Re: What is FSN and BSN values of the Link Status Massages in M2PA

Thanks Craig

    For the suggestions for the FSN and BSN calculation. and the changeover 
questions. But I have only one doubt regarding the FSN and BSN values for 
Link Status messages. Not the user data messages. Are we going to use zero 
"0" values of Link status messaegs i.e. M2PA Control messages?

    Secondly is it possible that the M2PA will have more that 2 SCTP streams 
which can be used for user data messages during changeover conditions?

    Is it possible that one M2PA link can transmit the user data messages 
different MTP3 standard such as ITU nad JTU etc? As MTP3 has a set of Link 
called as Linkset where as one M2PA layer can have one one Link or multiple 
set of Links?

    Please clarify some of my doubts.

Regards,
Bibhuti

----- Original Message ----- 
From: "Craig, Jeffrey" <[email protected]>
To: "Bibhuti Bhusan Tosh" <[email protected]>; <[email protected]>
Sent: Monday, May 15, 2006 11:51 PM
Subject: RE: [Sigtran] What is FSN and BSN values of the Link Status 
Massages in M2PA


Hello Bibhuti,

>Q1 What will be its value for Link Status messages?

The BSN is the FSN of the last non-empty user data message to be 
acknowledged
as received. If no non-empty user data messages has been received, then the
BSN is the initial sequence number minus one. The FSN is the M2PA sequence
number of the last non-empty user data message sent. If no non-empty user 
data
message has been sent, then the FSN is the initial sequence number minus 
one.
Note that except for the case of synchronization after processor recovery, 
the
sequence numbers of Link Status messages are ignored by the receiver.

>Q2 While retriving the FSN and BSN of these messages are lost and MTP3 
>transfers
>using new alternate M2PA layer or the differentSCTP Stream of same M2PA 
>layer as
>multiple User data streams may be available in underlying SCTP Association?

I am not sure I understand the question, but I'll attempt an answer. If MTP3
retrieves MSUs from an M2PA signaling link instance and re-routes the MSUs 
via
another M2PA signaling link instance, then the MSUs will become new M2PA 
user data
messages having sequence numbers appropriate for the new M2PA signaling 
link. The
situation would be similar if the new link was ATM or E1 or T1, rather than 
M2PA.

Regards,

Jeff
________________________________________
From: Bibhuti Bhusan Tosh [mailto:[email protected]]
Sent: Monday, May 15, 2006 6:20 AM
To: [email protected]
Subject: [Sigtran] What is FSN and BSN values of the Link Status Massages 
inM2PA

Hi All

Kindly clarify my following question on M2PA.

Q1. As per RFC 4165. the M2PA common header contains only the FSN and BSN 
values.

2.2.1. Backward Sequence Number (BSN)
This is the FSN of the message last received from the peer.
2.2.2. Forward Sequence Number (FSN)
This is the M2PA sequence number of the User Data message being sent.
The FSN and BSN values range from 0 to 16,777,215.

So the FSN and BSN values are updated in User Data Messages only. What will 
be its value for Link Status messages?

Q2. M2PA RfC 4165 says that The association SHALL contain two streams in 
each direction.Stream 0 is designated for Link Status messages. Stream 1 is 
designated for User Data messages, as well as Link Status messages that must 
remain in sequence with the User Data messages. During ChangeOver The MTP3 
retrivses the data from M2PA and transfers them using alternate links.

My Question is that While retriving the FSN and BSN of these messages are 
lost and MTP3 transfers using new alternate M2PA layer or the differentSCTP 
Stream of same M2PA layer as multiple User data streams may be available in 
underlying SCTP Association?

Regards,
Bibhuti