Overview
Click hier to see the diagram full-screen
EN 50221 - The beginning
EN 50221 is the core specification. It defines a PC-card based on PCMCIA version 5 including electrical details (like higher address pins being re-defined as parallel TS input/output in CI mode), the core transport protocols and the resources being used to identify and control a CAM.
CAMs built according to this specification can only descramble one MPEG2 transport stream at a time. (In theory, hosts could re-multiplex and combine multiple sources into a single stream passing through the CAM. Due to the high complexity of this task and in most cases also hardware limitations, only very few hosts implement such a mechanism.)
The specification supports multi channel descrambling in theory but a large number of CAMs only support descrambling a single service at a time.
EN 50221 - Extensions / TS 101 699
TS 101 699 defines several extensions to the original specification. Only very few of the new resources have ever been used in real world applications.
CI+ - More security, more complexity, higher cost
In 2007, a closed group of companies published the first version of the CI+ specification and proposed this as alternative to the supposedly insecure EN 50221 open standard that everyone could implement without the need for external certification or approval. Manufacturers need to pay annual license fees and receivers need pass a mandatory certification procedure that is under tight control of Resillion (formerly "Eurofins Digital Testing") as test center monopolist and only provider of "the official test kit" used for the certification.
DVB (attempting to) regain control
Since 2014 DVB has published several versions of the TS 103 205 specification. To the general public, this was communicated as "DVB is now taking control over CI+". This is however misleading. The entire legal construct that coerces manufacturers into payment of massive amounts of license payments and testing fees for features that are rarely or never used by CAMs in the real world (Operator Profile, LSC, wild "VoD" business case phantasies) is still in place. At no point has DVB ever "controlled" CI+. As of today, DVB specification proposals still need to be accepted and re-published by CI Plus LLP to have any chance of becoming a reality. DVB has no influence/control over any root key material.
The future - CI over USB
In September 2016, DVB released the latest update to the family of standards around DVB-CI. DVB BlueBook A173-1 defines a new form factor for common interface modules based on USB. In addition to the new hardware form factor, the specification also simplifies the communication protocols by eliminating some layers that have never been fully supported by large parts of the deployed CAM/host population.
One of the biggest advantages of this new specification will be the full native support for processing data from more than one transport stream at the same time. CI+ 1.4 already tried to achieve this with the introduction of the Multistream resource. Due to the complete lack of hardware support for this feature in practically every existing STB and CAM chipset, this feature did not make it beyond a few hardware engineering samples so far.