Subject: Re: ImmAckRequired

From: [email-masked]
Date: Tue, 20 Feb 2001 04:39:35 +0530

Hi all,

1. This flag reveals the fact that "response sending" entity is running a
retransmission timer for the response transaction. By having run Retransmission
timer,  the response sending entity would fasten the response arrival to the
sending entity since the response has already been delayed which resulted into
the generation of transaction pending.

2. One may argue that since the final response been generated after the
transaction pending, so the sending entity would gaurantee the generation
ResponseACK once the final reply is followed by pending. However, it is to be
kept in mind that IP transport being a "best effort" delivery shall not
gaurantee the ordered delivery of transaction pending and the final transaction
reply and they may be received out of order. In this case, sending entity is
not going to generate the ResponseACK. To take care of this, IA token is
required.

Thanks,
Prashant Jain

"Rosen, Brian" <[email-masked]> on 02/20/2001 03:15:02 AM

To:   "[email-masked]'" <[email-masked]>
cc:    (bcc: Prashant Jain/HSS)

Subject:  ImmAckRequired

Does anyone remember the function of the ImmAckRequired flag?
In D.1.4 it says:
   response.  Upon receipt of a final response following receipt of
   provisional responses, an immediate confirmation shall be sent, and
   normal repetition timers shall be used thereafter.  An entity that
   sends a provisional response, SHALL include the immAckRequired field
   in the ensuing final response, indicating that an immediate
   confirmation is expected.  Receipt of a Transaction Pending after
   receipt of a reply shall be ignored.

That is the only mention of the flag in the text other than the ASN.1
and ABNF.  I think this is a vestige of some old idea, and it is not
required.  It is NOT a way for an MG to indicate whether it does,
or does not want an ACK, ACKs are always required for final responses
when UDP is used.  Final response is easily distinguished (PEND
vs REPLY), so why do we need this flag?

Brian