RU2099877C1 - Identified-carrier access method - Google Patents

Abstract

FIELD: data transmission among logic entities in local computer networks; shared data-transmission channel access. SUBSTANCE: when using shared-channel access with carrier identification, on subscriber station of local computer network, shared channel is divided into time segments whose magnitude is determined as T_c≥t_p+t_id, where t_p is time of signal propagation between two most remote stations of local computer network; t_id is identification time of carrier free from data transmitted; segments are assigned to subscriber stations; carrier is analyzed only within its time space T_s; data transmission enable signal is sent to shared channel provided data transmission within own time space T_s from other subscriber stations of local computer network has been detected during t_id. EFFECT: enlarged functional capabilities. 2 cl, 2 dwg

Description

 The invention relates to the transmission of information between logical entities, for example, in local area networks (LANs), in particular, to methods for accessing a collective data channel.

 In local area networks, a significant number of subscriber stations can be connected to a shared channel. A necessary condition for reliable transmission of information to the LAN is the transmission of information in the channel at the same time only from one subscriber station. The access method determines the procedure for connecting subscriber stations to a shared channel, minimizes the likelihood of simultaneous transmission in a channel from more than one station, and thereby enables reliable information transmission.

A known method of access with a temporary separation of the channel of collective use [1]
In the known method, access to the shared channel of each subscriber station is allowed in a strictly fixed time interval for that station, which ensures that information is input into the data transmission channel free of information from other subscriber stations.

 The disadvantage of this method is the significant fixed time for a given LAN to wait for access to the channel even if an insignificant part of the subscriber stations from the number included in this LAN has information for transmission.

 The closest to the intended object by purpose, technical nature and the achieved result is a random access method with carrier identification [2] where carrier identification is defined as the station’s actions to detect transmissions from other stations in the physical medium.

 The known method of random access with carrier identification is that all stations collectively use a common physical environment, at each station that has data for transmission, monitor the state of the physical environment and, in the absence of transmissions from other stations, place their message in the physical medium sequentially in bits. If, after the start of transmission, the message in the channel collides with the message of the other station, then each of these stations provides a random combination to the physical environment, recognized at each station as false information. The station then waits for a certain, dynamically changing period of time before retrying the transmission.

 The disadvantages of this method include the fact that when using it there is a possibility of simultaneous transmission of several subscriber stations (collisions), which leads to loss of information, delays in its transmission. This probability is higher, the higher the intensity of information transfer to the LAN.

 The aim of the invention is to reduce the likelihood of collisions in a shared channel.

The essence of the invention lies in the fact that to solve the problem at the LAN subscriber station when using access to a shared channel with carrier identification, the shared channel is divided into time segments, the value of which is defined as T _c ≥ t _p. + t _op. where t _p. signal propagation time between the two most distant stations in the LAN; t _op. carrier identification time, free of transmitted data, received in this LAN; assign segments to subscriber stations; analyze the carrier during only its interval T _with ; give a signal permitting the transmission of information to a shared channel, provided that during its interval T _c no information transmission has been detected from other LAN subscriber stations; an enable signal is issued at the end of its interval T _s .

The signs that distinguish the proposed signal from the prototype include the fact that the shared channel is divided into time segments with a value of T _c > = t _p. + t _op. ; assign segments to subscriber stations; analyze the carrier during its interval T _s ; give a signal allowing the transmission of information to the shared channel, provided that during its interval T _with not detected the transmission of information from other LAN subscriber stations for t _op. ; an enable signal is issued at the end of its interval T _s.
The ability to achieve this goal, namely, to reduce the likelihood of collisions in a shared channel, is achieved by solving particular technical problems by applying the essential features of the method as follows.

 The possibility of collisions is due to the fact that the carrier identification intervals at subscriber stations begin at arbitrary points in time and depend on the moment the information for transmission appears. Since these moments are arbitrary for other subscriber stations, there is a likelihood that information will appear for transmission at these stations during the carrier identification time at the first station. Moreover, the probability of a collision is the higher, the higher the intensity of information transfer at stations of a given LAN.

Collisions can be avoided by establishing a carrier identification procedure in which each subscriber station will carry carrier identification for t _op. in its time interval T _s allocated for a particular subscriber station within a given LAN. Thus, dividing the collective use channel into segments reserved for each subscriber station within a specific LAN establishes a common discipline for the identification of the carrier for subscriber stations of a given LAN within its own segment, which excludes the possibility of simultaneously transmitting information from several subscriber stations to the shared use channel .

In order to exclude the possibility of simultaneous use of the carrier at several subscriber stations due to the fact that t _p. between subscriber stations in the LAN is not equal to 0, the value of T _with selected as t _p. + t _op. given the fact that t _p. this is the propagation time between the two most distant subscriber stations in the LAN.

 The determination of the moment of issuing the permission signal is dictated by the convenience of the data transmission system.

 In FIG. 1 is a structural electrical diagram of a subscriber station access control device for implementing the proposed method; figure 2 is a timing diagram of the division of the channel of collective use of the LAN into time segments and allocation of segments to the subscriber stations of the LAN.

 The device (Fig. 1) contains a timing unit 1, an access control unit 2, a receiver 3, a microprocessor 4, a transmitter 5.

 The proposed method can be implemented as follows.

From the moment the subscriber station is turned on in the LAN with an exact time signal (for example, from the SEB) or another signal common to this LAN, the timing unit 1 is started, with the help of which time intervals T _c , t _{p are formed.} and t _op. (Fig. 2a, b). Intervals T _with and t _op. allocated for the i-th subscriber station (where i = 1,2, N) in the control unit 2, to the other input of which a channel busy signal is received from the receiver 3, the interval on which the carrier is analyzed is allocated (Fig. 2.1, 2.2, 2 .N). If in the interval T _{with the} absence of information in the communication channel is detected for t _op. , at the end of the interval T _c , an access permission signal is generated, which is transmitted to the microprocessor 4 and determines the possibility of transmitting information from the microprocessor 4 through the transmitter 5 to the communication channel for collective use.

Implementation of the proposed access method allows avoiding collisions in the transmission of information due to the fact that each subscriber station carries out carrier identification and decides on the possibility of transmitting information only in its time interval T _s allocated for a particular subscriber station within a given LAN.

 Thus, by eliminating collisions in the transmission of information, the application of the proposed method will reduce the likelihood of loss and distortion of information and can increase the efficiency of using LAN bandwidth.

 Sources of information.

 1. Data transmission systems and computer networks, M. Mir, 1974.

 2. Scherbo V.K. Kirichev V.M. Samoilenko S.I. Standards for Local Area Networks, M. Radio and Communications, 1990.

Claims (2)

1. A method of access with carrier identification, in which all subscriber stations collectively use a common physical medium to transmit information, monitor the state of the physical medium and, in the absence of transmission from other stations, transmit their information, characterized in that the shared channel is divided into time segments with a value of T _c ≥ t _p + t _op (where t _{p is} the propagation time of the signal, and t _op is the carrier recognition time, assign segments with the value T _c t _p + t _op stations, identify the carrier on the interval of only "their" segments, and in the absence of a carrier on the interval t, the _{op of} its own segment gives a channel access permission signal for transmitting information at the end of its own segment. 2. The method of claim 1 access, characterized in that the interval only their recognition segments carrier begin through _p t after the beginning of the segment.

Images