[SIPForum-discussion] LPN and SIP

Thu Jul 28 03:50:08 UTC 2005

Rick --

I'm not speaking on behalf of a service provider, so this is merely  
an informed opinion.

I'm going to re-state some of what you said as a base on which to add  
my thoughts.

Let's use real-company examples.  Assume our user Joe is a Vonage  
customer, and gets this SIP URI from Vonage:
    joe at vonage.com

Then, let's presume Joe moves providers to, say, Verizon where his  
new URI would be:
    joe at verizon.net  (for example)

It's rational to make the case that Vonage "owns" the LHS of the  
Vonage URI, based on the precedent of how it works with email (as you  
said.)  To explain further, assume I have an email address  
jay at earthlink.net.  In order for me to have Earthlink continue to  
process my email (which might, or might not include forwarding to  
another account, e.g. a Gmail account named jay at gmail.com), I must  
maintain my business relationship with Earthlink.  When I terminate  
that relationship, the URI jay at earthlink.net "goes back" to Earthlink  
for possible use by somebody else with the name Jay.  This would tend  
to suggest that a user must have a relationship with a SIP service  
provider in order to continue to use the LHS of the URL they get from  
that service provider.

As you said, however, SIP Redirect is a goodie we have in the SIP  
world that might help us through the shortcomings of email.  Using  
the illustration above, Vonage could choose to let you set a SIP  
"forwarding" option.  On receipt on an INVITE to your account at  
Vonage, their SIP server could send back a Redirect to your  
configured forwarding target (e.g. jay at verizon.net).

While this mechanism exists in the protocol design, the key is that  
Vonage must choose to provide this, along with setting the terms on  
which they might offer it.  E.g. they might want you to remain a full- 
paying Vonage subscriber in order to get them to send a redirect.   
(They could, of course, also just invent an offering that costs a  
mere couple of bucks a year that will *only* sends a redirect for any  
INVITE received at Joe's "old" address.)

The way around this might be to take this last bit one step farther.   
If there were a service provider who offered a global "Redirect  
service," we might have a way out.  Presume this service can provide  
you a "SIP URI for life," that you then give to people as "your" SIP  
URI.  All your INVITEs go here, but this service provider exists  
solely to issue a Redirect to your "actual" (configured) SIP service  
provider of the moment.  (Note that this clever provider probably  
still "owns" the LHS of the URI-for-life that you get from them; it's  
just that they have a service that supplies "portability" to  
providers that actually set up calls.)  Voila - I get the same  
*effect* that "URI portability" would provide.

The counter precedent, of course, is the PSTN LNP experience, where  
the consumer has some ownership of their number.  Which is what you  
were looking for, I suspect.  Tough to say whether the email  
experience, or the PSTN LNP experience is the better precedent.  But  
at the moment, the email experience rules probably prevail.  And  
IMHO, I like it this way, since it provides for more business  
opportunities.

But SIP doesn't necessarily dictate these rules; the Redirect  
mechanism would seem to enable the movement of users, and that's all  
the protocol needs to do.  From there, it's up to clever businesses  
to figure out how to meet the desires of users.

Again, these are merely my humble thoughts.
-jb

-------
Jay Batson
batsonjay at sipforum.org
+1-978-824-0111

On Jul 27, 2005, at 6:28 PM, Ringel, Rick wrote:

>
> Hello group,
> I'm doing homework relating to Interconnect issues, and looking at  
> user mobility.   I have a question regarding mobility between  
> service providers.
>
> On the PSTN, number portability is a big issue, and thru regulatory  
> activity, this is being addressed in the circuit network.
>
> In a SIP network, the issue takes on a different nature.  Clearly,  
> as an endpoint behind an IP-PBX, the user's identity is owned by  
> the domain owner.  If Joe leaves Acme, he has to leave his  
> joe at acme.com identity behind.  No problems here.
>
> However, in residential services, a user wants to create and  
> publish an identity that they own, independent of any particular  
> service provider.   If Joe publishes his address as  
> joe at provider.net, then moves his service to joe at competitor.net, by  
> LNP thinking, either the owner of provider.net would have to  
> redirect Joe's calls to competitor.net, or the full address  
> 'joe at provider.net' would undergo a translation (DNS?) prior to  
> delivery at provider.net's service point.  Alternatively, Joe could  
> obtain his own domain name and point a DNS record to his service  
> provider, but that doesn't seem scalable.  I haven't found a  
> solution that appears satisfactory.
>
> In my view, the service provider and the domain name should not be  
> equated.  The same issue exists for e-mail services, but nobody  
> expects their e-mail account to be portable (yet).  I think it is  
> probable that expectations for IP phone service will be different,  
> and that eventually, SIP URI portability will become an issue.
>
> Does anybody know of any IETF tasks, public documents, or  
> discussions on this topic?  I've found lots of info on LPN relating  
> to TEL: URIs, but I have yet to see anything that addresses the  
> problem when users are addressed by a <username>@<domain> format.
>
> -Rick Ringel
>
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>

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