Subject: [Ieprep] Re: Levels of Priority

From: Scott Bradner <[email-masked]>
Date: Thu, 14 Mar 2002 10:34:14 -0500 (EST)

Ken sez:
> given the existing 5 levels of service for MLPP defined for the 
> telephony world, there would appear to be a requirement to have a 
> corresponding set of 5 levels or labels of signaling for SIP. 

1/ having an ability to transport a priority field to a SIP/PSTN
   gateway so that it can be forwarded to the PSTN makes a lot
   of sense

2/ knowing what to do with such a priority field in a SIP node
   or proxy is another thing altogether

3/ and both are VERY different than marking SIP signaling packets
   with 5 different diffserv markings

4/ and are VERY different than marking SIP voice packets with 5
   different diffserv markings

Scott

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---

From: "Bob Bell" <[email-masked]>
Date: Thu, 14 Mar 2002 10:55:25 -0600

Fred - 

Actually, they are sort of like packet dropping precidence in that if a call of a higher precidence is trying to be established, it can cause a lower precidence call to be terminated to free telephone resources (usually trunks) so that the higher precidence call can be completed.

Bob

>-----Original Message-----
>From: Fred Baker [mailto:[email-masked]]
>Sent: Thursday, 14 March, 2002 9:33 AM
>To: Ken Carlberg
>Cc: Scott Bradner; [email-masked]
>Subject: Re: [Ieprep] Levels of Priority
>
>
>At 07:12 AM 3/14/2002, Ken Carlberg wrote:
>>telephony world
>tell me - what are these five levels of precedence? I would 
>expect that 
>they are precedence in placing calls, not precedence in 
>dropping packets.
>
>

---

From: Fred Baker <[email-masked]>
Date: Thu, 14 Mar 2002 09:39:27 -0800

At 08:55 AM 3/14/2002, Bob Bell wrote:
>Actually, they are sort of like packet dropping precidence in that if a 
>call of a higher precidence is trying to be established, it can cause a 
>lower precidence call to be terminated to free telephone resources 
>(usually trunks) so that the higher precidence call can be completed.

but that's not what they are doing. They are placing the authorized call 
anyway, and then if congestion sets in (which could be in the form of 
synchronization between several data streams resulting from the use of a 
national 8 KHz clock, even in the presence of no other calls) dropping 
packets from the unauthorized call, resulting in a reduction of quality on 
that call.

---

From: Fred Baker <[email-masked]>
Date: Thu, 14 Mar 2002 10:24:48 -0800

At 10:01 AM 3/14/2002, Bob Bell wrote:
>The comment I made was in relationship to MLPP in the phone system. The US 
>public phone systems are prohibited by law from dropping a currently 
>active call in favor of another call. MLPP was developed in the AUTOVON 
>system (US Military) were the prohibition did not exist.

this is an excellent example of the reason to separate the policy from the 
label.

In the US phone system, one could in some manner reserve a few circuits for 
emergency use, and dole those out only to authorized users, and then only 
if non-emergency circuits were unavailable. To do so, one needs an 
authenticated label that says "this is an emergency call", and carries with 
it the necessary credentials and so on. One could also have groups of those 
and some additional policy for the use of those groups.

In AUTOVON, the exact same label could be used with a different policy - go 
ahead and use all of the available circuits for normal telephone service, 
but when such a call is placed, find a circuit to drop and do so.

The device identifies the call and presents the credentials. The network 
decides what policy is applicable and applies it.

But you can only do so if the label is policy-free. It has to say "this is 
a <mumble> call", without any prior expectations of what that might mean to 
the network.

---

From: "King, Kimberly S." <[email-masked]>
Date: Thu, 14 Mar 2002 14:35:05 -0500

All,

Clearly there are many misunderstandings about the MLPP/Assured Service.  A
good deal of these misunderstandings is caused because people haven't listed
their assumptions.  

Are we assuming users assert their own priority, are subject to no call
admission control, and mark their signaling and media streams with their
appropriate code point? (And because there is no call admission control
there is a need for 5 drop probabilities in EF?) 

Or are we assuming there is a call-admission control agent at the CPE
location (In H.323 parlance, this might be an enhanced gatekeeper) that
validates the priority of the call and intercepts incoming / outgoing call
setup messages?  Does any entity maintain call state about those calls
traversing the access link that could preempt a lower priority call when a
higher priority setup message was received? (And therefore all calls have
equal sound quality but the calls carried are those of highest priority.)

As was recently pointed out, before scrambling about the solution, it is
best to define the problem space and the underlying requirements.

Kimberly

-----Original Message-----
From: Bob Bell
To: Fred Baker; Ken Carlberg
Cc: Scott Bradner; [email-masked]
Sent: 3/14/2002 11:55 AM
Subject: RE: [Ieprep] Levels of Priority

Fred - 

Bob

---

From: "Garrity, Jack" <[email-masked]>
Date: Thu, 14 Mar 2002 16:33:22 -0500

Bob,

Sorry, my upcoming comment is not material to what's being discussed -- but
it is not illegal to drop (preempt) a call in progress.  It's simply a
custom.  Like other customs, it's sometimes violated, but not with such
frequency as to raise a commoner's hackles.

If anyone has a legal point, I'd be interested.  My lawyer can chat with
yours.

~~~ Jack ~~~
Work: 703/676-2358 | Fax: 703/848-0299
Home: 703/278-9250 | Cell: 703/508-0065
E-mail: [email-masked]

-----Original Message-----
From: Bob Bell [mailto:[email-masked]]
Sent: Thursday, March 14, 2002 1:02 PM
To: Fred Baker; [email-masked]
Subject: RE: [Ieprep] Levels of Priority

Fred, et. al -

The comment I made was in relationship to MLPP in the phone system. The US
public phone systems are prohibited by law from dropping a currently active
call in favor of another call. MLPP was developed in the AUTOVON system (US
Military) were the prohibition did not exist. I think what they are trying
to accomplish is to preserve the QoS of a higher precidence call at the
expense of the QoS for a lower precidence call. I guess it would make a
level of sense in that you probably wouldn't want the voice call from the
President telling SAC to recall the bombers and stand down the missles to be
so badly garbled that the Commander of SAC thought the President told him to
commit the attack. ;-)

Bob

>Sent: Thursday, 14 March, 2002 10:39 AM
>To: [email-masked]