Re: M2PA questions on synchronization and message handling

Dario,

Dario wrote:                                     (Mon, 17 Dec 2007 03:47:00)
> 
> HI,
> 
> here are three questions for M2PA RFC 4165:
> 
> 1.	Synchronization after PO during Initial Alignment
> the question is: is the synchronization in Initial Alignment identical to
> synchronization in stable PO state in terms of exchanged messages and
> procedures?
> (at least – during Initial Alignment , there was no User Data messages sent,
> so what is the purpose of such sequence?)

Sequence numbers do not need synchronization during initial alignment
because they are still at their initial values.

> 
> 2.	when FLUSH primitive is received from MTP level 3 in M2PA, should M2PA:
> a.	flush outgoing buffers
> b.	flush both outgoing and incoming buffers?
> 
> Perhaps it is not clear are both points a) and b) listed in RFC section
> 4.1.4.  to be executed?

Yes, both.  Note that in (a) incoming buffers are not flushed, just messages
that were queued and unacknowledged, which are the messages received during
processor outage that could not be delivered to MTP3 from earlier on in
section 4.1.4.

> 
> 3.	Unexpected FSN and/or invalid BSN
> The RFC states that 
> „If M2PA receives a User Data message with an FSN that is out of order, M2PA
> shall discard the message“. (RFC4165, section 4.2.1)

The statement in RFC 4165 section 4.2.1 applies to an FSN that is out of
order.

> 
> In addition to that, Q.703 states
> „In the case that a message signal unit or fill-in signal unit is received
> having a backward sequence number value which is not the same as the
> previous one or one of the forward sequence number values of the signal
> units available for transmission, the signal unit is discarded. The
> following message signal unit or fill-in signal unit is discarded.
> If any two backward sequence number values in three consequtively received
> message signal units or fill-in signal units are not the same as the
> previous one or any of the forward sequence number values of the signal
> units in the retransmission buffer at the time that they are received, then
> they are received, then level 3 is infomed that the link is faulty“
> (section 5.3.1)
> 
> If M2PA is to follow all these statements that it would mean that reception
> of message with invalid sequence number would cause transition to Out Of
> Service state:
> 
> For example:
> -	User Data message with either unexpected FSN or invalid BSN is received:
> discard it
> -	User Data with correct FSN (FSN=x) is received, it must be discarded due
> to Q.703 statement
> -	Nex User Data with FSN=x+1 is received. This is now unexpected FSN since
> previously received message is discarded. Etc.

The statement in Q.703 section 5.3.1 applies to a BSN that is invalid.

You compare apples and oranges.

--brian

-- 
Brian F. G. Bidulock
[email protected]
http://www.openss7.org/