Re: M3UA and SUA recommendations

Siu Chai,
   
  Please look bellow for the answers from my point of view.
   
  / Stanisalv Ivanovich
  

Siu Chai Tho <[email protected]> wrote:
    Hello SIGTRAN community !
   
  I have been reading the responses to questions posted on threads
"Upper boundary of Adaptation Layers" http://www1.ietf.org/mail-archive/web/sigtran/current/msg05691.html
and "Some very fundamental SIGTRAN question" http://www1.ietf.org/mail-archive/web/sigtran/current/msg05771.html
and I wonder if my understanding of SIGTRAN standards is still right:
   
  1) SUA and M3UA define signalling transport of SCCP-/MTP-user traffic over an IP network
  [Stanislav Ivanovich] The specifications do much more than that. They essentialy define a concept of application redundacy which is controlled by ASP SM/TM messages.
   
  2) The terminology "… User Adaptation Layer" (name of the RFCs) seems to define a layer, even though layer boundaries are not mandated to be followed by implementations. I also see that chapter 1.6 describes boundaries of this layer (are these just informative chapters ?). Even though an implementation is free to not use layers, the M3UA/SUA protocol functions are defined by use of a SUA/M3UA layer encapsulating protocol functions such as signalling processes, state machines and other stuff.
   
  [Stanislav Ivanovich] What specifications do tell you is how should signalling processes behave on the external protocol and what is the functionality the prcesses should contain. Internal structure of signalling processes is irrelevant for specifications.
   
   
  3) I understand the concept of signalling processes ASP/IPSP and SGP as entities that are seen as communication endpoints of SUA/M3UA protocol. Is it correct to assume that these concepts only apply within the boundaries described in chapter 1.6 or are these concepts defined across those boundaries i.e. does the N-UNITDATA include ASP/IPSP identification ??
   
  [Stanislav Ivanovich] No! ASP and IPSP are processes which contain user functions what is not the case for SGP. For example SGP-ASP protocol is designed to model communication between MTP3 and MTP3-user function for M3UA or SCCP and SCCP-user function for SUA. So ASP is container into which you load your user function. The essentce of the AS concepts (which make 80% of specifications for both M3UA and SUA) is that it supports application redundancy by means of ASP SM/TM messages.
   
  Thus you have an ASP into which you load a traffic control application and which is represented to SGP as AS ="ISUP for 2-100". Then if you want application redundacy you clone your application so you load it in another process (ASP2) and which connects to SGP for the same AS="ISUP for 2-100". So by means of AS related messages/concepts you control your application reliability by supporting application redundancy.
   
  
E.g. can any SCCP-user run over SUA without knowing about signalling processes (how many, what type, etc.) as long as the upper boundary defined in chapter 1.6.1 is preserved ?
  [Stanislav Ivanovich] Yes, but as I said it is irrelevant for specifications. They only mandate how your user function (ASP) is to behave externally. Nothing else, nothing more.
   
   
   
  4) Is it possible to map (inside  SUA layer) traffic from a single SCCP-user (or MTP-user) instance (SCCP-SAP/MTP-SAP) into several SUA/M3UA communication flows managed by several (local) ASPs as well as mapping traffic from multiple SCCP-user (or MTP-user) instances into a single (local) ASP ? 
   
  [Stanislav Ivanovich] Application granularity (ie. AS representation in SS7 language) is implementation choice thus not subject to specifications. But the specifications allow you to define your applications very flexibly (e.g. ISUP + BICC for DPC=2-100 shall be 1 AS).
   
   
   
  5) Is it possible that multiple signalling processes share the same SCTP endpoint (but different SCTP associations) for sending/receiveing messages ?
    Example : Can I run ASP process (talking to a SGP) and an IPSP (talking to another IPSP) over the same SCTP endpoint ?
  [Stanislav Ivanovich] Yes.
   
   
  6) Is the recommendation of a layered implementation seen as a benefit or best current practice ?
   
  [Stanislav Ivanovich] Again. This is implementation. You cannot answer thuis queston by looking into xxUA specifications but instead by looking into your current SS7 implementation product descriptions, sequence diagrams etc...
  
Thank you
  Joe
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