Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
2000-11-10
2004-08-17
Jung, Min (Department: 2663)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S477000, C709S231000
Reexamination Certificate
active
06778553
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention is related to the real-time transmission of media data from a sender to a receiver over a packet-based network.
2. Background Art
Real-time media, such as radio and television programs, are broadcast from a single sender to multiple, geographically distributed receivers, who have all “tuned” to that sender. Commonly, the signals are broadcast from the sender by a terrestrial antenna, but satellite and wired solutions also exist. For example, in cable TV, the signals are broadcast from a sender by propagating a voltage along a coaxial cable to receivers connected to the cable.
It is also possible to use the Internet infrastructure to broadcast audio and video information. This can be accomplished using the Internet Protocol (IP) Multicast mechanism and its associated protocols. An Internet broadcast (or more properly, “multicast”) is provided to the set of receivers who have first “subscribed” to the information. Specifically, through an announcement mechanism, such as a web page, a broadcaster announces the IP multicast group address to which it will send a particular broadcast. The multicast group address is just a special case of an ordinary IP address. However, unlike an ordinary address which is used to identify the “location” of a receiver where data is to be sent, a multicast group address is used by routers in the network to identify data being transmitted on the network as part of the broadcast, so that it can be routed to a subscribing receiver (who will have a completely different address). The receiver's address is not included in the broadcasted information. A receiver subscribes to the broadcast by notifying the network that it wishes to “join” the multicast group. The subscriptions cause various routers in the network to update their states, to ensure that the multicast information eventually reaches the subscribers. At some point the sender begins to send packets to the specified address. When a router receives a packet with that address, it sends copies of the packet through each outgoing interface that leads to a subscriber. This causes the packets to reach the subscribers at some point, albeit with the inevitable packet loss due to network congestion and buffer overflow.
Alternately, the audio and video information could be sent directly to a receiver using its Internet address. This form of audio and video data transfer would more accurately be referred to as a real-time unicast multimedia presentation, rather than a real-time broadcast or multicast multimedia presentation.
When data is transferred over a network, and particularly over the Internet, the channels between the sender and each receiver can vary dramatically in capacity, often by two or three orders of magnitude. These differences in capacity exist because the data transmission rates associated with the connections to a particular receiver can vary (e.g., phone line capacity, LAN and/or modem speeds). This heterogeneity in capacity can cause problems in the context of a unicast or multicast presentation of real-time audio and video information. For example, a particular receiver may not have the bandwidth available to receive the highest quality transmission that a sender is capable of providing. One early attempt to cope with this problem involved simulcasting or transmitting the audio and video data at different transmission rates to different receivers, with the quality being progressively better in the data transmitted at the higher rates. The receiver then received the transmission that suited its capability. However, this solution was very storage or bandwidth intensive as much of the same information had to be repeated for each transmission rate. To overcome this problem, audio and video information can be transmitted via a layered unicast or multicast presentation.
In a layered unicast or multicast presentation, audio and video information is encoded in layers of importance. Each of these layers is transmitted in a separate data stream, which are in essence a sequence of packets. The base layer is an information stream that contains the minimal amount of information, for the least acceptable quality. Subsequent layers enhance the previous layers, but do not repeat the data contained in a lower layer. In order to obtain the higher quality, a receiver must receive the lower layers in addition to the higher layers that provide the desired quality. Thus, the layers are hierarchical in that there is at least one base layer (typically one audio base stream and one video base stream), and one or more additional higher level layers. There can in fact be several hierarchical layers building up from a base layer with each subsequent layer being dependent on the data of one or more lower level layers and enhancing those lower level layers. In particular, it is possible to have two or more enhancement layers depending on the same lower level layer, but not depending on each other. Each of the layers would enhance the lower level layers on which they depend in a different way. For example, a stream in one higher-level layer might include data that enhances the frame rate of a foreground object in a preceding lower-level layer, while a separate higher-level layer might increase the resolution of a background object in this lower-level layer. A receiver may use either such enhancement layer without the other, or may use both such enhancement layers. However, a receiver may only use an enhancement layer if it also receives all of the layers on which it depends either directly or indirectly.
In addition, there can also be one or more error correction layers associated with each base and enhancement layer in the unicast or multicast presentation. For example, such a layered error correction technique was described in a co-pending U.S. patent application entitled “RECEIVER-DRIVEN LAYERED ERROR CORRECTION MULTICAST OVER HETEROGENEOUS PACKET NETWORKS”, which was filed on May 21, 1999, and assigned Ser. No. 09/316,869.
In a layered unicast or multicast presentation scheme, a receiver can subscribe to as many layers as it wants, provided the total bandwidth of the layers is not greater than the bandwidth of the most constrained link in the network between the sender and the receiver. For example, if the receiver is connected to the Internet by a 28.8 Kbps modem, then it can feasibly subscribe to one, two, or three 8 Kbps video layers. If it subscribes to more than three layers, then congestion will certainly result and many packets will be dropped randomly, resulting in poor video quality. Given this, a question arises as to which ones of the available layers should be transmitted to a receiver in view of the existing bandwidth constraint.
If the dependence between layers is sequential, for example, if a second layer depends on a first layer, a third layer depends on the second layer, and so on, then it is a simple matter to decide which layers to transmit: transmit the layers in order up to the bandwidth constraint. This maximizes quality subject to the bandwidth constraint. However, in many situations the dependence between layers is not sequential. For example, suppose both the second and third layers depend directly on the first layer, but not on each other. In this case there may be multiple sets of layers that can satisfy a given bandwidth constraint. Thus, the question arises as to which set of layers should be transmitted to a receiver.
SUMMARY
The present invention is directed at resolving the issue of determining which ones of the available data layers should be transmitted to a receiver in view of a bandwidth constraint and in view of the dependences between them. In its most general terms the system and process according to the present invention involves tagging prescribed portions of the data of each layer in a layered unicast or layered multicast presentation with an indicator of the importance or utility that the data provides to the receiver, and with an indicator of its bandwidth or cost of the data. Together with a graph of the
Jung Min
Lyon Katrina A.
Lyon & Harr LLP
Microsoft Corp.
LandOfFree
System and method for media streaming does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System and method for media streaming, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System and method for media streaming will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3328775