PATENT DOCUMENT

Abstract:
Support for a mixed network environment is provided which can contain multiple isochronous and/or non-isochronous LAN protocols such as Isochronous-Ethernet. Ethernet, isochronous-token ring, token ring, other isochronous-LAN or other LAN Systems. Support for a mixed environment includes a protocol detection mechanism which is embodied in a handshaking scheme. This handshaking scheme determines the signalling capability at the end points of the link and implements the correct protocol. This enables isochronous nodes and hubs to automatically detect the presence of Ethernet, token ring, or other LAN equipment at the other and of the network cable. If this detection occurs, the isochronous LAN equipment will fall-back to a LAN compliant mode of operation. Typically, only the hub will have the capability of operating at different networking modes, such as Ethernet, Token Ring isochronous modes. The hub will listen for some form of identification from the attached nodes as to the type of service to provide—isochronous or non-isochronous: Ethernet, token ring or other LAN service.

Full Description:
This application is a continuation-in-part of U.S. Ser. No. 07/971,018, filed Nov. 2, 1992, abandoned for “Network Link Endpoint Capability Detection,” incorporated herein by reference. 
    
    
     The present invention is directed to a method and apparatus for generating and detecting, in a network, such as a local area network, the link signals transmitted to or received from one or more endpoints of a data communication link, and in particular to a method and apparatus for generating one or a plurality of different link signals and determining whether a data source/sink at the end of a datalink has the capability of first data communication protocol or a second data communication protocol. 
     BACKGROUND OF THE INVENTION 
     A typical data communication network is configured to operate according to a single predetermined protocol, e.g., an Ethernet protocol, a token ring protocol, other LAN protocols, or an isochronous protocol. An example of an Ethernet system is an implementation known as 10 Base T which is described in the draft Nine supplement to IEEE standard 802.3, dated Nov. 15, 1989. Other examples of data communication protocols are X.25, and the Token Ring System, described for example, by IEEE Standard 802.5. Both Ethernet and token ring systems convey data in packets but each uses a different media access method. 
     As shown in  FIG. 1A , in a packet system, data is transferred in a plurality of packets  12 a,  12 b which can be either constant-sized or variable-sized. Each packet includes a field of data  14 a,  14 b which may be permeable information  16 a,  16 b housekeeping information such as data source information, data destination information, and the like  18 a,  18 b and a frame end marker  20 a. As seen in  FIG. 1A , because the fields provided for data  14 a,  14 b are not substantially continuous, the packetized scheme of  FIG. 1A  is not isochronous but “bursty” in nature. 
     In a token ring system, a node is permitted to transmit data only after receipt of an electronic “token.” As depicted in  FIG. 1B , a first station may transmit a token  22  which is received  24 a by second station whereupon the second station may begin transmission of data  26 a. After a period of data transmission, the second station transmits the token  22 b which is received by a third station  24 b that can then begin its own transmission of data  26 b. As seen in  FIG. 1B , because data transmission is synchronized with the occurrence of an event (the arrival of a token), the token ring system is not an isochronous data transfer system. 
       FIG. 1C  schematically depicts isochronous data transfer. In general terms, isochronous data is data which is non-packetized and of indeterminate, potentially continuous duration. In isochronous data transfer, the data transfer is initiated, such as by initiating a telephone conversation or beginning a video camera transmission  30 . After the data transfer or connection is initiated, transmission of the data, possibly accompanied by transmission of housekeeping information (such as destinations, audio or video trimming, and the like) is provided substantially continuously for an intermediate period such as until termination of the connection  32 . Although it may be that not every bit transferred represents a data bit (since “housekeeping” bits may also be transferred), the transfer of data is substantially continuous in the sense that there are no substantial periods during which no data bits are transferred. It is possible that the data being transferred is “Null” data such as silence during a telephone conversion or transfer of a black video image. One type of isochronous data transfer protocol is the Fiber Distributed Data Interface-II (FDDI-II) as described, for example, in FDDI-II Hybrid Multiplexer, Revision 2.4, dated Mar. 25, 1991. 
     Previous systems which were configured to use only a single-type protocol had the disadvantage that it was not possible to operate a mixed-protocol or “mixed-environment” system. Also when upgrading a network system, it was necessary to upgrade the entire system and it was infeasible or wasteful to upgrade only part of the system (such as only some of the nodes or such as upgrading nodes without upgrading hubs or upgrading hubs without upgrading nodes). Additionally, when a system or system components were installed, or repaired it was necessary for the installing personnel to be familiar with the particular single protocol for which the network was configured and to make such installation, upgrade, or repair in accordance with such a single protocol. Furthermore, it was necessary that apparatus connected to the system be configured for exclusive operation in accordance with the predetermined single protocol. 
     SUMMARY OF THE INVENTION 
     The present invention includes a recognition of the problems found in previous devices. According to an embodiment of the present invention an apparatus connected to one endpoint of a network link is able to detect which type of link signal, out of a number of possibilities is being received, thus indicating the protocol capability of the apparatus connected to the other end of the network link. In one embodiment, the apparatus is able to generate one of a plurality of link signals for transmission to the far end of the link, depending on the capabilities of each end of the link. Preferably, a first end of the network link has a capability of providing data communication under at least two different protocols and can select the appropriate protocol depending on what type of protocol capability is detected in the apparatus at the other end of the link. 
     Link endpoint capability detection takes advantage of the fact that different data communication protocols provide signals on the physical medium which have different characteristics. The various protocols can typically be detected by their unique timing and data patterns. According to one aspect of the invention, the network has a star topology with at least one hub and a plurality of nodes each node being connected to a hub by physical media constituting the link. The capability detection of the present invention can be performed by apparatus at either end of a link, and in particular, in a star topology network can be conducted by the hub or by any node. In one embodiment, capability detection is initiated by the hub. In a non-star topology at least one node can operate under two or more protocols and can detect the capability of another node with which it is connected. 
     Although, for convenience, much of the following description is in terms of hubs and nodes, aspects of the present invention can be implemented in topologies other than hub-and-node topologies (e.g., ring topologies, and tree topologies) as will be apparent to those of skill in the art. Descriptions of hub circuitry in the following can be implemented, e.g., on a PBX adapter card for a personal computer. 
     The apparatus which initiates capability detection, according to one embodiment, transmits a signal onto the physical medium. In one embodiment, the apparatus at the far end of the link outputs, onto the physical medium, a second signal. Preferably, a second signal will be output from the apparatus at the far end of the link, regardless or whether the apparatus at the far end operates according to a first protocol or a second protocol. However, the second signal which is placed onto the physical medium at the far end of the link has either a first form or a second form, depending on whether the apparatus at the far end has a first protocol capability or a second protocol capability. This difference in signal is detected at the first end of the link and this could be used as a basis for determining the protocol capability at the far end of the link. 
     In another embodiment, the first apparatus outputs a first signal. The second apparatus outputs a response only if it has a first protocol capability. If no response is output, the first apparatus outputs a second signal in an attempt to elicit a response according to a second protocol. This process can be repeated until the first apparatus outputs a signal to which the second apparatus responds, thereby indicating a protocol capability of the second apparatus. 
     According to one embodiment, the first signal which is output, also carries information regarding the protocol capability of the first endpoint. That is, preferably, the first signal has a first form if the first endpoint has a first protocol capability and it has a second form if the first endpoint has a second protocol capability. Preferably, the apparatus at the far end of the link will respond to either of these forms in the manner described above. 
     In the preferred embodiment, the apparatus which has detected the capability at the far endpoint adjusts its operation to accommodate that capability. For example, when the first endpoint detects that the far endpoint has a first protocol capability, the first endpoint will configure itself to conduct subsequent communication using the first protocol. However, if the first endpoint detects that the far endpoint has a second protocol capability, the first endpoint is able to configure itself to accommodate the second protocol capability. 
     In one embodiment the far endpoint will have only a single protocol capability. However, it is possible to configure a network in which both link endpoints have multiple protocol capabilities and both can detect one or more capabilities at the opposite endpoint. The endpoints can then configure themselves to operate at the best or most desired protocol level. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A ,  1 B and  1 C of the timing of a packet transmission system, a token ring transmission system, and an isochronous transmission system respectively; 
         FIG. 2  is a schematic block diagram showing three nodes connecting to a hub; 
         FIG. 3  is a schematic block diagram showing a number of hubs connected together using a ring structure; 
         FIG. 4  is a schematic block diagram of circuitry for multiplexing and preparing data for transmission over to media and for receiving information from the media and demultiplexing the data; 
         FIG. 5  is a schematic block diagram of hub receiver circuitry according to an embodiment of the present invention; 
         FIG. 6  schematic block diagram of a hub transmitter-circuitry; 
         FIG. 7  in a timing diagram showing the relative timing of transmissions and receptions at the hub and nodes; 
         FIGS. 8A-8E  are block diagrams depicting link endpoint capability detection for five different network configurations according to embodiments of the present invention; 
         FIG. 9  is a block diagram of a node receiver, according to an embodiment of the present invention; 
         FIGS. 10A ,  10 B and  10 C depict timing of 10 Base T link pulses, isolink pulse stream and isosleep link pulses, respectively; 
         FIG. 11  depicts a state machine for generating various types of link pulses; 
         FIG. 12  depicts a state machine for detection of 10 Base T links; 
         FIG. 13  depicts a state machine for detection of isochronous or isochronous-ethernet pulses or fast link pulses; 
         FIG. 14  depicts pulses for defining acceptance windows; and 
         FIGS. 15A-15D  are block diagrams depicting circuitry components that can be used to implement state machines according to one embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Before describing link endpoint capability detection, a general description of one type of network will be provided as one example of a data communication system in which the present invention can operate. A data communication system can be configured in a star-topology with a plurality of nodes of  42 a,  42 b,  42 c, ( FIG. 2 ) each coupled to a hub  44 a by data links comprising physical data transmission media such as one-way twisted pair wires  46 a- 46 f. The number of nodes can be adjusted depending on the data transmission needs and objectives of the system. In one embodiment, each hub is configured to accommodate connection with up to 16 nodes. Each  42 a,  42 b,  42 C includes circuitry  50 a,  50 b,  50 c for receiving data, converting it to a form suitable for transmission onto the physical media  45 a,  46 c,  46 e using transmitters  78 a,  78 b,  78 c and receipt of signals from the physical media  46 b,  46 d,  46 f using receivers  79 a,  79 b,  79 c and conversion to a form suitable for use by the data sinks. Each of the nodes  42 a,  42 b,  42 c includes data sources and sinks  48 a- 48 g. The data sources and sinks can be isochronous sources and sinks such as video cameras  48 a,  48 d and monitors  48 b,  48 a, non-isochronous sources and sinks such as an Ethernet media access controller  48 c,  48 g, and signaling or D channel sources and sinks such as an emulated or virtual key pad  48 f provided, for example, on a personal computer (PC) terminal. 
     Each of the nodes  42 a,  42 b,  42 c can include various types of sources and sinks such as strictly isochronous sources and sinks, such as depicted for node one  42 a, strictly non-isochronous sources/sinks as depicted for node three  42 c or both isochronous and non-isochronous sources and sinks as depicted for node two  42 b. The physical layer  52  of the network system depicted in  FIG. 2  has portions which include the physical medica  46 a- 46 f and physical layer devices such as the node data receivers and converters  50 a,  50 b,  50 c and the hub components  54 a,  54 b,  54 c and  56 . The physical layer can include devices for providing, e.g., transceivers for 10 Base T cables, data multiplexing, phase locked loop circuitry, FIFOs or other circuitry for cable length adjustment, smoothing, squelch and the like. 
     The hub  44 a includes circuitry  54 a,  54 b,  54 c for receiving data from the physical media  46 a,  46 c  46 e separating the isochronous-sourced data from the non-isochronous-sourced data and the D channel and M channel data and converting separated data into a form suitable for handling by downstream hub circuitry  56 . In the depicted embodiment the separated isochronous-sourced data is provided to a time slot interchange controller  58  for placing the data on a high-bandwidth bus (e.g., the TSI bus) so that it can be transported to destination nodes or other TSI controllers in the hub or other hubs (as depicted, e.q. in  FIG. 3 ) and/or retrieved by hub circuitry  54 a,  54 b,  54 c for transmission to various destination nodes  42 a,  42 b,  42 c, e.g. by a local loopback capability. The separated non-isochronous data is provided to circuitry  60  configured to convey the non-isochronous data to one or more of the hub circuitry  54 a,  54 b,  54 c for transmission to destination nodes  42 a,  42 b,  42 c. In an embodiment in which non-isochronous-sourced data includes Ethernet data, the hub circuitry  60  can be a standard Ethernet repeater processor. In this way, the present invention can be at least partially backward-compatible with previous Ethernet hub systems. The D channel and M channel information is provided to a signaling processor  62  which performs various maintenance and control functions such as identifying and alerting users of error conditions, and setting up requested calls or connections, i.e. source/destination paths e.g. by communicating with the isochronous and non-isochronous controllers  58 ,  60 , e.g. over data path  64 . The isochronous controller  58  can be, a data exchanger e.g. an isochronous switching device, such as that described in commonly-assigned application Ser. No. 08/146,337 entitled “Time Slot Exchanger Switching Mechanisms in a Network for Data Communication Having Isochronous Capability,” filed on even date herewith and incorporated herein by reference. The non-isochronous controller  60  can be, e.g., an Ethernet repeater. As depicted in  FIG. 3  a number of star-topology systems can be interconnected by connecting hubs  44 a,  44 b,  44 c to one another, e.g. by a time slot interchange (TSI) ring. 
     According to the present invention, data communication can be provided according to one or more of a number of protocols. Those skilled in the art are familiar with protocols, but in general, a “protocol” includes a standard set of rules that specify the format, timing, sequencing and/or error checking for data transmission. Several network protocols are referenced above, including an Ethernet protocol such as 10 Base T, an isochronous protocol such as FDDI-II, and a token ring protocol. Another possible protocol is one in which both isochronous and non-isochronous data are combined into a frame structure for transmission across physical media. A frame-structure protocol of this type is described in greater detail in commonly-assigned application Ser. No. 07/969,916 titled “Network for Data Communication with Isochronous Capability” filed on Nov. 2, 1992 and incorporated herein by reference. According to one such protocol, the incoming data from the various sources is provided to a multiplexer  70  ( FIG. 4 ) which performs time-division multiplexing on a four-bit basis. The pattern for the time division multiplexing is a repeating series of frames or templates. In this embodiment, the frames are repeated every 125 microseconds. The time division multiplexing is a multiplexing of isochronous-sourced data and non-isochronous-sourced data. The non-isochronous-sourced data can be data provided in accordance with a number of previously-available LAN systems and this protocol will be referred to, in general, as “isochronous-LAN” protocol. Several particular types of isochronous-LAN protocols are possible. When the isochronous data is multiplexed with LAN data which is provided according to an Ethernet protocol, such as a 10 Base T Ethernet protocol, the resulting time-division multiplexed protocol will be referred to as an “Isochronous-Ethernet” protocol. When the isochronous data is multiplexed with LAN data which is provided according to a token ring protocol, the resultant time multiplexed protocol will be referred to as an “isochronous-token ring” protocol. 
     The present invention will be described below by way of a particular example in which one available protocol is an Isochronous-Ethernet protocol and another potentially available protocol is a 10 Base T protocol. However, as will be clear to those skilled in the art, the present invention can also be used in connection with other combinations of protocols such as isochronous-token ring or other isochronous-LAN protocols, pure isochronous protocols such as FDDI-II, and can include three or more protocols. 
     Tables IA and IIB depict manners in which the various data streams, and additional data and control bytes can be time-division multiplexed in an Isochronous-Ethernet protocol. Each symbol in the Tables IA and IB represent four bits of data so that every group of two symbols represents one 8-bit byte of data. In Table IA, E represents four bits of data from the non-isochronous Ethernet stream  66 b (FIG.  4 ), B designates four bits of data from the isochronous stream  66 a, D represents four bits of data from the signaling or D channel stream  66 c, and M represents four bits of M channel data stream  66 d. In addition, certain byte-length patterns are provided. JK represents a frame synchronization pattern and EM (the first two bytes of block three in Table IA represents an Ethernet “pad” followed by a maintenance byte. As seen in Table IA each frame contains 256 bytes which can be considered in thirty-two groups of eight bytes each, or four blocks of sixty-four bytes each. The frame structure is described more thoroughly in commonly-assigned application Ser. No. 07/969,911 titled “Network for Transmitting Isochronous-Source Data with a Frame Structure” filed Nov. 2, 1992 and incorporated herein by reference. Frame structures other than that described in Table IA may be used to allocate bandwidth according to a particular purpose. Table IB shows one of the many alternate formats. In general, Table IB is similar to Table IA with replacement of “E” symbols with “B” symbols. As seen in Table IB, the last one or two bytes in each block are “Idle” data bytes. 
     As shown in  FIG. 4 , the time-multiplexed data is then encoded by an encoder  72 . In the depicted embodiment, the encoder performs four/five encoding. One particular form of four/five encoding conforming partially to the ANSI X3T9.5 standard, is depicted in Table II. The encoding scheme depicted in Table II is described in greater detail in commonly-assigned application Ser. No. 07/970,329 titled “Frame-Based Transmission of Data” filed on Nov. 2, 1992 and incorporated herein by reference. 
     The output from the encoding devices is sent to pre-emphasis circuitry  76 . The pre-emphasis circuitry compensates the signal transmitted onto the physical medium to reduce the jitter. The data output by the pre-emphasis circuitry  76  is sent to a transmitter or driver  78 b and the signal is transmitted over the physical medium  46 c. The physical medium  46 c can be any of a number of media types including twisted pair, coaxial or fiber optic cable. 
     The data sent over the physical layer interface is received in the hub  44 a. The hub contains a plurality of circuit devices  54 a,  54 b,  54 c, each one coupled to one of the nodes  42 a,  42 b,  42 c by the physical media  46 . As depicted in  FIG. 5  the data transmitted over the physical media  46  arrives serially at a de-serialized/decoder  80 . Link detect circuitry  82  also receives the data from the physical layer portion interface for detection of the mode or protocol in which the node is operating as described more fully below. The de-serializer/decoder  80  receives a reference clock signal  84 . The de-serializer/decoder includes circuitry which is functionally an inverse of the multiplexing/encoding circuitry described above. Referring to  FIG. 4 , the de-serializer/decoder includes phase lock decode circuitry  86 , the results of which are provided on NRZI decoder circuitry  88  which, in turn, provides the decode results to four/five decode circuitry  90 , in turn providing results to a de-multiplexer  92  which separates the received data into the isochronous-sourced data  94 a, the non-isochronous-sourced data  94 b and signaling data, such as D channel and M channel data  94 c. The de-serializer/decoder  80  also outputs a synchronization signal, derived from the JK frame synchronization symbols  96  for use by a framing timing generator  98 . 
     Both the non-isochronous-sourced data  104  ( FIG. 5 ) and the isochronous-sourced data  102  are made available to the various hub circuitry  56  or components  54 a,  54 b,  54 c, as needed for transmission back to destination nodes. In one embodiment, the separated isochronous data  102  and non-isochronous data  104  are reconfigured by the respective interfaces  58 ,  60  to provide isochronous output  102  and non-isochronous output  104  in a form suitable for processing so as to provide the data as needed for transmission to the destination nodes via the physical layer. In one embodiment, the non-isochronous data  94 b can be configured by the physical layer E interface  59  ( FIG. 5 ) so that the output data  104  can be processed by a repeater device  60  for eventual transmission to destination nodes. As an alternative to using a repeater for the non-isochronous data, packet connections may be linked through media access control layer bridges. Preferably, the output data  104  is in a form such that it can be handled by repeater circuitry of types previously available. For example, when the nonisochronous data  94 b within the physical layer is data which originated at the node  42 b from an Ethernet MAC, the output data  104  is in a form such that it can be handled by a standard Ethernet hub repeater  60  such as DP83950 “Receptor Interface Controller” (RIC) available from National Semiconductor Corporation, Santa Clara, Calif. 
     As shown in  FIG. 5 , the data received over the physical link  46  is also provided to an additional interface for handling data according to a second protocol, as described more thoroughly below. For example, when the second protocol is an Ethernet 10 Base T protocol, a 10 Base T interface  512  can be provided. The 10 Base T receive interface  512  can be a standard 10 Base T interface, such as Model DP83922 “Twisted Pair Transceiver Interface” (TPI) available from National Semiconductor Corporation, Santa Clara, Calif. A multiplexer  514  determines whether the repeater  60  receives a data stream from interface  59 z or the 10 Base T interface  512 . This selection by the multiplexer  514  is controlled by a mode select signal output over control line  516  from the link beat detect circuit  82  as described more fully below. 
     The data  198  output from the E transmit interface  168  is provided along with isochronous data output  164  and M channel D channel data  170  to encoder serializer circuitry  202 , depicted in FIG.  6 . The encoder/serializer  202  is configured substantially like the encoding circuitry found in the node and depicted in FIG.  4 . Specifically, the encoder/serializer  202  provides a multiplexer for combining the three streams of data  198 ,  170 ,  164 , a four/five encoder, an NRZI encoder, and pre-emphasis circuitry. The timing of transmission is controlled by transmit timing circuitry  204 . Output  206  from the encoder/serializer is selectively combined with link beams from a link beat generator  208  by multiplexer  210  for purposes of link end point detection, as described below. The clock signal and the data  166  from the repeater  60 , in addition to being provided to the E interface  168  is also provided to a second interface which operates according to a second protocol. When a second protocol is an Ethernet 10 Base T protocol, the interface is an Ethernet 10 Base T interface  520 . The Ethernet 10 Base T interface transmit  520  can be of a type substantially identical to 10 Base T interfaces provided in previous apparatus such as Model DP83922, “Twisted pair Transceiver Interface (TIP)” available from National Semiconductor Corporation, Santa Clara, Calif. The output from the Ethernet 10 Base T interface  520  is provided to the multiplexer  210 . Multiplexer  210  is able to select, in response to a control signal  522 , whether to output data originating from the repeater  60  according to a first protocol determined by the E interface  168 , or according to a second protocol determined by the Ethernet 10 Base T interface  520 , as described more fully below. The data sent from the hub  44 a to the nodes  42  is sent in a frame format which is preferably substantially the same as the frame format used for the data sent from the nodes  42  to the hub  44 a as described above. At the nodes  42 , the circuitry  50  includes devices ( FIG. 4 ) for decoding and de-multiplexing data, similar to that described for performing these functions in the hub, mainly a phase lock decode  86 , and NRZI decode  88 , a four/five decode  90 , and a de-multiplexer  92 . Decoded and de-multiplexed data is then delivered to the various data sinks in the nodes  42 . 
     As shown in  FIG. 7 , the timing of the system can be synchronized with a 125 microsecond reference clock signal  214 . In this example, the reference signal  214  provides an ascending clock edge every 125 microseconds. The reference signal can be provided by any of a number of sources. Preferably, an embodiment of the present invention is configured to permit a reference signal  214  to be synchronized to an external clock reference, such as a reference signal from a wide area network or from a FDDI-II ring. The reference signal can be supplied through one of the nodes and transmitted to the hub for distribution to the other nodes, or can be supplied directly to the hub for distribution. 
       FIG. 8A  depicts a network configuration in which the hub  530 a in a 10 Base T hub and the node  532 a is a 10 Base T node, both of which are found in previously-available devices. In this system, the 10 Base T hub sends a signal, specifically a link test pulse, in accordance with IEEE Standard 802.3, over the physical medium to a 10 Base T node  532 a. In a typical system, the 10 Base T hub outputs a signal upon being powered-up. The link test pulse used in previous devices is described in IEEE Standard 802.3. Briefly, a link test pulse can be described as a single 100 nanosecond pulse occurring at a nominal 16 millisecond interval. The 10 Base T node  532 a, typically in response to being powered-up, outputs onto the physical medium a second signal, which, in accordance with IEEE 802.3, is substantially identical to the above-described link test pulse. This link test pulse is received by the 10 Base T hub  530 a. At this point, a 10 Base T hub proceeds to operate on the basis that is connected to a 10 Base T node ( 532 a) and the node  532 a begins to operate on the basis that it is connected to a 10 Base T hub ( 530 a) and normal 10 Base T communication protocol. 
       FIG. 8B  depicts a configuration according to one invention in which an Isochronous-Ethernet hub  530 b is connected to a 10 Base T node  532 a. The Isochronous-Ethernet hub outputs a probe signal  534 . A probe signal differs from the link test pulse in that it has a faster link beat, for example having a beat period of less than about 2 milliseconds. The 10 Base T node  532 a is configured substantially identically to previously available 10 Base T nodes. Upon receipt of the probe pulse  534 , it continues to output a link test pulse onto the physical medium. The isochronous-Ethernet hub  530 b, upon receiving a link test pulse (rather than a probe pulse) can determine, on that basis, that the apparatus connected to the far end of the physical medium is a 10 Base T node  532 a (rather than, for example, an isochronous-Ethernet node). Preferably, the isochronous-Ethernet hub  530 b is capable of handling data either according to an isochronous-Ethernet protocol or a 10 Base T protocol. Upon receiving a link test pulse and determining that the node  523 a is a 10 Base T node, the isochronous-Ethernet hub  530 b will configure itself to conduct all future communications with node  532 a using a 10 Base T protocol. 
     Although  FIG. 8B  shows only a single node  532 a connected to the hub  530 b, in a typical configuration, a plurality of nodes will be connected to each hub. Preferably, the hub  530 b is capable of using different protocols with different nodes. Accordingly, an isochronous-Ethernet hub which is connected to both a 10 Base T node and an isochronous-Ethernet node can determine the capability of each node to which it is connected and can use the appropriate protocol for each node. 
       FIG. 8C  depicts a network configuration in which a 10 Base T hub  530 a is connected to an isochronous-Ethernet node  532 b. Upon initialization of the system the 10 Base-T hub outputs a link test pulse  533 . In the depicted embodiment the Isochronous-Ethernet node  532 b can operate according to an Isochronous-Ethernet protocol. Therefore, upon receiving the link test pulse  533 , it outputs a link test pulse  533 . Accordingly, the 10 Base T hub  530 a can only send Ethernet data and no isochronous data. 
       FIG. 8D  depicts a network configuration in which an Isochronous-Ethernet hub  530 c is connected to an isochronous node  532 c. In the embodiment depicted in  FIG. 8D , the node  532 c only has isochronous protocol capability, but the hub  530 C has both an isochronous-Ethernet protocol capability and an isochronous protocol capability. In this embodiment, upon initialization of the system, the hub  530 c outputs an isochronous probe pulse  535 . The isochronous node  532 c, upon receiving the isochronous probe pulse  535 , can determine that the hub to which it is attached is an isochronous-capability hub and will configure itself to conduct all future communications with the hub  530 c according to an isochronous protocol. Thus, the isochronous node  532 c preferably contains isochronous apparatus similar to apparatus found in the hub  503 c for detecting circuitry at the other end of the link or physical medium and thereafter, using the appropriate protocol. The isochronous node  532 c, in response to receipt of the iso probe pulse  535 , outputs an iso probe pulse  535 . The hub  530 c, upon receipt of the iso probe pulse, will commence normal isochronous hub operations. 
       FIG. 8E  a configuration in which an Isochronous-Ethernet hub  530 b is connected to an Isochronous-Ethernet node  532 b. When the system is initialized the Isochronous-Ethernet hub  530 b outputs a probe signal such as an isoEnet probe, on the physical medium. When the Isochronous-Ethernet node  532 b receives the isoEnet probe signal it is able to determine that the hub to which it is connected is an Isochronous-Ethernet hub. The Isochronous-Ethernet node  532 b then outputs an isoEnet probe signal  534  onto the physical medium which is received by the isochronous Ethernet hub  530 b. When the Isochronous-Ethernet hub  530 b receives an isoEnet probe signal it can determine that the node  532 b to which it is connected to an Isochronous-Ethernet node and will conduct all future communications with this particular node according to the Isochronous-Ethernet protocol. 
       FIGS. 5 and 6  depict components in the hub which are used in connection with link endpoint capability detection. As depicted in  FIG. 6 , a link beat generator  208  is provided for outputting the appropriate probe signal. A control signal  522  controls the multiplexer  210  so that the probe signal  208  is output onto the physical medium  46  at the appropriate time, e.g., upon initialization of the network system. 
       FIG. 9  depicts circuitry  50  in an Isochronous-Ethernet node. Circuitry  542  would be provided in a node which can operate in accordance with two protocols. Nodes which provide only a single protocol would not include circuitry  542  and the E interface  59 ′ would be connected directly to the Ethernet MAC  49 c. The probe pulse received over the physical medium  46  is detected by the link beat detector circuitry  82 . Circuitry  82  can include, for example a state machine, for detecting the sequence and interval of the pulse or link test pulse. The link beat detector circuitry  82  outputs a mode select signal  516  for controlling the multiplexer  514 . The control signal  516  is configured to set the multiplexer  514  such that the Ethernet MAC  48 C is connected to the output of the Isochronous-Ethernet interface  59 ′ so that future data received over the physical medium  46  is treated in accordance with the Isochronous-Ethernet protocol. If the link beat detector  82  detects the link test pulse rather than an iso pulse signal, it outputs a mode select signal  516  which configures the multiplexer  514  to connect the Ethernet MAC  48 C with the Ethernet 10 Base T interface  512  so that future data received over the physical medium is treated in accordance with Ethernet 10 Base T protocol. The mode select signal  516  also provides a signal to a control circuit in a node transmitter. The node transmitter is not separately depicted in detail since it is substantially identical to the hub transmitter depicted in FIG.  6 . 
     The node transmitter control  522  in response to the node select signal  516  (indicating receipt of a link test pulse or other probe pulse) configures the multiplexer to output an appropriate pulse signal from the link beat generator  208  onto the medium  46 . In some embodiments, nodes and/or hubs are configured to output a link test pulse or a probe pulse (depending on the capability of the hub or node), whenever the hub or node is powered-up. For embodiments in which the link beat detector  82  is able to discriminate between a link test pulse and a probe signal such as an iso probe pulse, the mode select  516  can configure the link beat generator  208  to output a link test pulse in response to a link test pulse and an iso probe pulse in response to a probe signal. The signal output by the node transmitter is received in the hub receiver  54  (FIG.  5 ). The hub receiver link beat detect circuitry  82  detects the output of the probe pulse from the node transmitter. When the signal is a probe signal, circuitry  82  outputs a mode select signal  516  which is effective to control the multiplexer  514  to connect the output from the E interface  59 ′ to the repeater  60 . In this way, the hub receiver is now configured to process future signals received from the node over medium  46  according to an Isochronous-Ethernet protocol. The node select signal  516  also provides an input to control signal  522  which, in response, configures the multiplexer to place the output  206  from the encoder/serializer  202  onto the physical medium  46 , rather than using the output from the 10 Base T interface  536 . In this way, the transmitter is now configured to output data according to the Isochronous-Ethernet protocol. 
     If the signal output from the node is a link test pulse rather than probe pulse, the link beat detector  82  outputs a mode select signal  516  which configures multiplexer  514  to connect the Ethernet 10 Base T interface  512  with repeater  60  and configures the multiplexer to send output  536  onto the physical medium  46 , rather than output  206 . 
     In one embodiment, generation and detection of link pulses involves a number of changes of state, as described below by way of state machine descriptions and diagrams. In one embodiment, the operation can be described by three state machines, a first state machine for generating various types of link pulses (“LINKGEN”), a second state machine for detection of a 10-Base T link (“LINKIOBTSM”) and a state machine for detection of isochronous or Isochronous-Ethernet pulses or fast link pulses (“LINKISOSM”). 10 Base T link pulses are transmitted and, in turn, detected on both sides of the medium such as the twisted pair medium, to signal the proper connectivity. In isochronous systems, the fast link pulses are generated during power-on initialization, during traumatic error recovery, or when a connection is running on a emergency power. Fast link pulses can be differentiated from 10 Base T link pulses since the fast link pulses occur in bursts rather than singly. A third type of link pulse “isosleep” is used to indicate that the device originating the pulses is in a low power or “sleep” mode and to convey cycle timing. Low power mode is described in commonly assigned application, U.S. Ser. No. 08/147,359 for “Low Power Isochronous Networking Mode” filed on even date herewith and incorporated herein by reference. The 10 Base T link pulses have the form of a 100 ns pulse generated every 16 ms (FIG.  10 A). In the depicted embodiment, the isolink pulse stream consists of pulse pairs. Each pair consists of a clock pulse and a data link pulse. In the depicted embodiment, the spacing between the clock pulse is 125 μs. This value is preferred because it is the same as the public network time and it is a clock time that is readily available to the system, as described above. The clock and data link pulses are separated from each other by 62.5 microseconds. The pairs are repeated 16 times and, following the 16the transmission of a pulse pair, an additional link pulse  1006  is transmitted 62.5 microseconds after the last data link pulse position. The isolink pulse stream is depicted in FIG.  10 B. As shown, clock link pulses  1002 a,  1002 b always occur, while data link pulses  1004 a,  1004 b occur to represent a data “1” (shown in phantom) and are missing to represents a data “0”. Thus, the isolink pulse stream can be used to transmit information and, in one embodiment, is used to encode information such as the type of device which is transmitting, (e.g., hub versus node) the isoethernet signaling data rate, and the information content of the isoetherent channel (e.g., clear channel, ATM mode, isochronous Ethernet). 
     The isosleep link pulses consist of one plate  1020 a,  1020 b transmitted every 125 μs in phase with the transmit sync signal, as depicted in FIG.  10 C. 
     In one embodiment, the hub initially begins generating an isoethernet “fast” link pulse to each node to which it is connected. If the far end is a 10 Base T node, this node will begin transmitting a 10 Base T link pulse after it has received the pulse or pulse train sent from the hub. If a 10 Base T node at the far end fails to receive a proper link pulse or stream of link pulses, it will enter a “link loss” state in which it will remain until it receives a specific sequence indicating that the network or link is now operable again. When the hub receives a 10 Base T link pulse from the node, it will configure itself to thereafter send out 10 Base T communications to that node. 
     If the far end of the link was an isoethernet node, the isoethernet node will respond to receipt of a proper isoethernet pulse train (fast link) by transmitting an isoethernet pulse train (fast link). Thereafter, both ends of the link will configure themselves to transmit in isoethernet mode. 
     In this way, the hub will be assured that the communication link is working properly in both directions. In certain previous systems, communications did not require a “handshake,” i.e., verification of properly working link in both directions and accordingly, in these previous devices it was possible for there to be a partially broken link (i.e., a link which was operating in one direction and not the other) that went undetected. 
       FIG. 11  depicts the LINKGEN state machine according to one embodiment of the invention. As seen in  FIG. 11 , this state machine has four states. State LG1 “LINKIDLE” is an idle state in which the link generator state machine is waiting for an event to generate a link pulse. State LG2  1104  is a link pulse state. The machine waits at this state for approximately 250 ns until the end of the interval when the cycle synchronization symbol is sent before generating a data link pulse. State LG3  1106  is the link data state. The machine waits at this state to generate a data link pulse. State LG4  1108  is the link clock state. The machine waits at this state to generate a clock link pulse. Equations governing the transition between states in pseudo “C” terminology are provided in Table III. In each case, the first line indicates the condition which causes the transition of state to occur and the remaining lines indicate values that are assigned, incremented, cleared or reset. The meanings of terms of Table III are provided in Table IV. 
     As seen from  FIG. 11 , the state machine leaves the link idle state under three conditions. The first 1114 is a 10 Base T link pulse timeout designated LG 11 . After waiting 16 ms from the previous link pulse, a link pulse is generated. In the isosleep link pulse timeout designated LG 12  ( 1112 ), after waiting 125 μs from the previous link pulse, a link pulse is generated. In the isolink link pulse timeout designated LC 13  ( 1110 ), after waiting 16 ms from the previous link pulse, a link pulse stream will be generated. 
     The state machine leaves the link pulse state  1104  after generating a link pulse. In the isolink data wait, after generating a link pulse, the machine makes a transition to begin timing the data link pulse. In the isolink clock wait, after generating a data link pulse, the machine makes a transition to begin timing the clock link pulse. 
     The machine leaves the link data state in either of two conditions. In the isolink 1 data pulse, after waiting a half cycle, a data link pulse will be transmitted. In the case of an isolink 0 data pulse, after waiting a half cycle, no data link pulse will be transmitted. 
     The machine leaves the ink clock state  1008  in the case of an isolink clock pulse. After waiting a half cycle, a clock link pulse will be transmitted. 
     The 10 Base T link detection state machine (“LINK10BTSM”) is depicted in FIG.  12 . This state machine can be compared to the 10-Base T detector described in IEEE Standard 802.3. However, the state machine depicted in  FIG. 12  includes the state “freeze-10-Base”  1202  which acts to disable this machine when fast link pulses are detected. Table V indicates the conditions for the various transitions shown in FIG.  12  and the variable assignments that are associated with each transition. 
     Table VI indicates the meaning of various parameters. Following a reset  1204 , the machine will enter the link test reset state  1208 . From this state, the machine will either remain in this state  1210 , transition to the link test fail state  1212 , transition to the link test extend state  1214  or transition to the freeze-10-base state  1202 . The transition to the freeze-10-base state occurs if the fastlink parameter is “true”. The same conditions will also cause a transition from the link test fail state  1212  or the link test extend state to the freeze-10-Base state. Once in the freeze-10-Base state  1202 , the state machine will, by default, remain in this state  1202  as long as the fastlink parameter is “true.” In this situation the freeze-10-base state will transition to the link test reset sate  1208 . In this way, the state machine will respond to receipt of a normal 10-Base T link pulse but will enter the freeze state  1202  in response to receipt of a fast link pulse. 
     The state machine which detects a fast link pulse (“LINKISOSM”) is depicted in FIG.  13 . Table VII indicates the conditions which cause state transitions as well as the assignment of variables or parameters associated with state transitions. Table VIII indicates the meaning of the various parameters. 
     The state machine depicted in  FIG. 13  has nine separate states. The iso-idle state  1302  is entered upon reset or receive activity. The isofirst pulse state  1304  is entered when a link pulse is detected but at a point when it does not yet qualify as a fast link pulse. The isofirst pass state  1306  is entered when a qualified fast link pulse is detected. The isosecond pass  1308  state is entered when a qualified second link pulse is detected. The isothird pass state  1301  is entered when a qualified third link pulse is detected. The isofast link state  1312  is entered after the requisite number of fast link pulses has been detected, but when the machine is waiting for data information or a clock pulse. The isofind clock state  1314  is entered when a clock pulse within a burst is detected. The isoshift 0 state  1316  is entered when 0 data pulse is detected and the isoshift 1 state  1318  is entered when a 1 data pulse is detected. 
     To distinguish between a clock pulse and a data pulse, a series of acceptance windows are defined from the beginning of the first pulse which is assumed to be a clock pulse. As depicted in  FIG. 14 , at the beginning of the first clock pulse  1402 , a first acceptance clock window  1404  of 31.25 μs is defined. Thereafter, a series of acceptance windows, alternating between an acceptable data window  1406  and an acceptable clock window  1408  are defined, each of these windows having a duration of 62.5 μs. 
     The state machines, described above, can be implemented in the context of a number of circuitry components. In one embodiment, the circuitry components include a link timer,  FIG. 15A , a number of link registers  1502  (FIG.  15 B), coupled to a link comparator  1504 , the link ISO state machine ( FIG. 15C ) and the link 10 Base T state machine (FIG.  15 D). Table IX describes the function of the various signal lines depicted in  FIG. 15A-15D , not previously described. 
     In general, the link timer circuit  1506  provides a number of timers which are used by the state machines to distinguish between pulse signals and other signals and to distinguish between various types of pulses and pulse streams, as described above. A number of the timers found in these circuits, and the function and default valves, are listed in Table X. 
     The link registers  1502  are used for storing information, including information encoded in the data pulses of the isoethernet pulse stream and for outputting information, such as information extracted from the data pulses. 
     In view of the above description, a number of advantages of the present invention can be seen. The present invention allows a network to be configured in a mixed protocol or mixed environment, with, for example, a single hub connected to a plurality of nodes which operate according to different protocols, with the configuration being achieved automatically, with the need for manually establishing a predetermined protocol beforehand for each node. The present invention permits networks to be upgraded incrementally so that it is not necessary to upgrade all nodes at the same time. Furthermore, it is not, in general necessary for service personnel to specifically configure nodes or hubs to accommodate particular protocols since the protocols are determined automatically and the nodes and hub configure themselves in accordance with the determined protocols. 
     A number of variations and modifications of the present invention can be used. Although an embodiment involving a 10 Base T protocol and an Isochronous-Ethernet protocol was described, the present invention can be made applicable to other protocols, including other LAN protocols such as a token ring protocol, an isochronous protocol and the like. Although the present invention described one particular signal characteristic used for determining the protocol, other characteristics could also be used. For example, a token ring could be detected by the presence of four or 16 Mbit/sec Manchester-encoded data. Other LANs can be detected by their unique timing and data patterns. Protocols could also be detected using such characteristics as the pattern of the presence or absence of a carrier, and the frequency spectrum of signals placed onto the physical medium. When a node has a capability of communicating under two or more protocols, e.g. either an Isochronous-Ethernet protocol or a pure Ethernet protocol, it would be possible for a hub to use both capabilities of a node, i.e., to communicate according to a first protocol during a first time period and a second protocol during a second time period. Although the present invention has been described in the context of a star topology, the invention could also be used in a non-star topology, such as a ring topology or a tree topology. The present invention can be used in networks which do not have a hub, such as a direct connections between two nodes with each node determining the protocol capabilities of the other node. Ad described above, the link test pulse and iso probe signals are related in that, for example, a 10 Base T node will respond in the same fashion to receipt of either type of pulse. However, the test signals could be provided in forms which are unique to each type of protocol. In such a system, a data source/sink would output a first type of test pulse or other signal and, if no response was received, would output a second type of test pulse or signal, and so forth until a response was received indicating the protocol capability at the other end of the link. A data source/sink could be configured to determine all possible protocol capabilities of the apparatus at the other end of the link rather than determining the “highest” or “best” capability available or using the first capability detected. The devices at each end could select a protocol capability other than the “highest” or “best” capability. It would be possible for a node to store an indication of its capabilities, such as in a table or other memory device, and to output the information upon receiving an inquiry. It would also be possible for a network to initialize in a common protocol, e.g., a 10 Base T protocol, and, thereby, exchange information, using that protocol indicating additional protocol capabilities of the components of the system. Thereafter, the systems could reconfigure themselves to use desired ones of the available protocols. 
     Although the present invention has been described by way of preferred embodiments and certain variations and modifications, other variations and modifications can also be used, the invention being defined by the following claims. 
     
       
         
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE IA 
               
               
                   
               
             
             
               
                 BLOCK 0: 
               
             
          
           
               
                 J 
                 K 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group0 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group1 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group2 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group3 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group4 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group5 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group6 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group7 
               
             
          
           
               
                 BLOCK 1: 
               
             
          
           
               
                 M 
                 M 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group8 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group9 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group10 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group11 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group12 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group13 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group14 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group15 
               
             
          
           
               
                 BLOCK 2: 
               
             
          
           
               
                 D 
                 D 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group16 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group17 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group18 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group19 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group20 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group21 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group22 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group23 
               
             
          
           
               
                 BLOCK 3: 
               
             
          
           
               
                 E 
                 M 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group24 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group25 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group26 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group27 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group28 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group29 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group30 
               
               
                 E 
                 E 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 B 
                 E 
                 E 
                 Group31 
               
               
                   
               
               
                 JK = Frame Synchronization Pattern  
               
               
                 MM = 8 Maintenance Bits  
               
               
                 D = D Channel  
               
               
                 EM = Ethernet Pad &amp; 4 Maintenance Bits  
               
               
                 E = Ethernet Packet Channel  
               
               
                 B = Isochronous Channel  
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE IB 
               
               
                   
               
             
             
               
                 BLOCK 0: 
               
             
          
           
               
                 J 
                 K 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group0 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group1 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group2 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group3 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group4 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group5 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group6 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 I 
                 I 
                 Group7 
               
             
          
           
               
                 BLOCK 1: 
               
             
          
           
               
                 M 
                 M 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group8 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group9 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group10 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group11 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group12 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group13 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group14 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 I 
                 I 
                 Group15 
               
             
          
           
               
                 BLOCK 2: 
               
             
          
           
               
                 D 
                 D 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group16 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group17 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group18 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group19 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group20 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group21 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group22 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 I 
                 I 
                 Group23 
               
             
          
           
               
                 BLOCK 3: 
               
             
          
           
               
                 I 
                 M 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group24 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group25 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group26 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group27 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group28 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group29 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 Group30 
               
               
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 B 
                 I 
                 I 
                 Group31 
               
               
                   
               
               
                 JK = Frame Synchronization Pattern  
               
               
                 M = Maintenance Channel  
               
               
                 D = D Channel  
               
               
                 I = Idle Data  
               
               
                 B = Isochronous Channel  
               
             
          
         
       
     
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE II 
               
               
                   
                   
               
               
                   
                 Symbol 
                 Encoded (5 bit) 
                 Description 
               
               
                   
                   
               
             
             
               
                   
                 0 
                 11110 
                 Data 0 
               
               
                   
                 1 
                 01001 
                 Data 1 
               
               
                   
                 2 
                 10100 
                 Data 2 
               
               
                   
                 3 
                 10101 
                 Data 3 
               
               
                   
                 4 
                 01010 
                 Data 4 
               
               
                   
                 5 
                 01011 
                 Data 5 
               
               
                   
                 6 
                 01110 
                 Data 6 
               
               
                   
                 7 
                 01111 
                 Data 7 
               
               
                   
                 8 
                 10010 
                 Data 8 
               
               
                   
                 9 
                 10011 
                 Data 9 
               
               
                   
                 A 
                 10110 
                 Data A 
               
               
                   
                 B 
                 10111 
                 Data B 
               
               
                   
                 C 
                 11010 
                 Data C 
               
               
                   
                 D 
                 11011 
                 Data D 
               
               
                   
                 E 
                 11100 
                 Data E 
               
               
                   
                 F 
                 11101 
                 Data F 
               
               
                   
                 I 
                 11111 
                 No Ethernet Carrier 
               
               
                   
                 S 
                 11001 
                 No Ethernet Data 
               
               
                   
                 V 
                 01100 
                 Unaligned Data 
               
               
                   
                 T 
                 01101 
                 Unassigned 
               
               
                   
                 J 
                 11000 
                 Frame Sync Part 1 
               
               
                   
                 K 
                 10001 
                 Frame Sync Part 2 
               
               
                   
                 Q 
                 00000 
                 Invalid 
               
               
                   
                 H 
                 00100 
                 Invalid 
               
               
                   
                 R 
                 00111 
                 Invalid 
               
               
                   
                 V 
                 00001 
                 Invalid 
               
               
                   
                 V 
                 00010 
                 Invalid 
               
               
                   
                 V 
                 00011 
                 Invalid 
               
               
                   
                 V 
                 00101 
                 Invalid 
               
               
                   
                 V 
                 00110 
                 Invalid 
               
               
                   
                 V 
                 01000 
                 Invalid 
               
               
                   
                 V 
                 10000 
                 Invalid 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
               
               
             
               
               
             
               
               
               
             
               
               
             
               
               
               
             
               
               
             
               
               
               
             
               
               
             
               
               
               
             
               
               
             
               
               
               
             
               
               
             
               
               
               
             
               
               
             
           
               
                   
                 TABLE III 
               
               
                   
                   
               
             
             
               
                   
                 LG 13: 
                 isolink &amp; 16ms 
               
             
          
           
               
                   
                 clr 16ms 
               
               
                   
                 index = 0 
               
               
                   
                 clr 62.5us 
               
               
                   
                 lp = 1 
               
             
          
           
               
                   
                 LG 11: 
                 !0baseT &amp; (16 ms | txen) 
               
             
          
           
               
                   
                 clr 16ms 
               
               
                   
                 lp=txen 
               
             
          
           
               
                   
                 LG 12: 
                 isosleep &amp; sync 
               
             
          
           
               
                   
                 clr 16ms 
               
             
          
           
               
                   
                 LG 21: 
                 !sync 
               
             
          
           
               
                   
                 lp = 1 
               
             
          
           
               
                   
                 LG 34: 
                 62.5 μs 
               
             
          
           
               
                   
                 clr 62.5 
               
               
                   
                 lp=data|index| 
               
             
          
           
               
                   
                 LG 43: 
                 62.5 μs &amp; iindex !=15) 
               
             
          
           
               
                   
                 :p=1 
               
               
                   
                 inc index 
               
             
          
           
               
                   
                 LG 41: 
                 62.5 μs &amp; iindex=15) 
               
             
          
           
               
                   
                 lp=1 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE IV 
               
               
                   
                   
               
               
                   
                 Term 
                 Meaning 
                 Value 
               
               
                   
                   
               
             
             
               
                   
                 isolink 
                 Enables Generation of isolink 
                 Not Applicable 
               
               
                   
                   
                 pattern 
               
               
                   
                 16ms 
                 16 ms timer 
                 16 ms 
               
               
                   
                 62.5us 
                 62.5 μs timer 
                 62.5 μs 
               
               
                   
                 lp 
                 limk pulse 
                 Not Applicable 
               
               
                   
                 txen 
                 Transmit enable 
                 Not Applicable 
               
               
                   
                 isosleep 
                 Enables Generation of link 
                 Not Applicable 
               
               
                   
                   
                 low power link pulses 
               
               
                   
                 sync 
                 Signal from template 
                 Not Applicable 
               
               
                   
                   
                 generator indicating start of 
               
               
                   
                   
                 cycle 
               
               
                   
                 10 Base T 
                 Enable Generation of 10 Base 
                 Not Applicable 
               
               
                   
                   
                 T link pulses 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
               
             
               
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
           
               
                   
                 TABLE V 
               
               
                   
                   
               
             
             
               
                   
                  ! reset 
               
             
          
           
               
                   
                 I0baset     = 1 
               
               
                   
                 linkgood = 1 
               
               
                   
                 setllt     = 1 
               
               
                   
                 setltmt    = 1 
               
             
          
           
               
                   
                  bp1 = receive + (linkpulse * 
               
             
          
           
               
                   
                  ltmtDone) 
               
               
                   
                 I0baset     = 1 
               
               
                   
                 linkgood = 1 
               
               
                   
                 setllt     = 1 
               
               
                   
                 setlterm  = 1 
               
             
          
           
               
                   
                  bp2 = fastlink 
               
               
                   
                  bp3 = lltdone *{overscore (receive *)} 
               
             
          
           
               
                   
                  {overscore (linkpulse)} 
               
               
                   
                 loadlc     = 1 
               
               
                   
                 I0baset     = 1 
               
             
          
           
               
                   
                  bp4 = receive 
               
             
          
           
               
                   
                 I0baset     = 1 
               
             
          
           
               
                   
                  bp5 = fastlink 
               
               
                   
                  bp6 = {overscore (receive *)} {overscore (linkpulse)} 
               
             
          
           
               
                   
                 I0baset     =  1 
               
               
                   
                 setltmt    = ! 
               
               
                   
                 setltxt  = 1 
               
             
          
           
               
                   
                  bp7 = LCDone + receive 
               
             
          
           
               
                   
                 I0baset     = 1 
               
             
          
           
               
                   
                  bp8 = fastlink 
               
               
                   
                  bp9 = linkpulse * ltmtDone 
               
             
          
           
               
                   
                 I0baset     = 1 
               
               
                   
                 declc   = 1 
               
             
          
           
               
                   
                 bp10 = {overscore (receive *)} 
                 ltxtDone 
               
             
          
           
               
                   
                 linkpulse * 
                 {overscore (ltmtDone)} 
               
               
                   
                 I0baset     = 1 
               
               
                   
                 loadlc     = 1 
               
             
          
           
               
                   
                 bp11 = {overscore (receive *)} {overscore (txc)} 
               
             
          
           
               
                   
                 I0baset     = 1 
               
               
                   
                 linkgood = 1 
               
               
                   
                 setllt     = 1 
               
               
                   
                 setltmt    = 1 
               
             
          
           
               
                   
                 bp12 =  fastlink * 
               
             
          
           
               
                   
                  receive * txe 
               
             
          
           
               
                   
                 bp13 = receive 
               
             
          
           
               
                   
                   I0baset      = 1 
               
             
          
           
               
                   
                 bp14 = receive 
               
             
          
           
               
                   
                   I0baset      = 1 
               
             
          
           
               
                   
                 bp15 = fastlink 
               
             
          
           
               
                   
                 loadlc     = 1 
               
               
                   
                 I0baset     = 1 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE VI 
               
               
                   
                   
               
               
                   
                 Term 
                 Meaning 
                 Value 
               
               
                   
                   
               
             
             
               
                   
                 IObaset 
                 Enable IObase·T Mode 
                 Not Applicable 
               
               
                   
                 linkgood 
                 IObaset state machine has 
                 Not Applicable 
               
               
                   
                   
                 detected good link pulses 
               
               
                   
                 setllt 
                 Set Limit Loss Timer 
                 Not Applicable 
               
               
                   
                 setltmt 
                 Set Link Timer Min Time 
                 Not Applicable 
               
               
                   
                 receive 
                 Now called ipact 
                 Not Applicable 
               
               
                   
                 linkpulses 
                 Link Pulses from Front End 
                 Not Applicable 
               
               
                   
                 ltmtDone 
                 Link Time Min Timer Done 
                 4 ms 
               
               
                   
                 fastlink 
                 Iso Link Detector 
                 Not Applicable 
               
               
                   
                 lltdone 
                 Link Loss Timer Done 
                 60 ms 
               
               
                   
                 loadlc 
                 Load Link Counter Counts Link 
                 Not Applicable 
               
               
                   
                   
                 Pulses 
               
               
                   
                 setltxt 
                 Set Link Test Max Timer · Same 
                 Not Applicable 
               
               
                   
                   
                 as sltxt 
               
               
                   
                 LCDone 
                 Link Counter Done 
                 Not Applicable 
               
               
                   
                 declc 
                 Decrement Link Counter 
                 Not Applicable 
               
               
                   
                 ltxtDone 
                 Link Test Max Timer Done 
                 32 ms 
               
               
                   
                 txe 
                 Transmit Enable 
                 Not Applicable 
               
               
                   
                 txc 
                 Transmit Clock 
                 Not Applicable 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
           
               
                   
                 TABLE VII 
               
               
                   
                   
               
             
             
               
                   
                  bp1 = linkpulse 
               
             
          
           
               
                   
                 setltmt = 1 
               
             
          
           
               
                   
                  bp2 = flmtDone 
               
               
                   
                  bp3 = linkpulse * {overscore (flmtDone)} 
               
             
          
           
               
                   
                 settlmt = 1 
               
             
          
           
               
                   
                  bp4 = flmtDone 
               
               
                   
                  bp5 = linkpulse * flmtDone 
               
             
          
           
               
                   
                 setflmt = 1 
               
             
          
           
               
                   
                  bp6 = flmtDone 
               
               
                   
                  bp7 = linkpulse * flmt + Done 
               
             
          
           
               
                   
                 setflmt = 1 
               
               
                   
                 fastlink = 1 
               
             
          
           
               
                   
                  bp8 = flmtDone * linkpulse 
               
             
          
           
               
                   
                 fastlink = 1 
               
               
                   
                 setflmt = 1 
               
             
          
           
               
                   
                  bp9 = flmtDone 
               
             
          
           
               
                   
                 fastlink = 1 
               
               
                   
                 setltxt = 1 
               
             
          
           
               
                   
                 bp10 = receive 
               
             
          
           
               
                   
                 setltxt = 1 
               
               
                   
                   fastlink  = 1 
               
             
          
           
               
                   
                 bp11 = receive * ltxt Done 
               
             
          
           
               
                   
                 resetreg = 1 
               
             
          
           
               
                   
                 bp12 = linkpulse 
               
             
          
           
               
                   
                 setfldt= 1 
               
               
                   
                 setltmt = 1 
               
               
                   
                 setltxt = 1 
               
               
                   
                 fastlink = 1 
               
             
          
           
               
                   
                 bp13 = ltmtDone 
               
             
          
           
               
                   
                 fastlink = 1 
               
               
                   
                 shiftrow = 1 
               
             
          
           
               
                   
                 bp14 = linkpulse * {overscore (fldtDone)} 
               
             
          
           
               
                   
                 shift1 = 1 
               
               
                   
                 setltxt = 1 
               
               
                   
                 settim = 1 
               
               
                   
                 fastlink = 1 
               
             
          
           
               
                   
                 bp15 = linkpulse * fldtDone 
               
             
          
           
               
                   
                 setltxt = 1 
               
               
                   
                 setlim = 1 
               
               
                   
                 settldt = 1 
               
               
                   
                 fastlink = 1 
               
             
          
           
               
                   
                 bp17 = linkpulse * fldtDone 
               
             
          
           
               
                   
                 setltxt = 1 
               
               
                   
                 setlim = 1 
               
               
                   
                 settldt = 1 
               
               
                   
                 fastlink = 1 
               
             
          
           
               
                   
                 bp18 = ltmDone 
               
             
          
           
               
                   
                 fastlink = 1 
               
               
                   
                 shiftrow = 1 
               
             
          
           
               
                   
                 unconditional 
               
             
          
           
               
                   
                 setrlm = 1 
               
               
                   
                 setltrm = 1 
               
               
                   
                 setltxt = 1 
               
               
                   
                 fastlink = 1 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE VIII 
               
               
                   
                   
               
               
                   
                 Term 
                 Meaning 
                 Value 
               
               
                   
                   
               
             
             
               
                   
                 setflmt 
                 Set Fast Link Max Timer 
                 156.25 μs 
               
               
                   
                 flmtDone 
                 Fast Link Max Timer Done 
                 Not Applicable 
               
               
                   
                 resetreg 
                 Reset Registers · Used to 
                 Not Applicable 
               
               
                   
                   
                 clear registers upon loss of 
               
               
                   
                   
                 carrier 
               
               
                   
                 setfldt 
                 Set Fast Link Data Timer 
                 93.75 μs 
               
               
                   
                 shiftrow 
                 Shift Pointer to next row of 
                 Not Applicable 
               
               
                   
                   
                 link data shift register 
               
               
                   
                 fldtDone 
                 Fast Link Data Timer Done 
                 Not Applicable 
               
               
                   
                 shift1 
                 Shift a 1 bit into the link 
                 Not Applicable 
               
               
                   
                   
                 data shift register 
               
               
                   
                 shift0 
                 Shift a 0 bit into the link 
                 Not Applicable 
               
               
                   
                   
                 data shift register 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
               
               
             
           
               
                   
                 TABLE IX 
               
               
                   
                   
               
               
                   
                 Signal 
                 Meaning 
               
               
                   
                   
               
             
             
               
                   
                 ethclock 
                 Ethernet clock 
               
               
                   
                 farack 
                 Far acknowledge · used in link 
               
               
                   
                   
                 protocol 
               
               
                   
                 isogood 
                 Used to indicate isolink pattern 
               
               
                   
                   
                 good 
               
               
                   
                 isotype 
                 field in isolink pattern indicating 
               
               
                   
                   
                 ISO usage · normal, wideband, none. 
               
               
                   
                   
                 reserved 
               
               
                   
                 loadrxmode 
                 Load receive mode register 
               
               
                   
                 porttype 
                 Field in isolink pattern indicating 
               
               
                   
                   
                 port type · node, hub 
               
               
                   
                 reset 
                 Hardware reset 
               
               
                   
                 resetlink 
                 Reset signal used to clear contents 
               
               
                   
                   
                 of the receive link registers 
               
               
                   
                 rxmodebus 
                 Conveys the contents of the received 
               
               
                   
                   
                 link pattern 
               
               
                   
                 setackrx 
                 Set receive link acknowledge bit 
               
               
                   
                 setlim 
                 Set link initialization match · used 
               
               
                   
                   
                 to indicate that the link pattern 
               
               
                   
                   
                 was received consistently 3 times 
               
               
                   
                   
                 and was compatible with mode of 
               
               
                   
                   
                 device 
               
               
                   
                 setlinm 
                 Set link initialization no match · 
               
               
                   
                   
                 used to indicate that the link 
               
               
                   
                   
                 pattern was received consistently 3 
               
               
                   
                   
                 times and was not compatible with 
               
               
                   
                   
                 mode of device 
               
               
                   
                 temptype 
                 Template type · field in link 
               
               
                   
                   
                 pattern · isoenet, isotoken, 
               
               
                   
                   
                 reserved 
               
               
                   
                 txe 
                 Transmit enable 
               
               
                   
                 window 
                 Used to frame a group of link pulses 
               
               
                   
                   
                 to ensure that there is exactly 16 
               
               
                   
                   
                 bits 
               
               
                   
                 tmodebus 
                 Link pattern to be transmitted 
               
               
                   
                   
                 conveyed by this bus 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE X 
               
               
                   
                   
               
               
                   
                 Term 
                 Meaning 
                 Value 
               
               
                   
                   
               
             
             
               
                   
                 llt 
                 Link Loss Timer 
                 60 ms 
               
               
                   
                 ltmt 
                 Link Test Min Timer 
                  4 ms 
               
               
                   
                 ltxt 
                 Link Test Max Timer 
                 32 ms 
               
               
                   
                 flmt 
                 Fast Link Max Timer 
                 156.25 μs 
               
               
                   
                 fldt 
                 Fast Link Data Timer 
                    94 μs 
               
               
                   
                 ipact 
                 Input Packet from Squelch 
                 Not Applicable 
               
               
                   
                 sflmt 
                 Set Fast Link Max Timer 
                 Not Applicable 
               
               
                   
                 sltxt 
                 Set Link Test Max Timer 
                 Not Applicable