Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!pyramid!hplabs!otter!ooi
From: ooi@otter.hple.hp.com (Stanley Ooi)
Newsgroups: comp.dcom.lans
Subject: Re: QPSX - 802.6 - Metropolitan LAN ?s
Message-ID: <2200001@otter.hple.hp.com>
Date: 24 Feb 88 20:31:42 GMT
References: <36@dogie.edu>
Organization: Hewlett-Packard Laboratories, Bristol, UK.
Lines: 29

> ... how does a node know which bus it should write data ...

The addresses on the station are in order i.e. if one node wants to
send to another node with an address greater than itself, it will use
the "ascending" bus and vice versa for a node with an address smaller
than the initiating node.

> The article talks about 'active' and 'passive' failure of a
> node?  What do these mean?  How will these be detected and
> bypassed?

The way QPSX works is by having its nodes attached to "access units"
(AU) which are nothing more than a shift registers. When a node wants
to transmit data, it will "OR" the appropriate bits into the data
stream going through the shift register. So, if a node dies, then as
the data stream does NOT go through the node, the rest of the network
is unaffected (i.e. passive MAC failure). However, if the power to
the AU should disappear (say), then it will be an "active"
failure i.e. the network will have to reconfigure in order to function
(as the shift register will stop shifting and the data stream is
essentially stopped).

> Who would be possible clients for such a net?

PTTs - it is proposed as a standard for a metropolitan area network and
that's the homeground of the PTTs. It could probably be used as a backbone
network connecting several (slower) Local Area Networks within a large
campus or manufacturing site.

Stan "why not QPSS?" Ooi