🚀 go-pugleaf

Moshe Braner <braner@TCGOULD.TN.CORNELL.edu> comments:
 
>One disadvantage of using a 2-layer C004 switching network is that,
>going through 3 C004's in a row, the data transfer rate on the link
>is reduced by a half ...
>Is there any solution for the layered approach (e.g. faster switch-chips)?
 
The C004 provides link switching and also clock resynchronization to
avoid signal skews adding up from one switch to the next. It is this
resynchronization that causes the delay of about 1.75 bit periods when
passing through each C004 in each direction. It would be very difficult
to reduce this in a new C004 design while still providing
resynchronization that is able to tolerate slightly different clock
rates at each end of a link.
 
In the ESPRIT Supernode project in which the Inmos T800 and the Parsys
SN1000 series were developed, much attention was paid to providing a two
layer switch architecture that would not impose significant bandwidth
restrictions on the link traffic. The overlapped acknowledge of the
T800 links was introduced to allow at least one clock resynchronization
to occur along a link connection without affecting bandwidth. In
addition, no clock resynchronization is used in the 72 wide Supernode link
switch, so only a small propagation delay of a fraction of a bit period
occurs.
 
The second layer switch for making Inter-node connections from one
Supernode to another does use C004 switches, and hence preserves signal
quality. Using this combination, a two layer switch can be built that
does not affect link bandwidth and allows simple configuration of any
transputer network.
 
Large systems of over 1000 transputers can be supported in
this way, though the physical size of such a system makes additional
buffering and resynchronization necessary for Inter-node connections.
These extra buffers make the Inter-node link delay similar to that in a
system using two layers of C004 switches. However, a wide switch at the
Supernode level was chosen so that each Supernode contains as many
transputers as possible. The number of link connections that have to
pass through the Inter-node switch is therefore minimized, allowing most
links to operate at full bandwidth.
 
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Trevor Carden                                    (01 or +44 1) 848 6504
Parsys Ltd.,
THORN EMI CRL
Dawley Road, Hayes,
Middlesex, UB3 1HH, England
 
Trevor_Carden_THORN_EMI_CRL%eurokom.ucd.irl@euroies.uucp