Date: Wed, 02 Dec 98 18:45:12 PST From: "Igor B. Bykhalo" <goshik@binep.ac.ru> To: freebsd-questions@FreeBSD.ORG Subject: Flow control on SLIP Message-ID: <MAPI.Id.0016.006f7368696b20203030303630303036@MAPI.to.RFC822>
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Hi! I have a few questions concerning SLIP usage over physical (leased) line. My system consists of two 486 PC-routers running FreeBSD 3.0-RELEASE connetcted via 4-wire line of about 1km length. Modems: external, 115.2 kbps, asyncronous, without hardware buffering/flow control, interface RS-232, 4-wire leased line, full duplex, line code AMI (quasiternary). (Zelax+ M-115A, http://www.zelax.ru/english) Serial ports: 16550A UART on one side and Startech ST16550 on the other. SLIP headers compression is on and MTU is 296. Problem is that I'm having from 1 to 15 percent of errors packets on received packets (according to netstat); also I get something like this: /kernel: sio2: 24 more interrupt-level buffer overflows (total 24) (not very frequently, though). I've asked Zelax's techs about use of XON/XOFF and DTR/DCD flow control, but they told me "this is OS and software dependable" and they could not tell me much about FreeBSD and its SLIP. Questions: 1. Is there a sence to turn on software (ixon/ixoff) flow control on sio port used by SLIP? Wouldn't it be an interference with transport protocol (TCP/IP)? 2. If answer to 1. is yes, would it be correct to make it with, say # stty </dev/ttyid3 ixon ixoff -crtscts 115200 # stty </dev/ttyld3 ixon ixoff -crtscts 115200 # stty </dev/cuaia3 ixon ixoff -crtscts 115200 # stty </dev/cuala3 ixon ixoff -crtscts 115200 script in rc.serial? 3. Does (sio | SLIP | TCP/IP) software require DTR control? Probably a couple of exerpts from Zelax+'s FAQs could be useful (I've translated them from russian, those FAQs are not available in english. Sorry). >From faq43: "... (M-115A) just pass software flow control symbols (XON/XOFF) through itself..." (they mean - as usual data) >From faq45: "... modems (mentioned) do not support data flow control. Because they do not have internal buffers, and speed on modem's port is always less or equal to line speed, modems itself can't delay data. The only possible limitation is the DTE's inability to receive data with required speed. When connecting these modems it is necessary either to turn off data flow control completely, or to use in-band (software, XON/XOFF) data flow control. When doing so remember that from the DTE's piont of view the modems mentioned are seen like five-wire null-modem cable (TD, RD, DTR-DCD in both direcions, and common wire)." Thanks in advance, Igor (aka Goshik) To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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