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SHARE SESSION REPORT
61 C209 Series/l DDp at Watchtower 24
access local Series/l disk as well as supporting many terminal
SHARE NO. SESSION NO. SESSION TITLE ATTENDANCE users of that editor. The Series/l also has a communication
Local Area Networks Barry Lay TY link to the host System/370 running VM. It is able to communi-
cate with a data base residing there. The advantages of using
PROJECT SESSION CHAIRMAN INST. CODE a distributed editor on the Series/l are (1) editors that nor-
mally run on the 3270 type terminals would now no longer
University of Toronto Computing Services, 255 Huron St., Toronto, Ontario,
require host cycles to do their work. (2) in the event that
Canada, (416) 978-3328
the host system would be down users of the Series/l editor
SESSION CHAIRMXN'S-COMPANY-;- ADDRESS~AND PHONE NUMBER could continue to work locally employing the Series/l disk.
In working towards the implementation of the Series/l dis-
tributed editor, there were many different tasks that had to be
ABSTRACT accomplished. The first of these to be discussed is communi-
cations. In order for any intelligent device to be useful to a
Use of the S/l as a front end text capture tool offers high function at low host system it is necessary that this device communicate with
cost. The problems of communications, word processing, and file management in a it. One of our problems in writing a host distributed Series/l
distributed environment will be discussed. The high speed 370 channel interface editor was that of file communications. Secondly, in addition
to communicating files or buffers between the two processors,
on the S/l is used as a communications tool for host data base file and
it is important to consider the security of the host data base
retrieval capabilities. Use of the 3101 as an interactive user friendly word
and how the access mechanism of data in the host would work.
processing terminal on the Series/l will be presented and contracted with use of
Thirdly, there was the question of word processing. What type
the Personal Computer.
of word processing would be used on the Series/I? Currently
there are several editors available for the Series/I, yet none
Distributed Processing is usually an important part of Data Processing. We at of them seemed to fit our needs or seemed to integrate into the
Watchtower have found it necessary in our installation to make use of this
file communications structure that we needed.
~aluable function. It is the evaluation of distributed editors and functions in
~ 370 host environment that is the subject of this presentation.
~ Therefore, it was decided that we would write our own edi-
The Series/l as a front end text capture tool offers the capability of tor for word processing. We chose to do our initial develop-
off-loading many functions from the host system. On the Series/l resides an ment using the IBM 3101, a TTY-type terminal of low cost. We
editor. This editor is able to felt that if we could make this low cost terminal perform in a
Series/l environment then it would make the best use of our
available resources, since numerous 3101s had already been pur-
chased. After spending many months of research, programming,
testing and prototyping, it is appropriate to present our find-
ings, evaluations and conclusions about the Series/I, its use,
the 3101 editor and other distributed data processing possibli-
ties.
The first topic of communications is the environment.
Where will my distributed processor be located? Which options
are available in my host? What cabling is already installed or
which is the most desirable to install if none are currently
available? What amount of through-put will there be on this
link? Will the users be interactive or batch? The answers to
these questions will aid the user in clearly seeing which sol-
ution best fits his requirements.
Our Series/Is were within the same Computer Room as our
370 System. Therefore, we chose a channel attachment interface
from the Series/l to the host. On the series/l it was neces-
sary to write a device driver for the channel attachment hard-
ware. On the VM/370 host it was necessary to write within a CMS
machine a device controller and interrupt handler. The
4/V/ear/3
Series/l appeared to the host to be managing many real the host. To send a block of text the Series/I: I} generates
addresses, these real addresses being attached as virtual an attention to the host, the host responds by doing a READ,
addresses to the user written CMS controller. requesting that the data on the Series/l be sent to it, 2} the
Series/l writes its data to the host, the host processes that
What did the Series/l channel hardware and device driver data and finishes the block transfer by writing its response to
do? The Series/l device driver and hardware emulated a 32-dev- the Series/I. Data transfers are fully interlocked. If the
ice 3270 controller. What type of controller? A 3272? Or a Series/l were sending a file of many blocks to the host, it
3274? Actually the answer is none at all. The console I/O sup- could not write them to the host one after another. The host
port of VM CP was not used for this interface. The Series/l to must acknowledge each Series/l block by a WRITE. The protocol
expects every READ to be followed by a corresponding WRITE.
host interface was a strictly defined Start I/O protocol which
supports READ, WRITE and ATTENTION only.
The next area of concern is data security and access man-
What happens within the Series/l when the host sends an agement. What are some of the objectives of a security and
interrupt? The Series/l hardware transfers control to our access management system? What were our objectives? One is
interrupt handler. It checks the device control block which is that the host must protect its data base. It was felt inappro-
set up by our application program to find the status of that priate to place the responsibility for protection in the
hardware address. If the device status is valid the I/O drivers Series/I, a distributed user. Therefore all requests made by
use the device control block to perform the I/O requested by the Series/l for data transfers need to be validated by a secu-
the host in behalf of the appropriate Series/l application. rity m.echanism within the host itself. It was determined that
When the I/O is complete the Series/l application program with this mechanism should be as close to the file access mechanism
which the host is communicating is informed. It can now contin- as possible. In our description so far a C~lS interrupt handler
ue as required. and a device controller were mentioned. These also should not
validate requests from the Series/l for files as they are too
What happens on the host when the Series/l generates an far removed from the actual data. Those programs that directly
interrupt? CP turns control of the interrupt over to the access the data base are in the best position to evaluate any
Co) user requests and are thus able to best protect the system's
W interrupt handler in our CMS application program. It interro-
gates the current CSW, channel status word, and determines the integri ty.
W
address of the interrupting device as well as its interrupt
code. Using this information, the application control block is Once a block of data or a request for data has been
searched to determine if this interrupt was appropriate. received by the CMS device controller how is that file access
Appropriate status information and address information reg?rd- accomplished? Our file access mechanism has three parts, the
ing any data are saved in the control block. The interrupt han- device controller, the security server and the file server,
dler posts the CMS device controll er application informing it which directly connects to our data base. The device control-
that there is work to be done. The device controller searches ler sends a block or a request which it has received from the
the control blocks and processes any outstanding work. This may Series/l to the security server by means of VMCF. That device
include the building of CCWs and the execution of Start l/Os. is marked as waiting for a reply. The W1CF message from the
When all work is done the controller waits on the interrupt controller will cause an INTERRUPT in the interrupt handler of
handler to signal it to begin again. the secur i ty server who saves the VHCF request block. The secu-
rity server application is posted that work is to be done. The
It is interesting to note that by the use of an interrupt request block or data block contains security and function
handler in conjunction with an application program and by the information. This allows the security server to validate the
careful use of control blocks in the form of status tables that work it receives. Besides request validation, data may need to
a multi-tasking environment within CMS can be simulated. be formatted or buffered to make it usable by the file server.
This is done in the secur i ty server. VMCF is used t.o send to
We have talked about how interrupts are handled in both the file server validated blocks or requests. The security ser-
the host and Series/I. How, then, is a block of text sent from ver marks the request as outstanding and continues with any
one processor to another. The sending of a block of data is other work it has to do.
driven by the Series/I. This is comparable to the way a 3277
terminal operator drives an application program. When that The file server is interrupted and eventually receives and
operator hits ENTER, it signals the host application to read processes the security server request. The dat~ is read from or
data. The host application processes that data and writes the written to the dat~ base according to the control information
appropriate reply back to the 3277. The Series/!, like the supplied by the security server. When this is complete, a
3277, always does a WRITE to the host followed by a READ from reply by means of VMCF is made to the security server. The
security server again receives an external INTERRUPT, this time ward and backward pointers. When a user reads a file it becomes
from the file server. This reply from the file server is ana- a working copy in his paging area. A directory entry fo~ that
lyzed to determine what was done and where the reply should go. user is made in the paging space for the copied file. This
The reply is forwarded by means of VMCF to the device control- entry is a known location to the editor such that when the copy
ler. The device controller is interrupted by the VMCF is referenced it need not be searched for but can be directly
response. When the response is processed an indication that the accessed. As work progressed on our paging system we also were
operation is complete is sent from the device controller back writing a local file manager for Series/I disk and a printer
to the Series/I. spooling routine. These tasks both required disk record man-
agement which was very similar to that used by paging. There-
In addition to simply being able to access the information fore it was decided that instead of having three systems doing
in our host data base, it is necessary to keep those files disk record management there would be one. Instead of dividing
secure. How is this done? Our data base is divided into two the disk into three separate pools of records we used but one
sections-- a directory and a data library. There is a third big area shared by all. Each task (paging, spoolinq and local
portion called Groups and Users. Groups and Users is actually a data base) would need its own directory, but because directo-
file that is used in conjunction with the directory to provide ries are treated like files this posed no real problem. This
data protection. The directory contains the publication and concept saved much work and some valuable main storage.
unit names of all files in our data base. In addition to that,
such things as the authorization for READ/WRITE privileges, How does paging work? Paging is a black box, meaning that
READ ONLY privileges, the date of creation, the date of last the internals of paging are not known to anyone of the appli-
update, the publication status and block key information are cation systems that use it. The editor knows about only one
found in the directory. line at