Re: SequenceNumber [was:minutes 21-Dec-2000 tr&p con-call]

[Nikola Stojanovic <nhomest1@twcny.rr.com>]

<SHIMAMURA Masayoshi>
...
(1) Guarantee of Message Order
(2) Effective Duplication Check

The MessageID element in MessageData can not realize the two functions
above. Especially, there is no way to guarantee Message Order except for
using SequenceNumber. Because current MS specification has not the
blocking restriction. The Sender can send some messages without waiting
for acknowledgement message. Thus when a communication error and retry
sequence occurs, sent messages will reach the Receiver in invalid order.
To correct the invalid order in the Receiver, the SequenceNumber must be
included in each message.
</SHIMAMURA Masayoshi>

In addition to MessageID element in MessageData there is a RefToMessageId
element as well. While using MessageID only for the purpose of temporal
ordering of messages (sequencing being just one instance of it) is not
enough, utilizing both MessageID and RefToMessageId can allow MS Handlers to
do sequencing and much more. In that case SequenceNumber doesn't need to be
included in each message.
It is not easy for me to understand a full meaning of "Effective Duplication
Check", but I can't see a problem in using the approach explained in the
current MS spec (0.9a) (again, without SequenceNumber).


<SHIMAMURA Masayoshi>
To realize (1)Guarantee of Message Order and (2)Effective Duplication
Check, the SequenceNumber is obviously needed.
</SHIMAMURA Masayoshi>

See comments above.

Regards,
Nikola