APPENDIX IV
                                
                    (to Recommendation X.223)
                                
      Differences between Recommendation X.223 and ISO 8878


       The following differences exist between Recommendation  X.223  and
ISO 8878.

IV.1   In Recommendation X.223, the text in  6.2.2.1.1 specifies  that  given
conditions a) through d), the address is always carried in the Address Field (AF). 
ISO 8878 specifies that given conditions a) through c) (ISO 8878 does not include 
condition d), the address may optionally be carried in the AF.

IV.2   In Recommendation X.223, the text in  6.2.4 specifies that if "no use of 
Expedited Data" is indicated or if the NL entity cannot support 32-octet INTERRUPT 
packets, then the EDN facility is always omitted. For the same case, ISO  8878
specifies that the EDN facility either may be carried specifying  "no  use  of
Expedited Data", or may be omitted.

IV.3   In  6.2.5.1 (Throughput QOS Parameters) of Recommendation X.223, two new 
paragraphs have been added which are not present in ISO 8878. These paragraphs are 
the last paragraph in  6.2.5.1.1, and the last paragraph in  6.2.5.1.2.

       Collectively, these paragraphs specify that whenever the Lowest Quality 
Acceptable sub-parameters of the Throughput QOS Parameters for both directions are 
"unspecified" in the N-CONNECT request, the MTCN facility is not included in the 
CALL REQUEST packet. ISO 8878 specifies that in such a case, the MTCN facility is 
encoded as 75 bits per second.

IV.4   In  6.2.5.2 (Transit Delay QOS Parameter) of Recommendation X.223, four 
new paragraphs have been added which are not present in ISO 8878. These paragraphs 
are the last paragraph in  6.2.5.2.1, the last paragraph in  6.2.5.2.2, the last 
paragraph in  6.2.5.2.3, and the last paragraph in  6.2.5.2.4.

       Collectively, these paragraphs specify that whenever the Target and Lowest 
Quality Acceptable sub-parameters of  the  Transit  Delay  QOS  Parameter  are
"unspecified" in the N-CONNECT request, the EETDN facility is not included in the 
CALL REQUEST packet. ISO 8878 does not explicitly address  such  a  case,  and
actually implicitly invalidates it per the conditions in items a) -d).

       Additionally, in  6.2.5.2.1 of Recommendation X.223, the last sentence in 
item d) specifies that in DTE-to-DTE operational environments the usage of the 
TDSAI facility is for further study. ISO 8878 does not have such a sentence.

IV.5   In  6.2.5.2.1 of Recommendation X.223, there is only one note after item 
d). ISO 8878 contains two notes after item d), the first of which is identical to 
the one note in X.223. ISO has initiated the necessary procedures to remove their 
second note.

IV.6   The scope of Recommendation X.223 does not include for provision of the 
OSI Connection-mode Network Service over 1980 X.25  sub-networks.  Conversely,
ISO 8878 provides for this and defines a protocol mechanism in Annex A.  Also,
material related to conformance issues, including those raised by the presence of 
Annex A, is included in Annex B to ISO  8878  and  is  not  included  in  this
Recommendation.