Abstract:
Handshaking is performed between a first host system and a second host system. First handshaking is performed between a host module within the first host system and a first transceiver within the first host system. The first handshaking includes passing from the first transceiver to the host module dummy information about the second host system. Second handshaking is performed between a second transceiver within the second host system and the first transceiver. The second handshaking includes obtaining, by the first transceiver from the second transceiver, first information about the second host system. Handshaking between the host module and the first transceiver is restarted. This includes passing from the first transceiver to the host module the first information about the second host system. The first information replaces the dummy information passed from the first transceiver to the host module during the first handshaking.

Description:
BACKGROUND  
         [0001]    The present invention pertains to networking systems and pertains particularly to multiple protocol handshaking between systems.  
           [0002]    When two host systems are communicating via a cable, each host system typically includes a transceiver that converts electrical signals received from the host system to signals that are suitable for the cable. Each transceiver also converts signals received from the cable to electrical signals usable by the host system. Generally, the transceiver can convert the signals one bit at a time or the transceiver can encode/decode the signals. In addition, the transceiver can be an electro-optic transceiver (which converts electrical signals to optical signals and vice versa) or an electrical transceiver (which converts electrical signals of one format to another format and vice versa). Typically, the “one bit at a time” transceiver allows handshaking to occur directly between two host systems and the “encoding/decoding” transceiver does not. Typically, the electro-optic transceiver allows the use of a receiver status signal to be sent when a cable connection is detected and the electrical transceiver does not.  
           [0003]    For example, in 1000BASE-X systems transceivers typically perform the conversion one bit at a time. The transceiver can be electro-optical or electrical in nature. When the transceiver is electro-optical, the two communicating systems are connected with a fiber optic cable. The electrooptic transceiver converts each bit in the electrical signal received from the host system to a bit in an optical signal to be sent across the fiber optic cable. Each electro-optic transceiver also converts optical signals received from the fiber optic cable to electrical signals used by the host system. When an electro-optic transceiver first receives light from a source at the other end of the fiber optic cable, the electro-optic transceiver updates its receiver status signal. When both electro-optic transceivers forward to their respective host systems a receiver status signal that indicates the reception of optical power the two host systems perform their handshaking protocol to establish a link.  
           [0004]    Whenever a fiber optic cable link between two electro-optic transceivers is broken, each electro-optic transceiver changes its receiver status signal to indicate optical power is no longer being received. When the fiber optic cable link between two electro-optic transceivers is restored, each electro-optic transceiver changes its receiver status signal to indicate the reception of optical power and the systems again perform handshaking.  
           [0005]    When two host systems are communicating via electrical (e.g., copper-based) cables, each host system typically includes an electrical transceiver that converts electrical signals in a format used by the host system to electrical signals in a format appropriate to be sent across the electrical cables. Each electrical transceiver also converts electrical signals received from the electrical cables to electrical signals in a format used by the host system. A typical 1000BASE-X transceiver converts data one bit at a time. Typically, in systems based on electrical cable, there is nothing equivalent to a receiver status signal that indicates the reception of optical power. This results in an incompatibility between protocols used between host systems using two electrical transceivers to exchange information over electrical cables and protocols used between host systems using two electro-optic transceivers to exchange information over a fiber optic cable.  
           [0006]    If 1000BASE-X host systems are communicating and non-1000BASE-X transceivers that encode/decode data are used, then direct handshaking between the host systems is not possible. For example, if 1000BASE-T electrical transceivers are used in two communicating 100OBASE-X systems, the data from a host system is encoded by the 1000BASE-T transceiver and the special handshaking codes sent by the system are not passed through the 1000BASE-T transceiver. In addition, as in the case when a 1000BASE-X electrical transceiver is used, the receiver status signal does not exist when the 1000BASE-T electrical transceiver is used in the system.  
           [0007]    For further information, see, for example, the IEEE Std. 802.3, 2000 Edition, Part 3: Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specifications, Clause 36 and Clause 37, in which pertinent parts of the 1000BASE-X protocol are discussed, and Clause 40 and Clause 28, in which pertinent parts of the 1000BASE-T protocol are discussed.  
         SUMMARY OF THE INVENTION  
         [0008]    In accordance with the preferred embodiment of the present invention, handshaking is performed between a first host system and a second host system. First handshaking is performed between a host module within the first host system and a first transceiver within the first host system. The first handshaking includes passing from the first transceiver to the host module dummy information about the second host system. Second handshaking is performed between a second transceiver within the second host system and the first transceiver. The second handshaking includes obtaining, by the first transceiver from the second transceiver, first information about the second host system. Handshaking between the host module and the first transceiver is restarted. This includes passing from the first transceiver to the host module the first information about the second host system. The first information replaces the dummy information passed from the first transceiver to the host module during the first handshaking. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a simplified block diagram illustrating handshaking between two host systems adapted to electro-optic transmissions when each host system utilizes an electro-optic transceiver in accordance with the prior art.  
         [0010]    [0010]FIG. 2 is a simplified block diagram illustrating failure of handshaking between two host systems adapted to electro-optic transmissions when each host system utilizes an electrical transceiver.  
         [0011]    [0011]FIG. 3 is a flowchart illustrating operation of an electrical transceiver in order to allow handshaking between two host systems adapted to electro-optic transmissions in accordance with a preferred embodiment of the present invention.  
         [0012]    [0012]FIG. 4 is a simplified block diagram illustrating handshaking between two host systems adapted to electro-optic transmissions when each host system utilizes an electrical transceiver in accordance with a preferred embodiment of the present invention.  
         [0013]    [0013]FIG. 5 is a simplified block diagram illustrating handshaking between two host systems adapted to electro-optic transmissions when each host system utilizes an electrical transceiver and a first handshaking is not performed in accordance with a preferred embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]    [0014]FIG. 1 shows a host  11  that includes an electro-optic transceiver  15  and a host module  12  adapted to electro-optic transmissions. A data path  13  represents data transmissions between host module  12  and electro-optic transceiver  15 . A receiver status signal  14  represents transmission of receiver status from electro-optic transceiver  15  to host module  12 . For example, host module  12  and electro-optic transceiver  15  are adapted to use the 1000 BASE-X protocol.  
         [0015]    A host  21  includes an electro-optic transceiver  25  and a host module  22  adapted to electro-optic transmissions. A data path  23  represents data transmissions between host module  22  and electro-optic transceiver  25 . A receiver status signal  24  represents transmission of receiver status from electro-optic transceiver  25  to host module  22 . For example, host module  22  and electro-optic transceiver  25  are adapted to use the 1000 BASE-X protocol.  
         [0016]    Electro-optic transceiver  15  and electro-optic transceiver  25  are connected via a fiber optic cable link  10 . When electro-optic transceiver  15  first detects light from fiber optic cable link  10 , electro-optic transceiver  15  transmits the receiver status signal  14  to host module  12  indicating reception of optical power. Likewise, when electro-optic transceiver  25  first detects light from fiber optic cable link  10 , electro-optic transceiver  25  transmits the receiver status signal  24  to host module  22  indicating reception of optical power. When each host module receives a receiver status transmission, handshaking  20  is performed between host module  12  and host module  22 . Electro-optic transceiver  15  and electro-optic transceiver  25  serve as conduits of information during handshaking  20 .  
         [0017]    [0017]FIG. 2 illustrates what occurs when fiber optic cable link  10  is replaced with an electrical cable link  33 , when within host  11 , electro-optic transceiver  15  is replaced by an electrical transceiver  31 , and when within host  21 , electro-optic transceiver  25  is replaced by an electrical transceiver  32 . In electrical cable base systems there is nothing equivalent to a receiver status signal that indicates the reception of optical power. Therefore, electrical transceiver  31  never transmits a receiver status transmission to host module  12  indicating reception of optical power. Likewise, electrical transceiver  32  never transmits a receiver status transmission to host module  22  indicating reception of optical power. Handshaking  34 , between host module  12  and host module  22  is never started and communication between host  11  and host  21  does not take place.  
         [0018]    In the preferred embodiment of the present invention, the protocol under which a standard electrical transceiver operates is modified to allow for communication between host  11  and host  21  over an electrical cable link.  
         [0019]    For example, FIG. 3 shows a flowchart illustrating operation of an electrical transceiver that allows for communication between host  11  and host  21  over an electrical cable link. In a preferred embodiment, the operation uses a three-step handshaking process that establishes a link between two BASE-X hosts with BASE-T transceivers while maintaining the receiver status signal functionality. Modifications are made only to the electrical transceivers to accommodate the new handshaking process. The host modules remain unchanged and thus are unaware that they are performing handshaking across an electrical link rather than a fiber optic link.  
         [0020]    In a block  41  handshaking begins. In a block  42 , handshaking is started between the transceiver and the host. This is illustrated in FIG. 4. FIG. 4 shows an electrical transceiver  51  placed within host  11 , and an electrical transceiver  52  placed within host  21 . Electrical transceiver  51  and electrical transceiver  52  are connected via an electrical cable link  53 .  
         [0021]    The starting of handshaking between the transceiver and the host is represented by handshaking  54  between host module  12  and an electrical transceiver  51 . Handshaking  54  is initialized by electrical transceiver  51  transmitting the receiver status signal  14  to host module  12  indicating reception of optical power. This is a dummy transmission since electrical transceiver  51  is not connected to an optical fiber cable and does not detect reception of optical power.  
         [0022]    The use of a dummy transmission allows initial initiation of a link and allows restoration of a link when recovering from a signal loss in an established link (e.g., caused by a cable being unplugged). After a predetermined amount of time after loss of signal, each electrical transceiver transmits a dummy receiver status signal  14  to its host indicating reception of optical power. The transmission of the dummy receiver status signal  14  causes the host module to be ready to begin handshaking. This allows handshaking  54  to begin between host module  12  and the electrical transceiver  51  after a link is disrupted. Further handshaking, however, will not be able to proceed until the link is restored.  
         [0023]    In the preferred embodiment of the present invention, the functionality of the receiver status signal is maintained by the use of a single pulse with pre-determined width (i.e., the pre-determined amount of time after loss of signal). In the prior art, when an electro-optic transceiver is used, the pulse width is not pre-determined; rather, the pulse width is determined by the length of time between when optical power is lost and when optical power is once again sent into the electro-optic transceiver. In the preferred embodiment of the present invention, when an electrical transceiver is used, the receiver status signal will change to alert the host system that the link has been broken. After a pre-determined amount of time, the status signal is returned to its “link-established” state and the host module is thereby informed that the handshaking process must resume. The pulse width is determined by the length of time required by a given host module to react to the change in receiver status. Individual host modules might have different requirements, so in the preferred embodiment, the pulse width is programmable within the electrical transceiver.  
         [0024]    During handshaking  54 , electrical transceiver  51  obtains information from host module  12  that electrical transceiver  51  will need to perform handshaking with electrical transceiver  52 . For example, when host module  12  and host module  22  operate in accordance with the  1000  Base-X protocol, electrical transceiver  51  obtains from host module  12  the FD (full duplex), HD (half duplex), PS1 (PAUSE), PS2 (ASM_DIR), RF (remote fault) bits from host module  12 . These bits are passed in a word (or collection of bits) called a “configuration register base page” or “config_reg base page”. For example, electrical transceiver  51  passes to host module  12  dummy values for these bits pertaining to host module  22  in order to perform handshaking  54 .  
         [0025]    After obtaining from host module  12  the information which electrical transceiver  51  will need to perform handshaking with electrical transceiver  52 , electrical transceiver suspends handshaking with host module  12 . For example, when host module  12  operates in accordance with the 1000 Base-X protocol, electrical transceiver  52  holds host module  12  in the idle_detect state while further handshaking (auto-negotiation) proceeds.  
         [0026]    In a block  43  (shown in FIG. 3) handshaking between transceivers is performed. This is represented in FIG. 4 by handshaking  55 . During the handshaking between the electrical transceivers, the transceivers agree on settings for optimal communication. In addition, the electrical transceivers share the information that they obtained from their respective host modules during the handshaking performed in block  42 . For example, when the host modules operate in accordance with the 1000 Base-X protocol, the information obtained from the host modules is composed of the FD (full duplex), HD (half duplex), PS1 (PAUSE), PS2 (ASM_DIR), RF (remote fault) bits.  
         [0027]    For example, when electrical transceiver  51  and electrical transceiver  52  operate in accordance with the 1000 Base-T protocol, the values of the FD, HD, PS1 and PS2 bits are used as the “local” values during Clause 28 autonegotiation (handshaking  55 ). PS1 and PS2 are sent in bits of the clause 28 auto-negotiation “page 1”. FD (Clause 28 1000FDX) and HD (Clause 28 1000HDX) are sent in bits of the clause 28 auto-negotiation “base pages/next pages”. Clause 37 logic does not implement next pages, which are only used in clause 28 logic for 1000Base-T. Conflicts in the pause encoding and/or the duplex status are resolved as in IEEE802.3:2000, annex  28 B, and the resulting values of these 4 bits are carried to the next auto-negotiation. The Clause 28 auto-negotiation also determines which module is the master and which is the slave.  
         [0028]    Once handshaking  55  is completed, in a block  44  (shown in FIG. 3), the electrical transceivers restart the traditional electro-optical handshaking with the host modules. This is represented in FIG. 4 by handshaking  56 . Handshaking  54  is terminated. In handshaking  56 , electrical transceiver  51  passes the actual information regarding host module  22  that electrical transceiver  51  received during handshaking  55 . Electrical transceiver  51  allows the handshaking with host module  22  to complete, thereby establishing the link with common settings at each end of the electrical cable link  53 .  
         [0029]    For example, when host module  12  and host module  22  operate in accordance with the 1000 Base-X protocol, during handshaking  56 , the config_reg base page electrical transceiver  51  receives from host module  12  is checked against the config_reg base page which electrical transceiver  51  received from host module  12  during handshaking  54 . If no difference is detected, then the bit values resulting from the resolution of handshaking  56  are placed into bits of a register in the host module and data is sent and received according to the protocol specified by these bits.  
         [0030]    If the config_reg base page which electrical transceiver  51  received from host module  12  during handshaking  56  is different than the config_reg base page which electrical transceiver  51  received from host module  12  during handshaking  54 , electrical transceiver  51  will force the entire handshaking process to start again, beginning with handshaking  54 .  
         [0031]    In an alternative embodiment of the present invention, handshaking  54  can be disabled provided the electrical transceivers can obtain necessary information to perform handshaking  55  and handshaking  56  without performing handshaking  54 . This is illustrated in FIG. 5, where handshaking  54  is eliminated from the initialization process.  
         [0032]    For example, when host module  12  and host module  22  operate in accordance with the 1000 Base-X protocol, during handshaking  55  (e.g., a clause 28 auto-negotiation), each electrical transceiver obtains the local values for PS1, PS2, FD and HD from values previously stored in registers within the electrical transceiver.  
         [0033]    When handshaking  54  is disabled, a preferred embodiment allows the option to set RX-LOS to be the opposite of link_status. In this case, the receiver status can reflect the actual status of the link.  
         [0034]    The present invention provides for assurance of link establishment when electrical transceivers are used in a system that was originally designed for electro-optic transceivers an when encoding/decoding transceivers are used in a system that was originally designed for transceivers that pass data bit for bit. In addition, improved system performance and integrity is achieved by providing expected acknowledgment of signal loss and acquisition to the system when electrical transceivers are used in a system that was originally designed for electrooptic transceivers.  
         [0035]    The foregoing discussion discloses and describes merely exemplary methods and embodiments of the present invention. As will be understood by those familiar with the art, the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.