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CommunicationsControlProgram
GeneralInformation
Manual
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57O2-SC1 Model10 Disk System
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T h i r d E d i t i o n ( D e c e m b e r1 9 7 5 )
T h i s i s a m a j o r r e v i s i o n o f , a n d o b s o l e t e : ; ,G C 2 1 - 7 5 7 8 ' 1 a n d T e c h n i c a l N e w s l e t t e r
G N 2 1 - 5 2 8 0 . C h a n g e sa r e i n d i c a t e d b y a v e r t i c a l l i n e a t t h e l e f t o f t h e c h a n g e ; n c w o r
e x t e n s i v e l y r e v i s e d i l l u s t r a t i o n s a r e d e n o t e d b y a b u l l e t { o ) a t t h e l e t l o f t h e f a g u r ec a p t r o n
C h a n g e s a r e p e r i o d i c a l l y m a d e t o t h e i n l o r m a t i o n h e r e i n , b e f o r e ru s i n g t h i s p u b l a c a t r o n
in connection with the operation of IBM systems,refer to Ihe IBM System/3
Eibliography, GC20-8080, for the editions that are applicable and current.
Requests for copies of IBM publications should be made to your IBM representatavc
or to the I BM branch office servingyour locality.
Address comments concerning the contents ot this publication to IBM Corporation.
Publications, Department 245, Rochester, Minnesota 55901. Comments become
the property of lBM.
O l n t e r n a t i o n a l B u s i n e s sM a c h i n e s C o r p o r a t i o n 1912, 1973, 1915
PREFACE
T h i s m a n u i ap r o v i d e s g e n e r ad e s c r i p t i o n f t h e C o m m u n i c a t i o n C o n t r o l P r o g r a m ,
l a l o s
a f e a t u r eo f S y s t c m / 3M o d e l 1 0 D i s k S y s t e m ,M o d e l 1 2 , a n d M o d e l 1 5 S y s t e m
C o n t r o lP r o g r a m m i r r g , o g r a mn u m b e r 5 7 0 2 S C 1 .5 7 0 b S C 1 ,a n d 5 7 0 4 - S C 1 ,
pr s .
r e s p e c i l v e l ' y l' t i s w r i t t e n f o r t h o s e w h o a r e r e s p o n s i b l eo r p r o v i d i n gt o t h e i r
. f
o r g a n i z a t i o na n e f f e c t i v e o m m u n i c a t i o n s - b a s ie d o r m a t i o ns v s t e m .
s c nf
This manual:
o D e s c r i b e sh e c o n c e p t , a d v a n t a g e s ,n d r e q u i r e m e n t s f a c o m m u n i c a t i o n s - b a s e d
t a o
svstem.
. s u r v e y st h e f a c i l i t i e so f f e r e d b y t h e c o m m u n i c a t i o n s o n t r o l p r o g r a m .
c
' G i v e se x a m p l e so f t h e u s e o f t e r m i n a l sw i t h t h e c o m m u n i c a t i o n s o n t r o t p r o g r a m .
c
o I n d i c a t e s h e r e l a t i o n s h i p s e t w e e nd i s k s y s r e mm a n a g e m e n t n d t h e c o m m u n i c a -
t b a
tions control program.
' L i s t st h e c o m m u n i c a t i o n st e r m i n a l sa n d f e a t u r e st h a t c a n b e u s e d w i t h t h e c o m -
murrications ontrol proqram.
c
' D e f i n e st h e m a c h i n ea n d p r o q r a m m i n gs y s t e m sr e q u i r e m e n t s o r i n s t a l l i n qt h i s
f
control program.
T h i s g e n e r a li n f o r m a t i o n m a n u a l i s a n i n t r o d u c t i o n t o t h e c o m m u n i c a t i o n sc o n t r o l
p r o g r a m a n d i t s f a c i l i t i e s ,a n d i s i n t e n d e dt o s e n r ea s a n a i d i n y o u r d e t e r m i n a t i o n
of
t h e u s e f u l n e s o f t h i s p r o g r a m i n s a t i s f y i n gy o u r o r g a n i z a t i o n ' sn f o r m a t i o n p r o c e s s -
s i
ing needs.
S Y S T E M /M O D E L
3 B
T h e S y s t e m / 3 M o d e l 8 i s s u p p o r t e db y s y s t e m / 3 M o d e l 1 0 D i s k S v s t e m c o n t r o l
P r o g r a m m i n g n d P r o g r a mP r o d u c t s . T h e f a c i l i t i e sd e s c r i b e di n t h i s p u b l i c a t i o nf o r
a
t h e M o d e l 1 0 a r e a l s oa p p l i c a b l e o t h e M o d e l 8 , a l t h o u g h M o d e l 8 i s n o t r e f e r e n c e d .
t
H o w e v e r ,t i ' r ei n t e g r a t e dc o m m u n i c a t i o n s d a p t e r ( l c A ) i s o n l y a v a i l a b l e n t h e
a o
M o d e l 8 . l f y o u h a v et h e l c A , i t i s a l w a y sd e s i g n a t e o n B S C A l i n e 2 . T h e r e f o r e ,
d
y o u m u s t s p e c i f y l i n e 2 w h e n e v e ri t i s r e q u i r e d ,o r e n t e r t h e B S C A O C L s t a t e m e n t
( / / B S C A L I N E 2 ) a t e x e c u t i o nt i m e .
I t s h o u l d b e rn o t e d t h a t n o t a l l d e v i c e s n d f e a t u r e sw h i c h a r e a v a i l a b l e n t h e M o d e l
a o
1 0 a r e a v a i l a b l e n t h e M o d e l 8 . T h e r e f o r e M o d e l 8 u s e r s h o u l db e f a m i l i a rw i t h
o , s
the content:; of IBM System/3 Modet 8 lntroduction, GCZ| 5.114.
ill
CONTENTS
Control programprovided?.
Why is the Communications "l
W h y M i g h t I N e e dT e l e c o m m u n i c a t i o n s
W h a t M a c h i n eC a p a b i l i t i e s r e R e q u i r e d
a
W h y W o u l d I N e e da C o m m u n i c a t i o n s o n t r o l p r o g r a m
C
Control programDo?
What Doesthe Communications 4
From the Viewpoint of the Terminal Operator
From the Viewpoint of the System Operator
From the Viewpoint of the programmer
Control programbe Tailored
How Can the Communications
to My Needs? 11
How Can I Usea Communications-Based
System? 14
Control programRelatedto
How is the Communications
Disk SystemManagement? 16
T w o P r o g r a mL e v e l s
U s eo f C o n r m u n i c a t i o n s O C S
I
Terminals
and Features
Supported 1B
SystemConfiguration 20
ut:::. I l J l \ 4 ( , l o n r n r r r r r r c ar r r g M a g r r e t r c ( l t r d
I
,d.,:::.
SELECTRIC (ETypewriter (via MLTA)
I B M 1 0 5 0 D a t a C o m m u n i c a t i o n v s t e m ( v i aM L T A )
S
I B M 3 2 7 0 I n f o r m a t r o nD i s p l a yS y s t e m( v i a E S C A )
IBM 2740 Communication Terminal (via MLTA)
I B M 3 7 3 5 P r o g r a m m a b l T e r m t n a l( v i a B S C A )
e
IBM 2741 Communication Terminal (via MLTA)
vl
e\
't
tt''a
Remote IBM System/3 (via BSCA)
IBM System/370 (via BSCA)
I BM 3741 Data Station
a IBM 3767 Communicatiorrs
T e r m i n a l{ v i a M L T A )
vtl
BSCA/MLTA Panel
lni
Ftrr
iBMEitem/3 Modetld DiskSystem wiih eiharySyncnionous
C o m m u n i c a t i oA d a p t e ( B S C A ) n d / o r u l t i p l e i n eT e r m i n a l
ns r a M L
Adapte(MLTA)
r
vill
SCA/MLTA Panel
o I B M s y s t e m / 3 M o d e l 1 2 w i t h B i n a r y s y n c h r o n o u sc o m m u n i c a t i o n s d a p t e r ( B S c A )
A
a n d / o r M u l t i p l e L i n e T e r m i n a lA d a p t e r ( M L T A )
B S C A / M L T AP a n e
*i,{,*l,ij
-st!t!t{*!t,}
'1
I B M S y s t e m / 3 M o d e l 5 w i t h B i n a r y S y n c h r o r r o u sC o m m u n i c a t i o n s A d a p t c r { B S C A )
a n d / o r M u l t i p l t - .L i n e T e r m i n a t A c l a p r e r ( M L T A )
W H Y I S T H E C O M M U N I C A , T I O N O N T R O LP R O G R A MP R O V I D E D T
C
T h e c o m m u n i c a t i o n s o n t r o l p r o g r a m ( C C P )p r o v i d e st h e c o n t r o l p r o g r a m s e r v i c e s
c
n e e d e d n a t e l e c o m m u n i c a t i o n s s t e mu s i n gt h e I B M S y s t e m / 3M o d e l 1 0 ,
i sy
M o d e l 1 2 , a n d l l l o d e l 1 5 D i s k S y s t e m s .l t e n a b l e s o u t o e s t a b l i s h t e l e c o m m u n i -
y a
c a t i o n ss v s t e mr , , r i t h i n i m u m c o s t a n d e f f o r t .
m
A brief discussionof the nered for, and the system requirementsfor, telecommunica-
t i o n s m a y h e l p y o u a p p r e c i a t e h e n e e d f o r a c o m m u n i c a t i o n s c o n t r o lp r o g r a m .
t
W H Y M I G H T I N E E DT E L E C O M M U N I C A T I O N S ?
For years,usersof large-sc;rle data processing equipment have enjoyed the benefits
o f t e l e c o m m u n i c a t i o n s .F o r o r g a n i z a t i o n s i t h t h e n e c e s s a r y q u i p m e n t ,t h e a b i l i t y
w e
to communicate ciirectly between a central computer system and a set of remotely-
located terminals has opened new and effective approachesto satisfying their infor-
mation processingneeds.
T e l e c o m m u n i c a t i o n s e l p st h e d a t a p r o c e s s i n g s e r r e d u c eb o t t l e n e c k si n t h e f l o w
h u
o f i n f o r m a t i o n n e e d e dt o o p e r a t ea n o r g a n i z a t i o n f f e c t i v e l y . W h e t h e r i t i s u s e d
e
t o t r a n s m i t a s h i p p i n gd o c u m e n t t o t h e w a r e h o u s e h i l e a n o r d e r i s b e i n g p r o c e s s e d ,
w
o r a s a m e a n so f i n q u i r i n g i n t o t h e c u r r e n t s t a t u so f a n a c c o u n t ,o r a s a w a y o f
c a p t u r i n gd a t a a b o u t a t r a n s a c t i o nf r o m t h e v e r y s o u r c eo f t h a t t r a n s a c t i o n , e l e -
t
c o m m u n i c a t i o n s ; e l p sy o u g e t s i g n i f i c a n t a t a f r o m t h o s e w h o h a v e i t , a n d t o m a k e
h d
c u r r e n t i n f o r m a t i o n a v a i l a L r lte D e o D l e h o n e e d i t .
o w
W H A T M A C H I N EC A P A B I I - I T I E S R E R E O U I R E DF O R T E L E C O M M U N I C A T I O N S ?
A
In the past, the machinesnecessary establisha communications-based
to system have
b e e n g e n e r a l l yr - r n a v a i l a btl o u s e r so f s m a l l e rc o m p u t e r s . T h e m a c h i n e r e q u i r e m e n t s
e
g o b e y o n d t h e c o m m u n i c a t i o n st e r m i n a l sa n d t h e m e a n so f a t t a c h i n gt h e m t o t h e
c e n t r a l p r o c e s s i n g n i t . B e c a u s e o s t u s e r sf i n d m o r e a n d m o r e a p p l i c a t i o n si n
u m
w h i c h a c o m m u n i c a t i o n s - o r i e n t ea p p r o a c hc a n c u t t h r o u g h a n i n f o r m a t i o n b o t t l e -
d
neck, telecommunicationssystems must be growing systems. The user must be f ree
t o e x p a n d d i r e c t - a c c e ss t o r a g ec a p a c i t yt o a c c o m m o d a t ea d d i t i o n a l o n l i n e f i l e s a n d
s
to enlarge main storageto permit severalapplicationsto operate concurrently. Ex-
pansion capability is a prerequisiteto consideration of a computer system as a com-
m u n i c a t i o n sp r o c e s s o r .
T h e s y s t e m / 3 o d e l10 D i s ks y s t e m , y s t e m / 3 o d e l12 , a n d t h e s v s t e m / 3 o d e l1 5
M s M M
m e e tt h e m a c h i n ee q u i r e m e n os a c o m m u n i c a t i o n s o c e s s o r i t h t h e a v a i l a b i l i to f :
r tf pr w v
Large-capacity
disk storage.
H i g h l y e x p a n d a b l em a i n s t o r a q e .
A v a r i e t y o f l i n e a n d t e r m i n a lc o n f i g u r a t i o ns u p p o r t e d y t h e m u l t i p l e l i n e
s b
t e r m i n a l a d a p t e r ( M L T A ) ; t h e b i n a r y s y n c h r o n o u s o m m u n i c a t i o n sa d a p t e r
c
( B S C A ) ;t h e l o c a l c o m m u n i c a t i o n s d a p t e r ( L C A ) o n t h e M o d e l 1 0
a and Model 15.
t h d i n t e g r a t e d o m m u n i c a t i o n s d a p t e r( l C A ) o n t h e M o d e l g a n d M o d e l 1 2 : a n d
c a
t h e d i s p l a ya d a p t e r ( D A ) o n t h e M o d e l 8 , M o d e l 1 2 , a n d M o d e l 1 5 .
With these capabilities,the System/3 can processa broad range of communications-
basedapplications.
W H YW O U L D N E E DA C O M M U N I C A T I O N S N T R O L R O G R A M ?
I CO P
A communication-basedinformation processing system requiresspecialcontrol pro-
g r a m f u n c t i o n s a s w e l l a s a s p e c i a lm a c h i n ec o n f i g u r a t i o n . T h e c o m m u n i c a t i o n s
control program provides the necessary control services for a Svstem/3 telecommuni-
cations system.
B e c a u s ee r m i n a l su s e c o m m u n i c a t i o n sl i n e s ,t h e p r o g r a ms u p p o r t f o r t e r m i n a l
t
i n p u t / o u t p u t m u s t c o n t r o l t h o s e l i n e sa n d t r a n s l a t e h e s p e c i a ld a t a c o d e su s e d b v
t
s o m e t e r m i n a l s . T h e p r o g r a m s u p p o r t t h a t g i v e sy o u r a p p l i c a t i o np r o g r a m st h e
a b i l i t y t o r e a d f r o m a n d w r i t e t o t e r m i n a l si s a c o m p o n e n t o f S y s t e m / 3 M o d e l 1 0 ,
M o d e l 1 2 , a n d M o d e l 1 5 D i s k S y s t e m M a n a g e m e n ti;t i s k n o w n a s t h e l o c s s u p p o r t
for the MLTA and for the BSCA.
B u t t h e c o m m u n i c a t i o n sI O C S p r o v i d e so n l y f o r t e r m i n a l i n p u t / o u t p u t . F u r t h e r
program support, besidesan input/output facility, is necessary
to operate a data
processing system effectively, even one without Jelecommunications. For example,
control programs are required to load and execute programs from a disk library,
to
access data files. and to communicate with the operator.
A system with telecommunications requires more flexible program support tnan a
system which performs jobs one at a time under control of one system operator.
The effectiveness a communications-based
of system stems from its ability to per-
form work presented,as required, by a number of operators at terminals. Operators
are seldom aware of what other operators are doing; they may be in separaterooms,
or in separatecities. Each request demands that a certain program be executed.
Frequently a request arriveswhile the system is still attempting to satisfy previous
requestsfrom other operators; the new request must be remembered and honored
at the earliest possiblemoment. The system should be designedin such a way that
it can execute severalprograms concurrently. In this way, the system will respond
quickly to many operator,s requests.
2
Program support of these capabilitieshas existed for some time on larger
computers,
m a k i n g p o s s i b l ei n f o r m a t i o n s y s t e m st h a t a r e h i g h l y e f f e c t i v ei n a v a r i e t y o f a p p l i -
cations' You may have heard such systemsdescribed in various terms, each empha-
sizing a characteristicthey possess:
-
Event-Driven work is performed required events
as by which occurwithin the
organization,
ratherthan in a rigid,predefined
sequence.
-
Transaction-oriented Eachtransactioncan be processed it happens, tne
as so
effectof that transaction
upon the organization be determined
can immediatelv.
-
o Real-Time The dataheld in the system reflects statusof the organization,s
the
a c t i v i t i ea so f t h e m o m e n t , n dc a ny i e l dt r u l y c u r r e n ti n f o r m a t i o n .
s a
The first systemsof this type were used by businesses with a network of many ter-
m i n a l s ,a c c e s s i n a h u g e d a t a - b a s ea n d i n v o l v i n gh u n d r e d so f a p p l i c a t i o np r o g r a m s .
g ,
Gradually, the principle of this mode of operation has also proven itself effective in
systemsof more modest scope.
N o w , t h e c o m m u n i c a t i o n s o n t r o l p r o g r a mo f f e r s t h e p r o g r a m s u p p o r t f o r a
c
c o m m u n i c a t i o n s - b a s eS y s t e m / 3 M o d e l 1 0 D i s k S y s t e m ,S y s t e m / 3 M o d e l 1 2 , a n d
d
S y s t e m / 3 M o d e l 1 5 . l t p r o v i d e st h o s e c o n t r o l c a p a b i l i t i e s e e d e dt o i m p r e m e n t
n
a n i n f o r m a t i o n s y s t e mo f t h e t y p e d e s c r i b e d . B e c a u s e f t h e f a c i l i t i e si t o f f e r s ,
o
t h e e s t a b l i s h m e no f s u c h a s v s t e mc a n b e a c c o m p l s h e dw i t h a m i n i m u m c o s t
t i
and effort.
W H A TD O E S H EC O M M U N I C A T I O N S N T R O L R O G R A M O ?
T CO P D
T h e c o m m u n i c a t i o n s o n t r o l p r o g r a mp r o v i d e sc o n t r o l p r o g r a m s e r v i c e s e e d e di n
c n
a t e l e c o m m u n i c a t i o n s v i r o n m e n t .l t i s a n e x t e n s i o n f s y s t e m / 3 M o d e l 1 0 ,
en o
M o d e l 1 2 , a n d M o d e l 1 5 D i s k S y s t e mM a n a g e m e n t .
T h e c o m m u n i c a t i o n sc o n t r o l p r o g r a ms u p p o r t sa n e t w o r k o f t e r m i n a l s . l t a l l o w s
t h e t e r m i n a l st o c a l l a s y n c h r o n o u s l y p o n a s e t o f u s e r a p p l i c a t i o np r o g r a m s , h e n
u t
permits those programs to access common data baseconsisting of a number of
a
d i s kf i l e s .
T h e C C P d o e s n o t i t s e l f i n c l u d et e l e c o m m u n i c a t i o n s p p l i c a t i o np r o g r a m s( p r o g r a m s
a
that access and processyour data). They, like the application programs you may De
w r i t i n g t o d a y , a r e n e c e s s a r i l u n i q u e t o y o u r o r g a n i z a t i o n ' s e q u i r e m e n t s .B u t t h e
y r
ccP does control the environment in which those programs must run, and it provides
a set of servicesupon which they can call. This relievesyou of most of the special
requirements i n establishin g a comm un ications-based
system.
Some of the control program servicesperformed by the communications control
program are:
Terminal Monitoring - The terminals of the system are monitored for program
r e q u e s t s n d s y s t e mc o m m a n d s .
a
Program Fetch - A terminal operator, or the system operator, may initiate the load-
i n g a n d e x e c u t i o n o f a n a p p l i c a t i o np r o g r a m .
ResourceManagement- The resources the communications-based of system (ter-
m i n a l s ,d i s k f i l e s , m a i n s t o r a g e p a c e )a r e m a n a g e db y t h e c o m m u n i c a t i o n sc o n t r o l
s
p r o g r a m a n d m a d e a v a i l a b l e a s r e q u i r e d ,t o e a c h a p p l i c a t i o np r o g r a m .
,
concurrent Program Execution - lf the system has sufficient main storage space,
and the user so specifies,severalapplication programs for different terminals may be
ru n concu rrentl y.
Disk File AccessManagement - ln a system where several programs execute concur-
rently, access disk files may be shared among those programs. The communica-
to
tions control program protects againsterroneous resultsthat might be causedby
c o n f l i c t i n ga c c e s s e s .
T h e c o m m u n i c a t i o n sc o n t r o l p r o g r a m i s d e s i g n e d o r e a s eo f u s e i n e s t a b l i s h i n g n
f a
o r g a n i z a t i o n ' s i r s t c o m m u n i c a t i o n s - b a s es y s t e m ;i t c a n b e r e a d i l y t a i l o r e d t o c o n -
f d
tain only the capabilitiesyou need. The significanceof the servicesit performs is
indicated by the freedom it offers you in the design,programming, and operation of
the system. For example:
Y o u c a n p l a n a n d d e s i g na t e l e c o m m u n i c a t i o n s y s t e mt h a t p e r f o r m s i t s f u n c -
t i o n s w h e r r r e q u e s t e d y t h o s e w h o n e e dt h e m .
b
Y o u c a n c r e a t ep r o g r a m si n d i v i d u a l l yt o p e r f o r m t h o s e f u n c t i o n s w i t h o u t b e i n g
c o n c e r n e da b o u t w h a t o t h e r f u n c t i o n s a r e o c c u r r i n gi n t h e s y s t e mo r w h a t s p e -
c i fi c t e r m i n a li s i n c o m m u n i c a t i o n i t h y o u r p r o g r a m .
w
Y o u c a n i r r c o r p o r a t e a c ha p p l i c a t i o np r o g r a m i n t o y o u r s y s t e ma s i t i s w r i t t e n
e
a n d t e s t e d ,w i t h o u t r e c r e a t i n g h e e n t i r e s y s t e m .
t
' Y o u r s y s t e mo p e r a t o r c a n c o n t r o l w h i c h t e r m i n a l sa r e p e r m i t t e d a c c e s so t h e
t
system.
T h e f o l l o w i n g p a g e s e s c r i b e h e f a c i l i t i e so f f e r e d a s t h e y w o u l d b e v i e w e d b y a n
d t
o p e r a t o r a t a t e r m i n a l , b y t h e o p e r a t o ro f t h e s y s t e m ,a n d b y a p r o g r a m m e r .
. . . F R O MT H E V I E W P O I N T F T H E T E R M I N A L O P E R A T O R
O
T o t h e o p e r a t o r o f a t e r m i n a l , t h e s y s t e m i s a r e s o u r c e o h e l p a c c o m p l i s ht a s k s .
t
T h e t e r m i n a l o p e r a t o r m a y t h i n k o f t h e s y s t e ma s b e l o n g i n gt o h i m o r h e r a l o n e ,
u n l e s st h e c o n r b i n e dd e m a n d su p o n t h e s y s t e ma r e g r e a t e n o u g ht o c a u s es o m e
d e l a y i n i t s r e s p o n s i v e n e s s . l l c o n t e n t i o n a m o n g t e r m i n a l o p e r a t o r sf o r u s e o f
A
t h e s y s t e mi s r n a n a g e d y t h e c o m m u n i c a t i o n s o n t r o l p r o g r a m .
b c
How the OperatorRequests Program
a
w h e n a t e r m i n a l i s n o t i n u s e ,i t i s m o n i t o r e d b y t h e c o n t r o l p r o g r a m f o r t h e
p r e s e n t a t i o n f a r e q u e s t . T h e o p e r a t o r o f a t e r m i n a l c a l l sf o r t h e a p p l i c a t i o n
o
p r o g r a mt o p e r f o r m a s p e c i f c f u n c t i o n b y s i m p l y e n t e r i n gt h e p r o g r a mn a m e a t t h e
i
t e r m i n a l . T h e C C P t h e n a t t e r n p t st o l o a d a n d e x e c u t et h e p r o g r a ma n d t o p u t t h a t
p r o g r a mi n c o m m u n i c a t i o n i t h t h e t e r m i n a lo p e r a t o r . F r o m t h e n u n t i l t h e c o m -
w
p l e t i o n o f t h e p r o g r a m ' se x e c u t i o n ,t h e i n t e r a c t i o nb e t w e e nt h e t e r m i n a l o p e r a t o r
a n d t h e s y s t e n ri s d i c t a t e d b y t h a t p r o g r a m .
W h e n t h e a p p l i c a t i o np r o g r a m h a s c o m p l e t e de x e c u t i o n ,i t y i e l d s c o n t r o l o f t h e t e r -
m i n a l t o t h e c o m m u n i c a t i o n sc o n t r o l p r o g r a m - T h e C C P o n c e a g a i nm o n i t o r s t h e
t e r m i n a l f o r a p r o g r a m r e q u e s t . T h e n e x t r e q u e s tm a y b e f o r t h e s a m e ,o r f o r a
different, unction.
f
E a c ht e r m i n a l o p e r a t o r m u s t b e t r a i n e d i n t h e f u n c t i o n s h e o r s h e c a n c a l l u p o n
a n d i n t h e p r o c e d u r e s o r i n t e r a c t i n g i t h t h e a p p l i c a t i o np r o g r a m st h a t p e r f o r m
f w
t h o s ef u n c t i o n s .
5
How the Operator Requests System Services
while monitoring for program requests,the communications control program can
also respond to commands to perform servicesfor the terminal.
T h e o p e r a t o rc a n c o n d i t i o n t h e s y s t e m ' sr e s p o n s e h e n i t i s u n a b l et o c o m p l y
w
i m m e d i a t e l yw i t h h i s o r h e r r e q u e s tf o r a p r o g r a m . T h e s y s t e mm a y b e t e m p o r a r i l y
t o o b u s y w i t h r e q u e s t sr o m o t h e r o p e r a t o r s . B y c o m m a n d , h e o r s h em a v c h o o s e
f
one of the following when this condition occurs:
o T h e s y s t e ms h o u l d d e n y h i s o r h e r r e q u e s ta n d a l l o w h i m o r
her to make some
other request.
' T h e s y s t e ms h o u l d h o l d h i s o r h e r r e q u e s ta n d h o n o r i t a t t h e e a r l i e s tp o s s i b l e
moment.
Once the operator of a terminal has specified one of these system responses,
the CCP
handlesall program requestsfrom that terminal accordingly until the operator gives
the other specification.
A f i l e s p e c i f i c a t i o n o m m a n d a l l o w st h e o p e r a t o r t o s p e c i f y t h e d i s k d a t a f i l e s t h a t
c
a r e t o b e a c c e s s e d y p r o g r a m sh e o r s h e r e q u e s t s .W i t h i n t h e i n f o r m a t i o n s y s t e m ,
b
t h e r e m a y b e s e v e r afl i l e s c o n t a r n i n gs i m i l a rd a t a i n t h e s a m ef o r m a t . A s c h o o l
s y s t e m ,f o r e x a m p l e ,m i g h t h a v e a s e p a r a t e t u d e n t r e c o r d sf i l e f o r e a c h s c h o o l . A n
s
a p p l i c a t i o np r o g r a m r e q u e s t e d y t h e o p e r a t o r m i g h t h a v e b e e n w r i t t e n t o a c c e s s n y
b a
o f t h e s ef i l e s , b u t t h e p r o g r a m m u s t b e t o l d w h i c h f i l e t o u s e o n a p a r t i c u l a rr u n . A
f i l e s p e c i f i c a t i o n o m m a n d i s s u e db y t h e t e r m i n a l o p e r a t o r a p p l i e st o a l l p r o g r a m s
c
r e q u e s t e d t t h a t t e r m i n a l u n t i l a c o n t r a d i c t o r vc o m m a n d i s i s s u e d .
a
A n o t h e r c o m m a n d p e r m i t s t h e t e r m i n a l o p e r a t o rt o s e n da m e s s a g eo t h e s y s t e m
t
operator.
The commands discussed far are issuedto the communications control program
so
w h i l e i t i s m o n i t o r i n g a t e r m i n a l f o r r e q u e s t s .O n c e a t e r m i n a l i s i n i n t e r a c t i o nw i t h
an application program, however, the input from that terminal is meaningful only
to the application program, with one exception. The CCP checks each message from
a terminal to a program for the appearanceof a certain string of characters,specified
to be significant in your system. When it detects the presenceof these charactersin
a message, the CCP interprets the message an attempt by the terminal operator to
as
escapefrom control of the application program and communicate directly with the
CCP' At this point, the communications control program acceptsa request from the
operator to cancel the execution of the application program, or to send a message to
the system operator. lf the requestwas to send a message, the terminal operator can
ask the CCP to resumeexecution of the application program after the message sent. is
[erminalSecurity
l f y o u a r e c o n c e r n e dw i t h s e c u r i t yo f a c c e s so t h e s y s t e m ,y o u c a n i n d i c a t et h a t a
t
p a s s w o r d e a t u r e b e i n c l u d e di n t h e c o m m u n i c a t i o n s o n t r o l p r o g r a m . T h e v a l i d
f c
p a s s w o r d o r t h e c u r r e n t r u n i s e s t a b l i s h e d y t h e s y s t e mo p e r a t o r w h e n h e o r s h e
f b
s t a r t se x e c u t i o no f t h e c o m m u n i c a t i o n sc o n t r o l p r o g r a m . Y o u m i g h t c h a n g et h a t
p a s s w o r d n e v e r y r u n , o r r e t a i n i t f o r d a y s o r e v e nw e e k s . I n a n y c a s e ,o n l y
o
o p e r a t o r sw h o k n o w t h e p a s s w o r da r e p e r m i t t e d a c c e s so t h e s y s t e m .
t
In a system with passwordprotection, no requestsare accepted from a terminal
u n t i l i t s o p e r a t o rp r e s e n t sh e c u r r e n t p a s s w o r d a n d t h e c o m m u n i c a t i o n s o n t r o l
t , c
p r o g r a mv e r i f i e si t . o n c e a n o p e r a t o rs i g n so n w i t h t h e p a s s w o r d , e o r s h e c a n
h
m a k e a n y n u m b e r o f r e q u e s t s i t h o u t r e p e a t i n g t . l f t h e o p e r a t o r i s n o t a l w a y sa t
w i
h i s o r h e r t e r m i n a l a n d i f o t h e r , p o s s i b l yu n a u t h o r i z e d , e r s o n s o u l d g a i n a c c e s so
p c t
t h a t t e r m i n a l ,h e o r s h es h o u l d s i g no f f t h e t e r m i n a l a n y t i m e h e o r s h e l e a v e s t .
i
W h e n h e o r s h e h a s s i g n e do f f , t h e c o m m u n i c a t i o n s o n t r o l p r o g r a m r e q u i r e s n y
c a
f u r t h e r u s eo f t h e t e r m i n a l t o b e a c c o m p a n i e d y t h e p a s s w o r d .
b
Y o u m a y a l s oc o n t r o l a c c e s so t h e s y s t e mb y w r i t i n g y o u r o w n s i g n - o nr o u t r n e .
t
T h e o p e r a t o r m u s t p r o v i d e a n y i n f o r m a t i o n r e q u i r e db v t h e r o u t i n e b e f o r e h i s o r
h e r r e q u e s ti s a c c e p t e d .
W h e n t h e s y s t e mo p e r a t o r i n i t i a t e se x e c u t i o no f t h e c o m m u n i c a t i o n sc o n t r o l
p r o g r a m ,t h e C C P a t t e m p t s t o i n f o r m e a c ht e r m i n a l i n t h e s y s t e mt h a t t h e i n f o r -
m a t i o n s y s t e m i s n o w a v a i l a b l e o r u s e . l f y o u h a v es p e c i f i e dt h a t n o s e c u n t y
f
f e a t u r e b e b u i l t i n t o y o u r s y s t e m ,p r o g r a m r e q u e s t s n d o t h e r c o m m a n d sa r e
a
a c c e p t e d r o m t h e t e r m i n a l a f t e r t h e o p e r a t o r s i g n so n ; h e o r s h e d o e s n o t n e e d
f
t o e n t e r a p a s s w o r co r o t h e r s e c u r i t v i n f o r m a t i o n .
l
. . . F R O MT H E V I E W P O I N T F T H E S Y S T E M P E R A T O R
O O
T h e s y s t e mo p e r a t o r e x e r c i s e si n a l c o n t r o l o v e r t h e c o m m u n i c a t i o n s - b a s es v s t e m .
f d
H e o r s h e i n i t i a t e si t s a c t i v i t y b y l o a d i n ga n d r u n n i n g t h e c o m m u n i c a t i o n sc o n t r o l
p r o g r a m . H e o r s h e d e t e r m i n e s h e n t h e s y s t e ms h o u l d r e f u s et o a c c e p tn e w
w
r e q u e s t s r o m t e r m i n a l o p e r a t o r s . W h i l e t h e s y s t e m i s i n o p e r a t i o n ,h e o r s h e m a v
f
i n i t i a t ec e r t a i n s y s t e ma c t i o n s ,d e t e r m i n et h e s y s t e m ' s t a t u s ,a n d a l t e r t h e s e t o f
s
t e r m i n a l sp e r r n i t t e ctlo a c c e s sh e s y s t e m . H e o r s h e m u s t a l s o m a k e d e c i s i o n s h e n
t w
e x c e p t i o ns i t u a t i o n s( s u c ha s e r r o r c o n d i t i o n s )a r e d e t e c t e db y t h e c o m m u n i c a t i o n s
c o n t r o l p r o g r a mo r a p r o g r a m r u n n i n g u n d e r i t s c o n t r o l .
o n c e t h e c c P h a s b e e ns t a r t e d ,a l l c o m m u n i c a t i o nb e t w e e nt h e c o n t r o l p r o g r a m
a n d t h e s y s t e mo p e r a t o r i s t h r o u g h m e s s a g ep r i n t e d o n t h e 5 4 7 1 P r i n t e r - K e y b o a r d
s
( f o r M o d e l s 1 0 a n d 1 2 |,t o r d i s p l a y e do n r h e 3 2 7 7 D i s p l a yS t a t i o n ( f o r M o d e l 1 5 ) .
S o m e m e s s a g ers Q u i r e e s p o n s e s , h i c h t h e o p e r a t o r k e y s o n t h e a p p r o p r r a t e
e r w
d e v i c e . A t a n y p o i n t d u r i n g t h e e x e c u t i o no f t h e c c p , t h e o p e r a t o r m a y w a n t t o
c o m m a n d a s y s t e ma c t i o n b y p r e s s i n g h e r e q u e s t( R E O ) k e v o n t h e 5 4 7 1 o r
t
p r o g r a mf u n c t i o n k e y 9 , 10 , o r 1 2 ( p F 9 . p F 1 0 , o r p F 12 ) o n t h e 3 2 7 7 , t h e n k e y i n g
the command.
Control program
Initiatingthe Communications
w h e n h e o r s h e s t a r t st h e e x e c u t i o n o f t h e c o m m u n l c a t i o n s o n t r o l p r o g r a m ,t n e
c
o p e r a t o rc a n e x e r c i s e e r t a i n o p t i o n s . F o r e x a m p l e ,h e o r s h e c a n :
c
Specify the system password to be used during this run.
Preventaccess certain disk data files that are normally accessible programs
tcl to
r u n n i n g u n d e r c o n t r o l o f t h e c o m m u n i c a t i o n s o n t r o l p r o g r a m ;f o r e x a m p l e ,t h e
c
file may not be built everyday.
Prohibit the requestingof certain application programs that are normally part of
the information system.
o Specify the set of terminals that can have access the information system at the
to
time the system beginsits activity.
. Causea serviceaid program to be included in the communications control oro-
gram if a malfunction in its operation is suspected.
SystemOperatorCommands
During
operation thecommunications
of program, system
control the operator
can
c o m m a n dt h e C C p t o :
o Disableor enable access the system by any terminal.
to
' Changethe terminal which will actually be addressed a program when that
by
program attempts to access terminal by name.
a
o Initiate the online test of a terminal to determine whether it is operating
correctly.
o I n i t i a t et h e e x e c u t i o no f a n a p p l i c a t i o np r o g r a m .
o C a n c e lt h e e x e c u t i o n o f a n a p p l i c a t i o np r o g r a mc u r r e n t l y r u n n i n g .
o Display information about the system,sstatus (seenote).
o Accept no new program requestsfrom terminars and notify
the system oper-
ator when all outstanding requestshave been satisfied.
' Cease activity of the system immediately and terminate execution of the
all
CCP.
I r O p e n a n d c l o s ed i s k f i l e s .
y'y'ote.-
some of the information about system status that may be displayed is:
o The identification of terminals currently permitted access the system.
to
. The complete status of any specific terminal in the system.
o The identification of programs currently executing, which terminal each is serv-
ing, and which program is currently in control of the central processingunit.
Messages
The system operator can receive messages
from the communications control pro-
gram or from an application program. The CCP prefixes each message
with the
identification of the program that issuedit. Messages which require a reply from
the operator are further prefixed with the indication that a reply is required.
Among the messages the system operator which require reply are halt codes. In
to
a system with severalapplication programs operating concurrently. a halt issuedfor
one program causesonly that program to suspendoperations until a responseis
supplied. The communications control program and other application programs
under its control continue to operate.
. . . F R O M H EV I E W P O I NO F T H EP R O G R A M M E R
T T
T h e c o m m u n i c a t i o n s o n t r o l p r o g r a m a i d st h e p r o g r a m m e ri n t w o p r i m a r y w a y s :
c
a R e l i e v e s a n y p r o g r a m m i n gc o n c e r n si n h e r e n t i n a n e v e n t - d r i v e n y s r e m ;
m s
t h e r e f o r ea l l o w s c o n c e n t r a t i o no n a p p l i c a t i o np r o g r a m st h a t s o l v et h e p r o b l e m s
of his or her orqanrzation.
o P e r m i t sw r i t i n g a p p l i c a t i o np r o g r a m st h a t i n c l u d ec o m m u n i c a t i o n si n p u t /
o u t p u t i n a h i g h - l e ' , r ea n g u a g e .
ll
Programsthat run under the communication control program can be written in any
of four languages:
. R P GI I
O COBOL
. FORTRANIV
. BasicAssembler
B y w r i t i n g i n R P G l l , c o B o L , o r F o R T R A N , y o u c a n a v o i dt h e s t r i c t r u r e s
r e q u i r e dw h e n u s i n g B a s i cA s s e m b l e rL a n g u a g e .
Although your program may have to contend with others for system resources,
y o u c a n i g n o r et h e p r o b l e m st h a t a r i s ef r o m t h i s . T h o s e p r o b l e m s
aremanaged
b y t h e c o n t r o l p r o g r a m . Y o u a r e a s s u r e d h a t a l l r e q u i r e dr e s o u r c e s r e a v a i l a b l e
t a
t o y o u r p r o g r a m e a c h t i m e i t i s e x e c u t e d . l f n e c e s s a r yt,h e c c p d e f e r st h e
e x e c u t i o no f y o u r p r o g r a m u n t i l t h o s e r e s o u r c e s r e a v a i l a b l e . l f y o u r p r o g r a m
a
s h a r e s c c e s so a d i s k d a t a f i l e w i t h a n o t h e r c o n c u r r e n t l ye x e c u t i n gp r o g r a m ,t h e
a t
c c P m a n a g e sh e c o n t e n t i o n a n d d o e s n o t p e r m i t t h e t w o p r o g r a m st o c a u s ea n
t
e r r o n e o u sr e c o r d u p d a t e t h r o u g h c o n f l i c t i n g r e a d sa n d w r i t e s .
Programsthat execute under the control of the communications control program are
written much the same as programs in the same languagefor a system without tele-
communications. That is, the statementsused to processdata and the handling of
data files are identical. The standard disk data management methods are supported
by the control program. Only two elements are likely to differ significantly:
o The overall design of the program.
o The statementsused to communicate with terminals or with the system operator.
ProgramDesign
lf you currently use a data processingsystem without telecommunications. many
programs in your system operate upon a long seriesof transactions- hundreds or
perhapsthousands. The data from those transactionsprobably updates a single
disk file. Once started, such a program processes the transactions before it is
all
finished. of course, the transactionsrepresentedby the data actually happened
earlier in the day, week, or month. The data is collected into a batch before it is
used to update the files of the system. When they have been updated, the files
contain information reflecting the state of your organization'saffairs as of the last
transaction in the batch.
It is also possibleto design programs that use the batch processingmethod to advan-
tage in a communications-based system. lf a terminal is located where transactions
are occurring and if data is entered regardingthe transactionsas they occur, the
system can reflect the current status of your organization.
Batch processingrequiresthat the terminal be dedicated to input of one kind, or
severalclosely related kinds, of transaction data. Frequently, however, during a
p e r i o d o f t i m e , a t e r m i n a l i s u s e dt o i n q u i r e i n t o i n f o r m a t i o n c o n t a i n e d i n a n u m b e r
of files, or to enter data concerning transactionsof many different types affecting
severaldifferent files. In these cases,it is unlikely that the terminal would be served
for any length of time by a single program. In fact, each program may be written to
p r o c e s s o m p l e t e l y o n l y a s i n g l et r a n s a c t i o no r i n q u i r y f r o m t h e t e r m i n a l , t h e n t e r -
c
m i n a t e i m m e d i a t e l y . I n p r a c t i c e ,t h e m a j o r i t y o f a p p l i c a t i o n s f t e l e c o m m u n i c a t i o n s
o
involve this kind of processing,therefore, programs are required to update all files
affected by a transaction, but handle only a single transaction per execution. This
certainly implies a program design different from that for a batch-oriented svstem.
TerminalInput/Output
T h e s e c o n ds i g n i f i c a n td i f f e r e n c ei n p r o g r a m m i n gu n d e r t h e c o m m u n i c a t i o n sc o n t r o l
p r o g r a m i s t h e m a n n e r o f p r o g r a m m i n gf o r c o m m u n i c a t i o n w i t h a t e r m i n a l a n d t h e
system operator.
T h e M L T A l O C S a n d B S C A I O C S f a c i l i t i e sa r e n o t d i r e c t l y a c c e s s i b l e y h i g h - l e v e l
b
p r o g r a m m i n gl a n g u a g e s . h e c o m m u n i c a t i o n sc o n t r o l p r o g r a m i n c o r p o r a t e s L T A
T M
I O C S o r B S C A I O C S ( o r b o t h . i f y o u h a v eb o t h l i n e t y p e s i n y o u r s y s t e m ) a n d
o f f e r s t h e a p p l i c a t i o np r o g r a m m e ra m e t h o d o f u s i n gt h e s e I O C S f a c i l i t i e st o i n t e r -
act with terminals.
Since there are no statements in the languages specify terminal actions, the appli-
to
cation program indicates those actions to the communications control program by
means of one of the following statements.each of which causesa Drancn to a sup-
plied subroutine:
. In COBOL or FORTRAN - CALL statement
o I n R P G l l - E X I T s t a t e m e n t ,o r u s e o f a S P E C I A L f i l e
. -
I n B a s i cA s s e m b l e r b r a n c h i n s t r u c t i o n
Each of these statements is accompanied by parametersto indicate the specificsfor
the operation.
10
Those specificsinclude the following information necessary
to control the terminal
action requested:
o The operation desired.
o The length of the message be sent, or
to the maximum rength of a message be
to
received.
' T h e n a m e o f t h e t e r m i n a l w i t h w h i c h t h i s c o m m u n i c a t i o ni s t o t a k e p l a c e .
r The area in main storagewhich contains the message be sent, or should contain
to
a messageto be received.
S o m e o p e r a t i o n st h a t c a n b e s p e c i f i e da r e :
a Read a messaqe
o Write a messaoe
. Write a message
and wait for a reply
o Release
the terminal from any further use in this program
Previousdiscussionmay have implied that an application program communicates
only with the terminal that requestedit. In fact, most communication by programs
r u n n i n g u n d e r t h e C C P i s w i t h t h e r e q u e s t i n g e r m i n a l . B u t t h e a b i l i t y a l s o e x i s t st o
t
addressother terminals. A terminal is addressedin the program by a name that is
chosen by the user; the name normally appliesto one particular terminal. However,
s h o u l d a c e r t a i nt e r m i n a l b e c o m e u n a v a i l a b l e u r i n g a r u n o f t h e c o m m u n i c a t i o n s
d
control program, the system operator can reassign the name to another terminal.
Any program addressing terminal by the reassigned
a name addresses the new termi-
nal. For the most part, the application program need not be concerned with the
type of terminalwith which it is communicatino.
w h e n a S y s t e m / 3 M o d e l 1 0 o r M o d e l 1 2 i s u s e d ,a n a p p l i c a t i o np r o q r a mc o m m u n -
1
i c a t e sw i t h t h e s y s t e mo p e r a t o r b y a d d r e s s i n gh e 5 4 7 1 p r i n t e r / K e v b o a r d
t as
a n o t h e rt e r m i n a l . T h e n a m e C O N S O L i s a l w a y s u s e dt o a d d r e s s h e 5 4 7 1 . W h e n
t
a s y s t e m / 3 M o d e l 1 5 i s u s e d ,a n a p p r i c a t i o np r o g r a mc o m m u n i c a t e s i t h t h e
w
s y s t e mo p e r a t o r b y u s i n gt h e s t a n d a r dM o d e l 1 5 c o n s o l ei n t e r f a c eo r b y a d d r e s s i n g
t h e t e r m i n a l n a m e C O N S O L . T h e o n l y o p e r a t i o n sa v a i l a b l e o t h e a p p l i c a t i o n
t
p r o g r a mw h e n i t i s c o m m u n i c a t i n gw i t h t h e s y s t e mo p e r a t o r
are:
o Write a messaoe
o Write a message nd wait for a reply
a
H O WC A N T H EC C PB E T A I L O R E D O M Y N E E D S ?
T
The communications control program feature of disk system management,like disk
system managementitself. can be tailored to suit your processingrequirements.
when you receivethe communications control program, you must first generatea
disk system for your installation if you have not already done so. At that point,
you are ready to tailor a communications control program according to number
a
of options you selecr.
11
Control program
Generating Communications
the
T h e c o m m u n i c a t i o n s o n t r o l p r o g r a mi s a h i g h l y m o d u l a r p r o g r a md e s i g n e d o y o u
c s
c a n i n c l u d e f u n c t i o n s y o u r e q u i r ea h d e x c l u d e t h o s e o f n o v a l u e t o y o u r i n s t a l l a t i o n .
The processof selectingfunctions you want is known asgeneratingthe control pro-
gram.
The processinvolves:
L C r e a t i n ga s e t o f c o n t r o l r o u t i n e sw h o s e s p e c i f i cc o n t e n t m a y b e a b s o l u t e l yu n i q u e
to your installation.
2 . J o i n i n g t h e s er o u t i n e sb y a l i n k a g ee d i t p r o c e s s .
C o p y i n g a p p r o p r i a t ea d d i t i o n a ls u p p o r t i n gr o u t i n e s .
The output of the generation processis a set of object modules and subroutines on
a d i s k p a c k s p e c i f i e db y y o u . T h i s o u t p u t i s y o u r v e r s i o no f t h e c o m m u n i c a t i o n s
control program. lt includes the program to be loaded and run each time the svs-
t e m o p e r a t o r i n i t i a t e sy o u r c o m m u n i c a t i o n