Subject: Re: [SIP] Overlap call setup

From: "Keith Robinson" <[email-masked]>
Date: Wed, 7 Feb 2001 11:28:37 +0000

Vendors could mandate that their SIP/PSTN gateways will always block up digits
and do everything en bloc; thats fine.

I  was raising issues I had with the mechanism for supporting overlap sending if
it was required to be performed because a particular administration wants to
use overlap signalling.

Regards,

Keith.

"Brian F. G. Bidulock" <[email-masked]> on 07/02/2001 06:49:08

Please respond to [email-masked]

                                                              

 To:      Keith Robinson/MAIN/MC1@MCMAIN                      
                                                              
 cc:      [email-masked],                  
          [email-masked],                  
          [email-masked],                        
          [email-masked], [email-masked]  

 Subject: Re: [SIP] Overlap call setup                        

Keith,

I hope that I don't seem too obtuse, but why are you wanting to process
overlap sending through SIP in the first place?  Why doesn't your
inter-working point merely collect all of the SAMs before it launches
the INVITE?

As I'm sure you are aware, overlap sending was just a way of getting
better performance through an antiquated PSTN by overlapping digit
analysis and routing with out-pusling.  A terminating switch (or a
switch at an inter-working point) should never SAM anyway!  Where are
you connecting your box in the PSTN that you are going to get overlap
sending?

Even if you do receive SAMs, what do you hope to achieve by attempting
to process them through the SIP network?

The only reason for including SAMs in ISUP was for backwards
compatibility with CAS trunking.  Even in the ISUP-SIP-ISUP case, the
fact that you have an ISUP switch on either side means that the
performance should be sufficient to do en bloc sending across the
inter-working.

As you know, the call cannot be connected until after the last digit is
sent, anyway.  Overlap sending was a way to remove the digit out-pulsing
delay from each CAS trunking hop and improve post-dial delay (a critical
PSTN grade of service parameter).  Unless you have an inter-working
point (CAS trunk) on both sides of the connection (e.g., CAS-ISUP-SIP-ISUP-CAS)
and a lot of them at that (i.e.  CAS-CAS-CAS-ISUP-SIP-ISUP-CAS-CAS-CAS)
there is no reason for overlap sending.

Even still, in this arrangement, I don't see the SIP hop as being able
to make routing decisions on the call (unless it is a proxy) until the
entire number is received.  Also, I would question the commercial
viability of:
                CAS-CAS-CAS-ISUP-SIP-ISUP-CAS-CAS-CAS

anyway.

Could you provide a practical example of when this would be necessary
and en bloc sending would not be sufficient at the inter-working point?

--Brian

Keith Robinson wrote:                         (Tue, 06 Feb 2001 16:55:39)
>
>
> Attached is an earlier posting I raised highlighting my concerns with some
> of the mechanisms outlined in the sip-isup document. This is the source of
> recent discussions.
>
> Regards,
>
> K. Robinson
[snip]

--
Brian F. G. Bidulock    ¦ The reasonable man adapts himself to the ¦
[email-masked]    ¦ world; the unreasonable one persists in  ¦
http://www.openss7.org/ ¦ trying  to adapt the  world  to himself. ¦
                        ¦ Therefore  all  progress  depends on the ¦
                        ¦ unreasonable man. -- George Bernard Shaw ¦

---

From: Gonzalo Camarillo <[email-masked]>
Date: Wed, 07 Feb 2001 17:30:28 +0200

Hello,

The idea of using always en bloc was present in the first version of the
draft. However, when I presented in DC (some IETFs ago), folks wanted
overlap signalling to be present also in the draft. That's why we
developed such a mechanism.

Anyway, I agree that it will not be used a lot. However, it is good to
discuss the open issues related to the mechanism to try to resolve all
of them.

Regards,

Gonzalo

Keith Robinson wrote:
>   ------------------------------------------------------------------------
> 
> Keith,
> 

-- 
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