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Claims  |
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What is claimed is:
1. Apparatus for automatically configuring media connectors of a node
interface device in a local area network of the type which has at least
two pairs of conductors between interconnected interface devices, with
data being transmitted in one pair, including link data, being in the
opposite direction relative to data being transmitted in the other pair,
each node interface device having at least a first pair of connectors
which are adapted to transmit data and at least a second pair of
connectors adapted to receive data, the connectors being adapted to be
selectively connected to the at least two pairs of conductors, said
apparatus comprising:
a switch responsive to a switching signal and an inhibiting signal and
adapted to selectively connect a first pair of connectors to a first pair
of conductors and a second pair of connectors to a second pair of
conductors when said switch is in a first position, and selectively
connect said first pair of connectors to a second pair of conductors and
said second pair of connectors to said first pair of conductors when said
switch is in a second position;
a signal generator for producing said switching signal for selectively
switching said switch between said first and second positions, said
switching signal having one of first and second values, said switching
signal values changing in a pseudo-random manner; and,
a detector for generating an inhibiting signal in response to link data
being detected in one of said pairs of connectors, said inhibiting signal
being applied to said switch to thereafter indefinitely prevent switching
thereof.
2. Apparatus as defined in claim 1 wherein said switching signal having one
of first and second values during each time period, each said time period
being constant and predetermined.
3. Apparatus as defined in claim 2 wherein said time period is within the
range of about 50 milliseconds and about 60 milliseconds.
4. Apparatus as defined in claim 3 wherein said signal generator is a
linear feedback shift register.
5. Apparatus as defined in claim 4 wherein said signal generator is a
linear feedback shift register adapted to execute the polynomial
expression 1+e.sup.9 +e.sup.11.
6. Apparatus as defined in claim 5 wherein said linear feedback shift
register is an 11 bit linear feedback shift register.
7. Apparatus as defined in claim 3 wherein said value is a digital 1 or 0.
8. Apparatus as defined in claim 3 wherein said signal generator includes a
clock signal generator for producing a sample clock signal for generating
a time base corresponding to said time periods.
9. Apparatus as defined in claim 2 further including a random time
generator for generating a reset signal for resetting said signal
generator after a second time period having a generally constant duration,
said second time period being substantially greater than said switching
signal generating time period.
10. Apparatus as defined in claim 9 wherein said random time generator
comprises an analog electrical circuit that generates said reset signal.
11. Apparatus as defined in claim 1 wherein said interface devices comprise
one of a Media Dependent Interface (MDI) Network Interface Card (NIC) used
as an end node device and a Media Dependent Interface X (MDIX) Network
Interface Card (NIC) used as a part of a repeater or switch.
12. Apparatus associated with at least one node interface device for
automatically configuring media connectors of the node interface device
directly connected to another node interface device in a network of the
type which has at least first and second pairs of conductors between
directly connected interface devices and wherein data, including link
data, is transmitted in the first pair in a first direction and in a
second direction in the second pair, each node interface device having at
least a first pair of connectors which are adapted to transmit data and at
least a second pair of connectors adapted to receive data, the apparatus
being adapted to selectively connect the two pairs of connectors to the
two pairs of conductors to alternate the connection of the first and
second pairs of connectors with the two pairs of conductors, said
apparatus comprising:
a switch adapted to selectively alternate the connection of the first and
second pairs of connectors with the two pairs of conductors when operated
responsive to a switching signal having a first predetermined value being
applied thereto;
a signal generator successively generating a switching signal having a
value that changes between said first predetermined value and a second
predetermined value for operating said switch; said switching signal value
changing in a pseudo-random manner; and,
a detector adapted to generate a signal for inhibiting the application of
said switching signal having said first predetermined value to said switch
in response to link data being detected in one of said pairs of
connectors.
13. Apparatus as defined in claim 12 wherein said node interface devices
comprise one of an end node device and an intermediate node device.
14. Apparatus as defined in claim 13 wherein an intermediate node device is
a repeater or control.
15. Apparatus as defined in claim 12 wherein said signal generator is a
linear feedback shift register.
16. Apparatus as defined in claim 15 wherein said signal generator is a
linear feedback shift register adapted to execute the polynomial
expression 1+x.sup.9 +x.sup.11.
17. A method of automatically configuring media connectors of a node
interface device in a local area network of the type which has at least
two pairs of conductors between interconnected interface devices, with
data being transmitted in one pair, including link data, being in the
opposite direction relative to data being transmitted in the other pair,
each node interface device having at least a first pair of connectors
which are adapted to transmit data and at least a second pair of
connectors adapted to receive data, the connectors being adapted to be
selectively connected to the at least two pairs of conductors, said method
comprising the steps of:
selectively connecting the first pair of connectors to the first pair of
conductors and the second pair of connectors to the second pair of
conductors when a switch is in a first position;
selectively connecting the first pair of connectors to the second pair of
conductors and the second pair of connectors to the first pair of
conductors when said switch is in a second position;
producing a switching signal for selectively switching said switch between
said first and second positions, said switching signal having one of first
and second values during each first time period, said switching signal
values changing in a pseudo-random manner;
detecting link data in one of the pairs of connectors;
generating an inhibiting signal in response to link data being detected in
one of the pairs of connectors; and,
applying said inhibiting signal to said switch to thereafter indefinitely
prevent switching thereof.
18. A method as defined in claim 17 wherein each said first time period is
constant and predetermined.
19. A method as defined in claim 18 wherein said first time period is
within the range of about 50 milliseconds and about 60 milliseconds.
20. A method as defined in claim 19 wherein said value is a digital 1 or 0.
21. A method as defined in claim 18 wherein said switching signal producing
step further comprises generating a clock signal a sample clock signal for
generating a time base corresponding to said time periods.
22. A method as defined in claim 18 further comprising generating a reset
signal for reinitiating said producing step after a second time period
having a generally constant duration, said second time period being
substantially greater than said first time period.
23. A method as defined in claim 17 wherein said switching signal producing
step further comprises executing the polynomial expression 1+e.sup.9
+e.sup.11.
24. A method of automatically configuring media connectors of a node
interface device directly connected to another node interface device in a
network of the type which has at least first and second pairs of
conductors between directly connected interface devices and wherein data,
including link data, is transmitted in the first pair in a first direction
and in a second direction in the second pair, each node interface device
having at least a first pair of connectors which are adapted to transmit
data and at least a second pair of connectors adapted to receive data, the
apparatus being adapted to selectively connect the two pairs of connectors
to the two pairs of conductors to alternate the connection of the first
and second pairs of connectors with the two pairs of conductors, said
method comprising the steps of:
selectively connecting the first pair of connectors to the first pair of
conductors and the second pair of connectors to the second pair of
conductors and the first pair of connectors to the second pair of
conductors and the second pair of connectors to the first pair of
conductors;
alternating the connection of the first and second pairs of connectors with
the two pairs of conductors;
detecting link data in one of the pairs of connectors or conductors; and,
inhibiting said alternating of the connection in response to link data
being detected.
25. A method as defined in claim 24 wherein said alternating of the
connection occurs in a pseudo-random manner.
26. Apparatus associated with at least one node interface device for
automatically configuring media connectors of the node interface device
directly connected to another node interface device in a network of the
type which has at least two pairs of conductors between directly connected
interface devices, so that data, including link data, that is transmitted
from a first node interface device is capable of being received in the
directly connected second node interface device, and visa versa, each node
interface device having at least a first pair of connectors which are
adapted to transmit data and at least a second pair of connectors adapted
to receive data, the apparatus being adapted to selectively connect the
two pairs of connectors to the two pairs of conductors to alternate the
first and second pairs of connectors with the two pairs of conductors to
achieve the configuration that results in bi-directional data
communication between the first and second node interface devices, said
apparatus comprising:
a switch adapted to selectively alternate the connection of the first and
second pairs of connectors with the two pairs of conductors when operated
responsive to a switching signal having a first predetermined value being
applied thereto;
a signal generator that successively generates a switching signal having a
value that changes between said first predetermined value and a second
predetermined value for operating said switch, and including a clock
generator for establishing a clock period during which one of said values
is generated, said switching signal value changing in a pseudo-random
manner that results in the maintenance of one of said values during at
least two successive clock periods; and,
a signal detector for detecting link data in one of said pairs of
connectors and generating a signal for inhibiting the application of said
switching signal having said first predetermined value to said switch in
response to link data being detected.
27. A method of automatically configuring media connectors of a node
interface device directly connected to another node interface device in a
network of the type which has at least first and second pairs of
conductors between directly connected interface devices and wherein data,
including link data, is transmitted in the first pair in a first direction
and in a second direction in the second pair, each node interface device
having at least a first pair of connectors which are adapted to transmit
data and at least a second pair of connectors adapted to receive data, the
apparatus being adapted to selectively connect the two pairs of connectors
to the two pairs of conductor s to alternate the connection of the first
and second pairs of connectors with the two pairs of conductors, said
method comprising the steps of:
selectively connecting the first pair of connectors to the first pair of
conductors and the second pair of connectors to the second pair of
conductors when a switch is in a first position;
selectively connecting the first pair of connectors to the second pair of
conductors and the second pair of connectors to the first pair of
conductors when said switch is in a second position;
producing a switching signal for selectively alternating the connection of
the first and second pairs of connectors with the two pairs of conductors,
said switching signal alternating the connection in a pseudo-random
manner;
detecting link data in one of the pairs of connectors or conductors;
generating an inhibiting signal in response to link data being detected;
and,
inhibiting said alternating of the connection in response to said
inhibiting signal being generated.
28. A method of automatically configuring media connectors of a node
interface device directly connected to another node interface device in a
network of the type which has at least first and second pairs of
conductors between directly connected interface devices and wherein data,
including link data, is. transmitted in the first pair in a first
direction and in a second direction in the second pair, each node
interface device having at least a first pair of connectors which are
adapted to transmit data and at least a second pair of connectors adapted
to receive data, the apparatus being adapted to selectively connect the
two pairs of connectors to the two pairs of conductors to alternate the
connection of the first and second pairs of connectors with the two pairs
of conductors, said method comprising the steps of:
selectively connecting the first pair of connectors to the first pair of
conductors and the second pair of connectors to the second pair of
conductors when a switch is in a first position;
selectively connecting the first pair of connectors to the second pair of
conductors and the second pair of connectors to the first pair of
conductors when said switch is in a second position;
producing a switching signal for selectively alternating the connection of
the first and second pairs of connectors with the two pairs of conductors,
said switching signal alternating the connection in a pseudo-random
manner;
detecting link data in one of the pairs of connectors or conductors; and,
inhibiting said alternating of the connection in response to link data
being detected. |
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Claims |
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Description |
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The present invention generally relates to computer local area networks,
and more particularly to node devices having Media Dependent Interfaces
(MDI) that are installed in such networks and their automatic connection
configuration.
Many local area network products (LAN) use a medium consisting of twisted
copper wire pairs for the transmission and reception of data. It is
generally a requirement that one or more pairs be used for transmission of
data in one direction and one or more other pairs to receive data in the
opposite direction. The connection between two node devices is a link. For
LAN technologies which employ a full-duplex medium, many have different
pairs for transmission than for reception and thereby require that each
end of the link use a defined assignment for its twisted pair connector to
a particular pair of wires. For example, a Network Interface Card (NIC) is
usually employed as an end node device, while a switch or a repeater will
be employed as a concentrator or central component in a star-based
network. For the link to operate, the NIC must transmit on a pair of wires
that is connected to the receiver of the hub or switch and the NIC's
receiver must be connected to the transmitter at the other end of the
link. If the transmit pair of wires of a device are connected to the
transmit connectors of the connected device, the communication link will
obviously fail.
Most LAN standards address this by assigning different connector pins to
the wires in the twisted pair which is typically referred to as the Media
Dependent Interface (MDI). In the IEEE-802.3's 10BASE-T standard, an end
node will assign pins 1 and 2 to the transmit pair while pins 3 and 6 are
for connection to a twisted pair for receiving. The hub, which is
typically a repeater or a switch for a 10BASE-T network, will assign its
transmitter to pins 3 and 6 while its receiver will be connected to pins 1
and 2. This works quite well for configurations where NIC's are attached
to repeaters, but there are a few cases that become more important to
consider with the emergence of switched networks. First there is a case
where the NIC is connected directly to another NIC, or a repeater is
connected to a repeater or a repeater is connected to a switch. Depending
upon the assignment of pins at the network interface, it may become
necessary to employ a crossover cable to address the fact that both
products employ the same pin designations on their interfaces.
Some products will use a manual "MDIX" switch, with MDIX being a hub,
repeater or switch configuration as opposed to an end node device, which
is known as a MDI configured device. The switch allows the products to
connect to other similar devices but requires an installer to manually
push a button. The approach worked well for limited applications like a
repeater-to-repeater port, but not in the general case where it is desired
to build a produet that attaches to either a repeater, NIC or switch
without manual intervention.
This resulted in the development of bus switches for making a solid state
version of a crossover type circuit that used a low frequency alternating
pin selection to perform an automatic operation. However, the product had
the drawback that if two such devices were attached together, they could
potentially get into a "lock step" operation where the necessary
connections for establishing a communication link became impossible.
Subsequently other products were developed which employed a similar
algorithm and were forced to use a different alternation rate to avoid the
lock step phenomena. While that worked for a limited set of products, it
did not solve the general case whereby a guaranteed connection between
nodes was achieved regardless of the manufacture or the model of product
that was being used.
Accordingly, it is a primary object of the present invention to effectively
solve the problem of lock step interaction in an improved automatic media
connection apparatus which can effectively be used with products of well
known manufacturers.
It is another object of the present invention to provide such an improved
apparatus by using a pseudo-random generating element, in addition to an
actual random elements to provide an implementation of an auto-MDIX/MDI
algorithm that is virtually impossible to be placed in a lock step
condition.
Yet another object of the present invention is to provide such an improved
apparatus that is inexpensive to implement. The low cost is achieved by
utilizing logic elements that exist in many node devices, so that
software, or very minor hardware implementations comprise the essential
cost that is involved.
Still another object of the present invention is to provide such an
improved apparatus which is robust in its functionality and requires no
user or customer intervention and which is operable whenever a device
embodying the present invention is added to a network. Once the physical
connections are made and the apparatus powered up, proper configuration is
virtually assured.
These and other objects will become apparent upon reading the following
detailed description, while referring to the attached drawings, in which:
FIG. 1 is a schematic diagram of the prior art and showing a media
dependent interface 10BASE-T network interface card connected to a similar
hub interface card;
FIG. 2 is a schematic diagram of the prior art and showing two 10BASE-T
media dependent interface hubs connected together with a crossover
connection to establish and maintain the communication links;
FIG. 3 is a perspective view of a female media dependent interface
connector of the type which has pin connectors pursuant to the
requirements of section 3FIGS. 1-4 of IEC603-7, detail specification for
connectors;
FIG. 4 is a plug connector adapted for use to connect with the female
connector shown in FIG. 3;
FIG. 5 is a table identifying the assignment of PHY signals to MDI and
MDI-X pin identification and configuration;
FIG. 6 is an electrical schematic diagram of a network interface card in
conjunction with a media switch, a processor and associated circuitry
which forms a part of the preferred embodiment of the present invention;
FIG. 7 is a schematic diagram of a state machine which represents the logic
of the operation of the apparatus embodying the present invention; and,
FIG. 8 is a chart illustrating the probability of not establishing a
communication link versus time.
DETAILED DESCRIPTION
The present invention generally relates to an apparatus for automatically
configuring media connections in a local area network. While the apparatus
embodying the present invention is particularly directed to apparatus for
automatically configuring connectors which use twisted copper wire pairs
for transmission of data in a first direction in a network, and other
twisted copper wire pairs for transmission of data in the opposite
direction, the present invention has application for other media. It is
particularly suited for local area networks (LAN's) which operate on a
10BASE-T standard, a 100BASE-T standard as well as for 1000BASE-T, and
also works for FDDI-TPPMD, Token Ring, and others.
The apparatus automatically determines and sets the configuration of end
node media dependent interfaces (MDI) or interfaces for repeaters,
switches and hubs which have a MDIX configuration. The apparatus provides
very rapid resolution of divisional nodes for configuring the node
properly in one of the MDI or MDIX configurations so that bidirectional
communication is enabled. The apparatus is extremely robust in that it is
virtually impossible for the automatic and accurate configuration not to
be set and that a lock-up condition occur. The apparatus is easily
implemented, is interoperable with existing products at an extremely low
cost and may be implemented with CMOS switches, or parallel transmitter
and receiver blocks for 10BASE-T and 100BASE-T LANs.
Turning now to the drawings, and particularly FIG. 1, a schematic diagram
of a 10BASE-T media dependent interface (MDI) is shown, with a network
interface card indicated generally at 10, being shown on the left with a
similar hub interface indicated generally at 12 shown on the right, with
the transmit pair of connectors of the NIC 10 having pins 1 and 2
connected to pins 1 and 2 of the hub 12 by a twisted pair cable 14. The
receive connectors for the NIC 10 are pins 3 and 6 whereas the transmit
pair of the hub 12 are pins 3 and 6 and are interconnected with a twisted
pair cable 16.
As shown in FIG. 2, another prior art configuration is illustrated with a
repeater or switch or hub 18 being interconnected with a similar repeater,
switch or hub 20. In this instance, a crossover connection is necessary so
that receive pins 1 and 2 of hub 18 are connected by pair 22 to the
transmit pair 3 and 6 of hub 20. Similarly, transmit connectors 3 and 6
are connected to receive connectors 1 and 2 of hub 20 by twisted pair 24.
The actual connections are made with MDI 8 pin connectors 26 and pin 28
shown in FIGS. 3 and 4, respectively, and the 8 contacts are connected in
the manner set forth in the chart of FIG. 5.
Turning to the apparatus of the present invention, partially shown in FIG.
6, the hub, repeater or switch 12 is shown on the right being connected
via twisted pairs 14 and 16 to a media switch 20. The media switch has
twisted pairs 22 and 24 that can be connected to another node in the
network. The pair 22 has arrows in the rightward direction indicating
transmission of data to the right, while the pair 24 shows transmission to
the left. The media switch 20 has four sets of contacts 26 which in the
position illustrated interconnect the pair 22 with the receive contacts
pins 1 and 2, and the pair 24 to the transmit pair pins 3 and 6. As
illustrated, the four contacts 26 are adapted to be switched from the
position as shown to the lower position responsive to a suitable
controlling signal applied to the switch 20. In the lower position, the
hub 12 contacts 1 and 2 are connected to the twisted pair 24 and contacts
3 and 6 to the pair 22. It should be apparent that the contacts 26 of the
switch 20 will effectively switch the receive and transmit contacts
between the pairs 22 and 24.
In accordance with an important aspect of the present invention, the
decision to operate the switch 20 and change the contact position, as well
as the timing thereof, is controlled by an 11 bit scrambler, indicated
generally at 30, which is a linear feedback shift register. The shift
register includes an exclusive OR gate 32 which generates a zero (0) if
both inputs are equal and a one if they are not. The inputs to the
exclusive OR gate are bits 8 and 10 of the shift register. The user can
initially load the shift register with a set of values that may be any
combination of ones and zeros with the exception that they cannot all be
zero. The scrambler 30 executes the polynomial 1+x.sup.9 +x.sup.11, and it
will repeat its pseudo-random sequence every 2,048 clock cycles.
If there is a similar shift register in another media switch associated
with a device that is on the other end of the link, then the possibility
of both shift registers having the same value at any one time is 1 in
2.sup.22. While a shorter or longer shift register may be used, the
illustrated 11 bit shift register that implements the above polynomial is
also used to scramble data in the 100BASE-T specification and is therefore
commonly available in the node devices being used. Since they are
available, they can obviously be used for the purpose of controlling the
switching of the media switch 20. In essence, the shift register 30 has
its 10th bit connected to the exclusive OR gate 32 as well as to the
control for the switch 20. When the 10th bit is high or a 1, combined with
other logic conditions as stated below, the switch is placed in a position
opposite that shown in FIG. 6 and corresponding to the table of FIG. 5.
Thus, contacts 1 and 2 are connected to pair 24 and contacts 3 and 6 are
connected to pair 22.
The apparatus of the present invention includes a signal detector to
determine whether any link pulses, or technology signals are present at
the receiver. The shift register is preferably clocked with a signal that
is derived from a 25 MHZ clock with 100 parts per million accuracy, which
is typically used for 100BASE-T and 10BASE-T devices. It should be
understood that other clock frequencies may be used in the system with the
operation of the network, if the reliability of consistently determining
the presence of link pulses or link data is provided. The 25 MHZ clock
develops a time unit that can conveniently be termed a time slot which is
defined to be preferably 62 milliseconds+-2 milliseconds. This time slot
duration is sufficiently long to insure accurate sampling of link pulses
which have a maximum spacing of 24 milliseconds. The time slot duration is
slightly more than twice the spacing of link pulses and thereby reliably
insures that a link pulse will be detected, even though the relative
timing of the shift registers of adjacent node devices may be slightly
different.
If the present invention is installed in a LAN whereby existing node
devices that are not switched are present, the apparatus will properly
configure the device so that two way communication will occur in -about
two time slots. However, if both devices are of the switching type and
each includes the shift register 30, then the proper configuration of both
devices will occur within 10 time slots. This is shown in the probability
chart versus run length in time slots illustrated in FIG. 8.
The present invention includes a processor 34 which is functionally
illustrated in FIG. 6 and which is connected to the media switch 20 and
the shift register 30. The processor includes a signal detector for
detecting signals of predetermined threshold values on the twisted pairs
22 and 24 when connected to the switch 20. The processing means also
includes a clock for clocking the shift register 30 as well as an analog
free-running timer, identified as an A_timer, for resetting the apparatus
including the shift register 30. The shift register 30 reduces the
probability of a lock step condition on the basis of two devices which
have been initialized at different times.
If both devices have a shift register 30, then there is only a 1 in
2.sup.22 chance that both shift registers will be in the exact same state
at the same time. This is the only condition in which a lock step
situation may exist for two adjacent node devices. Other than this single
instance, the two node devices are guaranteed to acquire a communication
link within ten slot times as shown in FIG. 8. This is mandated by the
fact that two 11 bit shift registers will not go more than 10 cycles in a
row with equal values unless they are completely synchronized. Thus, the
maximum time required for two node devices to establish a link is
approximately 620 milliseconds. While the length of the shift register may
be increased to reduce the probability of synchronization between nodes,
the maximum link establishment time will be necessarily increased. The
length of the shift register may also be reduced, but that would increase
the probability that a lock step condition could occur.
The processing means 34 may be a separate microprocessor or other
processing means such as a digital state machine or the like; it may be a
special chip that incorporates the media switch 20 as well as the shift
register. The shift register functionality may be implemented in the
processing means rather than an independent circuit such as shown in FIG.
6 and the processing means may be supplied by an interface processor that
is part of the node device. Similarly, the node device may include signal
detectors which will provide the necessary information to indicate when a
communication link has been established or broken, in which case, the
physical overhead for implementing the present invention may be virtually
free, with the apparatus operating with software routines of the type
known to those of ordinary skill in the art given the description of the
functionality that is provided herein.
The logic used to operate the present invention is best illustrated in a
state machine shown in FIG. 7. The processor 34 includes an A_timer which
is preferably an analog timer that has a time base that is provided by a
sloppy RC time constant so as to insure that every node device has a
random component that is different from all others. This is most easily
achieved by the RC time constant and the timer preferably times out
approximately every 1.3 seconds, plus or minus 25%. When it times out, it
generates a DONE pulse that is applied on line 40 diagrammatically
illustrated in the state machine of FIG. 7. When it times out, it sets the
media switch 20 in the MDI mode described in FIG. 5 and diagrammatically
shown in the block 42 of FIG. 7. In the MDI mode initialization, it starts
the sample timer which is the clock that drives the shift register 30 and
at the end of each time slot, the sample timer is done and if the 10th bit
on the shift register 30 is a zero or the Link_Detect signal is true, then
the apparatus is maintained in the MDI mode as diagrammatically shown by
line 44.
If the Link_Detect signal is true, that is an indication that communication
has been established. More specifically, the Link_Detect signal can be
true based upon a number of criteria. One is that a link pulse is
received, another is if MLT3 data is received, which is basically the
signaling for 100BASE-T technology. Another is if 10BASE-T signaling is
received. Another is if a fast link pulse, which is a series of link
pulses that are spaced closely together is received. All of these types of
signals can establish a true Link_Detect signal if the energies on the
receiver exceed a certain threshold, which is preferably a voltage in
excess of 500 millivolts for a duration of more than 50 nanoseconds.
If the apparatus is in the MDI mode and at the end of the sample timer time
slot, the tenth bit of the shift register 30 is a one and the Link_Detect
signal is false and a T-pulse is also false, the apparatus will switch the
media switch 20 into the MDIX mode which is shown by block 46. That will
cause the sample timer to be started, which when done, will result in
staying in the MDIX mode if the tenth bit of the shift register 30 is a
one or the Link_Detect signal is also true. If the tenth bit of the shift
register 30 is a zero at the end of the sample timer time slot and
Link_Detect is false and the T-pulse signal is also false, the switch 20
will switch back to the MDI mode as shown by line 50. In all situations,
when the Link_Detect signal is true, indicating that a communication link
has been established, the logic then ignores the sample timer and the
value of the tenth bit of the shift register 30 until the Link_Detect
signal goes false.
With regard to the T-pulse, it is a pulse that is generated when something
is being transmitted onto the wire pair. It is generated to preclude
switching between MDI and MDIX modes at that particular point in time. The
reason for doing so is that if a switch between modes is done in the
middle of a pulse transmission, it is possible that a reflection of the
pulse being transmitted could then come into the receiver because of the
switch occurring in the middle of transmission. It could appear to the
receiver that it detected something when in fact it was merely a
reflection of the pulse that was transmitted. So the T-pulse is used to
eliminate the probability of that pulse coming back and interfering with
the receiver. The MDI mode is the mode that the apparatus initially
establishes and is the mode that a reset will drive it to.
During operation, if someone were to unplug one of the pairs, the
Link_Detect will go false. At that point, either A-timer will have reset
itself, which will cause the apparatus to drop into the MDI mode and start
the sequence over again, or Sample_Timer will expire and depending on the
value of the 10th bit of shift register 30 the switch will either go back
to MDI mode or move to MDIX mode. Since the A_timer is a free running
timer, it outputs a pulse at the end of its time period of approximately
1.3 seconds. If A_timer is DONE, the Link_Detect signal is false, and
T_pulse is false, the conditions for transition 40 of FIG. 7 are true and
the state machine will go to the MDI_MODE state. When the Link_Detect
signal is false, the sample timer would very likely be done within
approximately 62 milliseconds and then depending upon the value of the
tenth bit of the shift register 30, would either switch to the other mode
or not.
From the foregoing, it should be appreciated that an extremely robust,
reliable and effective apparatus has been described which automatically
configures LAN devices so that bidirectional communication is enabled,
with the apparatus being inexpensive to implement and maintain. The
apparatus automatically determines and sets the interface configuration of
end node media dependent interfaces (MDI) or interfaces for repeaters,
switches and hubs which have a MDIX configuration. The apparatus is easily
implemented and is interoperable with nearly all existing products.
While various embodiments of the present invention have been shown and
described, it should be understood that other modifications, substitutions
and alternatives are apparent to one of ordinary skill in the art. Such
modifications, substitutions and alternatives can be made without
departing from the spirit and scope of the invention, which should be
determined from the appended claims.
Various features of the invention are set forth in the appended claims.
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