8 Nov
2021
8 Nov
'21
4:55 p.m.
This is true, particular in the case where you want to know "end of
current stream" or end of file, which is meta-data that can not be
gotten from TCP.
In FTP, you know this for the current file if you are not holding the
data port open because the port is closed, giving you end of file.?
Knowing end-of-file allows you to do some excellent optimizations; real
speed.
Paged file structures breaks all that because you don't know end-of-file
until the data stream tells you, which means large reads can become
problematic (I.E., you hang waiting for data).
Doing a send is fine because you don't need to care, but the receiver
has to decode the data stream on the fly instead of doing a big slurp.
This is the reason I didn't get the Extended mode FTP server done before
MRC passed.? All of the data handling code expected synchronized
meta-data to indicate end of file (I.E., port closed).? You can't do
that with a port held open, even with a push which may get swallowed.?
Urgent out of band data doesn't work, either because it may come in
before the end of the data stream.? Besides, that would break RFC959
compliance for 20's and TENEX sites that use the BBN server and client.
------------------------------------------------------------------------
On 11/8/21 10:32 AM, Paul Koning wrote:
On Nov 8, 2021, at 10:13 AM, Johnny
Billquist<bqt at softjar.se> wrote:
On 2021-11-08 15:27, Paul Koning wrote:
Streaming mode
DECnet sockets would be interesting to learn something about.
Because otherwise the problem is really that DECnet is packet based, and not byte based
like TCP. So there is potentially some problems with adapting TCP protocols for DECnet.
Not really. Stream based protocols are protocols that do not rely on message
boundaries -- more precisely, do not rely on boundaries being marked by lower layers. If
you have a transport that does report message boundaries, and you want to carry a stream
protocol, the simple answer is to ignore those boundaries.
The reason I'm interested in how Ultrix did streaming sockets is because of the
question "when do you send the message". That's actually a question with
TCP as well, which is why it has a "no delay" option. The trivial answer is
"for each send() call to the socket, send that data as a complete NSP message".
That would obviously work; the only question is whether something fancier is a useful
optimization.
Actually, there might be one other question. Consider HTTP: if the server wants to send
a file (say, a .jpg image) can it send the entire file as a single NSP message? From the
DECnet architecture point of view, sure. Do DECnet implementations put some limit on the
length of an NSP message? I don't know, except for RSTS which doesn't simply
because it leaves segmentation and reassembly to the application.
The mismatch that's harder to deal with is an application that needs message
boundaries, running over a transport that doesn't have these. The TCP/IP world is
full of these, and in every instance the application protocol concocts an ad-hoc solution
to this issue. Consider iSCSI and NFS as two examples, with different solutions (or
multiple solutions, if you take the "markers" hack in iSCSI seriously).
paul
On Nov 7,
2021, at 9:54 PM, Peter Lothberg<roll at stupi.com> wrote:
In the "old days" we did SMTP over DECnet, has anyone considered doing Telnet,
FTP, HTTP etc over
DECnet transport?
I've thought about http over DECnet. That would be really
easy. The obvious way to deal with any TCP-based protocol is just to send the byte
streams over DECnet messages, in the same fashion as DECnet/Ultrix streaming mode DECnet
sockets do. (Precisely how that works I don't remember.) In the case of HTTP, a
natural simplification would be to send the entire header, in both directions, as a single
message, with any data following in one or more additional messages.