Handshaking circuit for resolving contention on a transmission medium regardless of its length

A handshaking circuit for establishing a particular relationship between nodes interconnected by a transmission medium, comprising:

• a state detector for monitoring said transmission medium to detect a predetermined first state, a predetermined second state, a contention when said predetermined first and second states are simultaneously asserted on said transmission medium, and an idle state when either of said first and second states is not asserted on said transmission medium;
• a state machine connected to the state detector for asserting the first state on the transmission medium to initiate a handshaking process and relinquishing the first state when the contention is detected by the state detector;
• a receive counter connected to the state detector for continuously incrementing a receive count value from the instant the contention is detected to the instant said idle state is detected;
• a transmit counter connected to the state detector and the state machine for continuously incrementing a transmit count value from the instant the first state is detected to the instant said contention is detected;
• a comparator for comparing the receive count value with the transmit count value,
• decision means for producing a first decision output when the transmit and receive count values are lower than a predefined threshold and a second decision output when one of said transmit and receive count values is greater than the predefined threshold;
• and
• a random period timer arranged to be activated in response to the detection of the contention by the state detector;
• wherein said state machine is arranged to:
• respond to the first decision output for asserting the first state on the transmission medium if the random period timer expires during the absence of the first and second states on the transmission medium and asserting the second state on the transmission medium if the random period timer expires during the presence of the first state on the transmission medium;
• and
• respond to the second decision output for asserting the first state on the transmission medium when the transmit count value is greater than the receive count value and asserting the second state on the transmission medium when the transmit count value is smaller than the receive count value.

A handshaking circuit for establishing a particular relationship between nodes interconnected by a transmission medium, comprising:

• a random number generator for producing a random number;
• a threshold generator having a first threshold value, a second threshold value, an adjustable value, means for summing the second threshold value and the adjustable value to produce a summed threshold value greater than the first threshold value, and means for selecting of the first threshold value and the summed threshold value depending on said random number;
• a state detector for detecting predetermined first and second states and a contention between said nodes on the transmission medium;
• a counter for continuously incrementing a clock count in response to the detection of the contention by the state detector;
• a comparator for comparing the clock count of the counter with the selected threshold value and producing an output when the clock count equals the selected threshold value;
• and
• a state machine connected to the state detector for asserting the first state on the transmission medium to initiate a handshaking process and relinquishing the first state when the contention is detected, and asserting the first state on the transmission medium again if the comparator produces said output during the absence of the first and second states on the transmission medium and asserting the second state on the transmission medium if the comparator produces said output during the presence of the first state on the transmission medium.

A communication system comprising a handshaking circuit connected through a repeater to a remote site via a transmission medium:

• the handshaking circuit comprising:
• a state detector for monitoring said transmission medium to detect a predetermined first state, a predetermined second state, an idle state and a contention when said predetermined first and second states are simultaneously asserted on said transmission medium;
• and
• a random period timer responsive to the detection of the contention by the state detector for continuously incrementing a clock count value;
• a state machine connected to the state detector for asserting the first state on the transmission medium to initiate a handshaking process and relinquishing the first state when the contention is detected, asserting the first state on the transmission medium again if the random period timer expires during the absence of the first or second state on the transmission medium and asserting said second state on the transmission medium if the random period timer expires during the presence of the first state on the transmission medium,
• the repeater comprising:
• a two-way format converter connected in said transmission medium so that the transmission medium is divided into a local side and a remote side;
• a contention detector for detecting a contention on the local side of said transmission medium;
• a first idle detector responsive to the detection of the contention for detecting the idle state on the local side of the transmission medium;
• notification means responsive to the detection of the idle state by the first idle detector for asserting a third state on the local side of the transmission medium and disabling said converter;
• a second idle detector responsive to the detection of said contention for detecting the idle state on the remote side of the transmission medium;
• a state detector responsive to the detection of the idle state by the second idle detector for monitoring the remote side of the transmission medium for disabling the notification means when the first state is detected on the remote side of the transmission medium;
• and
• a random period timer for disabling the notification means when a random interval from the time of detection of said contention expires,
• the state detector of the handshaking circuit being arranged to detect the third state on the local side of the transmission medium,
• the state machine of the handshaking circuit being arranged to be disabled in response to the detection of the third state so that the state machine is prevented from responding to the expiration of said random period timer of the handshaking circuit as long as the third state is detected on the local side of the transmission medium.

A method for resolving a contention that occurs on a transmission medium between two network nodes, using transmit and receive counters, the method comprising:

• a) monitoring said transmission medium to detect a predetermined first state, a predetermined second state, an idle state when either of said predetermined first and second states is not present on the transmission medium, and a contention between said network nodes when said predetermined first and second states are simultaneously present on the transmission medium;
• b) asserting the first state on said transmission medium to initiate a handshaking process and enabling the transmit counter to start incrementing a transmit count value;
• c) when said contention is detected, relinquishing the first state, disabling the transmit counter to stop incrementing the transmit count value and enabling the receive counter to start incrementing a receive count value;
• d) disabling the receive counter to stop incrementing the receive count value when the idle state is detected;
• e) comparing the receive count value with the transmit count value;
• and
• f) asserting the first state on the transmission medium again when the transmit count value is greater than the receive count value and asserting the second state on the transmission medium when the transmit count value is smaller than the receive count value.

A method of determining status of local and remote nodes interconnected by a transmission medium, comprising the steps of:

• a) transmitting, from the local node, a first request signal to the transmission medium for asserting a first state;
• b) causing a transmit counter in said local node to start incrementing a count value thereof in response to the transmission of said first request signal;
• c) canceling said first request signal if a contention occurs on said transmission medium between the first request signal and a second request signal transmitted from said remote node, causing said transmit counter to stop incrementing the count value thereof, and causing a receive counter in said local node to start increment a count value thereof;
• and
• d) causing said receive counter to stop incrementing the count value thereof when an idle state is detected on said transmission medium and setting said local node in said first state or in a second state depending on the count value of said transmit counter relative to the count value of the receive counter.

A method of determining status of local and remote nodes interconnected by a transmission medium, comprising the steps of:

• a) transmitting, from the local node, a first request signal to the transmission medium for asserting a parent state defined by the IEEE 1394 standard;
• b) causing a transmit counter in said local node to start incrementing a count value thereof in response to the transmission of said first request signal;
• c) canceling said first request signal if a contention occurs on said transmission medium between the first request signal and a second request signal transmitted from said remote node, causing said transmit counter to stop incrementing the count value thereof, and causing a receive counter in said local node to start incrementing a count value thereof;
• and
• d) causing said receive counter to stop incrementing the count value thereof when an idle state is detected on said transmission medium and setting said local and remote nodes in said parent and child states, respectively, defined by the IEEE 1394 standard, if the count value of the transmit counter is greater than the count value of the receive counter, and setting said local and remote nodes in said child and parent states, respectively, if the count value of the transmit counter is smaller than the count value of the receive counter.

A handshaking circuit for establishing a particular relationship between nodes interconnected by a transmission medium, comprising:

• a state detector for monitoring said transmission medium to detect child and parent states defined by the IEEE 1394 standard, a contention when said child and parent states are simultaneously asserted on said transmission medium, and an idle state when either of said child and parent states is not asserted on the transmission medium;
• a state machine connected to the state detector for asserting the child state on said transmission medium to initiate a handshaking process and relinquishing the child state when the contention is detected by the state detector;
• a receive counter connected to the state detector for continuously incrementing a receive count value from the instant the contention is detected to the instant said idle state is detected;
• a transmit counter connected to the state detector and the state machine for continuously incrementing a transmit count value from the instant the child state is detected to the instant the contention is detected;
• and
• a comparator for comparing the receive count value with the transmit count value,
• said state machine asserting the child state on the transmission medium again when the transmit count value is smaller than the receive count value and asserting said parent state on the transmission medium when the transmit count value is greater than the receive count value.

A handshaking circuit for establishing a particular relationship between nodes interconnected by a transmission medium, comprising:

• a state detector for monitoring said transmission medium to detect child and parent defined by the IEEE 1394 standard, and a contention when the child and parent states are simultaneously asserted on said transmission medium, and an idle state when either of said parent and child states is not asserted on said transmission medium;
• a state machine connected to the state detector for asserting the child state on the transmission medium to initiate a handshaking process and relinquishing the child state when the contention is detected by the state detector;
• a receive counter connected to the state detector for continuously incrementing a receive count value from the instant the contention is detected to the instant said idle state is detected;
• a transmit counter connected to the state detector and the state machine for continuously incrementing a transmit count value from the instant the child state is detected to the instant said contention is detected;
• a comparator for comparing the receive count value with the transmit count value,
• decision means for producing a first decision output when the transmit and receive count values are greater than a predefined threshold and a second decision output when one of said transmit and receive count values is lower than the predefined threshold;
• and
• a random period timer arranged to be activated in response to the detection of the contention by the state detector;
• wherein said state machine is arranged to:
• respond to the first decision output for asserting the child state on the transmission medium if the random period timer expires during the absence of the child and parent states on the transmission medium and asserting the parent state on the transmission medium if the random period timer expires during the presence of the child state on the transmission medium;
• and
• respond to the second decision output for asserting the child state on the transmission medium when the transmit count value is smaller than the receive count value and asserting the present state on the transmission medium when the transmit count value is greater than the receive count value.

A method for resolving a contention that occurs on a transmission medium between two network nodes, using transmit and receive counters, the method comprising:

• a) monitoring said transmission medium to detect child and parent states defined by the IEEE 1394 standard, an idle state when either of said child and parent states is not present on the transmission and contention between said network nodes when the child and parent are simultaneously present on the transmission medium;
• b) asserting the child state on said transmission medium to initiate a handshaking process and enabling the transmit counter to start incrementing a transmit count value;
• c) when said contention is detected, relinquishing the child state, disabling the transmit counter to stop incrementing the transmit count value and enabling the receive counter to start incrementing a receive count value;
• d) disabling the receive counter to stop incrementing the receive count value when the idle state is detected;
• e) comparing the receive count value with the transmit count value;
• and
• f) asserting the child state on the transmission medium again when the transmit count value is smaller than the receive count value and asserting the parent state on the transmission medium when the transmit count value is greater than the receive count value.