IPP Mail Archive: RE: IPP> IPP, independently of HTTP, Requires Chunking?

IPP Mail Archive: RE: IPP> IPP, independently of HTTP, Requires Chunking?

RE: IPP> IPP, independently of HTTP, Requires Chunking?

Zehler, Peter (Peter.Zehler@usa.xerox.com)
Fri, 17 Apr 1998 07:45:31 PDT

Regarding IPP testing experience with chunking/IPP. I have not yet seen
anyone that has tried this. The tests I have been involved in, up to very
recently, used HTTP 1.0. This was due to the limitations of JDK. I have
not yet pursued the added complexity of chunking. This is a function of
IPP's underlying transport(HTTP 1.1). I have been concentrating on the IPP
PAD and method invocation. I would love to hear anyone with some concrete
experience with IPP and chunking.
The interoperability test plans calls for a print submission with and
without the client chunking its request. I had not thought of the server
chunking its reply. Should this be added to the "top 25" IPP tests?
I do not see where IPP requires chunking. I believe it currently is a
requirement of IPP's protocol mapping to handle the situation where the size
of the request/response is not known until the end. HTTP solved this by
chunking data. If IPP were mapped to another protocol we would depend on
the new protocol's method to handle this problem or pull the solution for
the problem up into the IPP layer.
Peter Zehler
Networked Products Business Unit
Email: Peter.Zehler@usa.xerox.com
Voice: (716) 265-8755
FAX: (716) 265-8792
US Mail: Peter Zehler
Xerox Corp.
800 Phillips Rd.
M/S 111-02J
Webster NY, 14580-9701

-----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


Here is my understanding of what we are seeing in testing. (Peter,
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

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
end-of-data is by closing the connection. (HTTP 1.0 is described in
Informational RFC 1945)

HTTP 1.1 provides persistent connections (connections that stay
intact for
multiple request-response transactions for the same client-server).
technique for signalling end-of-data for objects whose length may
not be
known at the beginning of the transmission is chunked encoding. In
1.1, you may still signal end-of-data by closing the connection, but
is not recommended, since you will then lose the benefits of the
connection. (HTTP 1.1 is currently described in the Standards Track
2068, but there will be a new RFC shortly reflecting implementation

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
>the client determines whether to use chunking for a particular HTTP

All transactions may use chunked encoding in either direction. The
requesting client determines whether to use it for POST or PUT
and the responding server determines whether to use it for

>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
>sending the document.

Strictly speaking, this is not a requirement, in that the client
close the connection to signal end-of-data.

>4) With the exception of the situation in 3) the client can always
>not to use chunking, but send even long documents in one request.
>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
>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
>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
>IPP transfers.

Our current implementation of IPP transaction support requires that
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 Van Andel
Allegro Software Development Corporation
43 Waite Road
Boxborough, MA 01719
(978) 266-1375
(978) 266-2839 fax

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