GB2449426A

GB2449426A - Transporting data streams between a first node and a plurality of second nodes in a broadcast network

Info

Publication number: GB2449426A
Application number: GB0709624A
Authority: GB
Inventors: Antony Rix
Original assignee: Technology Partnership PLC
Current assignee: Technology Partnership PLC
Priority date: 2007-05-18
Filing date: 2007-05-18
Publication date: 2008-11-26
Also published as: GB0709624D0

Description

INTERMEDIATE SIGNAL DELIVERY IN BROADCAST TRANSMISSION.

NETWORKS

The present invention relates to a method and a system, and in particular but not exclusively to a method and system for transmitting streamed data via a packet switched telecommunications network.

Digital broadcasting systems such as Digital Audio Broadcast (DAB) are known in the art and are used for broadcasting digital signals to a plurality of receivers over a national or regional area. Such systems use a plurality of transmission units to transmit the same data over the desired area. Streamed data is provided to these transmission units which transmit the data simultaneously.

Reference will now be made to Figure 1 in which an exemplary DAB system is illustrated. The system comprises a multiplexing unit 14, which receives input signals 12 such as radio or television data streams. These input signals are combined in signal multiplexer 16. The combined signal is then output from the multiplexing unit via a sending line interface (SLI) 18. This output is provided as an intermediate multiplexed signal known as an ensemble transmission interface (ETI) stream 20.

This ETI stream 20 is sent by means of dedicated links in a circuit-switched telecommunications network 22 to a plurality of transmission units 24. Each transmission unit has a receiving line interface (RLI) 26 for receiving this ETI stream. The received signal is processed by a coded orthogonal frequency division multiplexing (COFDM) modulation process 28, and broadcast as a high power radio frequency signal by antenna 30.

The COFDM modulation processes synchronize their outputs using a time reference signal obtained from a source 32 such as a global positioning system (GPS) receiver. This enables the signals from all transmission units to be co-ordinated in a single frequency network (SFN).

The signals are then received by receiver devices 34for presentation to users.

The COFDM modulation processes include circuitry to process a received signal. Typically this includes: a buffering and synchronization process to synchronize the outputs of all COFDM modulation processes; a modulation process to encode the data stream with forward error correction; interleaving and baseband OFDM modulation; and a radio frequency upconversion and amplification process that transforms the baseband signal into a high power radio frequency signal for input to the antenna.

The ETI stream is typically carried over a dedicated 2Mbit/s circuit-switched telecommunication link. This link may be wired, terrestrial microwave, or via satellite.

These dedicated circuit-switched telecommunication links are costly to operate. Both wired and terrestrial microwave connections require a dedicated circuit to be set up using expensive equipment. Satellite links, which are often used in DAB transmission networks, require a similar bandwidth to be allocated on a satellite transponder as is used for the actual terrestrial DAB transmission, and again make use of expensive dedicated equipment.

As an alternative to circuit-switched telecommunications, packet-switched telecommunications are known.

However, packet-switched telecommunication suffers from a number of problems which prevent its easy application to a broadcast network such as that shown in Figure 1.

Packet-switched telecommunication is subject to errors, packet loss and packet delay jitter. In a broadcast telecommunication system, delays are highly undesirable. Furthermore, errors and packet loss in the signal to a particular transmission unit may impact a large number of users who receive a signal from that particular transmission unit.

A further problem with the application of packet-switched links in a digital broadcast system is that they are inefficient. Each substituted link from a circuit-switched network requires additional network bandwidth. With potentially hundreds or thousands of transmitters in a national SFN, this inefficiency could prove a serious cost and engineering problem.

Typically COFDM transmission units are arranged in a national SFN. National services are transmitted identically by all transmission units in the national SFN. In addition, local services may be provided. These local services are transmitted by all transmitters in a given region, providing a regional SFN.

This provides a cost-effective means to deliver local services with a single transmission network. However such a system often results in poor coverage for the regional services near to the borders between regions, where different regional SFNs interfere. A further problem is that each region typically has its own multiplexing unit and requires regional dedicated circuit-switched telecommunication links to the transmission units. Consequently, the system is difficult to manage and more expensive than a single, purely national, network.

It is an aim of embodiments of the present invention to address one or more of the above identified problems.

According to a first aspect of the invention there is provided a method of transporting at least one data stream between at least one first node and plurality of second nodes, in a broadcast network, said method comprising: packetizing, at said at least one first node, said at least one data stream into at least one packet; sending one or more of said at least one packet via a packet-switched communications network from said at least one first node to said second nodes; receiving at least one of said one or more sent packets at said second nodes; processing, at said second nodes, said at least one received packet to form a signal stream; and outputting from said second nodes said signal stream as one or more radio frequency transmissions.

Preferably said at least one data stream is a multiplexed data stream.

Preferably said signal stream is a recreation of said at least one data stream.

Preferably said packetizing step comprises adding to said at least one packet at least one of: sequence information, format information and/or timestamp information.

Preferably said processing step comprises processing said at least one received packet based on said sequence information, format information and/or timestamp information.

Preferably said processing step comprises buffering and ordering said at least one received packet.

Preferably said processing step comprises encoding and/or modulating said signal stream.

Preferably said packet-switched communications network is one of a unicast packet-switched communications network and a multicast packet-switched communications network.

Preferably said method comprises: creating one or more error correction packets; and sending said one or more error correction packets to said second nodes.

Preferably said creating one or more error correction packets comprises: grouping said at least one packet into one or more groups; processing said one or more groups to create one or more error correction packets associated with said one or more groups.

Preferably said one or more error correction packets contain at least one of: parity information; low-density parity check information; Reed-Solomon error correction information; duplicate information.

Preferably said method comprises correcting errors in said at least one received packet using said one or more error correction packets.

The errors may comprise missing packets.

One or more of said at least one packet may be sent via a first route in a packet-switched communications network. One or more of said at least one packet may be sent via a second route in a packet-switched communications network. The second route may be used in dependence on a quality parameter of said first route.

Preferably the method comprises sending one or more of said at least one packet two or more times.

Preferably said processing is performed in dependence on time information.

Preferably said outputting is performed in dependence on time information.

Preferably two or more first nodes are provided, said first nodes packetizing the same or different data streams to produce a plurality of packets.

The method may comprise combining at said second nodes said packets received from said first nodes. The method may comprise synchronizing said packets received from said first nodes. The method may comprise interlacing said packets received from said first nodes.

Preferably the method comprises sending configuration information from a network management node to said second nodes.

Preferably the method comprises sending status information from said second nodes to a network management node.

Said status information may comprise at least one of: error information; and packet loss information.

Said data stream may comprise at least one of: a Digital Audio Broadcast, DAB, stream; a Digital Video Broadcasting -Terrestrial, DVB-T, stream; a Digital Video Broadcasting -Handheld, DVB-H, stream; a Switched Digital Broadcast -Terrestrial, SDB-T, stream; an Integrated Services Digital Broadcast -Terrestrial, ISDB-T, stream; a Digital Multimedia Broadcasting, DMB, stream; and a MediaFlo stream.

Preferably the method comprises additionally sending said data stream from said first node to said second nodes using a circuit-switched communications network.

Preferably the method comprises additionally sending said data stream from said first node to said second nodes using one or more broadcast satellite channels.

Preferably said packet-switched communications network comprises a wireless packet-switched communications network.

Preferably the method comprises selecting between a first data stream and a second data stream. The selection may be performed based on one or more quality parameters of said first and/or second data stream.

According to a second aspect of the invention there is provided a computer program product for performing the above method.

According to a third aspect of the invention there is provided a system comprising: at least one first node comprising means for packetizing at least one data stream into at least one packet; and means for sending one or more of said at least one packet via a packet-switched communications network from said first node to said a plurality of second nodes; said plurality of second nodes comprising means for receiving at least one of said one or more sent packets; means for processing said at least one received packet to form a signal stream; and means for outputting said signal stream as one or more radio frequency transmissions.

According to a fourth aspect of the invention there is provided a packetizer for use in a packet-switched telecommunications network comprising: means to packetize one or more data streams into at least one packet; and means for sending said at least one packet to a plurality of nodes via a packet-switched telecommunications network.

The packetizer may comprise means for creating one or more error correction packets based on said at least one packet.

The packetizer may comprise a multiplexer configured to combine one or more source data streams into said one or more data streams.

According to a fifth aspect of the invention there is provided an apparatus for use in a packet-switched telecommunications network comprising: means for receiving one or more packets; means for processing said one or more received packets to form a signal stream.

The apparatus may comprise: means for correcting for errors in said one or more received packets.

The apparatus may comprise: means for outputting said signal stream as one or more radio frequency transmissions.

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 illustrates a typical broadcast system as known in the art; Figure 2 shows a broadcast system including an exemplary embodiment of the present invention; Figure 3 shows a detailed view of the packetizer according to an embodiment of the present invention; Figure 4 shows a detailed view of the depacketizer according to an embodiment of the present invention; Figure 5 shows a broadcast system according to an alternative embodiment of the present invention.

A first embodiment of the invention will now be described with reference to Figure 2.

A multiplexing unit 14' comprises a signal multiplexer 16, a sending line interface 18 and a packetizer 36. The multiplexing unit 14' receives input signals 12. These input signals are combined in the signal multiplexer 16.

The combined signal is then output from the signal multiplexer 16 via the sending line interface 18 as ETI stream 20.

The packetizer 36 is arranged to receive this ETI stream. The packetizer comprises a RLI 38 that receives the ETI stream, a packetization and forward error correction (PFEC) process 40, and one or more Internet Protocol (IP) packet interfaces 42.

The IP packet interfaces each output a packet stream 44. These packet streams are carried over one or more packet-switched IP telecommunication networks 46 to one or more transmission units 24'.

At each transmission unit 24' a depacketizer 48 receives the packet stream(s) at one or more IP packet interfaces 50. The depacketizer performs a buffering synchronization and forward error correction (BSFEC) process 52 which receives the output of the IP packet interfaces. Synchronized frames of data from the BSFEC process are sent to a SLI 54.

The SLI 54 outputs an ETI stream 20' from the depacketizer that is input to the RLI 26 that is attached to an COFDM modulation process 28. The COFDM modulation process receives synchronization information from a time reference source 32 and outputs a radio frequency modulated signal to an antenna 30.

In preferred embodiments the ETI stream 20' output by the depacketizer is a delayed copy of the original ETI stream 20 which was input to the packetizer.

In some embodiments of the present invention, the packetizer may be integrated with the signal multiplexer. In these embodiments, frames of data in ETI format or some similar format are passed directly from the signal multiplexer process 16 to the PFEC process 40, and the IP packet interface(s) 42 of the packetizer is/are incorporated into the same physical device as the signal multiplexer. For some embodiments, this may avoid the need for the physical SLI and RLI that pass data in ETI stream format between the signal multiplexer and the PFEC process.

An SLI may still be provided in the signal multiplexer to support testing or operation with equipment that is not compatible with the packet stream.

In some embodiments of the present invention, the depacketizer is integrated with the COFDM modulator device. This may be achieved by incorporating the IP packet interface(s) of the depacketizer into the COFDM modulation process, and passing data between the BSFEC process and the COFDM modulation process directly. For some embodiments, this may avoid the need for the physical SLI and RLI that pass data in ETI stream format between the BSFEC process and the COFOM modulation process.

A further advantage of this embodiment is that the BSFEC process and the COFDM can be arranged to use a single time reference signal for synchronization and buffering in one of these processes only, removing the need for buffering that may be required either in the BSFEC process or the COFDM modulation process.

For example, the BSFEC process would be synchronized with the time reference signal so as to output frames of data exactly when they must be input to the COFDM modulation process. An RLI may still be provided in the COFDM modulator device to support testing or operation with equipment that is not compatible with the packet stream.

In the above embodiment the packetizer and depacketizer are shown as part of the multiplexing unit and transmission unit respectively. In alternative embodiments the packetizer and depacketizer may be distinct units.

It will be well understood that some embodiments of the present invention may be used to replace or supplement an existing circuit switched telecommunications link. Accordingly, in some embodiments of the invention the packetizer and depacketizer may be provided as add-on units to an existing system.

While figure 2 shows two packet-switched telecommunications networks and two IP packet interfaces in each of the packetizer and depacketizer, it will be well understood that one or more than two of either or both of the packet-switched telecommunications networks and two IP packet interfaces may be used.

In some embodiments separate P packet interfaces may send packets over the same packet-switched telecommunications network.

The operation of the packetizer according to one embodiment of the present invention will now be described in more detail with reference to Figure 3.

RLI 38 receives ETI stream 20. The RLI may be arranged to automatically detect from the data stream the line format (including the line code, data rate and framing format) used for the specific ETI stream, as only once the correct ETI stream line format settings have been identified will valid ETI frames be received.

Once synchronized with the ETI stream, the RLI extracts a sequence of ETI frames and passes these, together with information on the ETI stream line format, to the PFEC process 40.

The first part of the PFEC process is a packetization process 402 which packages the ETI frames together with packet length, timestamp, sequence number and format information to create a data packet sequence 404.

Each ETI frame may be divided into more than one data packet such that the packet size is suited to the underlying network transport system (such as Ethernet). This may balance the efficiency of transport with the need to avoid packet fragmentation. The position of each packet within the applicable ETI frame is indicated by means of flags or counter(s) inserted into the packet header.

A forward error correction (FEC) insertion process 406 may then be applied to the data packet sequence using methods of forward error correction for packet streams that are known in the art.

The packets may be stored in a buffer for the purposes of the FEC insertion process. The buffer may be of length equal to one or more packets.

In one embodiment, data packets are grouped or interleaved into groups of a specified size, for example 8 packets, and the FEC insertion process calculates an additional error correction packet for each group from the bitwise exclusive OR of the contents of the data packets in the group (if some data packets are shorter than others in the group, the shorter packets may be padded with zero bytes).

Alternatively or additionally, more computationally intensive methods using Reed-Solomon or LDPC encoding may be applied to compute one or more error correction packets. This provides an advantage in that the system is able to correct more than one lost packet in a group.

Alternatively or additionally, the FEC insertion process may create duplicates of one or more of the packets.

The error correction packets and the data packets may be inserted into the data packet sequence. Alternatively or additionally the error correction packets may be sent separately from the FEC insertion process.

The error correction packets (FEC packets) and data packets may be distinguished for the purposes of forward error correction decoding by means of a flag set in the packet header.

The FEC packets may be sent immediately after or within a short time after the last data packet in the group is sent. Alternatively or additionally the FEC packets may be sent before or during the sending of the data packets, the data packets being appropriately buffered until transmission. Any delay between the data packets and the FEC packets may be limited such that, in combination with the transmission delay of the packet-switched telecommunications network, the total delay does not exceed the maximum delay acceptable in the transmission link with high probability In embodiments of the present invention the error correction data produced in the FEC process may be included in the data packets of a group.

Alternatively or additionally the data packets may include their own error correction data. This error correction data being applicable to the packet itself and enabling errors in the packet to be corrected.

A packet sequence 408, which may include FEC packets and data packets, is sent to packet sending process 409 which outputs the packets through one or more IP packet interfaces 42.

The packet sequence 408 may include FEC packets and data packets, Alternatively or additionally the FEC packets may be sent to an alternative packet sending process and/or to one or more alternative IP packet interfaces.

While two IP packet interfaces are shown in the above embodiment, only one or more than two IP packet interfaces may be provided.

In a preferred embodiment the real-time protocol (RTP) is used to transport the packet sequence, and the real-time control protocol (RTCP) is used to transport extended timestamp, format and application-specific control information (see IETF RFC 1889).

The IP packet interfaces each output one or more of packets from the packet sequence as a packet stream 44. The packet stream may be sent to addresses that may be the same or may differ in either or both of the IP address and port number.

In some embodiments of the invention a plurality of IP packet interfaces output the same packets. Alternatively or additionally the packets are split between the IP packet interfaces.

While two lP packet interfaces are shown in the above embodiment, only one or more than two IP packet interfaces may be provided.

The operation of the depacketizer according to some embodiments of the present invention will now be described with reference to Figure 4.

Within the depacketizer 48, IP packet interfaces 50 are each subscribed to the packet streams 44. This enables the packet-switched telecommunication networks to begin forwarding the appropriate packets.

Packet receiving process 521 receives the packet sequence(s) from the IP packet interfaces, re-orders the packets into the correct sequence, discards duplicates and packets that have arrived too late to be used, and places the remaining packets in a receiving buffer 522.

Packet timestamps may be used to ensure that the buffer always contains packets up to a configured maximum delay before the present time.

The FEC decoding process 523 inspects the packets in the receiving buffer and uses any applicable error correction decoding method to recreate, if possible, packets from the original packet sequence that have been lost, damaged or excessively delayed in transmission. The FEC decoding process may use one or more error correction packets. The FEC decoding process may group data packets into groups.

A synchronization/framing process 524 reads the packet sequence 525 out of the receiving buffer and creates an Eli frame sequence 526 by assembling entire ElI frames from the respective packets as signalled in the packet headers.

The ETI frame sequence is passed to SLI 54, together with the ETI line format configuration taken from the packet headers or RTCP control stream, which the SLI uses to create the ETI stream 20'.

The ETI stream 20' may be output from the depacketizer 48 in dependence on time information received or created at the depacketizer.

In preferred embodiments the ETI stream 20' is a recreation of the ETI stream input to the packetizer.

In some embodiments of the present invention the packet switched telecommunication networks support multicasting. The packets are transmitted by the packetizer using a multicast address and is received by each of the depacketizers.

Alternatively or additionally the packet switched telecommunication networks may not support multicasting. The packet stream may instead be sent using a unicast method. The packetizer sends packets to each respective packet address and port of the IP packet interfaces that are desired to receive the packet stream.

In some embodiments of the present invention, one or more packetizers may be used to packetize a given ETI stream. Alternatively or additionally, one or more IP packet interfaces at the packetizer and/or depacketizer may be used.

The packets may be sent via one or more packet switched telecommunication networks. Alternatively or additionally, one or more routes through a particular packet switched telecommunication network may be used. If more than one network route is used, a first route may pass through one or more intermediate network router devices that are different from any intermediate network router devices used in another network route. This advantageously allows the amount of redundancy in the system to be varied and enables a balance to be found between operational cost and resilience.

In some embodiments of the present invention, a only a first packet stream from a first packetizer may be used. If this first packet stream should fail to be received at a transmission unit with acceptable quality, a second packet stream may be used. This second packet stream may be provided by an IP interface in the first packetizer. Alternatively or additionally the second packet stream may be provided by a IP interface in a second packetizer.

Acceptable quality may be determined by the number of errors received in a given period of time being below some threshold that may be pre-set or configurable.

In some embodiments, unicast packet streams may be used. When the first packet stream fails to be received at the transmission unit with acceptable quality, the transmission unit may be arranged to connect to an alternative lP packet interface.

In some embodiments, multicast packet streams may be used. When the first packet stream fails to be received at the transmission unit with acceptable quality, the transmission unit may be arranged to subscribe to a second multicast stream.

In embodiments, once the first packet stream has been restored with acceptable quality for a determined period of time, the second packet stream may be terminated.

In some embodiments, the second packet stream may only be transmitted by a packetizer when a first packet stream fails to be received at a transmission unit with acceptable quality. This allows redundant routeing to be provided while only using capacity on backup packet-switched network connections when necessary, though possibly at the expense of short periods of loss of service between the failure of a first packet stream and the start of reception of a second packet stream.

If more than one IP packet interface is used, the different IP packet interfaces may have different address and/or port numbers.

For example, the packetizer may have a plurality of lP packet interfaces which send packets to corresponding plurality of IP packet interfaces on each of the depacketizers. Each of the IP packet interfaces may send packets by a different route. These routes may be in the same packet-switched telecommunication network or in different networks. The different networks may comprise different communication mediums, for example wireless and wired.

In some embodiments of the invention, copies of the same packets may be sent and/or received by more than one IP packet interface in a given unit.

Alternatively or additionally these copies of packets may be sent by more than one route. This provides redundancy in the system. A depacketizer which receives more than one copy of the same packet may discard the duplicate packet.

In some embodiments of the invention the FEC insertion process and corresponding FEC decoding process may not be used. This may occur if duplicate packets are transported via the packet-switched telecommunication network.

In some embodiments of the invention, a packet stream may be divided between different IP packet interfaces and/or different routes. Thisoffers the advantage that multiple low bandwidth routes and/or IP packet interfaces can be combined to provide a high bandwidth connection.

In some embodiments of the present invention, more than one RLI may be incorporated into the packetizer and/or more than one SLI may be incorporated into the depacketizer. This enables the packetizer(s) and/or depacketizer(s) to transport the ETI signals from more than one signal multiplex without the need for additional equipment.

A second embodiment of the present invention will be described with reference to Figure 5.

In this embodiment, input signals 12 are sent to two or more multiplexing units 14'. The multiplexing units contain signal multiplexers 16 which multiplex the input signals and output ETI streams 20 by means of SLIs 18. The ETI streams are each passed to a packetizer 36 which outputs one or more packet streams 44. The operation of each packetizer may be the same as packetizers described in previous embodiments.

The packet streams are carried over one or more packet-switched telecommunication networks 46, via one or more separate routes, to each of one or more transmission units. At the transmission units the packet streams are processed in substantially the same way as set out according to the first embodiment above.

In embodiments of the invention the multiplexing units receive the same input signals and produce the same ETI stream.

Alternatively or additionally a multiplexed signal from a particular signal multiplexer may be routed to two or more packetizers.

Alternatively or additionally multiplexed signals from more than one signal multiplexer may be sent to one or more packetizers. These packetizers may be arranged to process the signal from a first signal multiplexer. In the event of this first signal multiplex failing, the packetizers may switch to process the signal from a second signal multiplexer.

The above embodiments may allow for redundancy to be included in the system.

Preferably the separate multiplexing units are synchronized with each other so to produce identical packet streams. In this case a depacketizer is able to receive packets from both multiplexing units and discard redundant packets.

Alternatively or additionally each received packet stream may be processed separately by the depacketizer. The depacketizer may switch from a first to a second packet stream if the first packet stream ceases or becomes received with a greater level of uncorrected errors than said second packet stream for longer than a threshold period of time. This may be necessary if the multiplexing units are not perfectly synchronized.

In some embodiments of the invention the two or more multiplexing units receive different input signals from one or more sources.

In these embodiments, a first multiplexing unit may provide national services as part of a national SFN and a second multiplexing unit may provide local services as part of a regional SFN.

The depacketizers may receive and multiplex the signals from the different multiplexing units. This may be done in the synchronization/framing process prior to the output of the ElI frame sequence. The depacketizer may otherwise operate in substantially the same way as described in previous embodiments.

For example, a local radio station may be broadcast by as few as one or two transmission units. In this case the audio signal from the local radio station would be encoded and transported to the transmission units over the same or similar packet switched telecommunication network or networks as a main packet stream such as that provided by a national service.

The received packet streams may comprise a main packet stream and an auxiliary packet stream. These streams may correspond to a national network and a regional network respectively.

After buffering and, if applicable, error correction, the streams may be merged to form a single ETI stream. This may involve overwriting a stream that already exists in the main packet stream. Alternatively or additionally this may involve inserting the auxiliary stream into spare capacity. This spare capacity may be in the main packet stream.

The depacketizer may modify the service framing and/or signalling as appropriate so that receivers in that locality will be able to list the local service by its name and decode it successfully. The timing of this remultiplexing process is useful as all COFDM modulation processes should be and remain synchronized in order to retain the favourable properties of an SFN.

Where two signal multiplexes (or services therefrom) are combined, the timestamp information present in the ETI frames is used to combine data from frames with matching timestamps. Where signals from a more basic transport are combined with a signal multiplex, the RIP and RTCP timestamp information, taken together, are used to determine an absolute timestamp for each frame of data and this is used to insert the data into the ETI frames with matching timestamps. A configurable delay may also be provided to allow a systematic time offset between streams to be applied at all COFDM modulation processes.

In a preferred embodiment of the present invention, a network management system may be provided. The transmission units may receive configuration information from the network management system over a packet-switched telecommunications network. Alternatively or additionally transmission units may send status, notification and/or error information to the network management system over a packet switched network. This status, notification and/or error information may indicate events such as equipment failures or errors in the received packet streams.

The transmitter devices may be provided with pre-determined network address or addresses known to a network management system.

The network management system may prepare configuration information to be provided to one or more of the transmission units. This configuration information may include identification information. The transmission units may receive this configuration information and configure themselves according to the received configuration information. This may include configuring the COFDM modulation processes.

The network management system may receive the status, notification and/or error information. The network management system may filter this information. This may be used to eliminate information not considered to be important. The network management system may comprise a display or alert means for indicating, for example, error events such as the failure of a transmission unit or loss of data.

The configuration, status, notification and/or error information may be provided over a packet switched network using a protocol such as the simple network management protocol (SNMP) or the real time control protocol (RTCP).

Advantageously, these widely-supported systems for configuration management may be translated at the depacketizer into less common or proprietary protocols for managing the COFDM modulation process such as the multiplex network signalling channel described in Annex A of ETSI ETS 300 799. This allows the broadcast transmission network to be managed using the same systems as an operator's other telecommunication equipment.

Examples of the parameters managed at each COFDM modulation process include without limitation the total transmission delay, the transmitter identification information, the radio frequency modulator centre frequency, and the radio frequency transmit power.

The above embodiments of the invention have been described in which the packet switched telecommunications network is used as an alternative to a circuit switched telecommunications network. However, embodiments of the invention may be applied to provide a redundancy in addition to a primary ETI stream distribution process operating over dedicated satellite or circuit-switched telecommunication networks.

It will be clear to a person skilled in the art that DAB is one of a number of digital broadcast systems, and that embodiments of this invention could also be applied to similar broadcast transmission technologies such as Digital Video Broadcasting -Terrestrial (DVB-T), Digital Video Broadcasting -Handheld (DVB-H), Switched Digital Broadcasting -Terrestrial (SDB-T), Integrated Services Digital Broadcast -Terrestrial (ISDB-T), Digital Multimedia Broadcasting (DM8), and MediaFlo.

Further, it may be understood that although the aforementioned systems are based on COFDM, embodiments of the present invention is equally applicable to other modulation methods that are based on synchronized transmission of signals, including the parallel sequence spread spectrum (PSSS) modulation scheme, or where the signals prior to modulation are identical but are not necessarily transmitted on the same radio frequencies (for example a multi-frequency network).

The above embodiments have been described in relation to the method and operation of particular entities in the present invention. It will be well understood by the person skilled in the art that embodiments of the invention may comprise, but are not limited to, hardware configured to perform a particular function, software configured to run on a processor, or a combination. Other means by which embodiments of the invention may be realized will be obvious to the person skilled in the art.

As will be understood by one skilled in the art, some embodiments of the present invention provide a means and process to create a broadcast network making use of packet-switched telecommunications between multiplexing units and broadcast transmission units, with the use of forward error correction, redundant routes and redundant multiplexer devices providing substantial protection against failures in the multiplexing unit, packet-switched network and even the receive interfaces on the broadcast transmission units.

This allows a network embodying the invention to attain a high degree of availability and freedom from interruption to service while potentially reducing its cost with respect to a traditional circuit switched network. Further, there may be an ability to add or multiplex services at the transmission units providing flexibility to add local or regional services in an otherwise national SFN without the need for separate multiplexer devices.

While this invention has been particularly shown and described with reference to preferred embodiments, it will be understood to those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appendant claims.

Claims

Claims: 1. A method of transporting at least one data stream between at

least one first node and plurality of second nodes, in a broadcast network, said method comprising: packetizing, at said at least one first node, said at least one data stream into at least one packet; sending one or more of said at least one packet via a packet-switched communications network from said at least one first node to said second nodes; receiving at least one of said one or more sent packets at said second nodes; processing, at said second nodes, said at least one received packet to form a signal stream; and outputting from said second nodes said signal stream as one or more radio frequency transmissions.
2. The method of any preceding claim wherein said at least one data stream is a multiplexed data stream.
3. The method of any preceding claim wherein said signal stream is a recreation of said at least one data stream.
4. The method of any preceding claim wherein said packetizing step comprises adding to said at least one packet at least one of: sequence information, format information and/or timestamp information.
5. The method of claim 4 wherein said processing step comprises processing said at least one received packet based on said sequence information, format information and/or timestamp information.
6. The method of any preceding claim wherein said processing step comprises buffering and ordering said at least one received packet.
7. The method of any preceding claim wherein said processing step comprises encoding and/or modulating said signal stream.
8. The method of any preceding claim wherein said packet-switched communications network is one of a unicast packet- switched communications network and a multicast packet-switched communications network.
9. The method of any preceding claim comprising: creating one or more error correction packets; and sending said one or more error correction packets to said second nodes.
10. The method of claim 9 wherein said creating one or more error correction packets comprises: grouping said at least one packet into one or more groups; processing said one or more groups to create one or more error correction packets associated with said one or more groups.
11. The method of claims 9 or 10 wherein said one or more error correction packets contain at least one of: parity information; low-density parity check information; Reed-Solomon error correction information; duplicate information.
12. The method of any of claims 9 to 11 comprising correcting errors in said at least one received packet using said one or more error correction packets.
13. The method of claim 12 wherein said errors comprise missing packets.
14. The method of any preceding claim wherein one or more of said at least one packet are sent via a first route in a packet-switched communications network.
15. The method of claim 14 wherein one or more of said at least one packet are sent via a second route in a packet-switched communications network.
16. The method of claim 15 wherein said second route is used in dependence on a quality parameter of said first route.
17. The method of any preceding claim comprising sending one or more of said at least one packet two or more times.
18. The method of any preceding claim wherein said processing is performed in dependence on time information.
19. The method of any preceding claim wherein said outputting is performed in dependence on time information.
20. The method of any preceding claim wherein two or more first nodes are provided, said first nodes packetizing the same or different data streams to produce a plurality of packets.
21. The method of claim 20 comprising combining at said second nodes said packets received from said first nodes.
22. The method of claim 20 or 21 comprising synchronizing said packets received from said first nodes.
23. The method of any of claims 20 to 22 comprising interlacing said packets received from said first nodes.
24. The method of any preceding claim comprising sending configuration information from a network management node to said second nodes.
25. The method of any preceding claim comprising sending status information from said second nodes to a network management node.
26. The method of claim 25 wherein said status information comprises at least one of: error information; packet loss information.
27. The method of any preceding claim wherein said data stream comprises at least one of: a Digital Audio Broadcast, DAB, stream; a Digital Video Broadcasting -Terrestrial, DVB-T, stream; a Digital Video Broadcasting -Handheld, DVB-H, stream; a Switched Digital Broadcast -Terrestrial, SDB-T, stream; an Integrated Services Digital Broadcast -Terrestrial, ISDB-T, stream; a Digital Multimedia Broadcasting, DMB, stream; and a MediaFlo stream.
28. The method of any preceding claim comprising additionally sending said data stream from said first node to said second nodes using a circuit-switched communications network.
29. The method of any preceding claim comprising additionally sending said data stream from said first node to said second nodes using one or more broadcast satellite channels.
30. The method of any preceding claim wherein said packet-switched communications network comprises a wireless packet-switched communications network.
31. The method of any preceding claim comprising selecting between a first data stream and a second data stream.
32. The method of claim 31 wherein said selecting is performed based on one or more quality parameters of said first and/or second data stream.
33. A computer program product for performing the method of any preceding claim.
34. A system comprising: at least one first node comprising means for packetizing at least one data stream into at least one packet; and means for sending one or more of said at least one packet via a packet-switched communications network from said first node to said a plurality of second nodes; said plurality of second nodes comprising means for receiving at least one of said one or more sent packets; means for processing said at least one received packet to form a signal stream; and means for outputting said signal stream as one or more radio frequency transmissions.
35. A packetizer for use in a packet-switched telecommunications network comprising: means to packetize one or more data streams into at least one packet; and means for sending said at least one packet to a plurality of nodes via a packet-switched telecommunications network.
36. The packetizer of claim 35 comprising means for creating one or more error correction packets based on said at least one packet.
37. The packetizer of claim 35 or 36 comprising a multiplexer configured to combine one or more source data streams into said one or more data streams.
38. Apparatus for use in a packet-switched telecommunications network comprising: means for receiving one or more packets; means for processing said one or more received packets to form a signal stream.
39. The apparatus of claim 38 comprising: means for correcting for errors in said one or more received packets.
40. The apparatus of claim 38 or 39 comprising: means for outputting said signal stream as one or more radio frequency transmissions.