Patent Application
20090158366
The present invention relates to the field of video transmission.
The present invention relates more particularly to a method falling within the framework of DVB-IP (DVB meaning: Digital Video Broadcasting and IP meaning: Internet Protocol).
The DVB-IP specification (ETSI TS 102 034) describes a mechanism for signalling services based on a data structure described in XML and 2 transport protocols of this data: HTTP and DVBSTP. The same information is transmitted according to these 2 protocols and the use of one or other, or both is left to the choice of system designers. We are interested here only in the use of DVBSTP, independently from the possible simultaneous use of HTTP.
The DVBSTP protocol (DVB Sd&S Transport Protocol) is itself based on the UDP and IP protocols for transmitting the data on a multicast group in a cyclic manner (carousel).
A simple interpretation of the text of the specification leads to an IP multicast group address being used to broadcast all the service information corresponding to a service provider, even to regroup the information of several service providers in the same stream.
The DVB-IP standard is typically intended to transmit the service information and video content on the access link of an ADSL subscriber. This type of link comprises bandwidth limitations that involve managing the bitrates in the best manner possible. Even if the service information represents a low weight, the information must be reduced to leave room for the video stream for example.
The broadcasting of all the information of a service provider on a single multicast stream can represent a non-negligible bitrate when there are a large number of services. This bitrate has a low limit as the specification requires a cycle time (to broadcast all of the information) of less than 30 seconds.
A carousel grouping all the data of a provider on a single multicast group thus has the disadvantage of having a bandwidth cost that can prove to be too great with respect to the overall assignment of this bandwidth.
The maximum cycle time of the carousel was selected to ensure that the modification that arise in the data can be fully accounted for in a reasonable time, particularly during the start up of a terminal that has no memory of this information. The DVB-IP specification proposes to allow better access times by repeating information more frequently. This repetition can be selective according to the importance attached to the data to give priority to some of this data. But this possibility only enables the times to be shortened by increasing the bitrate received by the terminal.
Finally, it is considered in DVB to extend the specification to enable a “regional” availability of some services to be signalled (by adding a “ServiceAvailability” field). But these services are described in the carousel for all the terminals, which creates an unnecessary consumption of bandwidth, the terminal receiving the descriptions of service that it must ignore when they are not available for it.
The US patent application No. US 2004/198371 discloses a scalable quality broadcast service in a mobile wireless communication network. The solution of this prior US patent application is explicitly dedicated to the mobile terminals, whereas the present application applies to DVB-IP (now DVB-IPTV), which relates to wired communication networks. The solution of this prior US patent application is based on a dynamical adaptation of video (and/or audio) streams, realized by analysing the needs in bandwidth at a given time. The present invention does not imply any dynamical adaptation of the streams that are transmitted on the network. Furthermore, the present invention applies to service information streams and not to media contents.
The present invention intends to overcome the disadvantages of the prior art by proposing a solution that enables service information to be broadcast on IP type networks by shortening the recognition time of modifications arising in the data and by preventing the unnecessary consumption of bandwidth.
For this purpose, the present invention relates, in the most generally accepted sense, to a method for broadcasting service information data streams comprising:
Preferably, the service information data streams are multicast.
Advantageously, the service information data streams are compliant with the DVB-IP standard.
According to one mode of implementation the service information is split into segments and the said first step consists in assigning a stream to each segment.
According to one embodiment, some segments are assigned to the same stream.
The present invention also relates to a broadcast server of service information data streams, comprising:
The method according to the present invention uses the fact that the specification does not forbid using several multicast streams to broadcast the service information of a same service provider. However, it remains silent as to the possible use and the interpretation of this possibility.
The method consists in partitioning the service information between the different multicast streams used to describe a service provider. This information being already split into “segments” by the DVB-IP specification, this therefore involves assigning to each segment one and one only multicast stream on which it will be present.
On each multicast stream, the cycle time of 30 seconds is respected. Hence, a terminal can acquire all the information of a service provider by connecting simultaneously to all of these multicast streams. The faculty of keeping the properties of the “normal” method is therefore maintained: same acquisition time for the same total bandwidth.
Each individual stream can be extremely reduced in size, such that a terminal wanting to save on bandwidth can do so by connecting to only one stream at a time. It retains the possibility of monitoring all the data by connecting successively to each of the streams (either by changing every 30 seconds, or by changing when it notices that it has received all of the data expected), only the update time is increased. Excluding the case of the starting up of the terminal, the update times are not critical, given that the service information modifications are rare.
The advantage of the method would be increased if an extension of the DVB-IP signalling were adopted, which would consist in adding the multicast streams of a provider to the existing description, enabling the terminal to establish listening priorities of the carousels.
The method according to the present invention has many advantages, among which the following are found:
The invention will be better understood from the following description of an embodiment of the invention provided as an example by referring to the annexed figures, wherein:
In a server implementing the method according to the present invention, a modification form of a segment can be used to choose the assignment of this segment to one of the carousels broadcast by the service provider. The choice is made from a drop down list that shows the addresses of the possible multicast streams.
The screen shown in
The XML description of a DVB-IP service provider that does not apply the method shown here will have the following form:
It can even use a lower number of segments.
To implement the method according to the present invention, the following description for example is used:
The smallest possible form for a segment is the one in which only the description of a single service is placed. For example, for the segment 0000:
The time sequencing scenario, illustrated in
Let us suppose that a service provider has 200 television channels in “broadcast” mode. The size of the data for each channel is estimated at 1 kilobyte (this depends on the descriptions).
A broadcast in a single stream of 200 k-bytes on a cycle of 30 seconds gives a bitrate of 53 kbits/s. By applying a maximum partition into 200 streams, a bitrate per stream of 266 bits/s is obtained. The maximum update time in this mode increases to 1 hour 40 minutes.
A more interesting approach is to set a suitable marginal bitrate for the reception of updates. If one considers 4 kbits/s for example, this gives 2 seconds to send a service of 1 kilobyte. One can therefore group 15 services per stream for a cycle of 30 seconds. 14 streams are therefore used in parallel. The maximum update time goes to 7 minutes for a sequential listening of the various streams. It remains at 30 seconds for a simultaneous listening where the 53 kbits/s is found.
One can therefore retain 200 streams in parallel each containing 1 service but by sending them at this same target bitrate of 4 kbits/s. The cycle time of each stream thus goes to 2 seconds. The maximum update time by listening in sequence depends on the behaviour of the terminal. If it listens systematically to each stream for 30 seconds, one remains at 1 hour 40 minutes. If it is able to note that it has received a full list in 2 seconds, the update time is still 7 minutes. Note that in this case a single segment being transmitted on a stream, if said segment has not changed content the terminal will know it as soon as it receives the first packet by reading the version number. It can therefore go on immediately to the next stream, shortening the global update time. This is valid as only one segment is generally modified at a time. With this tactic, the update time for simultaneous listening is lowered to 2 seconds, but requires a bitrate of 800 kbits/s to be used.
The method according to the present invention is applicable to the DVB-IP standard published to date (ETSI TS 102 034 v1.2.1). However, to facilitate the optimum use of the service information by a terminal, it may be considered to provide it with indications for directing the choices that it makes by connecting to such or such a stream. The composition strategy of the carousels is indeed established by the server of the provider, and it therefore has complete information for qualifying the composition of its streams. The terminal can do this by analysing the information, but this requires greater “intelligence” on its part, and could take up time as it is necessary to read all the data of the carousel to determine whether its content is more or less important for the terminal.
The present invention therefore also proposes the use of two mechanisms that would improve the efficiency of the method for the terminal. Each of them is useful separately and both can be used jointly.
The invention is described in the preceding text as an example. It is understood that those skilled in the art are capable of producing variants of the invention without leaving the scope of the patent.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0654383 | Oct 2006 | FR | national |
