EP0314217A2 — Controlled CSMA packet switching system

Claim 1

Independent Claim 151 words

A controlled carrier sense multiple access (CSMA) packet switching system comprising at least two stations each of the stations having means to sense a communication channel when it wants to transmit an information packet and means responsive to the channel being sensed idle for transmitting the information packet, wherein in the event of the channel being sensed busy, a new sensing point is scheduled at random in a dynamically determined time interval TS n where where TS u is the scheduling time interval that maximises the expected throughput when all the stations compete for the channel access, TS 1 is the scheduling time interval that maximises the expected throughput when two stations compete for the channel access, TS n-1 is a scheduling time interval determined in a preceding (n-1)th observation interval, G n-1 is the average offered load in the (n-1)th observation interval, and Go is a nominal average offered load.

Claim 2

Dependent Claim 151 words

A controlled carrier sense multiple access (CSMA) packet switching system comprising at least two stations each of the stations having means to sense a communication channel when it wants to transmit an information packet and means responsive to the channel being sensed idle for transmitting the information packet, wherein in the event of the channel being sensed busy, a new sensing point is scheduled at random in a dynamically determined time interval TS n where where TS u is the scheduling time interval that maximises the expected throughput when all the stations compete for the channel access, TS 1 is the scheduling time interval that maximises the expected throughput when two stations compete for the channel access, TS n-1 is a scheduling time interval determined in a preceding (n-1)th observation interval, G n-1 is the average offered load in the (n-1)th observation interval, and Go is a nominal average offered load.

Claim 3

Dependent Claim 14 words

A system as claimed in claim 1, wherein where a represents a smoothing factor.

Claim 4

Dependent Claim 52 words

A system as claimed in claim 1 or 2, wherein G n-1 is based on an estimation of the average idle period length; where G n-1 = ( E[I(1) ]-a) -1 and E [I(I) ] is the estimator of the average idle period and a is the switching time of a station.

Claim 5

Dependent Claim 62 words

A system as claimed in claim 3, wherein the average idle period length is estimated by averaging the lengths of the idle periods occurring during an observation period, that is the estimator of the average idle period E[I(I) ] = SI/NI where Sl is the current sum of the lengths of the idle periods and NI is the number of idle periods.

Claim 6

Dependent Claim 50 words

A system as claimed in claim 3 or 4, wherein each station includes estimating means for estimating the average idle period in the event of the station participating in a busy period which cannot detect the end of the preceding idle period and the beginning of the following idle period.

Claim 7

Dependent Claim 39 words

A system as claimed in claim 5, wherein said estimating means discards from its current estimation the idle periods which border the busy period in which its station is transmitting and bases its estimation on only fully observed periods.

Claim 8

Dependent Claim 104 words

A system as claimed in claim 5, wherein said estimating means integrates into its estimation an approximation of the combined length in the time domain of the idle periods immediately preceding and following the busy period in which the station transmits, said approximation being based on determining the commencement (t b (l m )) of the preceding idle period and the termination (t e (I m+1 ) of the next following idle period and upper bounding the length of the intervening busy period by (1 + a) and subtracting t b (l m ) and (1 + a) from t e (I m+1 ).

Claim 9

Dependent Claim 101 words

A system as claimed in claim 5, wherein the estimating means integrates into its estimation an approximation of the combined length in the time domain of the idle periods immediately preceding and following the busy period in which the station transmits, said approximation being based on determining the commencement (T b (l m )) of the preceding idle period and the termination (T e (I m+1 )) of the next following idle period and estimating the length of the intervening busy period E[I(B) m] in which the station transmits and subtracting tb(lm) and E[I(B) m] from t e (I m+1 ).

Claim 10

Dependent Claim 83 words

A system as claimed in claim 5, wherein the estimating means integrates into its estimation an approximation of the length of the preceding idle period by estimating the end of the preceding idle period and subtracting the time of occurrence of the preceding idle period, and an approximation of the length of the immediately following idle period by subtracting an estimation of the beginning of the immediately following idle period from the time of occurrence of the end of the following time period.

Claim 11

Dependent Claim 81 words

A system as claimed in claim 9, wherein the estimating means estimates the end of the preceding idle period as being later by 8 seconds than the instant (t 2 ) when the station having a packet for transmission found the channel idle, tht is at time t 2 + 6, where 5 contains the idle period correction and equals: where a is the receive to transmit switching time of the station and G is the load offered to the channel.

Claim 12

Dependent Claim 43 words

A system as claimed in claim 10, wherein the estimating means estimates the beginning of the next following idle period as being t 2 + 1 + 2a = 8 where 1 is the transmission time of an information packet (unity of time).

Claim 13

Dependent Claim 72 words

A system as claimed in claim 9, 10 or 11, wherein the observation period (U) is determined dynamically on the basis of U = max (2 x TS: U l ) where TS is the current control variable, U is the minimum time needed to obtain a confident estimation of G, and where n m is the minimum number of idle periods to be observed to obtain a confident estimation of G.

Claim 14

Dependent Claim 20 words

A controlled CSMA packet switching system substantially as hereinbefore described with reference to and as illustrated in the acoompanying drawings.

Claim 15

Dependent Claim 20 words

A controlled CSMA packet switching system substantially as hereinbefore described with reference to and as illustrated in the acoompanying drawings.

Claim 16

Independent Claim 140 words

A method of operating a controlled CSMA packet switching system of a non-persistent type, the system comprising at least two stations operating on at least one communication channel, wherein in the event of a station sensing that the or each channel is busy, a new sensing point is scheduled at random by the station in a dynamically determined time interval TS n where where TS u is the scheduling time interval that maximises the expected throughput when all the stations compete for the channel access, TS 1 is the scheduling time interval that maximises the expected throughput when two stations compete for the channel access, TS n-1 is a scheduling time interval determined in a preceding (n-1)th observation interval, G n-1 is the average offered load in the (n-1 )th observation interval, and Go is a nominal average offered load.

Claim 17

Independent Claim 140 words

A method of operating a controlled CSMA packet switching system of a non-persistent type, the system comprising at least two stations operating on at least one communication channel, wherein in the event of a station sensing that the or each channel is busy, a new sensing point is scheduled at random by the station in a dynamically determined time interval TS n where where TS u is the scheduling time interval that maximises the expected throughput when all the stations compete for the channel access, TS 1 is the scheduling time interval that maximises the expected throughput when two stations compete for the channel access, TS n-1 is a scheduling time interval determined in a preceding (n-1)th observation interval, G n-1 is the average offered load in the (n-1 )th observation interval, and Go is a nominal average offered load.

Claim 18

Dependent Claim 24 words

A method as claimed in claim 14, wherein the time interval TS n is updated dynamically in order to maximise the expected channel throughput.

Claim 19

Dependent Claim 56 words

A method as claimed in claim 14, wherein the dynamic updating of the time interval TS n includes estimating G n-1 on the basis of an estimation of the average idle period length E[I(I) ] during the observation interval, where G n-1 = ( E[I(1) ]-a) -1 where a is the switching time of a station.

Claim 20

Dependent Claim 45 words

A method as claimed in claim 16, wherein the estimator of the average idle period E[I(I) ] = SI/NI, where SI is the current sum of the lengths of the idle periods and NI is the number of idle periods contributing to the current sum.

Claim 21

Dependent Claim 69 words

A method as claimed in claim 16 or 17, wherein in the event of a station participating in a transmission on the or one of the channels and being unable to detect the end of a preceding idle period and the beginning of the next following idle period, then the immediately preceding and following idle period are discarded from said estimation which is based on fully observed periods only.

Claim 22

Dependent Claim 140 words

A method as claimed in claim 16 or 17, wherein in the event of a station participating in a transmission on the or one of the channels and being unable to detect the end of an immediately preceding idle period and the beginning of the next following idle period, then the combined length in the time domain of the immediately preceding and next following idle periods is approximated and the approximation is included in the estimation of E[I(I)], said approximation being based on determining the commencement (t b -(I m )) of the preceding idle period and the termination (t e (I m+1 )) of the next following idle period and upper bounding the length of the intervening busy period by (1 + a) and subtracting t b (l m ) and (1 + a) from t e -(I m+1

Claim 23

Dependent Claim 148 words

A method as claimed in claim 16 or 17, wherein in the event of a station participating in a transmission on the or one of th channels and being unable to detect the end of an immediately preceding idle period and the beginning of the next following idle period then the combined length in the time domain of the immediately preceding and next following idle periods is approximated and the approximation is included in the estimation of E[I(I) ], and wherein the approximation is based on determining the commencement (t b (l m )) of the immediately preceding idle period and the termination (t e (I m+1 )) of the next following idle period and estimating the length of the intervening busy period E[I(B m )] during which the station transmits and substracting t b (l m ) and E[I(B m )] from t e (I m+1 ).

Claim 24

Independent Claim 136 words

A method as claimed in 16 or 17, wherein in the event of a station participating in a transmission on the or or one of the channels and being unable to detect the end of the immediately preceding idle period and the beginning of the next following idle period then the lengths of said preceding and following idle periods are approximated and the approximations are included in the estimation of E[I(I) ], wherein the approximation of the immediately preceding idle period is made by subtracting the time of commencement of said idle period from an estimation of the end of said idle period and the approximation of the next following idle period is made by subtracting an estimation of the time of commencement of said idle period from the time of termination of said idle period.

Claim 25

Dependent Claim 79 words

A method as claimed in claim 21, wherein the end of the preceding idle period is estimated as being later by δ seconds than the instant (t 2 ) when the station having a packet for transmission found the channel idle, that is at time t 2 + δ, where δ contains the idle period correction and equals: where a is the receive to transmit switching time of the station and G is the load offered to the channel.

Claim 26

Dependent Claim 33 words

A system as claimed in claim 22, wherein the beginning of the next following idle period is estimated as being where 1 is the transmission time of an information packet (unity of time).

Claim 27

Dependent Claim 64 words

A system as claimed in claim 21, 22 or 23, wherein the observation period (U) is determined dynamically on the basis of where TS is the current control variable, U i is the minimum time needed to obtain a confident estimation of G, and where n m is the minimum number of idle periods to be observed to obtain a confident estimation of G.

Claim 28

Independent Claim 20 words

A method of operating a controlled CSMA packet switching system substantially as hereinbefore described with reference to the accompanying drawings.

Claim 29

Independent Claim 20 words

A method of operating a controlled CSMA packet switching system substantially as hereinbefore described with reference to the accompanying drawings.

Claim 30

Dependent Claim 192 words

A station for use in a non-persistent controlled CSMA packet switching system, comprising a receiver, a transmitter, switching means to switch either the receiver or the transmitter to a communications channel, said receiver having sensing means to sense the busy/idle state of the communication channel and to actuate the switching means to switch from the receiver to the transmitter in the event of the station having an information packet ready for transmission and the channel being sensed idle, wherein in the event of the station having an information packet ready for transmission and the channel is sensed busy, a new sensing point is scheduled at random in a dynamically determined time interval TS n where ; where TS u is the scheduling time interval that maximises the expected throughput when all the stations compete for the channel access, TS 1 is the scheduling time interval that maximises the expected throughput when two stations compete for the channel access, TS n-1 is a scheduling time interval determined in a preceding (n-1)th observation interval, G n-1 is the average offered load in the (n-1)th observation interval, and Go is a nominal average offered load.

Claim 31

Dependent Claim 192 words

A station for use in a non-persistent controlled CSMA packet switching system, comprising a receiver, a transmitter, switching means to switch either the receiver or the transmitter to a communications channel, said receiver having sensing means to sense the busy/idle state of the communication channel and to actuate the switching means to switch from the receiver to the transmitter in the event of the station having an information packet ready for transmission and the channel being sensed idle, wherein in the event of the station having an information packet ready for transmission and the channel is sensed busy, a new sensing point is scheduled at random in a dynamically determined time interval TS n where ; where TS u is the scheduling time interval that maximises the expected throughput when all the stations compete for the channel access, TS 1 is the scheduling time interval that maximises the expected throughput when two stations compete for the channel access, TS n-1 is a scheduling time interval determined in a preceding (n-1)th observation interval, G n-1 is the average offered load in the (n-1)th observation interval, and Go is a nominal average offered load.

Claim 32

Dependent Claim 14 words

A station as claimed in claim 26, wherein where a represents a smoothing factor.

Claim 33

Dependent Claim 56 words

A station as claimed in claim 26 or 27, wherein means are provided for estimating G n-1 on the basis of an estimation of the average idle period length, where G n-1 = E[I(I) ]-1) -1 and E[I(I) ] is the estimator of the average idle period and a is the switching time of a station.

Claim 34

Dependent Claim 62 words

A station as claimed in claim 28, wherein said means estimates the average idle period length by averaging the lengths of the idle periods occurring during an observation period, that is the estimator of average idle period E[I(I) ] = SI/NI where SI is the current sum of the lengths of the idle periods and NI is the number of idle periods.

Claim 35

Dependent Claim 48 words

A station as claimed in claim 28 or 29, further comprising estimating means for estimating the average idle period in the event of the station participating in a busy period and cannot detect the end of the preceding idle period and the beginning of the following idle period.

Claim 36

Dependent Claim 39 words

A station as claimed in claim 30, wherein said estimating means discards from its current estimation the idle periods which border the busy period in which its station is transmitting and bases its estimation on only fully observed periods.

Claim 37

Dependent Claim 103 words

A station as claimed in claim 30, wherein said estimating means integrates into its estimation an approximation of the combined length in the time domain of the idle periods immediately preceding and following the busy period in which the station transmits, said approximation being based on determining the commencement (t b (I m )) of the preceding idle period and the termination (t e (I m+1 )) of the next following idle period and upper bounding the length of the intervening busy period by (1 + a) and subtracting t b (l m ) and (1 +a) from t e (I m+1 ).

Claim 38

Dependent Claim 100 words

A system as claimed in claim 30; wherein said estimating means integrates into its estimation an approximation of the combined length in the time domain of the idle periods immediately preceding and following the busy period in which the station transmits, said approximation being based on determining the commencement (t b (I m )) of the preceding-idle period and the termination (t e (I m+1 )) of the next following idle period and estimating the length of the intervening busy period E[I(B) m] in which the station transmits and subtracting tb(lm) and E[I(B) m] from t e (t m=1 ).

Claim 39

Dependent Claim 83 words

A station as claimed in claim 30, wherein said estimating means integrates into its estimation an approximation of the length of the preceding idle period by estimating the end of the preceding idle period and subtracting the time of occurrence of the preceding idle period, and an approximation of the length of the immediately following idle period by subtracting an estimation of the beginning of the immediately following idle period from the time of occurrence of the end of the following time period.

Claim 40

Dependent Claim 81 words

A station as claimed in claim 34, wherein the estimating means estimates the end of the preceding idle period as being later by 8 seconds than the instant (t 2 ) when the station having a packet for transmission found the channel idle, that is at time t 2 + 6, where 5 contains the idle period correction and equals: where a is the receive to transmit switching time of the station and G is the load offered to the channel.

Claim 41

Dependent Claim 35 words

A system as claimed in claim 35, wherein the estimating means estimates the beginning of the next following idle period as being where 1 is the transission time of an information packet (unity of time).

Claim 42

Dependent Claim 63 words

A system as claimed in claim 34, 35 or 36, wherein the observation period (U) is determined dynamically on the basis of where TS is the current control variable, U i is the minimum time needed to obtain a confident estimation of G, and where nm is the minimum number of idle periods to be observed to obtain a confident estimation of G.

Claim 43

Dependent Claim 31 words

A station for use in a non-persistent controlled CSMA packet switching system, constructed and arranged to operate substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

Claim 44

Dependent Claim 31 words

A station for use in a non-persistent controlled CSMA packet switching system, constructed and arranged to operate substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

Controlled CSMA packet switching system

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