Flow and congestion control in packet switched networks
First Claim
1. A method in an ATM system for controlling flows of data cells and flow control management cells from a number of sources to a destination over connections passing a network element, while returning the flow control management cells from the destination via the network element to their respective sources,said network element being exposed to congestion due to contention between the connections, said contention necessitating queuing of the connections,said data cells including lower priority cells and higher priority cells, and said flow control management cells having an explicit rate field for an explicit rate value used to limit a source maximum allowed cell rate to a specific value, and a current cell rate field for receiving said specific value,comprising performing in the network element the steps ofcounting a predetermined number of higher priority cells due to be sent on an output link from the network element to the destination while keeping track of the time interval taken for performing the counting to produce a higher priority cell rate in the form of a ratio between the counted higher priority cells and the time interval,calculating an available rate value for lower priority cells as a difference between a total available link rate value and the higher priority cell rate,establishing a queue length reference forming a desirable queue length,calculating deviations from the available rate value and the queue length reference due to receiving varying amounts of cells on contending connections,calculating a modified explicit rate value as a function of these deviations, andintroducing the modified explicit rate value into the explicit rate field of the backward flow control management cells.
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Accused Products
Abstract
A control system in an ATM system controls flows of data cells and flow control management cells from a number of sources to a destination over connections passing a network element. The flow control management cells are returned from the destination via the network element to their respective sources. The network element is exposed to congestion due to contention between the connections, that necessitates queuing of the connections. The flow control management cells have an explicit rate field for an explicit rate value used to limit a source maximum allowed cell rate to a specific value. An operating function uses deviations from an available rate value for lower priority cells and from a queue length reference forming a desirable queue length, to calculate a modified explicit rate value as a function of these deviations. This modified explicit rate value is introduced into the explicit rate field of the backward flow control management cells.
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Citations
24 Claims
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1. A method in an ATM system for controlling flows of data cells and flow control management cells from a number of sources to a destination over connections passing a network element, while returning the flow control management cells from the destination via the network element to their respective sources,
said network element being exposed to congestion due to contention between the connections, said contention necessitating queuing of the connections, said data cells including lower priority cells and higher priority cells, and said flow control management cells having an explicit rate field for an explicit rate value used to limit a source maximum allowed cell rate to a specific value, and a current cell rate field for receiving said specific value, comprising performing in the network element the steps of counting a predetermined number of higher priority cells due to be sent on an output link from the network element to the destination while keeping track of the time interval taken for performing the counting to produce a higher priority cell rate in the form of a ratio between the counted higher priority cells and the time interval, calculating an available rate value for lower priority cells as a difference between a total available link rate value and the higher priority cell rate, establishing a queue length reference forming a desirable queue length, calculating deviations from the available rate value and the queue length reference due to receiving varying amounts of cells on contending connections, calculating a modified explicit rate value as a function of these deviations, and introducing the modified explicit rate value into the explicit rate field of the backward flow control management cells.
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9. The control system in an ATM system for controlling flows of data cells and flow control management cells from a number of sources to a destination over connections passing a network element, while returning the flow control management cells from the destination via the network element to their respective sources,
said network element being exposed to congestion due to contention between the connections, said contention necessitating queuing of the connections, said data cells including lower priority cells and higher priority cells, and said flow control management cells having an explicit rate field for an explicit rate value used to limit a source maximum allowed cell rate to a specific value, and a current cell rate field for receiving said specific value, comprising means for counting a predetermined number of higher priority cells due to be sent on an output link from the network element to the destination while keeping track of the time interval taken for performing the counting to produce a higher priority cell rate in the form of a ratio between the counted higher priority cells and the time interval, and means for calculating an available rate value for lower priority cells as a difference between a total available link rate value and the higher priority cell rate, establishing a queue length reference forming a desirable queue length, calculating deviations from the available rate value and the queue length reference due to receiving varying amounts of cells on contending connections, calculating a modified explicit rate value as a function of these deviations, and introducing the modified explicit rate value into the explicit rate field of the backward flow control management cells.
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17. A method in an ATM system for controlling slows of data cells and flow control management cells from a number of sources to a destination over connections passing an output buffer of a switch, while returning the flow control management cells from the destination via the switch to their respective sources,
said output buffer being exposed to congestion due to contention between the connections, said contention necessitating queuing of the connections, said data cells including lower priority cells and higher priority cells, and said flow control management cells having an explicit rate field for an explicit rate value used to limit a source maximum allowed cell rate to a specific value, and a current cell rate field for receiving said specific value, comprising performing the steps of obtaining values of a set of parameters and variables including y(t): - a contention rate at the output buffer at time t,
ytot (t);
a measured offered rate to the output buffer at time t,C(t);
available rate at the buffer for lower priority cells at time t,Q(t);
total queue length at the buffer at time t,p;
fraction of an available rate at the buffer strived for,M;
a buffer queue length reference,ai and bi ;
proportional constants for a connection i passing the output buffer,determining the explicit rate value xi (t) at time t for the connection i as xi t=y(t)[1-ai {1-pC(t)/ytot (t)}-bi {Q(t)-M/ytot (t)}], where i is an integer, and assigning the explicit rate value xi t to the explicit rate field of a backward flow control management cell. - View Dependent Claims (18, 19, 20, 21, 22)
- a contention rate at the output buffer at time t,
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23. A method in an ATM system for controlling flows of data cells and resource management cells from a number of sources to a destination over connections passing a respective input buffer and a common output buffer of a fair queuing switch, while returning the resource management cells as backward resource management cells from the destination via the switch to the respective sources,
said switch being exposed to congestion due to contention between the connections, said contention necessitating queuing of the connections in the input buffers and the output buffer, said resource management cells having an explicit rate field for an explicit rate value used to limit a source maximum allowed cell rate to a specific value, comprising obtaining values of a set of parameters and variables including rj (t): - output rate at time (t) at the input buffer for connection j,
p(t);
total load at time (t) on output from the input buffer calculated as the quotient number of ABR cells received at the input buffer per time unit/number of occasions to send an ABR cell per time unit,pref;
desired load on output from the input buffer,Qj (t);
queue length at time (t) at the input buffer for connection j,Mj ;
queue length reference at the input buffer for connection j,a and b;
proportional constants for connection j,determining the explicit rate value xj (t) at time t for the connection j as
space="preserve" listing-type="equation">x.sub.j (t)-max(r.sub.j (t))[1-a{1-pref/p(t)}-b{Q.sub.j (t)-M/max(r.sub.j (t))}]wherein max(rj (t)) is an operation performed on the individual connection output rates rj (t) of the switch in order to find a common output rate for the connections passing the common output buffer and thus avoid a divergence in the individual connection rates, and j is an integer, and assigning the explicit rate value xjt to the explicit rate field of a backward resource management cell passing the input buffer j. - View Dependent Claims (24)
- output rate at time (t) at the input buffer for connection j,
Specification