edition - HP Computer Museum

HP 3000 Series
For more information on this topic,
the DSNIMTS Reference Manual
(32193-90002), 2608s Reference Manual
(02608-90915) and the 2333A
Reference Manual (02333-90001)
should be of assistance.
Multipoint
Performance Vs.
Point-to-Point
Performance
Multipoint is different than pointto-point
connections. The two
major variables that differentiate
the two solutions are:
Cabling configurations
Performance considerations
By definition, point-to-point is one
terminal connected to one computer
port. This is a straightforward
way of sending data. Direct
transmission between the terminal
and computer takes place without
using any intermediate protocol.
As data is entered into the terminal
and the return key pressed, data is
sent to the computer.
Multipoint is defined as multiple
device connections to a single line.
Communication becomes a little
more complex. Because multiple
devices are connected to one line,
a certain amount of bandwidth
must be devoted to controlling access
to the line by the various devices.
This portion of the bandwidth
is not available for transmitting
data and constitutes multipoint
overhead. This overhead utilizes
approximately 33% of the
multipoint line. This means that
66% of the multipoint line can be
used for data transmission. In
order to successfully predict the
performance of devices on a multipoint
line, it is necessary to compute
the amount of data that is expected
to be transferred to and
from these devices. To do this, line
speed and expected data transmission
for the line are the two
variables necessary. For specific
details, refer to the DSNIMTS Sales
Training Manual.
1 6 January 1983
Computer News OEM Edt~on
The fact that point-to-point and
multipoint protocols differ does
not mean that user response times
in both situations differ. Provided
the multipoint configuration does
not exceed the line saturation,
multipoint users will see response
times similar to the point-to-point
users.
DSNIData Link and Remote Daisy
Chain are multipoint configurations
must commonly seen today.
With the advent of multipoint enhancements
to include HP 2608s
and HP 2333A support, new configurations
will be arising and the
question of performance (i.e., user
response time) rears its head once
more. Since both products are connected
to a multipoint line, the
same variables (amount of data and
line speed) exist when determining
line utilization and subsequent
performance.
HP 2333A and Multipoint - What
Kind of Performance Can Be
Expected
The 2333A Multipoint Cluster
Controller provides the user with
a point-to-point operation in a
multipoint environment. This is a
key statement. Even though the
2333A allows a Term Type 10 terminal
to be attached to a multipoint
environment, to run either character
or block mode, and be totally
transparent to the user, it still uses
multipoint protocol. For this
reason, performance (response
time) depends upon the configuration
of devices, the polling sequence,
the amount of data being
transferred and the speed of the
line. Provided data transmitted at
any one time does not exceed the
maximum multipoint line saturation,
the user response will be that
of a point-to-point configuration.
The only time there may be some
response time degradation is when
the system processor is doing extensive
110 tasks (e.g. LISTF, SYS
DUMP, TDP, SLATE, etc.). When
this happens, the system processor
is slower to read the data from the
multipoint line; subsequently, af-
fecting the multipoint user's response
time. Keep in mind that this
is true if the user is connected directly
to a multipoint line or to a
2333A Multipoint Cluster
Controller.
The conclusion is: When configuring
the 2333A into a multipoint environment,
all the multipoint variables
that affect performance must
be considered.
HP 2608s and Multipoint - What
Kind of Performance Can Be
Expected
The HP 2608s connected via HP-IB
runs optimally at 400 lpm using all
upper and lower case characters.
When connecting to a multipoint
line, the 2608s throughput (lpm) is
identical provided it is configured
properly. This means that line
speed, number of characters per
printed line and number of
connected devices are what
determine printer throughput.
To show how line speed affects
printer throughput (lpm), the
following test was performed. The
2608s was the only device
connected to a DSNIData Link. The
amount of data transmitted was
constant (i.e., 132 upper case
character length lines for 10
minutes). The baud rates tested
were 4800,9600, and 19,200 bps.
The results: As baud rate
increased, so too did the printer
throughput.
The results differ when more
devices are configured on the line.
When this occurs, a priority
scheme is introduced. Tests were
performed where the 2608s was
configured with three other
terminals. This was a Daisy Chain
configuration running at 9600 bps.
The printer was configured as High
(I), Normal (5) and Low (9)
priorities while the terminals were
configured at priority 5.
The results: When there are
multiple devices on the line, the
higher assigned priority for the
2608S, the greater the Line Printer
throughput (lpm).
Pp3