jtn@ADS.COM (John T. Nelson) (12/13/90)
Thanks to all who responded to my query about the Racal Vadic 9632 VP modem. I've got ZMODEM running now (without hardware handshake!) but looking at the throughput I have even MORE questions! Most binary files transfer from my Mac IIcx through the 9600 V.32 modem to the remote site (Telebit T2500) at about 300 bps -> 600 bps. Text files (like Macintosh HQX files) transfer at around 900 bps. ZMODEM claims that 900 bps is 98 percent effeciency. Ok... let's assume ZMODEM is telling the truth when it says that 1000 bps is the best I can expect. Why is it that binary files are doing the snail's pace of 300? There's more to it than that actually. Very often the performance gets as low as 60 bps! This is apparently because the transmissions are very "bursty" in character. There will be a sudden burst of characters to the remote modem and then a LONG 5 second delay of dead air and then a little more traffice and then another LONG delay of say 10 seconds and so on ad nauseum. Is this because ZMODEM is getting NAK packets of some kind back and retransmitting? Why the LONG delays? Here's another fun bit of info. Transfers from the remote machine TO my Mac are FAST! Always. Binary and ascii data crank at 98 percent effeciency all the time. Now why in the world would reception be faster than transmission? At least it works. I disable ALL flow control and use the latest copy of "rz" from mpace.cs.purude.edu (I think that's the place) and use the full 8 bit data path. Enjoy. -- ORGANIZATION: Advanced Decision Systems GEOGRAPHIC: Arlington, VA UUCP: kzin!speaker@mimsy.umd.edu INTERNET: jtn@potomac.ads.com SPOKEN: John T. Nelson PHONE: (703) 243-1611 PROJECT: Macintosh hacking -- "Love the Machine... Hate the Company"
lriggins@blackbird.afit.af.mil (L. Maurice Riggins) (12/13/90)
In article <9PF^W}#@ads.com> jtn@ADS.COM (John T. Nelson) writes: >Here's another fun bit of info. Transfers from the remote machine TO >my Mac are FAST! Always. Binary and ascii data crank at 98 percent >effeciency all the time. Now why in the world would reception be >faster than transmission? >At least it works. I disable ALL flow control and use the latest copy >of "rz" from mpace.cs.purude.edu (I think that's the place) and use >the full 8 bit data path. I experience the same thing here. But with the bsd system, I have to call sz with -w 8194 and ZNULLS set to 124 (for my SE) to get sz to work. Not may retransmissions (if any) on upload or download. Do have stty -tandem set also. I'm using White Knight with a Practical Peripherals PM9600SA going into a UDS 9600 (MNP only) which feeds a TRW ACU (with hardware handshake) going through Ethernet to the Vax. Any clues (other than the Vax buffers can't handle it)? Thanks, -- Maurice INTERNET: lriggins@blackbird.afit.af.mil (129.92.1.2) Opinions expressed here do not reflect those of my employer nor constitute an official position of any U.S.Government agency.
kianusch@ghost.UUCP (Kianusch Sayah-Karadji) (12/14/90)
> >Most binary files transfer from my Mac IIcx through the 9600 V.32 >modem to the remote site (Telebit T2500) at about 300 bps -> 600 bps. >Text files (like Macintosh HQX files) transfer at around 900 bps. >ZMODEM claims that 900 bps is 98 percent effeciency. Ok... let's >assume ZMODEM is telling the truth when it says that 1000 bps is the >best I can expect. Why is it that binary files are doing the snail's >pace of 300? > >There's more to it than that actually. Very often the performance >gets as low as 60 bps! This is apparently because the transmissions >are very "bursty" in character. There will be a sudden burst of >characters to the remote modem and then a LONG 5 second delay of dead >air and then a little more traffice and then another LONG delay of say >10 seconds and so on ad nauseum. Is this because ZMODEM is getting >NAK packets of some kind back and retransmitting? Why the LONG >delays? > >Here's another fun bit of info. Transfers from the remote machine TO >my Mac are FAST! Always. Binary and ascii data crank at 98 percent >effeciency all the time. Now why in the world would reception be >faster than transmission? ... if you modems have compression mode don't use Zmodem (use Y/X modem instead) ... if you do want to use Zmodem ... turn modem compression of and use only local error correction... same thing with compressed files, (zoo, compress, zip, ...) dont use Zmodem or Modem compression at all. The reason is that each of those try compress the data... worst scenario... transfering a compressed file, with zmodem using an compression modem protocoll... zmodem try's to compress ... but actually makes the file bigger ... now the modem get's a big-compressed file, which the modem in turn tries to compress ... and makes it even more bigger ... and everything slowes down... happend to me a few days ago... trying to tranfer a compressed (700k) file... using telebit PEP / COMPRESSION ... it took me 30min for the first 300k ... I aborted the transfer ... started all over again using PEP only (no compression) ... and the transfer was compleated in 12 minutes... Text files are not compressed... so either Zmodem, or Modem-compression will do a better job... Hope This helps Kianusch -- Kianusch Sayah-Karadji srhqla!unigold!ghost!kianusch kianusch@ghost.UUCP pacbell!unicom!ghost!kianusch