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Concern about print buffers on printservers and jet direct cards - won't they get overrun

Here is the issue, I have a situation where the customer has been using serial and parallel communications only with various print devices (laser, dot matrix, etc).  Handshaking in these protocols has allowed their accounting software to spool jobs of several hundred pages in length without issue.  As much as possible they will be converted to a networking backbone - for some of the serial printers we will use digi ts/4, however for the parallel and new usb printers we are considering using print servers and perhaps printers with jetdirect cards.  Now, all of these devices, (including the digi port server) have limited buffer space.  Considering warm up times on printers, etc how likely is this to be a problem when large print jobs are being sent.  It seems to me that 10mb network speeds will quickly overlfow the buffers - especially if the printer is offline because operator is loading/adjusting forms or laser is going through a warm up cycle.  Their software provider prefers not to have any printers connected through pc's to keep things simpler.  In the "good old days" everything used handshaking for serial or line control for parallel and so this was never an issue.  Print servers etc are used so extensively nowdays that I assume that this is really not a problem or one that has been solved in some easy fashion.  However my "If I don't understand it I don't like to do it" keeps me from just saying ok and moving on.    
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jon8034
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jon8034
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jlevieCommented:
Buffering on a networked print server shouldn't be a problem. The system the application runs on will be sending the jobe to the print server via one of the standard protocols and data will only be transfered to the print server as space is available in the print server's buffers. How many jobs might be queueed or how big they are is a function of queueing space on the application system only.
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jon8034Author Commented:
How does the system know that the print server buffer is full?  I spoke with a netgear engineer and he said that when the PS110 netgear 64k buffer is full the job is blown because the sending system has no way to know that it should not send more data.
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jlevieCommented:
I can't speak for the netgear device, but I think the engineer you spoke to was mis-informed. By his logic one would never be able to print anything bigger than 64k. The computer sending the data and the network will always be faster than the print server and printer, so something bigger than 64k would always fail.

The printing protocols that these print servers use generally operate on TCP/IP, which is a reliable transport. That means that after sending a data packet to the print server the job source machine has to wait for an ACK before sending more data. So when the buffer is full the print server can wait before sending the ACK or NAK the last transaction. That's over simplistic, but you can see the idea. Additionally the printing protocol itself can contain provisions for handshaking.

As long as you applications are submitting their print jobs through the host computers printing service you won't have any problems with buffers on the network print servers.
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