KR20020029428A - Network slot synchronization scheme for a computer network communication channel - Google Patents

Abstract

The present invention provides a method of maintaining synchronization in a typical communication channel with established transmission timeslots for various devices of a computer network, where previous timeslots have not been used by the device and / or end of transmission of other devices in the network. The present invention relates to a method for allowing transmission on an external channel of a set timeslot of the device only when a clear channel evaluation indicates that an indication of. The clear channel assessment preferably takes into account the set transmission timeslots of the devices of the communication channels associated with the other network devices, and the numerical representation of the set transmission timeslots of the devices of the communication channels associated with the other network devices and of the predetermined clear channel latency. It can be a product of time. The clear channel latency can itself be set by the network master device as part of the network connection process. The network device may be configured to construct one or more packets for transmission of the network prior to a timeslot set to accommodate early transmission.

Description

Network slot synchronization method for computer network communication channel {NETWORK SLOT SYNCHRONIZATION SCHEME FOR A COMPUTER NETWORK COMMUNICATION CHANNEL}

Recent computer networks have enabled communication between multiple nodes, such as personal computers, workstations, peripheral units, and the like. Network links sometimes transfer information between distant nodes. However, to date most computer networks have relied on wired links to transmit this information. Where a wireless link is used, it has become a component of large networks such as wide area networks that can use satellite communication links to interconnect distant network nodes. In this case, the transmission protocol used for the wireless link has generally been established by service providers, such as telephone companies and other service providers, that carry the data to be transmitted.

In a home environment, computers have traditionally been used as standalone devices. Recently, however, a number of measures have been taken that incorporate home computers and other devices. For example, in the so-called "smart home", computers are used to turn various devices on and off and to control their operating settings. In this system, a wired communication link is used to interconnect a computer to the device to be controlled. In addition to the original structure of these grooves, it is expensive to install a wired link.

To reduce the problems and costs associated with wired communication links, devices interconnecting computers and devices have used analog wireless links to transfer information between these units. The analog radio link operates at frequencies commonly used by cordless telephones. Although easier to install than conventional wired communication links, analog wireless communication links have several drawbacks. For example, degraded signals may occur on such links due to multipath interference. In addition, there may be interference from existing devices such as televisions, cellular telephones, cordless telephones, and the like. Therefore, analog wireless communication links do not necessarily provide optimal performance for home environments.

Co-pending application No. 09 / 151,579, incorporated herein by reference, discloses a computer network using a digital wireless communication link suitable for use in a home environment. This structure is arranged in a hierarchical manner and includes a plurality of network components connected to each other via communication links operating at different levels of hierarchy. At the highest level, a communication protocol is used that supports the dynamic addition of new network components of any level layer, which conforms to the bandwidth requirements of the communication channel operating at the highest level network layer.

The general structure of the network is shown in FIG. Subnet 10 includes server 12. In such a device, the term “subnet” is used to describe a group of network elements that includes a server and several clients associated with the server (eg, connected via a wireless communication link). However, depending on the context described, a subnet may be referred to as a network that includes a client and one or more subclients associated with the client. A "client" is a network node linked to a server via a wireless communication link. Example clients include audio / video devices such as televisions, stereo components, personal computers, satellite television receivers, cable television distributed nodes, and other home devices.

The server 12 may be a separate computer that controls the communication link, but in other cases, the server 12 may be an add-on card or other configuration attached to the host computer (eg, a personal computer) 13. It can be implemented as an element. Server 12 includes a wireless device 14 that is used to wirelessly connect server 12 to other nodes in subnet 10. Wireless links typically support both high and low bandwidth data channels and command channels. A channel is defined here as a combination of transmission frequency (more suitably transmission frequency band) and pseudorandom (PN) code used for spread spectrum communication. In general, multiple available frequencies and PN codes provide multiple available channels in subnet 10. As disclosed in the co-pending application, the server and client can search the available channels to find the desired channels that can communicate with each other.

Subnet 10 includes a number of clients 16, some of which have shadow clients 18 associated with clients 16. The shadow client 18 receives the same data input as the client 16 (either the server 12 or the other client 16) but exchanges commands with the server 12 that is independent of the client 16. Is defined as Each client 16 has a wireless device 14 that is used to communicate with the server 12 and some clients 16 have a corresponding subclient 20. The subclient 20 includes a keyboard, joystick, remote control device, multidimensional input device, cursor control device, display unit and / or other input device and / or output device associated with the particular client 16. The client 16 and its subclient 20 communicate with each other via a wireless (eg infrared, ultraviolet, spread spectrum, etc.) communication link 21.

Each subnet 10 is arranged in a hierarchical manner with several levels of hierarchy corresponding to the level at which communication occurs between intra network components. The highest level hierarchy resides in server 12 (and / or corresponding host 13) in communication with various clients 16 via a wireless channel. At another lower level, the client 16 communicates with various subclients 20 using a wireless communication link or a wired link, such as an infrared link.

Where half-duplex wireless communication is used in the wireless link between server 12 and client 16, a communication protocol based on a slotted link structure with dynamic slot assignment is used. This structure supports point-to-point connections within subnet 10, with slot sizes reassigned within the session. Therefore, the data link layer supporting wireless communication can coordinate data packet handling, time management for packet transmission and slot synchronization, error correction code (ECC), channel parameter measurement and channel switching. The high level transport layer provides all necessary connection related services, monitoring for bandwidth utilization, low bandwidth data handling, data broadcasting and optionally data encryption. The transport layer also allocates bandwidth to each client 16, periodically monitors its use of the bandwidth, and coordinates any bandwidth reallocation, either whenever a new client 16 is online or upon client. (16) (or the sub-client 20 in question) is required when greater bandwidth is required.

A slotted link structure of a wireless communication protocol for the transmission of real-time multimedia data (eg, frames) within subnet 10 is shown in FIG. 2. At the highest level in the channel, forward (11) (F) and backward (11) (B) slots are provided within each frame transmission time for a fixed (but changeable) time. During forward time slot F, server 12 sends video and / or audio data and / or commands to client 16 in listening mode. During the reverse time slot B, the server 12 listens for transmissions from the client 16. The transmission may include audio, video or other data and / or commands from the client 16 or the corresponding subclient 20. In the second level of hierarchy, each transport slot (forward or reverse) consists of one or more radio data frames 40 having an available length. Finally, at the lowest level layer, each radio data frame 40 consists of a server / client data packet 42 having a variable length.

Each radio data frame 40 consists of a server / client data packet 42 and corresponding error correction coding (ECC) bits. The ECC bit simplifies the detection of the beginning and end of data packets at the receiving end. Variable length framing is preferred over fixed length framing to allow small frame lengths in poor channel conditions, and vice versa. This adds to the robustness and bandwidth savings of the channel. However, although variable length frames can be used, the ECC block length is preferably fixed. Thus, whenever the data packet length is less than or equal to the ECC block length, the ECC block may be truncated (eg, using conventional virtual zero techniques). Similar procedures can be applied to the last block of ECC bits when the data packet is large.

As shown, each radio data frame 40 includes a preamble 44 that is used to synchronize pseudorandom (PN) generators of the transmitter and receiver. Link ID 46 is a fixed length field (e.g., 16 bits for one embodiment) and is unique to the link and thus identifies a particular subnet 10. The data of the server 12 / client 16 is of variable length as indicated by the length field 48. The cyclic redundancy check (CRC) bit 50 may be used for error detection / correction in a conventional manner.

In the illustrated embodiment, each frame 52 is divided into a forward slot (F), a backward slot (B), an idle slot (Q), and a plurality of wireless rotating slots (T). Slot F means communication from server 12 to client 16. Slot B is the time shared by a number of mini slots (B1, B2, ..., etc.) assigned to individual clients 16 by server 12 for separate transmission to server 12. Each mini slot (B1, B2, ..., etc.) has audio, video, voice, lost data (i.e. encoded / decoded data that can use lossy technology or allow loss of packets during transmission / reception), Lossless data (ie, encoding / decoded data using lossless techniques or that cannot tolerate loss of packets during transmission / reception), low bandwidth data and / or time to transmit a Cmd packet. Slot Q remains idle, so a new client can insert a request packet when logging in to subnet 10. Slot T appears upon a change from transmit to receive and on a change from receive to transmit, and adjusts the rotation time of the individual radio signal (i.e., half-duplex radio 14 may switch from transmit to receive operation and vice versa. time). The time of each of these slots and minislots can be changed dynamically through reallocation between the server 12 and the client 16 to achieve the best bandwidth utilization of the channel. When a full duplex wireless device is used, each directional slot (ie, F and B) may be full time directed in one direction, and no radio rotating slot is required.

Forward and backward bandwidth allocations follow the data handled by the client 16. If the client 16 is a video consumer, for example a television, a wide forward bandwidth is allocated for the client. Similarly, if the client 16 is a video producer such as a video camcorder, for example, a wider reverse bandwidth is assigned to that particular client. Server 12 maintains a dynamic table (eg, in memory of server 12 or host 13) that contains the forward and backward bandwidth requirements of all online clients 16. This information can be used to determine if a new connection is allowed to a new client. For example, if the new client 16 requires more than the bandwidth available in either direction, the server 12 will reject the connection request. Bandwidth requirement (or allocation) information can also be used to determine how many wireless packets a particular client 16 needs to wait before starting to send packets to the server 12. In addition, whenever the channel state is changed, the number of ECC bits may be increased / decreased to cope with the new channel state. Therefore, it is necessary to dynamically change the forward and backward bandwidth allocations depending on whether the information rate at the source is changed.

Given the slotted link structure of the communication channel, to ensure that the network master device (e.g., server 12 and other network device (e.g., client 16)) can communicate with each other as appropriate. A network slot synchronization method is required.

The present invention relates to a method for communication within a computer network, and more particularly to a method for synchronizing communication occurring between a plurality of client units and central servers via a wireless communication link.

The invention is explained with reference to the accompanying drawings.

1 illustrates a generalized network structure supported by the wireless protocol of one embodiment of the present invention.

2 illustrates a hierarchical device for data transmission of a subnet according to an embodiment of the present invention.

3 is a state diagram illustrating a process of adding a subnet to a client according to an embodiment of the present invention.

4 illustrates a network client device configured with a combination of timers and counters used to maintain network synchronization in accordance with one embodiment of the present invention.

5 is a state diagram illustrating a process of inserting a client into a subnet by a server according to an embodiment of the present invention.

6 is a state diagram illustrating a process for a server initiating a session for a new client according to an embodiment of the present invention.

7 is a state diagram illustrating a process of changing a channel of a subnet by a server according to an embodiment of the present invention.

8 is a state diagram illustrating processing relating to a channel change sequence of a subnet by a client according to an embodiment of the present invention.

9 is a state diagram illustrating a process of inserting a subclient online into a subnet according to an embodiment of the present invention.

In one embodiment, synchronization within a general communication channel with transmission timeslots set up for various devices of the computer network is only possible if the clear channel assessment indicates that the previous timeslot is not used by that device. Is maintained by enabling transmission outside the channel of the set timeslot of < RTI ID = 0.0 > The clear channel assessment preferably takes into account the established transmission timeslot of the device in the communication channel associated with the other network device. In one example, the clear channel assessment is a time corresponding to the product of a predetermined clear channel wait time and a numeric representation of a device's set transmission timeslot of the communication channel's device associated with another network device. It can be specified by the network master device as part of the processing.

The network device is configured to configure one or more packets for network transmission before its set timeslot. For example, the device may include a previous transmission timer configured to trigger the configuration of the packet before a set timeslot. This allows for fast transmission without undue delay.

In another embodiment, a transmission time timer in a first device configured to operate in a computer network where each device in the network has a typical communication channel set to a particular transmission time slot may cause the first device to transmit within that set transmission time slot. Is maintained to ensure that. However, when a first device receives a transmission end indicator of a second device in a computer network having a set transmission time slot preceding the first device regardless of whether transmission at the time specified by the transmission time timer is performed. Enable to be transmitted over the channel. For example, receipt of commands and tokens passed. In addition, the first device will configure one or more packets for transmission of the network prior to the communication time set to readily accept the token pass. In general, the first device transmits on a normal communication channel only if the channel is not used by another network device, which may be true regardless of whether the transmission time timer indicates that the first device's set timeslot has been reached. .

The first device maintains a clear channel assessment indicator that takes into account the established transmission timeslot of the first device of the communication channel associated with the other network device. Therefore, regardless of whether the first transmission time timer indicates whether the set transmission time of the first device has been reached, when the indication of the clear channel evaluation indicator that the channel can use for transmission arrives, the first device is a conventional device. It can transmit in communication channel. In general, a clear channel assessment indication is made upon expiration of a time corresponding to a product of a predetermined representation of a transmission time slot of a first device of a communication channel associated with another network device and a predetermined clear channel wait time. The clear channel latency is set by the network master device when a connection is made by the first device. The clear channel assessment transmission method may be used in connection with a method of providing an end-of-transmission indicator by command or token passing to enable transmission without excessive delay.

These features of the present invention will become apparent with reference to the drawings and detailed description.

A method of synchronizing network slots between a network master device (e.g., a server) and corresponding network clients in a communication channel of a computer network is disclosed. This method can generally be used in many network environments, but is particularly useful in wireless computer networks located in home environments. Therefore, this method will be described in terms of home environment. However, this description does not in any way limit the use of the invention in other network environments, and the technical idea of the invention is set forth in the claims of this description.

One important term used throughout the following description is "channel". As mentioned above, a channel is defined as a combination of transmission frequency (more suitably transmission frequency band) and pseudo-random (PN) code used for spread spectrum communication. In general, multiple available frequencies and PN codes may provide multiple available channels in a subnet. The network master and client can search the available channels to find the desired channel to communicate with each other. Table 1 below shows a typical channel scheme that follows the scheme.

Table 1

In one embodiment, a channel scheme employing two frequency bands is employed, so that a detailed description of channel selectivity of the scheme is described below.

The network slot synchronization of the subnet 10 may be divided into four network operational states: when the client is waiting; When a new client is online; When the channel is changed; When a client is absent or powered off: This state is described with reference to various finite state diagrams for the client 16 and the server 12. In the figure the operating states of the network elements are shown in circles. The state transition is made in accordance with the content of the processing output and / or the reception and input messages contained in the status quo. The received or sent message (ie command) is shown next to the status transition line. For example, "A / B" in the state transition line means that message "A" is received and message "B" is sent as a response while transferring to the next state. In other cases "A" may be an ongoing processing output and "B" may be an action taken by a finite state machine. "XX" represents "don't care" action, input or output. A complete description of the various instructions described in this figure is provided in the co-pending application described above.

As shown in Fig. 3, when the client 16 is waiting, it starts in the receive mode (state 60) and monitors the channel. If the client 16 detects activity on the channel, the server 12 monitors to determine if it is present in the channel change process (state 62) (described below). If the channel change process is recognized, the client 16 changes the channel like the rest of the subnet 10 (state 64). Of course, if no channel change has been processed, the client 16 will only detect standard channel communications. Regardless of whether a channel change is required, the client 16 waits for a slot Q and sends a connection request (CRQ) packet of that slot to the server 12. The format of communication packets other than the CRQ packet is disclosed in the co-pending application described above. However, the specific structure of these packets is not important in the current way for network synchronization.

In response to the CRQ packet, the server 12 checks the correspondence of the input request (eg, by sending the same request addressed to the sending client periodically every network frame until a response is reached). If the client's request is acknowledged (eg, by receiving an acknowledgment packet from the client after the client enters the wait state 68), the server 12 sends an access grant (ACG) packet to the client 16. send.

The package contains, among other things, information relating to the forward and backward bandwidths to which the new client 16 has entered (e.g., slots in the channel). In addition, the maximum number of bytes that the new client 16 can send and expect in each data packet is set to each type of packet (e.g., video data, audio data, etc.). The access authorization package contains the total number of data frames that the new client 16 needs to wait from the start of transmission of the server (i.e. before sending traffic) and of the previous client (i.e., the client that owns the previous reverse transmission slot). It may also contain information related to the confirmation.

Every client counts the number of data frames received from the start of transmission of the server and grants each access permission, and starts each transmission after the end of the last data frame received from the previous client. During counting, if the client encounters an indication of the end of transmission by a command (eg, a token) sent by the previous client, the client terminates counting and immediately starts its transmission. Thus, using the command is one mechanism by which network slot synchronization can be guaranteed in this manner.

After receiving the connection grant packet, client 16 configures itself to send its data to the assigned timeslot (e.g., B1, B1, etc.) and waits for that slot to return (state 70). . In the established timeslot, the client 16 may initiate standard communication with the server 12 (state 72) and send a possible command or command. In order to maintain proper timeslot synchronization, part of the configuration process may include programming the correct slot timer (AST).

4 illustrates a client 16 configured as an AST 54 in accordance with one embodiment of the present invention. The AST 54 is a register that increments or decrements in accordance with regular principles that are programmed using information provided by the network master as part of the connection process (e.g., a regular clock followed by a suitable clock signal maintained by the client device). Or a memory location). For example, the network master (eg, server 12) instructs the newly connected client that it is located in the slotted link structure of the communication protocol. Thereafter, by using the AST 54 to monitor the time (which can be reset at each master transmission or at each transmission of the relevant client), the newly connected client 16 can determine when the transmission starts. You can predict accurately.

Of course, this synchronization scheme is preferably used in connection with other techniques such as the disclosed clear channel assessment, previous packet configuration, and token pass operation so as not to improperly trigger or unnecessarily delay the transmission of the client. In addition, the expiration of the AST-monitored time does not permit transmission if the client detects that the transmission of the previous client has not yet completed. If not, the transmissions overlap and cause confusion in the network.

With regard to the use of the AST 54 and other synchronization schemes to be described below, when the client's transmission slot arrives, the client 16 sets an early trigger timer (ETT) 55 to ensure that the packet is ready for transmission on the subnet. You can also integrate. That is, the ETT 55 can be used to improve the internal configuration of packets for transmission, the purpose of which is to have the assembled packets and to prepare for transmission when the client's transmission slot is available. Therefore, the ETT 55 (which can be performed as a normal timer) triggers the packet information processing and its error detection bit, etc., in order to maintain several packets prepared before the actual start of transmission. For example, in one embodiment, packets are assembled and stored for transmission in one network frame before actual transmission. This preassembly helps to avoid idle time in the channel when the first packet for several transmission sequences is formed. Accumulating data in one network frame before transmission may alert the system to one network frame latency in the first transmission slot, which can be expected to be reduced to a few milliseconds.

The above description assumes that client 16 is waiting to find a channel in use. However, the channel will not be in use when the client 16 is waiting. In this case, client 16 may send a connection request packet, thinking that server 12 will respond and will wait for a random time (state 74). If no response is received, the client will change the channel. When receiving the mode of the new channel (state 76), if the client 16 detects activity, it negotiates with the server 12 for bandwidth allocation as described above. Otherwise, if no channel activity is detected, client 16 will send a connection request packet again and wait for a response (state 78). This process will be repeated for all available channels until server 12 is found. If no response is received, the client informs the user that no server is available and will be powered off (state 80). However, if a response is received from server 12 of one of the channels, the client negotiates for the connection (state 82) and initiates standard communication as described above (state 84).

From the server perspective shown in FIG. 5, the client 16 can be inserted online. For example, client 16 may wait after server 12 has already operated. Server 12 is configured to note slot Q for any connection request packet sent by a new client seeking a connection (state 90). After synchronizing with the new client 16 by another exchange of the connection request packet, as described above, the server 12 requests authentication of the host computer 13 storing the valid client ID to authenticate the client. Check (state 92). If the authentication test passes, server 12 assigns a new client session identifier (CS-ID) to the client (state 93) and re-allocates bandwidth for the channel (state 94). Bandwidth reallocation needs to accommodate new clients. Thereafter, the server 12 transmits a connection grant packet to the new client 16, and thus starts standard communication. As shown, each state 92, 93, 94 may have a corresponding timeout parameter (eg, maintained using an on-board timer). If no client response is received within the timeout time at any time, server 12 will reverse to attention in slot Q when client 16 is offline (state 90).

As shown in FIG. 6, when there is no online client 16, server 12 is configured to park on an empty channel and remain in receive mode until a client packet is detected (state 95). To determine if the channel is empty, the received signal strength (provided by the radio 14) for each channel is checked and the signal with the lowest energy is selected. Next, any received data is analyzed for the presence of valid data packets other than the connection request packet. If other packets are received, especially those marked as generated servers, the channel is declared busy. On the other hand, the channel is declared empty if the packet does not contain any valid data other than the connection request packet generated by the client waiting for connection on the channel. If no packets are received at all, server 12 remains in receive mode on the channel (state 95) and waits for a client's connection request packet. In the meantime, if the channel is currently occupied by another subnet near the server radio, the server switches to the other channel and waits for a client request. If all channels have been occupied, server 12 periodically changes channels until an empty channel is found. If client 16 continues to inspect packets from two servers 12, client 16 recognizes that an interference condition exists in the channel and cannot connect over the wireless link. Similarly, if server 12 continues to inspect packets from other servers, the server will not attempt to establish any client's connection in the channel. These two criteria ensure that servers in a subnet will not own clients in adjacent subnets. In addition, a unique identifier may be used for each subnet 10 to avoid capturing the client of one server by another server in a neighboring subnet.

The client 16 may set the server 12 to act by, for example, sending a connection request packet. Client 16 may then be inverted to slave mode (eg, timeout option). Once the client's request is received, server 12 periodically sends a connection request packet and waits for client 16 to join the line as described above (state 96). After the client's slave mode is confirmed by transmission, server 12 tests the client's authentication (state 97) and, if successful, provides connection permission to client 16. If authentication takes longer than the time required for the host computer 13 to respond to the client 16 during processing, the server 12 may send a connection grant packet without expecting any acknowledgment from the client 16. Sending again will delay client 16. After sending the access authorization, server 12 assigns a new CS-ID (state 98) and waits for client 16 to approve the transfer (state 99). Standard communication may then begin (state 100).

By first making the client the master and then changing back to the slave after the server 12 becomes available, low interference on the free channel is ensured when the subnet 10 is not working. Of course, in another embodiment, server 12 registers candidates for client 16 at regular intervals over the channel. However, this approach keeps the channel in use even when subnet 10 is not working and thus rejects the channel for the neighboring subnet.

In one embodiment, multiple clients 16 (or shadow clients 18) are supported with the same input of server 12. In this case, at least one copy of the forwarded data packet (client ID is the ID of the first client) needs to be transmitted. The remaining clients may be treated as shadow clients using respective command packets of server 12.

In many client schemes, when one of the clients 16 branches late, it waits for an idle (Q) slot and starts sending command packets in that slot. However, one or more clients may branch after the server 12, where the present scheme provides a means of resolving potential conflicts that may occur if two or more clients 16 each attempt to transmit in a Q slot. To avoid such a collision, the client 16 may randomly choose to insert (or not) each request in the Q slot. The client 16 first recognized by the server 12 will be added to the subnet 10 first.

Table 2 (where Tx represents the wireless device 14 in the transmit state and Rx represents the wireless device 14 in the receive state) details the various state diagrams and general state diagrams for online insertion of new clients. .

TABLE 2

Due to the set timeslot arrangement, if the client responds late for some reason, no other client can capture the set timeslot. This leads to a waste of previous bandwidth. Thus, the present approach provides a double solution to this problem.

First, each client 16 needs to keep track of the current client occupying the channel, thus trying to detect the client just before the line. If the channel is idle, the current client waits for a predetermined length of time before starting its transmission. In one embodiment, the length of the latency follows the idle time threshold allowed between the number of clients to be transmitted before the current client and the two clients (clear channel assessment or CCA time). For example, the latency may be a product of the number of devices to be transmitted and the CCA threshold. Thus, the latency calculation uses the order of transmissions established during connection setup. The only exclusion for idle time is the Q slot when all online clients 16 suppress transmission.

As mentioned above, CCA transmissions (i.e., delivery of clients based on latency termination) are basically the result of a decision made by the client that the channel is empty and therefore suitable for transmission. Each client device keeps track of how many devices terminate the transmission from the time the network master has completed its transmission. This can be done using a counter where a client transmission is detected and incremented every time a known counter is executed. Thereafter, by recognizing the index (the value received from the network master at the time the connection is established) regarding its position of the network frame, each client device can determine when to start the CCA transmission. This is shown by way of example.

Each client device may program a CCA timer 57 (see FIG. 4) associated with the predetermined value. The network master can specify this value at the time the master-client connection is established, which typically indicates the time that must be terminated before allowing the network client to assume that no other client is using the channel. The client device is present in the fifth transmission line prior to the master device and assumes that the device on the second line detects a clear channel (eg due to CCA timer 57 timeout) after completing the transmission. Since the device is on line 5, it cannot start its transmission immediately (after all, there are still two client devices in front of it). However, the fifth device may increment the relevant CCA counter 58 at this point. If the third and fourth devices are idle (i.e. if the fifth device's CCA timer 57 is terminated more than once in a row), the fifth device will again double its CCA counter 58, It will immediately begin its transmission on the third CCA detection.

In the above example, the third device in the line will detect the absence of the second device and thus immediately begin its transmission if there is traffic to send. That is, the wait time of the third device is only one CCA timeout due to the absence of the transmission of the second device, where the fifth device is a 3 CCA timeout time. Similarly, the fourth device in the line is present 2 CCA timeout time away from the second device. Using client slot assignment in determining when the CCA transmission begins may allow the client device to maintain a sequence relative to each other within the slotted link structure of the communication channel.

The second part of the solution to guarantee the transmission slot of the client is that it will not be captured if it responds late for the following reasons, because the server 12 observes any channel grasp and any continuously delayed client (s). Is to take appropriate action to connect / disconnect. When a delay in response occurs, the video generating the client / server consequently reduces the size of the output data of the next video slot. This allows to maintain proper slot time synchronization. The video generating the client / server monitors the idle channel length path and moderately reduces the output of the current / next video slot.

To accommodate the new client, the size of slot Q must be at least the length of the radio data frame 40 carrying the connection request packet. Therefore, the new client 16 can receive all data frames, knows the data frame structure of the current session, and inserts the connection request of slot Q between the transmission of the last online client and the server 12. This request can be confirmed after checking consistency for multiple transactions (ie, between server transfers). Wireless rotation time is required and should not be confused with the Q slot. This is confirmed using a timer.

In order to notify the new client that the server 12 has recognized the connection request, the server 12 needs to send a packet to the new client. Therefore, server 12 does not overlap the last packet sent by server 12 for a new client whose first client expected to begin transmission after the server (i.e., the client assigned slot B1) is the end of slot F. Should not. Thus, the server can broadcast the token pass at the end of the transmission. The first client of the line will begin its transmission after receiving the token pass from the server 12 (and after the radio rotation time, if necessary) or after the idle channel times out.

As mentioned above, when the channel is changed, all clients 16 need to synchronize with server 12. Channel switching can occur when either server 12 or client 16 experiences severe channel corruption (eg, antenna diversity and / or high ECC). In this manner, server 12 searches for another channel while trying to find a channel with less interference. If the new channel provides a better view of the communication operation, server 12 initiates a channel change or switching operation.

7 shows the channel change sequence for the two channel subnet by the server 12. If during standard communication (state 101), server 12 determines that the channel state is unacceptable, server 12 will remain idle for all clients 16 before searching for a new channel. Notify. This procedure is repeated a number of times (eg 5 times) to ensure that the message is received by all clients 16 (state 102). In response, the client expects to send an acknowledgment even if the acknowledgment has not been received from all online clients 16, and the timer of server 12 will expire, and server 12 will wirelessly check for another channel. Adjust device 14 (state 104). If the new channel is empty, server 12 switches back to the original channel (e.g. after a predetermined monitoring time, i.e. 4 msec), and a channel change message (repeatedly up to five times) to all online clients 16 ), Waiting for a separate change channel acknowledgment (Ack) message for client 16 (state 106). Each client 16 changes channels only after sending its change channel Ack message. If server 12 does not receive a response from one or more online clients 16 even after a predetermined time, server 12 determines that the client (s) has not arrived. Similarly, client 16 will spontaneously change the channel, determining whether server 12 has not arrived even after waiting a predetermined time or has not received any message from the server. Server 12 switches to a new channel after all online clients 16 have responded or terminated.

In the new channel, client 16 waits for server 12 to begin communication. Server 12 broadcasts a change channel Ack message from each client 16 to declare its presence in the new channel (state 108). If one or more clients 16 do not respond within a predetermined number of attempts, server 12 determines whether client (s) 16 are temporarily absent. Thus, server 12 changes the response sequence of client 16 to keep the client absent (eg, by sending a new connection grant). After waiting for all clients 16 to check for the absence of a new channel (state 110) (or during the end time), the server 12 updates the call-response slot for the new channel and sends it to all clients 16. Send a new connection permission. Standard communication may then be resumed (state 112).

If the client 16 arrives late for a new channel, it may need to wait for the server's call to respond. If the server 12 has already determined that the client 16 is absent, the client 16 still waits for resumption of standard communication, and then transmits the change channel Ack message of the slot Q in idle state. The server 12 receives the message, sends a connection authorization and includes a new device of the network.

In order to leave the user associated with the late client unaffected during this time, two criteria are used. First, all clients 16 are configured to provide video frame freeze and / or audio repetition to simulate a flexible session at the user level. Second, server 12 maintains a detailed session for a predetermined amount of time sufficient to allow easy reconnection. Only after the predetermined waiting time has expired is the absent client 16 finally removed from the server's online client list (state 114).

If server 12 has received a change channel Ack message from client 16 very late after being removed from the online list, client 16 is advised to make a new connection by sending a connection request. In this case, client 16 will inform the user that the link has been lost. This looks similar to a power fault at the user level and will allow the user to reestablish the link with the server 12.

During channel selection (eg, as part of or initially at a channel change operation), the server 12 needs to detect the subnet 10 that is pre-operating on the current channel, with the same PN code and / or link ID. It is necessary to detect the potential presence of a link with the. The likelihood of this is expected to be very small but not zero. It is assumed that the link ID is unique to the link / subnet / cell. To ensure this uniqueness, the user can enter a unique password (eg, social security number or other alphanumeric string of similar length) during subnet setup. This password is resolved by the server 12 (and / or host computer 13) and used to set a unique link ID and PN code. These values are the same for all sessions unless the user changes them (eg, by remounting subnet 10).

In one embodiment, an 11 bit PN code (Barker code) can be used, but a high bit length can also be used to ensure uniqueness and thus provide additional security. A table of available PN codes is maintained by the server 14 / host 13, one of the codes being selected based on the password entered by the user. Since the PN code uses the same PN code in the neighbor subnet 10, it will change whenever there is increased interference.

If both channels are occupied or have large interference, server 12 may take one of two actions. If there are fewer clients 16 from / to where the channel interference is severe, the server 12 will determine the disconnection. On the other hand, if the number of clients 16 is large, the server 12 will decide to wait for a while and try the channel after a while. In any case, server 12 needs to send subsequent retry commands to each client 16 until a Disconnect Ack message is received from each affected client 16.

Figure 8 illustrates the channel switching operation from the client side for a typical two channel subnet. If during standard communication (state 120), client 916 is instructed to be idle, client 16 sends an acknowledgment (e.g., disconnect Ack) and then waits for another command from server 12. (State 122). If server 12 broadcasts a change channel message, client 16 changes the channel after accepting. Optionally, client 16 will determine if server 12 is unreachable, have not received any message from the server after waiting for a period of time, and will voluntarily change channel.

In the new channel, client 16 waits for server 12 to initiate communication (state 126). The server 12 broadcasts a change channel Ack message to declare the presence of a new channel and expects a change channel Ack from each client 16. Accordingly, client 16 acknowledges its presence in the new channel and waits for a new connection acknowledgment from server 912 (state 128). When negotiating connection authorization with server 12 again, client 16 waits for standard communication to start again (state 130).

If the client 16 arrives late for a new channel, it may need to wait for the server's call to respond. If server 12 has already determined that client 16 is absent, client 16 waits for resumption of standard communication before sending a channel change Ack message to an idle (Q) slot (state 132). When server 12 receives the message, it sends a connection permission and includes the new device on the network. In order to leave the user associated with the late client unaffected during this time, the client 16 will provide video frame freeze and / or audio repetition to simulate a flexible session at the user level.

If server 12 has received a change channel Ack message from client 16 very late after being removed from the online list, client 16 is advised to make a new connection by sending a connection request. In this case, client 16 will inform the user that the link has been lost (state 134). This looks similar to a power fault at the user level and will allow the user to reestablish the link with the server 12. During channel selection, if client 16 loses connection with server 12 for an extended period of time, it will inform the user of the status and turn off (state 136).

Similar to the client 16, the subclient 20 can also be inserted online into the operational subnet (see, for example, hot insertion). As shown in Fig. 9, when the subclient 20 is active, it transmits a registration packet to the corresponding client via the communication link 21 (state 220). In some cases the communication link 21 may be a wireless link (eg, an infrared communication link), while in other cases it may be a wired link.

Upon receiving a transmission from the subclient 20, the client 16 authenticates the subclient, for example by checking a list of known / authenticated subclients and the registration information (state 222). In some cases, communication with server 12 may be required. If the subclient 20 is recognized, the client 16 constructs a subclient session identifier that will uniquely identify the new subclient and other clients operating online with the client. The client 16 then sends a subclient add command (see below) to the server 12 (state 224). The subclient add command includes the subclient identifier and the characteristics of the subclient as described in detail below.

When server 12 receives a subclient add command, it records the subclient session ID and whether the subnet can accommodate additional new subclients (e.g., sufficient bandwidth on the radio link to / from the new subclient). The subclient authentication process is completed by determining whether the command can be used to accept the sent / received command (state 226). If the authentication process is successful, the server adds a new subclient to the subnet by inserting it into the online service and sending the added subclient command to the client. If the new subclient is unacceptable or rejected, the server sends a subclient inhibit command.

Each time the server determines, the result of the authentication process is sent from the client to the subclient (state 228). If the subclient has been accepted, it starts standard operation and begins communicating with its client and server 12 (state 230). If the subclient is rejected, the connection is disconnected (state 232). In either case, the user will use the appropriate device message displayed on the display device to notify the addition or rejection of the subclient.

During network operation, the subclient 20 will be disconnected by either the server 12 or its client 16. For example, if the subclient 20 is inactive for more than a predetermined time, the client 16 will disconnect the subclient 20. In this case, the client 16 warns the server 12 of the status and requests that the disconnected subclient has been removed from the server's list of online devices (see erase subclient and erased subclient command below).

In other cases, server 12 will decide to erase subclient 20 immediately, for example if the application running on host 13 does not support a particular subclient (or current client). Network maintenance and power off operations also require that the subclient (and client) be automatically erased.

Thus far, a method of synchronizing communications in a computer network communication channel has been disclosed. Although described with reference to the examples, it is not limited thereto. Instead, the invention is limited only by the claims.

Claims (18)

A method of maintaining synchronization in a typical communication channel with established transmission timeslots for various devices in a computer network, A method for granting transmission on an external channel of a set timeslot of the device only if a clear channel assessment indicates that a previous timeslot has not been used by the device. 2. The method of claim 1, wherein the clear channel assessment takes into account the established transmission timeslot of the device of a communication channel associated with another network device. 3. The method of claim 2, wherein the clear channel assessment comprises a time that is a product of a numeric representation of a set transmission timeslot of the device of a communication channel associated with another network device and a predetermined clear channel wait time. 4. The method of claim 3, wherein the clear channel latency is specified by a network master device as part of network connection processing. 2. The method of claim 1, wherein the device is configured to configure one or more packets for transmission of the network before a set timeslot. 6. The method of claim 5, wherein the apparatus comprises an early transmission timer configured to trigger the configuration of one or more packets for transmission of the network prior to a set timeslot. A method of maintaining a transmission time timer in a first device configured to operate in a computer network having a normal communication channel, the method comprising: Each device of the computer network is configured with a particular transmission time slot to ensure that the first device is transmitted within a corresponding transmission time slot. 8. A token as claimed in claim 7, wherein a token passed by a second device of the computer network having a set transmission time slot preceding the first device, regardless of whether the transmission occurs at a time set by the transmission time timer. When the first device is authorized to transmit over a normal communication channel. 9. The method of claim 8, wherein the first device configures one or more packets for transmission in the network prior to a set transmission time. 8. The method of claim 7, wherein the first device configures one or more packets for transmission in the network prior to a set transmission time. 8. The method of claim 7, wherein the first device transmits over a normal communication channel only when a transmission time timer has not been used by another network device, regardless of whether or not the set time slot of the first device has arrived. Characterized in that the method. 8. The method of claim 7, wherein the first device maintains a clear channel assessment indicator that takes into account the set transmission timeslot of the first device of a communication channel associated with another network device. 13. The method of claim 12, wherein upon receiving an indication of a clear channel assessment indicator indicating that a channel can be used for transmission, regardless of whether a transmission time timer indicates that the set transmission time of the first device has been reached. And the first device transmits on a conventional communication channel. 14. The clear channel estimation instruction as set forth in claim 13, wherein the clear channel evaluation indication is made at the end of a time that is a product of a numerical representation of a set transmission timeslot of a first device in a communication channel associated with another network device and a predetermined clear channel wait time. Way. 15. The method of claim 14, wherein the predetermined clear channel wait time is set by a network master device when connecting by the first device. 16. The method of claim 15, wherein the first device configures one or more packets for transmission before a predetermined transmission time. 16. The apparatus of claim 15, wherein the first apparatus, upon receiving an indication of the end of transmission of a second apparatus of a computer network having a set transmission timeslot preceding the first apparatus, irrespective of clear channel evaluation being made. The method is characterized in that the transmission is permitted over the communication channel. 18. The method of claim 17, wherein the first device configures one or more packets for transmission before the set transmission timeslot.