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From: tony@cs.strath.ac.uk (Tony O'Grady)
Newsgroups: comp.dcom.lans
Subject: Re: Real-Time Over LAN
Message-ID: <4426@baird.cs.strath.ac.uk>
Date: 31 Jul 90 15:28:54 GMT
Sender: news@cs.strath.ac.uk
Reply-To: tony@cs.strath.ac.uk (Tony O'Grady)
Organization: Comp. Sci. Dept., Strathclyde Univ., Scotland.
Lines: 17

Another problem with "Real-Time" responsiveness is the queueing policy used
within the node transmit buffers. Work by Thomas E. Marchok, Jay K. Strosnider
and Hideyuki Tokuda at CMU has shown that there is commercially available 
802.5 hardware which uses FIFO Transmit Queues. Therefore, real-time messages 
must wait for any previously queued, lower priority messages to be 
transmitted before the high priority reservation mechanism can come 
into effect. 

For FDDI, there are separate Synchronous and Asynchronous transmit queues.
However, the Asynchronous queue is FIFO so the expected transmission order
from within a station will not occur, i.e., low priority messages will be
transmitted BEFORE high priority messages queued later.
                                           | Dept. of Computer Science
     tony@cs.strath.ac.uk		   | Livingstone Tower, 26 Richmond St.
                                           | University of Strathclyde
Tel: +44 (0)41 552 4400 ext 3160           | Glasgow, SCOTLAND
Fax: +44 (0)41 552 5330                    | G1 1XH