gandrews@netcom.COM (Greg Andrews) (03/17/91)
In article <1991Mar16.160708.152892@ramona.Cary.NC.US> andrew@ramona.Cary.NC.US (Andrew Ernest) writes: >In article <9908@discus.technion.ac.il> devil@techunix.BITNET (Gil Tene) writes: >>To detail : S120=12 means no use only LONG packets, no micro > >What are the side-effects of S120=16? This is the value Telebit >says turns off the short burst of V.25 tone at the beginning of >each PEP answer tone. This tone, which appeared in the BC5.10A >firmware upgrade for my TB+, caused my neighbors with older firmware >to no longer be able to connect to my modem. S120=16 solved the >problem but I am now curious if that register value (16) has any other >effect I should know about (like packet size, etc). > It turns off all of the mods put into the PEP modulation to combat trouble with echo cancellation devices on fiberoptic long distance carriers. One of the changes was a 3 second V.25 answer tone when the modem first answers the phone, even if PEP tones are first. Previous versions of firmware didn't put out the V.25 answer tone before the PEP tones. > >Can anyone guess why the V.25 tone was added? Any reason why turning it >off is a bad thing? (Not that I have any intention of turning it back >on...compatibility with my PEP neighbors is of the most importance to me.) > It was added to better conform to the V.25 recommendation, which says an automatically answering modem transmits a 2100 Hz tone when it goes off hook. Part of the reason for the V.25 answer tone is linked to the reason PEP was modified for the fiberoptic carriers - the tone helps to disable the telco's echo cancelling and/or echo suppressing equipment. PEP was having trouble over those types of lines, so it was modified to compensate. The V.25 answer tone was only part of those mods. Setting S120=16 disables ALL the mods - not just the V.25 answer tone. The V.25 answer tone probably isn't the problem. It's more likely to be due to how the mods work when you have PEP tones last. If PEP tones are first, only the oldest TrailBlazers have trouble with the V.25 answer tone before PEP, and many of those can set S50=255 to overcome it. When PEP tones are last, it's a different story. -- .-------------------------------------------. | Greg Andrews | gandrews@netcom.COM | `-------------------------------------------'
root@minixug.mugnet.org (MINIXUG-ONLINE System Manager) (03/23/91)
gandrews@netcom.COM (Greg Andrews) wrote: > In article <1991Mar16.160708.152892@ramona.Cary.NC.US> andrew@ramona.Cary.NC.US (Andrew Ernest) writes: >>In article <9908@discus.technion.ac.il> devil@techunix.BITNET (Gil Tene) writes: >>>To detail : S120=12 means no use only LONG packets, no micro >> >>What are the side-effects of S120=16? This is the value Telebit >>says turns off the short burst of V.25 tone at the beginning of >>each PEP answer tone. This tone, which appeared in the BC5.10A >>firmware upgrade for my TB+, caused my neighbors with older firmware >>to no longer be able to connect to my modem. S120=16 solved the >>problem but I am now curious if that register value (16) has any other >>effect I should know about (like packet size, etc). S120=16 causes the firmware to ONLY send "long" packets, like in file transfer ("spoofed") mode. This is nice for links that have clicks in them (like my link from The Netherlands to Japan), since the firmware spends less time re-synching. With micro-packets and short-packets (interactive resp. normal operation), the firmware sometimes gets completely out sync, after which it has to do a resynch ("retrain").. this is annoying, and sometimes this can be prevented by just simply increasing S120 to 12 (only short + long pkts) or even 16 (only long pkts). The disadvantage of 12 and 16 is, of course, that interactive operation (login and such) gets really bad, since for each _character_ typed in, the TB sends a _long_ packet, instead of a micropacket. This, of course, results in very long delay times. So, on my link to Japan, login is very inefficient, as is file switching during transfers. So: we only send _ONE_ large (4-10Mbyte) file per session, which makes up for login time loss... > It turns off all of the mods put into the PEP modulation to combat trouble > with echo cancellation devices on fiberoptic long distance carriers. > One of the changes was a 3 second V.25 answer tone when the modem first > answers the phone, even if PEP tones are first. Previous versions of > firmware didn't put out the V.25 answer tone before the PEP tones. No, that is S121=1 . S120 is for setting the low-level packet protocol specs (detail: packet sizes). With J6 (enter maintenance mode) you can also issue several other register commands to further optimize the PEP protocol for a given link situation... All this "low level PEP optimization settings" stuff is documented in a text file available from Telebit Corporation... I could post it here, but I am sure that is not what people want... Fred van Kempen waltje@uwalt.nl.mugnet.org
gandrews@netcom.COM (Greg Andrews) (03/24/91)
Fred posted an article where he quotes three other articles. I've added pointers to clarify who posted what. In article <910322577@minixug.mugnet.org> root@minixug.mugnet.org (MINIXUG-ONLINE System Manager) writes: >> In article <1991Mar16.160708.152892@ramona.Cary.NC.US> >>andrew@ramona.Cary.NC.US (Andrew Ernest) writes: >>>In article <9908@discus.technion.ac.il> devil@techunix.BITNET >>>(Gil Tene) writes: [Gil wrote] >>>>To detail : S120=12 means no use only LONG packets, no micro >>> [Andrew asked] >>>What are the side-effects of S120=16? This is the value Telebit >>>says turns off the short burst of V.25 tone at the beginning of >>>each PEP answer tone. This tone, which appeared in the BC5.10A >>>firmware upgrade for my TB+, caused my neighbors with older firmware >>>to no longer be able to connect to my modem. S120=16 solved the >>>problem but I am now curious if that register value (16) has any other >>>effect I should know about (like packet size, etc). > [Fred answers] >S120=16 causes the firmware to ONLY send "long" packets, like in file >transfer ("spoofed") mode. This is nice for links that have clicks in >them (like my link from The Netherlands to Japan), since the firmware >spends less time re-synching. > [I respond] No, that is S120=2. [Fred] >With micro-packets and short-packets (interactive resp. normal operation), >the firmware sometimes gets completely out sync, after which it has to >do a resynch ("retrain").. this is annoying, and sometimes this can be >prevented by just simply increasing S120 to 12 (only short + long pkts) >or even 16 (only long pkts). > [I respond] The firmware does NOT get "completely out of synch". Retrains are caused by getting too many data errors within a short period of time. The modems track the error profile and if it looks bad, they decide the modulation is not optimal for the line conditions, and perform a retrain in order to adapt to the present conditions. Micro packets don't work very well over satellite links because the link has rather long delays. The modems expect a response to a micro packet within a certain period of time. Same for short packets. The timing constraints are very tight for micros, looser for shorts, and loose for long packets. The delays introduced by satellite links can cause the micro response to exceed the timing limit and generate an error. Since micros are extremely brief blips of sound, echo suppressors may not be able to respond in time, cutting off part or all of the packet. Using shorts and/or longs can help eliminate these kinds of errors, reducing the need to retrain. > [Fred quotes my answer to Andrew] >gandrews@netcom.COM (Greg Andrews) wrote: >> It turns off all of the mods put into the PEP modulation to combat trouble >> with echo cancellation devices on fiberoptic long distance carriers. >> One of the changes was a 3 second V.25 answer tone when the modem first >> answers the phone, even if PEP tones are first. Previous versions of >> firmware didn't put out the V.25 answer tone before the PEP tones. > > [Fred responds] >No, that is S121=1. [I answer] That's not correct. The S121 register deals with echo **suppressors** of conventional design, not echo **cancellers** used on fiberoptic long distance lines. They are entirely different beasts, and setting S121=1 does not fix the trouble PEP was having over Sprint and MCI lines. As I said, PEP was modified to handle the echo cancellers used for that new technology. Those modifications are completely different than the calibration comb controlled by S121. S120=16 disables the modifications to PEP introduced in version 7 to solve the problems that existed over fiberoptic lines. [Fred continues] >S120 is for setting the low-level packet protocol specs (detail: packet >sizes). With J6 (enter maintenance mode) you can also issue several >other register commands to further optimize the PEP protocol for a given >link situation... [I answer] That's right. And that's why S120 contains the bit to disable the fiberoptic mods. That bit is bit 4, S120=16. [Fred continues] >All this "low level PEP optimization settings" stuff is documented in a >text file available from Telebit Corporation... [I answer] Yes, and it gives only three S120 settings: 12, 2, and 3. -- .------------------------------------------------------------------------. | Greg Andrews | UUCP: {apple,amdahl,claris}!netcom!gandrews | | | Internet: gandrews@netcom.COM | `------------------------------------------------------------------------'
root@Topsail.ORG (Chuck Murcko) (03/27/91)
Please post the Telebits text on adverse links. modems@telebit.com tells me they are no longer mailing it out due to problems with users misapplying the fixes. So, let those who read the post, beware! -- Chuck Murcko The Topsail Group 538 E. Church Rd., Elkins Park, PA 19117 Internet: cmurcko@topsail.Topsail.ORG UUCP: ...!uunet!lgnp1!gvlv2!topsail!cmurcko