Path: utzoo!attcan!uunet!husc6!bloom-beacon!atheybey@PTT.LCS.MIT.EDU From: atheybey@PTT.LCS.MIT.EDU Newsgroups: comp.sys.amiga Subject: Re: high-speed file transfer Message-ID: <8901131551.AA12559@PTT.LCS.MIT.EDU> Date: 13 Jan 89 15:51:38 GMT Sender: daemon@bloom-beacon.MIT.EDU Reply-To: atheybey@PTT.LCS.MIT.EDU Lines: 49 To: nntp-poster@PTT.LCS.MIT.EDU Repository: PTT Originating-Client: flower If you are connecting to some flavor of BSD Unix, DNet is wonderful. The ability to have multiple open connections is a *big* win. If I am in emacs and want to do something in the shell, I just pop to my CLI, type "run fterm", and get another window with a Unix shell. Of course, I could suspend the emacs, but then I would have to redraw its screen when I resumed it (at 1200 baud, this is a big deal). You can even continue to work on the remote computer (for example, reading USENET :-) while downloading files. Of course, things are then kinda slow, but it still works and is useful. That plug for DNet aside... I have tried DNet with the USRobitics HST modems, and have a few reservations. (I ended up deciding that I couldn't afford an HST modem, and so did not look for a solution too vigorously.) The HST modems have a *unidirectional* 9600 baud channel. The two modems negotiate which direction gets the high speed channel, based on the number of characters in the modems' buffers. The other direction is 300 baud. The echoing of characters (when typing to a Unix shell) was actually *slower* than at 1200 baud. I think that this is because DNet sends a packet of several characters when you type one character. The sending modem then thinks that it has large amount to send, and asks for the high speed channel. When the echo of the typed character comes back, it is also in a packet, and so the modem on the Unix end asks for the high speed channel. I think that the two modems spend a lot of time swapping the high speed channel when you type. For sending large amounts of data (I cat'ed and putfile'd the same file) the modems achieved about 3800 bps. I can't say whether this number is limited by the interaction of DNet with the modems, or by the sending ability of the remote computer. I (stupidly) did not time sending a file without using DNet. The setup was Amiga<-->some form of terminal concentrator<-->Ethernet<-->uVax II. I do know that other people dialing up to the terminal concentrator with the HST modems and terminals do achieve rates much closer to 9600 bps (at least fast enough that a VT100 can't handle it without flow control :-). If one could permamently assign the high speed channel to the Unix-->Amiga direction, I think that DNet would have performed better (except for uploads, of course). I don't know if it is possible with this modem. --------------------------------------------------------------------------- Andrew Heybey, atheybey@ptt.lcs.mit.edu Room 509, 545 Technology Square Advanced Network Architecture Group Cambridge, MA 02139 MIT Laboratory for Computer Science (617) 253-6011 ---------------------------------------------------------------------------