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The equipment installed beyond the interfaces (the data terminal equipment) and 
the usage of the transport services are in most countries oriented to CCITT-Re- 
commendations. As is known, data transport serves the purpose of communication 
between data sources and sinks which, to some extent, also fulfill data proces- 
sing functions. The electric transport of data signals between centralized or 
decentralized data processing systems or between centralized data terminal equip- 
ment and peripheral data terminal equipment (also called data terminals) is 
utilized for teleprocessing. 
For the transmission and switching of signals, economical digital systems have been 
introduced. The latest technological developments support the trend towards using 
them on an ever larger scale. The ultimate goal is to have a single telecommuni- 
cation network for all communication systems. Depending on the objective pursued, 
this network is called Integrated Digital Network (IDN) or Integrated Services 
Digital Network (ISDN). The reasons for the introduction of separate networks in 
the foreseeable future are still manifold. However, the term "integrated" is 
ambiguous, and it needs very close examination to understand its meaning exactly. 
Strictly speaking, the transmission network has always been integrated because the 
channels derived from the different transmission systems have also been used for 
the different telecommunication networks such as the Telephone Network. Telex Net- 
wOrk, Datex Network, Data Network for Fixed Connections, Leased circuits a.s.o. 
Speaking of the transport function of data communication, one is necessarily 
faced with the problem of compatibility. It can hardly be denied that data sources 
and sinks need to communicate unhampered with one another. Because of this fact, 
great efforts have been made over the last few years to obtain "open communica- 
tion systems", a lengthy discussion of which would be beyond the scope of this 
paper. However, since reference will have to be made to it in some cases, the 
hierarchical structure of an ISO architectural model is represented schematically 
in Figure 2. Although the uniformity of protocols up to level three of a com- 
munication network does not ensure complete compatibility of all systems, it may 
be regarded as the basis for reaching this objective. Efforts at standardization 
are made by the International Telegraph and Telephone Consultative Committee 
(CCITT) and the International Organization for Standardization (ISO). 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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femme DTE — Datacommurec ation Network — DTE — 1 
Figure 2 Systems Architecture « ISO Reference Model for Open Systems Interconnection 
  
An extremely strong potential for data communication exists in the field of data 
processing which, together with teleprocessing, may form the basis for completely 
new services. Data bases of the most different kind and data banks used in video- 
text centres have many text processing facilities and probably belong to the 
bordering area between data communication and text communication. No doubt, of- 
fice automation - the basis for the office of the future - and "electronic mail" 
Tietz 2