Patent Publication Number: US-7908392-B2

Title: Wireless transportation protocol

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention concerns a data transportation protocol for a wireless network. 
     2. Description of Related Art 
     Mobile devices with large storage capacity such as mobile computing devices, image capturing devices, and portable media player devices are becoming more prevalent. It is expected that wireless components such as IEEE 802.11a/b/g or Ultra Wideband (UWB) will be integrated with these mobile devices to provide high bandwidth data access and data sharing abilities. However, existing storage transportation protocols such as IP-based storage protocols (iSCSI, FCIP, iFCP) are not well suited for transporting storage commands and data over a wireless network. These protocols tend to be heavy protocols and are not optimized to appropriately deal with the high packet errors and high packet loss environment of a wireless network. In a wireless network, severe performance degradation of these protocols is encountered. 
     Typically, a mobile storage device provides a data sharing service that is file based or block based. File based data sharing services include NFS, FTP, CIFS. File based data sharing services suffer from excessive file operation and TCP/IP overhead on the server side. 
     Block based data sharing services include Internet Small Computer Systems Interface (iSCSI). Block based data sharing services alleviate the burden on the server by moving the file operation to be performed by the client. However, iSCSI is ill suited for wireless networks as it suffers performance degradation due to high bit error and packet loss rates. As most wireless networks are single hop, using the TCP/IP protocol stack is inefficient as there is significant overhead. One solution has been to offload TCP/IP processing to a TCP/IP offload engine (TOE) on a chip or Host Bus Adapter (HBA) In addition to TCP/IP offloading, the encoding and decoding of iSCSI protocol data units (PDUs) can be offloaded to a dedicated iSCSI offload engine to further enhance the performance of the host system. This adds to the total cost of ownership and requires purchase of specialized hardware devices. 
     Accordingly, there is a desire for an improved transportation protocol for wireless applications. In particular, there is a desire for a transportation protocol highly suitable for short range wireless applications. 
     BRIEF SUMMARY OF THE INVENTION 
     In a first preferred aspect, there is provided a method for transferring data within a wireless network, the method comprising: translating between block I/O storage protocol commands and network packets, in a single level; and transporting the network packets between a client and server within the network; wherein operations are performed directly on a storage device driver and a network device driver of the client and server. 
     In a second aspect, there is provided a data transportation protocol for transferring data within a wireless network, the protocol comprising: a block I/O interface layer to provide a single level of translation between block I/O storage protocol commands and network packets; and a wireless transport layer to transport the network packets between a client and server within the network; wherein the block I/O interface layer performs operations directly on a storage device driver and a network device driver of the client and server. 
     The protocol may serve the functions of the network layer or the transport layer in the Open Systems Interconnection Reference (OSI) model. 
     The protocol may serve the functions of the network layer in the OSI model, and the network device driver transfers data using Media Access Control (MAC) addressing of the data link layer in the OSI model. 
     The protocol may serve the functions of the transport layer in the OSI model, and the data is transferred according to a corresponding network layer addressing scheme. 
     The storage protocol commands may include any one of the group consisting of: SATA, ATA and SCSI. 
     The network packets may be Ethernet frames or corresponding network data link frames. 
     The network packets may be IP packets or corresponding network layer frames. 
     The wireless transport layer may comprise a sliding window transfer with packet loss control. 
     The wireless transport layer may comprise a fast receiver and sender timeout value obtained from underlying network architecture. 
     A repeated ACK packet may be used to report packet loss. 
     A new timeout value may be based on a round trip time of other wireless protocols. 
     The wireless transport layer may comprise fast packet loss detection and selective retransmission to selectively retransmit lost packets. 
     Packet losses may be detected by a hole detection algorithm in which continuous lost packets in the sliding window are defined as a hole, and various hole patterns detected by the algorithm enable errors to be recovered. 
     In a third aspect, there is provided a data packet when constructed according to the data transportation protocol as described. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An example of the invention will now be described with reference to the accompanying drawings, in which: 
         FIG. 1  depicts the protocol layering when a transportation protocol in accordance with a preferred embodiment of the present invention is used as a transport; 
         FIG. 2  is a pictorial diagram of features of the transportation protocol; 
         FIG. 3  is a pictorial diagram of a re-transmit event for the transportation protocol; 
         FIG. 4  is a histogram comparing CPU utilisation of iSCSI against the transportation protocol; 
         FIG. 5A  depicts a protocol data unit (PDU) constructed by the transportation protocol; and 
         FIG. 5B  depicts a storage command header. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The drawings and the following discussion are intended to provide a brief, general description of a suitable computing environment in which the present invention may be implemented. Although not required, the invention will be described in the general context of computer-executable instructions, such as program modules, being executed by a computer such as a personal computer, laptop computer, notebook computer, tablet computer, PDA and the like. Generally, program modules include routines, programs, characters, components, data structures, that perform particular tasks or implement particular abstract data types. As those skilled in the art will appreciate, the invention may be practiced with other computer system configurations, including hand-held devices, multiprocessor systems, microprocessor-based or programmable consumer electronics, network PCs, minicomputers, mainframe computers, and the like. The invention may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote memory storage devices. 
     Referring to the drawings, a wireless storage transportation protocol (WSTP)  13 ,  21  for a wireless network  6  is provided. These drawings illustrate the deployment of WSTP  13 ,  21  directly above the data link layer of the Open Systems Interconnection Reference (OSI) model. WSTP may also be deployed as the transport layer directly above the network layer. The protocol is a two layer protocol and comprises: a block I/O interface layer  40  which is the higher layer and a wireless transport layer  41  which is the lower layer. The block I/O interface layer  40  provides a single level of translation between block I/O storage protocol commands and network packets. The block I/O interface layer  40  handles the translation between existing block I/O storage protocols such as SATA, ATA, and SCSI into network packets, and vice-versa. This translation is performed in a single level. The wireless transport layer  41  transports the network packets between a client  6 A and server  6 B within the network  6 . The wireless transport layer  41  handles the network packet transportation between server and client. The protocol has a compact architecture which minimizes the overheads of network packet headers and its complexity. The block I/O interface layer  40  performs operations directly on a storage device driver  23  and a network device driver  14 ,  20  of the client  6 A and server  6 B. Preferably, WSTP is used for short range wireless local area networks (LANs) or personal area networks (PANs). 
     Turning to  FIGS. 1 and 2 , from an application  10  on the client side  6 A, mass storage I/Os are performed through a variety of system calls. When these I/Os reach the storage protocol layer  12 , device specific storage command headers are constructed to perform the requested operation. The storage protocol layer  12  may be SCSI, SATA, or ATA. A host memory buffer descriptor for transmission or receipt of data (if necessary) is constructed. This information is then passed to the WSTP protocol layer  13  where the block I/O interface layer  40  of WSTP  13  constructs a Protocol Data Unit (PDU) containing the storage command header and PDU data (if data is to be transmitted/written). The block I/O interface layer  40  provides block I/O to Ethernet PDU translation, where Ethernet is based on Media Access Control (MAC) addressing. Typically, block I/O means that the application  10  or file system  11  is sending blocks to the storage device  24  to be written or asking for blocks using a logical block address (LBA).  FIG. 5A  depicts a PDU. The PDU is then passed to the wireless transport layer  41  of WSTP  13 , where packetization for segments and datagrams is performed. Next, the datagram is passed to the wireless network driver  14 , where Ethernet frame packetization is performed. Finally, the Ethernet frames are placed on the network  6 .  FIG. 5B  depicts a storage command header of the PDU. 
     When wireless network driver  20  at the server side  6 B receives the Ethernet frames, it removes the frame encapsulation and passes the results up to the wireless transport layer  41  of WSTP  21 . The wireless transport layer  41  removes the datagram and segment encapsulation, leaving a PDU to be passed to the block I/O interface layer  40  of WSTP  21 . The block I/O interface layer  40  removes the storage command header and data (if present) from the PDU and passes them to the storage protocol layer  22  for interpretation. Finally, the requested mass storage operation is performed by the disk driver  23  on the storage device  24 . 
     At any stack layer below the application layer  10  on the client  6 A, the protocol  13  may be implemented in hardware. Hardware is meant to include tangible components as well as the firmware that runs on those components. Similarly, at any stack layer below the actual logical units  20  on the server  6 B, the protocol implementation may be in hardware. Layers below the first hardware implementation in either stack must also exist in hardware. 
     Referring to  FIG. 3 , WSTP  13  has sliding window transfer with packet loss control. Any packet dropping signal is considered a packet loss. No congestion exists in the peer-to-peer connection. Also, the sliding window does not shrink when there is packet loss. WSTP  13  has a fast receiver and sender timeout value taken from the underlying wireless network architecture such as IEEE 802.11 or Ultra Wideband (UWB). The new timeout value is computed based on round trip time of various other wireless protocols. 
     WSTP  13  also has fast packet loss detection and selective retransmission. The ACK of WSTP  13  produces more retransmission information than other transport protocols. WSTP  13  selectively retransmits lost packets in contrast to other transport protocols which retransmit the entire packet queue. Thus, recovery from lost or bad packets is fast under WSTP  13 . In the example of  FIG. 3 , the ACK ( 2 ) is transmitted within 10 ms of receipt of the first packet ( 1 ) when the second packet ( 2 ) is considered lost. When the ACK ( 2 ) is received, the second packet ( 2 ) is retransmitted. The third packet ( 3 ) is transmitted immediately after re-transmission of the second packet ( 2 ). 
     To save the battery life and improve the performance, WSTP  13  directly uses data link layer to transfer data using a Media Access Control (MAC) addressing method. WSTP  13  has a compact protocol layer architecture which enables less CPU utilization and longer battery life. 
     WSTP  13  uses block level access to move the computational load of file level operations to the client  6 A. WSTP  13  directly employs data link layer as a transmission connection to avoid transmission overhead commonly seen with other transportation protocols such as TCP/IP. In experiments, a wireless storage server using WSTP  13  has better performance and has less power consumption. Referring to  FIG. 4 , when working at same maximum throughput, a mobile device using WSTP  13  consumes half of the CPU power as that of other protocols such as iSCSI. 
     Although WSTP  13  has been described with reference to short range peer-to-peer wireless mobile storage applications, it is envisaged that it may also be applicable to long range wired or wireless networks. WSTP  13  also can be used as generic transportation protocol for all other possible data transportation beyond storage data and commands. WSTP  13  performs the transport layer function of the OSI model. In such a scenario, the block I/O interface layer  40  provides block I/O to the network layer PDU translation and WSTP  13  directly uses the network layer addressing scheme to communicate data between devices in the network  6 . 
     WSTP  13  is designed to be lightweight and incorporates mechanisms to react effectively in lossy wireless network in order to maximize the bandwidth available. Packet losses in a wireless network is addressed by a hole detection algorithm where continuous lost packets in a sliding window are defined as a hole. By detecting different hole patterns, errors may be quickly recovered. WSTP  13  may be implemented on mobile devices to provide low power consumption and data sharing services. 
     Although WSTP  13  is designed for a peer to peer wireless network, it can be extended to any wired, wireless or hybrid wired/wireless network and also for situations where an efficient and lightweight storage transportation protocol for mobile devices is required and in low bandwidth networks. 
     Since WSTP  13  is a transportation protocol, it can also be extended beyond storage data or commands, to support all other possible types of data transportation. WSTP  13  may be used alone or together with User Datagram Protocol (UDP). It achieves good performance in an error-prone network. 
     It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the scope or spirit of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects illustrative and not restrictive.