Subject: Re: [Sigtran] M3UA default AS

From: "TOLGA ASVEREN" <[email-masked]>
Date: Tue, 14 Jan 2003 08:29:19 +0200

Brian,                                                                   
                                                                            
   [...snip....]                                                            
   This can have a disasterous effect on ITU-T congestion management at     
   the AS,                                                                  
   if the ASPs were to indicate each SCON received by an ASP to a combined  
   AS                                                                       
   congestion state machine, but there may be cases where an ASP will       
   never                                                                    
   receive one of these SSNM.  Consider the following:                      

                     SG                                                     
                +-----------+                +-----------+                  
                |           |    Assoc 1     |           |                  
                |   SGP1    |----------------|   ASP1    |                  
                |           |\   Assoc 2     |           |                  
                +-----------+ \___________   +-----------+                  
                      |                   \                                 
                +-----------+              \ +-----------+                  
                |           |    Assoc 3    \|           |                  
                |   SGP2    |----------------|   ASP2    |                  
                |           |                |           |                  
                +-----------+                +-----------+                  

   When SGP2 issues a SCON, according to the M3UA spec, it will be sent to  
   APS2                                                                     
   only (because it is only sent to APSs which are active for the AS at     
   the SGP).                                                                
   So ASP1 does not receive SCON and continues sending traffic at full      
   rate to                                                                  
   SGP1.  When the distant point in the network response with TFC, it       
   might again                                                              
   appear at SGP2, only informing ASP2 and traffic is not throttled at      
   ASP1.  If                                                                
   ASP1 is, indeed, responsible for the congestion, part of the SS7         
   network will                                                             
   eventually fail with this approach.                                      
                                                                            
   [TOLGA]If ASP1 is INACTIVE, why is it used to send DATA? If both ASPs    
   are serving the same AS, shouldn´t the user part running on top of them  
   work as a single entity? In such a case, why is SCON arriving via ASP2   
   not enough to execute necessary procedures on user part level? I would   
   think it is the user part not the M3UA at ASP, which throttles traffic   
   when necessary.                                                          

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---

From: "Brian F. G. Bidulock" <[email-masked]>
Date: Tue, 14 Jan 2003 00:44:06 -0700

TOLGA,

TOLGA ASVEREN wrote:                            (Tue, 14 Jan 2003 08:29:19)
>                      SG                                                     

No, both ASP1 and ASP2 are ASP-ACTIVE for the AS.  Its just that SGP2 has
not association with ASP1 and SSNM is stated as being sent on by an SGP
(not by an SG).

If the ASPs deliver SCON to a "combined" view of the AS, then when SGP1
sends SCON to both ASP1 and ASP2 per the procedure, MTP-STATUS will appear
twice at the AS.  For ANSI (with level indicated) this might not be a problem,
but for ITU-T it is: the number of times within an interval that MTP-STATUS
indicating congestion is delivered to an MTP-User such as ISUP affects the
congestion algorithm.  The ASPs cannot correlate the SSNM, because it cannot
due to diagram and the current procedure.

--brian

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