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It is one of the mysteries of telephone communications that the caller pays long distance charges, but if the call is received by a mobile, the called mobile party pays for the airtime. Moreover, this asymmetry exists only in some countries (Canada and the United States, for example) but not in others. In Europe, by contrast, the caller pays for both long distance and airtime charges.
This method of billing calls, known as Calling Party Pays or CPP, encourages mobile users to leave their phones turned on, resulting in close to a 50:50 split between incoming and outgoing calls, rather than the 80:20 split in favour of outgoing calls found where the terminating mobile party pays. If all this capability did was shift calls from outgoing to incoming, it would not be of much interest to carriers. However, researchers believe that it does not affect the rate of outgoing calls, but radically increases the number of incoming calls. Now do the dollar signs start flashing before your eyes?
One of the myths of CPP is that it is due to some deficiency of the AMPS family of standards prevalent in North America, or to some advantage of GSM. But, GSM carriers in North America (like Microcell) have just as much trouble as their more established AMPS-based counterparts. Somewhat to compensate for the lack of CPP, PCS carriers invented the ‘first minute free’ feature, which gives mobile users 60 seconds to decide whether they want to pay for the privilege of talking to the caller. Packages that include lots of free minutes also soften the impact of the lack of CPP.
CPP is not just a benefit for the consumer, but wireless carriers can now see all other carriers (including landline and competing wireless carriers) as sources of additional revenues. All they have to do is figure out how to determine when CPP applies to a call and, more importantly, when they stand a chance of collecting revenue for the call.
There are four basic different methods for Calling Party Pays that can be considered. Each has advantages as well as drawbacks. A single choice will be necessary to make CPP a universally available service.
There are some existing Calling Party Pays systems in the United States. US West was the most enthusiastic carrier promoting CPP (now AirTouch, or maybe Vodafone). These solutions are based on segregating CPP customers into separate number blocks, usually on the basis of a Central Office (CO) code. When a LEC customer dials a local number in a CPP CO code, the call is forwarded to the wireless carrier normally. The LEC bills for the call, since the caller is one of their customers.
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This primitive form of CPP has a number of large problems that have caused many trials to be abandoned (most recently an AT&T trial in Minneapolis and the government mandated program in Argentina):
Why does this method of CPP work so well in Europe and elsewhere? This is because of major differences in the numbering plans and competitive environment. Wireless carriers are generally nationwide, so there are very few distinct entities in a country. Furthermore, each wireless carrier is assigned the equivalent of a separate area code, making the digit analysis required to recognize a wireless call trivial, even within the capabilities of a pay phone. In North America, phone numbers are generally distributed in blocks of 10,000. This would mean that a database with tens of thousands, if not hundreds of thousands, of entries would have to be maintained, indicating whether a block of numbers was wireless or not.
Even in Europe there are limitations to CPP – mostly that it is not an option, but a mandatory service. It is unlikely that too many North American businessmen would want potential customers to have to pay to reach them. Consequently, the simple European model is probably not applicable here.
Wireless carriers had looked at CPP enviously, and did not like the landline carriers being in charge of collecting all the revenue. They also did not like all the restrictions. The CTIA (Washington, DC based trade association and sometime promoter of wireless standards development) produced a White Paper on CPP, followed by a series of industry meetings culminating in a Standards Requirements Document that was presented to TIA subcommittee TR-45.2, responsible for the development of networking standards to support AMPS, TDMA (IS-136 D-AMPS) and CDMA (IS-95) systems.
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The CTIA SRD defined a capability that could be controlled by the wireless carrier, and not the originating carrier, requiring modifications to signaling protocols and overcoming billing record exchange barriers.
SS7 ISUP is the most advanced signaling protocol that is in common use for routing calls through the telephone network. Rather than sending tones over the voice facilities (with a blinding throughput of about 0.03 kbps), ISUP sends call setup messages over a separate channel at a speed of at least 56 kbps. Small modifications are needed to this protocol to support CPP, including a yes/no flag to indicate whether the calling line is blocked (e.g. a pay phone or a local-calls-only line) and the identity of the company responsible for billing the calling party (which, in the case of resellers, might not be the originating carrier). This, combined with existing information in ISUP messages, would allow the wireless switch to determine whether the call can proceed as CPP.
Calls that cannot be treated as CPP could be diverted to a system that could collect alternate billing information, such as a calling card or credit card number.
In this scenario it is the wireless carrier that recognizes that a call is CPP, and also that generates the call detail record, required for billing. Wireless carriers could bill directly for the call, but since CPP calls could come from anywhere, this would mean generating a huge number of bills that probably are not worth the cost to produce them. More likely, wireless carriers will simply provide billable records to the originating carriers, just as they do for roamer billing today. The major problem with this solution is that landline carriers use EMI/EMR record formats, and wireless carriers use CIBER. To date, there is no commercial process available for record interchange.
Other problems with this method are:
Since the CTIA abandoned their sponsorship of technical work in May 1999, the partially completed standards have languished. Perhaps when the US Federal Communications Commission completes its hearings on the CPP issue, technical work will be completed.
Some companies were not happy with the CTIA ISUP-based solution. They felt that it made more sense to base a solution on the LIDB (Line Information DataBase) that is used by landline carriers for operator services like collect calling, calling name delivery and third party calling. This solution requires no changes to the SS7 ISUP protocol, and only relatively minor changes to the LIDB database format (which is defined by Telcordia, formerly Bellcore).
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Wireless carriers would still be in control using this method. Until the call reached them, the CPP nature would not have been established. The wireless switch, recognizing that the mobile that the call is destined to has CPP, would issue a query to the LIDB. The information that was obtained would enable the wireless carrier to determine whether CPP billing is applicable.
Following processing of the call, handling of billing records would have to cross the same hurdle as for the ISUP solution.
Perhaps the most interesting solution that was proposed was from Nortel that proposed using an operator services platform as a surrogate MSC for all CPP mobiles. Using number portability to divert calls to this platform, access to LIDB and to landline billing formats would be provided. However, this solution would not immediately support access to the CIBER wireless billing format.
Perhaps the biggest problem with this solution is that wireless carriers do not support the LIDB database, and would probably prefer to use the TIA/EIA-41 or GSM MAP standards for access to the HLR which contains similar data for wireless subscribers.
Looking down the road a long, long way, there could be a perfect solution. It probably would be based on a separation of functions between the originating carrier and the terminating wireless carrier. Thinking of the most complicated case, the international case, it becomes obvious that the originating carrier should be in charge of user interactions (e.g. announcements), but that the wireless carrier should be responsible for determining which subscribers have CPP, and for determining the rate of the call.
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In this ideal world, the call would start out naively. When the first signaling message arrived at the wireless carrier’s MSC, it would immediately respond with a CPP indication, providing all the information needed to filter and validate the caller. Once this process had completed successfully, the originating carrier could proceed with setup. Billing might more easily be handled through a real-time exchange of signaling information, rather than through a complex post-call record exchange process.
This approach would involve international standardization, which means it is several years away from reality, and could easily be blocked entirely by a handful of countries (or companies) due to the fragile and consensus-based nature of international telecommunications standards setting.
If Calling Party Pays was easy to implement, it would be here already. Much more attention is given to the business problems that CPP faces, the fact that in North America local calls are often free, and that long distance calls are extremely cheap. It is impossible to bury CPP charges in toll charges, for example, when the CPP charges are more than most people pay for long distance service!
Furthermore, even if the technical challenges of CPP can be overcome, the business challenges remain. Since the US and Canadian telecommunications systems are tightly integrated, CPP would require every wireless carrier in Canada to have business agreements with every landline and wireless carrier in North America, as well as with resellers, and possibly even pay phone providers. Managing all these agreements would probably be impossible, so a third party clearing system would probably be necessary.
CPP within Canada would be a much simpler task, but would calls coming from the United States be denied because payment could not be collected?
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