Abstract:
A packet data system such as a TCP/IP network transmits packets containing a variety of data types along links in the network. Packets are transmitted in a stream between nodes interconnected by the links connections which conform to a transport layer protocol such as TCP, UDP, and RSTP, and includes wireless links, which transmit packets using a radio frequency (RF) medium. Typical protocols, however, are usually developed to optimize throughput and minimize data error and loss over wired links, and do not lend themselves well to a wireless link. By examining the data in a packet, performance characteristics such as a port number are determined. The performance characteristics indicate the application type, and therefore, the data type, of the packets carried on the connection. Since certain data types, such as streaming audio and video, are more loss tolerant, determination of the data type is used to compute link control parameters for the wireless link which that are optimal to the type of data being transmitted over the link.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/193,587, filed on Jul. 29, 2005, which issued as U.S. Pat. No. 7,944,845 on May 17, 2011, which is a continuation of U.S. patent application Ser. No. 09/777,555, filed on Feb. 5, 2001, which issued as a U.S. Pat. No. 6,937,562 on Aug. 30, 2005, the contents of which are hereby incorporated by reference herein. 
    
    
     BACKGROUND 
     In a typical data communication system, packets containing a variety of data types are transmitted between different nodes of a network, typically in a client-server manner. The packets are transmitted in a stream from a source node to a destination node. The nodes are interconnected via physical connections that conform to a link layer protocol such as HDLC, ATM, and frame relay, for example. These connections may include wireless links, which transmit packets using a radio frequency (RF) medium. 
     The transport layer, however, is typically indifferent to the link layer protocols and whether the link layer is a wireless or wired link. However, wired and wireless links usually exhibit different performance characteristics. For example, wireless links typically exhibit higher error rates, longer latency times, and limited throughput depending on the number of users supported. Many transport layer protocols, however, were developed according to wired link performance expectations, and do not lend themselves to efficient implementation over wireless links. Therefore, connections that include a wireless link may suffer from performance degradation since the transport layer protocols, such as TCP, UDP, and RSTP, are not sensitive to specific performance and behavior characteristics of wireless links. 
     The transport layer protocols are implemented to prevent inaccuracies in the data such as packet loss and transmission errors in the packet. However, certain applications employ data types that are more loss-tolerant and do not need to assure absolute accuracy in the received data stream. For example, data types such as streaming audio and video can tolerate lost packets and bit errors without substantially compromising the output perceived by a user. On the other hand, data types such as an executable file would likely result in unpredictable results if even one bit is inaccurately received. 
     It would be beneficial, therefore, to provide a system and method to determine the application and performance metrics corresponding to a connection, and modify related link control parameters of the wireless link according to a corresponding flow model. The link control parameters may adjust the physical layer characteristics, such as bandwidth, coding levels, and the like, to tolerate packet loss when appropriate. This increases the overall perceived throughput over the wireless link. 
     SUMMARY 
     A system and method for application specific control of wireless link control parameters determines link performance characteristics of a connection, and modifies the link control parameters of the connection according to a corresponding flow model to tolerate packet loss and error when appropriate to increase the overall throughput over the wireless link. Link performance characteristics indicative of a flow of a stream of packets are determined. The link performance characteristics are analyzed to determine a flow model. A transfer model is computed and mapped based on the flow model, and the link control parameters corresponding to the transfer model are then applied to the connection. 
     A packet in an incoming stream of packets received over a connection is examined to determine a corresponding set of link performance characteristics. A particular packet in the stream is usually indicative of other packets in the stream. Accordingly, the stream of packets will tend to conform to the link performance characteristics exhibited by any one of the packets in the stream. Link performance characteristics such as a protocol type, port number, payload type, control bits, and others may be examined. The link performance characteristics are analyzed by a link controller to determine a flow model, such as by matching the link performance characteristics to a flow model table having entries of link performance metrics. In TCP/IP packet systems, for example, a packet has a link performance characteristic called a port number. Certain predetermined port numbers correspond to particular applications. 
     The entries in the flow model table are mapped to a transfer model table. Alternatively, other computations could be performed to compute a transfer model based on the flow model. The transfer model table has entries containing link control parameters. The link control parameters may include, for example, modulation type, ARQ disable flag, coding rate, delay, jitter, minimum suggested bandwidth, average suggested bandwidth, maximum suggested bandwidth, and others. The link control parameters included in each transfer model are selected to provide optimal wireless transmission for the flow model selected. The link controller applies the link control parameters corresponding to the selected transfer model to the connection. In this manner, a wireless link can be optimized by modifying link control parameters according to the type of data carried in the packets based on a loss tolerance corresponding to the data type. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a wireless communication system suitable for performing application specific traffic optimization; 
         FIG. 2  is a block diagram of the traffic optimization system; 
         FIG. 3  shows the flow model table; 
         FIG. 4  shows the transfer model table; 
         FIGS. 5   a - 5   c  show a flowchart of application specific traffic optimization; 
         FIG. 6  shows an example of application specific traffic optimization; and 
         FIG. 7  shows a diagram of a particular architecture in a base station processor adapted for application specific traffic optimization as described herein. 
     
    
    
     DETAILED DESCRIPTION 
     A description of preferred embodiments of the invention follows. 
     Referring to  FIG. 1 , in a computer network, such as a network using the TCP/IP protocol, a logical connection is maintained between a local node or user  12  and a remote node  30 . The user node  12  may, for example be a personal computer (PC) and the remote node  30  may be a file server such as a web server. Data is carried between the user  12  and the remote node  30  by transmitting data in formatted packets, which flow in a stream over the connection. The connection includes both wired links  20 ,  24  and a wireless link  26 . The wireless link  26  is maintained by a base station processor  16  and a subscriber access unit  14 , which is in turn connected to the user  12 . The base station processor  16  connects to a public access network such as the Internet  28  via an internetworking gateway  18  over the wired link  24 . A user  12  can therefore maintain wireless connectivity to a remote node  30  via the wireless link  26  provided by the base station processor  16  and the subscriber access unit  14 . The connection between the remote node  30  and the user  12  conforms to a protocol, such as TCP/IP. As described above, TCP/IP was developed for wired networks, and, accordingly, does not lend itself directly to efficient transmissions over the wireless link  26 . 
     Referring to  FIG. 2 , a block diagram of the present invention is shown. The base station processor  16  maintains a table of link performance metrics  32  and link control metrics  40 . A link analyzer  36  includes a link controller  38 , a flow model table  34 , and a transfer model table  42 . The set of link performance metrics  32  is defined to enumerate link performance characteristics  44  that can be monitored. 
     The flow model table  34  is defined to specify link performance metrics  32  included in a particular flow model stored in the flow model table  34 . The link controller  38  is operable to analyze link performance characteristics  44  in the packets sent from the remote node  30  over the wired link  24 . The link performance characteristics  44  are analyzed by comparison with flow model entries in the flow model table  34 . The transfer model table  42  is defined from the link control metrics  40 , and stores transfer model entries including one or more link control parameters  46  corresponding to a particular flow model entry in the flow model table  34 . 
     The analysis of the link performance characteristics  44 , described further below, determines a flow model  34  indicative of the stream of packets being transmitted over the link. The link controller  38  computes a corresponding transfer model entry by mapping into the transfer model table  42 . The corresponding transfer model entry in the transfer model table  42  defines one or more link control parameters  46  of the transfer model entry. The link controller  38  then applies the link control parameters  46  to the wireless link  26  via the base station processor  16 . 
     Referring to  FIG. 3 , the flow model table  34  is shown having flow model entries  34   a ,  34   b , and  34   c . As described above, each flow model entry  34   n  defines link performance metrics  32  corresponding to the data type of a particular stream of packets. In one embodiment, a packet based network associates ports with applications. By examining the port associated with a transmitted packet, the application type can be determined. For example, in a TCP/IP network, certain well known port numbers  48  are predetermined and identified by RFC 1700 promulgated by the Internet Engineering Task Force (IETF). The flow model entry  34   n  corresponding to the well known port number  48  determines the application type  50 . The application type  50  is indicative of the loss tolerance of the stream. For example, flow model entry  34   c  indicates a streaming audio data type. Streaming audio is generally thought to be more loss-tolerant because lost or erroneous packets would merely be heard as a slight pop or glitch in the output audio signal heard by the user. On the other hand, flow model entry  34   b  corresponds to a file transfer, and accordingly, is not tolerant to lost or erroneous packets. The use of the port number as a link performance characteristic as defined herein is exemplary. Other performance characteristics, such as those defined in the flow model table  34  and others, could be employed in computing the transfer model. 
     The flow model is employed to compute a transfer model directed towards optimizing the packet traffic flow on a particular connection. Referring to  FIGS. 2 ,  3 , and  4 , each flow model entry  34   n  includes a transfer model index  52 . A transfer model entry  54   n  is computed by mapping the transfer model index  52  into the transfer model table  42  to determine the corresponding transfer model entry  54   n . The corresponding transfer model entry  54   n  includes link control metrics  40  operable to modify the connection. The link control parameters  46  of the corresponding transfer model entry are applied to the connection. In alternative embodiments, additional computations could be performed to compute the link control parameters. 
       FIGS. 5   a - 5   b  illustrate a flowchart of a particular embodiment of message flow, as defined herein, which invokes an IP port number as a link performance characteristic. An IP packet is received from the wired network, as depicted at step  100 . The protocol field is read from the IP header in the packet, as shown at step  102 . It should be noted, however, that other discriminating characteristics of the packets may be examined to construct message flows. In a particular embodiment, the protocol field is examined to determine if the protocol is TCP or UDP, as disclosed at step  104 . If the protocol is not TCP or UDP, then an alternate protocol is handled, as depicted at step  106 , and control continues as described below at step  112 . 
     If the protocol is TCP or UDP, the port numbers are then read from the header, as shown at step  108 . A typical header has both a source and a destination port. Either port may be indicative of an application and hence, a data type. A check is made to determine if there is at least one well-known port, as disclosed at step  110 . If there is not a well-known port, then the default flow model is allowed to persist, as shown at step  112 . Referring back to  FIG. 3 , if there is a well-known port, the flow model index  55  corresponding to the port is determined, as disclosed at step  114 , and the corresponding flow model entry  34   n  is determined, as disclosed at step  116 . The check may include parsing the flow model table to find a matching well-known port number  48 , and may include other operations directed towards determining a particular flow model entry  34   n.    
     Referring to  FIGS. 3 ,  4 , and  5   b , the selected flow model  34   n  is read to determine the corresponding transfer model index  52 , as depicted at step  118 . The transfer model index  52  is invoked to determine a transfer model entry  54   n  in the flow model table  42 , and the corresponding link control parameters  46  are retrieved, as shown at step  120 . Other computations may also be employed to determine link control parameters, in addition to the transfer model table  42  lookup described above. Packet transmission employing the link control parameters  46  is requested, as disclosed at step  122 , by applying the link control parameters  46  to the connection. 
     Referring to  FIG. 5   c , a check is made to determine if a wireless traffic channel is available, as shown at step  124 . If a wireless traffic channel is not available, a wait is performed until a traffic channel becomes available, as depicted at step  126 . When a traffic channel is available, a check is performed to see if the link control parameters can be applied at this time for this packet as shown in step  128 . If the check is successful, the transmitter of the wireless signal is optimized according to the link control parameters established for the connection, as depicted at step  130 . The packet is then sent on the packet traffic channel, as depicted at step  132 , and a wait is performed for the next packet to be received as depicted at step  134 . Control then reverts to step  100  above as new IP packets are received from the network. 
     Referring to  FIGS. 3 ,  4 , and  6 , an example of optimal packet flow parameters as defined by the present claims is shown. A packet flow including packet  60  has a port number value of 7070. Accordingly, the flow model index  55  is determined to be F3 stored in flow model table  34  entry  34   c . The transfer model index  52  corresponding to entry  34   c  is T30. Indexing into the transfer model table  42  with transfer model index T30 yields transfer model entry  54   c . The corresponding link control parameters for transfer model entry  54   c  include ARQ (automatic repeat request) disable  72  value of Y (yes), minimum suggested bandwidth  74  of 28 k, average suggested bandwidth  76  of 32 k, and maximum suggested bandwidth  78  of 40 k. Since the application ID  50  is realaudio, we know that this is a streaming audio connection and therefore is loss tolerant. Accordingly, the ARQ disable may be set to Y because we need not retransmit a lost packet for the reasons described above. Similarly, the suggested bandwidth fields  74 ,  76 , and  78  are set to the values corresponding to that application type. 
     On the other hand, the message packet  62  is analyzed to have a port number of  69 . Determining the flow model index  55  results in a value of F2. Indexing into the flow model table  34  using index  55  of F2 yields flow model entry  34   b , corresponding to transfer model index T20. Computing the corresponding transfer model entry  54   n  in the transfer model table  42  indicates that entry  54   b  corresponds to T20. The corresponding link control parameters  46  for entry  54   b  include ARQ disable value of N (no), minimum suggested bandwidth of 48 k, average suggested bandwidth of 64 k, and maximum suggested bandwidth of 80 k. Since flow model entry  34   b  indicates a data type of trivial file transfer protocol (tftp), error-free transmission is suggested. Accordingly, the ARQ flag should not be disabled, and the suggested bandwidths are relatively larger, as shown in entry  54   b , as is determined to be most efficient for the corresponding application type. 
     As indicated above, the foregoing example illustrates the use of a port number as a link performance characteristic and the ARQ flag and suggested bandwidth ranges as a link control parameter. In alternate embodiments other variables may also be employed without departing from the invention as claimed below. In particular, the application specific data derivable from a data packet is employed in computing a loss tolerance of the type of data on the connection, and modifying the connection to specific, optimal values for the particular data type. For example, the delay  80  link control parameter is used to specify a maximum delay which may occur between transmissions to avoid starving the user with real-time information, such as audio and video. Similarly, jitter  82  refers to the maximum variance between transmissions which should be permitted which still allows the user to maintain the incoming stream. 
       FIG. 7  shows a particular embodiment of base station processor  16  architecture for implementing application specific traffic optimization. This architecture is operable for wireless channel allocation and message transmission as described in co-pending U.S. patent application entitled “Dynamic Bandwidth Allocation for Multiple Access Communication Using Session Queues,” which is a continuation-in-part of a prior U.S. patent application Ser. No. 09/088,527, filed Jun. 1, 1998, entitled “Dynamic Bandwidth Allocation for Multiple Access Communications Using Buffer Urgency Factor.” The entire teachings of the above applications are incorporated herein by reference. 
     Referring to  FIG. 7 , at the base station  16 , incoming traffic is separated into individual traffic flows destined for separate subscriber access units  14  generally ( FIG. 1 ). The traffic flows may be separated by various means, such as by examining a destination address field in the TCP/IP header. The individual traffic flows are delivered first to transport modules  401 - 1 ,  401 - 2 , . . .  401 - n  with a transport module  401  corresponding to each of the intended subscriber units  14 . A given transport module  401  is the first step in a chain of processing steps that is performed on the data intended for each subscriber unit  14 . This processing chain includes not only the functionality implemented by the transport module  401  but also a number of session queues  410 , a session multiplexer  420 , and transmission buffers  440 . The outputs of the various transmission buffers  440 - 1 ,  440 - 2 , . . .  440 - n  are then assembled by a transmit processor  450  that formats the data for transmission over the forward radio links  110 . 
     Returning attention now to the top of the  FIG. 7  again, each transport module  401  has the responsibility of either monitoring the traffic flow in such a way that it stores data belonging to different transport layer sessions in specific ones of the session queues  410  associated with that transport module  401 . For example, transport module  401 - 1  assigned to handle data intended to be routed to subscriber unit  101 - 1  has associated with it a number, m, of session queues  410 - 1 - 1 ,  410 - 1 - 2 , . . . ,  410 - 1 - m . In the preferred embodiment, a given session may be characterized by a particular transport protocol in use. For example, in a session oriented transport protocol, a session queue  410  is assigned to each session. Such session transport oriented protocols include, for example, Transmission Control Protocol. In sessionless transport protocols, a session queue  410  is preferably assigned to each stream. Such sessionless protocols may for example be the Universal Datagram Protocol (UDP). Thus traffic destined for a particular subscriber unit  14  is not simply routed to the subscriber unit  14 . First, traffic of different types from the perspective of the transport layer are first routed to individual session queues  410 - 1 - 1 ,  410 - 1 - 2 , . . . ,  410 - 1 - m , associated with that particular connection. In accordance with the system as defined above, traffic indicating a new connection is analyzed to determine link performance characteristics  44  for the messages received on that connection. The link performance characteristics  44  are analyzed to determine a flow model index  55 , as described above with respect to  FIG. 3 . The flow model is then used to compute a transfer model entry  54  as described above with respect to  FIG. 4 . The transport module  401  invokes the link performance characteristics  46  corresponding to the computed transfer model entry  54 , and applies them to the session queue  410 - n - m  for this connection. 
     Another key function performed by the transport module  401 - 1  is to assign priorities to the individual queues  410 - 1  associated with it. It will later be understood that depending upon the bandwidth available to a particular subscriber unit  14 , traffic of higher priority will be delivered to the transmission buffer  440 - 1  before those of lower priority, as determined by the transfer model and the associated link control parameters  46  in the transfer model table  42 . This may include traffic that is not session oriented, for example, real time traffic or streaming protocols that may be carrying voice and/or video information. More particularly, the transport module  401 - 1  reports the priorities of each of the individual session queues  410 - 1  to its associated session multiplexer  420 . Traffic of higher priority will be selected by the session multiplexer  420  for loading into the transmit buffer  440 - 1  for loading traffic of lower priority, in general as determined by the link control parameters  46  from the entries  54  in the transfer model table  42 . 
     Those skilled in the art should readily appreciate that the programs defining the operations and methods defined herein are deliverable to a subscriber access unit and to a base station processor in many forms, including but not limited to: (a) information permanently stored on non-writeable storage media such as ROM devices; (b) information alterably stored on writeable storage media such as floppy disks, magnetic tapes, CDs, RAM devices, and other magnetic and optical media; or (c) information conveyed to a computer through communication media, for example, using baseband signaling or broadband signaling techniques, as in an electronic network such as the Internet or telephone modem lines. The operations and methods may be implemented in a software executable by a processor or as a set of instructions embedded in a carrier wave. Alternatively, the operations and methods may be embodied in whole or in part using hardware components, such as Application Specific Integrated Circuits (ASICs), state machines, controllers or other hardware components or devices, or a combination of hardware, software, and firmware components. 
     While the system and method for application specific traffic optimization have been particularly shown and described with references to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims. Accordingly, the present invention is not intended to be limited except by the following claims.