of 1200 bits per second. Telebit's DAMQAM sends very few channel symbols per second, but each one carries many bits. There appear to be three orthogonal issues: Imprimus, the number of channels; secundus, the number of channel symbols per unit time per channel; and tertius, the amount of information carried per channel symbol per channel. This is why I like my definition: it fits the situation. (There is, of course, a bias built into this situation!) >... In other words, if you send out an ASCII NUL character, you >will only get two state changes in the entire byte - one for the start >bit, and one for the stop bit. If you are transmitting at 19,200 bps, >this give you an effective baud rate of 3840! Well, that is certainly consistent with your definition of `baud'. Anyone have an official reference handy, so we can find out who is right (and if it is Wes, why the---to me---peculiar definition of `baud')? -- In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163) Domain: chris@mimsy.umd.edu Path: uunet!mimsy!chris
jim@fsc2086.UUCP (Jim O'Connor) (10/11/88)
In article <13924@mimsy.UUCP>, chris@mimsy.UUCP (Chris Torek) writes: > >>In article <1464@netmbx.UUCP> blume@netmbx.UUCP (Heiko Blume) wrote: > >>>as far as i remember the baud rate tells you how many changes of the > >>>discrete signal levels are possible. > > >In article <13842@mimsy.UUCP> I answered: > >>Not exactly. `Baud rate' means `number of channel symbols per unit > >>time'; multiplying this by `number of bits per channel system' gives > >>the more familiar bits per unit time, typically bits per second. > > In article <210@obie.UUCP> wes@obie.UUCP (Barnacle Wes) replies: > >Nope, Heiko was right. Baud refers to the number of state changes the > >carrier makes per unit time. How this relates to the bit rate depends > >on the modulation scheme you are using (NRZ, NRZ1, diphase, etc.). > > All three of these definitions are different. While it is not my [discussion deleted] > Anyone have an official reference handy, so we can find out who is right > (and if it is Wes, why the---to me---peculiar definition of `baud')? Since you asked for it, here's something that might be considered an "official reference". From _Computer Networks_, by Andrew Tanenbaum, page 93, " The time T required to transmit the character depends on both the encoding method and the signaling speed, [the number of times per second that the signal changes it value (e.g. its voltage) [ed. or e.g. its frequency]]. The number of changes per second is measured in *baud*. A 'b' baud line does not necessarily transmit 'b' bits/second, since each signal might convey several bits." If you read "number of changes per second" as "maximum possible number of changes per second" this basically sums up the ideas presented in the three earlier definitions, with only some minor changes in the exact terminology. ------ James B. O'Connor +1 615 821 4090 x651 Filtration Sciences Corp. UUCP: uunet!fsc2086!jim 105 West 45th Street or jim@fsc2086.UUCP Chattanooga, TN 37411
ron@ron.rutgers.edu (Ron Natalie) (10/12/88)
Of course, it is baud if you are talking about the RS-232 side of them modem. Thats the side I care about, it's the part that I have to deal with. The two modems could be sending morse code to each other for all I care. -Ron