Hardware - for those who want to connect a modem to the Spectrum.

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      The information presented here is already
 somewhat outdated relative to IBM
 movable cars. We printed this for those
 who wants to connect a modem to the Spectrum.
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      Manufacturer collaborations
 modems with groups establishing inter-
 international standards such as CCITT,
 in recent years it has been proven that modems
 different species can interact.
 There are three main areas in which
 modems can be standardized:
 dulation, error correction and data compression
 nykh.                                     
      The CCITT V.32 modulation standard defines
 shares the industry standard for duplex
 No communication 9600 bps. However, V.32 is
 is a relatively new standard,
 approved in 1988.  Modem, respectively
 corresponding only to the V.32 standard, it will not be possible
 connect with devices from a huge variety of
 features of widely used modems with
 low transmission speed, so it is painful
 Most suppliers also use other
 different, older module standards -
 tions.                                     
      If buyers are going to carry out
 communicate only within their own
 tvennye private networks, the modem must correspond
 greet the oldmore established
 standards such as the company's Bell 212A
 AT&T - the most common standard
 Dartu for baud rate 1200 bps
 or V.22 bis CCITT - the most common
 to the same standard for speed 2400
 bit/sec.                                 
      Although new modulation methods increase
 speed of modems, probability of interference in the
 telephone line, distorting data transmission
 nykh, also increases enormously.       
 Increased interference may affect the loss
 data when transferred from one modem to
 to another or that the data may
 symbols generated by
 furs.                                  
      Interactive users usually
 see the results of interference in the transmission line
 in the form of unusual symbols on the screen.  For
 detecting interference in the transmission line and failure
 for from incorrectly accepted data developed
 file transfer protocols such as XMO-
 DEM.                                     
      To solve the problem of eliminating
 fur in the Microcom transmission line
 Inc., Norwood, Massachusetts, created
 "de facto" standard with its own protocol
 MNP Class 4 error management protocol
 MNP Class 4 is offered by almost all
 suppliers of V.32 protocol modems, some
 Some sellers also create protocols in
 their modems with a transfer speed of 2400
 bits/sec.                                 
      Modems that implement the MNP protocol
 Class 4, interact using packages
 data analysis using identifying
 solving coding errors.                
      CCITT has also defined the management protocol
 error management, V.42, which is partially
 compatible (plug-in) with MNP Class 4.
 Some modem suppliers, accordingly
 applicable only to the MNP Class 4 protocol, based on
 call their modems "proto-compatible"
 stake V.42", although in fact they are not
 fully compliant with the V.42 standard.
      Data compression can give the user
 the channel capacity is more than
 9600 bps by squeezing
 more data in fewer quantities
 bit quality  The PC transmits data to the modem,
 which, in turn, carries out
 compression of data before sending it over
 telephone line.                        
 The receiving modem, before transferring
 restore data to a PC, restores them
 innovation  As a result, the compression procedure
 remains invisible to the user.     
      Microcom also created
 "de facto" standard with its own standard
 compression MNP Class 5. For data of some
 type, especially textual information in AS-
 CII, throughput according to
 tvii with MNP Class 5 can reach 19200
 bit/sec.Standard for V.42 bis group compression
 CCITT can improve throughput
 Data rate up to 38400 bit/sec. Development
 this standard was completed at the end
 1989.                               
      Although the V.42 bis compression protocol is not
 fully compatible with compression protocol
 MNP Class 5, most suppliers
 plans to use it to increase
 bandwidth of their modems, both
 method.                                  
      Buyers of V.42 protocol modems
 encore must ensure that the chosen
 with them the modem will be compatible with the already installed
 long basic modems of the MNP protocol
 Class 5. However, over time
 protocol V.42 bis, which received international
 new recognition will obviously be in the future
 standard for data compression.            
      Buyers looking for devices
 having the greatest compatibility and the most
 less chance of falling out of use, should-
 we choose a modem that matches all
 modulation standards plus cor- protocol
 error correction V.42.  Manufacturers
 revised the standards in such a way that, to
 for example, a V.32 protocol modem with
 V.42 error correction scrap can be
 connected to a V.32 protocol modem, in which
 there is no error correction.      
      So, without careful study, it is possible
modem capabilities, the buyer can detect
 pretend that he is burdened with the device,
 having characteristics that cannot
 be used.