Subject: [Sip] Reserving hardware resources in SIP to ISUP mapping

From: "El Moussawi, Ali" <[email-masked]>
Date: Thu, 2 Oct 2003 11:37:09 +0200

Hi all,
My question is about the meaning of the term "reserve hardware
resources" in SIP to ISUP mapping RFC 3398.
There is several steps needed to establish media path :
1 - Asking the MG (Media Gateway) to reserve a PSTN trunk and slot in
receive only mode.
2 - Asking the MG to reserve a RTP path in receive only.
3 - Modifying the PSTN circuit of 1 to send and receive.
4 - Modifying the RTP path of 2 to send and receive.

The RFC 3398 text doesn't give details on when to perform these actions,
but the call flows diagrams give suggestion on how to do it, and there
is sometimes a divergence. For example, in 7.1.1, IAM is sent before
reserving CIC, while 7.2.1 said the opposite (and in deed IAM can't be
sent without a CIC).

I see two ways of solving this. In SIP to ISUP case for instance
* First way :
On INVITE received, steps 1 and 2 are taken, then IAM is sent to PSTN
network.
Later on, when ANM is received, steps 3 and 4 are taken, then 200 OK is
sent to SIP network.

* Second way :
On INVITE received, setp 1 is taken. Then IAM is sent to PSTN network,
then step 2 is taken.
Later on, when ANM is received, steps 3 is taken, then 200 OK is sent to
SIP network. Finally step 4 is taken (no need to wait for ACK from the
SIP network ? ).

Which one is better acording to you ?
Thanks a lot,

Ali

---

From: "Peterson, Jon" <[email-masked]>
Date: Thu, 2 Oct 2003 21:16:17 -0500

Some notes below.
 
Jon Peterson
NeuStar, Inc.

-----Original Message-----
From: El Moussawi, Ali [mailto:[email-masked]]
Sent: Thursday, October 02, 2003 2:37 AM
To: [email-masked]
Subject: [Sip] Reserving hardware resources in SIP to ISUP mapping

Hi all, 
My question is about the meaning of the term "reserve hardware resources" in
SIP to ISUP mapping RFC 3398. 
There is several steps needed to establish media path : 
1 - Asking the MG (Media Gateway) to reserve a PSTN trunk and slot in
receive only mode. 
2 - Asking the MG to reserve a RTP path in receive only. 
3 - Modifying the PSTN circuit of 1 to send and receive. 
4 - Modifying the RTP path of 2 to send and receive.  

<JFP> I think that by the term "reserve hardware resources" we meant more
the acquisition of those DSP resources inside a gateway that are integral to
the process described in 3 and 4. Or we might have, if the term "reserve
hardware resources" actually appeared in RFC3398, which it doesn't.
"reserve" appears in 7.2.1 and 8.2.1 - as far as I know, those are the only
instances. 8.2.1 mentions DSP resource acquisition. 7.2.1 does mention TCIC
selection as a necessary prerequisite to IAM transmission. </JFP> 

The RFC 3398 text doesn't give details on when to perform these actions, but
the call flows diagrams give suggestion on how to do it, and there is
sometimes a divergence. For example, in 7.1.1, IAM is sent before reserving
CIC, while 7.2.1 said the opposite (and in deed IAM can't be sent without a
CIC). 

<JFP> In 7.1.1, an IAM is sent before reserving the CIC? Where does it say
that, exactly? 7.1.1 doesn't even talk  about any sort of reservation. In
fact, it passes over in silence when any necessary 'resources' are acquired.
</JFP> 

I see two ways of solving this. In SIP to ISUP case for instance 
* First way : 
On INVITE received, steps 1 and 2 are taken, then IAM is sent to PSTN
network. 
Later on, when ANM is received, steps 3 and 4 are taken, then 200 OK is sent
to SIP network. 

* Second way : 
On INVITE received, setp 1 is taken. Then IAM is sent to PSTN network, then
step 2 is taken. 
Later on, when ANM is received, steps 3 is taken, then 200 OK is sent to SIP
network. Finally step 4 is taken (no need to wait for ACK from the SIP
network ? ).

<JFP> Unfortunately, what you're really asking about here is "early media".
You want to know when the gateway should begin transmission of media in the
backwards direction in SIP-ISUP cases, and when it should transition to
bidirectional media. I might point you to section 5.5 of RFC3398, and
moreover to:

http://www.ietf.org/internet-drafts/draft-camarillo-sipping-early-media-02.t
xt
<http://www.ietf.org/internet-drafts/draft-camarillo-sipping-early-media-02.
txt>  

</JFP> 

 Thanks a lot, 

Ali