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question about Q.699 - ISUP/ISDN interworking

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ancientmoon

Programmer
Nov 7, 2007
1
US
Hi!

I have a question about ISDN/ISUP interworking - q.699.

in section "3.1.1.3 Sending of the Address Complete Message (ACM)", it has:

c) En bloc receiving is used on the DSS 1 side and a Progress indicator information element (except with value No. 8, in-band information or an appropriate pattern is now available, No. 3, originating address is non-ISDN, or No. 4, call has returned to the ISDN) is received in a CALL PROCEEDING message or in a PROGRESS message.

Why these 'exceptions'? especially for the PI=8 in call proceeding case?

thanks,
ancientmoon
 
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