Electrical computers and digital processing systems: multicomput – Computer-to-computer protocol implementing – Computer-to-computer data transfer regulating
Reexamination Certificate
1998-10-05
2002-08-20
Coulter, Kenneth R. (Department: 2154)
Electrical computers and digital processing systems: multicomput
Computer-to-computer protocol implementing
Computer-to-computer data transfer regulating
C710S053000, C710S056000, C709S214000, C711S170000
Reexamination Certificate
active
06438604
ABSTRACT:
SOFTWARE APPENDIX
This application is being filed with a software code appendix which contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the software code or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
INCORPORATION BY REFERENCE
A compact disc, and an identical duplicate thereof, containing a computer program listing appendix of the Software Appendix has been submitted, both of which are herein incorporated by reference. Each compact disc contains a single ASCII text file named “09
—
166,487 Appendix.Txt”, which was created on Jan. 22, 2002 and is 44 kilobytes in size.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a system for transmitting real time digital video data (including both audio and video) over a local area network. More specifically, the present invention relates to a system for transmitting digital video data from an isochronous source such as a digital video camera using IEEE 1394 isochronous protocol, through an asynchronous local area network, to an isochronous destination such as another digital video camera or a monitor via IEEE 1394 isochronous protocol, all while maintaining isochrony of transmission and delivery.
2. Description of Related Art
Local Area Networks (LANs) have traditionally been used for accessing files or sending print data to a networked printer. Data delivery on a network such as Ethernet is asynchronous, meaning that there is no synchronization between transmission time and delivery time. Rather, for the typical application, the most critical feature of the network is its guarantee that data will be delivered successfully.
Digital video data, on the other hand, is unique in that the timeliness with which data is delivered is more important than the guarantee of data delivery. Specifically, because of the fleeting nature of digital video data, if it is not delivered in time, then its guaranteed delivery at a later time is meaningless since the data will be stale and simply not used.
One popular protocol for carrying digital video data is the IEEE 1394 isochronous protocol, where the timely delivery of digital video data is more critical than the guarantee of its delivery. Digital video data is carried on an IEEE 1394 serial bus (popularly referred to by the trademark “Fire Wire”) as isochronous data. The term isochronous means equal-time, and in the context of IEEE 1394 protocol means that new data is available at cyclical intervals (such as every 125 microseconds) although the timing of data within any one interval is uncertain. The isochronous nature of this data is such that data of this type has no value if it is received after its specific time window of use. In fact, the timely delivery of this data is so critical that in the case of a transmission error no retries are attempted. It was recognized by the designers of the IEEE 1394 bus protocol that by the time any retry attempts could be made, the time window for the usage of isochronous data would be passed.
Digital video (“DV”) data is transmitted under IEEE 1394 as isochronous data packets that may contain both audio and video components. Although there is no guarantee that a packet can be sent exactly at a periodic rate, IEEE 1394 guarantees that data is available sometime within each periodic interval (equal to 125 micro-seconds). Another feature of the IEEE 1394 interface is that applications can reserve bandwidth (or “channels”) in the IEEE 1394 bandwidth and therefore delivery of a digital video packet can be guaranteed.
The IEEE 1394 industry standard interface provides superior bandwidth for high speed transmission of data. Because of its unique features, the IEEE 1394 high speed serial bus is used for transmitting full-motion digital video from a digital video camera, to a digital video recorder, to a personal computer, or to any peripheral device which may store or display the video. Currently, however, the IEEE 1394 standard interface has at least one shortcoming: the maximum cable length is limited to 4.5 meters. Therefore, digital video data cannot be transferred and viewed in real time at a remote location greater than 4.5 meters from the source of the video data.
Although the cable length limitation is being addressed by a new version of the IEEE 1394 standard, this newer version would involve costly and non-standard usages, such as a fiber optic cable with different IEEE 1394 components.
On the other hand, asynchronous networks such as Ethernet are in widespread use, and provide geographically remote access to large volumes of data. Particularly, with-the recent introduction of 100 BaseT and Gigabit Ethernet, fast access to large volumes of data is also provided. It is therefore expected that the Ethernet interface will continue to offer a lower cost, higher speed and longer distance connection than an equivalent IEEE 1394 connection. It is for this reason there is a benefit to find a way to provide the transport of isochronous digital video data across an asynchronous transport that does not inherently provide isochrony.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to transmit digital video data (video and audio) over a high speed local area network. More specifically, the present invention relates to sending isochronous data over an asynchronous network transport that does not specifically support isochrony.
It is another object of the present invention to provide a system for transmitting digital video data, which is output isochronously, between peripheral devices in real time by integrating a local area network between the transmitting digital video camera and the receiving digital video camera. It is also an object of the present invention to provide a method and an apparatus for maintaining real time transfer of the isochronous video data without degradation of the video signal.
Thus, according to one aspect, the present invention is a digital video network interface for transferring isochronous video data over an asynchronous local area network. The digital video network interface includes, on a transmitting side, an isochronous interface for receiving digital video data isochronously, a buffer comprising first and second memory areas for storing the isochronous video data, and a network interface for transmitting video data from either the first or second memory areas over the asynchronous local area network. On a reception side, the digital video network interface also includes a reception memory buffer manager for controlling receipt of the video data from the asynchronous network and the storage of the data into memory, which is not ordinarily partitioned into first and second memory areas. An input pointer is used to track where newly received asynchronous data is stored to memory, and an empty pointer is used to track where data is extracted from memory for conversion to isochronous data. The memory buffer manager shifts the input of data into the memory pointed to by the input pointer and begins outputting video data from the memory pointed to by the empty pointer to an isochronous packet handler that converts the asynchronous data to isochronous. The isochronous data may thereafter be utilized in accordance with IEEE 1394 protocol, such as by viewing on a digital video camera.
By virtue of the foregoing arrangement, even though the network is an asynchronous data carrier, isochronous data can be transmitted over a network that does not support isochrony, since it is the sending and receiving stations that are responsible for maintaining isochrony. In particular, buffering at the transmitting end accommodates delays that might occur while waiting to access to the asynchronous network, while buffering at the receiving end accommodates delays in new asynchronous packets, by buffering data packets that had previously arrived too quickly for the isochronous packet handler to accommodate. A
Beck Gregory F.
England Trent Lee
Ip Tony K.
Kuver Walter D.
Montenegro Elias
Canon Kabushiki Kaisha
Coulter Kenneth R.
Fitzpatrick ,Cella, Harper & Scinto
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