lance@richp1.UUCP (Lance Hall) (06/13/90)
A question to those folks who know --- The currently ratified standard for high speed modems is V.32 which consists of the following: - 9600 bits per second - full duplex operation over voice grade 2-wire connections - fallback to V.22bis -> V.22/Bell212 -> V.21/Bell103 - 600 baud with 16 point Trellis Coded Modulation (or is 32 point TCM required/recommended/commonly used for forward error correction?) - echo cancellation necessary - no inherent end-to-end reliability mode; i.e., V.42/Appendix is required for such - no inherent end-to-end compression mode; i.e., V.42bis is required for such I have seen reference to the V.32bis standard that is currently in progress which consists of the following: - 14,400 bits per second (why did this not double to 19,200 bps?) - full duplex operation over voice grade 2-wire connections - fallback mechanisms ??? - modulation scheme ??? TCM ??? DAMQAM ??? Other ??? - echo cancellation necessary - no inherent end-to-end reliability mode; i.e., V.42/Appendix is required for such - no inherent end-to-end compression mode; i.e., V.42bis is required for such I would appreciate some discussion to better understand what V.32bis is now and what it may be when ratified as compared to V.32. -- - - - - - Lance N. Hall lance@richp1.UUCP or lance@richsun.cpg.trs.reuter.com
tnixon@hsfmsh.UUCP (Toby Nixon) (06/14/90)
In article <920@richsun.UUCP>, lance@richp1.UUCP (Lance Hall) writes: - The currently ratified standard for high speed modems is V.32 which - consists of the following: - - - 9600 bits per second The current V.32 standard includes three operating modes: 4800bps non-trellis, 9600bps non-trellis, and 9600bps trellis-coded. - - full duplex operation over voice grade 2-wire connections - - fallback to V.22bis -> V.22/Bell212 -> V.21/Bell103 V.32 does not include fallback to anything. The CCITT recently agreed to add an appendix to V.32 which will define an Automode procedure for falling back to V.22bis and V.22, which is stable but will not be formally adopted until 1992. Telecommunications Industry Association (TIA) technical committee TR-30 is about to send out for committee ballot a TIA "Interim Standard" (IS-63) which will adopt this CCITT method as a US standard; TR-30 is continuing to work on this under TIA Project Number 2330 to add V.21, V.23, Bell 212A and Bell 103J, but it will be at least another 6 months before this work is complete. At that point, we will have a US standard for Automode; we'll never have a CCITT standard that defines Bell 103 or 212 as fallbacks. - - 600 baud with 16 point Trellis Coded Modulation - (or is 32 point TCM required/recommended/commonly used - for forward error correction?) V.32 always uses 2400 baud modulation. The 4800bps rate uses a four-point constellation. 9600 uses 16-point, and 9600 with trellis coding uses a 32-point constellation. Virtually all V.32 modems shipping now use 9600bps with trellis coding. - - echo cancellation necessary - - no inherent end-to-end reliability mode; i.e., V.42/Appendix - is required for such - - no inherent end-to-end compression mode; i.e., V.42bis is - required for such You are right on these points. - I have seen reference to the V.32bis standard that is currently in - progress which consists of the following: The proposed draft recommendation V.32bis was agreed in CCITT Study Group XVII at their last meeting in April, 1990. It will be submitted for approval under accellerated procedures at the October, 1990 meeting. If it receives unanimous support from those attending the meeting, it will then go out for a written ballot to all CCITT member nations; if 70% or more of those returning the written ballots vote to approve the standard, it will be adopted. The soonest we will have a V.32bis recommendation is February, 1991. - - 14,400 bits per second - (why did this not double to 19,200 bps?) The proposed V.32bis recommendation includes operation at 4800bps (non-trellis-coded) and trellis-coded operation at 7200, 9600, 12000, and 14400bps. It did not go to 19200bps, because it is beyond the power of current technology to run a 512-point constellation (which is what it would take to run 19200 trellis-coded on a 2400 baud carrier). The 128-point constellation for 14,400 is pushing it! - - full duplex operation over voice grade 2-wire connections And also two-wire leased lines. - - fallback mechanisms ??? The same Automode scheme as described above for V.32. However, during V.32bis operation, the modems may rapidly shift speeds up and down to accommodate changing line conditions. V.32 modems must perform a full retrain to change speeds, which takes several seconds; V.32bis modems can exchange a short series of tones and bits, and change speeds in less than 100 milliseconds. The data rate is always the same in both directions. - - modulation scheme ??? TCM ??? DAMQAM ??? Other ??? The modulation scheme is a straight logical extension of V.32; none of that DAM stuff. The CCITT has, however, embarked on study of modulation schemes that will allow operation at greater than 14,400bps, and the floor is open for contributions on new technologies. - - echo cancellation necessary - - no inherent end-to-end reliability mode; i.e., V.42/Appendix - is required for such - - no inherent end-to-end compression mode; i.e., V.42bis is - required for such Right again. Let me know if I can answer any other questions for you. -- Toby Nixon Standards Committee Representative, Hayes Microcomputer Products Chairman, TIA TR-30.4 Special Rapporteur on Question 14 (CCITT Study Group XVII) ----------------------------------------------------------------------------- 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!attmail!tnixon Internet: 70271.404@compuserve.com MHS: C=US / AD=ATTMAIL / PN=TOBY_L_NIXON / DD=TNIXON -----------------------------------------------------------------------------