Subject: Hardware handshaking with slip (was Re: network performance)
To: David Carrel <>
From: None <>
List: port-hp300
Date: 07/14/1994 23:53:03
I get the same problem with my 486 box -- it's because hardware
handshaking isn't working with slip for some reason.  Perhaps it is
something in the device-independent code.

I'm giving the "-link2" option to ifconfig, which should enable
hardware handshaking, although that wasn't documented in any man page
the last I checked (I sent a pr on it).

I know it's not a modem problem, because hardware handshaking works on
this machine with both Linux and FreeBSD.  I can see the "CS" (CTS)
light go on and off on my USR Courier, but the "SD" (Send) light keeps
going anyway.  With Linux or FreeBSD, the lights go on and off
together as they should.

Email:           | Brown University
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David Carrel <> writes:
> I started out testing throughput on my slip link.  I am using ttcp (a tcp
> test program).  When sending data TO my machine over a 28.8 modem with DTE
> set to 38.4 (the max on the hp300), I see transfer rates of around
> 3.62KBytes/s (~=36Kbaud).  Pretty nice!  (Obviously I am getting good
> compression in the modem.)  But when I tried reversing the direction
> (sending FROM my NetBSD machine) my transfer rate dropped to .97KB/s (close
> to one fourth).  I tried varying the packet lengths and the socket buffer
> sizes (socket buffer sizes have an amazing affect on SunOS) but I saw no
> appreciable effects under NetBSD.
> [...]
> Over the slip link, things happen slowly enough that you can watch TCP "as
> it happens" by watching the modem lights (you can count the ACKs).  When
> sending from NetBSD, there are large periods where nothing is being sent.
> It almost appears that TCP is backing too far off.  Seems like a tuning
> problem, but I am not a TCP wiz.