The Need for Address Translation

For Routing

Address Translations also provides the ability for incoming calls from different public and private networks to access the same host via different X.25 gateways all using different addresses.

It also enables you to use one address to access different ports, with the identification of the calling subscriber providing the differentiation. This could allow for different subscribers, all using one address i.e. 1001 to get routed to a different Host.