Content deleted Content added
No edit summary |
No edit summary |
||
Line 1:
:''CRID redirects here. CRID may also refer to a Current Rail Indicator Device, a safety device which indicates the presence of [[third rail]] power; cf. [http://www.trainweb.org/tubeprune/dictionary.htm].''
Line 43 ⟶ 44:
which would indicate a content (identified by the string “2d22”) that airs on a channel available on a DVB network identified by the address “112.4a2.5ec” (network “112”, transport stream “4a2” and service “5ec”), on 12/12/2012 at 10 p.m. and with a duration of 90 minutes.
== The ___location resolution process ==
The ___location resolution process is the procedure by which, starting from the CRID of a given content, one or several locators of that content are obtained. Resolving a CRID can be a direct process, which leads immediately to one or many locators, or it may also happen that in the first place one or many intermediate CRIDs are returned, which must undergo the same procedure to finally obtain one or several locators.
This procedure involves some information elements, among which we find two structures named Resolution Authority Record (RAR) and ContentReferencingTable, respectively. Consulting them repeatedly will take thereceiver from a CRID to one or many locators that will allow it to acquire the content.
'''The RAR table'''
The RAR table is one or many data structures that provide the receiver, for each authority that submits CRIDs, information on the corresponding resolution service provider. Among other things, it also informs about which mechanism is used to provide information to resolve the CRIDs from each authority. That is, one or many RAR records must exist for each authority that indicate the receiver where it has to go to resolve the CRIDs of that particular authority.
For example, in the record of the figure (expressed by means of a XML structure, according to the XML Schema defined in the TV-Anytime) there is an authority called “tve.es”, whose resolution service provider is the entity “rtve.es”, available on the URL “http://tva.rtve.es/locres/tve”, which means there is resolution information in that URL.
[[File:RAR record example.png|center|RAR table in XML format]]
These RAR records will have reached the receiver in an indefinite form, unimportant for the TV-Anytime specification, which will depend on the specific transport mechanism of the network to which the receiver is connected. Each family of standards that regulates distribution networks (DVB, ATSC, ISDB, IPTV...) will have previously defined such procedure, which will be used by devices certified according to those standards.
'''The ContentReferencingTable table'''
The second structure involved in the ___location resolution process is a proper resolution table which, given a content’s CRID, returns one or several locators that enable the receiver to access an instance of that content, or one or many CRIDs that allow it to move forward in the resolution process.
The figure shows an example of this second structure, an XML document according to the specifications of the XML Schema defined in TV-Anytime. In it, several sections are included (<Result> elements) that structure the information that describes each resolution case.
The first one declares how a CRID (crid://tv.com/Friends/all), which corresponds to a group content that encompasses several episodes (two) of the “Friends” series is resolved. The result of the resolution process provides two new CRIDs each of them corresponding to one of the three episodes.
The second <Result> element resolves the CRID of the first episode of the first season. The result of the resolution process is two DVB locators. The “acquire” attribute with “any” value indicates that any of them are good (the second one is a repetition broadcast a week later).
The third <Result> element gives information about the second episode. It indicates that it cannot be resolved yet (“status” attribute with the “cannot yet resolve” value), indicating a date on which the request for resolution information must be repeated.
'''The process'''
Once the user has selected a given content (identified by the corresponding CRID) to perform some action upon it, the receiver begins the ___location resolution process that shall lead to specific ___location information that allows access to a copy of the content.
This procedure depends mainly on the receiver’s connectivity. It is possible to make a basic distinction between unidirectional networks, where the receiver can only receive information through the broadcast channel, and bidirectional networks, where there is also a return channel through which the receiver can communicate with the outside (typically an Internet access).
For receivers connected only to a broadcast channel, it is clear that the resolution information must come directly from that channel, or be available somehow in an existing local storage system. After selecting a CRID, the first thing the receiver needs to do is check the information about where to find the resolution table. For this, it must find a RAR record associated with the authority of the selected CRID.
Once a RAR record corresponding to that authority is found, the receiver will know, by referring to the URL field, where to access (or, in this case, where to listen) to obtain the resolution information.
The information that will receive through that access point will consist of a message for each of the consulted CRIDs (for example, a <Result> element in the ContentReferencingTable).
== In web casting ==
| |||