Electrical computers and digital processing systems: multicomput – Computer-to-computer protocol implementing – Computer-to-computer data streaming
Reexamination Certificate
1999-06-10
2001-07-17
Geckil, Mehmet B. (Department: 2152)
Electrical computers and digital processing systems: multicomput
Computer-to-computer protocol implementing
Computer-to-computer data streaming
C709S232000
Reexamination Certificate
active
06263371
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a scheme for merging together information from multiple input data streams to produce an output data stream that includes fewer information “gaps” than any of the individual input data streams. In one example, the scheme is applied to live broadcasts of streaming content delivered via the Internet.
BACKGROUND
The Internet is a vast and expanding network of networks of computers and other devices linked together by various telecommunications media, enabling all these computers and other devices to exchange and share data. Sites on the Internet provide information about a myriad of corporations and products, as well as educational, research and entertainment information and services. An estimated 30 million people worldwide use the Internet today, with 100 million predicted to be on the “net” in a matter of years.
A computer or resource that is attached to the Internet is often referred to as a “host.” Examples of such resources include conventional computer systems that are made up of one or more processors, associated memory (typically volatile and non-volatile) and other storage devices and peripherals that allow for connection to the Internet or other networks (e.g., modems, network interfaces and the like). In most cases, the hosting resource may be embodied as hardware and/or software components of a server or other computer system that includes an interface, which allows for some dialog with users thereof. Generally, such a server will be accessed through the Internet (e.g., via Web browsers such as Netscape's Navigator™ and Communicator™ and Microsoft's Internet Explorer™) in the conventional fashion.
Briefly, if an Internet user desires to establish a connection with a host (e.g., to view a Web page located thereat), the user might enter into a Web browser program the URL (or Web address) corresponding to that host. One example of such a URL is “http://www.domain.com”. In this example, the first element of the URL is a transfer protocol (most commonly, “http” standing for hypertext transfer protocol, but others include “mailto” for electronic mail, “ftp” for file transfer protocol, and “nntp” for network news transfer protocol). The remaining elements of this URL (in this case, “www” standing for World Wide Web—the Internet's graphical user interface—and “domain.com”) are an alias for the “fully qualified domain name” of the host.
Each fully qualified domain name, in its most generic form, includes three elements. Taking “computer.host.com” as an example, the three elements are the hostname (“computer”), a domain name (“host”) and a top-level domain (“com”). Further, each fully qualified domain name is unique throughout the Internet and corresponds to a numerical Internet protocol (IP) address. IP addresses facilitate communications between hosts and clients in the same way that physical addresses (e.g., 123 Main Street, Anytown, Anycity) facilitate correspondence by mail. Each IP address is made up of four groups of numbers separated by decimals. Thus, in the case of the hypothetical host “computer.domain.com”, the corresponding IP address might be 123.456.78.91. A given host looks up the IP addresses of other hosts on the Internet through a system known as domain name service.
Thus, once a URL is entered into a browser, the corresponding IP address is looked up in a process facilitated by a top-level server. In other words, all queries for addresses are routed to certain computers, the so-called top-level servers. The top-level server matches the domain name to an IP address of a domain name server capable of directing the inquiry to the computer hosting the sought after Web page (or other content) by matching an alphanumeric name such as www.domain.com with its numeric IP address.
In addition to Web pages and the like, more and more Internet users are accessing multimedia content (e.g., files that include high quality graphical images, movies and/or sound). This creates difficulties because such files are usually quite large while the bandwidth available through the Internet is limited. Thus, in order to make multimedia files usable, streaming is often employed.
With conventional files (e.g., data files), clients (e.g., Web browsers) completely download the requested content before viewing it. This technique works well for relatively small files, but often suffers from unacceptable (from the point of view of the user) delays when large multimedia files are involved. Streaming is the term given to a technique wherein a client downloads a portion of a file, decompresses (if necessary) that portion, and starts playing the contents thereof (e.g., audio and/or video) before the rest of the file arrives. A buffer of information is built up before playback starts, so as to prevent underflows if the remaining data is delayed during transmission. Furthermore, subsequent portions of the multimedia file are downloaded during playback to keep the buffer relatively full. This technique thus accommodates the downloading and playing of large multimedia files without incurring lengthy delays before the content is available for viewing.
Multimedia files are often transported over the Internet using special transport protocols. For example, the real-time transport protocol (RTP) provides delivery service for multimedia applications and also provides means for multimedia applications to work over networks. RTP does not, however, provide guaranteed or in-sequence delivery (and hence it is referred to as an unreliable transport protocol), but does provide a packet sequence number that can be used to detect missing packets and to reconstruct an original transmission sequence.
RTP usually carries data in the form of packets, using the user datagram protocol (UDP) as the delivery mechanism. UDP provides a “wrapper” around data packets, with the wrapper providing for multiplexing and demultiplexing as well as error checking services. Essentially, a UDP packet is made up of a UDP header and UDP data encapsulated as the data portion of an IP packet. The IP packet itself includes an IP header (which includes the address information discussed above) as well as the user data (i.e. the multimedia content of interest) as a payload.
In some cases, RTP is used with other protocols, such as the transmission control protocol (TCP). Unlike UDP, TCP provides a reliable, error-free, full-duplex channel between two computers. TCP uses IP to transfer data, but provides mechanisms to take care of lost or duplicated IP datagrams (i.e., packets) and to ensure proper sequencing thereof. Thus, TCP provides reliable end-to-end transport, ensuring that what is received is an exact duplicate of what is transmitted.
Where broadcasts of “live” information are concerned, RTP usually uses UDP as the delivery transport. This is because TCP may introduce unacceptable delays in receipt. Further, when an application starts an RTP session, a second port for communication according to the real time control protocol (RTCP) is opened. RTCP works in conjunction with RTP to provide flow control and congestion control services. The idea is that the exchange of RTCP packets between a client and server can be used to adjust the rate of transmission of the RTP packets, etc.
Associated with RTP is the real time streaming protocol (RTSP). RTSP is a client-server multimedia presentation control protocol that control functionality such as content type, interactive stream control, error mitigation, bandwidth negotiation, multicast, live broadcasting and monitoring. Just as HTTP transports HTML (hypertext markup language—an instruction set that allows an HTTP client to render a desired image, etc.), RTSP handles data. The difference is that while HTTP clients always make requests and HTTP servers always service those requests, RTSP is bi-directional, with both servers and clients making requests and servicing them. RTSP accomplishes data transfer using TCP or UDP.
Thus, RTSP is a generally a TCP connection over which commands are sent and responses are returned. Clien
Geagan, III John B.
Kellner Michael D.
Periyannan Alagu S.
Blakely , Sokoloff, Taylor & Zafman LLP
Cacheflow, Inc.
Geckil Mehmet B.
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