rlin@cs.ubc.ca (Robert Lin) (07/01/90)
I just heard about V.32bis on this newsgroup, the wonderful 14.4Kbps full duplex modem protocol. I have several questions: 1. How does it achieve this phenomenal speed? With some sort of even more sophisticated constellation? How many points? 2. Does it have the adaptive nature of Telebit multi-carrier protocol, that takes advantage of any extra bandwidth beyond the promised standard? 3. Is this a finalized protocol, formally adapted by CCITT, and 4. has any one implemented this yet? If not, how many years can we expect to wait before it is a reality? Please post publicly, as I am sure many people are also interested to hear about the nitty gritties.
tnixon@hsfmsh.UUCP (Toby Nixon) (07/03/90)
In article <8516@ubc-cs.UUCP>, rlin@cs.ubc.ca (Robert Lin) asks:
- I just heard about V.32bis on this newsgroup, the wonderful 14.4Kbps
- full duplex modem protocol. I have several questions:
-
- 1. How does it achieve this phenomenal speed? With some sort of
- even more sophisticated constellation? How many points?
CCITT V.32 uses 2400 baud modulation with a 32-point constellation
(5 bits per baud; 4 data bits and 1 coding bit) to achieve 9600bps.
V.32bis also uses 2400 baud modulation, with a 64-point
constellation for 12000bps and a 128-point constellation for
14400bps.
- 2. Does it have the adaptive nature of Telebit multi-carrier
- protocol, that takes advantage of any extra bandwidth beyond
- the promised standard?
V.32bis doesn't use multicarrier modulation. It does, however,
incorporate a rapid speed-change mechanism that allows the modem to
change between the speeds supported (4800, 7200, 9600, 12000, and
14400) in under 100 milliseconds.
I'm not sure what you mean by "takes advantage of any extra
bandwidth beyond the promised standard"; either the phone equipment
supports signals at a particular frequency, or it doesn't.
Contributions to the CCITT have shown that attenuation and delay
distortion of signals outside of the 300-3100Hz band is appreciable,
making equalization very difficult. The CCITT is currently studying
modulation techniques that may use more of this 2800Hz bandwidth to
provide data rates in the 19200bps range (e.g., 2743 baud with a
256-point constellation would give you 19200bps; several existing
modems for leased line use already do this).
- 3. Is this a finalized protocol, formally adapted by CCITT,
- and
V.32bis is in an "agreed draft" form at this time, meaning that at
the last CCITT Study Group XVII meeting in April 1990 there were no
substantial objections to any of it. The Study Group will meet
again in October, at which time it will consider adoption of V.32bis
under the CCITT's accelerated procedures. If such adoption is
unanimously supported by the Administrations attending the meeting,
the standard will undergo a three-month written ballot of all CCITT
member countries. If 70% of them approve, the standard will be
formally adopted; the earliest we will know this result is around
then end of February, 1991.
- 4. has any one implemented this yet? If not, how many years can we
- expect to wait before it is a reality?
Forval America claims to have a V.32bis modem, but they can't
possibly have incorporated the changes made at the April meeting
(e.g., the rapid speed-change feature and modifications to the
startup handshake). Therefore, and also because the standard is not
yet adopted, the answer to your first question is No. There _are_
companies that have 14400bps duplex dial-up modems on the market
today (e.g., British Telecom) who will certainly adapt them
immediately to V.32bis compliance; at least two other companies have
demonstrated 14400 duplex modulation. I suspect that we will see
several V.32bis-compliant modems on the market around mid-1991, if
the standard is adopted (most companies would not release a product
then if the standard were still subject to change).
-- Toby Nixon (Chairman, TIA TR-30.4; Special Rapporteur
on Question 14 in CCITT Study Group XVII; Representative
in the CCITT from Hayes Microcomputer Products, Inc.)
-----------------------------------------------------------------------------
Toby Nixon, Principal Engineer Fax: +1-404-441-1213 Telex: 6502670805
Hayes Microcomputer Products Inc. Voice: +1-404-449-8791 CIS: 70271,404
Norcross, Georgia, USA BBS: 1-800-US-HAYES MCI: TNIXON
Telemail: T.NIXON/HAYES AT&T: !tnixon
UUCP: ...!uunet!hayes!tnixon Internet: hayes!tnixon@uunet.uu.net
MHS: C=US / AD=ATTMAIL / PN=TOBY_L_NIXON / DD=TNIXON
-----------------------------------------------------------------------------tjfs@tadtec.uucp (Tim Steele) (07/04/90)
Thanks for that comprehensive posting on V.32 and V.32bis. Are the modes half duplex (like Telebit's PEP) or full duplex? Thanks Tim -- tjfs@tadtec.uucp ...!uunet!mcvax!ukc!tadtec!tjfs Tadpole Technology plc, Science Park, Milton Road, CAMBRIDGE, CB4 4WQ Phone: +44-223-423030 Fax: +44-223-420772 Telex: 817316 TADTEC G
tnixon@hsfmsh.UUCP (Toby Nixon) (07/05/90)
In article <TJFS.90Jul4133623@tadtec.uucp>, Tim Steele asks:
- Are the modes half duplex (like Telebit's PEP) or full duplex?
In V.32bis, all of the modems are symmetrical, full-duplex; you
transmit in both directions simultaneously (using echo cancellation)
at 14400, 12000, 9600, 7200, or 4800. There was a proposal to allow
asymmetrical data rates but symmetrical baud rates (i.e. 2400
symbols per second in both directions but varying the number of bits
per symbol, so you could have, say, 9600 in one direction but 14400
in the other), but this was not accepted by the CCITT. So, with
V.32bis, you always have the same speed in both directions.
-- Toby
-----------------------------------------------------------------------------
Toby Nixon, Principal Engineer Fax: +1-404-441-1213 Telex: 6502670805
Hayes Microcomputer Products Inc. Voice: +1-404-449-8791 CIS: 70271,404
Norcross, Georgia, USA BBS: +1-404-446-6336 MCI: TNIXON
Telemail: T.NIXON/HAYES AT&T: !tnixon
UUCP: ...!uunet!hayes!tnixon Internet: hayes!tnixon@uunet.uu.net
MHS: C=US / AD=ATTMAIL / PN=TOBY_L_NIXON / DD=TNIXON
-----------------------------------------------------------------------------