Medium access control protocol for single bus fair access local area network

An apparatus for priority data transmission utilizing a medium access control protocol with a fair cell-access scheme in a local area network having an unidirectional looped bus and a plurality of network stations coupled to the bus for asynchronous cell transmission from one network station to other network stations, said apparatus comprising:

• a) a head-of-bus for generating continuously time slots to the bus, each of the time slots including a busy bit, a high priority reserved bit, a low priority reserved bit, a high priority slot reservation bit and a low priority slot reservation bit, each of said time slots permitting transport of high priority cells and low priority cells;
• b) a given one of said plurality of network stations delivering a high priority cell to its current time slot when neither the busy bit nor the high priority reserved bit is set in said current time slot, said given network station thereafter setting the busy bit;
• c) a given one of said plurality of network stations delivering a low priority cell to its current time slot if:
• (i) a high priority cell is not being delivered and (ii) neither the busy bit nor the low priority reserved bit is set in said current time slot, said given network station thereafter setting the busy bit;
• d) a given one of said plurality of network stations setting the high priority slot reservation bit in its current time slot to reserve a future time slot from the head-of-bus when the busy bit is set and the priority slot reservation bit is not set in said current time slot;
• e) a given one of said plurality of network stations setting the low priority slot reservation bit in its current time slot to reserve a future time slot from the head-of-bus if (i) the high priority slot reservation bit is not being set, (ii) the busy bit is set and (iii) the low priority slot reservation bit is not set in said current time slot;
• f) said head-of-bus generating a time slot to the bus and setting the high priority reserved bit in said generated time slot to indicate that a time slot has been reserved for high priority cell transmission when a time slot with the high priority slot reservation bit set is received by said head-of-bus;
• g) said head-of bus generating a time slot to the bus and setting the low priority reserved bit in said generated time slot to indicate that a time slot has been reserved for low priority cell transmission when a time slot with the high priority slot reservation bit set is received by said head-of-bus;
• h) a given one of said plurality of network stations delivering a high priority cell to its current time slot if:
• (i) said given network station had recently set the high priority slot reservation bit, (ii) the busy bit is not set in said current time slot and (iii) the high priority reserved bit is set in said current time slot;
• and
• i) a given one of said plurality of network stations delivering a low priority cell to its current time slot if:
• (i) said given network station had recently set the low priority slot reservation bit, (ii) the busy bit is not set in said current time slot and (iii) the low priority reserved bit is set in said current time slot.

A method of providing n-level priority data transmission utilizing a medium access control protocol with a fair cell-access scheme in a local area network having an unidirectional looped bus and a plurality of network stations coupled to the bus for asynchronous cell transmission from one network station to other network stations, said method comprising the steps of:

• a) continuously generating time slots from a head-of-bus to the bus, each of the time slots including a busy bit, n priority reserved bits, and n priority slot reservation bits where n is a number greater than or equal to 2;
• b) providing each of said plurality of network stations with said time slots to permit transport of priority cells;
• c) permitting delivery of a priority cell of a given priority level from a given network station to its current time slot if (i) the busy bit is not set in said current time slot and (ii) any priority reserved bits having priority levels higher than said given priority level are not set in said current time slot, said given network station thereafter setting the busy bit;
• d) setting the priority slot reservation bit of a given priority level in a current time slot at a given network station to reserve a future time slot from the head-of-bus if (i) the busy bit is set and (ii) no priority slot reservation bits having priority levels higher than said given priority level are set in said current time slot;
• e) said head-of-bus generating a time slot to said bus and setting the priority reserved bit of a given priority level in said generated time slot to indicate that a time slot has been reserved for priority cell transmission of said given priority level when a slot having the priority slot reservation bit of said given priority level set is received by said head-of-bus;
• f) delivering a priority cell of a given priority level from a given network station to its current time slot if:
• (i) said given network station had recently set the priority slot reservation bit of said given priority level, (ii) the busy bit is not set in said current time slot and (iii) the priority reserved bit of said given priority level is set in said current time slot.

An apparatus for n-level priority data transmission utilizing a medium access control protocol with a fair cell-access scheme in a local area network having a unidirectional looped bus and a plurality of network stations coupled to the bus for asynchronous cell transmission from one network station to other network stations, said apparatus comprising:

• a) a head-of-bus for generating continuously time slots to the bus, each of the time slots including a busy bit, n priority reserved bits, and n priority slot reservation bits where n is a number greater than or equal to 2, each of said time slots permitting transport of priority cells;
• b) a given one of said plurality of network stations delivering a priority cell of a given priority level to its current time slot if (i) the busy bit is not set and (ii) any priority reserved bits having priority levels higher than said given priority level are not set in said current time slot, said given network station thereafter setting the busy bit;
• c) a given one of said plurality of network stations setting the priority slot reservation bit of a given priority level in its current time slot to reserve a future time slot from the head-of-bus if (i) the busy bit is set and (ii) no priority slot reservation bits having priority levels higher than said given priority level are set in said current time slot;
• d) said head-of-bus generating a time slot to said bus and setting the priority reserved bit of a given priority level in said generated time slot to indicate that a time slot has been reserved for priority cell transmission of said given priority level when a time slot having its priority slot reservation bit of said given priority level set is received by said head-of-bus;
• and
• e) a given one of said plurality of network stations delivering a priority cell of a given priority level to its current time slot if:
• (i) said given network station had recently set a priority slot reservation bit of said given priority level, (ii) the busy bit is not set in said current time slot, and (iii) the priority reserved bit of said given priority level is set in said current time slot.

A method of providing asynchronous priority data transmission utilizing a medium access control protocol with a fair cell-access scheme in a local area network having a plurality of network stations coupled to a unidirectional looped bus having a head-of-bus, the method comprising the steps of:

• a) continuously generating time slots from the head-of-bus, each of said time slots permitting asynchronous priority data transmission between said network stations and each having a busy bit, high and low priority reserved bits and high and low priority slot reservation bits;
• b) permitting delivery of high or low priority cells from a given network station to its current time slot when neither the busy bit nor either priority reserved bit is set in said current time slot, said given network station thereafter setting the busy bit;
• c) setting one of said high or low priority slot reservation bits in a current time slot at a given network station to reserve a future time slot from the head-of-bus if the busy bit is set but (i) neither priority slot reservation bit is set in the case of a low priority reservation or (ii) the high priority slot reservation bit is not set in the case of a high priority reservation;
• and
• d) permitting delivery of either a high or low priority cell from a given network station to its current time slot if:
• (i) said given network station had recently set the corresponding high or low slot reservation bit, (ii) the busy bit is not set and (iii) the corresponding high or low priority reserved bit is set, said network station thereafter setting the busy bit.