Newsgroups: comp.protocols.iso
Path: utzoo!utgpu!cunews!bnrgate!bigsur!bcars53!mussar
From: mussar@bcars53.uucp (G. Mussar)
Subject: Re: Datapac Priority Calling Feature?
Message-ID: <1991Jan1.164943.1309@bigsur.uucp>
Sender: news@bigsur.uucp
Organization: Bell-Northern Research, Ottawa, Canada
References: <139433@pyramid.pyramid.com>
Date: Tue, 1 Jan 91 16:49:43 GMT

In article <139433@pyramid.pyramid.com> csg@pyramid.pyramid.com (Carl S. Gutekunst) writes:
>Can anyone out there in netland give me a correct description of the Datapac
>Priority Calling facility? As I have it in some existing code, it appears to
>be a facility 0x01 0x01 following the national marker, and its presense forces
>the packet size to 128. I don't know if this is correct, or if it invokes more
>things that I need to be aware of. For example, should my Call Accept daemon
>give it special preference?
>

I assume you are talking about the Datapac network in Canada even though your
organization line indicates that you are in California (there are lots of data
networks around the world called Datapac).

Datapac (Canada) uses Northern Telecom's DPN packet switching equipment. The DPN
equipment does not force 128 byte packets for priority calls. The default
packet size and allowable packet size for priority calls is programmable. 
Datapac has choosen to default priority calls to 128 byte.

Priority calls in the system get preference over normal calls:

   - priority traffic skips over normal traffic when transmitted across the
     network.
   - all traffic is subject to congestion/flow control. The thresholds for
     priority traffic are higher than normal traffic so that priority traffic
     is given preference in high load situations.
   - call setup is subject to thresholds based on system resources. Priority
     call threshold are again higher which allows priority calls to be 
     originated in high load situations.

Should your call accept daemon give priority calls special attention? That's
up to you. Once the call has reached you, it has already made it all the way
through the network. If you accept calls based on local resource usage, I 
would give priority calls a slightly better chance of getting accepted in
high utilization situations.

Should anything else be different? I hope not. X.25 is X.25 and I would hope
that the data transfer would be transparent to priority/normal (other than
priority being faster).
--
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