British Telecommunications Public Limited Company

British Telecommunications Corporation

Stephen Clifford Appleby

Michael Erling Nilsson

Rory Stewart Turnbull

Ian Barry Crabtree

Timothy Sean Stevens

Yousif Humeida

Timothy Stevens

Patrick J Mulroy

Robert J Briscoe

Andrea Soppera

Arnaud Jacquet

Alan P Smith

Tobias Moncaster

Brahim Allan

Ivan Roper

Yousif Humedia

Patrick Joseph Mulroy

Michael Eilling Nilsson

Robert John Briscoe

Alan Philip Smith

A method of managing a network for delivering content to a client device, where content segments are delivered to a proxy in a multicast group, before delivery from the proxy to the client device over unicast. The proxy intermittently leaves the multicast group to probe the network by making unicast request for content segments, receiving those segments over unicast from the content server and forwarding those segments onto the client device. This allows the client device to determine the maximum throughput between the content server and the client device via the proxy, and thus the client device can use its adaptive bit rate algorithms to determine if the network can support a switch to a higher bit rate stream, and request a higher bit rate stream accordingly. The higher bit rate stream can be serviced by the proxy joining or establishing a suitable multicast group.

Content delivery

A method of managing a network for delivering content to a client device, where content segments are delivered over multicast to a proxy. The received segments are stored at the proxy, before delivery of those segments is made from the proxy to the client device over unicast. Whilst the proxy receives further segments over multicast, it probes the network by making unicast requests for data (dummy data or additional content segments), and receiving those segments over unicast from the content server. The multicast rate reception rate and the unicast (probe) rate are measured and a maximum network throughput is calculated as the sum of these two rates. Subsequent segments are then delivered from the proxy to the client device at the calculated maximum network throughput rate, or at some rate dependent thereon. Thus, the client device will receive segments at a rate that is more indicative of the actual maximum network throughput, so can better use its adaptive bit rate algorithms to determine whether a switch to higher bit rate segments is appropriate.

Described is a method of managing a network for delivering content in a hybrid unicast/multicast network, where content is requested by clients over unicast, but all or some of the content is delivered in part over multicast. Typically, a client requests content (in the form of segments) via a first proxy. The segments are delivered to the first proxy over multicast from a second proxy, before onward transmission to the requesting client over unicast. The segments are also cached at the first proxy, and can be transmitted over unicast to other clients requesting those segments. However, problems can arise if cached segments are transmitted to clients too quickly. In one solution, the first proxy measures the multicast rate of delivery of segments from the second proxy over multicast, and limits the transmission rate of those segments over unicast to requesting clients to no greater than the measured multicast delivery rate.

Content delivery—setting the unicast rate

Described is a method of delivering content over a network using an approach referred to as 'Multicast Assisted Unicast Delivery' (MAUD), as a multicast network is used to assist, rather than substituting for, an otherwise unicast path. Content is requested by client devices from a content server over unicast. The responses containing the requested content are separated into two components: a first component containing elements that are specific to individual client devices (for example session specific data), and a second component that is common to all client devices (typically this is the video content being requested). The first component can be delivered over unicast and the second component over multicast. Identifiers are introduced into each of the first and second components to aid recombination of the components to form the original responses. The separation and recombination are handled by suitably configured proxy servers.

Multicast assisted delivery

Described is a method of delivery of content to a client device. In particular, the method can be applied to hybrid unicast/multicast delivery networks, where content is provided by a content server to a root proxy, and that root proxy delivers the content to edge proxies over multicast. However, requests for that content in the form of HTTP GET requests from a client device are received by an edge proxy, which subsequently sends an HTTP HEAD request for header information associated with that content directly to the content server. The content server responds over unicast with a suitable response to the HTTP HEAD request, which is received by the edge proxy. The edge proxy takes the response together with the payload from the content segment received over multicast, to generate a client specific content segment for delivery to the client device over unicast.

A method of delivering a video sequence in a network, the sequence including a plurality of temporal segments encoded at a plurality of qualities, the method including storing a dataset indicating the relative size of segments of the video stream; computing in dependence on that dataset a time schedule for delivery of the segments, the time schedule indicating a target delivery time for each segment sufficient to deliver all the segments in the sequence in time for decoding and being independent of the encoded quality of each segment; for each segment: setting one or more transmission parameters for the segment in dependence on the target delivery time for the segment and the relative size of the segment; and delivering the segment over the network using the one or more transmission parameters.

Transmission parameter control for segment delivery

Described is a method of managing a network for delivering content in a hybrid unicast/multicast network, where content is requested by clients over unicast, but all or some of the content is delivered in part over multicast. A client requests content (in the form of segments) and receive the responses (segments) over unicast via a first proxy. The first proxy measures the time between requests and associated requested segment sizes. These measurements are used to effectively determine a unicast request rate given by the segment size divided by the time between requests. Subsequent requested segments can then be delivered over multicast over a portion of the route to the client using a multicast rate that is set as a function of (for example, 110% of) the unicast request rate. In general, the multicast path will be from a second proxy to the first proxy.

In examples of the present invention, during delivery of content, the round trip times for each delivered data packet are measured and the congestion window used for delivery is adjusted accordingly. The congestion window is set to a relatively high value when the round trip times are relatively low, and set to a relatively low value when the round trip times are relatively high.

Congestion response

A method of determining the bandwidth of a link carrying a plurality of data streams between a plurality of sources and a plurality of destinations in a network, the method including sending data packets from a first data stream over the link from one source to one destination at a first transmission rate, and measuring an associated first packet loss rate; sending further data packets from the first data stream over the link from the one source to the one destination at a second transmission rate, and measuring an associated second packet loss rate; and determining the bandwidth of the link in dependence on the first and second packet loss rates and the first and second transmission rates.

Determining the bandwidth of a communication link

A method of delivering media content over a network, the media content including a plurality of temporal segments, wherein each temporal segment comprises a plurality of data packets, the method including: selecting an initial size of a first congestion window; delivering the plurality of data packets of a first segment using the first congestion window, the initial size of the first congestion window being used to control the size of the first congestion window for the duration of the first segment delivery; measuring the packet loss during the delivery of the first segment; determining an initial size of a second congestion window in dependence on the measured packet loss for the first segment; and delivering a second segment using the second congestion window, the initial size of the second congestion window being used to control the size of the second congestion window for the duration of the second segment delivery.

Managing congestion response during content delivery

In examples of the present invention, delivery of a segment of content is done using an initial congestion window, preferably chosen to give a delivery rate that ensures timely delivery of that segment. However, under high levels of packet loss, the delivery rate may not be sufficient. Hence, at any stage during delivery of a segment, the actual delivery rate is measured, and used, together with the previous congestion window size, the amount of content segment data still to be delivered, and the time left for delivery, to calculate an updated congestion window. The remainder of the segment is then delivered using this revised congestion window.

Congestion response for timely media delivery

Examples of the present invention provide a method of converting a multicast stream into unicast segments. In particular, sequence identifiers are generated based on a clock reference field in the transport stream packets that make up the multicast stream. Every time a new sequence identifier is calculated, a new unicast segment is generated and assigned with the new sequence identifier. Transport stream packets are placed into the new segment until a packet is processed that causes a new sequence identifier to be generated, at which point another new segment is generated and packets placed into that segment. In an improved method, random access indicators in the transports stream packets are used to further constrain when a new segment is generated, to ensure that new segments are coincident with a packet having a random access indicator. This improvement makes random access easier back and forth between and within a stream.

Multicast to unicast conversion

The invention presents a method of providing feedback for receipt of a multicast video stream. The feedback mechanism allows the number of clients receiving over multicast to be determined, which can then be used to manage multicast delivery, including switching decisions between multicast and unicast. Video content is delivered over a multicast stream from a content server to a plurality of client devices. The client devices are each configured to respond at regular intervals whilst receiving the multicast video stream by transmitting an HTTP HEAD request message to the content server. The HTTP HEAD request refers to metadata relating to a manifest file associated with the video stream. The number of client devices receiving the multicast video stream is determined based on the number of HEAD requests received at the content server. The multicast video delivery can then be managed accordingly, and can also take into account the number of unicast clients that are requesting the corresponding unicast stream to the multicast stream.

Multicast streaming

Examples of the present invention present a method of controlling content delivery in a network. A global quality of experience measure, QoE, is calculated based on the packet loss rate in the network. As packet loss rate varies as a result of congestion conditions in the network, so will QoE. A server delivering content over the network will attempt to reach QoEfor the content in its respective session. Those sessions with a quality of experience, QoE, less than QoEwill have its packet dispatch rate increased, and those with a QoE higher than QoEwill reduce its packet dispatch rate, subject to any delivery deadlines associated with the session. If the delivery deadlines of the sessions can be met without exceeding QoE, then all sessions will end up achieving QoE. Since QoEis only a function of packet loss rate that all sessions miming over the same shared network agree upon, all sessions should converge on the same QoE.

Deadline driven content delivery

A method for providing equitable media streaming between an HTTP server and a number of receivers via shared network. The streaming data is processed to split the data across a number of sub-streams. Each sub-stream contains non-contiguous data. A receiver requesting the streaming media establishes a number of TCP sessions, one for each sub-stream and the received sub-stream data is reassembled at the receiver so that the streaming media can be presented.

Growing community of inventors

Colchester, United Kingdom

Stephen Clifford Appleby