Newsgroup: it.comp.os.linux.iniziare
Titolo: Re: Qual e' la migliore Classe per ricevere Fax con modem esterno?

 da usare e con ocr in italiano tipo WinFax.
Ai ai ai ai.
Che io sappia c'è solo Hylafax...
-- 
Lorenzo `paulatz' Paulatto
Trieste
``Se Gauss fosse vivo oggi, sarebbe un hacker.''
      --Peter Sarnack (Princeton University)

Da quel poco che ne so quando il fax chiama c'è una fase di negoziazione dei
parametri variabili, tipo velocità, classe e altri parametri.
Credo che nel tuo caso, in cui il modem è solo in ricezione, non debba
preoccuparti di questo. Fissarti su una classe specifica potrebbe
precluderti la ricezione dai fax che non implementano la classe da te
scelta
Bye,
Raktzo

 tutti gli altri fax, sia a se stanti che altri modem/fax?
Ah, dimenticavo...Che programma mi consigliate sotto linux? Magari semplice
da usare e con ocr in italiano tipo WinFax.
Grazie.

Ciao a tutti,
dovrei attaccare un modem esterno (su porta seriale) V.92 al computer che fa
da server internet con linux acceso 24h/24h.
Anche il modem sarebbe acceso 24h/24h e dovrebbe servire solo per ricevere
fax, che di solito dovrebbero essere dei documenti d'identita'.
So che i modem hanno varie classi tipo, 1, 1.0, 2.0 ecc. Mi fareste
un'elenco preciso?
Qual'e' la migliore per quanto riguarda una massima compatibilita' verso
tutti gli altri fax, sia a se stanti che altri modem/fax?
Tutte le varie classi hanno una stessa massima risoluzione?
Sapevo che i UsRobotics (ne  ho avuto anche uno in passato) hanno una classe
non tanto buona per i fax, e' vero?
Grazie.
Ciao Paolo

Tutte le varie classi hanno una stessa massima risoluzione?
In classe1 dipende dal software, in classe 2 dal modem e devi vedere manuale
modem.
Su Linux direi che la scelta grosso modo, per programmi a costo 0, è
limitata a efax, mgetty, hylafax.
efax e hylafax gestiscono classe 1/2, mgetty solo 2.
Se vuoi spendere poco per il modem cercane uno con chipset conexant, classe
1/1.0.
Se vuoi spendere un po' prendi multitech MT5634ZBA-V92 che puo fare fax fino
a 33k e supporta alte risulozioni se lo vuoi usare in classe 2.1.
-- 
giu...@pobox.com

 scelta
Devo comprare un modem esterno usato, se ne trovano vari, causa passaggio ad
adsl.
Ma volevo sapere quale classe deve supportare il modem da comprare.
bye

 fino a 33k e supporta alte risulozioni se lo vuoi usare in classe 2.1.
Mi serve solo in ricezione e non mi interessa arrivare a 33k.
Ma la classe 1 arriva almeno a 14400?
Ciao Paolo

 modem e gli altri; gli altri non hanno idea se tu sei classe 1/2/...
Visto che la classe e' legata al software e non agli altri fax...
Sono arrivato alla conclusione che la migliore sia la Classe 1, visto che la
classe 2 implementa una fase in hardware (quindi usa meno cpu, ma chi se ne
frega) e quindi non e' facilmente upgradabile (firmware).
Mentre per la Classe 1 in caso di problemi, basta aggiornare o cambiare il
software, cosi' come dice questo vecchi documento che ho trovato.
Siete d'accordo su questa conclusione?
=========================================================================
From "The Modem Report", Rockwell International - Digital Communications 
 Modem Technology News. Issue No. 3, May 1993. 
 
CLASS 1 OR CLASS 2, DOES IT MATTER? 
----------------------------------- 
By Mark Chapman, Chris Sneed and Tony Zuccarino 
The widespread availability of low cost PC Fax modem boards has resulted in 
 explosive growth in PC fax communication. This in turn has spawned a range 
 of good PC fax applications software offering a variety of user friendly 
 features. 
 
To the user, the real questions are "how easy is it to send a fax" and 
 "will the software work with my hardware". 
 
There are many issues of standardization and much discussion in the 
 industry over just what overhead a real time task such as receiving a fax 
 will place on the PC. 
Standards 
International standards have facilitated reliable inter-working of modems 
 and software by creating command interfaces for modem hardware and
software. 
 As long as any modem board and any communications software package comply 
 with the same standards, they will work together. 
 
Compatibility 
To the end user, the interaction of the communication software and modem is 
 irrelevant as long as the system works. But the question, "are there 
 advantages to buying a modem complying with one standard versus a different 
 standard?", is often raised. 
The current industry debate centers on the relative merits of the two major 
 standards for PC fax , the Class 1 and the Class 2 specifications. 
 
About fax machines... 
To understand the issues, let's review fax operation and how this affects 
 the PC. A typical fax transaction consists of five phases: 
   * Phase A. Call Establishment (e.g., dialing or answering the phone). 
    * Phase B. Pre-message Procedure -- selecting parameters acceptable to 
      the calling and the called station (i.e., speed, fine resolution, 
      modulation etc.). 
    * Phase C. Message Transmission -- usually image data for one page. 
    * Phase D. Post-message procedure -- page break marker, and opportunity 
      to change settings (e.g., drop to a lower speed because of too many 
      errors detected during Phase C). 
    * Phase E. Call clear down (i.e. hanging up the phone). 
 
The actual operation of the five phases is specified by two CCITT standard 
 protocols, T.4, and T.30. 
 
T.4 defines the image transfer portion of the session used in phase C. 
 
T.30 defines the negotiation and inter page phases (ABD&E). A normal 
 multi-page transfer uses T.30 only at the beginning of the call, between 
 pages, and after the last page. 
 
Class 1 and Class 2: 
 
Class 1 and Class 2 standards specify command sets for modems and software 
 packages that allow modem manufacturers and software developers to build 
 products independent of each other. As long as both of the vendors support 
 either Class 1 or Class 2, their products will work well together. Class 2 
 is complex, supporting about 30 commands, while Class 1 supports less than 
 10. However, the main difference is that Class 1 requires the PC to handle 
 both T.30 and T.4 protocols, while in Class 2 only T.4 is done in the PC. 
 
                    Class 1        Class 2 
    T.30 Protocol    PC software    PC fax modem 
    T.4 Protocol     PC software    PC software 
 
So how much does this additional processing mode affect the PC, especially 
 one running Windows? 
 
Significantly, Phase C, using T.4, takes up about 95% of the time and CPU 
 effort during a typical facsimile transfer. This is because most of the 
 time is spent scanning, compressing (or decompressing if receiving) and 
 sending the pages, and very little time is spent by T.30 negotiating at 
 the start and end of the call as well as between pages. 
 
During the message transfer Phase C, Class 1 and Class 2 have the same 
 performance. The two situations where there could be a difference between 
 Class 1 and Class 2 in Phase C are: 
 
   * (1) receive line quality checking (to determine if the received line 
          is bad) 
    * (2) padding the transmitted line (to meet minimum line transmit times) 
 
Line quality checking is much more strenuous than line padding. 
 
Due to the many methods of line quality checking, and the vagueness of the 
 specifications, many, if not all, software packages perform this function 
 in any case irrespective of the modem type. This means that line quality 
 checking gets done in the PC irrespective of whether the modem supports 
 Class 1 or Class 2. 
 
As message transfer dominates fax transmission, most of the CPU intensive 
 tasks are incurred by Class 1 and 2 alike. In fact as the number of pages 
 increases, T.4 becomes by far the dominant factor in fax transmission and 
 the difference between Class 1 & Class 2 becomes negligible. 
 
Multitasking Environment 
 
There are certain stages in call set up and interpage negotiation during 
 which the modem requires the close attention of the PC. At these times, the 
 PC software must respond rapidly and for Windows-based software (the 
 application is controlling T.30), this means that the application cannot 
 relinquish control to other applications during these critical times. It is 
 this real-time constraint and associated interrupt overhead rather than any 
 processor load factor which affects operation under Windows. 
 
In practice, this effect can be largely prevented by suitable design of the 
 applications software where the time critical T.30 portions are included at 
 the driver level and these days all good commercial Class 1 fax packages 
 work as well as Class 2 under Windows. 
 
Class 1 Provides Flexibility 
 
Class 2 is a "closed" standard, in that any changes to the T.30 protocol 
 require a revision to the firmware (EPROM) on the fax modem board. 
 
Modem and software manufacturers occasionally develop T.30 code updates in 
 order to add additional features, correct errors in prior code revisions, 
 or resolve interoperability issues with particular fax machines (the T.30 
 standard leaves some room for interpretation). While a Class 2 fax modem 
 will require a firmware update (new EPROM) to incorporate the change, a 
 Class 1 fax modem user can incorporate the change simply by downloading new 
 software from a bulletin board, or ordering it from the software 
 manufacturer. 
 
There are about five different "Class 2" versions out there with no 
 guarantee of compatibility (there are software packages on the market that 
 do support all of the variants). However, most Class 2 fax boards support
an 
 interim working specification of Class 2 that has become the defacto Class
2 
 standard. Recently, the EIA-TIA approved a real class standard, but it will 
 take 6 months to a year before software and hardware will emerge based on 
 this new Class 2 standard. 
 
Non-standard facilities (allowed under T.30) are not supported by Class 2 
 but can be easily added to Class 1 boards extending the life of modem 
 hardware as new software or operating systems features become available. 
 
In short, the Class 2 standard is fixed, whereas Class 1 is more flexible 
 and can be maintained as software evolves. There are niche markets in which 
 unique technical constraints dictate that Class 1 is favored and other
niche 
 markets where Class 2 is optimum but for the vast majority of the computing 
 public, there is no discernible difference between Class 1 and 2. Both 
 standards send and receive faxes reliably and the end user will neither
care 
 nor need to get involved comparing Class 1 and Class 2 as long as the 
 application works. 
 
Enough theory... is there actually a difference? 
 
To evaluate the practical effect on CPU performance between Class 1 and 
 Class 2 fax, a series of tests were performed on a representative set up 
 using popular fax software packages. (See Figure 1). This was done by 
 measuring the effect of receiving a fax in background mode while the PC in 
 foreground is busy with a task. 
 
(Figure 1 showwed time results of Class 1 and Class 2 using three Fax 
 packages: Winfax, QuickLink II, BitFax on three CPU types: 386SX/25-MHz, 
 386DX/33-MHz, 486DX2/50-MHz. The times for a given CPU were within 5% of 
 each other independant of Class or Fax Software.) 
 
The task chosen for the series of tests was both CPU-and disk 
 storage-intensive, and consisted of compressing a large collection of 
 varied files. The received fax transmission consisted of 3 pages, including 
 a cover page and representative test fax pages. The tests were repeated 
 several times, and figures varied less than +/- 2% leading to a high degree 
 of confidence in the test results. 
 
Conclusions 
 
There is a measurable amount of time "stolen" from a PC's CPU by fax modems. 
 However, the difference between Class 1 and Class 2 in terms of foreground 
 processing load is negligible. In fact the comparison between individual 
 manufacturers fax packages is in some instances significantly greater than 
 the difference between Class 1 and Class 2. The effect diminishes 
 considerably as the processor power increases, and the difference between 
 Class 1 and Class 2 reception is further reduced as more pages are sent. 
 
End users have consistently demonstrated their preference by choosing the 
 low cost, flexibility and future upgrade capability of Class 1 over the 
 slightly faster speed of Class 2. Which one provides more functionality? As 
 most, if not all, software packages support both standards with the same 
 user interface, the answer is that to the end user, Class 1 and 2 are 
 transparent and offer the same functionality. Rockwell offers modems 
 supporting both standards allowing users to make their own choice, safe in 
 the knowledge that they are buying the leading solution in either case. 

Ma la classe 1 arriva almeno a 14400?
Tutti i modem-fax, classe 1 o 2, fatti in ultimi 8 anni (e forse +)
supportano 14400. Il multitech di sopra è unico modem seriale esterno che va
fino a 33k.
-- 
giu...@pobox.com