Patent Publication Number: US-7225243-B1

Title: Device discovery methods and systems implementing the same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Patent Application No. 60/189,639, filed Mar. 14, 2000, and entitled “ETHERNET STORAGE PROTOCOLS FOR COMPUTER NETWORKS.” This application is also a continuation-in-part of co-pending U.S. patent application Ser. No. 09/490,630, filed Jan. 24, 2000, from which priority under 35 U.S.C. § 120 is claimed, and entitled “METHODS FOR IMPLEMENTING AN ETHERNET STORAGE PROTOCOL IN COMPUTER NETWORKS” which claims the benefit of U.S. Provisional Patent Application No. 60/117,226, filed Jan. 26, 1999, and entitled “SCSI OVER ETHERNET,” and which also claims benefit of U.S. Provisional Patent Application No. 60/163,266, filed Nov. 3, 1999, and entitled “SCSI OVER ETHERNET.” The aforementioned applications Nos. 60/189,639 and 09/490,630 are herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to data communication, and more particularly to protocols for efficiently identifying peripheral devices on a network while reducing data congestion and decreasing device recognition time on the network. 
     2. Description of the Related Art 
     The art of networking computers has evolved over the years to bring computer users a rich communication and data sharing experience. Typically, in a network, numerous devices may be connected to a computer to maximize computing power and efficiency. As is well known, new levels of sophisticated communication technologies enable users to share information across both large and small networks. Most of the world&#39;s computers communicate via computer networks by communicating data from one node to another node utilizing various data transport protocols. One typical type of protocol utilizing networks for data transmission is TCP/IP. TCP/IP is a set of protocols developed to allow cooperating computers to share resources across a network. TCP (the “transmission control protocol”) is responsible for breaking up a message into variable length segments, reassembling them at the other end, resending anything that gets lost, and putting things back in the right order. IP (the “internet protocol”) is responsible for routing individual segments. Utilizing such protocols as IP, computer networks may transfer data from one node to another. 
     As a high level overview, take an exemplary data file that is selected for communication over a network using the TCP protocol. Initially, the TCP protocol will break up the data file into a plurality of variable length segments. Each variable length segment is then packaged with an associated TCP header. An IP header will also be added to the beginning of the packet. The packets are now transmitted over the network, where each packet may potentially travel a different path (e.g., through a plurality of routers and the like) in their journey to a destination. At the destination, the TCP protocol is charged with receiving the packets. 
     For example, TCP/IP may be utilized in a data storage network for the sending and receiving of data with a SCSI host adapter and a typical NIC. To do this, network interface cards (NICs) with initiators are often utilized to communicate data and peripheral device information throughout the network. NICs may generally connect a computer or other type of node to a network. NICs are typically a circuit, an ASIC, or a host adaptor card that are often utilized in Ethernet or token ring networks. Initiators generally are located within a NIC and originates an input/output command over a network, bus, etc. 
     Unlike general communication networks, which assume that all attached devices are peers and that any given device will want to communicate with only a small subset of other devices, storage networks are hierarchical, with a few initiators in communication with many targets, and with targets in communication only with initiators, or with other targets under the control of an initiator. Typically, this storage viewpoint requires that initiators be able to locate all the targets, and be able to communicate with many or all of them. 
     Problematically, present methods to manage and determine the peripheral devices connected to the network have high data transmission overhead and often requires an additional directory agent to keep track of all of the peripheral devices. In addition, frequent use of broadcasting in the prior art can cause congestion in switch based networks. Typically large networks have many targets and numerous initiators. In addition, large networks have a directory that is generally set up by network administrators. Large networks also generally require a network administrator to assign IP addresses to devices on the network so a directory agent may keep track of them. Furthermore, in the process of setting up directories, network administrators must often decide on the scope of each directory such as geographic extent or types of devices. In such a configuration, targets may register their existence and addresses with the directory agent, and initiators or hosts may then communicate with the directory agent and poll all of the targets to determine the existence of every peripheral device connected to the network. Therefore, every initiator generally polls all directory agents at certain intervals to determine the target connection. This arrangement can cause data transfer congestion. Unfortunately frequent polling generally occurs in an attempt to obtain quick discovery of targets, but the resulting network congestion can create the degradation of target discovery and reduction in the speed of target recognition due to packet dropping. Consequently, polling occasionally means new devices take a long time to be “found” by the initiators. 
     For example, although new targets will often broadcast a signal to state to the network that it exists and is connected to the network, if a directory is present, as is usually the case in large networks, the directory registers the device and it will only broadcast once. This may be good for bandwidth, but also means that some initiators may not “see” the target&#39;s broadcast (dropped packets) so even if they are listening for such broadcasts to find out if a new target has joined the network, they tend to miss its joining and will not find out till they are polled. Therefore, target recognition speed may be severely hampered, and in some circumstances, target recognition may not occur. 
     Unfortunately, in small networks, directory agents are generally not utilized so all of the initiators on the network tend to poll extremely often so they can find all of the targets on the network. Regrettably, such numerous pollings create excess data traffic on the network and therefore decrease available bandwidth. Furthermore, targets themselves attempt to broadcast that they are connected onto the network thereby increasing data congestion even more. In addition, because small networks typically do not have a network administrator who can perform tasks such as, for example, assigning IP addresses to targets, such networks do not generally operate in a centralized and organized manner because there is no entity to assist in the organization and centralization of network connections and configurations. Even medium size systems tend to need directories to keep the initiator polling overhead from getting too large which entails once again to have a network administrator to look over the network. 
     For example, at startup of a small network, initiators typically broadcasts a query of all of the targets to determine what devices may be connected to the network. At the same time, targets may broadcast signals throughout the network in an attempt to notify initiators of their existence. In such a configuration, initiators generally broadcasts signals to communicate with the targets. Once again, this creates excess data transmissions and network congestion. Therefore, in typical peripheral device discovery, the network becomes congested with the initiators and targets all trying to communicate to each other without any sort of organization. In essence, initiators and targets are involved in a “free for all” in an attempt to communicate with each other. This results in excessive data transmission and dramatically lowers the network&#39;s ability to transmit data. 
     Furthermore, when a new target such as a peripheral device is added to a network, the peripheral device generally sends a broadcast signal throughout the network indicating that the peripheral device is connected to the network. By the broadcast signal, the peripheral device communicates its existence to all of the initiators located on the network. Unfortunately, in a typical network, when a target such as a peripheral de ice is attached, the signal broadcasted throughout the network creates data traffic within the network thus slowing down data being transferred between the other peripheral devices and an initiator. This problem becomes progressively worse as multiple targets are added to the network. In addition, broadcasts may not reach all of the initiators due to congestion caused packet drops. Thus, some initiators may not find out about the new devices for quite some time thus detrimentally contributing to lengthened device recognition times. 
     In view of the foregoing, there is a need for a target discovery and management protocol that removes the data congestion produced by prior art device discovery protocols. There is also a need for an initiator recognition protocol that is optimized for storage and enables fast and efficient utilization in local area networks, wide area networks, and over the Internet. 
     SUMMARY OF THE INVENTION 
     Broadly speaking, the present invention fills these needs by providing a data transmission and target device discovery system that centralizes and streamlines the processing and communication of device data and reduces the data communication congestion and device discovery slowdown associated with prior art device discovery techniques. Although different names are used for identification purposes, it should be understood that the technical implementations remain the same. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, a method, or a computer readable medium. Several inventive embodiments of the present invention are described below. 
     A method for target device discovery on a network is disclosed. In this embodiment, the method includes multicasting a signal from a master initiator over the network. A unicast is received from a new target recently connected to the network where the new target is passive when no multicast signal from the master initiator is received. Then the new target is added to a list of targets connected to the network. The method concludes by sending out a next multicast to other initiators where the next multicast includes information regarding the adding of the new target to the network. 
     In another embodiment, a method for target device discovery on a network is disclosed. In this embodiment, the method includes multicasting a signal from a master initiator over the network. Then it is determined if a previously registered target re-registered with the master initiator by a unicast to the master initiator. The method also includes maintaining the previously registered target on a list of active targets connected to the network. The method further includes sending out a next multicast with information regarding the previously registered target to notify other initiators to maintain the previously registered target on the list of targets. 
     In yet another embodiment, a method for target device discovery on a network is disclosed. In this embodiment, a master initiator includes program instructions for multicasting a signal over the network where the multicasting is triggered continually at a predetermined interval, and for receiving a unicast from a new target recently connected to the network where the new target is passive and waits for a multicast signal from a master initiator. The master initiator further includes program instructions for adding the new target to a list of targets where the adding occurring in response to the directed unicast signal, and for determining if a previously registered target re-registered with the master initiator. The master initiator includes additional program instructions for maintaining the previously registered target on the list of targets where the multicasting transmits information regarding the maintaining and the adding of targets to the network. 
     In another embodiment, a system for target device discovery on a network is disclosed. In this embodiment, the system includes a master initiator where the master initiator sends a multicast throughout the network. The system also includes at least one target where the at least one target remains passive until a multicast is received from the master initiator. The system further includes at least one slave initiator where the at least one slave initiator receives target information from the multicast. In addition, the master initiator polls the at least one target by way of the multicast, and the at least one target responds to the multicast through use of a unicast directed to the master initiator. 
     The advantages of the present invention are numerous. By having discovery protocols and methods that intelligently centralize target device information reception and dissemination, excess data communication over a network may be reduced dramatically. Such a reduction in data communication congestion, enables the network to perform at an optimum efficiency by freeing up data transmission bandwidth. In addition, the present invention enables selecting of a master initiator that may facilitate the centralization and data congestion reduction process. Specifically, information and data regarding network targets may be piggybacked on multicasts from the master initiator that is usually sent for initiator identification purposes. Therefore, the network data or the network update data that are multicasted from the master initiator reduces great amounts of congestion in comparison to the prior art method where all of the initiators and targets attempt to communicate with each other on a one on one basis. In yet another advantage, unlike prior art system, the present invention may more quickly recognize a new target as being on the network therefore decreasing effective discovery time. As can be seen, the present invention reduces data congestion in a powerful but elegant manner, and advantageously enables an organized and centralized peripheral device discovery process. 
     Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, and like reference numerals designate like structural elements. 
         FIG. 1  shows a network utilizing data transmission and network management methods in accordance with one embodiment of the present invention. 
         FIG. 2A  shows a network that illustrates a master initiator selection process in accordance with one embodiment of the present invention. 
         FIG. 2B  illustrates the network after a master initiator has been determined in accordance with one embodiment of the present invention. 
         FIG. 2C  shows a network where a master initiator is multicasting a master initiator signal in accordance with one embodiment of the present invention. 
         FIG. 3  shows a diagram where one of a plurality of initiators detects a missed master initiator signal in accordance with one embodiment of the present invention. 
         FIG. 4  shows a graph where a second initiator is connected to the network after a first initiator has been established as a master initiator in accordance with one embodiment of the present invention. 
         FIG. 5  shows a discovery protocol data structure containing an IP version 4 address in accordance with one embodiment of the present invention. 
         FIG. 6  shows a discovery protocol data structure containing an IP version 6 address in accordance with one embodiment of the present invention. 
         FIG. 7  illustrates a target information field that may be utilized by peripheral device discovery packets in accordance with one embodiment of the present invention. 
         FIG. 8  shows a device type field as utilized within a target field in accordance with one embodiment of the present invention. 
         FIG. 9  shows a master identify packet in accordance with one embodiment of the present invention. 
         FIG. 10  illustrates a target identify packet in accordance with one embodiment of the present invention. 
         FIG. 11  depicts a master ACK packet in accordance with one embodiment of the present invention. 
         FIG. 12  illustrates a query packet in accordance with one embodiment of the present invention. 
         FIG. 13  shows a flowchart defining a method for determining a master initiator and obtaining target information in a network in accordance to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     An invention is described for a system for centralized network communication control and efficient but quick peripheral device discovery in a network environment. The peripheral device discovery system may also be known as peripheral discovery protocol (PDP). It should be understood that the method of the present invention may work in any type of network environment utilizing any type of data transfer protocol where data is transferred and where data congestion over a network is preferably lowered and target discovery time is reduced. Examples of such networks include, for example, Ethernet, token ring, or other networks with multicast capabilities. Examples of such data transmission protocols include, for example, TCP/IP, small transport protocol (STP) as described in U.S. patent application Ser. No. 09/490,630, entitled “Methods For Implementing An Ethernet Storage Protocol In Computer Networks,” etc. The aforementioned patent application is incorporated herein by reference. 
     A network utilizing the methods of the present invention will preferably include host computers equipped with hardware to enable communication using a transport protocol such as a TCP/IP over a network with multiple initiators and targets which would benefit from a reduction in data transfer congestion and inefficiencies associated with the prior art data transmission systems. In one embodiment, a network utilizing IP with the initiator-target communications system of the present invention will enable more efficient transfers of data over a communication link such as a local area network (LAN) by reducing unnecessary data transfer congestion resulting from inefficient network component management. In another embodiment, larger networks, such as the Internet with the additional implementation of the Internet Protocol (IP) may benefit from the present invention by reducing unneeded data communications overhead. Consequently, a flexible and efficient management of initiators in device discovery may be utilized on a local environment or over IP in a large network to reduce unneeded data traffic over any system. 
     In one embodiment, the present invention may be utilized by network interface cards (NICs) such as, for example, storage optimized or accelerating NICs and may be utilized within Ethernet systems or over TCP/IP for communication on a network to a desired target. The target, therefore, is preferably a storage target, such as a hard disk, a RAID array, a CD media device, a storage box, a network attached storage (NAS), or other peripheral device that can store and exchange data. It should be understood that the present invention may be utilized to find any network resource, such as, for example, printers, modems, etc. Such a target may be intelligently detected by a “master initiator” within a particular NIC which can map network target connections for use by other initiators within other NICs on the network. Therefore, other initiators do not have to individually poll the targets to ascertain what targets may be connected to the network thus cutting down the data traffic that often occurs. This reduction in traffic consequently enables more efficient data transfer within the network. In addition, targets that may be connected on a remote part of the network may be discovered more quickly than in prior art methods. 
     It will be obvious, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention. 
       FIG. 1  shows a network  100  utilizing data transmission and peripheral device discovery methods in accordance with one embodiment of the present invention. In this embodiment, a host- 1   110  and a host- 2   112  are connected to each other and to a target- 1   116  and a target- 2   118  by way of a switch  114 . It should be understood that the hosts  110  and  112  may include any type of NIC such as, for example, storage optimized or accelerating NICs. The host- 1   110  includes an initiator  111  and the host- 2   112  includes an initiator  113 . In one embodiment, the initiators  111  and  113  manage target connectivity information and acts as an input/output manager for the hosts  110  and  112  thus regulating input and output from the hosts  110  and  112  to the network  100 . It should be understood that the network  100  is only one embodiment and other types of networks with any number of initiators, targets, switches, and typical network components may benefit from the network management methods of the present invention. 
     In one embodiment, at power up, the initiators attempt to first determine which initiator is the master initiator. In this circumstance, as discussed in more detail in reference to  FIGS. 2A–2C  and  13 , initiators send multicast signals out to the network. Multicast signals are signals that do not go just to a specific destination but go to all nodes within the network  100 . In one exemplary embodiment of a master initiator selection process, the initiator- 2   113  receives a multicast-1 from the initiator- 1   111  while the initiator- 1   111  receives a multicast-2 from the initiator- 2   113 . The multicast-1 and the multicast-2 signals are master initiator signals without the master initiator bit being set. The master initiator bit is set when a master initiator has been determined. Thereafter, all multicasts sent by the master initiator resulting from the selection process has the master initiator bit set. It should be appreciated that any way of indicating that the master initiator signal is from the master initiator may be utilized. In one embodiment, a real_master flag is set in a master initiator multicast signal which identifies the master initiator and notifies other initiators that the master initiator already exists. 
     If multicasts are sent by two initiators and neither master initiator signal has a master initiator bit that is set (meaning neither has been selected as the master initiator yet), each of the initiators  111  and  113  compares the global unique identification number (GUID) number of the other initiator with its own GUID number. It should be understood that any unique identifier could be used in the present invention such as, for example, MAC address, EUI-64 numbers, or any other Globally Unique Identifiers. Each of the master initiator signals include a GUID number identifying the initiators. It should be understood that any other type of identification may be utilized to determine the master initiator as long as the identification process is a logical and consistent method. In one embodiment, the initiator with the higher GUID number (or in the case of more than 2 initiators, the highest GUID number) becomes the master initiator. 
     In one embodiment, the initiator- 1   111  has the higher GUID number and becomes the master initiator. In this circumstance, the intiator- 1   111  multicasts a master initiator signal with the master initiator bit that is set. It should be understood that the master initiator signal may be sent out in any time interval that enable adequate monitoring of targets that is connected to the system. In one embodiment, the master initiator signal with the master initiator bit set is multicasted once every second. When the master initiator bit is set, all the other initiator(s) connected with the network knows that a master initiator exists on the network. The master initiator signals (with, in one embodiment, the real_initiator flag) all targets (i.e. peripheral devices) that the initiator- 1  is the master initiator and is connected to the network. In one embodiment, in contrast to prior art systems, the targets do not respond until they receive a master initiator signal with the master initiator bit set. In this circumstance, each target knows that a particular initiator (such as initiator- 1 ) is the master initiator and it should unicast a data transmission to the master initiator so the master initiator may find out that the target is on the network. As opposed to a multicast, a unicast is a data transmission message directed to one recipient. When the unicast from a target is received by the master initiator, information regarding the target is added to a list of targets maintained by the master initiator. Therefore, as opposed to the prior art where the target multicasted its information throughout the network, the target in this embodiment only responds to one master initiator which lowers data transmission congestion significantly. Additionally, in one embodiment, when the master initiator next multicasts a master initiator signal over the network, the new target information is included in the multicast and the other initiators on the network will add the target information to their target lists. 
     In another embodiment, when a target- 3   120  is connected to the network  100 , the target- 3   120  awaits reception of a multicasted master initiator signal from the initiator- 1   111 . Once the master initiator signal with the master initiator bit set is received, the target- 3   120  sends a unicast response back to the initiator- 1   111  stating its existence and location (i.e. address). Therefore, through the feedback from the targets in response to the master initiator signal, the initiator- 1   111  (the master initiator) knows that the targets  116 ,  118 ,  120  are connected to the network  100 . Then, in one embodiment, as discussed below in further detail in reference to  FIG. 3 , the initiator sends out multicast signals including data showing the master initiator signal sequence number and the targets that have responded to the master initiator since the last master initiator signal was sent out. Therefore, in one embodiment, if the intiator- 1   111  has sent out 3 types of master initiator signals (with sequence number ranging from 1–3, a new sequence number being assigned when new target information is included), and before the next master initiator signal is sent out, the master initiator receives a unicast from the just added target- 3   120  showing that the target- 3   120  is attached to the network. Then, the initiator- 1   111  sends out a fourth multicast signal that has a sequence number of 4 with the master initiator bit set that includes new target data showing that the target- 3   120  is connected to the network. This way other targets and initiators may know that the target- 3   120  exists and is connected to the network  100 . 
     By using a master initiator sequence number of 4 for the fourth type of multicast signal, the other initiators may know that there were three previous types of master initiator signals with certain target data information. In one embodiment, the master initiator signal sequence number is changed only when a new development in the network occurs such as when a new target is found or an old target checks in the master initiator. In this embodiment, the master initiator keeps sending out master initiator signals that indicates to the targets that a master initiator exists and any signals showing a target&#39;s connection to the network should be sent to the master initiator. 
       FIG. 2A  shows a network  140  that illustrates a master initiator selection process in accordance with one embodiment of the present invention. In this embodiment, an initiator- 142 , an initiator- 2   144 , and an initiator- 3   146  are part of a network that also includes a target- 1   148  and a target- 4   150 . In this embodiment, the initiator- 1   142  sends out a master initiator signal  152  that has a global unique identification (GUID) number of 21 and a sequence number of 1 while the initiator- 2   144  sends out a master initiator signal  154  with a GUID number of 24, and the initiator- 3   146  sends out a master initiator signal  156  with a GUID number of 31. It should be understood that GUID numbers have numerous alphanumeric digits such as letters and numbers, and two digit numbers are utilized here as only as one embodiment and for ease of description. 
     In this exemplary embodiment, the sequence number of 1 shows that the master initiator signal is the first type of signal sent out by the respective initiators. In one embodiment, the sequence number only changes when new information is received from a target. In one embodiment, the GUID numbers of the initiators  142 ,  144 , and  146  are compared, and the initiator with the highest GUID number becomes the master initiator. It should be appreciated that any way of sorting the GUID number to determine the master initiator may be utilized such as for example, making the lowest GUID numbered initiator into the master initiator. Therefore, in this exemplary embodiment, the initiator- 3   146  becomes the master initiator because it has the highest GUID number. 
       FIG. 2B  illustrates the network  140  after a master initiator has been determined in accordance with one embodiment of the present invention. In this embodiment, the initiator- 3   146  has become the master initiator (as described in reference to  FIG. 2A ) and therefore multicasts master initiator signals with the master initiator bit set (e.g., with a real_master flag set). This multicast notifies all devices or components attached to the network that the initiator- 3   146  is the master initiator and all targets, or after startup, new targets, should unicast a signal to the master initiator so the target may be acknowledged as connected to the network. It should be understood that there may be any number of initiators and targets that the master initiator communicates with. By multicasting the real master initiator signal to all of the initiators and targets, all components connected to the network may know that the initiator- 3   146  is the master initiator and also know the status of the network with regard to device connection. It should be understood that the master initiator bit (such as, for example, a real_master flag) may contain any type of data that may notify other components on the network about important network configuration or status information. In this embodiment, the target  148  and the target  150  both respond to the master initiator&#39;s real master initiator signal in the form of a target unicast  158  and a target unicast  160  respectively. 
     The target unicasts  158  and  160  that are utilized to respond to the master initiator may also be known, in one embodiment, as a target identify packet. It should be understood that the target unicasts  158  and  160  may contain any type of information about a target. In one embodiment, both of the target unicasts  158  and  160  include information regarding the address of the targets. In another embodiment, the target receives a master initiator signal with the real_master flag and is instructed to re-register with the master initiator in a set interval of time so the master initiator knows that it is still connected to the network. In one embodiment, the re-register interval time is 10 minutes. If the target does not re-register within the set interval of time, the initiator assumes that the target is no longer connected to the network. Because, the slave initiators also receive the multicast with the re-register interval information, the slave initiators will also assume that the target has disconnected if a target re-registration is not indicated in a master initiator multicast. 
     After the target unicasts  158  and  160  are received, the master initiator resets its own target tables and prepares to transfer target information to the initiators  142  and  144  which in this embodiment are slave initiators. The target tables may contain any type of target information such as, for example, target address, device type, etc. When the slave initiators receive the next multicast from the master initiator and receive the update regarding the re-registration, the slave initiators will also reset their target tables and maintain the target on the target list. 
       FIG. 2C  shows a network  140  where a master initiator is multicasting a master initiator signal in accordance with one embodiment of the present invention. In this embodiment, the initiator- 3   146  is already a master initiator and is multicasting a second sequence (sequence number is 2) master initiator signal to a intiator- 1   142 , a initiator- 2   144 , a target  148 , and a target  150 . The master initiator signal with a sequence number of two is broadcasted after the master initiator has received target information data from the targets as described in reference to  FIG. 2B . Once the target tables containing data and address information about the targets  148  and  150  are updated, the target information for the targets  148  and  150  is incorporated into the master initiator signal. Because data in the original master initiator signal (with a sequence number of 1) is updated, the new master initiator signal is given a sequence number of 2. Therefore, in this manner, the master initiator may broadcast data about the targets  148  and  150  that are connected to the network to the initiators  142  and  144  with one multicast. Such a multicast reduces congestion on the network because extra data being transmitted from a target to all initiators is reduced and one multicast signal from the master initiator notifies all of the nodes on the network about the devices connected to the system. 
       FIG. 3  shows a diagram  200  where one of a plurality of initiators detects a missed master initiator signal in accordance with one embodiment of the present invention. In this embodiment, a master initiator signal  204  with a sequence number of 3 was missed by a slave initiator. The slave initiator knows that it missed the master initiator signal  204  because it successfully received a master initiator signal  202  with a sequence number 2 with new target data, but it received a master initiator signal  206  with a sequence number of 3 without new target data. Because there should be corresponding new target data every time a master initiator signal with a new sequence number is received with the signal, the slave initiator knows that is has missed some sort of new network or target. 
     Therefore, the slave initiator notifies the master initiator that it did not receive the master signal with the sequence number of 3 by way of a query packet. The query packet is described in more detail in reference to  FIG. 12 . When the master initiator receives the query packet, it resends the particular master initiator signal (as determined by the sequence number) that was missed. Therefore, slave initiators may use the sequence number to determine if it has received all of the target data updates from the master initiator. If there is a missing sequence number, the slave initiator knows that it must request a resend of the master initiator signal with the missing sequence number. The missing data is unicasted to only the slave initiator that missed the previously sequenced master initiator signal and a response from the master initiator will also be in the form of a unicast to cut down on excess data traffic over the network. In this way, the present invention may intelligently and powerfully reduce data transmission congestion in a network and therefore increase data transfer efficiencies of needed traffic. 
       FIG. 4  shows a graph  260  where a second initiator is connected to the network after a first initiator has been established as a master initiator in accordance with one embodiment of the present invention. In this embodiment, the first initiator multicasts a first master initiator signal  262  without a master initiator bit set. Because there are no other initiators connected to the network, the first initiator does not detect any other master initiator signals than its own. The first initiator then multicasts a second master initiator signal  264 , and still does not detect other master initiator signals. The first initiator then multicasts a third master initiator signal  266 . Again, the first initiator does not detect the presence of another initiator because no other master initiator signals besides its own is detected. Finally, at this time, the first initiator proclaims itself as the master initiator and multicasts a master initiator signal  268  with a master initiator bit set (as denoted by MI*). In one embodiment, the master initiator bit is a real_initiator flag. It should be appreciated that the first initiator may send out any number of master initiator multicasts before proclaiming itself as the master initiator as long as the first initiator multicasts enough times to be able to accurately determine that there is no other initiators connected to the network. 
     In one embodiment, then a second initiator is attached to the network. As soon as the second initiator is connected, it multicasts out a master initiator signal  270  without a master initiator bit set. At this time, the second initiator detects a master initiator signal  272  from the master initiator that has the master initiator bit set indicating that a master initiator already exists. In this circumstance, the second initiator becomes a slave initiator. 
       FIGS. 5 through 12  disclose exemplary types of packets that may be utilized in peripheral device discovery (PDD). Although some of the functionality of the packets is described in terms of SCSI specification, the packets may be organized differently or have some different components as long as the packets may operate in accordance with the disclosed methods as described in reference to  FIGS. 1–4  and  13 . 
       FIG. 5  shows a discovery protocol data structure  280  containing an IP version 4 address in accordance with one embodiment of the present invention. It should be appreciated that the discovery protocol data structure  280  may also be utilized for other types of addresses such as, for example, an IP version 6 address. In one embodiment, initiators and targets within a network utilizing internet protocol (IP) may effectively use the data transmission congestion reduction method of the present invention to detect peripheral devices without creating undue traffic congestion. In one embodiment, the present invention may be utilized over IP in an automatic fashion where the master initiator would use Dynamic Host Configuration Protocol (DHCP) to obtain local IP information, and pass it on to the other devices on the subnet. In this embodiment, IP addresses may be utilized to share information between local master initiators. The sharing could be via a global master initiator, or by more of a peer to peer protocol. Preferably, a master initiator is selective about what devices are published to the global space, so as to keep down the amount of traffic, and keep many local devices private. 
     In one embodiment of the protocol of the present invention, each of the peripheral discovery protocol (PDP) messages (i.e., master identify, target identify, master ACK, and query) may have a sixteen byte device ID field such as a four byte IP version 4 address  280   b . The field may contain either the four byte IP version 4 address or a sixteen bit IP version 6 address as shown in reference to  FIG. 6  below. In one embodiment, the type of address included may be determined by flag bits right justified in a standard flag field elsewhere in the specific message as shown below: 
                                                0x0001   PDP_IP_0           0x0002   PDP_IP_1                        
Together these bits indicate which version of IP address is included, if any. The following combinations are supported:
 
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 00 
                 Ethernet Address or no assigned IP address 
               
               
                   
                 01 
                 IP version 4 address 
               
               
                   
                 10 
                 IP version 6 address 
               
               
                   
                 11 
                 Future IP version address 
               
               
                   
                   
               
            
           
         
       
     
     In one embodiment, the type of address in the discovery protocol data structure  280  may include data full of zeros  280   a  and an IP version 4 address  280   b . By use of the IP version 4 address  280   b , the targets and initiators in a network may be intelligently identified and located. 
       FIG. 6  shows a discovery protocol data structure  290  containing an IP version 6 address in accordance with one embodiment of the present invention. It should be appreciated that the discovery protocol data structure  290  may also be utilized for other types of addresses such as, for example, an IP version 4 address. In this embodiment, the discovery protocol data structure  290  contains 16 bytes of IP version 6 address. 
       FIG. 7  illustrates a target information field  300  that may be utilized by peripheral device discovery packets in accordance with one embodiment of the present invention. It should be understood that any type or format of field containing target information may be utilized as long as the field is coherent, organized, and contains the needed information in a format acceptable to device discovery protocol. It should also be understood that the target information field  300  may be utilized in any peripheral discovery packet that is utilized by an initiator and/or target. In one embodiment, master identify and target identify packets utilize and/or incorporate the target information field  300 . As discussed above, the master identify packet, in one embodiment, is multicasted and may be utilized to identify the master initiator as an initiator to any receiving targets and supply the initiator&#39;s IP address (or any other type of address depending on the transmission protocol). The target identify packet, in one embodiment, is unicasted from a target to the master initiator in response to a master identify packet and may include device information such as, for example, device type and device address. The target information field may also include data such as Ethernet addresses, IP address, target LUN count, target type, and other information about target capabilities. In one embodiment, the size of the type field  300   a  is fixed to simplify implementation, but the IP address fields may be empty if IP headers are not being used. 
     Additionally, in one embodiment, the target information field  300  contains a GUID which is a number that can serve to identify a target device that is located on the network. The GUID is typically 64 bits with the first 32 bits being assigned to a company making the device and the other 32 bits being assigned to the device. 
     In one embodiment when used within a SCSI storage environment, a type field  300   a  may be the first two bytes of the data that would be returned by a SCSI INQUIRY command to LUN 0 of the target. Its format is defined in the SCSI specification. Another embodiment of a type field is described in further detail in reference to  FIG. 8 . 
     In this embodiment, a LUN count field  300   b  may also be included within the target information field  300 . In one embodiment a LUN count field  300   b  reflects the number of LUNs directly supported by a device. If this is a LUN bridge, there may be additional levels of bridging behind this bridge as defined in the SCSI specification. While SCSI defines an eight byte LUN field, in this embodiment, only two bytes apply at any level, so two bytes may be sufficient to report the total number of LUNs at this level. 
     The target information field  300  may further include a re-registration interval field  300   c . In one embodiment, the re-registration field  300   c  shows the time in seconds until a target should again register with the master initiator (i.e., send a target identify packet to the master initiator). When the target information field  300   c  is part of a target identify message, the re-registration interval field  300   c  contains the number of seconds the target would like to wait until it again registers. In one embodiment, the target is required to re-register with the master initiator to show that it is still part of the network. When the target information field is part of a master identify message, it is the time left until the target will re-register, as determined by the master initiator at the time it creates the message. 
     The target information field  300  may also contain a flag field  300   d  that consists of one or more bit flags that can be utilized to define any number of target information or features. In one embodiment, the flag field  300   d  includes the following exemplary bit flags (additional ones to indicate key target features may be defined in the future): 
                                    0x0001   PDP_IP_0       0x0002   PDP_IP_1       0x0100   PDP_REG_TOGGLE (Used as a one bit sequence number to           distinguish between successive target registrations                    
In addition, the target information field  300  also contains a GUID field  300   e  which, in one embodiment, may be utilized to hold a 64 bit GUID number for a particular device or initiator connected to a network. It should be understood that the GUID field  300   e  may contain any type of identification information for any type of device on a network. By comparison of the GUID numbers, a master initiator may be selected from among a plurality of initiators. In one embodiment, the initiator with the higher (or highest) GUID number becomes the master initiator.
 
     The target information field  300  also contains a target device ID field  300   f  which holds the address for a particular target. It should be understood that the target address field  300   f  may contain any type of target address depending on the type of network and protocol utilized for data transfer and communication such as, for example, Ethernet, TCP/IP, iSCSI, eSCSI, etc. In one embodiment, the target address field  300   f  includes a 16 byte IP address field which holds an IP address for the target in question. If IP addressing information is present, it is placed in a target device 16 byte address field and appropriate flags are set in the flag field. In one embodiment, if the target address field contains an IP address then an IP address is utilized in the target address field  300   f . In one embodiment, if IP0 and IP1 each are a “0”, this indicates that no IP address has been assigned to this target. 
       FIG. 8  shows a device type field  300   a  as utilized within a target field  300  in accordance with one embodiment of the present invention. It should be understood that any type of device information may be utilized within the device type field  300   a  such as, for example, information often utilized with a format as defined in the SCSI specification. The first three bits are the peripheral qualifier, where zero indicates that the logical unit (always LUN 0) is supported, which will always be the case. The Device type may also refer to LUN 0 of the target and have values specified in the following exemplary way: 
                                                0x00   Direct-access device           0x01   Sequential-access device           0x02   Printer device           0x03   Processor device           0x04   Write-once device           0x05   CD-ROM device           0x06   Scanner device           0x07   Optical memory device           0x08   Medium changer device           0x09   Communication device           0x0C   Storage Array Controller           0x0D   Enclosure Services device           0x1f   Unknown or no device type                        
In one embodiment, initially the only device type may be a LUN bridge (type 0x1f), but future native devices (or a bridge with only one device connected) can set the type field to the appropriate value for the attached device.
 
       FIG. 9  shows a master identify packet  340  in accordance with one embodiment of the present invention. In one embodiment, in its role of stimulating new targets (or old targets whose re-registration interval has expired) to unicast back a target identify, the master identify packet can be considered an efficient multicast polling mechanism. In an exemplary embodiment, the master identify packet  340  includes a header field  340   a , a update sequence number  340   b , a reserved field  340   c , a flags field  340   d , a master&#39;s address field  340   e , and a new target information fields  340   f . The master identify packet  340  announces that an initiator believes it is a master, and what its address is (such as, for example IP address). In one embodiment, a sequence number field  340   a  may be incremented every time a new target information is transmitted with the packet. In one embodiment, if there are new targets, the target information fields from their target identify packets may be appended to the master identify packet  340 . It should be understood that the present invention may multicast any number of new targets. If the present invention is utilized in an Ethernet system, up to 44 new targets can be multicast this way in a standard 1.5 KB Ethernet frame. If more than 44 have been added, they can be included in subsequent master identify packets, each with a higher sequence number. In another embodiment, an extension to Ethernet would allow 9 KB packets, or about 180 targets per master initiator 
     In one embodiment, any given group of new targets is only multicast once, since any initiators that miss the multicast will eventually send a query packet to get the full list. The flags field may contain any combination of the following in an exemplary flag system: 
     
       
         
           
               
               
             
               
                   
               
             
            
               
                 0x80 
                 Real Master - Indicates to targets that this Master has won the 
               
               
                   
                 Master Initiator selection process. If not set, targets should 
               
               
                   
                 ignore any information in the message, as this is only a slave 
               
               
                   
                 initiator trying to become a master. 
               
               
                 0x40 
                 Sending All Targets - The Master Initiator may decide to send a 
               
               
                   
                 complete list of targets whether a slave initiator requests a 
               
               
                   
                 complete list or only an update. Any time the full list is sent, 
               
               
                   
                 this flag must be asserted. 
               
               
                 0x20 
                 Bus Reset - Indicates that the bus reset is being asserted. In 
               
               
                   
                 one embodiment, only targets observe it and only for the purpose 
               
               
                   
                 of releasing unit reservations. 
               
               
                 0x08 
                 PDP_IP_MODE 
               
               
                   
                 If set, indicates that this packet is part of the IP based Global 
               
               
                   
                 Discovery protocol, and all MAC address fields in the target 
               
               
                   
                 information block are invalid. 
               
               
                 0x0001 
                 PDP_IP_0 
               
               
                 0x0002 
                 PDP_IP_1 
               
               
                   
                 The type of address information (MAC, IP v. 4, or IP v. 6) con- 
               
               
                   
                 tained in the Master&#39;s Device ID field. 
               
               
                   
               
            
           
         
       
     
       FIG. 10  illustrates a target identify packet  360  in accordance with one embodiment of the present invention. In one embodiment, the target identify packet  360  contains a header  360   a  and a target information  360   b . The target identify packet  360  is sent from a target to a master initiator to register with the initiator in response to a master identify multicast. The target will continue sending target identify packets with each receipt of a master identify from the master initiator with which it is trying to register until that initiator responds with a master ACK packet with matching registration toggle flag. 
     A target which is not currently registered will attempt to register with the first master initiator it sees (master identify packet with Real_Master flag set). It will not respond to master identify packets from any other initiator until master initiator signals (e.g. master identify packets) from the master initiator that the target is trying to register with have been absent for a master_missing period, whether or not it has succeeded at registering with that initiator. It should be understood that the master-missing period may be any length of time which would enable the target to determine that the master initiator is either no longer connected to the network or that the target identify packet was not received by the master initiator. 
       FIG. 11  depicts a master ACK packet  380  in accordance with one embodiment of the present invention. In one embodiment, the master ACK packet  380  includes a header field  380   a , a re-registration interval field  380   b , reserved fields  380   c–e , a flags field  380   f , a default router&#39;s address field  380   h , and a master device ID field  380   g . The master ACK packet  380  is sent from a master initiator to a target in response to a target identify packet and includes the required re-registration interval, some flags, and the master&#39;s address. 
     In one embodiment, the re-registration interval is the larger of the target&#39;s requested re-registration interval and the initiator&#39;s minimum re-registration interval. An exemplary flags field contains the following: 
     
       
         
           
               
               
             
               
                   
               
             
            
               
                 0x1000 
                 PDP_REG_TOGGLE 
               
               
                   
                 Used as a one bit sequence number to distinguish between 
               
               
                   
                 successive target registrations 
               
               
                 0x0001 
                 PDP_IP_0 
               
               
                 0x0002 
                 PDP_IP_1 
               
               
                   
                 The type of address information (MAC, IP v. 4 or IP v. 6) 
               
               
                   
                 contained in the Master&#39;s Device ID field. 
               
               
                   
               
            
           
         
       
     
       FIG. 12  illustrates a query packet  400  in accordance with one embodiment of the present invention. In one embodiment, the query packet  400  includes a header field  400   a , a requested sequence number field  400   b , a reserved space field  400   c , a flags field  400   d  and requesting initiator&#39;s address field  400   e . The query packet  400  is sent from a slave initiator to a master initiator to request a refresh of a slave&#39;s target list. The query packet  400  is often sent when the target realizes that it has missed a target update information due to the reception of a master initiator signal (e.g. master identify packet) with a new sequence number but without updated target information. In one embodiment, a sequence number included within the query packet  400  may be the sequence number of the last sequentially received (with update data) master identify packet. If this query is being sent from a newly detected Master Initiator, then a complete dump of the target information is requested by setting the PDP_REQ_ALL_TARGETS flag. 
     A query packet may also be used to request a bus reset, in which case the master initiator does not return any target information. Instead, the master initiator issues a bus reset in the next several master identify packets it sends. Exemplary flags which may be included in query packets are as follows: 
     
       
         
           
               
               
             
               
                   
               
             
            
               
                 0x4000 
                 PDP_REQ_ALL_TARGETS - The slave initiator requests a 
               
               
                   
                 complete dump of the Master Initiator&#39;s known target list. 
               
               
                 0x2000 
                 PDP_REQ_BUS_RESET - Request a bus reset. 
               
               
                 0x0001 
                 PDP_IP_0 
               
               
                 0x0002 
                 PDP_IP_1 
               
               
                   
                 The type of address information (MAC, IP v. 4, or IP v. 6) 
               
               
                   
                 contained in the Requesting Initiator&#39;s Device ID field. 
               
               
                   
               
            
           
         
       
     
       FIG. 13  shows a flowchart defining a method for determining a master initiator and obtaining target information in a network in accordance to one embodiment of the present invention. It should be understood that the processes depicted in the flowchart  500  may be in a program instruction form written on any type of computer readable media. For instance, the program instructions can be in the form of software code developed using any suitable type of programming language. For completeness, the process flow of  FIG. 13  will illustrate an exemplary process whereby a master initiator is selected and peripheral devices are detected on a network while at the same time reducing data congestion normally and decreasing device detection time associated with such a process. 
     In operation  502 , a multicast signal is broadcasted without a master initiator bit set. It should be understood that a signal may be broadcasted in any way that allows the nodes in a network to receive the signal. It should also be understood that any mechanism similar to not setting a master initiator bit may be utilized which may notify receivers of the master initiator signals that the initiator is or is not a master initiator. In this embodiment, a master initiator bit such as a real_initiator flag is not set which shows that the signal is not from a master initiator. 
     After operation  502 , the method proceeds to operation  504  where it is determined if there is an additional multicast signal from an additional initiator. In this operation, an initiator may monitor the network and look for multicasts from another initiator. 
     If operation  504  determines that there is no additional multicast signal from an additional initiator, the method moves operation  508  where an initiator broadcasting the multicast signal becomes the master initiator by default. In this operation, the master initiator starts to multicast master initiator signals with the master initiator bit set. In one embodiment, a real_initiator flag is set so other initiators and targets on the network know about the existence of a master initiator. In one embodiment, the master initiator broadcasts a master initiator multicast signal once a second. 
     Then, operation  510  receives response(s) to multicast signal from slave initiator(s) and/or target(s). Once the master initiator signal with the master initiator bit that is set is multicasted on the network, targets will know about the master initiator and will start to send target identification packets to the master initiator. 
     After operation  510 , the method advances to operation  512  where response(s) are analyzed to determine device(s) and initiator(s) connected to a system and responses are sent. In this operation, the master initiator examines any target identification packets received from targets connected to the network. In addition, once the identification packets are received, the master initiator sends an acknowledgement signal to the targets. It should be appreciated that any type of acknowledgement signal may be utilized to inform the target of information such as, for example, the master initiator address, re-registration interval, etc. In one embodiment, the acknowledgement signal consists of a master ACK packet which includes the required re-registration interval, some flags, and the master&#39;s address. 
     If a query request is received from one or more slave initiators because certain target data was not receive, the master initiator determines what information the slave initiator is missing. 
     After operation  512 , the method moves to operation  514  where device information obtained from previous responses to multicast signals are incorporated into a next multicast signal. In this operation, the device information from targets obtained after the last update of the master initiator signal is inputted into the next multicast signal that is outputted by the master initiator. By this updating, the master initiator may inform the network of any devices that was connected after the target update. In addition, if an expected re-registration of a particular target is not included in the update, this lack of information intelligently conveys that the particular target is no longer part of the network. 
     In addition, the master initiator may also receive query requests from the slave initiators. If a slave initiator receives the latest master initiator signal and finds that it has missed receiving the master initiator signal previously sent, the slave initiator sends a query request to the master initiator so the master initiator can unicast the missing data to the slave initiator. Therefore, the peripheral device discovery system may intelligently update the state of the devices attached to the network in a coherent, organized, and centralized fashion without creating congestion on the network. 
     After operation  514 , the method progresses to operation  515  where it is determined if there is a master initiator signal from an additional initiator. If there is a master initiator signal from the additional initiator, then the method moves to operation  516  which is described below. If there is no master initiator signal from the additional initiator, the method repeats operations  508 ,  510 ,  512 ,  514 , and  515  until the master initiator is replaced by a new master initiator which may occur in, for example, situations where two networks with two master initiators are connected to become one network. In one embodiment, if two networks are connected, the two master initiators of the two networks compare their GUID numbers and the initiator with the highest GUID number becomes the new master initiator of the combined network. 
     If operation  504  finds that there is an additional multicast signal from an additional initiator, the method advances to operation  506  where it is determined if there is a master initiator multicast signal from the additional initiator. In this operation, the master initiator signal received is analyzed to ascertain if a master initiator bit is set. A master initiator signal with a master initiator that is set is indicative that a master initiator already exists. In one embodiment, a bit such as a real_initiator flag may be utilized to show that there is already a master initiator. 
     If operation  506  determines that a master initiator bit is set in the additional master initiator signal then the method advances to operation  520  where the first initiator that broadcasted the multicast signal in operation  502  becomes a slave initiator and the additional initiator becomes the master initiator. 
     If operation  506  determines that the additional multicast signal is not from a master initiator then the method progresses to operation  516  which examines the additional signal from the additional initiator to determine a GUID number of the additional initiator. In this operation, the additional master initiator signal is examined to find a GUID number of the additional initiator for comparison later with a GUID number of the first initiator that sent out the multicast signal in operation  502 . 
     After operation  516 , the method advances to operation  518  where a determination is made if the GUID number of the additional initiator is greater than the GUID number from the multicast signal(s) broadcasted by the first initiator in operation  502 . This operation shows a selection process that is made between multiple initiators to determine which initiator becomes a master initiator. It should be understood that any way of determining the master initiator may be utilized as long as the determination is made on a coherent, intelligent, and logical basis. In one embodiment, the determination is made by comparing GUID numbers and making the initiator with the highest GUID number the master initiator. 
     If operation  518  determines that the GUID number from the multicast signal is greater than the GUID number from the additional master initiator signal then the method moves to operation  508  and completes operation  510 ,  512 , and  514 . 
     If operation  518  determines that the additional GUID number is greater than the GUID number from the multicast signal, the method advances to operation  520  where the original initiator stops multicasting and becomes a slave initiator while the additional initiator becomes the master initiator. In another embodiment, the original initiator becomes a slave initiator, and if it has not received a master initiator signal for a certain period of time, it may automatically assume the functionality of a master initiator. 
     The present invention may be implemented using any type of integrated circuit logic, state machines, or software driven computer-implemented operations. By way of example, a hardware description language (HDL) based design and synthesis program may be used to design the silicon-level circuitry necessary to appropriately perform the data and control operations in accordance with one embodiment of the present invention. By way of example, a VHDL® hardware description language available from IEEE of New York, N.Y. may be used to design an appropriate silicon-level layout. Although any suitable design tool may be used, another layout tool may include a hardware description language “Verilog®” tool available from Cadence Design Systems, Inc. of Santa Clara, Calif. 
     The invention may employ various computer-implemented operations involving data stored in computer systems. These operations are those requiring physical manipulation of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. Further, the manipulations performed are often referred to in terms, such as producing, identifying, determining, or comparing. 
     Any of the operations described herein that form part of the invention are useful machine operations. The invention also relates to a device or an apparatus for performing these operations. The apparatus may be specially constructed for the required purposes, or it may be a general purpose computer selectively activated or configured by a computer program stored in the computer. In particular, various general purpose machines may be used with computer programs written in accordance with the teachings herein, or it may be more convenient to construct a more specialized apparatus to perform the required operations. 
     Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.