Subject: Re: M3UA : some confusion over SG

From: [email-masked]
Date: Fri, 2 Nov 2001 05:22:05 +0200

resending...

Hi, Brian,

Thanks for your answer.
But other questions...

In the case 1, if SG can route DATA from ASP1 to ASP2 (ASP1 and ASP2 
are both connected directly to SG), then we will never need IPSP to IPSP

case if there is a SG. In this scenario,  these two IPSPs can connect to
SG 
and actually act as ASPs.

Besides, per the M3UA v9's defination:
<snip> 1.2
Signalling Gateway - An SG is a signaling agent that receives/sends SCN 
native signaling at the edge of the IP network [1].

The above texts do not say SG can receive/send non-SCN native signalling
in the middle of the IP network. I think DATA sent from ASP1 to ASP2 via
SG
is not a SCN native signalling, and in this situation the SG does not
sit at the 
edge of the IP network, at least part of the SG sits in the middle of
the IP network.
Did I misunderstanding something? Please correct me.

Best Regards.

Qun Qu

-----Original Message-----
From: ext Brian F. G. Bidulock [mailto:[email-masked]]
Sent: 01. November 2001 16:57
To: sigtran
Subject: Re: M3UA : some confusions over SG

Qun,

[email-masked] wrote:     (Thu, 01 Nov 2001 10:27:11)
> Hi,
> 
> I have some confusions, please correct me.
> 
> 1>  In this scenario, is it possible  that SGP routes
>  DATA from ASP1 to ASP2?
> My answer is NO, ASP1 can deliver DATA to ASP2
>  via IPSP/IPSP case. Why overlay such a function. 
> But I am not sure.
> 
>   ********   SS7   *****************   IP   ********
>   * SEP  *---------*      SGP      *--------* ASP  *
>   ********         *****************        ********
> 
>   +------+         +---------------+        +------+
>   | ISUP |         |     (NIF)     |        | ISUP |
>   +------+         +------+ +------+        +------+
>   | MTP3 |         | MTP3 | | M3UA |        | M3UA |
>   +------|         +------+-+------+        +------+
>   | MTP2 |         | MTP2 | | SCTP |        | SCTP |
>   +------+         +------+ +------+        +------+
>   |  L1  |         |  L1  | |  IP  |        |  IP  |
>   +------+         +------+ +------+        +------+ 
>       |_______________|         |______________|

My answer is YES.  In the following configuration, I don't
think that the SG/STP has a choice not to be able to
transfer messages between PC 10-10-10 and 20-20-20.  This
results in ASP to ASP data transfer via the SG.

                                ______                  
                               /      \                 
                         -----|  ASP1  |  AS PC=10-10-10
            ________    /      \______/                 
           |        |  /                                
     ______| STP/SG | /                                 
          /|        |/                                  
         / |30-30-30|\                                  
        /  |________| \                                 
       /        |      \        ______                  
      /         |       \      /      \                 
                |        -----|  ASP2  |  AS PC=20-20-20
                               \______/                 

> 
> 2> In the following scenario, is it possible that SGP
>  routes DATA from ASP1 to ASP2?
> My answer is YES, but this is because of sccp's GT
>  translation function of SGP, otherwise SGP only route DATA 
> from IP domain to SS7 domain, or vice versa. 
> I am not very sure of this either.
> 
>   ********   SS7   *****************   IP   ********
>   * SEP  *---------*               *--------*      *
>   *  or  *         *      SGP      *        * ASP  *
>   * STP  *         *               *        *      *
>   ********         *****************        ********
> 
>   +------+         +---------------+        +------+
>   | SCCP-|         |     SCCP      |        | SCCP-|
>   | User |         +---------------+        | User |
>   +------+           |   _____   |          +------+
>   | SCCP |           |  |     |  |          | SCCP |
>   +------+         +------+-+------+        +------+
>   | MTP3 |         | MTP3 | | M3UA |        | M3UA |
>   +------|         +------+ +------+        +------+
>   | MTP2 |         | MTP2 | | SCTP |        | SCTP |
>   +------+         +------+ +------+        +------+
>   |  L1  |         |  L1  | |  IP  |        |  IP  |
>   +------+         +------+ +------+        +------+
>       |_______________|         |______________|
> 

SCCP even requires that local SCCP users be able to transfer
messages between themselves via SCCP.  For SUA, this means
that this capability should be supported whether the SCCP
user is local to the SG or remoted to the ASP.  Again, the
answer is YES.  SUA ASPs can send data messages to each other
via the SG.

--brian

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

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From: "Brian F. G. Bidulock" <[email-masked]>
Date: Thu, 1 Nov 2001 23:34:38 -0600

Qun,

Please see comments below...

[email-masked] wrote:                                (Fri, 02 Nov 2001 05:22:05)
> resending...
> 
> Hi, Brian,
> 
> Thanks for your answer.
> But other questions...
> 
> In the case 1, if SG can route DATA from ASP1 to ASP2 (ASP1 and
> ASP2 are both connected directly to SG), then we will never need
> IPSP to IPSP case if there is a SG. In this scenario,  these two
> IPSPs can connect to SG and actually act as ASPs.

Well, I said that ASP1 and ASP2 could communicate via the SG
(where permitted by the SS7 protocol).

If the SG is not an STP, this means that they might actually
communicate via the SS7 network.  Your IPSP SG would have to
have STP MTP transfer/SCCP relay functionality.  Your IPSP
network would look like:

                         ______                             
                        |      |                            
                       /|SG/STP|\                           
                ___   / |______| \   ___                    
               /   \ /     |      \ /   \                   
              | ASP |    C-links   | ASP |                  
               \___/ \   __|___   / \___/                   
                      \ |      | /                          
                       \|SG/STP|/                           
                        |______|                            

Where the ASPs and SGs are connected with SCTP associations
as usual, but the SG/STPs are connected wtih SS7 C-links as
usual.  If you replace the C-links with an SCTP association,
each association is acting like an SS7 linkset.  In that case,
I think you want M2PA.

Aside from the fact that this foolishly overlays and SS7
network over an IP network and demotes SCTP to the role of
a pipe (circuit), it has these centrally located SG/STP boxes
that don't need to be there.  It is better to use the point-to
-point IPSP scenario with say M3UA as:

                ___                  ___                    
               /   \                /   \                   
              | ASP |--------------| ASP |                  
               \___/                \___/                   

avoiding the mangement, domain, ownership, administration,
maintenance, provisioning, capacity sizing, etc... issues
associated with the SG/STP middle boxes and letting IP routers
do their job.
> The above texts do not say SG can receive/send non-SCN native
> signalling in the middle of the IP network. I think DATA sent from
> ASP1 to ASP2 via SG is not a SCN native signalling, and in this
> situation the SG does not sit at the edge of the IP network, at
> least part of the SG sits in the middle of the IP network.  Did I
> misunderstanding something? Please correct me.

That is true, but read the framework document (RFC 2719).  That
document lays out the peer-to-peer architecture without these
middle boxes.  That's the architecture that we all agreed to, and
there doesn't seem to be a reason to alter that now.  We shouldn't
let a little bit of hard work stand in the way of DTRT.

--brian

> You are currently subscribed to sigtran as: [email-masked]

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

---

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From: [email-masked]
Date: Fri, 2 Nov 2001 10:49:48 +0200

Hi, Brian,

Thanks again for your answer. please see comments below...

Best Regards

Qun Qu

>(where permitted by the SS7 protocol).
[Qun]: But SS7 has no concept of ASP. Did you mean the following
scenario, ASP1 communicate to ASP2 via at least two SGs. If so 
I agree with you.
                         ______
                        |      |                            
                       /|SG/STP|                            
                ___   / |__1___|     ___                    
               /   \ /     |        /   \                   
              | ASP |    C-links   | ASP |                  
               \_1_/     __|___   / \_2_/                   
                        |      | /                          
                        |SG/STP|/                           
                        |__2___|          

>have STP MTP transfer/SCCP relay functionality.  Your IPSP

[Qun]  Brian, you confused me. In my first letter, I said SG can 
not route DATA between ASP1 and ASP2 if the SG has not SCCP
functionality. 
ASPs can communicate to each other via IPSP to IPSP case. But you 
said SG can. And now you say it is foolish to overlay such 
functionality. 
    ___     ______      ___  
   /   \   |      |    /   \      
  | ASP |--|SG/STP|---| ASP |     
   \_1_/   |______|    \_2_/     
              |   \
             _|_   \  ___   			   
            /   \   \/   \ 
           | SEP |  | SEP |
            \_1_/    \_n_/ 

Let me make a more typical assumption. In the above image, 
SG connect with SEPs via A-Links. There is no other node in SS7.
This SG has no SCCP functionality.  
M3UA layer in SG receives a DATA from ASP1. 

According to your words, SG can route DATA from ASP1 to ASP2. 
Then M3UA need to decide which is the DATA destination domain 
first, SS7 or local IP domain.( But I cannot find any 
implication of this in the draft.) Besides, if SEP1 is 
unavailable, the SG will send DUNA to ASPs. What will the SG do, 
when ASP1 is unavailable to the SG, if ASP1 and ASP2 communicates 
to each other via this SG.

I agree it is foolish to overlay this functionality to SG, 
while this can be done by IPSP. I think it is better to say 
this clearly in the draft, or exclude this foolish 
functionality off SG. 

>let a little bit of hard work stand in the way of DTRT.

[Qun] Sorry for my ignorance, what does DTRT mean?

---

---

From: "Brian F. G. Bidulock" <[email-masked]>
Date: Fri, 2 Nov 2001 03:45:41 -0600

Qun,

[email-masked] wrote:  (Fri, 02 Nov 2001 10:49:48)

-X-[snip]-X-

> scenario, ASP1 communicate to ASP2 via at least two SGs. If so 

The SG has a concept of an ASP.  SG interworks with SS7.  Why
remove those two associations?  ASP can communicate with more
than one SG.

> said SG can. And now you say it is foolish to overlay such 

Look at it this way:

 PC 10-10-10                             PC 20-20-20  
    ______                                 ______     
   |      |                               |      |    
   |  ASP |                               | ASP  |    
   |______|      ______       ______      |______|    
   |      |     |      |     |      |     |      |    
   | SCTP |-----| SCTP |     | SCTP |-----| SCTP |    
   |______|     |______|     |______|     |______|    
                |      |     |      |                 
                |  SG  |     |  SG  |                 
                |______|     |______|                 
                |      |     |      |                 
                |  NIF |     | NIF  |                 
                |______|     |______|                 
                |      |     |      |                 
                | STP  |-----|  STP |                 
                |______|     |______|                 
                  /               \                   
                 /                 \                  
                /                   \                 
               /                     \                
           ___/                       \___            
          /   \                       /   \           
         | SEP |                     | SEP |          
          \___/                       \___/           
                                                      
      PC 30-30-30                  PC 40-40-40        

In the above diagram it is clearly possible for ASP
representing PC 10-10-10 to send MSU to PC 20-20-20
on another ASP.  M3UA at SG may be unaware that these
are both ASPs.  MSUs may be routed between STPs in the
SS7 network.

Now, why should things be different in the following
case:

       PC 10-10-10                PC 20-20-20          
          ______                    ______             
         |      |                  |      |            
         |  ASP |                  | ASP  |            
         |______|      ______      |______|            
         |      |     |      |     |      |            
         | SCTP |-----| SCTP |-----| SCTP |            
         |______|     |______|     |______|            
                      |      |                         
                      |  SG  |                         
                      |______|                         
                      |      |                         
                      |  NIF |                         
                      |______|                         
                      |      |                         
                      | STP  |                         
                      |______|                         
                        /  \                           
                       /    \                          
                      /      \                         
                     /        \                        
                 ___/          \___                    
                /   \          /   \                   
               | SEP |        | SEP |                  
                \___/          \___/                   
                                                       
            PC 30-30-30     PC 40-40-40                

Certainly PC 10-10-10 can still be permitted to route
MSUs to PC 20-20-20.  Whether that is done within M3UA
at the SG or done within the STP depends on implementation.
M3UA spec cannot tell SS7 STP that it cannot route messages
from PC 10-10-10 to PC 20-20-20.

Now, why should things be different in the following:

       PC 10-10-10                PC 20-20-20          
          ______                    ______             
         |      |                  |      |            
         |  ASP |                  | ASP  |            
         |______|                  |______|            
         |      |                  |      |            
         | SCTP |------------------| SCTP |            
         |______|                  |______|            
         |      |                  |      |            
         |  SG  |                  |  SG  |            
         |______|                  |______|            
         |      |                  |      |            
         | NIF  |                  |  NIF |            
         |______|                  |______|            
         |      |                  |      |            
         |  STP |------------------| STP  |            
         |______|                  |______|            
            \                          /               
             \                        /                
              \                      /                 
               \                    /                  
                \___            ___/                   
                /   \          /   \                   
               | SEP |        | SEP |                  
                \___/          \___/                   
                                                       
            PC 30-30-30     PC 40-40-40                

One cannot conceive of a case where it should not be
possible to send messages between ASPs via an SG or
via the SS7 network.  In many configurations it is not
possible for the M3UA spec to tell the SS7 network
whether it can or cannot route MSUs between point codes.
> this clearly in the draft, or exclude this foolish 

It remains to be seen whether IPSP can do anything.

> [Qun] Sorry for my ignorance, what does DTRT mean?

Doing The Right Thing.

--brian

-X-[snip]-X-

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

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