dean@coplex.uucp (Dean Brooks) (06/18/91)
We have had a Telebit T2500 for quite some time now, and since
V.42 has become quite popular lately, I have had requests for me
to enable V.42 detection on our Telebit for people dialing in.
However, I have not been able to get it work. There is apparantely
a register S106=1 that will enable V.42 detection. Unfortunately,
whenever anyone tries to connect with V.42 enabled, it never
seems to work.
We are running a locked interface speed of 19,200 with hardware
flow control enabled. So, here are my questions:
1) How do I get V.42/V.42bis to be automatically recognized?
2) What in the world is LAP-M?
3) Is any of this stuff synonymous to MNP-5?
4) Help!
Regards, Dean Brooks
--
dean@coplex.uucp (Dean Brooks)
Copper Electronics, Inc.
Louisville, Kentuckygandrews@netcom.COM (Greg Andrews) (06/18/91)
In article <1991Jun17.225901.10900@coplex.uucp> dean@coplex.uucp (Dean Brooks) writes: > > We have had a Telebit T2500 for quite some time now, and since >V.42 has become quite popular lately, I have had requests for me >to enable V.42 detection on our Telebit for people dialing in. > > However, I have not been able to get it work. There is apparantely >a register S106=1 that will enable V.42 detection. Unfortunately, >whenever anyone tries to connect with V.42 enabled, it never >seems to work. > > We are running a locked interface speed of 19,200 with hardware >flow control enabled. So, here are my questions: > >1) How do I get V.42/V.42bis to be automatically recognized? > Set S97=1 and S106=1 in your modem. S98 controls V.42bis compression. Leave S98=3 to enable compression in both directions. These registers first appeared in Version 6.00 firmware. > >2) What in the world is LAP-M? > "Link Access Protocol (for) Modems" is the name of the error correction protocol introduced in the V.42 recommendation. LAP-M is just the acronym for the protocol's name. The V.42 recommendation defined two error control protocols, LAP-M and an "Alternate" protocol. LAP-M is a new protocol, while the "alternate" protocol is identical to MNP4. This means V.42 modems can get an error controlled connection with modems that only handle MNP. Since two protocols are defined, the V.42 recommendation also includes a way to negotiate which one you want, LAP-M or the "alternate" (MNP). The T2500 has a register to enable each of the two processes: The LAP-M protocol itself (S97), and the V.42 negotiation between LAP-M and the "alternate" protocol (S106). > >3) Is any of this stuff synonymous to MNP-5? > Not to MNP5 (the data compression algorithm). You can say that it's synonymous because MNP4 and LAP-M are both 'error control protocols', but beyond that they are somewhat different. >dean@coplex.uucp (Dean Brooks) -- .------------------------------------------------------------------------. | Greg Andrews | UUCP: {apple,amdahl,claris}!netcom!gandrews | | | Internet: gandrews@netcom.COM | `------------------------------------------------------------------------'
zjdg11@hou.amoco.com (Jim Graham) (06/18/91)
In article <1991Jun17.225901.10900@coplex.uucp> dean@coplex.uucp (Dean Brooks) writes: [lots deleted about V.42/V.42bis and LAP-M] Most of your questions were already covered in another followup article, so I won't hit on those...but..... >3) Is any of this stuff synonymous to MNP-5? well, sort of....but not quite. V.42/V.42bis are SIMILAR to MNP4/MNP5 in that like MNP4, V.42 is an error control protocol, and like MNP5, V.42bis is a data compression technique. However, to say that V.42 == MNP4, or that V.42bis == MNP5 would not be true. Personally, I'll take V.42/V.42bis over MNP4/5 any day..... [those who've seen some of my previous posts on the subject already knew that, I'm sure.... :-) ] hope that helps! --jim Standard disclaimer....These thoughts are mine, not my employer's. ------------------------------------------------------------------------------ Share and Enjoy! (Sirius Cybernetics Corporation, complaints division) 73, de n5ial Internet: zjdg11@hou.amoco.com or grahj@gagme.chi.il.us Amateur Radio: TCP/IP: jim@n5ial.ampr.org (44.72.47.193) Packet: BBS went QRT for good...still searching for new one. ------------------------------------------------------------------------------
mju@mudos.ann-arbor.mi.us (Marc Unangst) (06/19/91)
dean@coplex.uucp (Dean Brooks) writes: > 1) How do I get V.42/V.42bis to be automatically recognized? For V.42 operation, set S106=1 (V.42 auto-detect) and S97=1 (V.42 enable). For V.42bis operation on top of V.42 operation, set S98 to 1, 2, or 3 (depending on whether you want to compress transmitted data, received data, or both, respectively). > 2) What in the world is LAP-M? Link Access Protocol for Modems, aka V.42 and V.42bis. > 3) Is any of this stuff synonymous to MNP-5? Sort of. V.42 is the CCITT equivalent of MNP-4 (i.e., it does error detection and correction), but is *not* the same protocol. V.42bis is the CCITT equivalent of MNP-5 (i.e., it does realtime compression of data), but is *not* the same protocol (the most important feature over MNP-5 is that it does not attempt to compress already-compressed data; under MNP-5, already-compressed data can expand to 120% of its original size after "compression"). You want to use V.42 and V.42bis over MNP-4 and MNP-5 whenever possible, since they're generally faster and more robust than their MNP counterparts. > 4) Help! All of this is explained nicely in the release notes for the GF7.00 T2500 ROMs. If you have a ROM revision earlier than GF7.00, V.42 and V.42bis aren't supported, and you'll need to get new ROMs from Telebit. -- Marc Unangst | mju@mudos.ann-arbor.mi.us | "Bus error: passengers dumped" ...!hela!mudos!mju |
bob@uis-oc.UUCP (Robert J. Mathias Jr.) (06/22/91)
In article <1991Jun18.123604.9315@hou.amoco.com> zjdg11@hou.amoco.com (Jim Graham) writes: >well, sort of....but not quite. V.42/V.42bis are SIMILAR to MNP4/MNP5 in that >like MNP4, V.42 is an error control protocol, and like MNP5, V.42bis is a data >compression technique. However, to say that V.42 == MNP4, or that >V.42bis == MNP5 would not be true. Personally, I'll take V.42/V.42bis over >MNP4/5 any day..... [those who've seen some of my previous posts on the >subject already knew that, I'm sure.... :-) ] Some of us like to squeeze the last ounce of speed out of our equiptment, so we poor miss guided souls prefer to disable V.42 and go with MNP4. As to V.42bis and MNP5, V.42bis is the winner but since I do alot of file xfers of ZIPed files, I also disable compression on my modem. -- Bob Mathias uucp: ccicpg!uis-oc!bob@uunet.uu.net Unisys Corporation CServ: 70340,165 A and V Series Systems Engineering voice: (714) 727-0323 Irvine, California
tnixon@hayes.uucp (06/26/91)
In article <78@uis-oc.UUCP>, bob@uis-oc.UUCP (Robert J. Mathias Jr.) writes: > Some of us like to squeeze the last ounce of speed out of our equiptment, so > we poor miss guided souls prefer to disable V.42 and go with MNP4. A good V.42 LAPM implementation can go faster than MNP4. Why? Because the maximum frame size of MNP4 is 256 octets. You have 7 octets of overhead per frame, and, considering the average occurrence of a zero bit insertion every 63rd bit, the maximum throughput of an MNP4 modem is 119.7% of a non-error-correcting modem (e.g., 1150cps on a 9600bps modem). But LAPM can negotiate much larger frame sizes, limited only by the amount of buffer space in the modem and the effectiveness of the FCS chosen (for example, the 16-bit FCS isn't as effective if you send more than 4096 bytes in a frame). Hayes modems, for example, support up to 512 bytes in a frame, which, if enabled, would give you throughput of (1.25*512/519*62/63=) 121.4% of a non-error-correcting modem (e.g., 1165cps on a 9600bps modem). But, as you probably know, the default frame size for LAPM is 128 bytes (116.6% throughput, or 1120cps on a 9600bps modem). Unless the modem you happen to be using allows you to specify a larger frame size, that's what you'll get. The smaller frame size does allow for faster recovery from line errors, should they occur. > As to > V.42bis and MNP5, V.42bis is the winner but since I do alot of file xfers > of ZIPed files, I also disable compression on my modem. V.42bis allows the transmitting modem to switch between sending compressed and uncompressed data. Most V.42bis modems incorporate a performance feedback mechanism, so that the modem detects when data is uncompressible and switch to sending the raw data automatically. Thus, leaving V.42bis enabled all the time will normally not impact on your throughput at all when sending pre-compressed files, but will quickly kick in and increase your throughput on uncompressed text during interactive periods between files. -- Toby Nixon, Principal Engineer | Voice +1-404-840-9200 Telex 151243420 Hayes Microcomputer Products Inc. | Fax +1-404-447-0178 CIS 70271,404 P.O. Box 105203 | UUCP uunet!hayes!tnixon AT&T !tnixon Atlanta, Georgia 30348 USA | Internet tnixon%hayes@uunet.uu.net