Subject: RE: [Ieprep] Preemption

From: "Gunn, Janet NE" <[email-masked]>
Date: Wed, 27 Mar 2002 11:17:00 -0500

It doesn't necessarily have to be a single network.  For instance, even
within the Telephony world, a call might be initiated on a GSM wireless
network which supports eMLPP, traverse the (landline) PSTN which carries the
MLPP indicators, but doesn't DO any queueing or pre-emption on the call, and
terminate on a CDMA wireless network which ignores the MLPP indicators. (Or
it could terminate on another GSM wireless network which DOES translate the
indicators from MLPP to eMLPP and acts on them.)
 
To follow your analogy, the call could pre-empt in the originaing GSM
network, and them be blocked in the  (landline) PSTN. 
 
We also can have situations where the call setup queues in one network but
not another. 
 
Yes, I would expect it to be acceptable for the same thing to happen in an
internet (littlei ), sInce this is at least as good as the telephony
network.  But it would be desirable (dependant on the even higher level
protocol of negotiating SLAs between networks) to at least have the
technical possibility of implementing a consistent policy.

-----Original Message-----
From: Stuart (Stu) Goldman [mailto:[email-masked]]
Sent: Wednesday, March 27, 2002 10:58 AM
To: Gunn, Janet NE
Cc: [email-masked]
Subject: Re: [Ieprep] Preemption

Janet, 

I guess I had best ask the question. 

From your wording below it would seem that the model in your mind is that of
a single network, The model in my mind is that a call may cross a series of
networks to reach the termination point. Each network in the path may have a
different policy in regard to preemption. The policy would apply to the
resources used in that particular network. Thus a given call path could be
the result of the policies expressed in each network through which the call
progressed. 

Could then a call preempt in network 1, but be prevented from preempting in
network 2, on its way toward termination in network 3? This would of course
mean that a call had been preempted even though the priority call was not
successfully set up. I think the answer would be yes, and that this would be
acceptable. 

"Gunn, Janet NE" wrote: 

 To clarify- Yes it is a policy decision. The "network authority" may
determine, a priori, the indicator settings  associated with each priority
level- leaving no choice to the user.  Or it may determine a range of
settings that a particular user can chose from.The question is, once the
policy has been established, will the protocol allow  (at a minimum) the
indicators to be transported across the IP network, and (preferably) can the
IP network implement the actions associated with the indicators? 

-----Original Message----- 
From: James M. Polk [ mailto:[email-masked] <mailto:[email-masked]> ] 
Sent: Tuesday, March 26, 2002 6:01 PM 
To: Gunn, Janet NE; [email-masked]'; Ken Carlberg 
Cc: [email-masked] 
Subject: RE: [Ieprep] Preemption 
 
At 04:05 PM 3/26/2002 -0500, Gunn, Janet NE wrote: 

It may be a bit more complicated than that. 

I am not sure about MLPP, but in eMLPP there are THREE indicators (in
addition to level): 
Queueing allowed/Queueing NOT allowed 
CAN pre-empt a lower level call/CANNOT pre-empt a call 
CAN be pre-empted by a higher level call/CANNOT be preempted by another
call, no matter what the priority. 

Typically the "Ordinary" call has the lowest priority, but may neither
pre-empt, nor be pre-empted.

I believe *all* you listed above are policy decisions that are local in
nature. If left to the end-users, they would choose "cannot preempt" every
time. Perhaps this could be dealt with via user authentication as to whether
a call from that user is or is not allowed to be preempted.... 

It seems to me that there MAY be a need for all three indicators in the
context of an IP network also.

starting to get complicated with 3 indicators 

The indicators MIGHT be tied directly to the level, but (especially if a
single IP network is transporting calls from more than one carrier) might
also be set on a call by call basis. So, it would be desirable for the
protocol to have a way of capturing all 3 indicators. 

Janet 

-----Original Message----- 

************************************* 
"People generally demand more respect for their own rights than they are
willing to allow for others"

 James M. Polk 
Consulting Engineer 
Office of the CTO 

Cisco Systems 
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w) 972.813.5208 
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---

From: Alistair Munro <[email-masked]>
Date: Wed, 27 Mar 2002 16:44:41 +0000

Dear All,

I'm new to this list but not to GSM network design and implementation.

It's often "impossible" to transfer "standard" semantics across
inter-network interworking points because of design decisions made by
implementors of network elements and operational policies. Janet
describes one of many such situations. Isn't this one of the best
practice issues we are trying to expose?

I'm not sure if this thread is in scope - it's very useful but I can't
match it to the charter.

Regards,

Alistair

> It doesn't necessarily have to be a single network.  For instance,
> even within the Telephony world, a call might be initiated on a GSM
> wireless network which supports eMLPP, traverse the (landline) PSTN
> which carries the MLPP indicators, but doesn't DO any queueing or
> pre-emption on the call, and terminate on a CDMA wireless network
> which ignores the MLPP indicators. (Or it could terminate on another
> GSM wireless network which DOES translate the indicators from MLPP to
> eMLPP and acts on them.)To follow your analogy, the call could
> pre-empt in the originaing GSM network, and them be blocked in the
> (landline) PSTN. We also can have situations where the call setup
> queues in one network but not another. Yes, I would expect it to be
> acceptable for the same thing to happen in an internet (littlei ),
> sInce this is at least as good as the telephony network.  But it would
> be desirable (dependant on the even higher level protocol of
> negotiating SLAs between networks) to at least have the technical
> possibility of implementing a consistent policy.

---

From: Ken Carlberg <[email-masked]>
Date: Wed, 27 Mar 2002 22:01:08 +0000

> I'm not sure if this thread is in scope - it's very useful but I can't match
> it to the charter. 

at least from my perspective, don't be shy about discussing topics that
are generally related to the Charter.  its just that with specific
IEPREP related drafts, we may be a bit more careful about what goes in
(or out) of them.

-ken

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---

From: Alistair Munro <[email-masked]>
Date: Thu, 28 Mar 2002 14:11:53 +0000

Hi Ken,

> IEPREP related drafts, we may be a bit more careful about what goes in

I wonder if anyone on the operational side of PSTN, ISDN, GSM has any comment on
the preemption issue? It would certainly help my understanding of practice.

Regards,

Alistair

---

From: Fred Baker <[email-masked]>
Date: Thu, 28 Mar 2002 21:02:03 -0800

>I'm not sure if this thread is in scope - it's very useful but I can't 

I would deem it in scope. We are supposed to make recommendations 
concerning "best practices" (by which we mean "the best we can think of", 
not "the best currently employed"), and set up requirements for any 
protocols that we think may need to be significantly changed from current 
definition or practice. This applies both to telephony and data traffic 
used in an emergency setting.

Janet, it sounds to me like you have a pretty good handle on some of the 
issues here.

(a)Do you feel that they are adequately covered in the framework draft? if 
not, could you propose language to go into it covering the issues?
(b)Do you see specific requirements not being met in industry standard 
protocols? If so, do you feel that either Hal Folts white paper or my draft 
cover the issues, and if so specifically which sections? In not, would you 
be willing to suggest text to cover those issues?

At 11:31 AM 3/27/2002, Gunn, Janet NE wrote:
>But I do think it is useful to identify the FUNCTIONALITY that is 
>available in the Telephony domain, that is (or may be) used by Emergengy 
>Preparedness Systems, and to explore what kind of protocol support would 
>be needed  to provide equivalent functionality in the Internet (or an 
>internet).

Yes. Specifically an example of this has been requested by the Area 
Director - we have been asked to provide requirements for the 
implementation of MLPP in SIP. I would expect that this would include

(a) identifying what problem it solves (such as "it exists in the PSTN and 
we need to be able to carry the signalling across an Internet island, 
whether we actually implement it or not", or "research/experience 
documented at <place> demonstrates that this set of functionality is 
materially helpful in solving <specified> class of problems")
(b) identifying two or more implementation approaches (such as 
authorization us use of an overhead space in GETS and preemption of lower 
priority calls in AutoVon),
(c) identifying what is the minimum necessary to implement the 
functionality in an Internet domain, and
(d) identifying what is necessary to carry the signaling from one 
PSTN/GSM/etc domain to another PSTN/GSM/etc domain across an internet domain

It would also include identification of practices that are not helpful and 
should not be replicated in the Internet, if appropriate.

---

From: "Stuart (Stu) Goldman" <[email-masked]>
Date: Fri, 29 Mar 2002 10:36:37 -0700

Alistair,

I am not in operations, but I can offer is that in the USA circuit switched PSTN,
preemption is not done.

> Alistair Munro wrote:

---

From: Ken Carlberg <[email-masked]>
Date: Fri, 29 Mar 2002 21:37:21 +0000

> I wonder if anyone on the operational side of PSTN, ISDN, GSM has any
> comment on the preemption issue? It would certainly help my
> understanding of practice.

from my experience, the preemption that has been deployed is almost
exclusive to private networks, and I'll have to pass on comments.

my understanding is that the UK, under the guidance of Oftel, has
deployed multiple priority indicators for their cellular/mobile
telephony service, but i don't believe preemption is part of that
service.  i'll look into that.

-ken