Put another way, OCAP is a software layer that resides above an incumbent operating system, and below any applications, such as electronic program guides, on-demand wares, or clickable items that come along with a specific TV program.
OCAP requires an 8×16 memory footprint (8 Megabytes of flash memory, 16 Megabytes of dynamic random access memory, or DRAM). In processing power, it requires at least a 130 MHz processor (the faster, the better).
OCAP 1.0, the first version of the specification, includes three main parts. First is the Java Virtual Machine, or JVM. Its role is to “unfold and run” interactive applications; technologists often call this “the executable engine.”
Second is a set of Java “packages,” which is Java-speak for the software modules that enable application program interfaces, or APIs. APIs are the programming calls available to developers when making interactive applications.
Third, OCAP 1.0 needs a mechanism for applying business policies, such as via a “monitor app” (see definition). A monitor application handles resource allocation, such as software downloads and overall applications management.
In 2008, OCAP was re-branded to “Tru2way,” for consumer devices, like HDTVs, with OCAP inside. The body of technical specifications that is OCAP will remain under the OCAP name; anything consumer-facing but reliant on OCAP is now called “tru2way.”
Key to these interface specifications was the definition of a removable security module, which was the basis for making the devices fully portable from one cable system to another regardless of the network operator. This milestone — and federal mandate — was met by its deadline of July, 2000.
In addition to crafting the interface specifications, OpenCable also oversees the processes and facilities necessary to test and certify the interoperability of OpenCable devices. Web site: www.opencable.com
The easiest way to visualize what a set-top operating system does is to consider the PC operating system — such as Microsoft Windows, Unix, and MacOS. PC operating systems do the heavy lifting across several fronts, including the control of: the CPU chip, the movement of data to and from hard disks, printers, floppy disks, and other peripheral devices; memory usage, and file systems/data storage.
Because digital set-tops generally don’t contain the firepower of a standalone PC, the set-top operating system, by necessity, must run lean. The hardware components lining the inside of the digital set-top box, such as CPU and memory chips, are smaller and slower than in PCs. All things managed by the set-top OS must be capable of happening in real time, and without delays of more than a few nanoseconds — otherwise, the TV viewer will likely become disengaged and resentful. (Imagine your reaction if channel up/down took seconds to complete.)
Notably, however, cable providers are increasingly specifying “middleware” software, such as OCAP (OpenCable Applications Platform) which runs on top of a set-top operating system, to manage a widening list of interactive applications. This is primarily because cable providers were and are wary of ceding too much applications control to the operating system provider community.
Usage: Most of the first upgrade was about adding opto-electronics into the system, for reliability and segmentation.
Cable first dipped its toes into the world of OSI stacks when it, through CableLabs and DOCSIS, established an interoperable cable modem specification. So far, cable broadband generally sticks to the bottom two layers — Physical link and Data link. The layers, best visualized to correspond with the children’s jingle “the neck bone’s connected to the backbone” (because one layer doesnt exist well without the others,) are described below:
7 (top layer): Application: Defines common applications and how to link them, over a system, to a user.
6: Presentation: Establishes a common syntax between applications, so that apps can run independently, but in a coordinated fashion.
5: Session: Describes the control structure for intra-application communications (how an application talks to another application, like the billing interface). Defines how cooperating applications establish, manage and end communication.
4: Transport: Describes how to reliably transfer information from one end point to another, while describing end-to-end error recovery and flow control.
3: Network: Establishes how to switch and route packets; describes how to establish, maintain and terminate connections.
2: Data Link: Defines how information is reliably transferred over the physical link (wires), and describes how chunks of data (known as “frames”) should be synchronized, how transmission errors are controlled, and how data flows.
1: Physical: Defines how bits move over physical media (wires), and organizes mechanical, electrical, functional and procedural characteristics inherent to those wires.
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