Subject: Re: SDP, IPP>PRO Proposal for TIPSI-like protocol

From: Harry Lewis <[email-masked]>
Date: Wed, 6 May 1998 19:52:15 -0400

One thing it would buy is a simpler (than 1284.4) way to flow IPP over bidi
parallel - no? Isn't this basically what Lexmark has found? I'm confused why
TIPSI has a packet structure, Lexmark was shipping it on parallel and then .4
was invented - maybe some background could help (I always thought it was to
flow SNMP over parallel ;-). If it's true that the .1 packet is only still
there for legacy I might buy Bob's argument. But I suspect .4 is a much more
complex implementation.

Bob, doesn't your proposal say we would have to invent a transport (if not
already there) to "IPize" every physical layer (ex. serial)?

Harry Lewis - IBM Printing Systems

[email-masked] on 05/06/98 05:32:34 PM
Please respond to [email-masked]
To: [email-masked]
cc: [email-masked]
Subject: SDP,  IPP>PRO Proposal for TIPSI-like protocol

I just finished scanning IEEE 1284.3 and IEEE1284.4.  The most interesting
part is Chapter 8 "Service Provider Interface (SPI)" in IEEE 1284.4.  This
chapter describes a "Berkeley Sockets-compatible interface for clients and
servers to access the services provided by 1284.4".

So if I understand the intent of 1284.4, it is to provide a layer that
supports sockets over parallel connections. All we need to do in IPP is
reference sockets for TCP/IP and 1284.4 and we don't have to worry about the
issues at that layer.

So, I conclude that we don't need to packetize IPP or do much of what is
proposed in Roger and Harry's paper. Instead, we can send IPP directly on
sockets layered on top of TCP/IP or 1284.4.  There are a few easy-to-solve
dangling
issues, such as chunking for document data and intermediate acknowledgement
when attributes are verified for PrintJob. But otherwise IPP stays as is.

If you disagree with my conclusions, I would like to know what the
TIPSI-like packetizing layer provides that sockets don't also provide?

Bob Herriot

---

From: Robert Herriot <[email-masked]>
Date: Wed, 06 May 1998 17:29:35 -0700

Harry,

You are correct, my assumption is that there is a socket-like layer for any
type of 
connection that we connect a printer to and that IPP rides on top of this 
layer.  This assumption is true for TCP/IP and for parallel connection with 
1284.4 support. If we encounter a connection, such as serial where that is 
not the case, then we must define a similar layer to implement sockets, which 
hopefully borrows a lot from 1284.4. [Question to 1284.4 experts: could it 
work with serial or USB with very few changes?] 

In effect, I want the socket layer to handle the issues of multiplexing and 
read/write blocking and let the IPP layer concentrate on printer operations 
transmitted over a virtual connection.

Bob Herriot