Abstract:
A LAN terminal equipment comprises a plurality of slots, each capable of accommodating a LAN control board, at least one ROM socket capable of holding a MAC ROM, and an input/output control unit. The input/output control unit determines a correspondence between the LAN control board and the MAC ROM, thereby ensuring the uniqueness of MAC address and also making a primary/spare dual configuration possible.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a division of application Ser. No. 08/588,008 filed Jan. 17, 1996, now U.S. Pat. No. 6,058,446. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a network terminal equipment wherein a plurality of communication control units can be installed in one terminal equipment, such as a workstation or the like, and more particularly to network terminal equipment, such as a workstation, that can accommodate a plurality of communication control units to permit connection by a plurality of protocols and/or to realize a dual configuration of the communication control unit. 
     2. Description of the Related Art 
     Each terminal equipment connected to a local area network (LAN), such as an Ethernet or an FDDI (fiber distributed data interface) network, is assigned a medium access control (MAC) address for uniquely identifying the terminal equipment in the network. 
     Conventionally, the MAC address has been assigned to each individual LAN control unit that is plugged into a slot in a workstation and that controls transmission and reception to and from LAN transmission channels. The MAC address is written in a ROM or like memory which is mounted on the LAN control unit. The reason that the MAC address is stored in a ROM or like memory is to prevent accidental alteration of the MAC address that could lead to a malfunction in the network. 
     If the LAN control unit has failed, it has to be replaced with a new unit. Since the same MAC address as that of the failed unit must be assigned to the new unit, the ROM holding the MAC address (hereinafter referred to as the MAC ROM) has to be removed from the failed unit and mounted on the new unit. 
     Previously, it has sometimes practiced to install the MAC ROM in the workstation itself, not on the LAN control unit. In such cases, if the LAN control unit has failed, it is simply replaced with a new unit. 
     If the known method described above is to be adopted for a workstation capable of accommodating a plurality of LAN control units in its slots to permit connection by a plurality of protocols and/or to realize a primary/spare dual configuration with two LAN control units, the workstation itself must be constructed to accommodate a plurality of MAC ROMs to correspond with the plurality of LAN control units. Furthermore, the plurality of MAC ROMs must have a one-to-one correspondence with the plurality of LAN control units to ensure the uniqueness of the MAC address. Moreover, when two LAN control units are used in a dual configuration, one as the primary and the other as the spare, the two control units must be constructed to be able to access a common MAC ROM, while disabling or prohibiting the operation of the spare LAN control unit by some means in order to ensure the uniqueness. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a construction that facilitates the replacement of communication control units for a network terminal equipment capable of accommodating a plurality of communication control units. 
     It is another object of the present invention to provide means for ensuring the uniqueness of a MAC address for a network terminal equipment capable of accommodating a plurality of communication control units. 
     According to the present invention, there is provided a network terminal equipment comprising: a plurality of slots each capable of accommodating a communication control unit; at least one socket for holding therein a memory device where fixed data is stored that is used by each of the plurality of communication control units installed in the slots; and an input/output control unit for determining a correspondence between the communication control units installed in the slots and the memory device mounted in the socket. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a LAN terminal equipment according to a first embodiment of the present invention; 
     FIG. 2 is a diagram showing the details of an I/O control unit  32  in FIG. 1; 
     FIG. 3 is a block diagram of a LAN terminal equipment according to a second embodiment of the present invention; 
     FIG. 4 is a diagram showing the details of an I/O control unit  32  in FIG. 3; 
     FIG. 5 is a memory mapping diagram for the LAN terminal equipment of FIG. 3; 
     FIG. 6 is a diagram for explaining primary/spare switching in the LAN terminal equipment of FIG. 3; 
     FIG. 7 is a block diagram of a LAN terminal equipment according to a third embodiment of the present invention; 
     FIG. 8 is a diagram showing the details of an I/O control unit  32  in FIG. 7; and 
     FIG. 9 is a diagram showing the details of a LAN control board in FIG.  7 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a block diagram of a LAN terminal equipment according to a first embodiment of the present invention. As an example, the LAN terminal equipment  10  shown here includes slots  12 ,  14 , and  16  with slot IDs 00, 01, and 02, and ROM sockets  26 ,  28 , and  30  with ROM IDs 00, 01, and 02. When a LAN control board inserted in a slot whose slot ID is i (=00, 01, 02, . . . ) tries to access a MAC ROM, an I/O control unit  32 , as conceptually shown in FIG. 1, controls input/output channels so that the LAN control board accesses the MAC ROM mounted in a ROM socket whose ROM ID is i. 
     In the example shown in FIG. 1, the slot  12  of slot ID 00 is mounted with a SCSI (small computer systems interface) board  18  which does not require a MAC ROM; therefore, no MAC ROM is mounted in the ROM socket  26  whose ROM ID is 00. On the other hand, the slot  14  of slot ID 01 is mounted with a LAN control board  20 , so that a MAC ROM  34  for the LAN control board  20  is mounted in the ROM socket  28  whose ROM ID is 01. Likewise, the slot  16  of slot ID 02 is mounted with a LAN control board  22 , so that a MAC ROM  36  for the LAN control board  22  is mounted in the ROM socket  30  whose ROM ID is 02. 
     The function of the I/O control unit  32  conceptually shown in FIG. 1 is implemented, for example, by making connections as shown in FIG.  2 . The MAC ROMs mounted in the ROM sockets  26 ,  28 , and  30  in FIG. 2 are mapped in an address space in decreasing order of their ROM IDs. When the board installed in each slot accesses its associated MAC ROM, some of the bits constituting the address output from the board are replaced by the value of the slot ID of that slot. 
     In the LAN terminal equipment shown in FIG. 1, since the slots have a one-to-one correspondence with the MAC ROM sockets, the uniqueness of the MAC address is retained. Furthermore, since the MAC ROMs are installed in the LAN terminal equipment  10  itself, the MAC ROMs need not be replaced when replacing the LAN control boards. However, there is a possibility that an unused address space and ROM socket may occur, as indicated by ROM socket  26  shown in FIG.  1 . 
     FIG. 3 is a block diagram of a LAN terminal equipment according to a second embodiment of the present invention. The elements corresponding to those shown in FIG. 1 are designated by like reference numerals. The LAN terminal equipment shown in FIG. 3 includes memories  40 ,  42 , and  44  for storing the values of the ROM IDs for identifying the MAC ROMs provided in corresponding relationship to and for use by the respective boards  18 ,  20 , and  22  installed in the slots  12 ,  14 , and  16 , and memories  46  and  48 , provided in corresponding relationship to the ROM sockets  28  and  30 , for storing the values of the slot IDs for identifying the slot IDs of the slots in which the boards that use the respective MAC ROMs are installed. In FIG. 3, the memories  40 ,  42 , and  44  are shown as if they are mounted on the respective boards, but it will be appreciated that these memories can be mounted inside the terminal equipment  10  itself. 
     Suitable values are stored as environment settings in the memories  40 ,  42 ,  44 ,  46 , and  48  by an operator&#39;s operation, etc. In the example shown in FIG. 3, as in the example of FIG. 1, the SCSI board  18  and the LAN control boards  20  and  22  are installed in the slots  12 ,  14 , and  16 , respectively. Since the SCSI board  18  does not require a MAC ROM, a meaningless value “20” is stored as a ROM ID value in its associated memory  40 . Since the LAN control board  20  uses the MAC ROM  34 , a ROM ID value “ 00 ” is stored in the memory  42 . Likewise, since the LAN control board  22  uses the MAC ROM  36 , a ROM ID value “01” is stored in the memory  44 . With this setting, the MAC ROM  34  is referred to by the LAN control board  20 , while the MAC ROM  36  is referred to by the LAN control board  22 . In the LAN terminal equipment of FIG. 3, an unused address space or an unused ROM socket does not occur. 
     The memories  46  and  48  are provided for the MAC ROMs in order to ensure the uniqueness of the MAC address. As an example, consider a case where the LAN control boards  20  and  22  are erroneously set to use the same MAC ROM  34 . Even in such a case, only the LAN control board installed in the slot identified by the contents of the memory  46  is allowed to access the MAC ROM  34 . When an attempt to access one or the other of the MAC ROMs is detected, the I/O control unit  32  compares the slot ID of the slot where the board that made the attempt is installed with the slot ID stored in corresponding relationship to the MAC ROM to which an access was attempted; when they match, the access is allowed, but when they do not match, the access is interpreted as an abnormal operation and an interrupt is issued to the CPUs in the LAN control board side and the terminal equipment  10  side. 
     FIG. 4 shows an example of a detailed configuration of the I/o control unit  32  for implementing the above function. The MAC ROMs,  34  and  36 , and the memories,  46  and  48 , for storing their associated slot IDs, are mapped in an address space in alternate fashion as shown in FIG.  5 . An adder  50  adds  6  to an address used to access the MAC ROM and thereby generates an address for reading the slot ID. The slot ID thus read out is compared in a comparator  52  with the slot ID of the current slot. If the two slot IDs do not match, an interrupt generating circuit  54  causes an interrupt to the CPUs on the LAN control board and in the terminal equipment  10 . At the same time, one input of an OR gate  56  is driven low. When a LAN control board is already installed in the slot, the other input of the OR gate  56  is low, so that the output of the OR gate is low, which causes an AND gate  58  to close. As a result, a buffer  60  provided in an outgoing path from the LAN control board to the terminal equipment does not conduct even when a read/write signal is output from the LAN control board, thus preventing the malfunctioning of the LAN control board from causing an adverse effect on the terminal equipment. 
     If the slot ID of the slot matches the slot ID read out of the terminal equipment as a result of the comparison in the comparator  52 , the output of the OR gate  56  goes high, and the AND gate  58  is opened. This allows data to flow from the LAN control board to the terminal equipment. If the board installed in the slot is not a LAN control board, the output of the OR gate  56  is high regardless of the level of the other input thereof, so that data flow from the board to the terminal equipment is allowed. 
     In the LAN terminal equipment described with reference to FIGS. 3 to  5 , the ROM IDs for identifying the MAC ROMs used are stored for the respective LAN control boards installed, as previously described. For the MAC ROMs also, the slot IDs for identifying their associated LAN control boards are stored. This ensures the uniqueness of the MAC address. 
     In the LAN terminal equipment of FIG. 3, if the ROM IDs of the LAN control boards  20  and  22  installed in the slots of slot IDs “01” and “02” are both set to “00” and the slot ID of the MAC ROM whose ROM ID is “00” is set to “01”, as shown in FIG. 6, the LAN terminal equipment can be constructed in a dual LAN control board configuration with the LAN control board  20  as a primary board and the LAN control board  22  as a spare. In the event of failure of the primary LAN control board, the contents of the memory  46  is altered from “01” to “02” by automatic means or by a manual operation by the operator, thereby accomplishing the switching from the primary to the spare board. 
     In the dual-configuration LAN terminal equipment described with reference to FIG. 6, since the operation of the LAN control board designated as the spare is initially disabled, when making the primary-to-spare switching it is necessary to terminate the current communication session first and then initiate a new session after the switching has been made. 
     FIG. 7 shows a LAN terminal equipment capable of accomplishing the primary-to-spare switching at high speed, according to a third embodiment of the present invention. In FIG. 7, the ROM IDs of the LAN control boards  20  and  22  are both set to “00, and a slot ID for identifying a slot is not stored for the MAC ROM identified by the ROM ID “00”. Therefore, the LAN control boards  20  and  22  perform the same operation concurrently. The LAN control board  20  on the primary line is set ON and the LAN control board  22  on the spare line is set OFF by a select signal given from the terminal equipment  10  in setting the environment. For the LAN control board  20  which is set ON, outputs to the network and the terminal equipment are enabled, while for the LAN control board  22  which is set OFF, outputs to the network and the terminal equipment are disabled. 
     FIG. 8 shows an example of the I/O control unit  32  for implementing the above control. The difference from FIG. 4 is that the OR gate  56  is supplied with a select signal from the terminal equipment instead of the output of the comparator  52  in FIG.  4 . The select signal is also supplied to the LAN control board installed in the slot. When a LAN control board is already installed in the slot, and when the select signal supplied from the terminal equipment is low (OFF), the output of the OR gate  56  is low, and data flow from the LAN control board to the terminal equipment is disallowed. 
     FIG. 9 shows an example of the LAN control board for implementing the above control. A transmitted signal from a transmission channel control circuit  62  is passed through a three-state buffer  64  and a line driver  66  and output on the LAN transmission channel. A received signal from the LAN transmission channel is directed to the transmission channel control circuit  62  via a line driver  68 . 
     The select signal supplied from the terminal equipment via the I/O control unit is passed through an inverter  70  and given to the three-state buffer  64  as a control signal. When the select signal is OFF (low), the output of the three-state buffer  64  is put in a high impedance state, thus prohibiting the transmission of the transmitted signal to the LAN transmission channel.