Subject: Re: DHCP option tags for SIP

From: James Kempf <[email-masked]>
Date: Sun, 20 Feb 2000 17:02:58 -0800 (PST)

>1) if I have a residential gateway, say, which runs 
>   SIP on its two POTS lines, with SLP can I find 
>   the (different) first hop proxies for each port? 

I'm not quite sure I understand the scenerio (I'm new to SIP, sorry).
What is looking for the first hop proxy, the residental gateway?
My feeling is that the answer to this must be "no" because
if the gateway is sitting on a POTS line, then the protocol on
the POTS line must be something other than IP. Or do you mean
having a phone in the house find the first hop proxy which would
be the residential gateway? If that's the case, then because
the scenerio states that there are different first hop proxies,
there must be two residential gateways, or? If that's the case,
then the phone could select a gateway using SLP, if the service
advertisements for the gateways distinguished them in some way.

>2) Suppose I have some IP phones at home which are
>   gateway'd through my home SIP proxy which allow
>   me to set up local dial plans. Would SLP be adequate
>   to configure the 1) phones 2) my home proxy for learning
>   their next hope proxy?
>

Let me speculate about the intent of this question (please correct
me if I'm wrong). Is the intent of this question to see whether
SLP can configure a home phone with a custom dial plan? If so,
then I would say that that is probably not the right use for
SLP. I would venture to guess that would involve some kind of
negotiation with the telephone company's subscriber database.
I would presume a AAA protocol would get involved somehow, to
authenticate your phone for access to the dial plan.
As for 1), this depends on what you want to configure the phones
with. You can't configure them with an IP address, because you
need an IP address to use SLP. You could configure them with
basic stuff like outbound proxy address. Similarly for 2), you could
have the proxy find the next hop proxy using SLP if you wanted.

>I'm not trying to diss the idea, but SLP seems to
>have been written with enterprises in mind --
>which is fine -- but the more complicated
>situations will probably need to be considered
>where we start splitting up the monolithicly
>administered network into various administrative
>domains, and differently administered services.
>

There is nothing specific to the enterprise in SLP's design, though
it is not designed to be used on the Internet (large "I" here).
SLP has some features for home-style networks, like using multicast
in the simplest case. As Jonathan points out, it is primarily of
value when the client has choices for a server. If you take a look
at the SLP template draft we submitted the other day, you can get
an idea of the kinds of attributes we are proposing for distinguishing
servers.

		jak

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From: Francois Menard List Account <[email-masked]>
Date: Mon, 21 Feb 2000 08:29:37 -0500 (EST)

The question has to do with generic means for capabilities exchange
between two devices, using a common set of semantics.

I can easily see how an XML DTD for a specific industry (i.e. in some
cases Internet Telephony for SIP), could be used to agree on capabilities  
parameters of other UA's, Proxy Servers, PSTN Gateways & RTP Mixers.

In this sense, and to answer some private concerns of others, I feel that
SLP is a better end-to-end protocol than DHCP in order to perform these
tasks.  I dont like the approach, of "if all you want to do is pass on the
IP address of the first Proxy Server, then DHCP is fine". To me this
violates the notion of end-to-end capabilities exchange (and gives all the
power to a mighty-god Proxy server). 

To this end, my proposal for an SLP DTD for SIP appliances could 
resembles the Call Processing Language.  Maybe the XML DTD
for CPL (with some tweaks) could be used for caps exchange using SLP.

For example, Mediatrix has a device which is very unique, i.e. a VoIP
gateway with more RTP mixing capabilties than end-points, 3 fxs ports and
one fxs/fxo port.  Being able to advertise this functionality through SLP
is a very unique situation.

Hence my warm welcome of SLP to the SIP scene.  Its simply better than all
those nasty broadcast packets on LANs using DHCP.

-=Francois=-

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From: Jonathan Rosenberg <[email-masked]>
Date: Mon, 21 Feb 2000 10:36:08 -0500

I'd like to try and keep this discussion focused in order to quickly
answer the following question:

  Should we "fast track" a DHCP options for finding a SIP server
document?

Neither DHCP nor SLP are capable of providing complicated application
layer configuration parameters, such as dialing plans or addresses.
Neither are good for capabilities exchange, which is something different
altogether IMHO. With DHCP, you can at least find the server to register
to, and that may provide much of this information in registration
responses. Certainly, it doesn't preclude using DHCP to point to a
specialized configuration server down the road either.

Both DHCP and SLP will do the same thing - get you the adress of a
server. With SLP, you can be picky about which server you want, based on
its capabilities (like ability to support CPL). I see roles for both.

-Jonathan R.

-- 
Jonathan D. Rosenberg                       200 Executive Drive
Chief Scientist                             Suite 120 
dynamicsoft                                 West Orange, NJ 07052
[email-masked]                     FAX:   (732) 741-4778
http://www.cs.columbia.edu/~jdrosen         PHONE: (732) 741-7244
http://www.dynamicsoft.com

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From: Francois Menard List Account <[email-masked]>
Date: Tue, 22 Feb 2000 01:41:15 -0500 (EST)

I also think that it ought to be possible to do it with DHCP.

I agree with Jonathan here.

-=Francois=-

> Neither are good for capabilities exchange, which is something different

James, do you have a rebuttal for this ?

-=Francois=-