Multiplex communications – Data flow congestion prevention or control
Reexamination Certificate
2000-02-07
2004-08-17
Pezzlo, John (Department: 2662)
Multiplex communications
Data flow congestion prevention or control
C370S231000, C370S235000, C370S401000
Reexamination Certificate
active
06778493
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to multimedia networks, and specifically to the synchronization of multicast distributed media content when played by multiple multimedia devices, e.g., monitors and audio systems.
BACKGROUND OF THE INVENTION
In some situations, such as at conventions and in exhibition halls, it is required to play the same video contents synchronized at multiple video monitors. Generally, it is also required to synchronize audio and video between separately located monitors and speakers. Current real-time media transmission technology allows transferring an audio/video stream over non-guaranteed quality of service (QoS) packet networks with reasonable quality and at a lower cost than provided by higher quality networks. Thus, there will be a demand for playing multimedia contents, delivered to a plurality of receivers over packet network, in synchronized manner.
FIG. 1
depicts a prior art multimedia content delivery system, generally at
10
, which uses a packet network. A multimedia server
12
generates a stream of multimedia packets
14
that contain multimedia audio/video contents. Normally, server, or source,
12
generates multimedia packets at a constant rate (packet rate); e.g., one packet every 20 ms. Packet size depends on the multimedia codec, which may result in fixed size or variable sized packets. The generated multimedia packets are then transferred through a packet network
16
, having plural routers, or nodes,
18
,
20
,
22
,
24
,
26
,
28
and
30
therein, and are delivered to a plurality of multimedia receivers,
32
,
34
,
36
and
38
. The mechanism:m for delivery to multiple devices is well known as “multicast.” All the receivers that wish to receive multimedia contents from the server join a multicast group. The routers in packet network
16
are aware of the multicast group, and transfer received multimedia packet to multiple routes. Each receiver is equipped with a speaker and/or a video display, and each plays the contents in the received multimedia packet in real-time. The multimedia receivers may buffer received multimedia packets for some duration in order to absorb the variance in delay caused by the network, and to playback multimedia packets in right order.
In conventional packet network, such as an IP network, packets are queued in each router. How long a packet stays in a queue depends on the amount of traffic that a particular router is handling. Hence, each multimedia packet delivered to each multimedia receiver has an unpredictable delay. As a result, the audio/video contents may be played at multiple locations without synchronization.
As previously noted, real-time multimedia transmission technology currently allows transferring an audio/video stream over non-guaranteed quality of service (QoS) packet networks with reasonable quality. As mobile Internet access increases, with its data transfer over bandlimited communication channels, such as wireless data networks, the technology to transmit real-time multimedia packets requiring minimum bandwidth becomes essential and of increases importance.
A packet-based real-time media transmission system is illustrated in
FIG. 2
, generally at
40
. A multimedia source, or server,
42
, periodically transmits multimedia packets
44
having audio/video multimedia contents to a packet network
46
. In packet network
46
, each multimedia packet is routed by a plurality of network nodes, or routers,
48
,
50
,
52
and
54
, and delivered to a receiver
56
. Each multimedia packet includes timing information that is used to set timing for playback at a receiver
56
. The multiple routers and receivers of
FIG. 1
are not shown in
FIG. 2
for the sake of clarity.
Packet network
46
causes a: variable length delay in the delivery of each multimedia packet. In addition, network
46
does not guarantee the delivery of the multimedia packets in the same order as transmitted. Thus, a receiver is normally equipped with a buffer to handle delay variances and/or disorders in multimedia packet receipt. However, due to the real-time property of the contents, the receiver will discard a received multimedia packet if the delay in its arrival exceeds a certain value, or if the multimedia packet does not arrive by the time it is to be played.
FIG. 3
shows an example of packets received and played back by the receiver, where each packet contains the timing information. Line I depicts seven multimedia packets transmitted in sequential order by server
42
. Line II depicts the order of receipt of the multimedia packets at a receiver. Line III depicts a play order by the receiver. The figure depicts that the multimedia packet with timing information
3
is discarded due to an excessive delay. Basically, the routers in the prior art packet network are not aware of delays in packets transmission and receipt, nor are they aware of disordering of packet transmission. Thus, each router re-directs every received real-time multimedia packet to the next router or the receiver, even if the multimedia packet may not have any chance of being played at the receiver. If a physical link between some two routers, or the physical link between the receiver and the adjacent router has limited bandwidth, the transmission of the multimedia packets which will be discarded at the receiver possibly wastes substantial portion of valuable bandwidth on the link. Delay and disordering is illustrated by the variable routing of multimedia packets from router
48
through router
50
, router
52
and router
54
, or directly from router
48
to router
54
.
U.S. Pat. No. 4,506,358, for Time stamping for a packet switching system, to Montgomery, granted Mar. 19, 1985, describes a method of measuring the network delay in a packet network by including an information field in each packet that indicates the cumulative network delay, time stamping each packet's arrival and re-transmission in each network node, and updating the information field in each network node for each packet by adding the delay occurring in each node, i.e., re-transmission time—arrival time.
U.S. Pat. No. 4,530,091, for Synchronization of real-time clocks in a packet switching system, to Crockett, granted Jul. 16, 1985, describes a means to synchronize a remote real-time clock to a standard real-time clock via an X.25 (CCITT) network, but does not teach or suggest how to synchronize a multimedia stream, and does not consider network delay caused in a packet network.
U.S. Pat. No. 4,918,687 for Digital packet switching networks, to Bustini et al., granted Apr. 17, 1990, describes a method to avoid consecutive packet loss by clipping voice packets whose contents indicate whether the packet is eligible for clipping, if required, in a node queue within the network.
U.S. Pat. No. 5,432,790 for Method for allocating internodal link bandwidth in a packet oriented communication network to guarantee delay quality-of-service, to Hluchyj et al., granted Jul. 11, 1995, describes a method to allocate bandwidth on internodal links such that worst case maximum delays and worst case average delays are guaranteed while providing statistical gains in maintaining predetermined end-to-end delay QoS.
U.S. Pat. No. 5,444,709 for Protocol for transporting real time data, to Riddle, granted Aug. 22, 1995, describes a method to maintain the isochronous nature of the real-time data transmission by discarding data that is not timely received.
U.S. Pat. No. 5,450,394 for Delay monitoring of telecommunication networks, to Gruber et al., granted Sep. 12, 1995, describes a means to measure a round-trip-delay of network transit time, however, the delay which must be known for multimedia transmission and synchronization is a one-way network delay.
U.S. Pat. No. 5,557,724 for User interface, method, and apparatus selecting and playing channels having video, audio, and/or text streams, to Sampat et al., granted Sep. 17, 1996, describes a user interface in a computer system to playback multimedia streams.
U.S. Pat. No. 5,594,660 for Programmable audio-video synchronization
Pezzlo John
Robert D. Varitz, P.C.
Sharp Laboratories of America Inc.
Tsegaye Saba
LandOfFree
Real-time media content synchronization and transmission in... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Real-time media content synchronization and transmission in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Real-time media content synchronization and transmission in... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3330675