Speaking of Standards

Do “intrastate” versus “interstate” billing rates make any sense whatsoever in the world of SIP where geography ceases to be relevant?

There is a fundamental disconnect today between the legacy world of PSTN billing practices and this new world of SIP-based interconnection that we are all building. The Internet ignores geography. We can connect to any random points in the cloud, regardless of where they are physically located.

But until the day when we have truly built the IP-interconnect and can all be bypassing the PSTN, we do have to deal with the PSTN… and all the legacy tariff/billing infrastructure that goes with it. How do you mesh the two worlds?

Consider this case within the US:

• A company in Massachusetts with phone number 617-555-1111 calls a customer also in Massachusetts with phone number 617-555-2222.

• The Caller ID presented to the receiving party is 617-555-1111.

• The company calling is billed the intrastate rate because the call appears to have originated and terminated within Massachusetts. For this example, and purely picking a number out of the air, let’s say the call at intrastate rates would have cost $5.

• However, the company in MA was actually using a hosted telephony service and while the call appears to have originated from Massachusetts based on the CallerID presented to the user (and transmitted as “6175551111@sipgw.carrier.com” in the SIP From and/or P-Asserted-Identity headers), the number actually entered the PSTN from a data center in New York with the number 212-555-1111.

• Had the calling company presented their billing identifier as 212-555-1111, they would have been billed the interstate rate for calling and for this example let say that the call would have only cost $3. (And yes, for those of you outside the US, this is true, calls within a state are more expensive than calls between states!)

• Naturally, the calling company wants to present its Caller ID to the end user as its own number of 617-555-1111 but it is contracting with the SIP telephony hosting provider in part to get cheaper rates. The hosting provider would naturally like to be billed at the interstate rate versus the intrastate rate when the calls enter the PSTN from their data centers.

There is the disconnect. PSTN billing is still tied to the identity of the originating number as seen through the carrier’s billing systems. Yet with SIP, the caller identity can be different from the identity of the PSTN interconnect point. (And yes, “Caller ID” can be spoofed on the PSTN but there are still underlying billing identifiers in the PSTN signaling.) As long as we continue to have tariffs in North America that have different rates based on geography, we’ll continue to have this problem.

A few years back, the folks over at Sonus Networks came up with an idea to address this disconnect - pass a custom SIP header called “P-Charge-Info” in the SIP INVITE that sets up the call and include in that header the SIP address to which to charge the call. They added this header to some of their equipment and some carriers started using it. So in the case above, the SIP headers might include headers like these:

From: <sip:617555111@sipgw.carrier.com>
P-Charge-Info: <sip:2125551111@proxy.hostingprovider.com>

To the person receiving the call, nothing has changed. The “Caller ID” that is presented on their phone is the same identity they saw before. But inside the cloud, the billing identity has been changed.

[Do note that there's a double-edged sword here. If the hosting provider and the carrier agree to use P-Charge-Info as the authoritative header for billing purposes, and then in my example above the Massachusetts customer starts making a lot of calls into New York they will wind up being charged the higher intrastate rate based on the P-Charge-Info header. So some analysis of calls needs to be done before agreeing to use this special header.]

Anyway, as one of the largest providers of VoiceXML/CCXML hosting, we are always looking at ways to ensure our customers receive the fairest billing. Late last year after one of our carriers suggested we look at using the P-Charge-Info header, we did so and were quite pleased with the results. Subsequently we have now started using this with multiple carriers.

Being strong proponents of open standards, we noticed that P-Charge-Info was not yet registered on IANA’s list of SIP parameters and so we approach Sonus Networks about going through the RFC 3427 process of registering a custom P-header. They agreed and so Tolga Asveren from Sonus Networks and I submitted an Internet Draft defining the P-Charge-Info header. We received a good bit of feedback/critique and our fourth version (-03) was just posted today.

Why are we going through this registration process, which can be quite lengthy? Several reasons:

• Expanded Usage - We would like to use this with other carriers but until this draft there was no specification for exactly how the header should be used. We would like this to be available as something to point other carriers/service providers to.

• Prevention of Further P-header Proliferation - Right now, if someone is looking for a SIP header to pass billing information, odds are they will look at IANA’s registry to see what headers have been added to SIP. Today the only billing headers are those of the 3GPP defined in RFC 3455 which do differ in intent from what P-Charge-Info does. If they don’t like the RFC 3455 P-headers, they may very well go off and invent their own P-header (anyone can) to deal with passing billing information.

  Our concern is that as we all in the industry continue building this IP interconnect, sooner or later we’re going to want to find ways to exchange billing information and if we have six different headers in production use it’s going to be a real headache. In the ideal world we would have a standard header (not a P-header) for passing billing information and probably we eventually will… but that will take some time to get developed and then deployed. In the meantime, let’s document and register what’s out there now so that people can see the choices they have and not necessarily go right off creating yet another billing information header.

• Prevention of Identity Conflict - It’s very possible that someone going off and creating their own SIP P-header could very well choose to call their header “P-Charge-Info”. One would hope that someone creating a new P-header might use Google to search for the header name they are planning to use (in which case they would discover this existing usage of P-Charge-Info), but someone might not and start using it. It could then happen that some day someone out there would wind up needing to interoperate with two different pieces of equipment that both use a “P-Charge-Info” header, but in different ways. IANA registration is designed to help prevent this.

• It’s The “Right Thing” To Do - If you read section 4.2 of RFC 3427 it states very clearly:

  Any P-header used outside of a very restricted research or teaching environment (such as a student lab on implementing extensions) MUST meet those requirements [of section 4.1] and MUST be documented in an RFC and be IANA registered.

  Now obviously no one is enforcing this. There are many P-headers in common usage today that are not documented. No one will slap you down and revoke your right to use SIP if you don’t. But it’s the right thing to do for the reasons outlined above as well as to respect the process defined in RFC 3427.

So where is P-Charge-Info in the RFC 3427 process of IANA registration? Well, Tolga and I now have a fourth revision of our Internet Draft out (it’s the fourth because the first was “-00″) and we would very definitely like comment on the draft. Please do send them in via email (or leave them as comments here). Once the document has gone through more review (perhaps another draft or two) we will then continue the steps in section 4.1 of RFC 3427 and request “expert review”. Ultimately the goal is to have the document published as informational RFC so that it can be registered with IANA.

As I said, comments and feedback are definitely welcome. What do you think of the document? of the problem we are trying to solve?

Technorati Tags: ietf, sip, standards, voxeo, sonus networks, p-charge-info, voip, telecommunications, telephony, pstn

Tags: IETF, SIP, Standards

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