KR20010006688A - Method and apparatus for recovering data stream clock - Google Patents

Abstract

PURPOSE: A data stream clock recovery method and system is provided to recover and synchronize clocks of video data stream received in a digital home network for displaying the video data on home electronics, for example a TV. So it can simplify a complex network interface method by a set top box in the conventional method. CONSTITUTION: A data stream clock recovery method comprises the steps of distributing MPEG clock to an internal network by recovering MPEG clock from data stream received from an external network, a network interface unit recovering MPEG related clock from the MPEG data stream received from the external network, selecting a program from the stream by using an MPEG transmission chip positioned in the network interface unit, synchronizing local clock as the recovered MPEG related clock to supply internal clock for the internal network, transmitting the MPEG data from the network interface unit to the internal network according to the internal clock, and synthesizing the MPEG clock from the MPEG data transmitted to the internal network.

Description

Method and apparatus for recovering data stream clock

This patent application discloses US application Ser. No. 08 / 561,758, filed November 22, 1996, entitled Home multimedia network architecture; US application Ser. No. 08 / 561,757, filed November 22, 1995, entitled Set-top electronics and network interface unit arrangement; US Application Serial No. 08 / 561,534, filed November 22, 1995, entitled Crossbar / Hub arrangement for multimedia network.

TECHNICAL FIELD The present invention relates to a multimedia digital network, and more particularly, to recovering and synchronizing with respect to the clock of a video data stream received in a digital home network for conversion to use and display by a home appliance such as a television.

The rapid increase in digital technology and telecommunications has increased the hope of having a home network that will interconnect various home appliances to each other and to the outside world. The range of external services available includes interactive services, cable video and audio services, satellite networks, telephone company services, video on demand and other kinds of information services. However, the penetration rate of personal computers in homes in the United States is about 33 percent, which is only increasing slowly, even if the government is encouraging "telecommunications" and reducing traffic and pollution on the channel, hoping for a wider penetration rate. The further penetration of computers in the home stems from the purchase of user entertainment and information products, including embedded computers and operating systems that are obscured by obscure user interfaces. Such a product is a conventional set-top box.

Set-top boxes are multimedia computers that increase the use of television. A typical set top box has an external network interface module that connects the set top box to an external network and a data provider. The network interface module must perform a number of complex operations, such as interfacing, tuning, demodulating, error correction, video descrambling, MPEG clock recovery, and encryption and decryption specific to the external network. After all, network interface modules are a relatively expensive component of set-top boxes. Even when only one television is in the house, this cost is necessary. However, most homes have multiple televisions, each providing its own set-top box and associated network interface module, which is a duplication of expensive components.

One of the functions of the network interface unit is Motion Pictures Expert Group (MPEG) clock recovery, and MPEG-1 and MPEG-2 are two differently accepted standards for transmitting digitized video data. MPEG data is typically a continuous stream of data clocked at 27 MHz. In a typical architecture, when the network interface unit is connected to the set top electronics by a bus, there is little or no risk of video signal attenuation due to jitter since the local bus will not attract substantial jitter. Conversely, if video data is placed on a shared network and distributed through a hub, jitter is likely introduced by the home network because the video data will be buffered behind other data at some point in the network. The higher the jitter, the more difficult it is to recover the clock as required by the set top electronics.

In order to provide a relatively inexpensive home multimedia network where MPEG data can be used in multiple set top electronics connected to the network, it is necessary to accurately recover the MPEG clock in each set top electronic unit.

An object of the present invention is to provide an MPEG clock recovery method and apparatus for allowing transmission of MPEG video data through a relatively cheap home network without causing jitter.

1 is a schematic block diagram of a home network constructed in accordance with an exemplary embodiment of the present invention.

2 shows a typical installation of the home network of the present invention in a house.

3 is a logical diagram of the home network of FIG.

4 is a schematic diagram of a network interface unit and a set top electronic circuit unit constructed in accordance with preferred embodiments of the present invention.

5 is a block diagram of a network interface of a set top electronic circuit constructed in accordance with an exemplary embodiment of the present invention.

6 is a block diagram of a network interface of a network interface unit constructed in accordance with an embodiment of the invention.

7 is a block diagram of a hub and integrated circuit crossbar, constructed in accordance with one embodiment of the present invention, connected to a network interface unit and a set top electronic circuit unit.

8 is a logic diagram of an exemplary user interface for a home network of the present invention.

The above and other problems will be solved by the present invention which provides a method and apparatus for accurately recovering an MPEG clock from an MPEG data stream. In some embodiments, the MPEG clock is first recovered from a network interface unit connected to an external network. The frequency synthesizer in the network interface unit synchronizes the recovered MPEG clock to an internal network clock such as an Ethernet clock. For example, the MPEG clock may be 27 MHz and Ethernet may be 10 MHz. Then, when data packets are sent from the network interface unit to the set top electronics, they are synchronized to the recovered MPEG clock 27 MHz. In the internal network set-top electronics stage, another synthesizer regenerates a 27 MHz clock from the synchronized version of the clock sent with the data packets over the internal network.

The present invention provides the advantage of allowing transmission of MPEG video data over a relatively cheap home network, such as Ethernet, without causing jitter. A further advantage of the present invention is that once a signal is synchronized to the recovered MPEG clock, it is easier and faster to synchronize to any set top electronics unit or signal.

The above and other features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the invention taken in conjunction with the accompanying drawings.

1 is a schematic diagram of a home multimedia network 10 constructed in accordance with an embodiment of the present invention. This embodiment is merely illustrative, and the network 10 may be implemented in a variety of different ways within the scope of the present invention and may include different devices connected to the network 10. Additionally, the present invention is not limited to networks located in homes, but is also applicable to networks installed in other types of buildings such as offices, apartment buildings, and the like. However, for purposes of illustration, typical embodiments will be described in the context of home installation.

Network 10 is a digital network that provides access to different types of equipment for the world outside the home. This equipment is for example an analog television (12), digital television (14), digital VCR (16), digital camcorder (18), personal computer (20), audio equipment (22), printer (24) ), The facsimile machine 26 and the telephones 28. In addition to connecting these devices to the outside world, the network 10 also interconnects digital video, digital audio, computer and telephone equipment internally in the home. This unifies communication and control in the house, making sufficient power of external network connections or internal data sources available to any terminal on the network 10.

Communication with the outside world is carried out through a number of independent network interface units (NIU's) 32, each network interface unit allowing the connection between the different external network and the home network 10 at the input unit 30 ( 32) and will be physically combined. The different external networks carry different types of signals. These may be, for example, hybrid optical coaxial cables (coax) or broadcast signals carried on optical cables (of digital or analog / digital mixture). Other types of signals are ISDN, broadcast / digital satellite service, FTTC, FTTH, ADSL. At a minimum, data types such as compressed video, compressed audio, compressed Internet WWW graphics and data, Internet email and other data, computer file data and control message data will be carried.

Logically all terminals of the home network 10 receive the same access to the network interface units 32 and the user will not be able to perceive their physical observations. The number of network interface units 32 required is determined not by the number of terminal units in the house, but by the number of different program channels (i.e. video, audio, etc.) required at the same time.

In certain preferred embodiments, the cable or antenna television remains unmodified with distribution by standard household coaxial cable (ordinary old television, or POTV). Plain old telephone service (POTS) is also performed on the home digital network 10.

Digital signals are distributed throughout the home via an internal network 34. In some preferred embodiments, the internal network 34 is substantially a 10 base-T type Ethernet or a 100 base-T twisted pair, but a special switch hub is used to allow the network each to have a high bit. It makes it possible to measure any number of terminal units capable of receiving rate video.

The home network 10 connects products with such computers or embedded computers that can support network bandwidth, protocols, routing, buffering and addressing. Other high-bandwidth products that do not support this complex feature must belong to host units, either directly or through a local perimeter network to achieve information processing interoperability. Examples of a computer or computer embedded products located in the home network 10 that serve as end user devices include: I / O computers of network interface units that perform conversion and control from an external network to a home network; Computers such as set-top electronics (STE), etc .; PCs; Workstations; High end printers; And special computers that provide gateway / control functions. Other end user devices that may be coupled to the network 10 include: digital compression (MPEG) and decompressed video supplies; Digital video camcorder products; Video products such as digital video tape recording products and digital TV display products and analog TV display and recording products. Audio products that may be connected to the network 10 include: digital compression (MPEG) and decompressed audio articles; HIFI stereo; Digital audio tape recording products. Other kinds of products that can be connected to the network 10 are data products such as printers and other peripherals. Other products that can be controlled via the network 10 include: home automation and applications such as central heating / AC, security controllers, microwave ovens and other kitchen appliances, lighting, sprinklers and other power controls. Include.

Some embodiments of the home network 10 include future I-frame-only-MPEG video devices, audio devices, printers that only have very high bit rates, motion-JPEG or I-frames. And one or more peripheral networks 15 that provide a local connection to the peripherals. These devices require a continuous local digital connection to high bandwidth, for example, data transmission from digital cameras to digital VCRs. Accepting such devices directly on the internal network 34 will require much larger network bandwidth than would normally be needed across the entire network 34. Instead, the local peripheral network 15 is generally connected to the internal network 34 by a gateway for information processing interoperability. However, in some other embodiments of the present invention, home network 10 is provided with hardware and software that accommodates high speed devices such that local area network 15 is not required.

The home automation network 17 is provided for home automation. This home automation network 17 can be operated on a power line or other low bit rate network to control home appliances, home security systems, lighting, and the like. This motivation comes from a control computer 20 located in the house.

A typical model of the installation of the home network 10 of the present invention in a house 36 is shown in FIG. The home network 10 is, for example, a long range of backbones from which the cable can run up to 100 m from the switched hub 38 forming a part of the internal network 34. In the typical installation depicted in FIG. 2, an input unit 30 having several network interface units 32 is placed in the usable area of the house along the switched hub 38.

Twisted pair cable extends into each room of the house 36 and ends in a wall socket. For example, when performing installation, a Cat-5 twisted pair (for 100 Mbits / s) can be used because most of the cost is wage. In retro-installation, the twisted pair cable is small enough that it can be customized under the carpet edge. A home user will connect a computer product in a room by plugging the Ethernet port of the computer product into an Ethernet wall socket.

In the embodiment of FIG. 2, the hub 38 is depicted as a separate device, but in other embodiments the hub 38 is integrated into one or more network interface units 32. The hub 38 provides connectivity to all areas of the home and one or more network interface units 32. Upgrading and expanding both the total bandwidth and connectivity of the internal network 34 is accomplished by additional plugging or changing to a larger hub. The hub will be described in more detail later.

1 and 2 separate the function of the network interface units 32 from the set top electronic device 40. Typically, a set top box includes a network interface unit whose components are internally connected to the set top electronic components by a bus. In contrast, however, the present invention provides that the network interface units 32 and the set top electronics 40 are separated from each other, with the internal network 34 interposed therebetween. This configuration makes it possible for several set top electronics to be distributed throughout the house 36 less expensively, since the electronics of the network interface unit do not need to overlap for each set top electronics. In addition, having independent network interface units 32 connected to other external networks and a common internal network 34 frees the homeowner from forcing a homeowner to receive all programming from a single source, such as a telephone or cable company. do. This separation may also allow the homeowner to add, cancel or change services by simply changing one of the network interface units 32 without having to replace all set top electronics 40 throughout the house 36. have.

In some embodiments, a "master" set top box is equipped with several network interface units. However, this embodiment is logically the same as described above since the network interface units are connected to the internal network in this embodiment and not to the set top electronics by the bus.

3 is a logic diagram of the home network 10 of the present invention. As is clear from the diagram, the multi-port switched hub 38 forms the center of the network connection. In some embodiments where cross-packet jitter is suitably controlled, a generic, commercially available packet switched hub is employed. In other preferred embodiments, such as shown in FIG. 3, the switched hub 38 is a combination of networked ports and direct (circuit) switched ports for the duration of one session. Directly connected ports (and systems) may be phase locked via a network (coded) clock. To provide this function, the switched hub 38 has a relatively simple and inexpensive hub 42 and an integrated circuit crossbar 44. In some preferred embodiments the hub 42 may be a commercially available device such as Am79C981 manufactured by Advanced Micro Devices (AMD) of Sunnyvale, California. Details of the integrated circuit crossbar 44 will be described later in connection with FIG. 7.

Satellite topology, as defined by Ethernet 10/100 Base-T, is used in connection with the switching hub 38. The switching hub 38 provides fan out in most rooms in the house 36. The maximum system bandwidth is a number of wire bit rates ((bit rate x number of ports) / 2), for example, a bit rate of 20 ports and 100 Mbits / s is a maximum maximum bandwidth of 1 Gb / s.

The switched hub 38 enables special measures by routing these cases directly from the transmitter to the receiver for severely asymmetric traffic, such as compressed digital video and Internet data. This traffic is thus separated from the internal network 34 and allows the total total bandwidth to be limited only by the scalability of the hub 38, although it will continue to be limited to 10 Mbits / s per branch. The use of 100 base-T technology instead of 10 base-T technology will uprate the network when needed.

Direct synchronous (Manchester or block coded) connections of the switching hub are mainly used for MPEG video transmissions requiring continuous, high bit rate, long duration connections. High bit rate video in compressed form can be as high as 8 Mbits / sec and is needed for live video and high activity movies and sports. Low bit rate video is 1.5 Mbits / sec. According to the present invention, MPEG digital video is maintained throughout the network 10. The conversion to real video only occurs in the display device (eg, television 12) or set top electronics 40.

Two separate integrated circuits are depicted as in the example of FIG. 3. For example, the network interface unit 32 connected to the ISDN network is directly connected to the personal computer 20 of the local peripheral network 15 via the integrated circuit crossbar 44. Another separate integrated circuit is provided by the integrated circuit crossbar 44 between the other network interface unit 32 (eg, connected to a hybrid optical coaxial cable) and the set top electronics 40 coupled to the television 12. . Devices that are not directly connected through the integrated circuit crossbar 44 remain networked because they belong to the hub 42.

With regard to the switching hub architecture, where a direct point-to-point path is implemented, all data across this path is the last point terminal of the path, up to what is intended for one or more other terminals. Are provided directly to Thus, in some preferred embodiments, the multiplexed data along with the high speed data (generally messaging) must be provided to the networked terminals by the final point of the direct path that returns those packets to the hub 38. The rule follows. For example, messages sent over an unscheduled ISDN network for a device on the local peripheral network 15 may be returned to the hub 38 by the local peripheral network host 20 for distribution. This rule is demultiplexing distributed at the end point (s), not central, which saves the cost and complexity of having a packet router type of switched hub, asymmetric data flow and locality, without being tied to the layers of switches. Works well for the destination.

The advantage of the directly switched paths is that all potential delays in gaining access to the network 34 (and possibly breaking the delicate clock reference timing carried in the MPEG stream) are all avoided.

In some preferred embodiments, the hub 38 is a "full-duplex" meaning that the route routed directly connects only the transmitter terminal "up" path to the receiving terminal "down" path. Need to be "notification). In contrast, the path down to the transmitter and the path up to the receiver will usually be attached to the network as it is not affected by the integrated circuit, ie it will be attached to all remaining terminal paths connected together.

Specific routing occurs in response to user service requests. The messages are extracted by hub control and any direct routing changes implemented. The devices are not switched from the network connection and no routing is required.

MPEG clock recovery is performed at the network interface units 32 as described later. Along with the MPEG clock recovery at the network interface units 32 and the direct circuit setup to the home network destination, jitter of the signal received at the destination (such as television 12) is substantially eliminated. The integrated circuit function works well for the severely asymmetric point-to-point traffic expected in entertainment (video) home movies.

For analog only services, such as transitional cable TV, for example, this is not considered part of a digital network. In mixed digital / analog services such as hybrid optical fiber coaxial cable (HFC) and newer forms of mixed cable TV, this is considered to be in a transitional state and is treated as a temporary addition to all digital systems of the present invention. . The signal from the hybrid optical coaxial cable is provided directly to the set top electronics 40 or the network interface unit 32 / set top electronics 40 combination. Two ports are required to connect to the home network 10, one for the network interface unit 32 and one for the set top electronics 40. In some preferred embodiments a bypass is provided to link analog signals to the audio / video circuits of set top electronics 40.

The home network 10 is controlled through a handheld commander or computer keyboard for software running on local terminals, such as personal computers 20 or set top electronics 40. Control software local to each home terminal manages source availability, source selection, route management by communication with network interface units 32 and external gateways. External network protocols are buffered in network interface units 32 to provide a standard interface for terminals on home network 10. 8 shows an example of a user interface. In this embodiment, home network 10 is transparent and the user only knows it indirectly from the number of connected services.

4 is a block diagram illustrating a single network interface unit 32 connected to a single set top electronic unit 40 by an internal network 34. The remaining parts of the home network 10, including the switching hub 38, are not shown in FIG. 4 for purposes of illustration and description.

The network interface unit 32 includes one or more network interface modules 50 for interfacing the network interface unit 32 to a specific external network. In the example of FIG. 4, network interface module 40 provides an interface to an external network that carries MPEG video data. MPEG video data is provided to an internal network interface device 52 that prepares the data for transmission through the internal network 34. In some preferred embodiments, the net network 34 is an Ethernet network, so the internal network interface device 52 is an Ethernet interface device.

The structure of the present invention is that in some networks, the first step of demultiplexing in the network interface unit 32 is a definable bandwidth limit (one stream, rather than a temporary bandwidth defined by the structure of the incoming stream (various streams). Suppose you need to be inside). Assuming that MPEG-2 video is being used, there is demultiplexing from multiple program transport streams into a single program transport, as defined in the MPEG-2 specification. This is done by an MPEG transfer chip 54, such as the 9110B chip, which is commercially available from the C-cube. (The second step of demultiplexing to separate video, audio and other data still takes place in the set top electronics, while decoding is preferably performed only on the display terminal or computer). In this attempt, there is no need to transmit high bandwidth streams throughout the house, and the terminals in house 36 only need to know a standardized single program interface. For example, compression is required for video generated in the home, such as security front door cameras or video conferencing cameras.

All external network interfacing, decryption, access control, demultiplexing into a single program stream, and the like are performed by the network interface module 50. Thus, the network interface module 50 buffers home network hardware and software from the features of the connected external network. Several different programs require multiple network interface crossbar connections, depending on whether they are from one provider or multiple providers. In some embodiments, a dual module is prepared for two connections to the crossbar, providing two programs received from the same external network.

The MPEG transmission chip 54 performs MPEG clock recovery to provide the recovered 27 MHz clock and the selected program to the internal network connection 56. For example, when the internal network 34 is a 10 base-T Ethernet network, the 27 MHz clock is received by the MPEG into the network synthesizer 58 and converted to a 10 MHz clock. The 10 MHz clock, along with the selected program, is provided to a conventional transceiver 60 (such as an Ethernet transceiver) connected to the internal network 34. Synthesizer 58 operates to synchronize the Ethernet clock with the recovered MPEG clock. When a data packet is sent from the network interface unit 32 to the set top electronics 40, the set top electronics 40 are synchronized with the recovered MPEG data of 27 MHz. In the set top electronics 40, the 27 MHz clock is reproduced from the Ethernet 10 MHz clock by another synthesizer.

Data is received by the set top electronic device 40 by the network interface device 62 including the network interface 64. The 10 MHz clock recovered by the network interface 64 from the data stream outside the network 34 is gated to the MPEG synthesizer 68 through the gate 66 for the network. Gating is required for the locking function to be performed only when there is a packet with data present. The 10 MHz clock is converted into a 27 MHz clock provided to the MPEG decoder 70 and the video decoder / encoder 72. The selected program is provided by the network interface 64 to the MPEG decoder 70, which decodes the MPEG data and provides it to the video decoder / encoder 72. The data stream is converted by video encoder 72 into a format (e.g., NTSC or SVideo) suitable for use by a display device, such as a television. The video decoder is used for the case when there is an NTSC analog signal to be digitized and merged with the onboard graphics hardware.

The network 34 of FIG. 4 is shown schematically, from the previous description that video data can be located on the network 34 via the hub 42, but the network interface unit 32 and the network ( It should be understood that the integrated circuit of set top electronics 40 through the integrated circuit crossbar 44 of 34 is preferred over providing transmission of jitter-free video data.

FIG. 5 is a more detailed diagram of an exemplary embodiment of the network interface device 62 of the set top electronic device 40 shown in FIG. Network interface device 62 includes a network synthesizer 68 coupled to a program logic device that operates as a gating device 66. The network synthesizer 68 may be implemented by a commercially available chip, such as the MC145151 manufactured by Motorola. Program logic device 66 may be implemented by a commercially available chip such as MC7958, also manufactured by Motorola. The voltage controlled crystal oscillator 80 operates at 27 MHz and sends the signal to the program logic device 62, which gates the 10 MHz signal to the synthesizer 68 when there is a received data packet. The synthesizer divides the 10 MHz and 27 MHz frequencies into a common frequency given to the phase detector of synthesizer 68. The output of the phase detector of synthesizer 68 is provided to the voltage controlled crystal oscillator 80 as a control signal, which can be adjusted to raise or lower the local frequency to synchronize with the incoming Ethernet frequency.

A signal informing the program logic device 66 about the receipt of the data packet, and a 10 MHz clock, is provided by the serial interface adapter 82 used as a receive enable. A commercially available product suitable for a serial interface adapter is Am7992B manufactured by Advanced Micro Devices (AMD).

The data stream is received via a transformer / filter 84, such as PE68026, a commercially available product of pulse engineering. Collision information is also received through other transformers / filters 86, which may be of the same type as transformers / filters 84. The received data is sent to a first network transceiver 88, such as a twisted pair Ethernet transceiver plus Am79C100. The output (received data) of the first network transceiver 88 becomes available to the receive enable 82 and the controller 90. The controller 90 is a commercially available product, such as the single-chip Ethernet controller Am79C970 (manufactured by AMD). The controller 90 sends the data received from the network 34 to a bus 92, such as a peripheral component interconnect (PCI) bus, to send the data to the MPEG decoder 70 of the set top electronic device 40. Connected.

The second network transceiver 92 is connected to the controller 90 and may be implemented by the same type as the first transceiver 88. The second network transceiver 92 provides a transmission path for data from the controller to the network 34 via the transformer / filter 84.

The collision information is routed to the controller 90 through the transformer / filter 86 and the second transceiver 92.

6 is a more detailed diagram of the internal network connection 56, which includes an MPEG to network synthesizer 58 that synthesizes a 10 MHz clock from a 27 MHz MPEG clock recovered by the MPEG transfer chip 54. The crystal oscillator 96 is a 20 MHz oscillator, the frequency generated by the synthesizer is 20 MHz, which is simply divided by 10 MHz in the receiver (set-top electronics 40). A commercially available synthesizer is MC145145-2 manufactured by Motorola.

The 10 MHz clock is sent to the microprocessor interface 98, which is responsible for the interface to the microprocessor 100. The microprocessor interface 98, together with the microprocessor 100, forms a transceiver 60 that connects to the internal network 34 through the transformer / filter 102. The microprocessor interface 98 may be, for example, a MC68160 chip manufactured by Motorola, and the microprocessor may also be a MC68EN360 manufactured by Motorola. The transformer / filter 102 may be of the same type as the transformer / filter 84, 86 of FIG. 5.

Separation of the network interface from the set top electronic device 40 provides several advantages as described above. The functions of conventional set top boxes with integrated network interfaces are divided in embodiments of the present invention. For example, in preferred embodiments, network interface unit 32 is responsible for performing external network specific interfacing, tuning demodulation and error correction. It provides external network specific video descrambling and encryption / decryption (credit card numbers, user passwords, etc.). The network interface unit 32 also provides an external network specific program guide. It also performs MPEG transmission demultiplexing for single stream and MPEG reference clock recovery. In preferred embodiments of the present invention, the network interface unit provides home network Ethernet interfacing and MPEG / Ethernet clock synchronization. It also provides software to support external network and home network protocols for various streams and various users. The network interface unit also acts as a gateway for the home network and provides software for controlling the buffering of data when needed.

Set top electronics 40 operate in preferred embodiments as an application computer having substantially audio, video, graphics, and analog television interfaces. Set-top electronics, for example, provide home network-specific interfacing and data buffering when needed. It provides Ethernet clock / emp clock clock synchronization in preferred embodiments. The set top electronic device 40 recovers digital audio / video by decoding MPEG video and audio. It performs digital / analog conversion on audio and video and supports commands from infrared remote control. Set top electronics 40 provide support for analog video input (NTSC). It interfaces printers, game ports, etc., supports a boot-level operating system and can download full systems from external networks. Set top electronics 40 support communications and application programs to network providers and program video servers via network interface units.

7 is a block diagram illustrating in more detail an exemplary embodiment of the hub 42 and integrated circuit crossbar 44 configuration of the present invention and its connection with the network interface unit 32 and set-top electronics 40. Integrated circuit crossbars 44 and 42 optionally provide a simple circuit connection through a hub 42 or direct circuit between a particular network interface unit 32 and set-top electronics 40. In FIG. 7, only portions of network interface unit 32 and set top electronics 40 are shown for purposes of illustration and description.

In preferred embodiments of the present invention, hub 42 is a relatively simple and inexpensive hub because it does not include any kind of packet routing switch or storage and forwarding switch. There is no intelligence to inspect the traffic and dynamically switch the hub according to the send and receive addresses as in hubs with packet routing switches.

Although only one network interface unit 32 and one set top electronics 40 are shown in FIG. 7, depending on the size of the crossbar 44, any number of pairs of directly connected cross circuit crossbars 44 ) Can be connected. The network interface unit 32 and the set top electronics 40 are each shown with five pin positions or connection terminals, each of which is paired. This corresponds to a typical telephone plug, where telephone RJ45 has ten pin positions.

Internal network 34 provides a connection between network interface units 32, set top electronics 40, and integrated circuit crossbar 44. In preferred embodiments, the internal network 34 is 10 or 100 base-T Ethernet.

The selection of the network connection or the direct circuit between the network interface unit 32 and the set top electronics 40 is set by a number of switches 108, which are letter suffixed to distinguish them from each other in the description that follows. 7 is shown in FIG. In the example of FIG. 7, the network interface unit 32 and the set top electronics 40 are directly connected to each other, where the network interface unit 32 transmits data to the set top electronics 40. The microprocessor 110 controls the position of the switches 108 in response to user commands requiring an integrated circuit to operate and perform as a controller for the integrated circuit crossbar 44. For example, a user may choose to watch a movie from a Video on demand service and then make this selection on a hand-held wireless control. In response to this selection, the microprocessor 110 changes the position of the switches 108 so that it is connected to a network interface unit 32 connected to an external network that transmits video on demand services, and to a television receiver for which the user wishes to watch a movie. Between the set top electronics 40, a direct circuit is set.

In this case, the switch 108a is moved to its illustrated position to connect the transmission lines of the transceiver 88 of the network interface unit 32 to the line 112 of the direct circuit crossbar 44. The transmission lines of the transceiver 88 are no longer connected to the network at the Tx1 port of the hub 42. Similarly, the receiving lines of the transceiver 92 of the set top electronics 40 are connected to the same line 112 of the direct circuit crossbar 44 via a switch 108g. With this integrated circuit just set up, data entering the home via the network interface unit 32 is not broadcast to the network via the hub 42, but instead directly to the set top electronics 40 at the location where the data is to be used. Is provided.

The integrated circuit established by the integrated circuit crossbar 44 provides an excellent path for data from the network interface unit 32 to the set top electronics 40, but all of the data entering the network interface unit 32 is the set top electronics ( It may not be intended for 40). For example, an email may be received via this particular network interface unit 32, and the homeowner may wish to send the email to a personal computer, not television. However, once the direct circuit is established, there is no connection to the network 34 due to the direct circuit.

In order to solve this problem, the set top electronic device 40 examines data packets received by the set top electronic device 40 to perform routing functions for data not intended for the set top electronic device 40. The data is rerouted via the hub 42 onto the network 34 by the set top electronic device 40. This re-routing by the end point connection (set top electronics 40 in this example) allows the system to avoid the need for expensive and complicated routers. Set top electronics 40 have a microprocessor and associated memory to identify and route data packets back to network 34.

While the integrated circuit between the network interface unit 32 and the set top electronics 40 provides jitter-free connection in the video data, the rerouting of other data to the network 34 through the hub allows one or more types of data to be networked. Allowed to be transferred to the home by the interface unit (32). Once a direct circuit is established between the network interface unit 32 and the set top electronics unit 40, collision detection is required by the set top electronics so that the set top electronics 40 can transmit to the hub 42. Set top electronics 40 need to be aware of collisions and retransmit data to network 34 when such collisions occur. In some embodiments, network interface unit 32 may be arranged such that a collision is not possible because a collision cannot occur on the direct circuit. However, in some embodiments, the same collision pair is included for convenience in both the network interface unit port and the set top electronics port (to the network 34 via the crossbar 44).

In some preferred embodiments, it is possible for one of the five pairs of wires to provide a picture-in-picture function for the system. For example, the network interface unit 32 may provide a second stream of data over a different transceiver 88a onto a separate crossbar connection line 114 through a second pair of transmission wires. Set-top electronics 40 having another transceiver 88a, also connected to line 114, receives a second stream of this data through an integrated circuit and provides an on-screen picture on the television screen. Thus, the two screens will be provided without jitter by separate integrated circuits.

In some preferred embodiments of the invention, the crossbar switches 108 are implemented by analog MOS array transistors, which are controlled in response to signals from the controller 110. This is merely exemplary and as will be appreciated by those skilled in the art, other embodiments may employ switches of a different structure.

Although the description of the present invention depicts a structure having some logical feature on the functionality of the various components, these logical features may be different in other embodiments. For example, hub 42 is described as being connected to an internal network. However, the hub 42 may logically be considered part of the internal network or part of which forms the network, along with the remaining wiring forming means for connecting the end terminals to the hub 42. Thus, those skilled in the art will understand that the logical features described and described herein are merely exemplary.

The separation of the network interface unit and the set top electronic device according to the invention makes it possible to inexpensively connect several devices to one another in the house and to the outside world.

Although the invention has been described and illustrated in detail, it is to be understood that it is only by way of illustration and example and is not to be taken as limiting, the spirit and scope of the invention being limited only by the appended claims.

According to the present invention, it is possible to allow transmission of MPEG video data through a relatively cheap home network without causing jitter.

Claims (14)

In a method for distributing an MPEG clock to an internal network by recovering an MPEG clock from a stream of data received from an external network, Recovering an MPEG related clock from a stream of MPEG data received from an external network in a network interface unit; Selecting a program from the stream using an MPEG transport chip located in a network interface unit; Directly synchronizing a local clock with the recovered MPEG related clock to provide an internal clock for an internal network that is synchronized to the recovered MPEG related clock; Transmitting MPEG data from a network interface unit to an internal network in accordance with the internal clock; And And synthesizing an MPEG clock from MPEG data transmitted to an internal network according to the internal clock in a set-top electronic device connected to an internal network. The method of claim 1, wherein the internal network is an Ethernet network, an MPEG clock is 27 MHz, and a local clock is 10 MHz. The method of claim 1, wherein synthesizing the MPEG clock comprises: Supplying an internal clock and a signal indicative of MPEG data reception to a frequency synthesizer. The method of claim 1, wherein synthesizing the MPEG clock comprises: And only in response to a signal indicative of MPEG data reception, synchronizing the synthesized MPEG clock to data received at the set-top electronic device via an internal network. An apparatus for recovering an MPEG clock from a stream of MPEG data, the apparatus comprising: A network interface unit for receiving an MPEG data stream from an external network and transmitting the MPEG data to a predetermined set-top electronic device, The network interface unit includes an MPEG clock recovery circuit for recovering an MPEG clock from a stream of MPEG data, an MPEG transmission chip for selecting a program from the stream, and a first frequency synthesizer for synchronizing an internal clock with the recovered MPEG clock. and; And said predetermined set top electronic device comprises a second frequency synthesizer for synthesizing the MPEG clock from the MPEG data clocked for the internal network in accordance with an internal clock. The method of claim 5, The internal network includes a plurality of set top electronics including the predetermined set top electronics, and a switching hub connecting the network interface unit to at least the predetermined set top electronics having the second frequency synthesizer; The switching hub is configured to directly connect the network interface unit to the predetermined set top electronics to transfer the MPEG data from the network interface unit to the predetermined set top electronics for synthesizing the MPEG clock in the predetermined set top electronics. Including synchronous connections (parts), Accordingly, an MPEG clock recovery apparatus can be avoided when connected to a network and a delay of clock reference timing breaks included in the MPEG data stream. The method of claim 1, wherein the transmitting step, Providing a direct synchronous connection between the network interface unit and the set top electronic device; And Using a direct synchronous connection to transfer the MPEG data to the set-top electronics, thereby avoiding delays in connecting to the internal network and in clock timing overruns contained in the received MPEG data stream. Way. A method for recovering and distributing an MPEG clock from a stream of MPEG data, the method comprising: Recovering an MPEG related clock from a stream of received MPEG data at a network interface unit connected to an external network; Selecting a program from the stream using an MPEG transport chip placed in a network interface unit; Directly synchronizing the local clock with the recovered MPEG related clock to provide an internal clock; Transmitting the MPEG data from the network interface unit to the set top electronics connected to the internal network in accordance with the internal clock; And A method for recovering and distributing an MPEG clock comprising synthesizing an MPEG clock from an MPEG data and an internal clock in a set-top electronic device connected to an internal network. The method of claim 8, wherein the transmitting step, Providing a direct synchronous connection between the network interface unit and the set top electronics, and Using a direct synchronous connection to transfer the MPEG data to the set-top electronics, thereby avoiding delays in accessing the internal network and clock timing hashes included in the received MPEG data stream. Distribution method. The method of claim 1, wherein synthesizing the MPEG clock Supplying an internal clock synchronized with the recovered MPEG related clock to a frequency synthesizer, Using the internal clock to adjust a local oscillator signal corresponding to the MPEG clock, thereby providing an output signal from the frequency synthesizer that matches an MPEG clock and is synchronized to the recovered MPEG related clock. MPEG clock distribution method. The method of claim 3, Providing said internal clock to an MPEG synthesizing means, supplying a local oscillator signal to an MPEG synthesizing means, and adjusting said local oscillator signal in accordance with said internal clock and said signal indicative of reception of MPEG data. Thereby supplying an output signal from said MPEG synthesizing means synchronized with said recovered MPEG related clock. 4. The method of claim 3, further comprising: using the signal instructing reception of MPEG data to gate the internal clock to MPEG synthesizing means when MPEG data is received, the gated internal clock to MPEG synthesizing means; Providing a local oscillator signal corresponding to an MPEG clock to an MPEG synthesizing means, and adjusting the local oscillator signal in accordance with the gated internal clock, during the time the MPEG data is received. And an output signal from said MPEG synthesizing means synchronized with said internal clock. 6. The apparatus of claim 5, wherein the second frequency synthesizer is coupled to receive an internal clock synchronized with the recovered MPEG clock, And further comprising means for adjusting the local oscillator using the internal clock to adjust a local oscillator generating a local oscillator signal corresponding to the MPEG clock and a local oscillator signal generated accordingly, And an output signal from the second frequency synthesizer synchronized with the recovered MPEG related clock. The method of claim 13, Means for providing to said second frequency synthesizer a signal indicative of receipt of MPEG data into an internal network by said predetermined set top electronic device, and Means for gating an internal clock with the second frequency synthesizer when MPEG data is received in response to the signal informing of reception of MPEG data, And an output signal from the second frequency synthesizer synchronized with the internal clock for a time when the MPEG data is received.