METHODS OF BROADCASTING AND RECEIVING SCRAMBLED MULTIMEDIA PROGRAMS, A TERMINAL AND A NETWORK HEAD END FOR SAID METHODS
The present invention relates to methods of broadcasting and receiving scrambled multimedia programs, and to terminals and network head ends for implementing said methods.
To be more precise, methods exist for broadcasting via a network multimedia programs generated by different service operators. In existing broadcasting methods:
• each network head end multiplexes one or more multimedia programs scrambled using a control word and a cryptogram of that control word to obtain a multiplexed content and then broadcasts the multiplexed Content to the terminals via the network; and
• in parallel with this, one of more network head ends broadcast(s) service messages specific to each service operator for adapting the operation of each terminal so that it is authorized or prohibited to access the multimedia programs.
There also exist methods of receiving multimedia programs broadcast by the above broadcasting method.
In existing receiving methods:
• each terminal receives and demultiplexes the multiplexed content and then, provided that it is authorized to do so, decrypts the cryptogram"of the control word and descrambles the multimedia program to obtain a multimedia stream that can be used by the terminal, which includes a memory; and
• each terminal receives the service messages and then, as a function of the content of the service message received, the terminal adapts its operation so as to be authorized or prohibited to access the multimedia program.
Existing broadcasting and receiving methods use a broadband network, for example, such as a microwave or
satellite network or an IP telecommunications network, for example.
In existing broadcasting and receiving methods, the service messages of a particular operator are incorporated into the multiplexed content and then broadcast to each of the terminals. The same operator can generate a number of multimedia programs, which can lead to the parallel broadcasting of different multiplexed contents by the same service operator.
In contrast, the terminal can generally receive and demultiplex only one multimedia content at a time.
Thus if this operator wishes to send a service message to all the terminals able to receive and to demultiplex one or more of the multiplexed contents that they are broadcasting, they incorporate a copy of the same service message in each of the multiplexed contents broadcast in parallel. This therefore increases the number of copies of the same service message broadcast and therefore increases the bandwidth necessar\' to broadcast them. This problem exists even if the operator groups their multimedia programs into a smaller number of multiplexes, as the service messages are incorporated in that many multiplexes.
The problem is exactly the same if the network used is an IP network, for example. The multiplexed contents and the service messages are then broadcast to multicast
a
addresses to which each of the terminals listens.
The invention aims to solve this problem when the broadcasting and receiving methods use a broadband network in which information can be routed to a multicast address so that only one group consisting of several terminals corresponding to that multicast address receives the information, and other terminals connected to the same network do not receive the information.
The invention therefore consists in a method of broadcasting multimedia programs in which the network head end(s) broadcast(s) to a reference multicast address a list associating service operator identifiers with one or more first-level service multicast addresses, the reference multicast address being known beforehand to all terminals adapted to receive and demultiplex the broadcast multiplexed contents and that reference multicast address being different from all the broadcast multicast addresses.
The invention also consists in a method of receiving multimedia programs broadcast by means of the above broadcasting method in which, in response to broadcasting the list to the reference multicast address, the terminal listens at one or more first-level service multicast addresses specified in that list to receive service messages.
In the above methods, the reference add:^ess is different from all the broadcasting multicast addresses. Accordingly, whatever the number of multiplexed contents broadcast in parallel on behalf of the same service operator, only one copy of the list is broadcast to the reference multicast address in order to be received by all the terminals. This is referred to as broadcasting the list "out of band". In particular this saves on bandwidth.
Moreover, because the reference multicast address is used to indicate to the terminals which service multicast addresses to listen to and is not directly and systematically used to transmit all service ige^sages of all service operators, the option of managing the quantity of information transmitted to that reference multicast address can be retained. For example, the service multicast addresses specified by the list can all be different from the reference address, and so no service message is transmitted to the reference address, which considerably reduces the amount of information transmitted to that address. Conversely, if the list associates the reference address with each service operator identifier, all service messages of the
operators, which can constitute a large amount of information, are transmitted to the reference address.
Implementations of the broadcasting method can have one or more of the following features:
• the network head end(s) broadcast(s) to the reference multicast address a list in which one or more service multicast addresses associated with an operator identifier differ(s) from the other service multicast addresses associated with other service operators;
• the network head end(s) broadcast(s) to one or more first-level service multicast addresses associated with a service operator identifier a table defining one or more second-level service multicast addresses used by that operator.
Implementations of the receiving method can have one
a t
or more of the following features:
• the terminal selects in the list the service multicast address(es) corresponding to a service operator identifier prestored in its memory, then listens at the selected service multicast addresses to receive service messages and does not listen at the multicast addresses not selected from this list;
• in response to the broadcasting of the table, the terminal listens at one or more second-level service multicast addresses specified in that table;
• the first- or second-level service multicast
addresses are also all different from the broadcast
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multicast addresses;
• the broadband network is an IP (Internet Protocol) network.
These implementations of the broadcasting and receiving methods have the following advantages:
• using different service multicast addresses for different operators is a simple and fast way to eliminate at the network layer level messages that are not relevant to the terminal;
• because a table is used to define the second-level service multicast addresses it is possible to use hierarchically organized service multicast addresses, which simplifies management of those addresses,' and
• using service multicast addresses different from all the broadcasting addresses makes it possible to limit the bandwidth necessary for broadcasting service messages.
The invention also consists of a terminal including an access control software module adapted to implement the above receiving method.
The invention further consists of a network head end adapted to broadcast scrambled multimedia programs using the above broadcasting method.
The invention can be better understood on reading the following description, which is given by^vcciy of non-limiting example only and with reference to the drawings, in which:
• Figure 1 is a diagram showing the architecture of a system for broadcasting and receiving scrambled multimedia programs;
• Figure 2 is a flowchart of a method of broadcasting and a method of receiving scrambled multimedia programs;
• Figure 3 is a diagram showing the structure of a list used in the Figure 2 method;
• Figure 4 is a diagram showing the structure of a table used in the Figure 2 method; ® ■
• Figure 5 is a diagram showing the architecture of a service multicast address tree used in the Figure 2 method;
• Figure 6 is a flowchart of a method of modifying a reference address in the Figure 1 system;
• Figure 7 is a flowchart of a method of updating first-level service multicast addresses in the Figure 1 system; and
• Figure 8 is a flowchart of a method of updating second-level service multicast addresses in the Figure 1 system.
Figure 1 shows a system 2 for broadcasting and receiving multimedia messages. This system 2 includes one or more network head ends that broadcast(s) multimedia programs in a scrambled form and a multitude of terminals that receive the scrambled multimedia programs and descramble them so that they can use them. For example, the terminal uses the received multimedia programs to generate a video stream that can be displayed in clear on a screen.
To simplify Figure 1, only one network head end 4 and three terminals 6, 1 and 8 are shown.
The network head end 4 comprises:
• an entitlement control message (ECM) generator 10;
• an entitlement management message (EMM) generator
12;
• a module 14 adapted to broadcast the rnuitiplexed contents to one or more broadcast multicast addresses; and
• a private messaging manager (PMM) 16 able to broadcast service messages to one or more service multicast addresses.
The module 14 scrambles each multimedia program received using a control word CW. The module 14 also multiplexes the scrambled multimedia program with entitlement control messages generated by the generator

• in a step 88, the module 14 multiplexes the scrambled multimedia program, the entitlement control messages, and the entitlement management messages to obtain a multiplexed content;
• in a step 90, the module 14 encapsulates the multiplexed content in IP (Internet Protocol) packets;
• in a step 92, the IP packets containing the multiplexed content are broadcast to a predefined broadcasting multicast address by the operator that generated the scrambled multimedia program.
The steps 80 to 92 are repeated for each multimedia program of each service operator.
In parallel with this, the network head®end broadcasts service messages.
To be more precise, in a step 100, the manager 16 generates an ASP (Address Signaling Protocol) message and encapsulates it in a UDP (User Datagram Protocol (RFC768)) datagram. This ASP message contains a list associating one or more service multicast addresses, referred to as first-level addresses, with service operator identifiers. One example of a structure for this list is shown in Figure 3. The service operator identifiers are in a column 104. For each service operator identifier, there is a first-level service multicast address in a column 106. Sufficiei^': 'data is present in the columns 104 and 106. Complementary data specific to a particular implementation can be associated with it, however, as shown in the column 108.
In Figure 3, "Opl" and "Op2" are the identifiers of the operators 20 and 22, respectively. These identifiers Opl and Op2 are associated with service multicast addresses @SSP1 and @SSP2, respectively. In this example, each identifier from column 104 is further associated with a description of the service operator in column 108, represented by the symbol "xxx", which can be displayed on the terminal.
Then, in a step 102, the ASP message is^broadcast to the multicast address ©ASP. This address @ASP is stored beforehand in each of the terminals liable to access a multimedia program broadcast by the network head end 4. This address @ASP is the same for all the terminals, regardless of the operator with which the user of the
terminal has a contract. Thus all the terminals of the system 2 can receive the ASP message.
The reference address @ASP is an IP address associated with a port to be listened to or a domain name. The address @ASP is different from all the broadcast multicast addresses used to broadcast multimedia contents and is used to exchange information "out of band". ® ^
The steps 100 and 102 are repeated, for example at intervals of one minute.
Then, in a step 110, the manager 16 generates SSP (Service Status Protocol) messages specific to each of the operators and encapsulates them in UDP datagrams. Here the SSP message specific to each operator contains a table relating to the services provided by that operator and concerning the terminals. These services are, for example:
• broadcasting of individual or collective information to the terminals, in multicast mode by the operator; for this kind of service the SSP message specifies the broadcasting modes, in particular a second- level service address, that a terminal must use to access this information;
• the exchange of information between the operator and the terminal during transactions resulting from a connection set up at the initiative of the terminal; for this kind of service the SSP message specifies how to set up the connection;
• the activation of particular behaviors of the terminal.
Figure 4 shows one example of this kind of table for the operator 20.
The Figure 4 table contains:
• in a column 114, the identifier of the service operator that generated the table;
• in a column 116, the type of each service;
• in a column 118, the parameters of each service;
and
• in a column 120, the identifiers of each service. The natures of the service parameters 118 and the
service identifiers 120 depend on the type of service,
for example: reference of the message broadcast service
and its multicast address, reference of the server to be
called and its unicast IP address, designation of a
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specific behavior and its particular parameter settings.
In Figure 4, column 114 indicates the operator OPl from which the table originates. Column 116, with the identifiers from the column 120, indicates a service message broadcasting service PMPl, two transactional services Serverl and Server2, and two behavior activation services Indicl and Indic2.
Column 118 describes the parameters of each of these services:
• for the service message broadcasting service PMPl, the column 118 gives the multicast address @PMP1; this address ®PMP1 is used by the generator 16 under the control of the operator 2 0 to broadcast particular service messages, for example requests for connection of the terminal to the network head end;
• for each transactional service Serverl, respectively Server2, the column 118 specifies the unicast address @IP1, respectively @IP2, to which the terminal must be connected by a point-to-point connection to execute a transaction with a server of the operator; the choice of server depends on the nature of the transaction to be executed;
• for each behavior activation service, the column
118 specifies the behavior Indicl, respectively Indic2,
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to be activated and the parameters Valuel, respectively Value2, of that activation.
In a step 122, an SSP message generated by the operator 20 is broadcast to the address @SSP1 defined in the Figure 3 list. Similarly, SSP messages generated by
the operator 22 are broadcast to the address ©SSP2 associated with the identifier of that operator in the Figure 3 list.
The SSP messages of an operator are broadcast at intervals of one minute, for example.
Finally, in a service message broadcasting service, at the command of the operator 20, the generator 16 sends a PMP (Private Message Protocol) message in a step 12 6 that preferably contains the identifier of the,terminal for which it is intended and the identifier of the operator that generated it. For example, the PMP message intended for a terminal can be a request for connection to a server of the operator whose address the terminal has received via a transaction-type SSP service.
Note that, depending on the implementation, the service at the SSP behavior activation level can be supported by a particular PMP message.
In the step 126, under the control of the operator 22, the manager 16 can also send to a service multicast address (iPMP2 a service message containing a connection request. The address ®PMP2 is the address associated with the identifier PMP2 in column 12 0 of the table broadcast in the step 122 by the operator 22. The address @PMP2 is preferably different from the address @PMP1.
Moreover, in practice, all the addresses used to broadcast service messages, i.e. the addresses @SSP1, @SSP2, @PMP1, and @PMP2 here, are each different from the broadcast multicast addresses used to broadcast multiplexed contents in the system 2.
In parallel with the steps 80 to 126, each terminal executes the process 7 8 for receiving multimedia programs and service messages. « ,
Initially, in a step 13 0, the terminal 8 looks up the address ©ASP in its memory 5 8 and then listens at that multicast address. Then, in a step 132, it receives the ASP message broadcast by the network head end 4. In a step 134, in response to reception of this ASP message, the terminal selects only addresses in column 106 that are associated with a service operator identifier matching one contained in its own list 62.
Then, in a step 13 6, the terminal listens only at the addresses from the Figure 3 list selected in the step 134.
It is assumed here that the terminal 8 listens only at the address (iSSPl of the operator 20.
By listening at that address, in a step'^138, the terminal receives the SSP message broadcast by the operator 20.
In response to that SSP message, in a step 140, the terminal stores the table contained in the SSP message received. The table can be stored on reception of each message or only when the content has changed relative to the last time it was broadcast. The values of the indicators contained in the stored table are used during special processing operations.
The unicast addresses @IP1 and @IP2 contained in the column 118 are used to set up a point-to-point connection with the server corresponding to them.
In response to reception of the address @PMP1, in a step 142, the terminal 8 begins to listen at that service address.
In a step 144, the terminal receives the PMP messages by listening to the address @PMP1. For example, the terminal receives a connection request. Then, in a step 146, the terminal verifies that this connection request was generated by the operator 20 and is intended for it. For example, in the step 146, the terminal verifies that:
• the operator identifier contained in this request matches one of those stored in its list 62; and
• the terminal identifier contained in the request matches its own terminal identifier.
If not, the next step is the step 142; if so, the terminal proceeds to a step 148 of setting up a point-to-point connection.
In the step 148, the terminal sets up a point-to-point connection to a server of the operator 20. To set up this point-to-point connection, the terminal uses one of the unicast addresses contained in the table stored in the step 140 corresponding to the service specified in the connection request.
Once this point-to-point connection has-been set up, in a step 150, an exchange of bidirectional data between the terminal and the contacted server is executed. This bidirectional exchange of data can, for example, provide the terminal 8 with the secret data enabling it to descramble received scrambled multimedia programs.
In parallel with the steps 13 0 to 150, the terminal also receives the broadcast scrambled multimedia programs. To this end, in a step 160, the terminal listens at a broadcast multicast address and the module 46 then demultiplexes the received multiplexed content. Then, in a step 162, the entitlement control message of the multiplexed content is sent to the processor 42 which, in a step 168, obtains the control word CW by decrypting the cryptogram CW*.
The processor then sends the control word CW to the module 46 which, in a step 170, descrambles the scrambled multimedia program using the received control word.
The descrambled multimedia program is then decoded, in a step 172, by the module 46 in order to generate a multimedia stream. In a step 174, that multimedia stream is sent to the screen 52, which displays it in clear. The steps 172 and 174 constitute one example of use of the descrambled multimedia program.
The Figure 2 method is used to construct a tree of service multicast addresses for each operator as shown in Figure 5. In that tree, the address @ASP is the root node. The addresses @SSP1 and (assp2 are the first-level
son nodes and the addresses @PMP1 and @PMP2 are the second-level son nodes respectively attached to the addresses @SSP1 and @SSP2.
The Figure 2 method can of course be used to construct service multicast address trees containing more than two first-level service multicast addresses and more than one second-level service multicast address associated with each father node.
Figure 6 is a flowchart of a method of modifying the address @ASP in each of the terminals of the system 2.
Initially, in a step 200, the network head end broadcasts the ASP messages at the same time to the old address @ASP, here denoted gASPoidr and to a new address @ASP, here denoted @ASPnGw- The step 200 applies the Figure 2 method to a heterogeneous installed base of terminals in which some terminals use the address @ASPoid and the other terminals use the address ©ASPnov
Then, in a step 202, a reference address modification entitlement management message; is sent to each of the terminals. This entitlement management message can be incorporated into the multiplexed content received by this terminal or sent in a service message generated by the generator 16 . It contains new
address @ASPnow
In response, in a step 204, each terminal stores the new address ©ASPnew instead of the old address @ASP,,irt.
Then, in a step 206, the receiver 40 verifies that the new address has been stored correctly by testing the value of an update indicator, the value of which is modified by the processor 42 in the event of successful storage of the new address OASPnew- If the value of this indicator shows that the update has succeeded, the terminal proceeds to a step 208 of listening at the new address @ASPnew and no longer listens at the old address @ASPoici. " ^
If, in the step 206, the value of the indicator shows that the update has not succeeded, the terminal
does not proceed to the step 208 and continues to listen at the address @ASPoid-
In all cases, the method returns to the step 2 00 after the step 206 or the step 208.
How the terminal 8 updates the address (iSSPl is described below with reference to Figure 7.
Initially, in response to a modification of the address @SSPl contained in the ASP message, in a step 220, the module 48 stops listening to the first-level multicast addresses (@SSPl) and the higher level multicast addresses, such as the address @PMP1.
The method then continues through the steps 132, 134 and 136 described with reference to Figure 2.
How the terminal 8 responds to receiving an SSP message informing it of a new address OPMPluow is described below with reference to Figure 8.
Initially, in a step 230, in response to reception of this new address (iPMPlnow/ the module 48 stops listening at the old address (aPMPloiri. The method then continues through the steps 142 and 144 described with reference to Figure 2.
Numerous other embodiments are feasible. For example, networks other than those using the Internet Protocol can be used instead of the network 30 provided that the network in question uses multicast addresses in a similar way to the Internet Protocol.
The security processor 42 can be integrated into the receiver 40. Alternatively, the modules 46 and 48 can be implemented in a removable module.
The various functions of the terminal 8 can be divided between different units interconnected by a local area network. For example, they can be divided between a local "home gateway" and a local decoder, one of which can include the security processor 42. The gateway is then the element connected to the network 3 0 that listens at the various multicast addresses. Information received from the network 3 0 is then forwarded over the local area
network to the local decoder. For example, in this kind of architecture, the gateway can be responsible for processing the entitlement control messages to extract from them the control words necessary for descrambling scrambled multimedia programs. Other architectures for the terminal 8 are obviously feasible.
The multicast addresses of the first and higher levels can be IP addresses that are either fixed or assigned dynamically by the Figure 2 method. The addresses @SSP1 and @SSP2 can be identical. The terminal then distinguishes service messages intended for it by means of an identifier of the carrier contained in the SSP messages. Similarly, the second-level service multicast addresses can be identical to each other and also identical to the first-level service multicast addresses. Service messages intended for the terminal 8 are then distinguished from those that are not intended for it by carrier identifiers included in the SSP and PMP messages. The address @ASP can also be identical to or different from the service multicast addresses used.
The modem 44 can be integrated into the receiver 40 or an external modem.
Alternatively, the address (iASP is stored in the receiver 40 instead of in the security processor 42.
The Figure 2 method has been described in the particular situation where the Figure 5 tree comprises three levels. A simplified version uses only two levels, that is to say the address @ASP and the first-level service multicast addresses. Alternatively, more than three levels can be used. This variant enables different service multicast addresses to be assigned, typically according to the service message types and/or the organization of the installed base of terminals.
If each service operator uses a set of service multicast addresses different from that used by the other operators, then the operator identifier contained in the Figure 4 table can be omitted. Similarly, the operator
identifier contained in the SSP, PMP service^messages can be omitted.
The description of the operator or the service contained in columns 108 and 120, respectively, can be omitted.

CLAIMS
1. A method of broadcasting multimedia prograasi; generated by different service operators via a broadband network in which information can be routed to a multicast address so that only one group of terminals corresponding to that multicast address receives the information whereas other terminals connected to the same network do not receive that information, in which method:
• each network head end multiplexes (step 88) a multimedia program scrambled using a control word and a cryptogram of that control word in order to obtain a multiplexed content and then broadcasts the multiplexed content to a broadcast multicast address used to set up a point-to-point multipoint connection between®che network head end and the terminals via the network; and
• one or more network head ends broadcast(s) service messages specific to each service operator in parallel (steps 122, 126) to one or more service multicast addresses to adapt the operation of each terminal so that it is capable of descrambling and using the broadcast multimedia program or, to the contrary, to disable that capability;
• the method being characterized in that the network head end(s) broadcast(s) (step 102) to a reference multicast address (@ASP) a list (Figure 3) associating service operator identifiers with one or mor^ first-level service multicast addresses (@SSP1), the reference multicast address being known beforehand to all terminals adapted to receive and demultiplex the broadcast multiplexed contents and that reference multicast address being different from all the broadcast multicast addresses.
)
2. A method according to claim 1, wherein the network head end(s) broadcast(s) (step 102) to the reference multicast address (@ASP) a list in which one or more service multicast addresses associated with an operator

identifier differ(s) from the other service multicast addresses associated with other service operators.
3. A method according to either preceding claim, wherein the network head end(s) broadcast(s) (step 122) to one or more first-level service multicast addresses associated with a service operator identifier a table (Figure 4) defining one or more second-level service multicast addresses used by that operator.
4. A method of receiving multimedia programs broadcast by means of a broadcasting method according to any preceding claim, in which method:
• each terminal receives (step 160) the multiplexed
e *
content by listening at a broadcast multicast address, demultiplexes the multiplexed content, and then, provided that it is authorized to do so, decrypts (step 168) the cryptogram of the control word, descrambles (step 17 0) the multimedia program, and uses the descrambled multimedia program (step 172), the terminal including a memory and being adapted to listen simultaneously at a number of multicast addresses; and
• each terminal receives (steps 13 8, 144) service messages by listening at the service multicast address(es) as a function of the content of the service message received and the terminal adapts its operation so as to be capable of descrambling and using the broadcast multimedia program or, to the contrary, to disable that capability;
• the method being characterized in that in response to broadcasting the list to the reference multicast address, the terminal listens (step 134) at one or more first-level service multicast addresses specified in that list to receive service messages.
5. A method according to claim 4 for receiving multimedia programs broadcast using a method according to claim 2, wherein the terminal selects (step 134) in the list the service multicast address(es) corresponding to a service operator identifier prestored in its memory, athen listens (step 136) at the selected service multicast addresses to receive service messages and does not listen at the multicast addresses not selected from this list.
6. A method according to claim 4 or claim 5 for receiving multimedia programs broadcast using a method according to claim 3, wherein, in response to the broadcasting of the table, the terminal listens (step 142) at one or more second-level service multicast addresses specified in that table.
7. A method according to any preceding claim^. wherein the first- or second-level service multicast addresses are also all different from the broadcast multicast addresses.
8. A method according to any preceding claim, wherein the broadband network is an IP (Internet Protocol) network.
9. A terminal for receiving scrambled multimedia programs, characterized in that it includes an access control software module (48) adapted to implement a reception method according to any one of claims 4 to 8.
10. A network head end adapted to broadcast scrambled multimedia programs, characterized in that it is adapted to use a broadcasting method according to any one of claims 1 to 3 and 7 to 8.