Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-09-30
2004-11-02
Vanderpuye, Kenneth (Department: 2661)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S486000
Reexamination Certificate
active
06813271
ABSTRACT:
BACKGROUND TO THE INVENTION
This invention relates, in general, to the interworking of a satellite communication system with a broadband transport mechanism and is particularly, but not exclusively, applicable to a transport methodology in which multiple asynchronous transmission mode (ATM) cells are encapsulated into and recovered from an MPEG/DVB data-piping environment.
SUMMARY OF THE PRIOR ART
Communication systems, in general, each have specific frame structures and signalling protocols. Unfortunately, when designers subsequently attempt to utilise one communication environment to support the effective transfer of data emanating from a different communication environment, efficient and robust packaging of encapsulated traffic becomes an issue, especially since frame lengths are seldom directly compatible.
To date, it is believed that the merging of multiple ATM traffic streams onto a satellite channel has not been considered, although there are clearly significant technical issues that need to be resolved. For example, the encapsulation of ATM traffic in a digital video broadcasting satellite (DVB-S) frame using data piping would cause ATM cells to be split over contiguous transport stream packet boundaries. Indeed, if more than one ATM stream is present in the satellite up-link, then efficient use (i.e. full packing) of the transport stream can result in data corruption. More specifically, the interleaving of different sources onto the transport stream in a bandwidth efficient manner will generally result in the corruption of certain of the ATM cells at the point of their recovery. In effect, there is an attempt to merge several transport streams (carrying data) into a single transport stream that is receivable by one or more terminals using on-board processing in the satellite. In this context, a natural model is to consider the satellite as a switch and then to reconcile destination terminals as ATM end systems attached to the switch. Extending this thought process leads to a possible solution in which a single ATM stream is directed towards a terminal and such that it resembles a single MPEG/DVB elementary stream, i.e. that the single stream should be on a single PID. However, if one merges transport stream packets form multiple sources on a PID then the system only works if the start and end of the transport stream packets are always cell boundaries, and this therefore requires the use of padding (and the loss of useable bandwidth).
In generality, an MPEG transport (data-) stream is prepended by a sixteen-bit header; this is the Program Identity (i.e. the PID). The PID is indicative of a label of an information source (sometimes referred to as a “content provider”). If padding is not used to correlate transport stream boundaries with ATM cell boundaries then the use of a single PID for all up-links and the multiplexing of the data onto a single transport stream hence results in a specific ATM cell (from an identified data source) being dispersed in time and such that the data of the specific ATM cell is partitioned between non-contiguous transport streams. At re-assembly of the specific ATM cell at a node (such as a terrestrial network connection), error is therefore likely. Furthermore, to recover and coherently decode an ATM stream at an addressed unit, different content providers cannot use the same VPI/VCI combination.
Each transport stream packet has an overall length of about 188 bytes, and so is about three-and-a-half-times (3.5×) longer than a conventional ATM cell (nominal length of fifty-three bytes). Clearly, therefore, efficient packaging involves the partitioning of ATM frames and the associated problems of coherent data recovery, whereas ATM cell boundary alignment is only maintained at the expense of loss of bandwidth (and the use of an additional bit in the header that identifies “padding”). More specifically, in the latter instance, multiple ATM sources can be interleaved into a MPEG/DVB-S frame in a non-optimum fashion by using padding, whereby only whole ATM cells are packaged into a particular transport stream. Alternatively, the MPEG (Motion Picture Expert Group) layer can be removed. In any event, the virtual path identifier (VPI) and virtual circuit identity (VCI) space must be coordinated between the data sources.
It is envisaged that one could contemplate the use of virtual path (VP) multiplexing, but this would only mitigate the coordination issue and would not address the requirement for padding.
With only a limited frequency spectrum available, any waste of bandwidth is of considerable concern to system operators, especially since it represents an associated cost burden. Indeed, sub-optimum use in capacity is undesirable and generally causes the system to be less competitive and, usually, less profitable.
In the context of DVB, there are various derivatives employed within different environments. There are three forms of forward channel, namely DVB-T (for terrestrial): DVB-C (for Cable): and DVB-S (for Satellite). And there are at least three kinds of return channel, namely terrestrial PSTN, DVB-RCCL (return channel for cable and LMDS) and DVB-RCD (return channel for satellite). DVB-MPE (for multi-protocol encapsulation systems) and DVB-Data piping are two of at least three ways of carrying data over any of the forward channels. More especially, the DVB-MPE derivative is configured to implement segmentation and re-assembly of Internet protocol (IP) datagrams over an MPEG stream, whereas the data piping derivative (as already implied) is used to carry generic data streams (such as ATM cells) in a DVB environment.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided a method of conveying data from a plurality of content providers across a satellite system supporting broadband communication, the method comprising: encapsulating, utilising a digital video broadcasting (DVB) protocol, a mixture of full and partial broadband cells but at least a partial broadband cell into a transport stream packet having a physical identity (PID) header: the step of encapsulating further including: mapping the broadband cells from a particular content provider onto a PID associated with that particular content provider; whereby each transport stream packet contains information from a specific content provider identified by the PID header of the transport stream packet.
In a preferred embodiment, the satellite system comprising at least one satellite and at least one station having an up-link, and the method further comprises: DVB multiplexing transport stream packets having different PID header at at least one of said at least one satellite and said at least one station having said up-link.
Preferably, at a recipient device responsive to the transport stream packet, a preferred embodiment of the operating methodology further includes: deriving a broadband PHY from the PID header: and, from the transport stream packet, recovering and then outputting broadband cells with their associated broadband PHYs.
Preferably, the method further comprises the step of determining whether the transport stream packet received by the recipient device is part of an elementary stream assigned to carry broadband traffic. The step of determining typically further comprises cross-referencing the PID of the transport data packet with broadband PHY information.
The preferred method of the first aspect of the present invention may also include the further steps of buffering any partial broadband cell received in the transport stream packet and referencing any such buffered partial broadband cell with a stream label.
In relation to any buffering, the method further comprises the steps of: reviewing the stream label of any buffered partial broadband cell upon receipt of successive transport stream packets; and outputting the buffered partial broadband cell with an associated broadband PHY in the event that the successive transport stream packet contains an associated partial broadband cell that is complementary to the buffered partial broa
Nortel Networks Limited
Vanderpuye Kenneth
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