Multiplex communications – Diagnostic testing – Determination of communication parameters
Reexamination Certificate
1999-01-29
2001-05-15
Marcelo, Melvin (Department: 2663)
Multiplex communications
Diagnostic testing
Determination of communication parameters
C348S700000
Reexamination Certificate
active
06233226
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to the delivery of video streams over a switched network. More particularly, the invention relates to a system and method for facilitating the scheduling and transmission of video streams over a switched network, such as an Asynchronous Transfer Mode (ATM) network.
II. List of Acronyms
The written description provided herein contains acronyms which refer to various techniques, services, groups, modes and standards. Although known, use of several of these acronyms is not strictly standardized in the art. For purposes of the written description provided herein, these acronyms are defined as follows:
ABR—Available Bit Rate
ATM—Asynchronous Transfer Mode
B-Picture—Bidirectionally-Coded Picture
CBR—Constant Bit Rate
CDV—Cell Delay Variation
CDVT—Cell Delay Variation Tolerance
CLR—Cell Loss Ratio
CTD—Cell Transfer Delay
DCT—Discrete Cosine Transform
EBW—Effective Bandwidth
GCRA—Generic Cell Rate Algorithm
GoP—Group of Pictures
I-Picture—Intra-Coded Picture
ISDN—Integrated Services Digital Network
JPEG—Joint Photographic Experts Group
LAN—Local Area Network
MBS—Maximum Burst Size
MBS
s
—Sustainable Burst Size
MCR—Minimum Cell Rate
MPEG—Moving Picture Experts Group
P-Picture—Predictively-Coded Picture
PCR—Peak Cell Rate
QoS—Quality of Service
SCR—Sustained Cell Rate
TCP\IP—Transmission Control Protocol\Internet Protocol
UPC—Usage Parameter Control
VBV—Video Buffer Verifier
WAN—Wide Area Network
III. Background and Material Information
Switched networks are used for transporting various types of data, including audio and video data. The transmission of video data is much more network intensive than the transmission of audio data. However, video quality over a switched network can be maintained when sufficient bandwidth capacity and other network resources are provided. As a result, video retrieval, video-on-demand and other video or multimedia services are often implemented through switched-based networks to provide the transfer of video from a source to one or more destinations.
Switched networks transport data through the use of connections or routes that are established by switch elements in the network. These routes may be fixed or temporal with respect to the data that is transferred. An example of a switched-based network that creates fixed connections or routes between two points is an ATM network. ATM is a core technology for B-ISDN networks, and is commercially deployed in local area networks (LANs) and wide area networks (WANs). In an ATM network, data is transferred in cells or packets over a connection that is created and fixed when the data transfer begins. This differs from other network technologies, such as Transmission Control Protocol/Internet Protocol (TCP/IP), in which messages are divided into packets that can take different routes from source to destination.
Current implementations of ATM support data transfer rates of rates up to 2.4 Gbps (gigabits per second). This compares to a maximum of 1 Gbps for Ethernet, a technology that is used for most LANs. In addition, small-fixed size cells (53 bytes) are utilized in ATM to allow multiplexing of various data types with guaranteed cell rate, cell loss and cell delay variation parameters. These capabilities make ATM well suited for real-time applications such as video or multimedia applications.
When provisioning ATM services, a user has a choice of several different types of service rates. The available service categories are defined in the Traffic Management 4.0 specification issued by the ATM Forum Traffic Management Group. (ATM Forum, “ATM Traffic Management Specifications 4.0,” 1996). One type of service is Constant Bit Rate (CBR) service. With CBR service, a fixed bit rate is specified so that data is sent in a steady stream similar to the service provided by a leased line. CBR traffic is given the highest priority in the network and, therefore, provides bounded cell relay, cell delay variation, and cell loss characteristics. Another ATM service is Variable Bit Rate (VBR) service, which is frequently used for transporting audio and video data. With VBR service, a specified throughput capacity is guaranteed, but data is not sent evenly at a fixed rate. The VBR service category is divided into two subclasses, one for real-time and the other for non-real-time services. The real-time VBR service category is used for services that have variable bit rates combined with stringent real-time requirements. Real-time VBR traffic provides strict bounds on cell delay, cell delay variation, and cell loss. The non-real-time VBR service category is used when timely delivery of information is important, but some amount of jitter can be tolerated. Non-real-time VBR does not strictly bound cell delay and cell delay variation like real-time VBR does.
A third type of ATM service is Unspecified Bit Rate (UBR) service. UBR service does not guarantee any throughput levels and is the lowest priority traffic class. UBR service is used for applications in which the transfer rate is not critical, such as file transfers and other applications in which delays can be tolerated. A fourth type of ATM service is Available Bit Rate (ABR) service. ABR service provides a guaranteed minimum capacity but also allows data to be bursted at higher capacities when the network is free. ABR is the only service category in which the network provides feedback to the sender or source about transmission rates. If the network becomes congested, resource management cells are sent to the user asking that the transmission rate be reduced. ABR service is designed to provide a low cell loss rate, but bounds for the maximum delay and delay variation are not provided.
A unique feature of ATM is the ability to provide guaranteed throughput levels. The ATM Forum has defined Quality of Service (QoS) parameters which quantify end-to-end network performance at the ATM layer. (ATM Forum, “ATM Traffic Management Specifications 4.0,” 1996). The QoS parameters include a traffic descriptor which specifies the rate and characteristics of users traffic, negotiable network performance parameters, and fixed non-negotiable characteristics of the network. A traffic contract may contain two or more of the following parameters: Peak Cell Rate (PCR), Sustained Cell Rate (SCR), Minimum Cell Rate (MCR), Cell Delay Variation Tolerance (CDVT), and Maximum Burst Size (MBS).
The traffic descriptor or contract describes the rate Roth peak and average), the burstiness, and jitter tolerance for a connection. The PCR defines the maximum instantaneous rate at which a user can send data, while the SCR is the long term average rate over an interval. For CBR services over an ATM network, the peak and sustained cell rates will be the same while for other service classes the sustained rate will be lower than the peak rate. In addition to having different peak and average rates, VBR services define an MBS which specifies the maximum number of back-to-back cells that will be generated at the peak rate. The cell delay variation tolerance is the maximum jitter allowed in user data before it enters the network. The minimum cell rate is a minimum bandwidth guaranteed by the network. For ABR service the actual rate will be between the minimum rate and the peak rate depending on how congested the network is. Three QoS parameters have been identified which may be negotiated between the end user and the network when a connection is established: the Cell Transfer Delay (CTD), the Cell Delay Variation (CDV), and the Cell Loss Ratio (CLR). The CTD is the average transmission time for a cell, while the CDV is the maximum variation from the average transmission time allowed. The CLR is the fraction of the transmitted cells that are not delivered to their destination.
In order to reduce resource requirements for storing and transmitting video steams, compression techniques such as Moving Picture Experts Group (MPEG) and motion-Joint Photographic Experts Group (motion-JPEG) are utilized. MPEG achieves high compression rates by
Basch Evert
Gringeri Steven
Shuaib Khaled Ali
Marcelo Melvin
Suchyta Leonard Charles
Verizon Laboratories Inc.
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