Re: Something improper with ASP state change procedures.

Hi Naveen,
 
it seems that ASP does not behave correctly after reception of out-of-blue ASP Up Ack message.
According to RFC4666, section 4.3.4.1:
 
"If the ASP receives an unexpected ASP Up Ack message, the ASP should consider itself in the ASP-INACTIVE state. If the ASP was not in the ASP-INACTIVE state, it should send an Error message and then initate procedures to return to its previos state."
 
So in your case, ASP shall initiate ASP Active procedure again after which it will align the state with SGP.
 
BR Dario


--- On Tue, 11/23/10, Naveen Kottapalli <[email protected]> wrote:


From: Naveen Kottapalli <[email protected]>
Subject: [Sigtran] Something improper with ASP state change procedures.
To: [email protected]
Date: Tuesday, November 23, 2010, 3:36 PM



Hi All,
 
We are seeing some strange in the M3UA ASP state change procedures.  Please find the description of the problem below.
 
ASP                                                              SGP
=======================================
ASPUP               -------------->  Processes ASPUP and sends ASPUP_ACK
 
Move ASP to
INACTIVE state   <-------------   ASPUP_ACK
 
SCTP-SACK
for ASPUP_ACK  ------------->  Missed or lost in the network
 
ASPAC               -------------->  Processes ASPAC and sends ASPAC_ACK

 
Move ASP to
ACTIVE state      <-------------   ASPAC_ACK
 

SCTP-SACK
for ASPAC_ACK  ------------->  Missed or lost again in the network
 

Move ASP to
INACTIVE state   <-------------   SCTP layer at SGP retransmits the ASPUP_ACK, ASPAC_ACK because of lost SACKs.
because of
ASPUP_ACK
in ACTIVE state
 
SCTP-SACK        ------------->  Reached the SCTP layer of SGP
 
In the above behavior the M3UA at SGP thinks that the ASP is in ACTIVE state whereas it is not the case.  Since ASP is in INACTIVE state, all the data packets that were sent by SGP will be dropped (without sending any error message back to network).  The above problem will lead to a potential message loss in the network.
 
Considering the above behavior, I think the state machine should be tuned accordingly.
 
Please pass on the comments on this.
 
Thanks & Regards,
Naveen.

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