Patent Publication Number: US-6343321-B2

Title: Method and apparatus for network transport independence

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to computer network communications, and more specifically to a method and apparatus for network transport independence. 
     Portions of the disclosure of this patent document contain material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure as it appears in the Patent and Trademark Office file or records, but otherwise reserves all copyright rights whatsoever. 
     2. Background Art 
     Computers are used to send and receive data with other computers. The Internet is one example of a transport mechanism and other examples include local area networks (LANs) and wide area networks (WANs). Using a network, a software application (a sender) that resides on one computer system can exchange information with another application (a receiver) that resides on a remote computer system, for example. Information is sent via a network in the form of a message. A communication protocol specifies the format of a message. 
     There are different types of communication protocols each of which has a unique message format. For example, asynchronous transfer mode (ATM), hypertext transfer protocol (HTTP), user datagram protocol (UDP), transmission control protocol (TCP) and real time transport protocol (RTP) each have its own message format. 
     In a network environment, it may be necessary for the sender and/or receiver to be able to understand more than one communication protocol&#39;s message format. For example, a receiver may receive messages from different senders that have different message formats. Further, a single message may be composed using multiple message format. For example, an RTP message may be embedded in a TCP message. The receiver must be able to understand both the TCP and RTP message formats to extract the data contained in the message. 
     To process a message, a software application must include one or more modules that can parse the message format and extract the information contained in the message. Such modules are needed for each message format that the software application is likely to encounter. This adds to the complexity of the software application which negatively impacts the development and maintenance costs associated with a software application. 
     SUMMARY OF THE INVENTION 
     Embodiments of the invention make the underlying transport mechanism transparent to the sender and/or receiver. Using embodiments of the invention, it is not necessary for a sender or receiver to interface with the transport mechanism. Messages are received in a single format which eliminates the need for the sender or receiver to accommodate multiple message formats. 
     A socket mechanism implements bi-directional transmissions and acts as a buffer between the sender or receiver and the underlying transport mechanism. The socket mechanism interfaces with a transport delivery mechanism that receives packets from the physical network. The socket forwards messages received from the transport delivery mechanism to a message processor. Further, the socket forwards messages from the message processor to the transport delivery mechanism. The transport delivery mechanism removes the transport header from messages received off the network and adds a transport header to messages to be sent over the network. 
     In one embodiment of the invention, the socket mechanism is comprised of a data channel and a control channel such as those used in an RTP environment. Both the data channel and the control channel include an input stream and an output stream. The input and output streams are push data streams such that the data sender (an originator of the data located on the same or a different host) initiates and controls the flow of the data being transmitted. The socket mechanism interfaces with an RTP session manager (RTPSM), that acts as a message processor in this embodiment, and the transport delivery mechanism 
     A set of object classes are used in one embodiment of the invention to implement the socket mechanism comprised of data and control channels. An RTPIODataSource object class implements the control channel. A subclass of the RTPIODataSource object class, an RTPSocket class, implements the data channel. The RTPIODataSource and RTPSocket provide bi-directional data flow that can receive data for as well as receive data from the RTPSM. 
     The data and control channels each contain an output stream that implement a PushSourceStream interface and an input stream that implements a PushDestStream interface. The output stream sources data from the underlying transport mechanism to the RTPSM while the input stream receives data from the RTPSM and forwards it to the underlying delivery mechanism. In this manner all details of the underlying transport are hidden from the RTPSM. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an embodiment of a computer system capable of providing a suitable execution environment for an embodiment of the invention. 
     FIG. 2 illustrates an overview of message flow and message processing according to an embodiment of the invention. 
     FIG. 3 illustrates an overview of an RTP environment according to an embodiment of the invention. 
     FIG. 4 provides an illustration of a socket comprising a data channel and a control channel according to an embodiment of the invention. 
     FIG. 5 provides a process flow for sending/receiving messages according to an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A method and apparatus for network transport independence is described. In the following description, numerous specific details are set forth in order to provide a more thorough description of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without these specific details. In other instances, well-known features have not been described in detail so as not to obscure the invention. 
     Embodiment of Computer Execution Environment (Hardware) 
     An embodiment of the invention can be implemented as computer software in the form of computer readable program code executed on a general purpose computer such as computer  100  illustrated in FIG. 1. A keyboard  110  and mouse  111  are coupled to a bi-directional system bus  118 . The keyboard and mouse are for introducing user input to the computer system and communicating that user input to central processing unit (CPU)  113 . Other suitable input devices may be used in addition to, or in place of, the mouse  111  and keyboard  110 . I/O (input/output) unit  119  coupled to bi-directional system bus  118  represents such I/O elements as a printer, A/V (audio/video) I/O, etc. 
     Computer  100  includes a video memory  114 , main memory  115  and mass storage  112 , all coupled to bi-directional system bus  118  along with keyboard  110 , mouse  111  and CPU  113 . The mass storage  112  may include both fixed and removable media, such as magnetic, optical or magnetic optical storage systems or any other available mass storage technology. Bus  118  may contain, for example, thirty-two address lines for addressing video memory  114  or main memory  115 . The system bus  118  also includes, for example, a 32-bit data bus for transferring data between and among the components, such as CPU  113 , main memory  115 , video memory  114  and mass storage  112 . Alternatively, multiplex data/address lines may be used instead of separate data and address lines. 
     In one embodiment of the invention, the CPU  113  is a microprocessor manufactured by Motorola®, such as the 680X0 processor or a microprocessor manufactured by Intel®, such as the 80X86, or Pentium® processor, or a SPARC® microprocessor from Sun Microsystems®. However, any other suitable microprocessor or microcomputer may be utilized. Main memory  115  is comprised of dynamic random access memory (DRAM). Video memory  114  is a dual-ported video random access memory. One port of the video memory  114  is coupled to video amplifier  116 . The video amplifier  116  is used to drive the cathode ray tube (CRT) raster monitor  117 . Video amplifier  116  is well known in the art and may be implemented by any suitable apparatus. This circuitry converts pixel data stored in video memory  114  to a raster signal suitable for use by monitor  117 . Monitor  117  is a type of monitor suitable for displaying graphic images. 
     Computer  100  may also include a communication interface  120  coupled to bus  118 . Communication interface  120  provides a two-way data communication coupling via a network link  121  to a local network  122 . For example, if communication interface  120  is an integrated services digital network (ISDN) card or a modem, communication interface  120  provides a data communication connection to the corresponding type of telephone line, which comprises part of network link  121 . If communication interface  120  is a local area network (LAN) card, communication interface  120  provides a data communication connection via network link  121  to a compatible LAN. Wireless links are also possible. In any such implementation, communication interface  120  sends and receives electrical, electromagnetic or optical signals which carry digital data streams representing various types of information. 
     Network link  121  typically provides data communication through one or more networks to other data devices. For example, network link  121  may provide a connection through local network  122  to host computer  123  or to data equipment operated by an Internet Service Provider (ISP)  124 . ISP  124  in turn provides data communication services through the world wide packet data communication network now commonly referred to as the “Internet”  125 . Local network  122  and Internet  125  both use electrical, electromagnetic or optical signals which carry digital data streams. The signals through the various networks and the signals on network link  121  and through communication interface  120 , which carry the digital data to and from computer  100 , are exemplary forms of carrier waves transporting the information. 
     Computer  100  can send messages and receive data, including program code, through the network(s), network link  121 , and communication interface  120 . In the Internet example, server  126  might transmit a requested code for an application program through Internet  125 , ISP  124 , local network  122  and communication interface  120 . In accord with the invention, one such downloaded application is the Method and Apparatus for Network Transport Independence described herein. 
     The received code may be executed by CPU  113  as it is received, and/or stored in mass storage  112 , or other non-volatile storage for later execution. In this manner, computer  100  may obtain application code in the form of a carrier wave. 
     The computer system described above is for purposes of example only. An embodiment of the invention may be implemented in any type of computer system or programming or processing environment. 
     Overview 
     Information can be transmitted using a transport mechanism that consists of a physical network and a protocol for transmitting a message via the physical network. The physical network can be, for example, a local area network (LAN), wide area network (WAN) or the Internet. A communication protocol specifies the format of the message that is sent over the network. A message format is standardized such that both a sending software application (sender) and a receiving software application (recipient) can interpret a message generated using a communication protocol&#39;s message format. 
     Before a message can be sent, the sender generates a message using a message format. A message typically contains a header portion and a data portion. The header includes information about the data portion such as the data&#39;s type and length. The header may also include information that identifies the source and/or destination of the message (e.g., network address) and sequencing information (i.e., the number of the message in a series of messages). The receiver may use the header information to determine whether the message is intended for the receiver. If so, the receiver can use the header to extract the data and, if the data is part of some larger piece of data, combine the data. 
     There are different types of communication protocols each of which has a unique message format. For example, asynchronous transfer mode (ATM), hypertext transfer protocol (HTTP), user datagram protocol (UDP), transmission control protocol (TCP) and real time transport protocol (RTP) each have its own message format. 
     In a network environment, it may be necessary for the sender and/or receiver to be able to understand more than one communication protocol&#39;s message format. For example, a receiver may receive messages from different senders that have different message formats. Further, a single message may be composed using multiple message format. For example, an RTP message embedded in a TCP message. The receiver must be able to understand both the TCP and RTP message formats to extract the data contained in the message. 
     Embodiments of the invention make the underlying transport mechanism transparent to the sender and/or receiver. Using embodiments of the invention, it is not necessary for a sender or receiver to interface with the transport mechanism. A message is always in a single format which eliminates the need for the sender or receiver to understand multiple message formats. FIG. 2 illustrates an overview of message flow and message processing according to an embodiment of the invention. 
     Network  210  is the physical network such as a LAN, WAN or the Internet. Network packet  206  is a message that is being transmitted via network  210 . If network packet  206  is a message that is received from network  210 , it is received by transport delivery module  204 . If network packet  206  comprises multiple protocols such as when one packet is embedded within another packet (e.g., an RTP packet is embedded within an ATM packet), transport delivery  204  extracts the inner packet embedded within the outer packet. 
     The message is forwarded from transport delivery  204  to socket  208 . Socket  208  represents a two-way data message transmitter that provides a buffer between message processor  202  and the underlying transport mechanism. Message processor  202  can be either a sender or receiver of messages, or both. To receive a message from network  210 , transport delivery  204  removes the transport header and forwards the RTP packet to socket  208  which forwards it to a message processor  202 . 
     If message processor  202  generates a message, it sends the message to socket  208  which forwards the message to transport delivery  204 . Transport delivery  204  creates network packet  206  from the message (e.g., embeds the message within a transport header) and sends it out on network  210 . 
     There can be multiple instances of transport delivery  204  each of which is capable of generating network packet  206  using a communication protocol&#39;s message format. A connection is formed between transport delivery  204  and an instance of socket  208 . A connection is also created between an instance of socket  208  and an instance of message processor  202 . 
     In one embodiment of the invention, socket  208  is an RTPSocket that interfaces with transport delivery  204  and message processor  202  to process RTP messages. In this embodiment, message processor  202  acts as an RTP session manager. During an RTP session real time data such as audio or video data is generated, for example. An RTP packet contains the real time data (i.e., a data portion of the RTP packet) and a header portion. 
     The header portion includes payload information that identifies the type of real time data contained in the RTP packet. The payload information can specify that the RTP packet contains video data, for example. Video data that constitutes a movie, for example, can be contained in multiple RTP packets. The header portion of the RTP packet also includes sequencing information that identifies the order in which each packets data portion is to be replayed. 
     FIG. 3 illustrates an overview of an RTP environment according to an embodiment of the invention. RTP session manager (RTPSM)  302  manages the operations involved in the creation and/or output of real time data. For example, RTPSM  302  manages the flow of the real time data to media player  320  for output to a display. Further, RTPSM  302  forwards RTP packets received from RTPSocket  308  to depacketizer  322  to extract the real time data and assemble the data into data frames. The data frames are forwarded to RTPSM  302  which forwards them to media handler  320 . 
     In one embodiment of the invention, before an instance of RTPSM  302  is created to manage each real time data session an RTPSocket  308  instance is created and its content type is set (e.g., RTP raw audio or RTP raw video). RTPSocket  308  is handed to media manager  324  which creates an instance of RTPSM  302  based on the content type specified in RTPSocket  308 . For example, if the content type indicates that the data contained in the RTP packet is video data, an instance of RTP session manager  324  that is capable of managing the video data is created. Media manager  324  provides proxy  326  to RTPSM  302  as a handle to RTPSocket  308 . 
     Network  210  transmits network packet  206  to transport delivery  204 . Network packet  206  includes an embedded RTP packet inside another packet (e.g., an ATM, HTTP, UDP or TCP packet). Transport delivery  204  receives the incoming network packet  206  and removes the transport header portion of network packet  206  to generate an RTP packet. 
     The incoming RTP packet is forwarded to RTPSocket  308  which forwards it to RTPSM  302 . RTPSM  302  sends the RTP packet received from network  210  via RTPSocket  308  to depacketizer  322  to extract the incoming real time data and assemble the data frame. The assembled data frame is sent back to RTPSM  302  which forwards it to media player  320  for display. 
     An outgoing data frame is processed in the reverse manner. A data frame is received by RTPSM  302  and forwarded to packetizer  332  for inclusion in one or more RTP packets. An outgoing RTP packet is sent back to RTPSM  302  and then forwarded by RTPSM  302  to RTPSocket  308 . RTPSocket  308  forwards the outgoing RTP packet to transport delivery  204  to generate network packet  206  (e.g., add a transport header such as a UDP, HTTP or ATM header) which is sent out over network  210 . 
     An RTP message can be either a control message that contains control information or a data message that contains data (e.g., video or audio data). RTPSocket  308  includes both a data channel for forwarding data messages and a control channel for forwarding control messages. FIG. 4 provides an illustration of a socket comprising a data channel and a control channel according to an embodiment of the invention. 
     Data channel  402  of RTPSocket  308  transmits RTP data packets between RTPSM  302  and network  210  via transport delivery  204 . RTPSocket  308 &#39;s control channel  404  transmits RTP control packets between RTPSM  302  and network  210 . Data channel  402  and control channel  404  include output streams  406  and  410  (respectively) and input streams  408  and  412  (respectively). 
     An RTP data packet received from network  210  is forwarded to RTPSM  302  via output stream  406  of RTPSocket  308 &#39;s data channel  402 . An RTP data packet sent by RTPSM  302  is transmitted to network  210  via input stream  408  of RTPSocket  308 &#39;s data channel  402 . An RTP control packet is transmitted to network  210  from RTPSM  302  via input stream  412  of RTPSocket  308 &#39;s control channel  404 . Output stream  410  of RTPSocket  308 &#39;s control channel  404  forwards an RTP control packet from network  210  to RTPSM  302 . 
     Object-Oriented Programming Languages 
     In one or more embodiments of the invention, RTPSocket  308  is implemented as a set of objects in an object-oriented programming language such as Java®. 
     Java is an object-oriented programming language. Object-oriented programming is a method of creating computer programs by combining certain fundamental building blocks, and creating relationships among and between the building blocks. The building blocks in object-oriented programming systems are called “objects.” An object is a programming unit that groups together a data structure (instance variables) and the operations (methods) that can use or affect that data. Thus, an object consists of data and one or more operations or procedures that can be performed on that data. The joining of data and operations into a unitary building block is called “encapsulation.” 
     Object-oriented programming languages are predominantly based on a “class” scheme. A class provides a definition for an object that typically includes both instance variables and methods. An object class is used to create a particular instance of an object. An instance of an object class includes the variables and methods defined for the class. Multiple instances of a the same class can created from an object class. Each instance that is created from the object class is said to be of the same type or class. 
     A hierarchy of classes can be defined such that an object class definition has one or more subclasses. A subclass inherits its parent&#39;s (and grandparent&#39;s etc.) definition. Each subclass in the hierarchy may add to or modify the behavior specified by its parent class. 
     In addition to the class hierarchy, some object-oriented programming languages (e.g., Java) provide the ability to group object classes and define a hierarchy among the groupings. For example, in Java, a package is a collection of classes. Packages can be nested to form a hierarchy. 
     Data and Control Channel Classes 
     A DataSource object class manages the transmission of information. In an embodiment of the invention, information is transmitted as streams. A DataSource is either a pull DataSource or a push DataSource depending on whether it manages a pull data stream or a push data stream. A pull data stream allows a data requester to initiate and control the flow of data transferred via the pull data stream. With a push data stream, the data sender initiates data transfer and controls the flow of data transferred via the push data stream. A push DataSource is typically used for real time data such as video-on-demand (VOD) data. 
     In an embodiment of the invention, data channel  402  and control channel  404  are push DataSources that manage push data streams. Data channel  402  and control channel  404  are bi-directional DataSources. That is, data channel  402  and control channel  404  have an output data stream and an input data stream. Data that flows in or out of data channel  402  or control channel  404  is a stream of bytes in the form of an RTP packet, for example. 
     The following table identifies methods of a push DataSource object class referred to as an RTPIODataSource object class, according to an embodiment of the invention. 
     
       
         
           
               
            
               
                   
               
               
                 Example RTPIODataSource Object Class Methods 
               
            
           
           
               
               
               
            
               
                   
                 Method 
                 Description 
               
               
                   
                   
               
               
                   
                 connect( ) 
                 Sets boolean to true. 
               
               
                   
                 disconnect( ) 
                 Sets boolean to false. 
               
               
                   
                 getContentType( ) 
                 Retrieves the type description for the 
               
               
                   
                   
                 media provided via the DataSource. 
               
               
                   
                 getInputStream( ) 
                 Identifies the DataSource&#39;s input stream. 
               
               
                   
                 getOutputStream( ) 
                 Identifies the DataSource&#39;s output stream. 
               
               
                   
                 getStreams( ) 
                 Get the collection of streams managed the 
               
               
                   
                   
                 DataSource. 
               
               
                   
                 isStarted( ) 
                 Specifies whether the DataSource has 
               
               
                   
                   
                 been started. 
               
               
                   
                 setContentType( ) 
                 Sets type description for media provided 
               
               
                   
                   
                 via the DataSource. 
               
               
                   
                 setInputStream( ) 
                 Sets an input stream for the DataSource. 
               
               
                   
                 setOutputStream( ) 
                 Sets an output stream for the DataSource. 
               
               
                   
                 start( ) 
                 Initiates data transfer. 
               
               
                   
                 stop( ) 
                 Stops data transfer. 
               
               
                   
                   
               
            
           
         
       
     
     Control channel  404  is an instance of the RTPIODataSource object. Data channel  402  is an instance of an RTPSocket object class which is a subclass of the RTPIODataSource object class. Data channel  402  extends the methods of the RTPIODataSource object and implements a GetControlChannel method which returns the identity of RTPSocket  308 &#39;s control channel (i.e., control channel  404 ). The following table identifies methods of the RTPSocket object class, according to an embodiment of the invention. 
     
       
         
           
               
            
               
                   
               
               
                 Example RTPSocket Object Class Methods 
               
            
           
           
               
               
               
            
               
                   
                 Method 
                 Description 
               
               
                   
                   
               
               
                   
                 connect( ) 
                 Sets boolean to true and calls the control 
               
               
                   
                   
                 channel&#39;s connect method. 
               
               
                   
                 disconnect( ) 
                 Sets boolean to false and calls the control 
               
               
                   
                   
                 channel&#39;s disconnect method. 
               
               
                   
                 getContentType( ) 
                 Retrieves the type description for the 
               
               
                   
                   
                 media provided via the DataSource. 
               
               
                   
                 getControlChannel( ) 
                 Returns the control channel associated 
               
               
                   
                   
                 with the data channel. 
               
               
                   
                 getInputStream( ) 
                 Returns the DataSource&#39;s input stream. 
               
               
                   
                 getOutputStream( ) 
                 Returns the DataSource&#39;s output stream. 
               
               
                   
                 getStreams( ) 
                 Get the collection of streams managed the 
               
               
                   
                   
                 DataSource. 
               
               
                   
                 isStarted( ) 
                 Specifies whether the DataSource has 
               
               
                   
                   
                 been started. 
               
               
                   
                 setContentType( ) 
                 Sets media type description and calls 
               
               
                   
                   
                 same control channel method. 
               
               
                   
                 setInputStream( ) 
                 Sets an input stream for the DataSource. 
               
               
                   
                 setOutputStream( ) 
                 Sets an output stream for the DataSource. 
               
               
                   
                 start( ) 
                 Initiates data transfer and calls same 
               
               
                   
                   
                 control channel method. 
               
               
                   
                 stop( ) 
                 Stops data transfer and calls same 
               
               
                   
                   
                 control channel method. 
               
               
                   
                   
               
            
           
         
       
     
     As part of its initialization, RTPSocket  308  creates an instance of RTPIODataSource for control channel  404 . The control channel RTPIODataSource instance can be accessed via methods of the data channel RTPSocket instance. Methods of the data channel RTPSocket instance call similar methods on the control channel RTPIODataSource instance. For example, if a connect method call is invoked on the data channel RTPSocket instance, the method calls the connect method on the control channel RTPIODataSource instance. Similarly, disconnecting, starting and stopping the RTPSocket will cause the same operation to be performed for the control channel RTPIODataSource instance. Thus, a single call to these methods on the RTPSocket instance results in an automatic call to the same-named method on the RTPIODataSource instance. In this embodiment, the setInputStream and setOutputStream methods are invoked separately for the RTPSocket (data channel) and RTPIODataSource (control channel) instances. 
     Data Streams 
     Output streams  406  and  410  and input streams  408  and  412  transmit data in streams (e.g., once it is begun, the flow of data is continuous). In one embodiment of the invention, data channel  402  and control channel  404  each contain an output stream that implements a PushSourceStream interface and an input stream that implements a PushDestStream interface. The following table identifies the methods of a pushSourceStream interface implemented by an output stream used in one embodiment. 
     
       
         
           
               
            
               
                   
               
               
                 Embodiment of a pushSourceStream Interface 
               
            
           
           
               
               
            
               
                 Method 
                 Description 
               
               
                   
               
               
                 endOfStream( ) 
                 Specifies whether the end of the stream 
               
               
                   
                 has been reached; It returns true, if there 
               
               
                   
                 is no more data. 
               
               
                 getContentDescriptor( ) 
                 Retrieves the type description for the 
               
               
                   
                 media sent via this stream. 
               
               
                 getContentLength( ) 
                 Retrieves the size in bytes of the content 
               
               
                   
                 on this stream, LENGTH_UNKNOWN is 
               
               
                   
                 returned if the length is not known. 
               
               
                 getMinimumTransferSize( ) 
                 Returns the size of the buffer needed for 
               
               
                   
                 the streaming transfer. 
               
               
                 read( ) 
                 Reads a specified number of bytes into a 
               
               
                   
                 specified buffer at a specified location in 
               
               
                   
                 the buffer. Returns the number of bytes 
               
               
                   
                 read or −1 when the end of the media is 
               
               
                   
                 reached. 
               
               
                 setTransferHandler( ) 
                 Specifies the destination or data handler 
               
               
                   
                 to which the data is to be transferred. 
               
               
                   
               
            
           
         
       
     
     The setTransferHandler method of output stream  406  is called to register RTPSM  302  as the destination of the data being streamed by output stream  406 , for example. The getMinimumTransferSize method can be called to determine the minimum size of the buffer needed to store the data stream. The getContentLength can be called to determine the size of the data that is to be streamed. To send the data, the read method is called and a buffer is specified from which the data can be read. An offset at which the data is stored in the buffer and length of data to be read is also specified. A “−1” value is returned when the end of the data is reached. 
     Input streams  408  and  412  implement a pushDestinationStream interface. The pushDestinationStream interface implements a write method that specifies the buffer from which input streams  408  and  412  copy the data (e.g., the data contained in the buffer is copied to a network buffer). The offset and length information specifies the location at which and the amount of data to be written. 
     Processing Flow Example 
     The data channel  402  and control channel  404  represent a two way data source. That is, data channel  402  and control channel  404  act as a data source and a data sink for RTPSM  302 . Both data channel  402  and control channel  404  contain an output stream of type PushSourceStream (e.g., output streams  406  and  410 , respectively) and an input stream of type PushDestStream (e.g., input streams  408  and  412 ). An output stream acts as a source of data from the underlying transport to RTPSM  302 . An input stream acts as a receiver of data from RTPSM  302  to the underlying transport. It is not necessary for RTPSM  302  to have knowledge of any of the aspects of the underlying transport. 
     RTPSocket  308 &#39;s data channel  402  and control channel  404  are created to act as an interface for RTPSM  302  to the underlying transport. In one embodiment of the invention, data channel  402  is created as an instance of RTPSocket  308  which creates an instance of RTPIODataSource for control channel  404 . Input and output streams of data channel  402  and control channel  404  are specified and a handle to the RTPSocket instance is handed to RTPSM  302 . 
     To send a message to RTPSM  302  a client streams the message (e.g., control or data message) to RTPSocket  308 . RTPSocket  308  forwards the message to RTPSM  302 . Similarly, RTPSM  302  streams a message (e.g., data or control) to RTPSocket  308  which forwards the message to the client. 
     FIG. 5 provides a process flow for sending/receiving messages according to an embodiment of the invention. At step  502  the RTPSocket and RTPIODataSource instances are created. In this embodiment, the RTPSocket constructor invokes the RTPIODataSource constructor as part of the creation of the RTPSocket instance. At step  504 , the input and output streams are set for the RTPSocket and RTPIODataSource instances. At step  506 , a handle to the RTPSocket instance is provided to RTPSM  302 . At step  510 , the start method is invoked for the RTPSocket and RTPIODataSource instances. In this embodiment, the start method of the RTPSocket instance invokes the start method of the RTPIODataSource instance. 
     Steps  520 - 522  and  524 - 526  are used to transmit a message from and to RTPSM  302 . If at step  512 , an input message (i.e., a message being input to network  210  from RTPSM  302 ) is being transmitted, steps  524 - 526  are performed. If it is an output message (i.e., a message that is output from network  210  to RTPSM  302 ), steps  520 - 522  are performed. If a stop operation is determined at step  514 , a stop method of the RTPSocket instance is invoked which invokes a stop method of the RTPIODataSource instance. 
     To transmit a message on the network, RTPSM  302  writes the message to a data buffer at step  524 . RTPSM  302  calls a write method of the output stream (e.g., output streams  406  or  410 ) specifying the data buffer and the location of the data within the data buffer at step  526 . Processing continues at step  512  to process any subsequent messages. 
     To receive a message from the network, transport delivery  204  writes the message to a data buffer at step  520 . Transport deliver  204  calls a read method of the input stream (e.g., input steam  408  or  412 ) specifying the data buffer and the location of the data within the data buffer at step  522 . Processing continues at step  512  to process any subsequent messages. 
     Appendix A provides an example of an RTP over UDP player which will receive RTP UDP packets and stream them to an RTPSM using one or more embodiments of the invention. 
     Thus, a method and apparatus for network transport independence has been provided in conjunction with one or more specific embodiments. The invention is defined by the claims and their full scope of equivalents. 
     
       
         
           
               
             
               
                   
               
               
                 AFFENDIX A 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 import javax.media.rtp.*; 
               
               
                 import javax.media.*; 
               
               
                 import javax.media.protocol.*; 
               
               
                 import java.io.*; 
               
               
                 import java.net.*; 
               
               
                 import cpm.sun.media.ui.*; 
               
               
                 /** 
               
               
                 * A RTP over UDP player which will receive RTP UDP packets and stream 
               
               
                 * them to the JMF RTP Player or (RTPSM) which is not aware of the 
               
               
                 * underlying network/transport protocol 
               
               
                 */ 
               
               
                 public class GenericRTPPlayer{ 
               
            
           
           
               
               
            
               
                   
                 / / our main rtpsocket abstraction to which we will create and send 
               
               
                   
                 / / to the Manager for appropriate handler creation 
               
               
                   
                 RTPSocket rtpsocket = null; 
               
               
                   
                 / / the control RTPIODataSource of the RTPSocket above 
               
               
                   
                 RTPIODataSource rtcpsource = null; 
               
               
                   
                 / / The GUI to handle our player 
               
               
                   
                 PlayerWindow playerWindow; 
               
               
                   
                 / / The handler created for our RTP session, as returned by the Manager 
               
               
                   
                 Player player; 
               
               
                   
                 / / maximum size of buffer for UDP receive from the sockets 
               
               
                   
                 private int maxsize = 2000; 
               
               
                   
                 public static void main(String[] args){ 
               
               
                   
                 new GenericRTPPlayer(); 
               
               
                   
                 } 
               
               
                   
                 public GenericRTPPlayer(){ 
               
            
           
           
               
               
            
               
                   
                 / / create the RTPSocket 
               
               
                   
                 rtpsocket = new RTPSocket();. 
               
               
                   
                 / / set its content type : rtpraw/video for a video session and 
               
               
                   
                 / / rtpraw/audio for an audio session 
               
               
                   
                 rtpsocket.setContentType(″rtpraw/video″); 
               
               
                   
                 / / set the RTP Session address and port of the RTP data 
               
               
                   
                 UDPHandler rtp = new UDPHandler(″224.144.251.104″, 49152); 
               
               
                   
                 / / set the above UDP Handler to be the sourcestream of the rtpsocket 
               
               
                   
                 rtpsocket.setOutputStream(rtp); 
               
               
                   
                 / / set the RTP Session address and port of the RTCP data 
               
               
                   
                 UDPHandler rtcp = new UDPHandler(″224.144.251.104″, 49153); 
               
               
                   
                 / / get a handle over the RICP Datasource so that we can set 
               
               
                   
                 / / the sourcestream and deststream of this source to the rtcp 
               
               
                   
                 / / udp handler we created above. 
               
               
                   
                 rtcpsource = rtpsocket.getControlChannel(); 
               
               
                   
                 rtcpsource.setOutputStream(rtcp); 
               
               
                   
                 rtcpsource.setInputStream(rtcp); 
               
               
                   
                 / / start &amp; connect the RTP socket data source before creating 
               
               
                   
                 // the player 
               
               
                   
                 try{ 
               
            
           
           
               
               
            
               
                   
                 rtpsocket.connect(); 
               
               
                   
                 rtpsocket.start(); 
               
               
                   
                 player = Manager.createPlayer(rtpsocket); 
               
            
           
           
               
               
            
               
                   
                 }catch (NoPlayerException e){ 
               
            
           
           
               
               
            
               
                   
                 System.out.printIn(e.getMessage()); 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 catch (IOException e){ 
               
            
           
           
               
               
            
               
                   
                 System.out.printIn(e.getMessage()); 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 / / send this player to out playerwindow 
               
               
                   
                 playerWindow = new PlayerWindow(player); 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 / / method used by inner class UDPHandler. to open a datagram or 
               
               
                   
                 / / multicast socket as the case maybe 
               
               
                   
                 private DatagramSocket InitSocket(String address, int port){ 
               
            
           
           
               
               
            
               
                   
                 InetAddress addr = null; 
               
               
                   
                 DatagramSocket sock = null; 
               
               
                   
                 try{ 
               
            
           
           
               
               
            
               
                   
                 addr = InetAddress.getByName(address); 
               
               
                   
                 if (addr.isMulticastAddress()){ 
               
            
           
           
               
               
            
               
                   
                 MulticastSocket msock = new MulticastSocket(port); 
               
               
                   
                 msock.joinGroup(addr); 
               
               
                   
                 sock = (DatagramSocket)msock; 
               
            
           
           
               
               
            
               
                   
                 }else{ 
               
               
                   
                 sock = new 
               
            
           
           
               
               
            
               
                   
                 DatagramSocket(port,addr);. 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 return sock; 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 catch (SocketException e){ 
               
            
           
           
               
               
            
               
                   
                 return null; 
               
            
           
           
               
               
            
               
                   
                 } 
               
            
           
           
               
               
            
               
                   
                 catch (UnknownHostException e){ 
               
            
           
           
               
               
            
               
                   
                 return null; 
               
            
           
           
               
               
            
               
                   
                 } 
               
            
           
           
               
               
            
               
                   
                 catch (IOException e){ 
               
            
           
           
               
               
            
               
                   
                 return null; 
               
            
           
           
               
               
            
               
                   
                 } 
               
            
           
           
               
               
            
               
                   
                 }/ / end of InitSocket 
               
               
                   
                 / / INNER CLASS UDPHandler which will receice UDP RTP Packets and 
               
               
                   
                 / / stream them to the handler of the sources stream. IN case of 
               
               
                   
                 / / RTCP, it will also accept RTCP packets and send them on the 
               
               
                   
                 / / underlying network. 
               
               
                   
                 public class UDPHandler extends Thread 
               
               
                   
                 implements PushSourceStream; PushDestStream{ 
               
            
           
           
               
               
            
               
                   
                 Thread thread = null; 
               
               
                   
                 DatagramSocket sock = null; 
               
               
                   
                 DatagramPacket dp = null; 
               
            
           
           
               
               
            
               
                   
                 SourceTransferHandler outputhandler = null; 
               
            
           
           
               
               
            
               
                   
                 String address = null; 
               
               
                   
                 int port; 
               
               
                   
                 public UDPHandler(String address, int port){ 
               
            
           
           
               
               
            
               
                   
                 this.address = address; 
               
               
                   
                 this.port = port; 
               
               
                   
                 thread = new Thread(this); 
               
               
                   
                 thread.setDaemon(true); 
               
               
                   
                 thread.start(); 
               
               
                   
                 sock = InitSocket(address,port); 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 public void run(){ 
               
            
           
           
               
               
            
               
                   
                 int len; 
               
               
                   
                 while(true){ 
               
            
           
           
               
               
            
               
                   
                 try{ 
               
            
           
           
               
               
            
               
                   
                 do{ 
               
            
           
           
               
               
            
               
                   
                 dp = new DatagramPacket(new byte[maxsize],maxsize); 
               
               
                   
                 sock.receive(dp); 
               
               
                   
                 len = dp.getLength(); 
               
               
                   
                 if (len &gt;(maxsize &gt;&gt; 1)) 
               
            
           
           
               
               
            
               
                   
                 maxsize = len &lt;&lt; 1; 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 while (len &gt;= dp.getData().length); 
               
            
           
           
               
               
            
               
                   
                 }catch (IOException e){ 
               
               
                   
                 } 
               
               
                   
                 if (outputhandler != null) 
               
            
           
           
               
               
            
               
                   
                 outputhandler.transferData(this); 
               
            
           
           
               
               
            
               
                   
                 } 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 / / methods of PushSourceStream 
               
               
                   
                 public Object[] getcontrols() { 
               
            
           
           
               
               
            
               
                   
                 return new Object[0]; 
               
            
           
           
               
               
            
               
                   
                 } 
               
            
           
           
               
               
            
               
                   
                 public Object getControl(String controlName){ 
               
               
                   
                 return null; 
               
            
           
           
               
               
            
               
                   
                 } 
               
            
           
           
               
               
            
               
                   
                 public ContentDescriptor getContentDescriptor(){ 
               
               
                   
                 return null; 
               
            
           
           
               
               
            
               
                   
                 } 
               
            
           
           
               
               
            
               
                   
                 public long getContentLength(){ 
               
               
                   
                 return SourceStream.LENGTH_UNKNOWN; 
               
            
           
           
               
               
            
               
                   
                 } 
               
            
           
           
               
               
            
               
                   
                 public boolean endOfStream(){ 
               
               
                   
                 return false; 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 public int read(byte buffer[], 
               
            
           
           
               
               
            
               
                   
                 int offset, 
               
               
                   
                 int length){ 
               
            
           
           
               
               
            
               
                   
                 System.arraycopy(dp.getData(), 
               
            
           
           
               
               
            
               
                   
                 0, 
               
               
                   
                 buffer, 
               
               
                   
                 offset, 
               
               
                   
                 dp.getLength()); 
               
            
           
           
               
               
            
               
                   
                 return dp.getData().length; 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 public int getMinimumTransferSize(){ 
               
            
           
           
               
               
            
               
                   
                 return dp.getLength(); 
               
            
           
           
               
               
            
               
                   
                 } 
               
            
           
           
               
               
            
               
                   
                 public void setTransferHandler(SourceTransferHandler 
               
            
           
           
               
               
            
               
                   
                 transferHandler){ 
               
            
           
           
               
               
            
               
                   
                 this.outputhandler = transferHandler; 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 / / methods of PushDestStream 
               
               
                   
                 public int write(byte[] buffer, 
               
            
           
           
               
               
            
               
                   
                 int offset, 
               
               
                   
                 int length){ 
               
            
           
           
               
               
            
               
                   
                 InetAddress addr = null; 
               
               
                   
                 try{ 
               
            
           
           
               
               
            
               
                   
                 addr = InetAddress.getByName(address); 
               
               
                   
                 }catch (UnknownHostExcephon e){ 
               
            
           
           
               
               
            
               
                   
                 } 
               
               
                   
                 DatagramPacket dp = new DatagramPacket(buffer,length,addr,port); 
               
               
                   
                 try{ 
               
            
           
           
               
               
            
               
                   
                 sock.send(dp); 
               
            
           
           
               
               
            
               
                   
                 }catch (IOException e){} 
               
               
                   
                 return dp.getLength(); 
               
            
           
           
               
               
            
               
                   
                 } 
               
            
           
           
               
               
            
               
                   
                 } 
               
            
           
           
               
            
               
                 }// end of Test