Telebit PEP protocol optimalization - The Document
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From nmrdc1.nmrdc.nnmc.navy.mil!nlmug!roxette.uwalt.nl.mugnet.org!root Tue Oct 6 12:28:47 1992 From: WonderBoyReceived: by roxette.uwalt.nl.mugnet.org (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 Telephone +31-252-230-205 To: randy@psg.com Subject: Re: Telebit PEP protocol optimalization - The Document Message-Id: Date: Tue, 6 Oct 92 18:26:55 Status: OR Randy, > 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 ================================================================================ TELEBIT PEP MODEM CONSIDERATIONS FOR 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. INTERNATIONAL CALLS 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. CELLULAR, MICROWAVE, AND SATELLITE CALLS 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. DIAGNOSING AND SOLVING MODEM COMMUNICATIONS PROBLEMS 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- mission. 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 PEP FINE TUNING REGISTERS 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 is. 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" (ATS70?). 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. UNIX 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 /usr/lib/uucp/dialTBIT.c 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" /usr/lib/uucp/L.sys The "echo suppression" option is invoked by the "e" option in the following manner: hostname Any ACU 19200 NNNNNNNucpe "" \d ogin: Usys word: XXXXXX NOTES: 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) (J6S36=2) 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 1-800-TELEBIT (408) 734-4333 UUCP: {ames, uunet, sun, pyramid}!telebit!modems INTERNET: modems@telebit.com 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... Fred.