Subject: Re: DHCP Option for Call Control Servers

From: Henry Houh <[email-masked]>
Date: Tue, 2 Feb 1999 18:41:29 -0500 (EST)

Rich Woundy <[email-masked]> writes:

>  These hosts are often called "residential gateways". It does make
>  sense for most of these residential gateways to obtain call
>  gateway/call agent information from DHCP. Many of these gateways
>  may be devices such as cable modems that already obtain
>  configuration from DHCP (other examples of residential gateways
>  include set-top boxes, xDSL devices, and broadband wireless
>  devices).

>  While I like the concept of your draft, this draft looks like it
>  supports "NBX Call Control Servers" only, which I assume is a
>  vendor product. What protocol(s) do these NBX servers support? I
>  would think that the Internet community needs support in this realm
>  for more standard VoIP protocols, such as H.323 and MGCP, as well
>  as other up-and-coming protocols (DOSA?).

Yes, the sub-option in the draft is for a specific vendor.  NBX (my
company) has a proprietary signaling protocol.  I really would like to
include other protocols as more sub-fields, but I don't know what else
to put in.  That's also why I tried to add a section on adding new
sub-option fields.

Someone on DHC mentioned using vendor OUIs to identify who owns a
sub-option field for another option.  That might be a good thing to do
here, if we also define specific OUIs that represent standard
protocols.

>  While I am not a VoIP expert, I do know that there are several special
>  configuration considerations for MGCP:

>  1. The call agents are identified by *domain names*, not by IP addresses.

Yes, in MGCP, the call agents are identified by their domain names for
improved reliability.  From perspective of Call Agents locating other
Call Agents, it's surely better this way, but that doesn't mean that
we must pass domain names of the Call Agent in DHCP options during the
boot-up process of a gateway.

I believe that from the boot-up perspective of a gateway, it's better
to use the network address.  This network address is controlled by the
administrator of the DHCP server serving the gateway, same as all
other server addresses that may be returned as a DHCP option.  Plus,
not all gateway devices will be capable of performing DNS queries at
boot-up time - or at all ever (maybe the MGC does this for you in some
systems to lower the gateway costs).

I tried to follow the standard options as closely as possible.  In all
the server type options listed in RFC 2132, the servers are identified
by IP addresses, for the reason above, I believe (someone interject if
they know the history).

>  Should we work on this together? Who else is interested?

Sounds good to me, anyone else interested?

>  -- Rich

>  P.S. More information about MGCP can be found at:

>  http://search.ietf.org/internet-drafts/draft-huitema-mgcp-v0r1-02.txt
>  http://search.ietf.org/internet-drafts/draft-huitema-mgcp-flows-00.txt
>  http://sgcp.bellcore.com

Wen-Ping Ying <[email-masked]> also responded:

>  Digitmaps are passed as part of the MGCP protocol
>  (EndpointConfiguration) and should not require DHCP
>  provisioning. Call Agents (MGC) and Gateway names are stored as
>  part of the DNS and may not need DHCP provisioning either. I don't
>  think MGCP provides a mechanism to allow a gateway to report to the
>  Call Agent/MGC the resources it manages. With this, there may be a
>  registration process required before an MGC can manage and control
>  the calls to/from the residential gateways.

I'm somewhat familiar with MGCP/SGCP and have been following megaco,
but I'm missing the part where the gateway "boots up" and figures out
which Media Gateway Controller to bind to.  I think that's why this is
necessary.  

Say your cable company comes in and installs a new cable box that your
phone plugs into.  You turn your cable box on, and maybe it already
uses DHCP to get an IP address, so we also add the call control server
option to get a MGC IP address as well.  

I'm not sure how gateway names being stored in the DNS helps the MGC
find the cable box residential gateway when it's turned on.  Shouldn't
it be up the the cable box to register with the MGC as opposed to the
MGC polling every device in a DNS domain?  You turn on the cable box,
it gets the MGC IP address via DHCP (no DNS indirection necessary
here), it notifies the MGC it has just been turned on, and then the
MGC sends it configuration information, including its own domain name,
digit collection string and such.

Comments?

Henry