Mediation & SIP Billing Issues

Submitted by ACE*COMM

Abstract:

SIP (Session Initiation Protocol) is an IETF-draft control protocol for managing sessions in an IP network. However, it was not designed to provide network usage information for billing purposes. This contributed editorial discusses the issues involved with using SIP as the source of billing information, and how a mediation system can resolve these issues.

Article:

SIP (Session Initiation Protocol) is an IETF-draft control protocol for creating, modifying and terminating IP sessions such as multimedia conferences and IP telephony calls. It provides the capability to set up and tear down Internet communications sessions, performing functions very similar to SS7 functions in the PSTN (Public Switched Telephone Network) world. In this capacity, SIP is robust and reliable. However, issues begin to arise if SIP is used as the sole source of network usage information for billing purposes.

By their nature, standards promote a significant level of interoperability. The SIP standard brings with it many benefits, such as a standard set of attributes that are necessary for billing. However, SIP was not designed to provide a direct source of billable usage data. It is an event-based protocol that produces many reporting events for a single usage session.

There are two basic problems with using events in a billing environment. First, from a billing perspective the different events are incomplete at best, and may even be completely useless. The main problem, however, is the sheer amount of records. A steady stream of events is provides real-time feedback about activity on the network, but it introduces a scalability problem when it comes to billing. The flood of SIP events for a single session could end up costing the service provider more for the billing system to process than it receives back in revenue.

Aggregation through a mediation system solves both problems by consolidating all events for a session into one summary record. Yet, aggregation has the flexibility to periodically generate incremental information - with all known information to date rather than just individual events - to systems that require real-time updates

Another issue is that by definition, SIP produces the signaling time points of a session, which may not correspond to the user-perceived start and end times for the session (whether it is a phone call or a movie download). This may be a source of contention from a billed customer. As well, SIP does not provide any information about the corresponding media transfer portion of the session, which is critical in usage-sensitive billing scenarios such as when the subscriber is billed according to the volume of data transmitted.

Mediation helps solve these problems by capturing other accounting streams (from application servers, media servers, softswitches, etc.) and correlating it with the SIP information. The result is a clearer picture of the session from a billing perspective.

A mediation system can also augment the usage records with other important information that SIP was not designed to provide, such as the subscriber's address or other contact information. It can also pre-rate the augmented usage data in preparation for billing. For example, aggregated usage records can be tagged with an appropriate code if the subscriber has exceeded a set number of minutes.

Thus, while SIP is an effective signaling protocol, it has limitations when used as the sole source of billing data. The scalability issues introduced by the event-based reporting mechanism, and the limited perspective offered by the signaling point of view can be overcome by using a mediation layer. Further, use of a mediation system allows the introduction of other value-added functionality that have proven their worth for other technologies.

By:
Jonjie Sena, Director of Product Management, Convergent Mediation
Ty Roach, Engineering Manager

ACE*COMM Corporation
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