the integration of pliant systems which do not support the accepting of responsibility standards, and this is reflected in current developments. In the EDI for a message must forward that responsibility to the next system in world this is the emergence of X.435 as the standard for EDI over the network. X.400. This will allow an organisation to utilise a single physical also contains mechanisms to provide proof of content re- (OSI) connection to carry all its text messaging whether structured ceived and non repuditable proof of content received. or unstructured. The X.500 directory services will allow the off-net Proof of content received is equivalent to returning a copy of the processes to address and route the data to the correct endpoint. original content to the sender on receipt of a message. Further work is being done in the area of office document archi- Non repuditable proof allows the originator of a message to be tecture (ODA). This will further integrate the messaging media as it sure the receiver cannot say it was never received. It is similar in allows a separation of the content of a document from the layout and concept to the above but the copy sent back can be considered to be formatting of the content. Thus it is possible not only to transmit the notarised as a certificate of origin is passed between the parties. content of a document but instructions for its presentation. It also allows for multimedia documents SO a document which includes a picture can be sent in a single transmission and interpreted correctly at the far end. 38.8 Global VAN topologies In assessing future trends in the VANS we must look at services under development today. Clearly there are three thrusts for the With the trend to global marketplaces and global networks three future. These all concern the shift of focus up the OSI stack towards styles of global VAN are evident. the abstract user orientated functionality. This will protect users' In the first case a VAN operates its processing in a single location current investme