IMS supports the following relevant functions.
- User authentication via the HSS.
- User service profiles via the HSS.
- Billing based on the user service profile.
- Bandwidth allocation via the Go interface between P-CSCF and the first service routing device (GGSN).
- Session admission control (via many components, most notably the P-CSCF).
- VOD server functionality via IMS Application Servers.
On this basis, there is no question of the adequacy of IMS to manage and bill the VOD service. However, IMS does not directly support the encryption and key management requirements of a Conditional Access (CA) system. Unfortunately, the CA system is quite tightly coupled to user authentication and billing, so unless CA systems are re-engineered in a modular fashion to interwork with IMS, this appears to be a significant roadblock.
Most organisations which have a history of ‘pay TV’ will already have systems which do many of the middleware functions which IMS abstracts and modularises. This will impede take-up in the short-to-medium term. However, if a company wishes to broaden its portfolio, e.g. introduce a ‘quadruple play’ of multimedia-sessions + data + IPTV/VOD video + mobile, then the increased generality of IMS may justify its deployment.