RFC 1328 (rfc1328) - Page 2 of 5
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Alternative Format: Original Text Document
RFC 1328 X.400 1988 to 1984 downgrading May 1992
3. Addressing
In general there is a problem with O/R addresses which use 88
specific features. The X.419 downgrade approach will mean that
addresses using these features cannot be specified from 84 systems.
Worse, a message originating from such an address cannot be
transferred into X.400(1984). This is unacceptable. Two approaches
are defined. The first is a general purpose mechanism, which can be
implemented by the gateway only. The second is a special purpose
mechanism to optimise for a form of X.400(88) address which is
expected to be used frequently (Common Name). The second approach
requires cooperation from all X.400(88) UAs and MTAs which are
involved in these interactions.
3.1 General Approach
The first approach is to use a DDA "X400-88". The DDA value is an
std-or encoding of the address as defined in RFC 1327 [Kil92]. This
will allow source routing through an appropriate gateway. This
solution is general, and does not require co-operation. For example:
88:
PD-ADDRESS=Empire State Building; PRMD=XX; ADMD=ZZ; C=US;
84:
O=MHS-Relay; PRMD=UK.AC; C=GB;
DD.X400-88=/PD-ADDRESS=Empire State Building/PRMD=XX/ADMD=ZZ/C=US/;
The std-or syntax can use IA5 characters not in the printable string
set (typically to handle teletext versions). To enable this to be
handled, the std-or encoded in encapsulated into printable string
using the mappings of Section 3.4 of RFC 1327. Where the generated
address is longer than 128 characters, up to three overflow domain
defined attributes are used: X400-C1; X400-C2; X400-C3.
3.2 Common Name
Where a common name attribute is used, this is downgraded to the
Domain Defined Attribute "Common". For example:
88:
CN=Postmaster; O=A; ADMD=B; C=GB;
84:
DD.Common=Postmaster; O=A; ADMD=B; C=GB;
The downgrade will always happen correctly. However, it will not
always be possible for the gateway to do the reverse mapping.
Hardcastle-Kille