-----Original Message-----
From: Bob Van Andel [SMTP:bva@allegrosoft.com]
Sent: Friday, April 17, 1998 10:01 AM
To: ipp@pwg.org
Cc: Peter.Zehler@usa.xerox.com
Subject: RE: IPP> IPP, independently of HTTP, Requires
Chunking?
All,
Here is my understanding of what we are seeing in testing. (Peter,
please
correct me if I'm wrong).
IPP is a request-response protocol that sits on top of HTTP (a
request-response protocol) that sits on top of TCP (a connection
protocol).
TCP provides the end-to-end message integrity including packet
retries for
lost or mis-ordered transmissions.
HTTP 1.0 uses a single TCP connection for each request-response
transaction. In many cases, this is because the only way to signal
the
end-of-data is by closing the connection. (HTTP 1.0 is described in
the
Informational RFC 1945)
HTTP 1.1 provides persistent connections (connections that stay
intact for
multiple request-response transactions for the same client-server).
The
technique for signalling end-of-data for objects whose length may
not be
known at the beginning of the transmission is chunked encoding. In
HTTP
1.1, you may still signal end-of-data by closing the connection, but
this
is not recommended, since you will then lose the benefits of the
persistent
connection. (HTTP 1.1 is currently described in the Standards Track
RFC
2068, but there will be a new RFC shortly reflecting implementation
experience)
At 12:31 PM 4/16/98 , Carl-Uno Manros wrote:
>Randy et al.,
>
>Here is my take on the use of chunking for IPP:
>
>1) Each HTTP 1.1 implementation is mandated to support chunking.
Yes, but all transactions do not need to use chunked encoding.
>
>2) All POSTs are initiated by the client, which I assume also means
that
>the client determines whether to use chunking for a particular HTTP
request.
>
All transactions may use chunked encoding in either direction. The
requesting client determines whether to use it for POST or PUT
requests,
and the responding server determines whether to use it for
responses.
>3) The only situation where chunking is absolutely necessary for
IPP, is
>the case where the client does not know the document length when it
starts
>sending the document.
Strictly speaking, this is not a requirement, in that the client
could
close the connection to signal end-of-data.
>
>4) With the exception of the situation in 3) the client can always
decide
>not to use chunking, but send even long documents in one request.
The
>downside of doing that is that if something goes wrong on the lower
>protocol layers, the client has to start over and send the whole
document
>again from the beginning. The main advantage of using chunking is
that if
>you get an error on the lower layers, you only have to resend the
latest
>chunk, not the whole document.
This is not correct. Lower layer transmission errors will be
handled at
the TCP layer regardless of whether chunked encoding is used.
>
>5) Again, with the exception of the case in 3), you can in practise
>actually use HTTP 1.0, which does not support chunking, for most of
your
>IPP transfers.
>
Our current implementation of IPP transaction support requires that
HTTP
1.1 support be turned on. In practice, Peter overrode this
constraint and
is successfully running IPP over HTTP 1.0 regardless of whether job
size is
known at the beginning.
Bob
----------------------------------------
Bob Van Andel
Allegro Software Development Corporation
43 Waite Road
Boxborough, MA 01719
(978) 266-1375
(978) 266-2839 fax
Information on the RomPager embedded web server toolkit is at
<http://www.allegrosoft.com/>