GB2336745A - Implementing a Command Interface over an IEEE 1394 Bus - Google Patents

Abstract

A digital multi-media device comprises an IEEE 1394 serial bus port for communicating Command Interface data, a coder for converting transport objects of the Command Interface into AV/C-CTS (Audio/Video Control-Command Transactions) opcodes and a transmitter for transmitting the opcodes through the port. The device has a corresponding receiver and a decoder for converting AV/C-CTS opcodes into transport objects. The command interface is able to function over the IEEE 1394 bus without modification and furthermore, since the AV/C-CTS protocols are extended, the operation of the IEEE 1394 bus is not significantly altered. Preferably the device comprises a Conditional Access Module (CAM) whose functions are available to other devices on the bus.

Description

2336745 1 DIGITAL M-=TI-MEDIA DEVICE A1CD METHOD RELATING THERET The

present invention relates to a digital multimedia device such as a digital video device and an arrancement and method which allows the device to communicate with another device on a common bus.

In the field of digital video processing, it is known to code dicital video signals such that special processing s needed in the receiver to be able to reproduce the video signals. In particular, it has been proposed to provide a Conditional Access Module which can perform all of the descramblinc and other conditional access functions of the digital TV receiver. This allows conditional access and signal decoding functions to be separated froT-n a host receiver, such that a generic dig-ital TV receiver can operate wJth many different conditional access systems in different Conditional Access Modules.

To allow communication between a Conditional Access e an. a d-'gita7 TV e-e-ver, a Common Interface has been proposed and standardized by CENELEC (ENS0221 Common Interface Specificat ion for Conditional Access and other Digital Video Broadcasting Decoder Applications). This standard Common Interface defines a transport stream interface in which various virtual channels are time multiplexed and a Command Interface over which various additional command data are sent. The Common Interface thus allows connection of a Conditional Access Module to a dillaital TV receiver or indeed any other digital video device.

As a basis for the present invention, it is now recognised that it would be advantageous to provide a Conditional Access Module on a local network of digital multi-media devices including audio and video devices, such that the various functions available in the Conditional Access Module can be provided to all of the devices on the network.

A standard has been proposed for connecting together vari.ous digital video devices on a local network. In particular, I= 1394 is a 1995 IEEE standard for a high performance serial bus and defines a bus, which will be refe'-red to as an I= 1394 Serial Bus, for connecting together various digital consumer audio/visual products.

The I= 1394 specification defines a physical connector, electrical signalling and a set of link and tra-nsaction protocols allowing the serial bus to self cG.n'-'zure and carr-,, and control efLficiently.

A further set of additional protocols have also been defined to carry MPEG data and provide control mechanisms between different items of equipment on the IEEE 1394 Serial Bus. These protocols are defined in the specification "Digital Interface for Consumer Electronic Audio/Vide-C7 Equipmeht11 (IEC 1883).

The I= 1394 specification defines mechanisms and protocols to carry two types of data, namely asynchronous and isochronous data.

Asynchronous data generally has no requirements on the transport mechanism regarding time, for example the jitter imposed or the delay in transmission. This data can be used for instance for file data or general command and status data.

on the other hand, isochronous data has strong recr.iirements for low jitter and a fixed or bounded delay for transmission and may be used for MPEG coded audio and video data.

In view of the developments with the I= 1394 Serial Bus, it is now considered to connect a Conditional Access Module to a number of different digital multi-media devices such as audio and/or video devices using the I= 1394 Serial Bus. Unfortunately, however there are significant pro]..-'-ems in implementing such a system. I= 1394 related T:rotoco'Ls have been developed that are intended for use w-'th streams of single channel MPEG data and its own 2 CJ proLocols are provided for-various command data. In particular, the Conditional Access Common Interface and the lEE7- 1394 serial bus have set different standards.

The present invention concerns implementing the Command Interface over the I= 1394 Serial Bus.

According to the present invention, there is provided a method of implementing a Common Interface Command Interface over an I= 1394 Serial Bus comprising:

extending AV/C-CTS Protocols used for communication over the bus to include opcodes corresponding to transport objects of the Command Interface.

According to the present invention, there is also provided a digital multi-media device comprising:

a port for an I= 1394 Serial Bus for communicating command data of a Command Interface; a coder for converting transport objects of the Command Interface into AV/C-CTS opcodes; transmitter for transmitting the AV/C-CTS opcodes the port.

io a through According to the present invention, there is also 'ded a digital multi-meda device 1,rcv- comprising:

a port for an IEEE 1394 Serial Bus for communicating --5 command data of a Command Interface; a receiver for receiving AV/C-CTS opcodes through the port; and a decoder for converting appropriate AV/C-CTS opcodes ntcorresponding 'ransp::,rt objects of the Command '-''-rter,:ace.

Tn th-1s way, the Command Interface is able to functlon as previously intended without modification, but Can onerate over the IEEE 1394 Serial Bus. Furthermore, operat--'Lon of the I= 1394 Se--ial Bus is not significantly 2.5 altered, since the AV/C-CTS Protocols are already in accordance with the IEEE 1394 Serial Bus and an exzension of their command set will not interfere with operation, but only extend it.

Preferably, a Conditional Access Module is constructed according to the invention.

In this way, the functions of the Conditional Access module will be available to many devices on the IEEE 1394 Serial Bus. Furthermore, the Conditional Access Module can be located in any suitable position and take any suitable form.

The present invention is applicable to any digital io multi-media device including devices handling audio data, v'deo data, other multi-media data or a mixture thereof. it --'Is particularly advantageous for digital video devices hand-1-Ing at least video data.

Preferably, the eleven transport objects of the Command Interface have eleven corresponding AV/C-CTS o-Dcodes.

In this way, each of the eleven transport objects are u-ic-j.e-'y defined by a respective AV/C-CTS opcode, such that = distinction need be made upon receint of an AV/C-CTS opcode relating to the Command Interface.

Preferably, the objects of the Command Interface are encoded within the payLoad of the AV/C-CTS opcodes using a PC Card Implementation Transport Layer syntax.

In this way, the Generic Transport Layer of the Comimand Interface need only consider lower functional layers in the same way as was intended for the PC Card Implementation.

Preferably, the Generic Transport Layer of the Command Interface is supported by a Common Interface IEEE 1394 specific transport layer, in turn supported by an AV/C-CTS Implementation Link Layer providing the AV/C-CTS 5 Protocols.

In this way, the Common Interface I= 1394 Specific Transport Layer replaces the PC Card Implementation Iransport Layer previously used, such that the Generic iransport Layer is transferred to the AV/C-CTS Implementation Link Layer with no knowledge required of its existence.

Thus, by virtue of the present invention, it is possble to preserve the higher layers of the existing DVB Common Interface as defined in ENS0221, to make use of exist-ing protocols developed for the IEEE 1394 Serial Bus, to ensure opera-Lion alongside existing products designed 'or use with the IEEF 1394 Bus, to ensure that the -lows further expansion to the DVB Common __Plementation al_. 7nterface standard to provide mechanisms to take advantage 2r, c4_ the networked architecture of the IEEE 1394 Se--ial Bus and to ensure any extensions required to the DVB Common interface will still be compatible with the present fication.

spec-j_ The invention will be more clearly understood from Lhe fo-'low-'.ng description, given by way of example only, wth reference to the accompanying drawings in which:

Figure 1 illustrates a DVB Common Interface 7 architecture; Figure media devices; with a 2(a) illustrates a network of digital multi- Figure 2(b) illustrates a network of digital devices Conditional Access Module; Figure 3 illustrates an I= 1394 protocol stack; Figure 4 illustrates a DVB Common Interface PC card implementation protocol stack; Figure 5 illustrates a DVB Common Interface I= 1394 10 implementation protocol stack; Figure 6 illustrates schematically a device for im-lementing a Common Interface Command Interface over an 1394 Serial Bus; Figure 7 illustrates a DVB Common Interface I= 1394 m'ementation protocol stack; p- -L Figure 8 illustrates a device for implementing a Com.mon Interface Command Interface over an I= 1394 Serial cure 9 illustrates a Common Interface configuration 2C us--'ng an IEEE 1394 Serial Bus; and Figure 10 illustrates a DVB Common Interface I= 1394 implementation Transport Stream Interface protocol stack; and Figures 11(a) and (b) illustrate a transport stream 25 and associated table.

As mentioned above, a standard has already been spec-'fied for a Common Interface for a Conditional Access - 8 Module. Fiaure 1 illustrates the architecture of this standard.

As illustrated, a receiver or host 2 is connected to a Common Interface Module such as a Conditional Access Module 4 by means of the Common Interface 6. Other types of Common Interface Module might include RF input front ends for receiving, for instance, satellite transmissions, audio decoders for "Auditel" scene description for the visually impaired, audience metering modules, etc.

The DVB (Digital Video Broadcast) Common Interface specification currently defines the physical layer of the common interface to conform to the PC card standard as s-pec ed by the PCMCIA. In other words, physically the connection forming the Common Interface comprises a 68-way connector with the standard PC card arrangement- as used in many personal computers today. However, the DVB Common Interface has been designed with a layered architecture to a-low new physical layers (for example the smart card form to be used with the same upper layer protocols. In other words, the processing conducted on either side of the physical connection has been designed such that different physical arrangements can be used for the connection without changing the way in which the standardized processing operates.

As illustrated in Figure 1, the DVB Common Interface includes two main parts, namely a transport s't-ream -L - 9 - 2 rl, interface 8 and a command interface 10.

The transport interface 8 is used to transfer a transport stream from the receiver or host 2 to the module 4 and back to the receiver 2. In particular, the receiver 2 receives an RF input 12, a particular band is selected usina a tuner 14 and this band is demodulated in the demodullator 16. The output of the demodulator 16 comprises a transport stream including time multiplexed virtual channels. These are transmitted over the transport stream interface 8 to a descrambler 18 in the module 4. The descrar..ibler 18 identifies those virtual channels for which it is 1ntended and sends back to the receiver 2, over the transport stream interface 8, a transport stream in which selected virtual channels have been descrambled. In the receiver 2, a demultiplexer 20 selects a required virtual channel and passes MPEGY packets relating to that virtual channel to an. MPEG decoder 22 which, in turn, outputs an output 24.

The second part. of the DVP Commion Interface is the command interface 10. This provides a high level protocol allowing the host receiver 2 and the module 4 to communicate and, furthermore, for Applications in either the host receiver 2 or module 4 to access Resources across the interface. In particular, standardized codes and data format-s are provided for communication over the Command interface.

A microprocessor 26 of the host receiver 2 and a - 10 r microprocessor 28 of the module 4 can communicate using the Command Interface. Furthermore, the overall system may include a MODEM, a graphics generator, etc and the Command Interface can be used to transfer control information to these devices also. As an example, the module 4 may wish to communicate with a remote control centre via a MODEM for details of subscription fees and then control a TV display to indicate messages according to the subscription status. This communication can be achieved by means of the Command interface 10.

As mentioned above, it has been proposed to link various digital video devices together using an IEEE 1394 Serial Pus. Figure 2a illustrates a network in which a digital TV receiver 30 is connected to a digital video recorder 32, in turn connected to a digital video disk 7,.ac.-1--ne 34, in turn connected to a personal computer 36.

The IEEE 1-394 bus is a serial bus that allows a low ccs'. mechanism to transmit audio, video and control -ween equipment. It is very well suited to -nfc----m,a -Lon be. consumier audio/visual applications and is expected to become widely used for many new digital consumer audic/visual products. It is particularly attractive in that it offers a "plug and playll operation. In other words, an additional device may be connected into the network without any special reconfiguring of the network and protoccis are included whereby devices on the network automatically determine what other devices are present.

2 - The I= 1394 Trade Association is an industry grouping that brings together all of the interested industry parties for the IEEE 1394 Serial Bus. This Trade Assoc-Lation has worked to define a set of protocols which 5 offer a set of commands to be carried over the I= 1394 Seriall Bus in the format of the IEC 1883 Function Control Protocol (FCP) mentioned above. The set of commands are kno%-.. as Audio/Video Control- Command Transactions (AV/CCTS', and are specified in the AV/C digital Interface Command Set Document developed by the I= 1394 Trade Association (see AV/C Digital Interface Command Set Version 2.OD March 26, 1997 Audio/Video Working Group of the I= 1394 Trade Association). The AWC-CTS provides general set-up and control commands and sets of commands 5 spec:--'f.-'L--a-_,ly for a digital VCR and tuner. They are encoded us'na a header and a payload. The header contains infcr7,alk--ion such as the destination address and the opcode "y-'ng 1.

spec- L -he function of the command. Further operands of the commands are carried in the payload of the command.

Thus, the communication of data over the I= 1-394 Serial Bus may be considered as a layered structure, with the protocol stack, formed of the various protocol layers, beina illustrated in Figure 3.

For command information, for instance instructing a videc, recorder to start replaying a video signal, data is sent as asynchronous data over the IEEE 1394 Serial Bus. Th.'s is illustrated in the left hand side of the protocol 12 stack of Figure 3.

The commands are sent using the AV/C-CTS protocol, w'th a particular AV/CCTS command having a header which is specific to its destination unit, for instance a video recorder, and indicating the basic required function, for instance replay of a video tape. In particular, the AV/C CTS header specifies fields for command type (eg. control, status, inquiry, notify, etc), subunit type and subunit identifier, such that it defines the destination subunit for a command AV/C frame and the source subunit for a response AV/C frame. In this way, the AV/C-CTS works with a command/response scheme with a first subunit sending a command AV/C frame to a second subunit and the second subunit responding back with a response AV/C frame.

The opcode for the command is also specified in the header so as to indicate the basic function. The payload may be arranged to specify other operands or additional in-formation, for instance indicating that play should occur at a certain speed, such as slow forward, fast for-ward, fastest forward.

The protocol layer of the AV/C-CTS has been designed to conform to the protocol layer beneath it, the IEC 1883 Function Control Protocol. This is a particular protocol for addressing a node (a unit on the network) with attached data. Thus, in this case, the IEC 1883 FCP would function to transmit the AWC-CTS as the attached data.

AV/C-CTS protocols are a specific command set 13 implementation of FCP. The M/C-CTS commands are encoded using an FCP frame, the header of which specifies the I= 1394 node (device) destination and source addresses, frame data length, CRC and other information. In particular, the first four bits of the FCP frame payload make a field which specifies the command set being carried by the FCP frame. The FCP frame header carries a value of 1,011 in this field to indicate that it is carrying an AV/C- CTS command. Command sets other than AV/C-CTS could be carried by the

FCP frame using different values in this field. The rest of the FCP frame payload contains the AV/C header and payload. The protocol layers defined in the I= 1394 specificaticn include a I= 1394 transaction layer which handles delivery and acknowledgement data for the data and a =EE 1394 link layer which provides the various data links to the various units. Finally, the lowest layer is the IEEE -11.394 physical layer comprising the physical connections. 20 The transaction layer provides a set of services to applications running in devices on the IEEE 1394 bus, in particular for asynchronous data only. These are services such as read and write and enable devices to access other devices on the bus by specifying a node id of the device and address within that node. The services are designed to prov'de reads and writes and provide acknowledgements back tc the requester. The transaction layer also provides "lock" services. These are defined as llatoTriic" operations, - 14 meaning the operations are indivisible in time, so that for instance a "test and set" operation from one device on another does not get interrupted half way through by another device modifying the same location. This is very important for a peer-to-peer bus such as I= 1394 where many devices can access each other with equal priority.

The link layer provides the packetisation of the asynchronous and isochronous data. The link layer also provides cycle control which allows isochronous data to be io carried with low latency and bounded jitter.

The lowest layer is the physical layer (or PHY layer in IEEE 1394 terminology). This provides the low level electrical signalling and encoding of the data bits to be The PHY layer provides the lowdevices on the bus so that only bus at a time. The PHY layer also defines the connector and the required characteristics for the cable media.

The protocol layers for isochronous data, such as MPEG data, are illustrated on the right hand side of Figure is transmitted and received. level arbitration between one device is driving the The isochronous data is transmitted according to the IEC 1883 protocol layer. This is supported directly by the IEEE 1394 link layer, which sets up the various connections W'th the IEEE 1394 physical layer. In particular, the IEC -1.

1883 protocol layer sets up an isochronous channel between two devices on the bus.

2 C - is - The I= 1394 specification defines the lower layers for the carriage of isochronous data, these being the physical and link layers as described above. The IEC 1883 protocols provide mechanisms to allow the efficient transport of AV data utilising a Common Isochronous Packet (CIP) header. This allows AV data packets to be split up for transport over the IEEE 1394 bus and also has fields to s'gnal data format (standard or high definition video data, 50 or 60Hz field rate). The IEC 1883 specification also provides the concept of logical channels and plugs for the carriaae and connection of AV data between devices on the I= 1394 bus.

In this way, the IEEE 1394 Serial Bus and its related protocols provide a mechanism for audio/video peripherals to com-municate command and control information, together wi!--'., dicital audio/video data.

As a basis for the present invention, it is proposed that a Common Interface Module such as a Conditional Access Y,c)dul.e could also be connected to a network of digital video devices using an I= 1394 Serial Bus.

Figure 2b illustrates the network of Figure 2a, but further including a Conditional Access Module 38. This arrangement has a number of significant advantages over using the previously proposed PC card implementation of the.7VB Co-mmon Interface.

with the Conditional Access Module provided on the network, the conditional access functions can be used equally by every peripheral. Furthermore, no particular 2 G peripheral has to provide power to the Module or has to act as a protocol bridge through which the Module communicates with the rest of the network.

Since the module on the network need not be closely physically bound to any particular receiver, there is more flexibility in the physical form and positioning of it. In other words, whereas previously a Conditional Access Module might be connected to the back of a receiver or video recorder, a network allows the module to be placed in any convenient position and in any convenient form.

Finally, even if conditional access functions are embedded in a particular device, such as a receiver, rather than in a separate Conditional Access Module, the network makes it possible for other devices to make use of the embedded conditional access functions.

F-i.gure 4 illust-rates the various protocol layers orm-Ing the protocol stack for the Command Interface of a Common 'Interface as implemented in a PC card format. The varlous sections of the Common Interface standards document 7-NS0221 mentioned above are also given in this figure.

At the highest layer, the Application Layer, the various Applications and Resources are provided.

Below this is the Session Layer. Thus, when a particular device has an application requiring the use of a resource, it sets up a session by means of the Session Layer with another Resource.

The process utilises each of the layers down to the - 17 lowest physical layer. From the lowest physical layer, all the various layers are then utilised up to the Resource of the other device. In other words, the data is transmitted between the resource and application by processing the data down from the application through each layer to the physical layer where it is then processed back up to the resource. The data can then return in a similar way from the resource back to the application.

In general, lower layers are transparent to the upper layers, such that when an Application requires a session with a Resource, it is not aware of how the Session Layer or lower layers achieve that session.

The lowest generic layer of the DVB Common Interface is the Generic Transport Layer. This layer provides a set c- eleven transport objects that are used to control the creation and deletion of transport connections and carry data over these transport connections.

Below the Generic Transport Layer, the PC card transport layer actually sets up the transmission of data to be suitable for transmission over the PC Card defined electrilcal/physical interface. Thus, since lower layers are transparent, it is not important to the Generic Transport Layer how further communication of data takes place. In particular, it is not important to the Generic Transport Layer whether the PC card format is used.

With reference to Figure 5, a solution is proposed to the problem of providing the Command Interface on the I= 1394 Serial Bus.

This solution is based on sending the command data of the Command Interface by means of asynchronous data on the I= 1394 Serial Bus and proposes that the AV/C-CTS 5 proto-wols be extended to carry the command data.

As illustrated in Figure 5, the PC card transport layer which previously handles the higher Generic Transport Layer is replaced by a Common Interface I= 1394 Specific Transport Layer.

As mentioned above, the lower layers are transparent to the Generic Transport Layer. Therefore, the Generic Transport Layer and higher layers need not be aware of the different Specific Transport Layer and the functioning of the standard Command Interface is not changed.

Commands are produced in the Generic Transport Layer in the same way as before. However, these are then handled by the CDmmon Interface IEEE 1394 specific Transport Layer in accordance with the IEEE 1394 arrangement rather than the PC card arrangement.

The extended AV/C-CTS protocols provide a mechanism for carry-ing the command interface protocols. In effect, the AV/C-C7PS protocols carry the newly defined Common interface I= 1394 Specific Transport Layer.

The proposed extensions to the AV/C-CTS protocols are as follows. The eleven objects of the Command Interface are each given an AV/C-CTS opcode, such that there is a senarate AV/C-CTS command for each one of the eleven obiects of the Command Interface. The object of the Com7mand Interface can then be encoded within the payload of the AV/C-CTS command using a similar syntax as is used in the PC Card Implementation.

The AV/C-CTS protocol may be extended to cover other peripherals defined as "sub-unit types" and the Conditional Access Module can be defined as a new sub-unit type. In this way, each of the eleven new AV/C-CTS opcodes will be recognised as being intended for a Conditional Access Module, in contrast to opcodes intended for the TV receiver, video recorder, etc.

In this way, the Command Interface can continue to functlon in the same way as previously defined for the PC Card Implementation. There is no need for modification of the upper layers or, indeed, any awareness of the means of the lowe.r layer communication. Similarly, communication of the com-mand interface data is achieved using the standards aready def'Lned for the I= 1394 Serial Bus, such that no modifications are recraired to these standards.

Thus, it is possible to provide a Conditional Access Module which operates over the I= 1394 Serial Bus, merely by providing additional AV/C- CTS opcodes corresponding to transport objects of the Command Interface.

Figure 6 illustrates schematically a device such as a h--st rece4Lver 2 or Conditional Access Module 4 implementing a Command Interface over an IEEE 1394 Serial Bus.

A microprocessor 26,28 can continue to produce and 2 0 receive command data in the normal way. However, additional functional blocks, namely a coder 40 and a decoder 42, are provided to convert the data according to the extended AV/C-CTS protocols.

The code.r 40 produces appropriate AV/C-CTS commands with headers including appropriate ones of the eleven opcodes corresponding to the eleven objects of the Command Interface. objects of the Command Interface can then also be included in the payloads of the AV/C-CTS commands using a syntax similar to the PC Card Implementation syntax.

The decoder 42 on the other hand produces appropriate Command Interface objects from the opcodes and payloads of the received AWC-CTS commands.

A transmitter 44 is provided to transmit the AV/C-CTS 1-5 commands, for instance under the IEC 1883 protocol, via a p=t 48.

A receiver 46 receives AV/C-CTS, commands from the pcrt 4E and distinguishes appropriate AV/C-CTS commands by --dg-ntfyng ones of the eleven new Common Interface type opcodes as opposed to opcodes used for other units.

Figure 7 illustrates an alternative solution to the problem of communicating Command Interface data over the IEEE 1394 Serial Bus.

In particular, it is proposed to use an isochronous channel to carry the Command Interface data. This has the advantage of being able to guarantee a bandwidth for DVB Common Interface Command Interface data, which is very 1 - 21 use-ful when running applications that require a fast response and low delay, eg. graphics. It is proposed that, u-,Don initialization, two isochronous channels would be created, one running from the host to the module and the 5 other from the module to the host.

By comparing Figures 4 and 7, it will be seen that the implementationtransport layer of Figure 7, namely the PC card transport layer, has been replaced by a common interface IEEE 1394 specific transport layer.

Since lower layers are transparent to the Generic Transport Layer, replacement of the PC card transport layer will have no effect on the Generic Transport Layer and the Common Interface IEEE 1394 Specific Transport Layer will merely handle the data of the Generic Transport Layer in a manner sutable for the I= 1394 Serial Bus. Thus, when a sess-'. on is required to communicate Com-mand Interface data bezween an Application and a Resource, the common interface 17-7-7- 1394 specific transport layer and IEC 1883.m-,:ementation link layer operate together to set up two isochronous channels over which the command data may be transmitted.

Figure 8 illustrates schematically a device such as a host receiver 2 or a module 4 with a corresponding mcroprocessor 26 or 28.

As illustrated, an additional functional block 50 is provided. This communicates with other devices over the I= 1394 Serial Bus, for instance by means of the IEC 1883 n n 5 L - 22 protocol, to set up isochronous channels. The command data of the Command Interface may then be sent or received over an appropriate channel.

Once the isochronous transmission channels are set up, there is no need for acknowledgements and such like. Therefore, the IEEE 1394 Serial Bus side of the interface need not have a knowledge or require any modification in view of the Command Interface data being transmitted. Preferably, however, this implementation can include features of that discussed above. In particular, the AV/CC7S protocol may nevertheless be extended so as to define a Condiltional Access Module as another sub-unit type in addition to previous units such as the receiver and video recorder. This will allow increased inter-operability with other devices on the IEEE 1394 Serial Pus, in particular a'low2ng the Conditional Access Module to be identified by peripherals on the IEEE 1394 Serial Bus.

The transport objects of the Command Interface consist of objects used for transport connection creation and deletion and objects used to carry the data for upper protocol layers. The control related objects can be encoded as AV/C-C-AS commands, either each in separate A7,7/C-CTS commands or in one generic AV/C-CTS command.

The objects used for data carriage could then be used to carry the data to and from the module on the isochronous channels In other words, the generic transport layer defines 1 5 2 23 eeven objects - these can be separated into two sets. One set is used for connection management, setting up and closing down transport connections. The other set is used for data carriage over an existing transport connection previously set up using the other transport objects. Generally transport connections are set up infrequently and the most heavily used transport objects are those used to carry data.

Use of the isochronous channel guarantees bandwidth for applications. Hence, the transport objects used most on the isochronous channel would be transport objects carry-Ing data; not setting up connections etc. Hence, the connection management transport objects could be still carried as AV/C-CTS commands as previously discussed and it would not affect the efficiency of the scheme much. Since a layered scheme is used, the generic transport layer need not be aware of whether the objects were carried as asynchronous or isochronous data. The connection management transport objects can be considered to be more su2-table to be carried as A.V.IC-CTS commands.

On the other hand, all eleven of the transport obects of the command interface could be encoded in the same way as with the current DVB common interface specification and then carried in the I= 1394 isochronous channels. This avoids the use of the AV/C command set, since this is only required for use with the asynchronous data.

- 24 A disadvantage of using an isochronous channel for the Command Interface is that bandwidth allocated to the Command Interface will be wasted if it does not completely fill the isochronous channels provided. In particular, bandwidth allocated for intensive applications will be wasted when those applications are not active.

It would be possible to allocate the bandwidth of the recy,.i-Lred isochronous channels dynamically, depending on how much the applications require at any one time. In part-Lcular, a host and module could initialize to a default low value bandwidth for the Command Interface isochronous channels and then request allocation of more bandwidth if an aiDo'ication requires a faster response. In particular, the device (host or module) requiring the extra bandwidth can contact the isochronous resource manager and request the extra bandwidth required. If available the bandwidth can then be allocated to that device. Bandwidth can be given up in the same way. The device requesting the ba---'-w--"dzh can then output on the existing isochronous channel using the extra bandwidth and over the existing connection.

The isochronous resource manager is a device required on the bus if isochronous channels are to be allowed. Several devices could be isochronous resource manager capable and will arbitrate to allow one device to become the isochronous resource manager.

In order for a Conditional Access Module to be put on - 25 an IEEr- 1394 Serial Bus network as mentioned above, it is also necessary for transport streams to flow to and from the Conditional Access Module.

The DVB Common Interface PC card implementation carries the transport streams usincr dedicated electrical connections on the host and module connectors. The IWE 1394 Serial Bus provides no such physical connection, but only a set of isochronous channels providing logical connections between host and module. Therefore, a connection protocol needs to be defined to allow transport stream connections to be Trade between host and module.

The IEC 1883 implementat ions regarding Serial Bus management are compliant with the I= 1394 Interface Standard. According to these implementations and L5 standards, an item of equipment, known as a node, connected to the I= 1394 through an interface board shall be cycle master capable. In other words, a cycle master unit is ided to control the timing of the isochronous channels provL used by all the nodes on the IEEE 1394 Serial Bus. Each node is also isochronous resource manager capable, such that an isochronous resource manager can control the allocation of isochronous resources to nodes on the IEEE 1394 Serial Bus. In other words, the resource manager can set up particular isochronous channels between particular nodes. Finally, a node which is transmitting or receiving isochronous packets shall provide plug control registers wh-Lch themselves are used to set up and control 26 audio/visual connections between nodes on the IEEE 1394 Serial Bus.

The protocols described in the IEC 1883 Standard provide a method of controlling isochronous data flow between devices connected using the I= 1394 Serial Bus.

According to this standard, devices have input and output plugs for transmitting and receiving isochronous data flows. Each plug can only carry one isochronous data flow and that isochronous data flow is carried in one isochronous channel which itself can carry only one isochronous data flow.

A connection is made between two plugs and defines the isochronous channel number and the bandwidth recruired.

Connections can be overlaid on one plug to allow an isochronous data flow to be connected to more than one destination plug. In this case, although there is more than one connection, there is still only one isochronous channel carrying the data flow.

Fig-ire 9 illustrates a possible configuration where a 22 0 Conditional Access Module 38 is connected on an T-EEE -1394 Serial Bus.

Thus, it is proposed to use isochronous channels to carry the MPEG transport streams. In particular, it is proposed that isochronous channels will use IEC 1883 protocols to carry the MPEG transport stream using the common isochronous packet (CIP) header described above.

Figure 10 illustrates the various protocol layers 1 5 1 making up the appropriate protocol stack.

Thus, the upper layers correspond to the MPEG upper layers which would be used for the Common Interface, such that the higher generic protocol layers of the Common inter-face do not need any modifications.

To implement this system it is proposed that the Conditional Access Module and the host receiver each -Include at least one input plug and one output plug as defined in IEC 1883, a master input and output plug control rezister as defined in IEC 1883 and an input and output p -5ug control register for each plug implemented, as defined in IEC- 1883.

For the arrangement illustrated in Fig-are 9, there will now be described a connection protocol which could be use- to transmit transport streams between the host receive.- 30 and Conditional Access Module 38.

First, the host 30 identifies all the DVB Common interface Modules present on -the network, preferably using th_= s.--'---unit mechanism def -2ned the AV/C-CTS protocol The host 30 then requests from the isochronous resource manager L-he use of two isochronous channels each of the bandwidth necessary to carry the required transport stream.

The host 30 then configures the input plug control register of the Conditional Access Module 38 to receive a transp=t stream on the first isochronous channel and configures its own output plug control register to output the transport stream on that channel. The host 30 then - 28 configures the output plug control register of the module to output the transport stream on the second isochronous channel and configures its own input plug control register to receive the transport stream on that channel.

The host 30 can then send a scrambled transport stream over the first isochronous channel and receive the descrambled transport stream back from the module 38 on the second isochronous channel.

Since the Conditional Access Module 38 is not connected to any particular device, it is no longer essential that a descrambled clear transport stream must be sent back to the source 30 of the scrambled stream. Thus, the Conditional Access Module 38 may be used more flexibly and may send a clear stream to a different device to that which the scrambled stream was received.

Clearly, the scrambled transport stream received by receiver 30 must be sent to the Conditional Access Module 38. However, it is then possible for the Conditional Access Module to send the descrambled transport stream only to the digital video recorder 32 (through the receiver) or to both the digital. video recorder 32 and the receiver 30. Thus, the Conditional Access Module 38 must transmit to either one or two destinations.

In the example illustrated in Figure 9, a first proposal is that the receiver 30 will have the necessary transport stream switching resources to receive the transport stream from the Conditional Access Module 38 and i 0 - 29 then reroute it on to the digital video recorder 32 via a thJ:-rd isochronous channel either as a normal IEEE Serial Bus transmission or as a Common Interface transport stream. Indeed, these resources will be used to route clear streams to the digital video recorder 32 when the Conditional Access Module 38 is not required. This proposal would alow only the program stream of interest to be sent to the digital video recorder 32, rather than the whole transport stream.

A second proposal is to use two transport stream connections, namely one from the host 30 to the module 38 and the other from.. the module 38 to the digital video recorder 32.

These connections could be set up and configured in a s--,,..JLlar way to that described above, but with the second socAnronous channel being set up between the module 38 and the video recorder 32. This would have L-he ad-.-antage of avoiding the need for the host receiver 30 to -tse7-.-" switch the program back to the digital video recorder 32. This in turn, will allow the use of the resources in the host receiver 30 for other applications or a cheaper implementation of the host.

of course, in this case, the digital video recorder 32 would receive the whole transport stream, but could be arranged to strip out all of the streams which are not of interest either under the direction of the host 30 or in a stand alone mode.

The arrangement of Figure 9 may also be configured as described below.

Instead of the host receiver 30 switching a required program stream back out to the digital video recorder 32, overlaid connections can be used. In particular, having set up isochronous connections between the host receiver 30 and the Conditional Access Module 38, the host receiver 30 then overlays a connection from the Conditional Access Module 38 to the digital video recorder 32. As mentioned above, overlaying a connection uses the same isochronous channel, but directs it to an additional destination, in thi.s case, the digital video recorder 32.

This configuration has the advantage that the sw_-.ch-ng resources of the host receiver 30 are not used anJ also that no additional bandwidth is used in tranS7.-'ltt-'Lno the transport stream on to the digital video recorder 32 in addition to the host receiver 30.

once again, the second destination, in this case the video recorder 32, would receive the whole transr)--r'. stream. However this, could be an advantage where the second destination is perhaps a display in another room. in particular, it would allow the selection of the program, stream to be made independently from the host receiver 30.

The use of Conditional Access Modules in conjunction w-'-L-h the I= Serial Bus brings about the possibility of communication of another type not previously considered for i 5 - 31 the IEEE 1394 Serial Bus. As an example, rather than return a descrambled transport stream to the host receiver 30, the transport stream can be passed on to a second Conditional Access Module (not shown) for further processing or descrambling of other virtual channels of the transport stream. To do this, it is proposed that the host receiver 30 contacts the isochronous resource manager to request a third isochronous channel, configures the output control register of the first module 38 to remove the return connection between the first module 38 and the host 30 and sets up a new connectlon between the first 38 and second modules using the second isochronous channel. The hcst. 30 then configures the input plug register of the second module to receive a transport stream on the second schronous channel and configures the output plug control re=-'ster of the second module to set up a connection between the second module and the host 30 using the third..so--hronous channel. It then configures its own input plug register to receive the transport stream on the 20 thIrd isochronous channel.

Thus, whether all available modules or a selection of modules are utilised is at the option of the host.

According to the PC card implementation of the Cond--"tional Access Module, the full transport stream. as rece-ived by the host receiver is passed to the Conditional Access Module. Placing the transport stream at this level silmplifies the interface, since the host receiver needs no 1 1 5 - 32 knowledge of the operation of the Conditional Access Module. In particular, the Conditional Access Module can receive and use private streams of which the host receiver has no knowledge or understanding. These streams can include descrambling information, subscription information, etc.

The DVB Common Interface defines the transport stream bit rate as being at least 58 Mbit/s. Hence, to carry a transport stream to and from a Conditional Access Module 10 over the I= 1394 Serial Bus requires a minimum of 116 Mbit/s of bandwidth. Furthermore, each additional module would require at least a further 58 Mbit/s of bandwidth. 7he I= 1394 Serial Bus has various standard bandwidths. wowever, as will be apparent from the above, the 100 Mbit/s Serial Bus would be precluded and the 400 Mbit/s Serial Bus wc,.^"d soon be filled up using Conditional Access Modules.

According to the I= 1394 Serial Bus standards, 63 may be used on any one bus. However, with Access Modules s-ch arze bal-d-,,;-'d,hs, there is a relatively low limit on the number of independent Modules which can be used on the bus.

Transmission of the full transport stream over the network is a very inefficient use of bandwidth, since any one Conditional Access Module usually descrambles only one or two v, rl.-ual channels of the transport stream. The Conditional Access Module may also require other data streams in the transport stream, but these are generally of - 33 relatively small bit rates compared to the program streams contalning video and audio information. Hence, it is likely that a large amount of information will be transferred around the network with only very little of it being processed by the Conditional Access Modules. This results in a restriction of the applications of the Conditional Access Module and other devices using the I= 1394 Serial Bus.

One solution to this problem would be for the receiver 30 to send out only those program streams which are to be processed. Since generally only one or two program streams are used at once, this would dramatically reduce the bit rate required and since the transport stream c a stream of packets, packets may be stripped out ILS independently of the packets of other streams so as to leave a transport stream which is still compatible with the DVE Common Interface.

However, a Conditional Access Module usually requires streams contain-ing entitlement and encryption information. If the host receiver caInnot identify these streams, it is not able to determine which streams to send to each Conditional Access Module. Indeed, even if these streams can be identified, there may be so many different streams of information, that the number is beyond the capability of the host receiver to filter out and send.

Clearly, if these additional streams are not sent to the Conditional Access Module, then correct functioning of - 34 the module cannot be achieved.

A transport stream usually contains a table or map, for example MPEG Program Specific Information (PSI), 171dicating the various program streams present and other identifying maps. However, since not all the data in the transport stream need be identified in the table, a host receiver may not be able to identify the presence of certaL-- data.

it would be possible for a Conditional Access Module 0 to sanal to the host receiver which streams it requires.

I:--wever, this would necessitate an extension or modification to the higher layer functionality of the Commion Interface standards and this is preferably to be avoided.

ZLgure ii(a) illustrates schematically time exed data streams, together with an associated -L -1e.

ab Figure 11(b) illustrates schematically the table of il(a).

As will be anparent, from the table, a device can determine the content of associated data streams, for example that data stream 1 relates to program Channel D. Fowever, as illustrated, not all the data streams need be identified in the table.

t is proposed here that rather than have the host receiver identify the program streams which are required, it should identify the program streams which are known not - 35 to be required. In this way, the host receiver can safely strip out all the program streams which are not required whilst ensuring that any other data streams required by the Conditional Access Module will still be present in the transport stream. sent to the Conditional Access Module.

Thus, for the example of Figure 11, if Channel B is to be descrambled by the Conditional Access Module, then the host receiver strips out streams 1, 2 and 6, which it can determine from the table relate to broadcast Channels A, C and D. In this way, if there is any additional information in streams 3 and 5 which are required by the Conditional Access Module, this will still be sent to the Conditional Access Module.

In the case of MPEG streams, only program streams the hcst receiver can identify from the MPEG Progran Specific 7i.nfc--T-,,ation (PSI) data are removed. This PSI data is spi-:--cif.ed in the MPEG-2 system. specification (ISO/IEC 13818-1 GenerJc Coding of Moving Picture and Associated

Systems) and' is always present in an MPEG transport szrea7 and therefore can be used to identify the program streams present. By removing known program streams, prIvate data of which the host receiver could have no knowledge is retained in the transport stream sent over the Common Interface on the I= 1394 Serial Bus.

As the dominant portion of the transport stream will consist of video proaram., streams, removing unwanted video program, streams will significantly reduce the bandwildth required by the Common Interface on the I= 1394 network.

Claims (12)

1. A digital multi-media device comprising:

a port for an I= 1394 Serial Bus for communicating command data of a Command interface; a coder for converting transport objects of the Command Interface into AV/C-CTS opcodes; a transmitter for transmitting the AV/C-CTS opcodes through the port.

io

2. A digital multi-media device according to claim 1 further comprising:

a receiver for receiving M/C-CTS opcodes through the port; and a decoder for converting appropriate AV/C-CTS opcodes into corresponding transport objects of the Command Interface.

3. A digital multi-media device comprising:

a port for an I= 1394 Serial Bus for communicating command data of a Command Interface; a receiver for receiving AV/C-CTS opcodes through the port; and a decoder for converting appropriate AV/C-CTS opcodes into corresponding transport objects of the Command interface.

4. A digital multi-media device according to claim or 3, comprising a Conditional Access Module.

5. A digital multi-media device according to claim 1, 2 or 3 comprising a digital video receiver.

2 _n

6. A digital multi-media device according to any preceding claim wherein said device is a digital video device for handling at least video data.

7. A method of implementing a Common Interface Command Interface over an I= 1394 Serial Bus comprising:

extending AV/C-CTS Protocols used for communication over the bus to include opcodes corresponding to transport objects of the Command Interface.

8. A device according to any one of claims 1 to 6 or a method according to claim 7 wherein the eleven transport objects of the Command Interface have eleven corresponding respective AV/C-CTS opcodes.

9. A device or method according to any preceding claim, wherein the AV/CCTS opcodes are included in the header of AV/C-CTS commands and the objects of the Command interface are encoded within the payload of the AV/C-CTS commands using a syntax at least based on the PC Card imnlementation Transport Layer.

10. A device or method according to any preceding claim wherein the Generic Transport Layer of the Command Interface is supported by a Common Interface IEEE 1394 Specific Transport Layer, in turn supported by an AV/C-CTS Implementation Link Layer providing the AV/C-CTS Protocols.

11. A digital multi-media device constructed and arranaed as hereinbefore described with reference to and as illustrated by Figures 2(b) and 5 to 11 of the accompanying 39 - drawings.

12. A method of implementing a Conditional Access Module Command Interface over an IEEE 1394 Serial Bus substantially as hereinbefore described with reference to and as illustrated by Figures 2 (b) and 5 to 11 of the accompanying drawings.