EA005625B1 - System and method for multipoint to multipoint data communication - Google Patents

Abstract

A system and method is providing for multipoint to multipoint data communication. In an embodiment of the invention, a system comprises a communications medium interconnecting at least one central server and a plurality of communication nodes. The central server transmits information to the nodes via a Forward Channel and the nodes transmit information via a Reverse Channel. Before transmitting, each of the nodes listens (monitors) during an assigned slot of a Clear Channel Assessment interval of the communications cycle to ascertain whether any other node is transmitting. A give node transmits data only when that node determines that the network is clear. The nodes listen in sequential order, eliminating the probability of collisions caused by simultaneous transmissions from nodes. A query channel interval is provided for nodes not assigned a slot within clear channel assessment interval to request a slot. Assigned slots not used by nodes are allocated to other nodes. The data traffic is accordingly aggregated, thus providing efficient utilization.

Description

The present invention relates to data transmission, in particular, to systems and methods for providing multipoint communication lines.

2. Description of the relevant area.

In local area networks (LAN), a group of devices is interconnected through a shared network environment. Referring to FIG. 1 shows a line-up of traditional LAN 100. having a bus topology. The LAN 100 is typically referred to as a “Multipoint” system, because any one of multiple system devices can send information to one, several, or all other multiple system devices. In particular, the shared communication environment 110 operatively interconnects the devices. Communication medium 110 typically consists of an optical cable, coaxial cable, hybrid fiber-coaxial (GVK) network, wireless media, or any combination thereof. The device includes a central server 120 that performs a variety of functions, including coordinating interactions among the H series of other communication devices 130, as well as connected to the shared medium 110 in a manner that is well known to those skilled in the art. Moreover, with this configuration of the LAN, the central server 120 appears with respect to the external networks as a gateway acting for all devices 130, in addition to controlling the access of the LAN. In general, communication devices 130 related to nodes are the same computing devices as computers or printers. Despite the fact that the tire topology is presented, a specialist will easily understand that other topologies, including ring topology, star topology, and a combination of bus, ring and star topologies, can also be used.

It is known that the two main objectives that are pursued in the design of networks or any other communication systems are speed and reliability. In other words, it is important that information elements (“packets”) placed on the network using any device connected to the network reach their destination quickly and reliably. The main phenomenon that hinders the achievement of goals, occurs when one or several devices connected to the network try to use the network simultaneously. This can lead to a data-level conflict that can prevent any information from reaching its intended destination. As a result, both devices involved in a conflict situation will be forced to try to send their information again, reducing the speed and efficiency of the network.

There are many configurations known from the prior art used to reduce the likelihood of conflict situations and to optimize recovery in the event of a conflict.

Summary of Invention

The presented invention is focused on systems and methods for providing effective multipoint communication. The invention allows to overcome the interference of conventional systems and protocols by dynamic bandwidth allocation based on graphical requests.

In one of the embodiments of the invention, communication is provided in the state of the LAN, which includes a central server and multiple nodes. During operation, the central server sends information in the form of packets to nodes through a forward channel of the communication cycle, and one of the nodes sends data packets to one or more other nodes and / or the central server using a reverse channel. Despite this, before sending on the reverse channel, each node waits (that is, controls) the network signal during the evaluation interval of the free channel allocated for this by the central server in order to detect whether the network is being used by any node. Each node that has information to send, after the free channel has been established during the evaluation of the fact that the network is free, sends this information. Nodes are waiting for a signal in sequential order, while eliminating a conflict situation caused by simultaneous sending of nodes.

This arrangement allows you to efficiently and dynamically accumulate data flow. A node that starts sending at the moment when the channel estimate indicates that the network is no longer in use receives a continuous return channel for use. If many nodes have information for its placement in the network, then access to the reverse channel is distributed in accordance with the needs of these nodes. None of the nodes is denied access to the reverse channel with an excessively large number of cycles, and access to the network for the node that has information to send is not lost. Moreover, the use of the reverse channel is achieved without supporting mediation, thus avoiding any delays associated with it.

Another feature of the invention is that the order in which the nodes expect a response from the reverse channel can alternate periodically. Thus, a favorable outcome for forwarding is equally guaranteed, as a rule, for all nodes.

The above and other features and advantages of the invention will be revealed from the following, more detailed description of preferred embodiments of the invention, taking into account the drawings and the attached claims.

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Brief Description of the Drawings

For a more complete understanding of the present invention, its objectives and advantages, reference is made to the following description in connection with the accompanying drawings, in which FIG. 1 is a diagram of a typical topology of a conventional multipoint communication system;

FIG. 2 is a communication cycle diagram in accordance with an embodiment of the invention;

FIG. 3 is a block diagram of a method implemented by an inactive node in order to gain access to a network, in accordance with an embodiment of the invention;

FIG. 4 is a block diagram of a method implemented by a central server in order to redistribute OSC slots with respect to inactive nodes, in accordance with an embodiment of the invention;

FIG. 5 is a block diagram of an active node operation in accordance with one embodiment of the invention; and FIG. 6 is a block diagram of the operation of the active node in accordance with another embodiment of the invention.

A detailed description of the preferred embodiments of the invention.

Preferred embodiments of the invention will be described with reference to FIG. 1-6, on which identical references point to the same elements and are discussed here in the context of the implementation of the Protocol for the Provision of Multi-Station Information Exchange.

The access system (PMMD) is carried out in the local network. The invention, however, can be applied to provide information (eg, digital data, digital voice) in a wide range of applications. Moreover, the invention may also be applied in other embodiments that appear obvious to a person skilled in the art.

The content of the American Patent Application under the number 09 / 482,054, filed January 13, 2000 and entitled System and method for ensuring data transmission between single-point and fixed point-to-point systems, is included in the current application in its entirety.

Referring to FIG. 2, communication cycle 200 is shown in accordance with an embodiment of the invention. In particular, the communication cycle 200 includes the Forward Channel (PC) 210 interval, the Request Channel Interval (CC) 220, the Free Channel Rating Interval (FCC) 230 and the Reverse Channel Interval (C) 240. The FCC spacing 230 includes the number of FCC slots 235, each of which is intended solely for an individual node 130. The interval of the PC 210 is initialized by the central server 120 and includes data packets that are pending transmission to one or more of the nodes 130 during the cycle 200. The total width of the PC of the interval 210 may vary from cycle to cycle depending on the volume idle data. The central server 120 at the end of the interval, the PC 210 forwards the synchronization flag 215 to synchronize all active nodes 130 across the entire LAN. Correspondingly, the periods of the nodes 130 appear during the specified CCA of slot 235 in accordance with the appearance of the synchronization flag 215. The bit lengths, intervals and slots shown in the drawing are merely indicative and can be selected for any desired value.

The CP 220 interval is designed so that the nodes 130 that have the data expected to be transmitted, but which currently do not have the USC slot 235 prescribed for them, allow them to notify the central server 120 of their presence. In accordance with the following detailed description, upon receipt of a notification about the desire of an inactive node to send data, central server 120 may assign an individual CCA slot 235 to this node for its inclusion in the upcoming communication cycle. The preferred width of the CZ 220 interval is set, which, however, changes from cycle to cycle if necessary.

At the set time, after the PC 210 interval expires, that is, after the set CP 220 interval has expired, the CCS 230 interval begins. The CCM 230 interval includes a number of USC slots 235 assigned to those individual nodes 130 that are currently connected to the network and which have recently were active while sending data. As a rule, the active node is the node that transmitted data either immediately during the previous cycle, or during one or more cycles from a certain set of previous cycles, that is, during a specified deadline. In the proposed embodiment of the invention, the CSC interval 230 is divided into many CSC slots 235 of equal duration. In general, each node 130 is dynamically assigned an SSC slot 235, during which it waits for a signal to determine if the network is free. USC slots 235 follow each other in sequential order.

The interval OK 240 occurs after the interval of the USC 230 and is the period during which only one of the nodes 130 forwards the data. Typically, the first node or node 130 of the highest priority, whose CSC of slot 235 in the sequential order of the CSC of the slots will appear first, starts sending the packet on the reverse channel directly during the CSC 230 (if it has data to transmit) and continues until the start time and possibly at OK 240 interval duration. The OK 240 interval duration can vary to a previously specified maximum value. The end of the interval OK 240 is identified by a special flag byte (not shown). For example, in response to identifying a special flag byte, the central server 20 begins to send data during the PC interval of the next communication cycle.

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All nodes 130 that are not involved in the transfer, waiting for a signal from the reverse channel in order to determine whether the packet is sent to the network. Only one node 130 is allowed to transmit on the reverse channel of any given communication cycle. Transmission node 130 may forward multiple packets to multiple destinations. Due to the use of appropriate flags, numerous packages are delimited according to preference, which can obviously be realized by a specialist in this field. Long data files are preferably divided into packets of standard sizes and are sent through multiple cycles. In the present embodiment of the invention, there is no confirmation mechanism when moving and / or at network levels.

A specific feature of the invention is that the central server 120 distributes the CSC slots 235 only to the active nodes 130. However, those nodes that are not active, which are generally nodes, but which have not been assigned an individual CSC slot 235, for example, a new or previously disconnected node, or any node that wants to start work on the network (i.e., they will become active within the network) can be provided with a prescribed USC slot 235 by establishing a connection with the central server 120 during the KZ 220 interval. For example, referring to FIG. 3, the inactive node 130 implements the method 300, corresponding to an embodiment of the invention, in order to acquire the intended CSC slot 235. In particular, the inactive node 130 (step 310) establishes the beginning of the SC 220 interval. During the SC 220 interval, the inactive node 130 transmits ( step 320) the node identification packet (IDU) to the central server 120. The node ID packet contains the node ID identifying the name or address of the inactive node that the central server 120 assigns the CSC slot. In turn, the inactive node 130 receives an acknowledgment (step 330) from the central server 120, including identifying the CSC of slot 235 assigned specifically to that node. Typically, such an acknowledgment may be sent by the central server 120 to the inactive node 130 during the PC interval of the next communication cycle itself or the future communication cycle. The latter may become necessary if, later, before assigning the USC slot, the usual acknowledgment and protection methods are used, the implementation of which is obvious to a specialist in this field. After receiving the prescribed SSC of slot 235, the currently activated node can identify (block 340) the presence of the SSC prescribed for it and wait for the signal for action, thereby allowing the node to send its data while the reverse channel is free.

During the CP 220 interval, all inactive nodes that wish to connect to the network are attempting to forward the node packet ID to the central server 120. The likelihood of collisions, i.e. distorted shipments, is high due to the real possibility that many nodes 130 have to do at the same time trying to send the host ID packet 120 to the server at the same time. Accordingly, in practicing the invention, conventional collision checks and methods for their prevention can be used, the implementation of which is obvious to a person skilled in the art. For example, at the same time during the transmission of the node ID packet, a node might wait for a signal to determine when a collision occurs, thereby justifying the node’s execution of a random delay algorithm to resend the node packet ID.

Referring to FIG. 4, method 400, in accordance with an embodiment of the invention, is implemented at central server 120 to assign slots 235 to slots 235 to nodes 130 that wish to communicate with the network. In particular, central server 120 identifies (step 410) the existence of a fault zone 220. During this interval, central server 120 waits for a signal (step 420) to forward the node packet ID. If the node packet ID is received, then the central server 120 assigns (step 430) a slot for the identified node during the CCA interval 230 from the immediately following or future communication cycle. During the interval, the PC 210 from the corresponding communication cycle, the central server 120 forwards (step 440) a confirmation, including a list of assigned slots 235 to all nodes that have been assigned a slot 235 by the CCA. In another embodiment of the invention, the central server 120 only sends recently acknowledged nodes and any nodes that have a replaced personal assigned USC slot 235.

According to an embodiment of the invention, the prescribed CCA slot 235 can be taken away from a node that did not use its turn to transmit data during the OK 240 interval at the appointed time. In particular, if the central server 120 determines that a particular node 130 has not used the opportunity presented to it to use the network for a certain number of cycles 200, then the assignment of the CSC of slot 235 can be canceled to disable the node. For example, central server 120 may send a data packet during the next interval of PC 210, which contains a notification that the node no longer has an assigned CSC slot 235. Accordingly, a new CSC list of slots 235 may be sent according to the schedule with all active or only waiting for replacement nodes. If the deactivated node later has data that it wishes to place on the network, it will notify the central server 120 of its presence during the next appropriate interval of KZ 220, in order to request the assignment of a new USC slot 235 in the upcoming USC interval 230.

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Each node 130 is waiting for a signal to transmit data over the network during its specified slot USC slot 235, and if there is no transmission (that is, if some other node with an early USC slot has not yet started sending), then the node can send data. In other words, during the CSC of interval 230, each node 130 until the assigned CSC of slot 235 is in standby mode to receive a data transmission signal over the network. The first node 130 (i.e., node 130 to which the central server 120 assigned the FCC slot the highest priority) first waits for a signal. After the first USC of slot 235 has expired, the second node 310 (i.e., node 130 to which the central server 120 assigned the USC of the next highest priority slot) waits for a signal. Similarly, the Nth node waits until the beginning of the Nth USC slot 235 to wait for a signal. Node 130, which has data to send, does so only if this node waits for a network signal during the assigned slot CWC 235 and when it is sure that no other node 130 is sending data (i.e., there is a clear channel). In an embodiment of the invention, the node 130 starts forwarding immediately after it has been established that the return channel is clear during the assigned CSC slot. In other words, the transfer occurs during the CSC of the interval 230. In another embodiment, the node 130 starts the transfer if there is a CSC of the slot intended for the data recipient. In the following embodiment of the invention to start sending data on the reverse channel, the transmission node 130 waits for the presence of an interval of OK 240.

In the above example, if the first node does not have any data to send, then that node spends its CCA slot 235 on waiting for the signal and does not perform the transfer, even if the network is free. The second node begins to wait for a signal during its USC slot 235 and assesses whether the network is indeed free. In this example, the network is free, because the node with the previous slot 235 had no data and no other node (that is, the node that was assigned the later slot) still has no way to send. If the second node has no data to send, it waits for a signal during its CCA slot 235 without any data transfer in the same way as the first node. If, however, the second node has data to send, then it does so immediately after it determines that the network is free. In accordance with the implementation of the invention, the second node will send data during the time allotted for the previously present interval OK 240. As soon as the time allotted for the second USC of slot 235 has expired, nodes with later slots, in turn, wait for the signal. Each of them will find that the second node is sending data. Accordingly, these later nodes will determine that the network is busy and will not attempt to send data during the current communication cycle.

In order to ensure that all nodes have equal opportunity to transfer data in the network, the order of slot assignment for the CCS can be alternated from cycle to cycle. Otherwise, nodes 130 having slots 235, which appeared earlier in order (in the above example, the first and second nodes) would always be able to use the network, except nodes that have slots that appear later, and nodes that have later slots will not have the potential to use the network in many cycles. The assigned USC slots 235 may alternate in a circular system for each communication cycle 200. For example, a node that waits for the signal last in the immediately preceding cycle waits for the signal first in the next cycle, because its SC slot 235 was shifted to the beginning of the CCA interval 230. USC the slots for each of the other nodes are shifted in order to be repeated later during a specific USC slot. The alternation, after several cycles, provides each connected node 130 with equal opportunities for priority data transfer. It is obvious to a specialist that the assignment and reordering of the order established for slots 235 can be achieved by other algorithms different from the above-implemented circular system. Equal access to the bandwidth is an important feature of those embodiments that provide movement, responsive to time, or that require small and consistent delays. In addition, the invention can be implemented with other structures of USC slots. For example, one or more nodes can be assigned a pre-installed and fixed USC slot. In such versions, some nodes can be guaranteed priority if the particular embodiment of the invention assumes this is desired.

In an embodiment of the invention, the buffer sizes of the active nodes 130 have been verified by the central server 120. In particular, the type of information transmitted may have a value when voice transmission was evaluated for other types of data. For example, the transmitted information can be divided into rigid and flexible information. Hard information includes voice data, and flexible information includes data such as internal commands or Internet data. To prevent the node from permanently capturing the reverse channel with flexible information, the central server 120 monitors at each active node the size of the buffer containing the flexible information. If central server 120 determines that the node's flexible information buffer overflows (becomes redundant), then the slot slot CSC priority switches to the node having a lower priority slot. In other words, CSC slots with higher priority (which occur at the beginning of CSC interval 230) are preferably assigned to nodes that transmit hard information as opposed to flexible information.

- 4 005625 operations. Other nodes transmitting flexible information are assigned CSC slots with lower priorities.

During the CSC of the 230 interval, each network node waits for a signal to establish whether other nodes transmit information. If the first node that has data packets to send to any other device on the network determines that none of the other nodes send data, then the first node sends its data packets to the destination (s) within the allotted time and then sends a special byte flag signaling the end of the interval is OK 240. Since each node waits for signals from all shipments made from any other node, each other node detects the transfer of the first node and refrains from sending.

FIG. 5 shows a communication method 500 corresponding to an embodiment of the invention implemented by each node 130. In operation, node 130 receives data (step 510) sent by central server 120 during the interval of PC 210. When receiving synchronization flag 115, node 130 determines the time (step 520), which the assigned CSC slot 235 removes, based on the reception time of the synchronization flag and the priority of the assigned CSC slot 235. Based on this set time, the node 130 waits (step 530) for its assigned CSC slot 235. Of the assigned slot CSC, node 130 determines (step 540) whether the network is free. If the network is not free, then node 130 waits for a signal for packets (step 550) addressed to it on the return channel. If the network is free, then node 130 determines (step 560) whether the data has been sent on the reverse link (step 570). If there is no data to send, node 130 enters a signal standby mode (step 550).

Active nodes must not acknowledge their presence by sending the node packet ID while they periodically send data. For example, central server 120 monitors the availability of the OK 240 interval and controls the transfer of communication between nodes 130. However, if the node did not have data for a pre-set number of cycles, but it wants to remain connected, it can transmit a dummy packet, however that is, a packet not addressed to any particular node 130.

FIG. 6 shows a communication method 600 according to the invention for implementing a dummy packet transmission. The communication method 600 is identical to the communication method 500, with the exception of two additional steps. In particular, after the node 130 establishes (step 560) that there is no data to send, it determines (step 610) whether it is necessary to maintain the slot assigned to it by the CCS, i.e. stay connected. If the node wishes to remain connected, then it forwards (step 620) the dummy data packet. Otherwise, the node 130 waits (block 550) for its addressed packets.

In carrying out the invention, guard intervals are provided for matching delays, each of which corresponds to the variants of its implementation and allows optimizing each performance according to its technical characteristics (for example, extremely low error rate, minimized synchronization time, etc.). The guard intervals are preferably placed at the beginning and at the end of the PC 210 interval, the OK 240 interval and the CCA interval 230. Other arrangements can be used to match the aforementioned and other delays. As noted above, the invention can be implemented in various ways with different topology and construction of nodes. Each embodiment of the invention assumes some compensation due to propagation delays associated with the transfer (function of the distance between nodes), and delays associated with the scheme (hardware), processing and frequency of switching nodes. It is obvious to a person skilled in this field the calculation or measurement of such a time delay.

In accordance with the invention, each node determines whether it is necessary to send data using the CCA slot 235. In this respect, the invention does not require a central server 120 for an intermediary or to provide access to the OK 240 intervals between different nodes 130. Accordingly, any propagation delays caused by mediation.

Although the invention has been presented and described in detail with reference to several preferred embodiments, those skilled in the art will recognize that various changes in form and detail can be made inherently from the spirit and scope of the invention as reflected in the appended claims.

Claims (36)

CLAIM 1. A multipoint communication system comprising a shared media, a server connected to a shared media and capable of forwarding a forward channel signal to a shared media over a predetermined forward channel interval of a communication cycle, and - 5 005625 many nodes, each of which is connected to a shared data medium and is able to control a direct channel signal, as well as monitor a shared data medium with a view to its use during the free channel estimation slot within the free communication channel estimation interval and providing a reverse channel signal after the aforementioned node as a result of monitoring a shared data medium with a view to using it for the specified slot free channel estimation determines that the shared transmission medium is free, characterized in that said clear channel assessment interval is divided into a certain number of free channel estimation slots, each slot clear channel assessment prescribed exclusively for one of said nodes. 2. The system according to claim 1, characterized in that the server is capable of receiving a reverse channel signal, with each node being available to receive a forward channel signal. 3. The system according to claim 1, characterized in that the forward channel signal and the reverse channel signal contain data packets. 4. The system according to claim 1, characterized in that the direct channel signal contains an address, and each node is assigned a unique node address, and it is available for receiving information encoded on the direct channel signal as soon as the address of the direct channel is in accordance with the assigned unique host address. 5. The system according to claim 4, characterized in that the node address is the Internet Protocol. 6. The system according to claim 1, characterized in that each of these slots estimates the free channel has an equal duration. 7. The system according to claim 6, characterized in that the server dynamically assigns the nodes free channel estimation slots. 8. The system according to claim 7, characterized in that the assignment of slots for estimating the free channel alternates in a circular pattern. 9. The system according to claim 1, characterized in that the return channel signal is provided during a predetermined interval of the return channel. 10. The system according to claim 9, characterized in that it further comprises guard intervals delimiting the forward channel interval, the reverse channel interval and the free channel estimation interval. 11. The system according to claim 1, characterized in that the server is capable of sending a synchronization signal after completion of the forward channel signal transfer. 12. The system according to claim 11, characterized in that the synchronization signal is a flag synchronization. 13. The system according to claim 11, characterized in that each of the nodes is able to calculate the time interval between the appearance of the synchronization signal and the appearance of the assigned free channel estimation slot. 14. The system according to claim 9, characterized in that the server is capable of controlling a shared data medium during the interval of the communication cycle request channel. 15. The system of claim 14, wherein the interval of the request channel appears after the interval of the forward channel and continues to the interval of the reverse channel. 16. The system according to 14, characterized in that it further comprises at least one inactive node, while the inactive node is able to forward an identification packet (ID) of the node containing the identification identifying the inactive node during the interval of the request channel. 17. The system according to clause 16, characterized in that the server is able to assign an inactive node slot evaluation channel free. 18. The system according to claim 1, characterized in that the server is able to annul the slot for estimating the free channel of the node if it determines that the node is inactive. 19. A method for providing multi-point communication in a system containing a shared data medium, a server and a plurality of nodes, including operations of forwarding a direct channel signal from a server to a shared data medium, monitoring a shared data medium to provide a direct channel signal at each node from a plurality and monitoring of a shared data transmission medium for providing a reverse channel signal at each node from a plurality, wherein each of the plurality of nodes monitors the free channel estimation slot within the free channel estimation interval, forwards the return channel signal from one of the many nodes if the return channel interacting with one of the many nodes is free during the free channel estimation slot and if one of the many nodes has information for sending to the server as a reverse channel signal, characterized in that the free channel estimation interval is divided into a number of free channel estimation slots, each free estimation slot a channel is assigned exclusively for each of the nodes. - 6 005625 20. The method according to claim 19, characterized in that the forward channel signal contains free channel estimation slots, each of which has an equal duration. 21. The method according to claim 19, characterized in that it further includes the operation of dynamically assigning free channel estimation slots to each of the plurality of nodes. 22. The method according to item 21, wherein the free channel estimation slots are assigned in a circular system. 23. The method according to claim 19, wherein the forward channel signal is provided for a predetermined forward channel interval time, and the reverse channel signal is provided for a predetermined reverse channel interval. 24. The method according to p. 23, characterized in that it further includes the operation of providing the guard intervals of the interval of the forward channel, the interval of the return channel and the evaluation interval of the free channel. 25. The method according to claim 19, characterized in that it further includes the operation of synchronizing the server with multiple nodes through a synchronization signal sent by the server. 26. The method according A.25, characterized in that it further includes the operation of calculating the time interval between the appearance of the synchronization signal and the appearance of the assigned slot estimates the free channel for each node. 27. The method according to claim 19, characterized in that it further includes the operation of monitoring a shared data medium during the interval of the request channel on the server. 28. The method according to item 27, characterized in that it further includes the operation of sending during the interval of the request channel from the inactive node of the identification packet (ID) of the node, including recognition of the identification of the inactive node. 29. The method according to p. 28, characterized in that it further includes the operation of assigning a slot evaluation channel free channel inactive node. 30. The method according to claim 19, characterized in that it further includes the operation of canceling the slot evaluation channel free channel, if the server determines that the node is inactive. 31. The format of the communication cycle to ensure data transmission within a multi-point communication system, including a data transmission medium connecting at least one server and a plurality of nodes, including a forward channel interval, in which a forward channel interval indicates sending a direct channel signal from the server, the free channel estimation interval, in which the free channel estimation interval is divided into a number of free channel estimation slots, with each free channel estimation slot assigned to only one of the nodes, and the evaluation slots the free channel, indicating the time interval, is allocated to the node for monitoring the data transmission medium, the interval of the request channel, in which the interval of the request channel indicates the time interval for the node, which was not assigned a free channel rating slot for requesting the server to assign a free channel rating slot , and the interval of the return channel, in which the interval of the return channel indicates the length of time for sending one of the nodes of the signal of the reverse channel. 32. The format of the communication cycle according to p, characterized in that the interval of the direct channel is variable in duration. 33. The format of the communication cycle according to claim 32, characterized in that it further includes a synchronization period, which indicates the length of time during which the server sends a synchronization signal indicating the completion of the direct channel signal during the communication cycle. 34. The communication cycle format according to claim 33, wherein the request channel interval is constant in duration, the synchronization signal provides a free channel estimation slot to each of the assigned nodes to determine the occurrence of the assigned free channel estimation slot. 35. The format of the communication cycle according to p, characterized in that the said interval of the reverse channel is variable in duration. 36. The format of the communication cycle according to p, characterized in that the interval of the request channel appears between the interval of the forward channel and the evaluation interval of the free channel.