[Standards] Client Acknowledgement of Subscription State Change Notifications

[Ian Paterson]

Section 9.4 of RFC 3921 (Appendix B.4 of RFC 3921bis) states that "A 
server MAY require the recipient to acknowledge receipt of all state 
change notifications... In order to require acknowledgement, a server 
SHOULD send the request or notification to the recipient each time the 
recipient logs in, until the recipient acknowledges receipt".

The acknowledgement of subscription requests is clearly necessary, but 
can anyone please tell me why servers are permitted (but not encouraged) 
to insist on acknowledgements for the other three notifications?

A couple of suggestions for 3921bis:
1. Since a client has no way of discovering if the server requires an 
acknowledgement or not, it should always acknowledge notifications. So 
perhaps RFC 3921bis could highlight the importance of clients responding 
by also specifying something like: "The recipient SHOULD/MUST affirm or 
deny every notification to prevent some servers flooding it with an 
ever-increasing number of notifications upon each login."
2. Hopefully someone will enlighten me, but if not, perhaps we could 
also consider depricating this repeated notification behaviour?

Apologies in advance if this subject has already been discussed with 
regard to 3921bis.

- Ian