Subject: [Sigtran] Re: [M3UA] AS state machine sharing between SGPs

From: "Brian F. G. Bidulock" <[email-masked]>
Date: Wed, 22 Feb 2006 15:06:57 -0700

Tolga,

This excerpt should make it clear where the statements in the RFC came from.

It is good to refer to the mail archive when memory fades.

--brian

Sidebottom, Greg [BCNR:7M01:EXCH] wrote:                       (Tue, 15 May 2001 14:31:25)
> 
>    [Greg]  I think it is fair to conclude that having multiple SGPs in an
>    SG  does  not  in  itself  buy  any  extra  functionality  in terms of
>    redundancy  over  the  multiple  SG model.  I think we've been bending
>    over   backwards   in  the  protocol  description  to  accommodate  an
>    implementation  option  (the  "distributed  multi-site  SG"  described
>    above).    So  where  does  this implementation option make sense? - I
>    think the answer is for the case where the signalling between the PSTN
>    and  IP  networks is to go through a single SG with a single SS7 Point
>    code but with site/processor redundancy for the SG.  Paired SGs won' t
>    do  because  two  Point Codes would be required.   I don't really have
>    problem with supporting this case.
> 
>    I  think  we  can  change a few things in the spec to support this but
>    remove some of the confusion that it brings:
> 
>    1)  Simplify the protocol description so it is described as between an
>    SGP  and ASP only.  That is, SCTP associations are always between SGPs
>    and  ASPs.   Today the spec goes back and forth between the SGP and SG
>    terms and adds qualifying text in various places.
> 
>    2)  The  SG  becomes  explicitly  a  virtual  thing  not unlike an AS,
>    containing  one  or more SGPs.  The spec today seems to shade back and
>    forth on whether an SG is a physical thing or not.  Of course if an SG
>    is implemented using a single SGP, then that is fine  2;^)
> 
>    So  a  paired  SG  architecture  is  now  two  SGPs on different hosts
>    represented  to  the  SS7  network  with  a  Point  Code per host.  No
>    coordination  of  MTP3,  SPMC  or  AS/ASP  states  between the SGPs is
>    required.   A  single  distributed  SG  is  the same except that it is
>    represented  to  the  SS7 network with a single SS7 Point Code for the
>    set  of  SGPs.   The  SGPs  SHOULD support MTP3, SPMC and AS/ASP state
>    sharing  and  re-routing  of  traffic  between  the two SGPs.  How the
>    inter-SGP  protocol accomplishes this is not described in the protocol
>    spec.
> 
>    3) The ASPs do not need to know the grouping of SGPs in virtual SGs so
>    they  treat  each  SGP as an independent route out to the SS7 network.
>    But an ASP MAY choose to maintain such knowledge.   The SSNM messaging
>    from  the  SGPs to the ASP is therefore processed independently.  Note
>    that  for  Operators  that choose not to combine SGPs into virtual SGs
>    (i.e.,  use  paired  physical  SGs),  then  nothing has really changed
>    here.    ASPs  that  choose  to  keep  knowledge of SGP groupings into
>    virtual SGs MAY interpret SSNM messaging from one of the SGPs so as to
>    apply  to  all the SGPs in the virtual SG but should only do so if the
>    SGPs coordinate their SSNM messaging to the ASPs.
> 
>    Hope this helps,
> 
>       Greg Sidebottom

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

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