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Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L67/00—Network arrangements or protocols for supporting network services or applications
  • H04L67/14—Session management
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L12/00—Data switching networks
  • H04L12/02—Details
  • H04L12/16—Arrangements for providing special services to substations
  • H04L12/18—Arrangements for providing special services to substations for broadcast or conference, e.g. multicast
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L65/00—Network arrangements, protocols or services for supporting real-time applications in data packet communication
  • H04L65/40—Support for services or applications
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
  • H04W4/06—Selective distribution of broadcast services, e.g. multimedia broadcast multicast service [MBMS]; Services to user groups; One-way selective calling services

Definitions

• This invention relates to a method, a computer program, a computer program product, a system, a sender, a receiver and a protocol for transmitting common data from one sender to a plurality of receivers within a transmission session.
• Broadcast/multicast services are services intended to provide flexible and efficient mechanisms to send common (the same) information from one sender to multiple receivers.
• the Multimedia Broadcast/Multicast Service is used in the Universal Mobile Telecommunications System (UMTS) as standardized by the Third Generation Partnership Project (3GPP).
• UMTS Universal Mobile Telecommunications System
• 3GPP Third Generation Partnership Project
• the broadcast service describes a unidirectional point-to-multipoint transmission of multimedia data (e.g. text, audio, picture, video) from a single source entity (the sender) to all users (the receivers) in a broadcast area or areas.
• multimedia data e.g. text, audio, picture, video
• the broadcast mode is intended to efficiently use radio/network resources, e.g. data is transmitted over a common radio channel. Data is transmitted to broadcast areas as defined by the network.
• a broadcast service received by the user may involve one or more successive broadcast sessions.
• a broadcast service might, for example, consist of a single on-going session (e.g. a media stream) or may involve several intermittent sessions over an extended period of time (e.g. messages).
• An example of a service using the broadcast mode could be advertising or a welcome message to the network. As not all users attached to the network may wish to receive these messages then the user shall be able to enable/disable the reception of these broadcast services on his User Equipment (UE).
• UE User Equipment
• the broadcast mode differs from the multicast mode in that there is no specific requirement to activate or subscribe to the MBMS in broadcast mode.
• a multicast service received by the UE may involve one or more successive multicast sessions.
• a multicast service might, for example, consist of a single on-going session (e.g. a multimedia stream) or may involve several intermittent multicast sessions over an extended period of time (e.g. messages).
• An example of a service using the multicast mode could be a football results service for which a subscription is required.
• the multicast mode Unlike the broadcast mode, the multicast mode generally requires a subscription to the multicast subscription group and then the user joining the corresponding multicast group.
• the subscription and group joining may be made by a Public Land Mobile Network (PLMN) operator, the user or a third party on their behalf (e.g. company).
• PLMN Public Land Mobile Network
• FLUTE File Delivery over Unidirectional Transport
• IETF Internet Engineering Task Force
• FLUTE represents a protocol for the unidirectional delivery of files over IP (Internet Protocol) based networks, which is particularly suited to multicast networks, wherein common data is sent from one IP based entity to a plurality of IP based hosts.
• the FLUTE specification builds on the Asynchronous Layered Coding (ALC) protocol, the base protocol designed for massively scalable multicast distribution.
• AAC Asynchronous Layered Coding
• FLUTE is applicable to the delivery of large and small files to many IP based hosts, using delivery sessions of several seconds or more. For instance, FLUTE could also be used for the delivery of large software updates to many IP based hosts simultaneously. It could also be used for continuous, but segmented, data such as time-lined text for subtitling.
• FEC Forward Error Correction
• a general object of the present invention to provide a method, a computer program, a computer program product, a system, a sender, a receiver and a protocol that allow the communication of parameters, which are related to a transmission of common data from a sender to a plurality of receivers within a transmission session, to said plurality of receivers.
• a method for transmitting common data from one sender to a plurality of receivers within a transmission session comprising communicating at least one session parameter, which is related to said transmission of said common data within said transmission session, to said plurality of receivers via a communication protocol, and transmitting said common data from said sender to said plurality of receivers within said transmission session.
• Said common data may comprise all kinds of information that can be represented in electronic form, for instance text, audio, images and video.
• Said common data may be streaming data, which is continuously transmitted from said sender to said plurality of receivers in a synchronized manner, or non-streaming data.
• Said data is common, i.e. the same data is transmitted to each receiver of said plurality of receivers in a point-to-multipoint fashion.
• Said transmission of said common data may take place in a wire-bound or in a wireless network, or in a combination thereof.
• the sender thus may for instance be an Internet server, and the receivers may be IP based hosts. Equally well, said receivers may also be mobile receivers in a wireless network.
• Said receivers may be of the same type or of different types.
• Said transmission of said common data takes place within a transmission session that may be of limited duration.
• Said at least one session parameter is related to said transmission of said common data within said transmission session.
• Said at least one session parameter may for instance describe the error protection, channel coding, modulation and/or interleaving that is used for said transmission of said common data.
• Said at least one session parameter may equally well comprise information related to delay or memory constraints imposed on the receivers, on the content of the common data, on congestion control, on error recovery, or on any other topic related to the correct transmission and reception of said common data. For instance, information on a repair session that may be required subsequent to said transmission of said common data if said common data is not correctly received at one or several receivers and thus has to be at least partially re-transmitted within a repair session may be contained in said at least one session parameter.
• Said at least one session parameter is communicated to said plurality of receivers via a communication protocol.
• Said communication protocol may for instance be the Session Description Protocol (SDP), the File Transfer Protocol (FTP), the Hypertext Transport Protocol (HTTP), the Short Message Service (SMS), the General Packet Radio Service (GPRS) or similar protocols.
• Said at least one session parameter may for instance be communicated in protocol data units that are exchanged between communication protocol entities in different peers, wherein one peer may be the sender, and another peer may be one of said plurality of receivers.
• Said communication protocol may be particularly specified or defined for the communication of said at least one session parameter.
• said at least one session parameter is communicated to said plurality of receivers before or during the establishment of said transmission session.
• the receivers then are provided with said at least one session parameter, which is related to said subsequent transmission of said common data within said transmission session, early enough so that a proper reception of said common data at said plurality of receivers is possible.
• said communication protocol is a Session Description Protocol (SDP).
• SDP Session Description Protocol
• Said SDP may be intended for describing multimedia sessions for the purposes of session announcement, session invitation, and other forms of multimedia session initiation.
• Said SDP may provide a standard representation for the description of media details, transport addresses and other session description metadata being required when initiating multimedia teleconferences, voice-over-IP calls, streaming video, or other real-time sessions.
• Said session description metadata provided by said SDP may be conveyed to the participants of the multimedia sessions before the actual multimedia session takes place.
• Said SDP may be independent on the actual way in which information is transported.
• Said SDP may purely be a format for session description without incorporating a transport protocol, and may be intended to use different transport protocols as appropriate, including for instance the Session Announcement Protocol (SAP), the Session Initiation Protocol (SIP), the Real-Time Streaming Protocol (RTSP), or the Hypertext Transport Protocol (HTTP).
• SAP Session Announcement Protocol
• SIP Session Initiation Protocol
• RTSP Real-Time Streaming Protocol
• HTTP Hypertext Transport Protocol
• Said SDP may be intended to be general purpose so that it may be used in a wide range of network environments and applications.
• Said SDP may for instance be operated by SDP protocol entities in said sender (or another instance such as a content server or similar) and SDP protocol entities in said plurality of receivers.
• Said SDP may for instance be the SDP that is defined by the Internet Engineering Task Force (IETF).
• IETF Internet Engineering Task Force
• Said at least one session parameter is communicated to said plurality of receivers via said SDP.
• This may for instance be achieved by a plurality of attribute fields that are defined by said SDP, wherein each attribute field may be capable of incorporating the information of one or more session parameters.
• said common data is transmitted from said sender to said plurality of receivers at least partially over an IP based network.
• said sender may be an Internet server or a similar instance within the Internet
• said receivers may be mobile receivers of a wireless communication system the core network of which is connected to the Internet and thus to said sender.
• said common data is transmitted from said sender to said plurality of receivers in a broadcast or multicast operation.
• point-to-multipoint operation takes place.
• said common data is streaming data or non-streaming data.
• Streaming data may be characterized as data that is continuously and in a synchronized manner transmitted from said sender to said plurality of receivers, for instance in the form of streaming video or audio.
• said common data is real-time data or non-real-time data.
• said common data is transmitted from said sender to said plurality of receivers at least partially over a wireless network.
• said receivers may be mobile receivers in a wireless communication network that is connected to a sender residing on an IP based network.
• Said wireless network may for instance be a mobile radio communication network according to the Universal Mobile Telecommunications System (UMTS) standard, or a Wireless Local Area Network (W-LAN) such as IEEE 802.11 or HiperLAN/2, or a satellite-based network.
• UMTS Universal Mobile Telecommunications System
• WLAN Wireless Local Area Network
• said wireless network is a mobile network that at least partially implements a Multimedia Broadcast/Multicast Service MBMS as defined by the Third Generation Partnership Project 3GPP.
• said communication protocol contains a Forward Error Correction (FEC) attribute that specifies at least an FEC encoding scheme that is used for said transmission of said common data within said transmission session.
• FEC Forward Error Correction
• Said attribute contained in said communication protocol may be a primary means for extending said communication protocol, and may be defined to be used as “session-level” or “media-level” attribute, or both. Said attribute may add information about the media stream. It may further also convey additional information that applies to said transmission session as a whole rather than to individual media. Attributes may be either property attributes or value attributes.
• Said FEC encoding scheme said FEC attribute specifies may for instance be an Automatic Repeat Request (ARQ) scheme.
• ARQ Automatic Repeat Request
• said FEC attribute further specifies an FEC encoding identifier.
• Said FEC encoding identifier may contain information on an FEC decoding matrix or FEC byte-code.
• said communication protocol contains an FEC machine attribute that specifies the location from which FEC decoding information can be downloaded.
• said FEC decoding information such as an FEC decoding matrix or FEC bytecode has to be downloaded from said location by at least one of said plurality of receivers in an error-free fashion.
• At least one of said plurality of receivers uses a Hypertext Transport Protocol (HTTP) or a Transport Control Protocol (TCP) based point-to-point connection to download said FEC decoding information.
• HTTP Hypertext Transport Protocol
• TCP Transport Control Protocol
• At least one of said plurality of receivers uses a time dispersion function to determine a time when the downloading of said FEC decoding information from said location starts or determine the time when to start a repair session.
• This time dispersion function may reduce the number of receivers that may concurrently attempt to download said FEC information from said location or perform repair sessions, for instance by prescribing a randomized starting time for said download.
• said communication protocol contains an FEC buffering attribute that specifies the buffering requirements imposed on said plurality of receivers during the transmission of said common data from said sender to said plurality of receivers in said transmission session.
• said buffering requirements are a buffering delay and/or a buffering memory size.
• said communication protocol contains a congestion control attribute that specifies a congestion control scheme that is used for said transmission of said common data within said transmission session.
• said repair session is a point-to-point or a point-to-multipoint repair session.
• said communication protocol contains a repair Uniform Resource Identifier URI attribute that specifies a URI of said repair server.
• said communication protocol contains a repair threshold attribute that specifies an error threshold, and that said error threshold is related to a reception quality of said common data as received by said plurality of receivers from said sender within said transmission session.
• Said error threshold may for instance quantify a maximum tolerable number of bit errors per packet or time.
• an entering into said repair session by one of said plurality of receivers depends on the relationship between a reception quality of said common data as received by said receiver from said sender within said transmission session and said error threshold. If for instance said receiver receives said common data during said transmission session with an error of 10 bytes in a window of 300 seconds, and if said error threshold states that only up to 1 byte error in a window of 300 seconds is allowed in order to start the repair session, said receiver may refrain from entering said repair session.
• said error threshold is quantified in terms of an error unit, an error value, a measurement window unit and a measurement window value.
• Said error unit may for instance be bytes, bits, packets or a percentage, said error value may be a real-valued number, said window unit may for instance be seconds, packets, bits or bytes and said window value may be a real-valued number.
• An example of an error threshold quantified in this manner may thus be 10 erroneous bytes in a window of 300 seconds or a similar combination.
• said error threshold is quantified in terms of an error value. It may also be possible to specify said error threshold by a real-valued error value, for instance 0.01. The error unit, the measurement window unit and the measurement window value may then for instance be pre-defined.
• a plurality of error thresholds is used for said transmission session, and wherein said error thresholds are explicitly or implicitly labelled.
• Said error threshold may for instance be explicitly labelled with an integer, so that a first, second, etc. error threshold may be differentiated.
• Said error threshold may equally well be inherently labelled, for instance by prescribing that the error thresholds are sorted according to their value and then labelled in ascending (or alternatively in descending) order, starting with the lowest or highest error threshold. Labelling error thresholds is particularly advantageous when different backoff modes, which may for instance describe how long a receiver has to wait until a request for a repair session may be started, are supported and when each error threshold then corresponds to a respective backoff mode.
• the entrance of receivers into a repair session then may be controlled depending on the magnitude of the reception errors, so that, for instance, receivers with large reception errors enter said repair session at first or at last.
• said communication protocol contains a backoff-mode attribute that provides information on when a receiver that did not correctly receive said common data from said sender within said transmission session can start a request for said repair session.
• said communication protocol contains a backoff-mode attribute that specifies a backoff mode, wherein said backoff mode provides information on when a receiver that did not correctly receive said common data from said sender within said transmission session can start a request for said repair session, wherein a plurality of backoff modes is used for said transmission session, and wherein at least one of said error thresholds is linked to at least one of said backoff modes, respectively. For instance, each error threshold may then be linked to a respective backoff mode. This linking may for instance be achieved by labelling both the error thresholds and the backoff modes, so that corresponding labels are understood to represent a link.
• said backoff modes are assigned to a receiver in dependence on the relationship between a reception quality of said common data as received by said receiver during said transmission session and a reception quality as demanded by said error thresholds. Based on the error rate that is experienced by a receiver during the reception of said common data within said transmission session, and the linking between said error thresholds and said backoff modes, it may then be possible to assign a backoff mode to said receiver. In this way, for instance receivers with a high error rate (above a first error threshold) are assigned to a first backoff mode, and receivers with a lower error rate, below the first error threshold but above a second error threshold, are assigned to a second backoff mode. The receivers in the first backoff mode then may be allowed to transmit before or after the after the receivers in the second backoff mode, thus allowing for a Quality of Service (QoS) control.
• QoS Quality of Service
• said information is represented by a backoff unit, a backoff value and a backoff window.
• Said backoff unit may for instance be a relative time in seconds, an absolute Network Time Protocol (NTP) time, bytes, bits or packets.
• NTP Network Time Protocol
• Said backoff value may for instance be a real-valued number.
• Said backoff window may for instance be a real-valued number with a unit that may be the same as the unit specified by said backoff unit.
• Said information may be related to an absolute or relative time basis.
• said backoff unit is seconds
• said backoff value is 60 and said backoff window is 120
• this may indicate that a receiver may start a request for a repair session between 60 and 180 ( 60+120) seconds from the end of the transmission session, wherein said starting time may be randomly chosen from said interval between 60 and 120 seconds, for instance based on a uniform distribution.
• said information is represented by a variable that indicates if absolute or relative timing is used, and a time value.
• said time value may specify an absolute NTP time at which a request for a repair session may be started (or around which or starting from which a starting time may be randomly chosen).
• said time value may for instance specify that said request may be randomly started in an interval starting with the end of the transmission session and ending after a duration as indicated by said time value.
• Said time value may also be defined as a maximum repair availability time, i.e. the time until the repair operation is possible, and then may be preferably expressed in NTP time, enabling a so-called lazy repair.
• said information comprises an error threshold and three values X, Y and Z, and that at least one of said plurality of receivers, if a reception quality of said common data as received by said at least one receiver from said sender within said transmission session is better than a reception quality dictated by said error threshold, said request for said repair session is started randomly within a time interval of duration X, wherein said interval starts at the end of said transmission session; and otherwise starting said request for said repair session randomly within a time period between Y and Y+Z, wherein Y is counted from the end of said transmission session.
• said communication protocol can be used to communicate the number of said plurality of receivers to said plurality of receivers.
• Information on the number of receivers may be advantageously used by said receivers when determining backoff times for said repair session.
• said communication protocol contains a repair type parameter attribute that specifies if said repair session can be a point-to-point session, a point-to-multipoint session, or both.
• said communication protocol contains a repair token attribute that specifies the type of said repair session, and/or information on which parts of said common data that is not correctly received at least one of said plurality of receivers within said transmission session will be transmitted from said repair server to said at least one receiver within said repair session.
• Said information on said parts may for instance specify a file identifier, a Source Block Number (SBN) and/or Encoding Symbol ID (ESI) of said common data, or pairs or ranges based on these values.
• said communication protocol contains a content description attribute that specifies how said sender indicates to said plurality of receivers the URI where a content description of said common data is stored.
• Said URI may for instance be an Extended Markup Language (XML) scheme such as an File Delivery Table (FDT) XML schema, or an entry point to an Internet Media Guide (IMG) data model, or another entry point to a schema or model.
• XML Extended Markup Language
• FDT File Delivery Table
• IMG Internet Media Guide
• said transmission of said common data from said sender to said plurality of receivers is at least partially controlled by a File Delivery Over Unidirectional Transport FLUTE protocol.
• Said FLUTE may represent a protocol for the unidirectional delivery of files over the Internet, which may be particularly suited to multicast networks.
• Said FLUTE protocol may be based on Asynchronous Layered Coding (ALC).
• said communication protocol contains a FLUTE channel attribute that specifies how many channels are used by the sender to transmit said common data to said plurality of receivers within said transmission session.
• said communication protocol contains a FLUTE Transmission Session Identifier TSI attribute that specifies the value of a TSI within said transmission session.
• said communication protocol contains a media description that specifies a media that is used within said transmission session.
• This media description may also be referred to as “m-line”.
• said media may be audio, video, application, data and control.
• Said media description may for instance describe that video data is transported on a channel that uses FLUTE over a User Datagram Protocol (UDP).
• UDP User Datagram Protocol
• said communication protocol contains a connection data that specifies an address of a channel used within said transmission session.
• This connection data may also be referred to a “c-line”.
• Said connection data may comprise a network type, an address type and a connection address. This connection data thus may, for instance. indicate an IPv6 address.
• Said processor may for instance be integrated in said sender, receiver, or both.
• Still further proposed is a computer program product comprising a computer program with instructions operable to cause a processor to perform the above-described method steps.
• a system for transmitting data, comprising at least one sender and a plurality of receivers, wherein said at least one sender and said plurality of receivers comprise means arranged for communicating at least one session parameter, which is related to said transmission of said common data within said transmission session, from said at least one sender to said plurality of receivers via a Session Description Protocol communication protocol; and wherein said at least one sender and said plurality of receivers comprise means arranged for transmitting said common data from said sender to said plurality of receivers within said transmission session.
• a sender for transmitting common data to a plurality of receivers within a transmission session, the sender comprising means arranged for communicating at least one session parameter, which is related to said transmission of said common data within said transmission session, to said plurality of receivers via a Session Description Protocol communication protocol, and means arranged for transmitting said common data to said plurality of receivers within said transmission session.
• a receiver for receiving common data that is transmitted from one sender to a plurality of receivers within a transmission session, comprising means arranged for receiving at least one session parameter, which is related to said transmission of said common data within said transmission session, and which is communicated to said plurality of receivers via a Session Description Protocol communication protocol, and means arranged for receiving said common data that is transmitted from said sender to said plurality of receivers within said transmission session.
• a Session Description Protocol comprising a definition of at least one session parameter that is related to a transmission of common data from a sender to a plurality of receivers within a transmission session.
• FIG. 1 a flowchart of a possible embodiment of the method according to the present invention.
• FIG. 2 a schematic view of a possible embodiment of the system according to the present invention.
• the present invention proposes to deploy a communication protocol in order to communicate session parameters to a plurality of receivers that are to receive common data from a sender via a point-to-multipoint connection.
• a Session Description Protocol SDP will be used for this purpose.
• said SDP contains attributes, media descriptions and connection data that are defined to allow for the communication of said session parameters.
• 3GPP Third Generation Partnership Project
• FLUTE File Delivery over Unidirectional Transport
• IETF Internet Engineering Taskforce
• the Forward Error Correction (FEC) attribute describes the FEC encoding scheme used.
• the FEC attribute describes also the FEC encoding identifier (and its association with the FEC encoding scheme used). For example, in the IETF FLUTE protocol draft, a description of the FEC encoding ID for the FLUTE protocol is given. There may be multiple encoding identifiers associated to an FEC encoding scheme.
• value is a numerical value representing the FEC Encoding scheme used.
• value-single represents the FEC Encoding scheme (with values between 0 and 127 in this example).
• value-couple represents a (FEC Encoding scheme, FEC encoding-ID) pair (with values respectively between 128 and 255 for the FEC encoding scheme, and between 0 and 255 for the encoding-ID in this example).
• the FEC attribute may preferably be a session level-only attribute (however, it is not excluded to use it as media-level attribute).
• the sender indicates in the above example that multiple FEC IDs are used.
• the sender does not need to map these to specific channels of the FLUTE session.
• a further example for the use of the FEC attribute according to the present invention is:
• the limitation of only a single (FEC encoding ID) parameter for FEC encoding IDs 0-127 being useful is specified by ALC version 1.
• the use of a second parameter (FEC Instance ID) for FEC encoding IDs 0-127 may also be envisaged according to the present invention to further extend the number of fully specified FEC schemes, which may be signalled.
• the sender In case a universal FEC machine is used (i.e., a system that allows to download the FEC scheme or the FEC decoding matrix to the receivers before starting a session), the sender must signal the exact location of the FEC decoding matrix or the FEC bytecode to be downloaded from the receiver in order to decode the data that are going to be transmitted on the multicast/broadcast channel.
• Downloading of this data advantageously is performed in error free fashion, preferably (but not limited to) via an HTTP/TCP point-to-point connection. If the bytecode or the FEC matrix are not delivered error-free to the receivers, it might be difficult for the receiver to correctly receive the common data within a multicast/broadcast session.
• the sender may signal the location of the FEC file during the SDP session announcement and thus before the session starts. It may be advantageous that the receivers fetch the error-free FEC file before the start of the session, in order to get the system ready for decoding the data. In order to avoid network overload due to the many receivers' requests for FEC file downloading, the receivers may start this point-to-point downloading with a randomized starting time. This time may for instance be computed by the receivers between the time 0 (when the session description is received via said SDP) and the time indicated as session start time in the (first) t parameter value contained in the same session description.
• the FEC machine attribute may preferably be a session level-only attribute. It is however not excluded to use it as media-level attribute.
• the receivers may randomize not only in the time dimension, but also based on the multiple FEC-machine locations.
• An example for the use of the FEC machine attribute according to the present invention is:
• the receiver fetches the FEC matrix file from the address above.
• the FEC buffering attribute describes the requirements or constraints imposed by a FEC encoding scheme to the receivers when receiving a multicast/broadcast data stream. These constraints may for instance be in terms of a first parameter additional delay (i.e., latency expressed in the time dimension, e.g., in milliseconds) and/or a second parameter memory requirement (i.e., number of bytes required at the receivers to perform FEC decoding).
• a first parameter additional delay i.e., latency expressed in the time dimension, e.g., in milliseconds
• second parameter memory requirement i.e., number of bytes required at the receivers to perform FEC decoding
• the first parameter is advantageously applicable to real-time sessions (such as multicast media streaming sessions). It may be used to guarantee real-time and pause-less decoding of FEC-encoded media data, and playback at the receivers.
• the second parameter is advantageously applicable to real-time sessions, but also to non-real-time sessions (e.g., file download sessions). It may be used by a receiver to determine its terminal capabilities against the session requirements, and to allocate an adequate amount of memory to enable efficient FEC data decoding.
• Both parameters may preferably be session level-only attributes. It is however not excluded to use them as media-level attributes.
• the sender tells to the receiver(s) that the FEC scheme 127 produces 500 ms delay and requires 1000000 bytes of memory.
• the memory requirement parameter is missing.
• the delay parameter is missing.
• the congestion control attribute describes the congestion control scheme used.
• value may be a numerical or alpha-numerical value representing the Congestion Control scheme used. This may be a session level-only attribute.
• These may preferably be session-level-only attributes. It is however not excluded to use them as media-level attributes. In the description which follows below, four attributes related to repair parameters will exemplarily be defined.
• the URI of the repair server attribute describes the address of the repair server to be used by the receivers for establishing a point-to-point or point-to-multipoint repair session.
• URI is a valid URI for the repair server, which may be used by the receivers to establish a repair session.
• the client may select the suitable server based on the following criteria:
• the sender indicates in the above example the repair server to be used by the receivers to establish a point-to-point repair session in the case that the entire session is not received correctly.
• SDP attributes related to an error rate repair threshold includes two aspects as described below.
• the error rate repair threshold attribute may describe a threshold beyond which the receivers should not request repair requests.
• value1 is the error unit used for the error rate threshold.
• An example of the values that could be used for this purpose is:
• value3 is the measurement window unit.
• An example of values that could be used for this purpose is:
• error thresholds these may be implicitly labelled in incremental order (0, 1, 2, . . . n) according to the most challenging error threshold criteria (i.e., the lowest error rate threshold) to the least challenging (i.e., the highest error rate threshold).
• the most challenging error threshold criteria i.e., the lowest error rate threshold
• the least challenging i.e., the highest error rate threshold
• the next most challenging criteria e.g., less than 0.01 bits per second, but more than 0.000001
• the least challenging reception criteria earns the label “error rate n”.
• the number of thresholds specified is n+1 according to this labelling and may be invariable. The significance of this virtual labelling is to map the error thresholds to the different backoff modes that might be employed.
• a repair-threshold: “(A,B,C,D) (W,X,Y,Z)”.
• the threshold values may be linked to back-off modes, as will be explained in more detail below. A simple an elegant method for this would be that the order of the quadruple determines the mode of behaviour of the receiver.
• the first threshold specified (threshold 1) corresponds to the first back-off mode specified (back-off 1) and so on.
• the sender indicates the receivers that the repair threshold is 10 bytes per second with a window of 300 seconds.
• the sender indicates to the receivers that the repair threshold is 5% packet loss rate.
• the back-off mode attribute (equivalent names may be suppression mode, response timing mode, time dispersion function, or time spread function) describes the way a sender tells the receivers when to start the request for repair operation, or how to compute this starting time. This may include the signalling of a single value (in time units) over which the receivers may randomize the repair request starting time, or a set of values that might enable a receiver to compute the repair starting time (e.g., a more complex set of thresholds or the number of receivers involved in the multicast transmission).
• a scheme similar to the one defined for the error rate threshold may also be used with a set of modes.
• An example syntax for a backoff mode attribute according to the present invention is given below as:
• value1 is the measurement unit.
• An example of values that could be used for value1 is:
• value2 is the measurement value. For instance, 10 seconds, 20 bytes, 30 packets. This value may represent an offset value and may be negative. It should be noted that for a measurement of time, this value can be absolute or relative. Where session lengths are of finite and relatively short time, the best mode for relative may be relative to the end of the session (as advertised in the descriptor). For never ending sessions (not MBMS), the end of another entity (such as the end of a transmission object signalled by a transport header flag) may be used.
• value3 represents a window.
• the unit for this may be the same as for value2, i.e. that defined by value1.
• a smaller number of parameters than three may also be possible. For instance, the presence of only 2 parameters may indicate that it is defaulted to relative time. Likewise, just one parameter could indicate relative time with zero offset.
• a message e.g. repair request
• the back-off modes may be implicitly labelled in incremental order (0, 1, 2, . . . , m) according to the order of presentation in the description instance.
• the first mode described e.g., from the start of an SDP file
• the next to appear would be identified as mode 0 and so on until the last mode described earns the label “mode m”.
• the significance of this virtual labelling is to map from the error rate threshold (as defined above), which may tell the receiver which mode to employ. Thus, if error rate 1 is experienced, the receiver may employ back-off mode 1.
• Good design may ensure that the number of modes (m+1) equals the number of error rate thresholds specified.
• the mode m may be used for all error rates m and greater; and where n ⁇ m the back-off modes n+1 to m may be silently ignored.
• the purpose of multiple modes depending on error rate criteria is to allow quick and slow repair types of service, which may maximize user perceived QoS over the whole multicast/broadcast group, by allowing the users with the least demanding repair requirement priority in repair scheduling.
• it may make sense to ensure that mode 0 provides the most timely-early-repair and mode m the least timely.
• this is not mandatory so that alternative schemes are also allowed.
• a backoff-mode: (0, 0, 60)
• the example shows non-overlapping message windows, although overlapping windows (across different modes) are also in the scope of this invention.
• An alternative operation is to add a 4 th value to each backoff-mode line which may give the mode label either as an integer number—which may be mapped to error rate as above—or as some other label which requires a similar label to be either introduced to the error-threshold lines or a separate mapping descriptor to also be used.
• the receivers should randomize the starting time of the repair request between the end of the delivery session and 30 seconds. If the error rate is 10 bits per second or greater but less than 20 bits per second, then the receivers should wait 30 seconds after the end of the delivery session, and then randomize the repair request between the end of the 30 seconds waiting time and 60 more seconds (i.e. between 30 and 90 seconds after the end of the session). If the error rate is 20 bits per second or greater, then the receivers should wait 60 seconds after the end of the delivery session, and then randomize the repair request between the end of the 60 seconds waiting time and 240 more seconds (i.e. between 60 and 300 seconds after the end of the session).
• An alternative back-off operation according to the present invention may obey the following rule:
• a negative-acknowledgement message may for instance correspond to starting a request for a repair session.
• This alternative back-off operation requires the description of some SDP parameters.
• the parameters are ERROR RATE, X, Y and Z, where ERROR RATE is expressed in the same units as the error rate threshold defined above, and X, Y, Z and expressed in units of time (e.g., in seconds).
• ERROR RATE is expressed in the same units as the error rate threshold defined above
• X, Y, Z is expressed in units of time (e.g., in seconds).
• value1 is the error rate as defined above in the error rate repair threshold.
• value2 is the back-off time if the error rate is below value, since the end of the delivery session.
• value3 is the waiting time in case the error rate exceed the threshold given by value1.
• value4 is the back-off time if the error rate is above value. It can be a displacement value relative from value3 after the end of the delivery session, or a displacement value relative to the end of the delivery session (in the latter case value4>value2).
• the receivers should randomize the starting time of the repair request between the end of the delivery session and 10 seconds. If the error rate is greater than 5%, the receivers should wait 20 seconds after the end of the delivery session, and then randomize the repair request between the end of the 20 seconds waiting time and 30 seconds.
• This example contains multiple a lines with the same attribute.
• the second rule is made for handling cases of 10% error rate, with similar semantics as in the previous example.
• a relative time from the reception of the SDP is considered.
• the sender may tell the receivers to start the repair session at a random time between the end of the session and value (expressed in seconds). If “+” is not used, then an absolute NTP time unit is used.
• value may also be defined as the maximum repair availability time (the time until the repair operation is possible), and it may preferably expressed in NTP time. In this case a lazy repair might be enabled.
• the sender may also signal via SDP the number of receivers that have joined a multicast session, being this a number that can be given in input (together with the random time above) to the function that calculates the back-off time for the start of the repair session.
• the sender tells the receivers to start the repair session at a random time between the end of the session and 500 seconds.
• the sender tells the receivers to compute the back-off time taking into account that there are 5000 users that have joined the multicast session.
• This parameter describes both the repair type (i.e. point-to-multipoint repair, point-to-point repair, both) as well as the repair token.
• the first is used to describe what type of repair is possible.
• the second describes how a specific object (e.g., a file) is going to be repaired (i.e., the repair type), and what parts of the object are going to be repaired (for example, if point-to-multipoint repair is used).
• repair-type “ptp” / “ptm” / “both” and of the repair token attribute according to the present invention is given as:
• ESI (%d) / (”(” %d *(”,” %d) ”)”) /(”(”%d ”—” %d ”)”)
• SBN is the Source Block Number
• ESI is the Encoding Symbol ID.
• the ESI and SBN may be in pairs and the ESI and SBN may be a range or a list of ranges. However, the ESI may not be present alone in this descriptor.
• the repair token may be sent per each object (e.g., file).
• object e.g., file
• the File-ID text string is expected to be a URI or part thereof.
• repair token attribute examples for the use of the repair token attribute.
• the repair is done via point-to-multipoint for the file indicated.
• the blocks that are going to be repaired are those with SBN 10 and ESI 20, and SBN 12 and ESI 134.
• the repair is done via point-to-multipoint for the file indicated.
• the blocks that are going to be repaired are those for SBNs 10 to 14 and ESI 34 of SBN 16.
• the repair is done via point-to-multipoint for the file indicated.
• the number of bytes to be repaired are 150, starting from byte 10.
• SDP attributes related to multiple channels includes three aspects as will be described below.
• the multiple channel attribute describes the number of channels used by the sender to transmit. It may also be used to check the number of channels against the SDP m-lines.
• value is the number of channels used by the sender to transmit data in a FLUTE session.
• This parameter may indicate to the receivers that the sender is using multiple channels in the FLUTE session to transmit data. This may also indicate the number of channels used by the sender.
• the value specified by this descriptor may be used by a receiver to check that it has received all the m-lines describing the destinations. For example, if the value of this parameter is 2, then there should be 2 channels specified by the m-lines.
• TSI Transmission Session Identifier
• m-line media descriptor
• c-line connection data
• the m-line indicates the media used and the c-line indicates the corresponding channel.
• the m-line indicates that the media is transported on a channel that uses FLUTE over UDP.
• the c-line indicates the channel address, which, in this case, is an IPv6 address.
• the sender indicates that the receivers should include the given IP address (2001:210:1:2:240:96FF:FE25:8EC9) into the session.
• This pair of the (source IP address, TSI) together uniquely identifies a session.
• the sender uses the SDP attributes defined in section 7 for session repair. These parameters allow the receivers to locate the correct repair server, allows the sender to set a pre-defined repair threshold and allows the sender to define the repair type and other parameters.
• the content descriptor pointer attribute describes how the sender indicates to the receivers the URI where the content description is stored.
• URI is a valid URI for the Content Description.
• the URI may be an Extended Markup Language (XML) schema such as a File Description Table (FDT) XML schema, an entry point to an Internet Media Guide (IMG) data model or other such entry point to a schema or data model.
• XML Extended Markup Language
• FDT File Description Table
• IMG Internet Media Guide
• FIG. 1 depicts a flowchart of a possible embodiment of a method according to the present invention.
• a physical or logical connection is established between the sender and the receivers.
• session parameters as for instance information on an FEC encoding scheme that will be applied in a transmission session or information related to the buffering requirements at the receiver site, are communicated from the sender to the receivers via the communication protocol, for instance SDP.
• said session parameters may then be communicated via SDP attributes as exemplarily defined in the above description of the present invention.
• the point-to-multipoint transmission of common data from the sender to the receivers is performed, which is at least partially defined by said session parameters.
• FIG. 2 schematically depicts a possible embodiment of a system according to the present invention.
• the system comprises a sender 902 , a network 903 and receivers 901 - 1 , 901 - 2 and 901 - 3 .
• Said sender 903 may for instance be an MBMS server.
• From a communication unit of said sender 903 data is transmitted to reception units of said receivers 901 - 1 , 901 - 2 and 902 - 3 via said network 903 , which may for instance be an IP based broadcast/multicast network, within a point-to-multipoint session.
• session parameters Prior to said point-to-multipoint session, session parameters are communicated from said sender 903 to said receivers 901 - 1 , 901 - 2 and 901 - 3 via said communicated protocol, which may for instance be the SCP.
• the invention provides methods for sending to the receivers, outside of a FLUTE session, parameters required for the reception of the session at the receivers.
• the invention also provides a method of sending parameters to receivers that are required for establishing point-to-point repair sessions in a situation where the receiver does not receive all the required data during the session. Once again, these parameters are by nature required to be sent outside the session. The use of SDP for sending these parameters to the receivers provides an ideal method to achieve the same.
• the invention enables simple and powerfully scalable multiple-back-off-algorithms to be employed according to differential reception recovery demands, in particular by linking different error thresholds to respective back-off modes.
• the present invention is applicable to all types of broadcast/multicast systems over IP networks, and it is not restricted to mobile networks or 3GPP MBMS systems.
• the present invention is by no means restricted to FLUTE sessions, but may equally well be applied to other types of sessions.

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