Subject: [Speermint] LUF vs. LF

From: Daryl Malas <[email-masked]>
Date: Fri, 14 Dec 2007 14:18:25 -0700

The topic of the two terms Look-up Function (LUF) and Location Function
(LF) has come up a number of times during and post-Vancouver.  I would
like to present my opinion of these terms and their definitions.

Look-up Function -

This term defines the mechanism for looking up information to determine
the next hop path for sending a SIP request to a peer.  Examples of this
mechanism is ENUM, DNS (host or domain resolution to an IP address), SIP
Proxy (acting as a Redirect server).  This function is purely the
determination of the appropriate mechanism for the internal or assisted
(and/or Federation) databases of record for peering.

Location Function -

This term defines the method for deriving the information.  Although
this truely takes place within the protocol mechanism, the term
indicates an additional function in the peering process.  This also
encompasses defining the fact the associated method may use a local or
assisted entity for providing the database of record for peering.

I personally believe we could combine these two terms into a single
"Location Function", but some have argued the granularity provides
clarity.

Please comment, as I believe, this is the last remaining sticky point in
the terminology draft.

Thanks...--Daryl

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From: "Elwell, John" <[email-masked]>
Date: Mon, 17 Dec 2007 07:26:36 +0000

Daryl,

Thanks for raising this on the list, because it was I who expressed
concerns to you on this subject.

I think it is extremely unlikely that an average reader would
understand, from the present definitions of LF and LUF, the meanings you
have described below. Therefore something has to be done.

My preference would be just to define LF. Use of the term LUF in other
drafts is very marginal. The use cases draft talks about "LF and LUF" in
several places, but does not make a distinction - I think it could just
refer to LF. The architecture draft does not mention "LUF". Therefore I
don't see a compelling reason to have a definition of LUF.

John

> -----Original Message-----
> From: Daryl Malas [mailto:[email-masked]] 
> Sent: 14 December 2007 21:18
> To: [email-masked]
> Subject: [Speermint] LUF vs. LF
>

---

From: David Schwartz <[email-masked]>
Date: Mon, 17 Dec 2007 10:48:41 +0200

Hi John.

If indeed LUF is scarcely used in other drafts than I would say the  
problem is there and not with maintaining this definition in the  
terminology draft. I need to re-read the use case draft since the  
draft I wrote which was incorporated into the consolidated use-case  
draft clearly had such a function and this needs to be recaptured.

The definitions as they appear in .14 are as follows:

4.3.1. Look-Up Function

    The Look-Up Function (LUF) provides a mechanism for querying an
    internal and/or external database, which maintains a list of peered
    host domains.

4.3.2. Location Function

    The Location Function (LF) develops SED by discovering the Signaling
    Function (SF), and SF's reachable host (IP Address and port).

What is unclear about this? Why do we keep circling the wagons on this?

D.

On Dec 17, 2007, at 9:26 AM, Elwell, John wrote:

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From: "Elwell, John" <[email-masked]>
Date: Mon, 17 Dec 2007 09:27:36 +0000

David,

There are several things that are unclear - see below. If other people
on this list come forward and say that the definitions are perfectly
clear, then I guess I will have to back down. But to me it seems there
are just a few of us, talking at cross purposes, and this gives me an
uneasy feeling about the maturity of the drafts.

John 

> From: David Schwartz [mailto:[email-masked]] 
> Sent: 17 December 2007 08:49
> To: Elwell, John
> Cc: Daryl Malas; [email-masked]
> Subject: Re: [Speermint] LUF vs. LF
> 
> Hi John.
> 
[JRE] What is the input to the query, and what is the output from the
query? Without this information the definition is far too vague. Is the
input to the query a domain, and it looks to see if that domain is in
the list and answers yes/no and perhaps also responds with other
information about that domain? Or is the input a SIP URI or some other
form of target address and the output the domain that can be used to
reach that target? I believe it is the latter, but the definition
certainly does not tell me that.

>     Function (SF), and SF's reachable host (IP Address and port).
[JRE] What is the input to the discovery process?
Also, what is the relationship between LUF and LF. I thought at first
that the LUF was performed first, and the output from the LUF would be
the input (or one of the inputs) to the LF. Daryl tells me I am wrong -
that the LUF is part of the LF, or more precisely, the LUF is a
mechanism that the LF uses.

---

From: "Lee, Yiu" <[email-masked]>
Date: Mon, 17 Dec 2007 04:45:53 -0500

John,

I think LUF was defined to allow some Assisted SSP to provide only
registry service. My understanding is many SSP can form a federation
where a common registry can translate some input (not defined) to a
routable AOR. The LUF only returns an AOR. The LF will take the AOR and
determine the target proxy to route the session to. Even thought most
people don't see the difference, but in fact these are two different
procedures. I agree that most people don't see the difference. If we
consolidate these two terms into one function, how do you suggest the
text to describe the new LF?

Thanks,
Yiu

-----Original Message-----
From: Elwell, John [mailto:[email-masked]] 
Sent: Monday, December 17, 2007 4:28 AM
To: David Schwartz
Cc: [email-masked]
Subject: RE: [Speermint] LUF vs. LF

David,

John 

> > understand, from the present definitions of LF and LUF, the meanings

> > you have described below. Therefore something has to be done.
> >
> > drafts is very marginal. The use cases draft talks about "LF and 
> > LUF" in several places, but does not make a distinction - I think it

> > could just refer to LF. The architecture draft does not mention 
> > "LUF".
> > Therefore I
> >> (LF) has come up a number of times during and post-Vancouver.  I 
> >> would like to present my opinion of these terms and their 
> >> definitions.
> >>
> >> Look-up Function -
> >>
> >> This term defines the mechanism for looking up information to 
> >> determine the next hop path for sending a SIP request to a peer.
> >> Examples of this
> >> mechanism is ENUM, DNS (host or domain resolution to an IP 
> >> address), SIP Proxy (acting as a Redirect server).  This function 
> >> is purely the determination of the appropriate mechanism for the 
> >> internal or assisted (and/or Federation) databases of record for 
> >> peering.
> >>
> >> Location Function -
> >>

> >> encompasses defining the fact the associated method may use a local

> >> or assisted entity for providing the database of record for 
> >> peering.
> >>

> >> Please comment, as I believe, this is the last remaining sticky 
> >> point in the terminology draft.
> >>
> >> Thanks...--Daryl
> >>
> >>

---

From: "Elwell, John" <[email-masked]>
Date: Mon, 17 Dec 2007 13:50:55 +0000

Yiu,

In fact my initial understanding was in line with your understanding
below. However, in trying to clarify if further in that direction, I
encountered a different opinion.

John 

> From: Lee, Yiu [mailto:[email-masked]] 
> Sent: 17 December 2007 09:46
> To: Elwell, John; David Schwartz
> Cc: [email-masked]

---

From: "Rodrig, Benny (Benny)" <[email-masked]>
Date: Mon, 17 Dec 2007 10:14:59 -0500

John,

My understanding of this was that the LUF could get e.g. an E164 number
and return a domain name and then the LF follows taking the domain name
as input and returning how to route to it (i.e. SED). In many cases they
would be combined, but I suppose there could be cases where you go to
one mechanism (e.g. 'assisting') with a number to find it belongs to
example.com and then you go to another mechanism (e.g. internal) to find
how to route to example.com. I don't know if this is really what David
meant. Under this interpretation, if you're starting with e.g.
[email-masked] you don't really need the LUF, or you can say it is
trivial. You go straight to LF.

Benny

-----Original Message-----
From: Elwell, John [mailto:[email-masked]] 
Sent: Monday, December 17, 2007 8:51 AM
To: Lee, Yiu; David Schwartz
Cc: [email-masked]
Subject: RE: [Speermint] LUF vs. LF

Yiu,

John 

> routable AOR. The LUF only returns an AOR. The LF will take the AOR 
> and determine the target proxy to route the session to. Even thought 
> most people don't see the difference, but in fact these are two 
> different procedures. I agree that most people don't see the 
> difference. If we consolidate these two terms into one function, how 
> do you suggest the text to describe the new LF?
> 
> Thanks,
> Yiu
> 

> query? Without this information the definition is far too vague. Is 
> the input to the query a domain, and it looks to see if that domain is

> in the list and answers yes/no and perhaps also responds with other 

> the input (or one of the inputs) to the LF. Daryl tells me I am wrong 
> - that the LUF is part of the LF, or more precisely, the LUF is a

---

From: "Elwell, John" <[email-masked]>
Date: Mon, 17 Dec 2007 16:14:53 +0000

Benny,

Quite so, but the definitions don't make this clear and I am not sure
everyone agrees.

John 

> From: Rodrig, Benny (Benny) [mailto:[email-masked]] 
> Sent: 17 December 2007 15:15
> To: Elwell, John; Lee, Yiu; David Schwartz
> Cc: [email-masked]

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From: Otmar Lendl <[email-masked]>
Date: Mon, 17 Dec 2007 21:28:43 +0100

John,

that's my impression as well. IMHO we just need to pepper the
terminology draft with a few examples and it should be clearer
whether we're all interpreting the definitions the same way.

/ol
-- 
// Otmar Lendl <[email-masked]>, T: +43 1 5056416 - 33, F: - 933
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