SIP extensions to support (micro)payments

SIP is a protocol designed to create and manage multimedia sessions such as telephone calls over the Internet, distributed conferences, or, in general, every kind of communication between two or more peers. The introduction of payment in SIP is an interesting idea in order to charge for this media services. This payment services have been proposed in several scenarios such as charging for accessing to services, microbilling or as a solution to SPAM in VoIP systems. In this context, there is a proposal for making payments on SIP that is based on SAML. However, this proposal is not good enough to make low payments or micropayments because involves that the payment service provider participates in every payment. This implies that the transaction costs are high and therefore it is not suitable for this kind of payments. Additionally, this proposal only deals with the scenario in which the payment covers the whole session. Finally, this proposal does not take into account that streams with different quality could be used in the session, and therefore the amount to pay could be different. In response to these limitations we propose a new extension for supporting payments on SIP which, being payment-independent protocol, solves interoperability problems and links payment information to requests. For this purpose, we have extended both SDP and SIP to facilitate the access to SIP services based on payment. The extension supports an offer/answer model that allows the choice of the quality of the streams as well as the payment method to use. Furthermore, it is extensible and not only supports payment but also more complex business models such as loyalty models, credentials and subscriptions. Thus, we facilitate the incorporation of new payment methods and business models in the vendor's software. This paper describes this extension as well as some scenarios where it can be applied.