The CIA World Factbook 1992/k3bimage.iso/sel/04/0011/combine.txt

Text File | 1991-12-02 | 7.5 KB | 127 lines

           What is v.32?  What's the difference between it and v.42?

The v.32 standard is a "modulation" standard.   I like to compare it to the
AM and FM standards used  in radio broadcasting.   Not only are they at
different frequencies but they use different modulation  techniques.  There
are different modulation standards for 300,  1200 and 2400 baud.  The v.32
standard is a full duplex  (data going both  ways simultaneously at the
rated speed) standard for 4800 and 9600 bps connections.

The v.42  standard is an error  correction standard.   It is more correctly
referred to as v.42bis It is a method  by which data is packetized and sent
between modems to ensure that the data that arrives at the receiving end is
the same as what was transmitted.  It also includes the ability  to compress
data  on the  fly  to  enable higher  throughput  without requiring a
different modem modulation scheme.

MNP is another error correction standard.   In fact, the v.42 standard
includes MNP as an "alternate" method in case a modem is not v.42
compliant ..  in other words  v.42  modems  can  connect with  MNP
modems  and  achieve  a "reliable" connection.

A commonly asked  question is if  v.32 modems  will work with  v.42 -- and  the
answer is yes and no.   If you asked the question "can I  transmit ENGLISH over
an FM RADIO  FREQUENCY and have the  listeners understand" the answer  would be
the same and for virtually the same reasons  (comparing the  v.42 method  of
packetizing data to English and the v.32 method of modulation to FM).

The  v.42  and   v.32  standards   are  for  two   completely  different   (but
complimentary) areas of  communication.  In  fact, you'll most likely  discover
that every  v.32 modem  you find  has v.42,  MNP or  some other  kind of  error
correction control built into it.

So... a v.32 modem can talk to a v.42 modem -- if the modem on the other end
is a v.32 modem and if it can understand the v.42 method of packetizing data
(or the MNP method since MNP is included in the v.42 standard).

                               High Speed Modems

We  have  received numerous  messages  asking  about high  speed  modems, their
capabilities  and compatibility  between  modems from  different manufacturers.
The following text  basically discusses the US Robotics HST 9600 bps modems and
the Hayes V-Series 9600 bps modems.  It also covers the subject of v.32 modems.


1) The old USR HST  had a top transmission speed  of 9600 bps.  This  is before
   taking into account any kind of  MNP compression.  Typical throughputs  with
   the old  HST ranged  from 1150  cps  on a  compressed file  with the  modem-
   compression-DISABLED  to  1900  cps  on  a  regular text  file  with  modem-
   compression-ENABLED.

   The HST  will only transmit  at 9600 bps when  connected to another  HST but
   will connect at 300/1200/2400 baud to other standard modems.

2) The new  USR HST (termed  the 1440) is  able to  transmit data at  14400 bps
   (again, this is  before taking into  account MNP compression, etc).  Typical
   throughputs with  the  new HST  will range  from about  1500-1700  cps on  a
   compressed file with modem-compression-DISABLED to about 2300-2400  cps on a
   text  file with  modem-compression-ENABLED -- this  is assuming  that you've
   opened your comm port at 38400 bps.

   The new 1440 HST will  only transmit at 9600  bps when connected  to another
   HST  but  will connect at 300/1200/2400 baud to other standard modems.

3) The Hayes V-Series 9600  modems are similar to the old  USR HST described in
   #1 above.   You will typically see throughputs  as high as 1900  cps on text
   files but only about 960 cps on compressed files.

   The Hayes  V-Series 9600 will  only transmit at  9600 bps when  connected to
   another V-Series 9600 modem but will  connect at 300/1200/2400 baud to other
   standard modems.

4) Hayes has recently begun shipping its V-Series modems with new ROM  chips in
   them giving  them v.42  compatibility.   This means that  the V-Series  9600
   modems can  now provide  an error-corrected  session when  connected to  any
   regular MNP modems at 2400 bps.  This is because  v.42 implements MNP levels
   1 through  4  (which excludes  MNP  compression).   You will  typically  see
   throughputs of about 260-280  cps on a 2400 bps line  due to MNP's stripping
   of the start and stop bits.

5) The  v.32 modems (such  as those made  by US Robotics and  MultiTech) run at
   9600 bps  and will  give you similar  throughputs to  those described  in #1
   above (i.e.  v.32 will give you slower transmission speeds than will the new
   HST's running at  14400 described in #2).   However, the advantages  of v.32
   are that it provides you  with better "interactive response times"  (such as
   when typing) and that  because v.32 is a CCITT "standard"  they will connect
   at 9600  bps to modems made by OTHER manufacturers.   By "other" I mean that
   you can connect US Robotics v.32's to MultiTech v.32's to any  other v.32's.
   The v.32 standard appears to be one that remain for some time to come ..  so
   purchasing  a v.32  modem may be  a better  investment if you  are concerned
   about  future  compatibility.   However,  v.32  still  costs  more than  the
   proprietary standards such as the HST 9600 or the V-Series 9600.

6) The USR  Dual Standard is BOTH a  v.32 and an HST modem.   When it is in the
   "HST  mode" everything said in #2 above  (about the new 1440 HST's) is true.
   When it is in "v.32 mode" then everything said in #5 (about v.32 modems)  is
   true.  In other words in v.32 mode you will not get the full speed advantage
   of the Dual Standard for file transfers.   However, one BIG advantage to the
   Dual  Standard is that it is compatible not  only with the v.32 standard but
   with  all of the existing  HST modems as  well.  This  may or may  not be an
   advantage  for you  depending on  which modems  you frequently dial  into or
   which modems dial into you.

7) Hayes is  working on a  v.32 modem that  is similar to the  v.32 description
   given in #5 above.   I cannot comment further  on this modem due to  lack of
   details that have been given to me.

8) A final note on HST US ROBOTICS non v.32 modems.  Both the standard 9600
   HST and the 14.4 HST operate in a non-standard mode.  That is, as you
   now can surmise, they cannot communicate with any 9600 modems other than
   other HSTs.  They are less expensive than v.32 modems because they are
   not BIDIRECTIONAL 9600 or 14.4.  That is, most standard protocols, i.e.
   300, 1200 and 2400 are capable of transmitting at that baud rate in
   both directions at the same time.  (Thus the invention of the BIMODEM
   protocol.)  The old HST's did not have a standard to move data at 9600
   or higher speeds in both directions at the same time.  The HST's got
   around the problem by moving at the high speed in only one direction at
   at time.  The rate of the data flow would force the switch.  The non-
   high speed direction flowed at a rate of 450.  This made practical sense
   since for large time segments of modem usage, data flow is usually
   predominantly heavy in one direction for a long time.  As noted before,
   the HST can switch the high speed direction.  It is for this reason that
   the HSTs cannot communciate with V.32 which do run at 9600 in both
   directions silmutaneously and this explains why the HST's are cheaper
   and why the DUAL standard which can HST and v.32 are the most expensive.