Processing a variable length device command word at a control unit in an I/O processing system

A computer program product, apparatus and method for processing a variable length device command word (DCW) at a control unit configured for communication with an input/output (I/O) subsystem in an I/O processing system. The computer program product includes a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method. The method includes receiving a DCW at the control unit from the I/O subsystem. The DCW specifies one or more I/O operations and includes a command, a control data count, and control data having a varying length specified by the control data count. The control data is extracted in response to the control data count. The command is then executed in response to the extracted control data to perform the specified one or more I/O operations.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present disclosure relates generally to input/output (I/O) processing, and in particular, to processing a variable length device command word at a control unit in an I/O processing system.

2. Description of Background

Input/output (I/O) operations are used to transfer data between memory and I/O devices of an I/O processing system. Specifically, data is written from memory to one or more I/O devices, and data is read from one or more I/O devices to memory by executing I/O operations.

To facilitate processing of I/O operations, an I/O subsystem of the I/O processing system is employed. The I/O subsystem is coupled to main memory and the I/O devices of the I/O processing system and directs the flow of information between memory and the I/O devices. One example of an I/O subsystem is a channel subsystem. The channel subsystem uses channel paths as communications media. Each channel path includes a channel coupled to a control unit, the control unit being further coupled to one or more I/O devices.

The channel subsystem may employ channel command words (CCWs) to transfer data between the I/O devices and memory. A CCW specifies the I/O command to be executed. For commands initiating certain I/O operations, the CCW designates the memory area associated with the operation, the action to be taken whenever a transfer to or from the area is completed, and other options.

During I/O processing, a list of CCWs is fetched from memory by a channel. The channel parses each command from the list of CCWs and forwards a number of the commands, each command in its own entity, to a control unit coupled to the channel. The control unit then processes the commands. The channel tracks the state of each command and controls when the next set of commands are to be sent to the control unit for processing. The channel ensures that each command is sent to the control unit in its own entity. Further, the channel infers certain information associated with processing the response from the control unit for each command.

Performing I/O processing on a per CCW basis may involve a large amount of processing overhead for the channel subsystem, as the channels parse CCWs, track state information, and react to responses from the control units. Therefore, it may be beneficial to shift much of the processing burden associated with interpreting and managing CCW and state information from the channel subsystem to the control units. Simplifying the role of channels in communicating between the control units and an operating system in the I/O processing system may increase communication throughput as less handshaking is performed. Simplifying the role of channels in communication may include grouping multiple commands into a single I/O operation.

Some commands require both control data and customer data. Currently, a single command word (e.g., a CCW) cannot transfer both control data and customer data. A command that includes both control data and the customer data requires multiple transfers to specify both the control and customer data. This impacts the increase in throughput that can be gained by grouping commands. Performance may be improved by providing the ability for a single command word to transfer both control data and customer data.

BRIEF SUMMARY OF THE INVENTION

An exemplary embodiment includes a computer program product for processing a variable length device command word (DCW) at a control unit configured for communication with an input/output (I/O) subsystem in an I/O processing system. The computer program product includes a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method. The method includes receiving a DCW at the control unit from the I/O subsystem. The DCW specifies one or more I/O operations and includes a command, a control data count, and control data having a varying length specified by the control data count. The control data is extracted in response to the control data count. The command is then executed in response to the extracted control data to perform the specified one or more I/O operations.

Another exemplary embodiment includes an apparatus for processing a variable length DCW in an I/O processing system. The apparatus includes a control unit configured for communication with an I/O subsystem. The control unit performs a method that includes receiving a DCW at the control unit from the I/O subsystem. The DCW specifies one or more I/O operations and includes a command, a control data count, and control data having a varying length specified by the control data count. The control data is extracted in response to the control data count. The command is then executed in response to the extracted control data to perform the specified one or more I/O operations.

A further exemplary embodiment includes a method for processing a variable length DCW at a control unit configured for communication with an input/output (I/O) subsystem in an I/O processing system. The method comprises receiving a DCW at the control unit from the I/O subsystem. The DCW specifies one or more I/O operations and includes a command, a control data count, and control data having a varying length specified by the control data count. The control data is extracted in response to the control data count. The command is then executed in response to the extracted control data to perform the specified one or more I/O operations.

Other articles of manufacture, apparatuses, and/or methods according to embodiments will be or become apparent to one with skill in the art upon review of the following drawings and detailed description. It is intended that all such additional articles of manufacture, apparatuses, and/or methods be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with an aspect of the present invention, input/output (I/O) is facilitated by allowing a single command word to include control data and also to transfer customer data. A one byte count field is added to the command word to define the byte count of the control data required by the command. Thus, the command word includes two count fields, one for the control data and the other for customer data. In an exemplary embodiment, the variable length control data directly follows the command word.

This facilitates I/O processing by reducing communications between components of an I/O processing system used to perform the I/O processing. For instance, the number of exchanges and sequences between an I/O communications adapter, such as a channel, and a control unit is reduced. This is accomplished by sending both control and customer data to the control unit as a single entity (e.g., as part of the same control word) for execution by the control unit.

The plurality of commands (e.g., device command words or “DCWs”) are included in a block, referred to herein as a transport command control block (TCCB), an address (indirect or direct) of which is specified in a transport control word (TCW). In an exemplary embodiment, the TCW is sent from an operating system (OS) or other application to the I/O communications adapter, which in turn forwards the TCCB in a command message to the control unit for processing. The control unit processes each of the commands absent a tracking of status relative to those individual commands by the I/O communications adapter. The plurality of commands is also referred to as a channel program, which is parsed and executed on the control unit rather than the I/O communications adapter.

One example of an I/O processing system incorporating and using one or more aspects of the present invention is described with reference toFIG. 1. I/O processing system100includes a host system101, which further includes for instance, a main memory102, one or more central processing units (CPUs)104, a storage control element106, and a channel subsystem108. The host system101may be a large scale computing system, such as a mainframe or server. The I/O processing system100also includes one or more control units110and one or more I/O devices112, each of which is described below.

Main memory102stores data and programs, which can be input from I/O devices112. For example, the main memory102may include one or more operating systems (OSs)103that are executed by one or more of the CPUs104. For example, one CPU104can execute a Linux® operating system103and a z/OS® operating system103as different virtual machine instances. The main memory102is directly addressable and provides for high-speed processing of data by the CPUs104and the channel subsystem108.

CPU104is the controlling center of the I/O processing system100. It contains sequencing and processing facilities for instruction execution, interruption action, timing functions, initial program loading, and other machine-related functions. CPU104is coupled to the storage control element106via a connection114, such as a bidirectional or unidirectional bus.

Storage control element106is coupled to the main memory102via a connection116, such as a bus; to CPUs104via connection114; and to channel subsystem108via a connection118. Storage control element106controls, for example, queuing and execution of requests made by CPU104and channel subsystem108.

In an exemplary embodiment, channel subsystem108provides a communication interface between host system101and control units110. Channel subsystem108is coupled to storage control element106, as described above, and to each of the control units110via a connection120, such as a serial link. Connection120may be implemented as an optical link, employing single-mode or multi-mode waveguides in a Fibre Channel fabric (e.g., a fibre channel network). Channel subsystem108directs the flow of information between I/O devices112and main memory102. It relieves the CPUs104of the task of communicating directly with the I/O devices112and permits data processing to proceed concurrently with I/O processing. The channel subsystem108uses one or more channel paths122as the communication links in managing the flow of information to or from I/O devices112. As a part of the I/O processing, channel subsystem108also performs the path-management functions of testing for channel path availability, selecting an available channel path122and initiating execution of the operation with the I/O devices112.

Each channel path122includes a channel124(channels124are located within the channel subsystem108, in one example, as shown inFIG. 1), one or more control units110and one or more connections120. In another example, it is also possible to have one or more dynamic switches (not depicted) as part of the channel path122. A dynamic switch is coupled to a channel124and a control unit110and provides the capability of physically interconnecting any two links that are attached to the switch. In another example, it is also possible to have multiple systems, and therefore multiple channel subsystems (not depicted) attached to control unit110.

Also located within channel subsystem108are subchannels (not shown). One subchannel is provided for and dedicated to each I/O device112accessible to a program through the channel subsystem108. A subchannel (e.g., a data structure, such as a table) provides the logical appearance of a device to the program. Each subchannel provides information concerning the associated I/O device112and its attachment to channel subsystem108. The subchannel also provides information concerning I/O operations and other functions involving the associated I/O device112. The subchannel is the means by which channel subsystem108provides information about associated I/O devices112to CPUs104, which obtain this information by executing I/O instructions.

Channel subsystem108is coupled to one or more control units110. Each control unit110provides logic to operate and control one or more I/O devices112and adapts, through the use of common facilities, the characteristics of each I/O device112to the link interface provided by the channel124. The common facilities provide for the execution of I/O operations, indications concerning the status of the I/O device112and control unit110, control of the timing of data transfers over the channel path122and certain levels of I/O device112control.

Each control unit110is attached via a connection126(e.g., a bus) to one or more I/O devices112. I/O devices112receive information or store information in main memory102and/or other memory. Examples of I/O devices112include card readers and punches, magnetic tape units, direct access storage devices, displays, keyboards, printers, pointing devices, teleprocessing devices, communication controllers and sensor based equipment, to name a few.

One or more of the above components of the I/O processing system100are further described in “IBM® z/Architecture Principles of Operation,” Publication No. SA22-7832-05, 6th Edition, April 2007; U.S. Pat. No. 5,461,721 entitled “System For Transferring Data Between I/O Devices And Main Or Expanded Storage Under Dynamic Control Of Independent Indirect Address Words (IDAWS),” Cornier et al., issued Oct. 24, 1995; and U.S. Pat. No. 5,526,484 entitled “Method And System For Pipelining The Processing Of Channel Command Words,” Casper et al., issued Jun. 11, 1996, each of which is hereby incorporated herein by reference in its entirety. IBM is a registered trademark of International Business Machines Corporation, Armonk, N.Y., USA. Other names used herein may be registered trademarks, trademarks or product names of International Business Machines Corporation or other companies.

In one embodiment, to transfer data between I/O devices112and memory102, channel command words (CCWs) are used. A CCW specifies the command to be executed, and includes other fields to control processing. One example of a CCW is described with reference toFIG. 2A. A CCW200includes, for instance, a command code202specifying the command to be executed (e.g., read, read backward, control, sense and write); a plurality of flags204used to control the I/O operation; for commands that specify the transfer of data, a count field206that specifies the number of bytes in the storage area designated by the CCW to be transferred; and a data address208that points to a location in main memory that includes data, when direct addressing is employed, or to a list (e.g., contiguous list) of modified indirect data address words (MIDAWs) to be processed, when modified indirect data addressing is employed. Modified indirect addressing is further described in U.S. application Ser. No. 11/464,613, entitled “Flexibly Controlling The Transfer Of Data Between Input/Output Devices And Memory,” Brice et al., filed Aug. 15, 2006, which is hereby incorporated herein by reference in its entirety.

One or more CCWs arranged for sequential execution form a channel program, also referred to herein as a CCW channel program. The CCW channel program is set up by, for instance, an operating system, or other software. The software sets up the CCWs and obtains the addresses of memory assigned to the channel program. An example of a CCW channel program is described with reference toFIG. 2B. A CCW channel program210includes, for instance, a define extent CCW212that has a pointer214to a location in memory of define extent data216to be used with the define extent command. In this example, a transfer in channel (TIC)218follows the define extent command that refers the channel program to another area in memory (e.g., an application area) that includes one or more other CCWs, such as a locate record217that has a pointer219to locate record data220, and one or more write CCWs221. Each write CCW221has a pointer222to a data area224. The data area includes an address to directly access the data or a list of data address words (e.g., MIDAWs or IDAWs) to indirectly access the data. Further, CCW channel program210includes a predetermined area in the channel subsystem defined by the device address called the subchannel for status226resulting from execution of the CCW channel program.

The processing of a CCW channel program is described with reference toFIG. 3, as well as with reference toFIG. 2B. In particular,FIG. 3shows an example of the various exchanges and sequences that occur between a channel and a control unit when a CCW channel program is executing. The link protocol used for the communications is FICON (Fibre Connectivity), in this example. Information regarding FICON is described in “Fibre Channel Single Byte Command Code Sets-3 Mapping Protocol (FC-SB-3), T11/Project 1357-D/Rev. 1.6, INCITS (March 2003), which is hereby incorporated herein by reference in its entirety.

Referring toFIG. 3, a channel300opens an exchange with a control unit302and sends a define extent command and data associated therewith304to control unit302. The command is fetched from define extent CCW212(FIG. 2B) and the data is obtained from define extent data area216. The channel300uses TIC218to locate the locate record CCW and the write CCW. It fetches the locate record command and data306(FIG. 3) from the locate record CCW217(FIG. 2B) and locate record data220. The write command and data308(FIG. 3) is fetched from write CCW221and data area224(FIG. 2B). Each is sent to the control unit302.

The control unit302opens an exchange310with the channel300, in response to the open exchange of the channel300. This can occur before or after locate command and data306and/or write command and data308. Along with the open exchange, a response (CMR) is forwarded to the channel300. The CMR provides an indication to the channel300that the control unit302is active and operating.

The control unit302provides the status to the channel300and closes the exchange312. In response thereto, the channel300stores the data, examines the status and closes the exchange314, which indicates to the control unit302that the status has been received.

The processing of the above CCW channel program to write 4 k of data requires two exchanges to be opened and closed and six sequences. The total number of exchanges and sequences between the channel and control unit is reduced through collapsing multiple commands of the channel program into a TCCB. The channel, e.g., channel124ofFIG. 1, uses a TCW to identify the location of the TCCB, as well as locations for accessing and storing status and data associated with executing the channel program. The TCW is interpreted by the channel and is not sent or seen by the control unit.

One example of a channel program to write 4 k of data, as inFIG. 2B, but includes a TCCB, instead of separate individual CCWs, is described with reference toFIG. 4. As shown, a channel program400, referred to herein as a TCW channel program, includes a TCW402specifying a location in memory of a TCCB404, as well as a location in memory of a data area406or a TIDAL410(i.e., a list of transport mode indirect data address words (TIDAWs), similar to MIDAWs) that points to data area406, and a status area408. TIDAW zero412, TIDAW one414and TIDAW two416(collectively TIDAWs412-416) can reference different locations in the data area406for acquiring or storing data. The TIDAWs412-416can reference non-contiguous blocks of data or contiguous blocks of data. The TIDAWs412-416in TIDAL410may be located sequentially in memory or located non-contiguously relative to each other. While only three TIDAWs412-416are depicted in TIDAL410, it will be understood that any number of TIDAWs can be included in the TIDAL410.

The processing of a TCW channel program is described with reference toFIG. 5. The link protocol used for these communications is, for instance, Fibre Channel Protocol (FCP). In particular, three phases of the FCP link protocol are used, allowing host bus adapters to be used that support FCP to perform data transfers controlled by CCWs. FCP and its phases are described further in “Information Technology—Fibre Channel Protocol for SCSI, Third Version (FCP-3),” T10 Project 1560-D, Revision 4, Sep. 13, 2005, which is hereby incorporated herein by reference in its entirety.

The embodiment of the link protocol depicted inFIG. 5is utilized when XFER_RDY is enabled. In the embodiment depicted inFIG. 5, the channel500cannot send the data506to the control unit502until it is requested by the control unit502via the XFER_RDY IU510. In an alternate exemplary embodiment, XFER_RDY is disabled and the control unit does not transmit a XFER_RDY IU510to the channel500. Thus, the channel500does not have to wait for the control unit502to request the data506before sending the data506. This alternate embodiment, where XFER_RDY is disabled may be utilized when the channel500and the control unit502are located geographically far apart from each other (e.g., greater than twenty kilometers, greater than fifty kilometers) to improve performance. Unless otherwise specified, the discussion herein assumes that XFER_RDY is enabled.

In a further example, to write 4K of customer data, the channel500uses the FCP link protocol phases, as follows:1. Transfer a TCCB in the FCP_CMND IU and sequence initiative to the control unit502.2. Wait for a XFER_RDY IU indication that the control unit is ready to receive the data502.3. Transfer the IU of data, and sequence initiative to the control unit502.4. Final status is sent in a FCP status frame that has a bit active in, for instance, byte10or11of the FCP_RSP IU Payload. The FCP_RSP_INFO field or sense field is used to transport FICON ending status along with additional status information.

By executing the TCW channel program ofFIG. 4, there is only one exchange opened and closed (see alsoFIG. 5), instead of two exchanges for the CCW channel program ofFIG. 2B(see alsoFIG. 3). Further, for the TCW channel program, there are four communication sequences (seeFIGS. 4-5), as compared to six sequences for the CCW channel program (seeFIGS. 2B-3).

The number of exchanges and sequences remain the same for a TCW channel program, even if additional commands are added to the program. Compare, for example, the communications of the CCW channel program ofFIG. 6with the communications of the TCW channel program ofFIG. 7. In the CCW channel program ofFIG. 6, each of the commands (e.g., define extent command and data600, locate record command and data601, write command and data602, write command and data604, locate record command and data606, write command and data608, and write command and data620) are sent in separate sequences from channel610to control unit612. This CCW channel program requires two exchanges to be opened and closed (e.g., open exchanges622,624and close exchanges626,628), and ten communications sequences. This is compared to the four sequences and one exchange for the TCW channel program ofFIG. 7, which accomplishes the same task as the CCW channel program ofFIG. 6.

As depicted inFIG. 7, a channel700opens an exchange with a control unit702and sends a TCCB704to the control unit702. The TCCB704includes the define extent command, the two locate record commands, and the four write commands in DCWs, as described above. The channel700transmits 16 k of data706to the control unit702in a single sequence upon receipt of the XFER_RDY IU710. The channel700may insert a CRC every 4K of the 16 k of data706in the sequence. The insertion of a CRC every 4K allows the control unit702to verify the 16K of data incrementally, rather than buffer the entire 16K for verification before completing the write commands in the TCCB704. Additionally, the control unit702provides status to the channel700and closes the exchange708. Thus, the TCW channel program ofFIG. 7requires much less communications to transfer the same amount of data as the CCW channel program ofFIG. 6, while supporting incremental data verification via multiple CRC insertion in the output data stream from the channel700.

Turning now toFIG. 8, one embodiment of channel124in the channel subsystem and the control unit110FIG. 1that support TCW channel program execution are depicted in greater detail. The control unit110includes CU control logic802to parse and process command messages containing a TCCB, such as the TCCB704ofFIG. 7, received from the channel124via the connection120. The CU control logic802can extract DCWs and control data from the TCCB received at the control unit110to control a device, for instance, I/O device112via connection126. The CU control logic802sends device commands and data to the I/O device112and receives status information and other feedback from the I/O device112. For example, the I/O device112may be busy because of a previous reservation request targeting I/O device112. To manage potential device reservation contention issues that can arise when the control unit110receives multiple requests to access the same I/O device112, the CU control logic802keeps track of and stores device busy messages and associated data in a device busy queue804. In an exemplary embodiment, an OS103ofFIG. 1reserves I/O device112to keep other OSs103from accessing the I/O device112while the reservation is active. Although device reservation is not required for all I/O operations, device reservation can be used to support operations that necessitate exclusive access for a fixed duration of time, e.g., disk formatting.

The control unit110may further include other buffer or memory elements (not depicted) to store multiple messages or status information associated with communications between the channel124and the I/O device112. For example, a register located on the control unit110may include a maximum control unit exchange parameter that defines the maximum number of open control unit exchanges that the control unit110supports.

The channel124in the channel subsystem108includes elements to support communication with the control unit110. In an exemplary embodiment, the CHN control logic806controls communication between the channel subsystem108and the control unit110. The CHN control logic806may directly interface to the CU control logic802via the connection120to send commands and receive responses, such as transport command and response IUs. Alternatively, messaging interfaces and/or buffers (not depicted) can be placed between the CHN control logic806and the CU control logic802.

FIG. 9depicts one embodiment of a TCCB900in accordance with an aspect of the present invention. The TCCB900inFIG. 9is located at the address indicated in by the TCW. This address may be a direct address or an indirect address, allowing the contents of the TCCB900to be in one storage location or to be spread among multiple non-contiguous storage locations. As described previously, the TCCB900is a control block built by software and then the channel124sends it to a control unit110(e.g., in a Transport Command IU) for execution. The TCCB900contains the commands to be executed by the control unit110and any control data required by the commands. The channel124does not look at the contents of the TCCB900. The channel124packages the TCCB900and sends it to the control unit110. This allows FCP transport protocols to be utilized instead of FICON.

The TCCB900includes a transport control area header (TCAH)902which, in an exemplary embodiment, includes information about the transport command area (TCA)904and operations within the TCA904(e.g., length, service code). The TCCB900depicted inFIG. 9also includes a variable length TCA904which includes one or more DCWs906which may each include DCW control data908. In an exemplary embodiment, the DCW control data908is variable length. In an exemplary embodiment, each DCW906includes a command flags (chaining), control data length, and read/write data length. DCW control data908is optional (depending on the DCW906) and includes control parameters for the DCW906. For example, DCW control data908may include define extent and/or prefix parameters. In an exemplary embodiment, the DCW control data is located at the end of the DCW906within the TCA904and is not pointed to by the DCW906. Finally, the TCCB900includes a TCA trailer (TCAT)910that contains data such as the count of the bytes to be transferred in the TCCB900.

FIG. 10depicts one embodiment of a DCW1000in accordance with an aspect of the present invention. In an exemplary embodiment, the DCW1000is eight bytes in length plus the length of the control data1002. The DCW includes a command field1004, a flags field1006, a reserved field1008, a control data (CD) count field1010, and a data byte count field1012. The DCW command field1004is one byte in length and is the same as the CCW command byte utilized in a CCW (but may include additional command codes not utilized by a CCW). The flags field1006includes eight bits; in an exemplary embodiment, the second bit is a chain command to the next DCW1000in the TCA904. When this flag bit is set to zero, it indicates that this is the last DCW1000of the DCW program in the TCA904. The other bits in the flag field1006are reserved and set to zero.

The CD count field1010is a one byte field that contains the byte count of the control data1002used by this DCW1000. The control data1002is tacked on to the end of the DCW1000. In an exemplary embodiment, the space used between DCWs1000when control data1002is present is the size of the control data1002padded up to the next four byte boundary so that the DCWs1000always start on a four byte boundary. The data byte count field1012is a four byte DCW byte count field. This is the DCW count of customer data (e.g., the data406inFIG. 4). In an exemplary embodiment, this count does not include padding or CRC bytes to be transferred by this DCW command. This DCW byte count field1012has the same meaning as the count field in a CCW, except that it can be much larger. If the DCW command is a command immediate or a no-op command (i.e., contains no customer data), then the data byte count field1012is equal to zero.

In an exemplary embodiment, the control data1002is in the same TCA904at the end of the DCW1000with which the control data1002is associated. In an exemplary embodiment, the control data1002is padded out to the next four byte boundary in the TCA904. The CD count field1010reflects the number of bytes of control data1002. In an exemplary embodiment, the maximum length of the control data1002in a TCA904is two hundred and thirty two bytes assuming one DCW1000and the rest of the TCA904is taken up by the control data for the DCW1000.

FIG. 11depicts one embodiment of a process for providing a variable length DCW in accordance with an aspect of the present invention. At block1102a control unit receives a variable length DCW1000. The DCW1000specifies multiple equivalent legacy I/O operations (e.g., define extent, locate record and then a read operation or a write operation, etc.) defined by command1004, control data count1010, and variable length control data1002. The length of the control data is specified by the control data count. At block1104, the control data1002is extracted from the DCW using the control data count to determine how many bytes at the end of the DCW1000are to be included in the control data. At block1106, the command is executed by the control unit using the control data as input to the executing. The execution results in multiple equivalent legacy I/O operations being performed. If the DCW also includes customer data (e.g., the data byte count1012is non-zero) then the command is executed in response to the to the control data and to the customer data. In addition, the control unit may transmit a completion status of the command (e.g., completed successfully, error conditions, etc.) to the host computer system.

Thus, referring back toFIGS. 2B and 10, an exemplary embodiment of the present invention may be utilized to combine the define extent CCW212, locate record CCW217and write CCW221into a single DCW. This DCW is a combined command that means: define extent, locate record, and write customer data. In this exemplary embodiment, the extent and locate record parameter data is the control data that is part of the DCW whose length is defined by the control data count1010. The customer data length is controlled by the data byte count1012. The customer data transferred can only be a write (output) or a read (input), not both, in the same DCW. This combination of commands within a CCW could not have been performed in current implementations because the only way to get the control data (the define extent parameters and the locate record parameters) to the control unit was for the channel to transfer these parameters as data to the control unit.

Technical effects of exemplary embodiments include the ability to transfer customer data and control data within the same DCW. This may lead to improved performance by requiring fewer exchanges to perform the same number of functions.

As described above, embodiments can be embodied in the form of computer-implemented processes and apparatuses for practicing those processes. In exemplary embodiments, the invention is embodied in computer program code executed by one or more network elements. Embodiments include a computer program product1200as depicted inFIG. 12on a computer usable medium1202with computer program code logic1204containing instructions embodied in tangible media as an article of manufacture. Exemplary articles of manufacture for computer usable medium1202may include floppy diskettes, CD-ROMs, hard drives, universal serial bus (USB) flash drives, or any other computer-readable storage medium, wherein, when the computer program code logic1204is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. Embodiments include computer program code logic1204, for example, whether stored in a storage medium, loaded into and/or executed by a computer, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code logic1204is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. When implemented on a general-purpose microprocessor, the computer program code logic1204segments configure the microprocessor to create specific logic circuits.