Telebit PEP protocol optimalization - The Document

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From!nlmug!!root Tue Oct  6 12:28:47 1992
From: WonderBoy 
Received: by
          (U-MAIL 4.00alpha/PA+INET); Tue,  6 Oct 92 18:29:34 +0200
Organization: MicroWalt Corporation Software Development
              Hoefbladhof 27, 2215 DV  VOORHOUT, The Netherlands
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Subject: Re: Telebit PEP protocol optimalization - The Document
Date: Tue,  6 Oct 92 18:26:55
Status: OR


> No, you  never did.  I would certainly be pleased if you did happen to have
> a copy of the document you were willing to send.
Oops!  Sorry 'bout that.... :-(

Here it is:

Telebit Corporation                 Revision 1.00                    01 SEP 1990



                        ADVERSE COMMUNICATIONS LINKS

                    By TELEBIT CORPORATION Technical Support
     Edited by C. E. Castillo, UNIX Communications Specialist, TELEBIT Corp.

        The Telebit modem's advanced multi-carrier design, utilizing the
        patented Packetized Ensemble Protocol (PEP), is ideally suited to
        operate over international circuits which can often cause insur-
        mountable obstacles to standard "slow" or other high speed modems.
        There are several things to consider when attempting to establish
        a link over such a line that should help insure reliable connections
        with the maximum performance possible under the conditions.


        When originating a call and dialing internationally, you should
        increase the time to wait for carrier from the default of 40
        seconds, to about 80 seconds, to allow more time to dial, get a
        connection to the other end and then negotiate carrier.  This is
        controlled in the modem by the S7 register, which can be set any-
        where up to 255 seconds as needed.  Your software package may also
        have a parameter that controls the time to wait for carrier so be
        sure to set that accordingly.

        Leave the answering modem S7=40, because if 40 seconds has elapsed
        without establishing a connection, it is likely that it will fail
        to do so and it would be better to redial.  If possible, set S50=
        255 to force the modem to only send PEP connect tones.  This will
        not allow the answering modem to connect at any slow speed.

        It is usually good to set S110=1, (only on a TrailBlazer Plus,
        T2000, or T2500) so the modems can negotiate to do data compression.
        Do not use the data compression feature if the files have been com-
        pressed prior to transmission.  If you are going to use Kermit,
        Xmodem or UUCP to do a file transfer, set the S111 to the approp-
        riate value to allow the modems to negotiate for protocol support.
        It is recommended that you use one of the supported protocols to
        optimize throughput to the maximum level the telephone line will
        allow.  Zmodem and variations might also attain good results
        without any protocol support, but there is no need for complex
        sliding window protocols with the protocol support feature in
        TELEBIT modems.

        Echo suppression equipment on long distance circuits can cause
        timing delays that disrupt our packet transmission.  The modem
        can be configured to compensate for this problem if S121=1.
        This is a negotiated feature, which means that it is not re-
        quired to set S121 on both modems, only one of the two need be
        set to allow us to compensate for echo suppression.  Experimen-
        tation is about the only way to determine if echo supression
        equipment is present on the circuits.  If you seem to be able to
        operate without setting S121, don't change it.  But if you are
        experiencing problems with frequent long delays in data trans-
        mission, try setting this and see if there is an improvement.


        In satellite and microwave channels, Compansion may be an obstacle
        to obtaining good data throughput.  Compansion is the Compression
        and Expansion (amplification) of an analog signal over a voice or
        data communications link.  The use of Compansion to ensure the best
        voice quality possible over a satellite or microwave link may cause
        PEP packets to be "clipped" during a data connection.  Uncompanded
        communications channels may be available from the satellite or
        microwave service provider.  Experimentation is the best way to
        determine which type of service will best suit your application.
        The S121, S120, and J6 S36 registers will allow for a reliable and
        effective connection over either of these services.

        In cellular communications channels Compansion may also be a
        factor, but the leading obstacle is usually signal strength.
        Due to the use of passive or active RJ-11 adapters, the modem
        signal strength is crucial to maintaining a reliable and effective
        connection.  The CellBlazer product has software registers (S175)
        which set signal strength on the modem. Other TELEBIT modems have
        the ability to set signal strength via an internal gain resistor or
        an external (RJ-45 connector) gain resistor.  The S121, S120, and
        J6 S36 registers, in combination with the proper signal strength
        adjustments, will provide a reliable and effective connection over
        cellular channels.
        The communications equipment providing the RJ-11/RJ-45 interface
        to the modem may also be an important factor in cellular, microwave,
        or satellite connections.  Active RJ-11/RJ-45 adapters are highly
        recommended for cellular use via cellular telephones.  The satellite
        tracking mechanisms of a ship/earth station terminal may be just
        as important as its signal processing and transmission capabilities.
        The ability to adjust signal strength for any modem interfacing unit,
        along with the S121, S120, and J6 S36 registers, will provide a
        reliable and effective communications link.


        Some indications that your TELEBIT modem is experiencing difficulty
        in communicating are:

            1) Inability to connect after several attempts at "Handshaking"
               (the PEP connect tones) resulting in a NO CARRIER status.

            2) After connection, frequent pauses during which there is
               no response nor data received for 10 to 30 seconds at a time.

            3) Disconnection after a delay of 60 seconds with no data trans-

        In many cases, depending on the types of communications link, it
        is possible to "fine-tune" PEP to allow for more reliable
        connections and maximum performance.  TELEBIT Technical Support
        prefers to troubleshoot these situations on a case by case basis.
        It is therefore recommended that they be consulted prior to 
        modifying your TELEBIT modem modulation characteristics.  TELEBIT
        Technical Support should be able correct most, if not all, of these
        problems.  Contact TELEBIT Technical Support at 408-734-5200 (U.S.)
        or 1-800-TELEBIT (U.S.) or one of the TELEBIT international offices
        listed in this document.

        Many international calls will connect without any problems, but
        if difficulties in connecting or maintaining connections occur, the
        following settings are recommended.

        The three levels are in order of severity of line difficulties,
        from minor to major.

        Level 1.

           AT S120=12 J6 S36=1

        Generally, Level 1 will have a very minor impact on performance,
        both in interactive use and file transfer.  It is useful, however,
        for achieving a degree of reliability, even when the communication
        lines are very good.  The J6 S36 register may be incremented up to
        4 in order to better survive adverse line conditions.

        Level 2

           AT S120=2 J6 S36=2

        Level 2 will impact interactive performance severely while file
        transfers remain at close to normal performance.

        Level 3

           AT S120=3 J6 S36=3

        Level 3 is a last resort setting which will severly impact interactive
        performance and limit file transfer speeds to a maximum of 6000 bps.
        Data compression, S110=1, can make up some of the difference, but only
        if the data has not been previously compressed.

        The S121=1 register will enable compensation for echo cancellation on
        the circuit, and can be enabled at any of these levels.

        If a stand alone modem is in use, the special register commands
        should be sent to the modem and saved to Non-Volatile Memory, by
        sending the save command "AT&W".

        In situations where a mixture of local and long distance calls are
        being placed, it is recommended that these special settings be
        made in a modem initialization file or that the A/B selection
        switch be used.


        The S120 register is a non-documented register that governs your PEP
        packet size.  The modem operates on three different packet sizes:
        Micro Packets which are sent very frequently, Small Packets which
        are sent a little less frequent, and Long Packets which the modem
        automatically switches to when a file transfer begins.

        Sometimes over long-distance phone lines the modem has trouble staying
        in Micro Packet mode and has to perform a re-train, which you can hear
        by leaving your speaker on all the time with "ATM2".   This is what
        you sometimes experience when you get long delays before you receive
        any data.

        Setting S120=12 eliminates Micro Packets and uses Small or Long Packets
        depending on the size of the file to be transmitted.  Setting S120=2
        eliminates Small Packets and only uses Long Packets. Configuring your
        modem to the proper settings is dependent on how bad the line quality

        The J6 S36 register adds a little tone in front of the packet being
        transmitted to keep the front of the PEP packet from getting
        "clipped off" during a long distance file transfer over adverse line
        conditions.  Thus, if anything gets "clipped off" it will be this tone
        and not the data-carrying PEP packet.  The more you increase the value
        of S36 the more tone you add to the front of the packet.  Again, turn
        your speaker on to listen to the tones and set this register depending
        on how bad the line quality is.  As a word of caution, J6 S36 should
        not be set above 4.  This will result in a tone that is equal in size
        to the PEP packet and a 50% or more reduction in data throughput.

        The S120 and the J6 S36 are completely independent of each other. If
        S120 is set to a value other then default (S120=0) on one side only,
        the other side automatically negotiates to that value (i.e. setting
        S120=12 will force the other side to negotiate a value of S120=12 also).

        On the other hand J6 S36 is completely independent and must be set at
        each side.  Sometimes it is only necessary to set one side, or which
        ever side has the most trouble transmitting data (answering modem is
        active vs. calling modem is passive).  Please read your TELEBIT product
        reference manual for information on the S70-S76 registers and their
        functions.  This will assist you in assessing which modem will need
        these registers set in accordance to its "instantaneous transmit rate"

        Do not set S110=1 to enable Data Compression if the data you are 
        transmitting has been previously compressed.  Data compression on
        top of data compression adds too much overhead and will actually
        lower throughput on file transfers.


        In UNIX UUCP environments, it is recommended that the "chat script"
        in the L.sys file (Version2 UUCP) or the Dialers file (HoneyDANBER
        UUCP) be used to set these registers on a per site basis.  These
        registers may also be added to intelligent" dialers, such as the
        the dialTBIT dialer provided by SCO in their XENIX and UNIX systems.
        Here are some register entry examples:

        /usr/lib/uucp/Dialers (/etc/uucp/Dialers)
        This entry is one line:

        tbpepmod =W-, "" A\pA\pT OK ATS50=255S52=2S120=12J6S36=2DT\T CONNECT

        /usr/lib/uucp/L.sys (/etc/uucp/L.sys)
        This entry is one line:

        hostname Any cua0 19200 cua0 "" ATX0S50=255S52=2S120=12J6S36=2\r OK
        ATDNNNNNNNNNN\r  CONNECT  "" ""-\r-login: \r login: Uyoursysname
        ssword: XXXXXXXX

        This section of the SCO dialTBIT.c dialer is the only one modified.
        The option is invoked via the dialing string in the L.sys or Systems
        file, with the appropriate entry to the L-devices or Devices file.

         LINES 204-209 [MODIFICATION]:

          *      MDECHOSUP       - Enable Echo Supressor Compensation
          *      S121=1  - Enable Echo Suppressor Compensation
          *      S120=12 - Enable Long and Short PEP packets only
          *      J6s36=2 - Enable calibration tone on the PEP packets
          #define MDECHOSUP       "ATS120=12J6S36=2S121=1\r"

        The "echo suppression" option is invoked by the "e" option in the
        following manner:

        hostname Any ACU 19200 NNNNNNNucpe "" \d ogin: Usys word: XXXXXX        

        u     =     UUCP protocol support enabled (S111=30)
        c     =     Data compression enabled      (S110=1 )
        p     =     PEP connection only enabled   (S50=255)
        e     =     Echo suppression enabled      (S121=1 )
                    Special registers:            (S120=12)

        This document is meant to take a VERY general approach to the
        configuration of TELEBIT modems in interactive, file transfer, and
        networking applications over domestic, international, cellular,
        microwave, and satellite communications links.

        TELEBIT welcomes any questions, comments, and suggestions on this or
        any of our other product or configuration documents at the following
        U.S. or international mail address, telephone number, or network
        electronic mail account:

        Michael Ballard/Cerafin E. Castillo
        Telebit Corporation
        1315 Chesapeake Terrace
        Sunnyvale, CA  94089
        (408) 734-4333

             UUCP:     {ames, uunet, sun, pyramid}!telebit!modems


   Telebit Technologies Canada, Inc.       Telebit Network Technologies, S.A.
   500 Alden Road, Suite 203               255, Route d'Arlon
   Markham, Ontario, Canada L3R 5H5        L-18011 Strassen
   1-800-387-0455                          G.D. de Luxembourg
                                           +352 31 96 45

      Mail accounts are also available for sales literature, special
      incentive programs, public relations, and special interest topics:

                sales     corpcomm     idndp     slip 

Hope this helps, although it is not of much use on my WorldBlazer, sigh...