CA2010716A1 - Method and apparatus for accessing a distributed communications network - Google Patents
Method and apparatus for accessing a distributed communications networkInfo
- Publication number
- CA2010716A1 CA2010716A1 CA002010716A CA2010716A CA2010716A1 CA 2010716 A1 CA2010716 A1 CA 2010716A1 CA 002010716 A CA002010716 A CA 002010716A CA 2010716 A CA2010716 A CA 2010716A CA 2010716 A1 CA2010716 A1 CA 2010716A1
- Authority
- CA
- Canada
- Prior art keywords
- station
- token
- access
- local bus
- channel
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
- H04L12/42—Loop networks
- H04L12/427—Loop networks with decentralised control
- H04L12/433—Loop networks with decentralised control with asynchronous transmission, e.g. token ring, register insertion
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
- H04L12/40—Bus networks
- H04L12/407—Bus networks with decentralised control
Abstract
IN THE CANADIAN PATENT AND TRADE MARKS OFFICE
PATENT APPLICATION
entitled : METHOD AND APPARATUS FOR ACCESSING A DISTRIBUTED
COMMUNICATIONS NETWORK
in the name of: Jean A. PICANDET
assignee: JS TELECOM
Société Anonyme ABSTRACT OF THE DISCLOSURE
Stations (S1, ..., Sn, ..., Sp), having a number of data transmission terminals (T1-1 to T1-n1, ..., Tn-1 to Tn-n, ....
Tp-1 to Tp-np), connected thereto are joined by links (PCM1-2, ..., PCM(n-1)n, PCMn-(n+1), ..., PCMp-1) defining at least one virtual loop that forms at least one communications channel passing through all stations. The channels convey frames that carry at least one access token, signalling information and data.
Each station has its own local bus (BL1, ..., BLn, ..., BLp) into which write access by the data transmission terminals is governed by acontention system, the terminal gaining access to transmit on the communications channel via a local bus. Means are provided for intercepting access token for transmission on the communications channel in response to an access request coming from one or several terminal(s) depending from the station. Means are provided for re-transmitting the access token into the communications channel once the requesting terminal(s) has/have successively transmitted its/their respective message(s) via the local bus.
PATENT APPLICATION
entitled : METHOD AND APPARATUS FOR ACCESSING A DISTRIBUTED
COMMUNICATIONS NETWORK
in the name of: Jean A. PICANDET
assignee: JS TELECOM
Société Anonyme ABSTRACT OF THE DISCLOSURE
Stations (S1, ..., Sn, ..., Sp), having a number of data transmission terminals (T1-1 to T1-n1, ..., Tn-1 to Tn-n, ....
Tp-1 to Tp-np), connected thereto are joined by links (PCM1-2, ..., PCM(n-1)n, PCMn-(n+1), ..., PCMp-1) defining at least one virtual loop that forms at least one communications channel passing through all stations. The channels convey frames that carry at least one access token, signalling information and data.
Each station has its own local bus (BL1, ..., BLn, ..., BLp) into which write access by the data transmission terminals is governed by acontention system, the terminal gaining access to transmit on the communications channel via a local bus. Means are provided for intercepting access token for transmission on the communications channel in response to an access request coming from one or several terminal(s) depending from the station. Means are provided for re-transmitting the access token into the communications channel once the requesting terminal(s) has/have successively transmitted its/their respective message(s) via the local bus.
Description
20107~6 METHOD AND APPARATUS FOR ACCESSING A DISTRIBUTED COMMUNICATIONS
NFTWORK
BACKG~OUND OF THE INVENTION
1. Field of the Invention 05 The present invention relates to a communications network for transmitting frames containing data or signalling information, comprising a set of links connecting data transmission terminals and providing the network with an arbitrary topology, each link carrying one or several signalling and data channel(s). The invention more specifically relates to a protocol for transmission access onto the network that optimizes its exploitation while avoiding collisions between terminals.
NFTWORK
BACKG~OUND OF THE INVENTION
1. Field of the Invention 05 The present invention relates to a communications network for transmitting frames containing data or signalling information, comprising a set of links connecting data transmission terminals and providing the network with an arbitrary topology, each link carrying one or several signalling and data channel(s). The invention more specifically relates to a protocol for transmission access onto the network that optimizes its exploitation while avoiding collisions between terminals.
2. Prior Art It is known that several data transmission terminals ~5 connected to a single network can sometimes seek to transmitsimultaneously onto the latter. Various procedures have been devised to solve this problem.
A first known procedure consists in using a bus access protocol of the CSMA/CD type (Carrier Sense Multiple Access/Collision Detection~. According to this protocol, the terminal seeking to transmit first ensures that the bus is free by detecting its rest state. But, because of the propagation time in the network, collisions can nevertheless occur between data transmitted virtually simultaneously from terminals for which the network appeared free at the local level. A procedure makes it possible, in these events, to ro-initialize the transmissions after a time delay that varies according to the sender9 so avoiding a new collision.
This procedure is well suited to local networks in which the data are transmitted in the form of asynchronous frames.
On the other hand, it does not allow transmission of synchronous data, and in particular speech transmission on the same network. Moreover, when the length of the latter increases, the propagation times become large, risks of collision are multiplied and transmission efficiency decreases. Thus, in a - . . . : . , ~ : ,, .:
; - : ... ~ .. .
2(~0716 network that is theoretically capable of a flow rate of 10 Mbits/s, the maximum flow rate in practice is only 5 Mbits/s.
Accordingly, the length of the network is ùsually limited to a few kilometers. Likewise, in cases where the number of messages to 05 be sent begins to increase, the collision probability rises, so reducing the systems efficiency.
A second known procedure consists in having a token circulating in a network configured as a loop. The *oken authorizes transmission to the transmission terminal that intercepts it.
This allows the coexistence, on a same network, of data transmissions in the form of both asynchronous packets and synchronous speech data, possibly with a dynamic allocation of time channels of each frame in a packet mode (data) or a circuit mode (speech). -Performance is little affected by the propagation times -thus making it possible to manage very extensive networks.
However, in the case of very long networks, it is necessary to provide costly connection interfaces between the network and the data transmission terminals.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and apparatus for accessing a distributed communications network linking several synchronous or asynchronous data transmission terminals and avoiding the above-mentioned drawbacks of networks employing a CSMA/CD type or a token type protocol.
In particular, the invention has for object a process and apparatus for accessing a network, offering the possibility of simultaneously transmitting asynchronous data, packets or signalling information, and synchronous data over a large distance without calling for costly connection interfaces at the level of each terminal.
This object is attained by means of a method for accessing a distributed communications network of the type comprising stations having data transmission terminals connected 201~ 6 thPreto and which are joined by links according to an arbitrary topology, said links conveying at least one token, or access token, which, when intercepted by a station, authorizes said station to grant its terminals access for transmission on a link 05 corresponding to said token and to which said station is connected, wherein said links define at least one virtual loop forming at least one communications channel passing through all said stations and conveying frames that carry at least one token, signalling information, and data; wherein said terminals connected to a station having taken a said token for access to a said communications channel can gain access to said channel by a common local bus that is specific to said station and into which right of access by said terminals is controlled by a contention system;
wherein said station having intercepted a token for transmission access to a communications channel in response to a request for access from one or several terminals connected to said station, retransmits said access token on said communications channel after the said one or several said requesting terminal(s) has/have successively transmitted its/their respective message(s) via said local bus.
Here, the term contention system to control right access onto the local bus is taken to mean a protocol of the CSMA/CA (Access/Collision/Avoidance), CSMA/CR (Carrier Sense Multiple Access/Collision Resolution) or CSMA/CD (Carrier Sense Multiple Access/Collision Detection) type, or a similar protocol.
Therefore, the invention combines a token system for granting a communications channel to a station wishing to transmit, and a ~CSMA type or similar procedure to solve local contention problems at the level of each station.
By virtue of this combination, the proposed solution combines the advantages of both proceduras while avoiding each of their drawbacks. The network can be very extensive and the connection cost per data transmision terminal can be relatively low. Furthermore, the possibility of conveying synchronous data in sddition to asynchronous data frames makes it possible to h3ve - 20~07~6 non-speech data transmission terminals coexisting with speech processing terminals.
In each station, except the one having intercepted a communications channel access token, the signalling information 05 and/or data circulating in that channel are fed into the local bus for resd access by the terminals connected to the station.
But, in the station having intercepted the communications channel access token, the loop forming the latter is open for retransmission of data on the channel. Loop closure in that channel is carried out in response to reception of a second token, or looping token, which is transmitted on the communications channel when the station has finished transmitting on that channel.
The looping token can be transmitted by the station having just finished transmitting, immediately after retransmitting the access token. Accordingly, if the access token is intercepted by a new station informed of a request for transmission access on the communications channel, the looping token will be ahead when it reaches the station that has just finished transmission, after having gone round the loop forming the communications channel.
Alternatively, the looping token can be transmitted by station located downstream of the one tha~ has just finished transmitting, e.g. by the new station having intercepted the access token. The links joining the stations together can be made to define several virtual loops forming several communication channels passing through all stations and each having a transmission access token. The virtual loops forming the different channels may have different topologies while passing through all stations.
The transmission mode may be asynchronous, e.y. ATM
(Asynchroncus Transfer Mode) or any other type, or synchronous, e.g. conveying PCM (Pulse Code Modulation) type frames, or of the FDDI type (Fiber Distributed Digital Interface). As an example, each link can csrry four bi-directional PCM synchronous channels, each at 2,048 kb/s, conveying synchronization information and data The access token for a channel need not necessarily be conveyed on that channel. For instance, the access tokens for ~...
-` 2010~6 :
different channels could be transmitted on a single channel or distriSuted over a limited number of channels.
Likewise, the signalling data relative to the different channels can be transmitted over a single chsnnel or over a limited 05 number of channels.
When the signalling information and data are transmittsd on respective channels, the signalling channel conveys a third token which, when intercepted by a station, grants the latter transmission access to the signalling channel, the third token being distinct from the access token conveyed by the data channel.
Finally, still in the case where the links between stations support a plurality of communication channels, a mixing can be carried out at each station between the communications channels and a number of channel~ carried by a local bus.
The flow rates on the, or each, communications channel and on the local buses can be different. In that case, a change in modulation speed is performed between the, or each, communications channel passing via a station and the local bus of the latter.
Likewise, a change of modulation speed can be performed in a station between the data transmission terminals and the local bus, in the form of time multiplexing or demultiplexing going from the terminals' transmission outputs to the local bus and 8 time demultiplexing or multiplexing going from the local bus to the terminals' receiving inputs.
The invention also relates to an apparatus for implementing the above process. `
BRIEF DESCRIPTIûN OF THE DRAWINGS
Other features and advantages of the invention shall be more clearly understood from reading the following description of the preferred embodiments, given as a non-limiting example, with reference to the appended drawings in which:
- Figure 1 is a general diagram of 3 communications network access according to the present invention;
- Figure 2 is a general disgram of a station inserted .~,, , - .. : ... ~ , ... . : . .. . .. .. .
20~0716 into the network of figure 1;
- Figure 3 depicts an embodiment of a PCM interface circuit forming part of the station shown in figure 2; and - Figure 4 illustrates an embodiment of a terminal 05 interface circuit forming part of the station shown in figure 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The network, as shown in figure 1, comprises a transmission medium consisting of links in the form of bi-directional PCM channels that interconnect stations S1, S2, ~.., S(n-1), Sn, S(n+1), ..., Sp. References PCM(n-1)-n and pcmn(n+1) designate the PCM channels respectively connecting station S(n-1) to station Sn, and station Sn to station S(n+1).
On each link, there can be e.g. four PCM channels having a data rate of 2,048 kb/s" They each support a time multiplex capable of transmitting, within frames, asynchronous data (packets), synchronous data (digitized speech) and signalling information.
A communications channel for the data and signalling information passing through all stations is set up by successively employing the PCM channels in one propagation direction, with tha return to the initial station for looping obtained by using the opposite propagation direction along the same PCM channels or another path. In the present example, since a link between two stations consists of four bidirectional PCM channels, it is possible to define four looped communication channels that pass through all stations without necessarily having the same topology.
~ Each of the stationsicomprises a local bus BL1, BL2, ....
BLn, ..., BLp to which several data transmission terminals or speech processing terminals are connected. Thus, terminals T1~
T1-2, .... , T1-n1 are connected to bus BL1, terminals T2-1, T2-2, ..., T2-n2 are connected to bus BL2, terminals Tn-1, Tn-2, ....
Tn-nn are connected to bus BLn and terminals Tp-1, Tp-2, ... , Tp-np `
are connected to bus BLp.
To each communications channels configured as a loop going ~hrough all the stations there is associated a first token, ' ~:
' ~
20~07~6 or access token, that circulates concomitantly with the conveyed data and/or signalling information. The access token is conveyed by the communications channel to which it is associated. It is also possible to convey four tokens on a same communications 05 channel and, if needs be, on at least one other for redundancy, or to distribute these tokens over two channels.
Only the station that intercepts the access token associated to a given communications channel is authorized to transmit on the latter. The station retains the access token all lû the while it transmits data or signa~ling information on the corresponding communications channel. At the end of transmission, it frees the access token which then propagates along the communications channel in the same direction and at the same speed as the data or the signalling information travelling along that communications channel.
The data transmission terminals connected to a same local bus can trans~it on that bus according to a contention system of the CSMA/CA, GSMA/CR, CSMA/CD type or similar, in order to prevent collisions thereon, or to accommodate for them. Each message transmitted from a terminal on the local bus is thus available at the input of all terminals connected to this same local bus. It may be noted that the use of a protocol allowing collisions, such as CSMA/CD is not too troublesome since the number of potential transmitters on the bus is limited to the number of terminals attached to the station having intercepted the access token, and the probability of virtually simultaneous transmission is low, owing to the short propagation time of the bus. It may also be noted that the ChSA/CR protocol can here be used at high modulation speed since the contention only occurs on the local bus having a limited length, and since moreover the length of the links between stations does not come into play, which is not the case in a simple bus network structure where it is necessary to wait till a bit has propagated from one end of the bus to the other before transmitting the following bit.
Each local bus comprises a time multiplex of four 8 ~0~
bi-directional PCM channels, as for the link between the stations.
Advantageously, the local bus is enabled for writing on one or several PCM channel(s) only during the time when the station possesses the access token(s) associated to the communications 05 channel~s) corresponding to the PCM channel(s) of the local bus.
In this way, for a given communications channel, when the associated access token has not been intercepted by a station, the corresponding PCM channel of the local bus is disabled for writing onto the bus by the station.
As soon as a terminal wishes to transmit data or signalling information, it sends a transmission request signal to the station to which it belongs. The station intercepts the first passing access token and write enables the local bus for the PCM
channel of the bus corresponding to the communications channel associated to the intercepted access token. The requesting terminal can then transmit its message e.g. data in the form of frames, over that PCM channel of the local bus according to a chosen contention system: CSMA/CA, CSMA/CR, CSMA/CD, or similar.
The data sent by the terminal are transmitted over the communications channel corresponding to the intercepted access token. In each of the other stations, these data are fed into the the local bus for read access by the various terminals attached thereto. Thus, the same data are supplied to all the connected terminals of the network without requiring intermediate storage.
The communications channel is opened by interrupting the retransmission of the PCM channel data entering the transmitting station in the opposite direction to the data in order to prevent that data from being transmitted a second time by that station.
ûnce the transmitting terminal has finiæhed its transmission, the PCM channel of the corresponding local bus becomes available to any other terminal attached to the same station and having addressed a transmit request signal. When all the local transmit requests addressed to the station have been satisfied, or when the maximum allocated time for keeping an access token is exceeded, the token is freed, making the 201~
corresponding communications channel available. At the same time, a second token is transmitted by the station immediately behind the data just transmitted. This second token, or looping token, follows these data up to the transmitting station. The latter is 05 thus informed that all the data it has transmitted have arrived at their destination and that it can close the communication channel at its level.
Alternatively, the looping token is transmitted by a station located downstream of the transmitting station, e.g. by the new station intercepting the access token that has been freed, just before this new station transmits on the corresponding communications channel. Any other solution resulting in the looping token being received at the initial transmitting station before the arrival of data originating from a downstream station is of course possible.
The looping token can be transmitted on the corresponding communications channel or on any other channel, e.g. a channel conveying the signalling information in so fsr as that channel does not have a path exceeding that of the data.
By providing several bidirectional PCM channels in each link between the stations - four channels in the present example -it is possible, as already shown, to exploit four relatively independent communications channels in the form of loops.
Thus, should there occur a collision between seYeral terminals on a local bus, one of the terminals having lost the contention will be able to retransmit if an access token on another communications channel appears. The same applies for terminals attached to differènt stations: the fact that a station has intercepted a communications channel access token does not block transmissions for the other stations, along the other communications channels. This therefore provides a decrease in the average wait time. It is also possible to customize the communications channels, e.g. by having some that will only allow a token to be kept for a limited time, so as to minimize the maximum wait time.
- : .:: :: ~ ~ :: :: : . : : . . : : -; .
~0~0716 By configuring the four communications channels so that they have different topologies, it is also possible, in the case of point-to-point transmissions, to select the communications channel access token for which the path to the target is the shortest, so 05 minimizing token utilization time.
Also, the availability of several access tokens reduces the risk of a total failure of the network in ca~e of the loss of a token. Finally, it is possible to specialize the communications channels~ so that each deals with a limited number of types of transmission: packets or circuits, and to authorize connection to a communications channel only to those terminals corresponding to a type of transmission for which the channel is destined. In the same general concept, the signalling information relative to the four communications channels can be conveyed on a single channel as well as possibly on at least one other channel for redundancy, rather than passing the signalling information for a respective channel on each channel.
As already explained, the data and or signalling information conveyed by the four communications channels are fed into the local bus of each station ~o be made accessible to their data transmission terminals. The local bus is, in this case, a high-speed bus supporting four time multiplexed bidirectional PCM channels and, in the present case, operating at a speed of 4 x 2,048 kbit/s. The bits of the four communications channels are interlaced on the local bus, and a mixing may be carried out by the station between the four communications channels and the four PCM channels of the local bus.
iHowaver, should ~the components providing the interface between the terminals and the local bus not be capable of operating at 4 x 2,048 kb/s and working on 1 out of every 4 bits, the following alternatives will be required:
- while keeping the high-speed local bus, providing 3 multiplexer between the transmission outputs of the terminals and the local bus, and a demultiplexer between the local bus and the retransmission inputs of the terminals; or 2010~6 - physically separating the local bus into several elementary bidirectional buses e.g. four 2,048 kb/s bidirectional buses, and placing a multiplexer between the elementary buses forminy the local bus and the link supporting the communications 05 channels and passing through the station, and a demultiplexer between the link passing through the station and the elementary buses forming the local bus.
There shall now be given a more detailed description of a station Sn in the context of the invention when applied to an Integrated Service Private Branch eXchange (ISPBX) having a decentralized architecture.
A PCM interface circuit 10 (figure 2) is connected to the PCM(n-1)-n and PCMn-(n+1) channels and is joined to a local PCM
bus to form an interface between the external PCM channels and the PCM channels of the local bus. The data transmission terminals and optionally the speech processors served by the station Sn are locally connected to the latter through interface links S (as defined by note I430 of the CCITT). The terminals at interface S
are connected to circuits 30 of that interface S, which control the latter and are themselves connected to the local bus BLn. Also9 the PCM interface circuit 10 receives transmit request signals TR~
coming from the terminals via the circuits 30 of the interfaces, when the terminals wish to transmit, and produces by ready-to-transmit signals RTT applied to the circuits 30 of the interface S to authorize transmission from the requesting terminals according to a CSMA/CA, CSMA/CR or CSMA/CD procecdure.
Exchanges between the circuits 30 of interface S and the PCM
interface circuit 10 are through the local bus BLn.
Each link to the interface S joining the terminals to the station Sn is capable of conveying speech, data and signalling information between the corresponding terminal and the station in both directions.
As an example, there shall be considered the transmission of signalling data. The latter are transmitted in the form of normalized High-level Data Link Control (HDLC).
20~716 In the overall frame, or superframe, conveyed by a communications channel, time interval N 16 or TI16, is reserved for conveying signalling frames between stations. Likewise, TI16 of one of the PCM channels of the local bus is reserved for 05 exchanging signalling information between the circuits 30 of interface S and circuit 10 of interface PCM.
The signalling channel conveys signalling information used to manage the channels in a circuit mode in the communications channels and to provids the signalling associated to each packet.
lû The latter can also be conveyed in the data channels at predetermined positions or according to specific codes.
When a terminal wishes to transmit a signalling frame, the associated interface circuit S sends a TRQ signal to the PCM
interface circuit 10. The latter intercepts the first access token coming from the PCM communications channel as soon as it arrives and sends an RTT signsl intended for all the circuits 30 of interface S. Correspondingly, the TI16 connection, which is normally established between the PCM(n-1)-n and PCMn-(n~
channels, is temporarily interrupted in the propagation direction of the intercepted token, and replaced by TI16 of the concerned PCM channel of the local bus. The interface circuit S
corresponding to the requesting terminal can then transmit its signalling frame which shall be transmitted throughout the communication~ channel to be made present on all the local buses of all stations connected to that communications channel.
If several circuits 30 of the interface S belonging to a same station request to transmit, a CSMA/CA, CSMA/CR or CSMA/CD
procedure is established on T116 of the PCM channel on ~he local bus to avoid collison, or accommodate for them without undue 3û waste of time, and to transmit the signalling frames in succession.
When there are no more requests to be satisfied, the PCM
interface circuit 10 frees the access token, sending it to the external PCM communications channel and at the same time sends a looping token which re-establishes the TI16 connection between the PCM(n-1)-n and PCMn-(n+1) sections in the propogation directiùn when it returns to the transmitting circuit 10.
An embodiment of the PCM interface circuit is shown on figure 3.
A processing unit 11 e.g. based on the 80188 û5 microprocessor from Intel Corp.of the USA controls the different successive phases of the procedure carried out by the active components of circuit 10 which are connected to the bus 12 of the microprocessor unit 11.
The PCM interface circuit is adapted to the external PCM
channels PCM(n-1)-n and PCMn-(n+1) by means of two respective circuits 13, 14. The latter are connected to a switching matrix 15 via respective circuits 16, 17 that serve to manage the PCM frames and adapt them to the switching matrix. The latter can be controlled by the processing unit 11 to carry out all possible connections between the different TI's of the external PCM
communications channel and the PCM channel of the local bus to which the switching matrix is also connected. A circuit 18 is provided for the exchange of signalling frames between TI1~ of the PCM channel of the local bus and the processing unit 11.
Circuits 13 to 18 can e.g. be produced using components from Siemens of West Germany. Accordingly, the adaptor circuits 13 and 14 are of the "IPAT-PEB 2235" type, the PCM frame management circuits are of the "ACFA PEB 2035" type, the switching matrix of "PEB 2045" type and circuit 18 of the "3SAB 82520 HSCC" type.
When circuit 18 intends to transmit signalling data, it produces a TRQ signal to a gate 19 providing a logical OR
function. The gate also receives TRa signals from the interface circuits S upon reqùest of the terminals connected to the station.
The output of the OR gate is acknowledged by the processing unit 11 to control the interception of the access token at its following passage, in response to the appearance of a TRQ
signal. The token can e.g. be in the form of a bit transmitted in the time interval N O (TIO) on the external PCM channel.
Once the access token is intercepted, the processing unit 11 sets high the contents of a register 20 whose output is Z0~07~6 connected to the input of a gate 21 providing an AND funcion. The passage through ~he gate 21 is authorized when TI16 of the PCM
channel of the local bus is enabled. This authorization to transmit at the output of register 20, after passage through gate 21, 05 constitutes the ready-to-transmit signal RTT applied to circuits 18. The RTT signal is also applied in parallel to the circuits 3û of interface S. At the same time, the processing unit 11 sends a command to the switching matrix 15 to cut off locally the transmission of TI16 of the external communications channel, in the propa~ation direction, so as to prevent looping of the signalling information that would otherwise have gone round the loop formed by that external channel a first time.
Once all the TRQ requests have been satisfied, the drop in logic state of output of gate 19 commands, via the processing unit 11 the retransmission of the access token for the external PCM communications channel and the transmission of the looping token the return of which serves to signal to the processing unit 11 that it must instruct the switching matrix 15 to locally close the previously interrupted TI16. The looping token can also be in the form of a bit transmitted in TIO.
An embodiment of a circuit 30 of the interface S is shown in figure 4.
The illustrated circuit 3û allows connection of several terminals (three in the example shown) onto interfaces S connected to interface lines 31, 32, 33. Each of the latter serves to adapt the logic signals of a respective circuit 34, 35, 36 used for the local processing of that interface and connected to a bus of a local processing unit controlled by a microprocessor 38.
The interface processing circuits 34, 35, 36 are also connected to a circuit serving to provide connection of the B
channels to the PCM channel of the local bus BLn to which it is connected. It is known that the interface according to the S
protocol is characterized by two channels termed B channels at 64 kb/s occupying 2 x 8 bits in the frame, a signalling channel, or D
channel, at 16 kb/s occupying two bits in the frame, the , .
;
~"~ , " ",~ - "~
Z0107~6 re-reading of the signalling bus tCSMA/CR procedure) at 16 kb/s occupying two bits and the parity control occupying four bits. In the present example, the focus is on the signalling. The two signalling bits are read cyclically in successive frames to be 05 configured as a HDLC format message. The signalling frames, exchanged on the D channels of the different terminals, are transmitted over a bus 37 of the control unit 38 and by a circuit connected to the PCM channel of the local bus flow in TI16 of that local PCM channel according to the above described procedure.
To that end, the circuit 4û sends a TRQ signal to gate 19 of the PCM interface circuit in response to a transmission request coming from a channel and interpreted by the control unit 38 and the circuit 41 receiving the RTT signal.
The circuits 34, 35, 36 can e.g. comprise ~ISAC-S PE~
~085" type components from Siemens men~ioned above, while circuits 39 and 40 can e.g. respectively consist of "PBC-PEB 2050~ and ~SAB-82520 HSCC" components from the same company.
Naturally, the above described procedures for conveying signalling information can be used to transmit data within a frame.
In the case of data transmission, time intervals different to TI16 can be used. It is also possible to increase the flow rate by making the data link support several B channsls having an access circuit 30.
The above example of channels carried by syncronous PCM
frames is not limiting. In particular it is possible to use synchronous frames such as FDDI or others as well as asynchronous frames.
The physical nature of the transmission medium can alternatively include a twisted wire pair, coaxial cable, optical fibers, etc. ... The coupling between the external communications channel and the local bus can be achieved by means of e.g. coaxial couplers, controllable optical couplers, etc. ...
In each station, the local bus, having a limited size, can be made using a different technology and can operate at speeds higher than the link between stations. This will in particular 201;0716 allow local exchanges between terminals connected to a station in addition to the exchange of traffic with the external PCM channels.
lQ
~ : , .
~ ;
A first known procedure consists in using a bus access protocol of the CSMA/CD type (Carrier Sense Multiple Access/Collision Detection~. According to this protocol, the terminal seeking to transmit first ensures that the bus is free by detecting its rest state. But, because of the propagation time in the network, collisions can nevertheless occur between data transmitted virtually simultaneously from terminals for which the network appeared free at the local level. A procedure makes it possible, in these events, to ro-initialize the transmissions after a time delay that varies according to the sender9 so avoiding a new collision.
This procedure is well suited to local networks in which the data are transmitted in the form of asynchronous frames.
On the other hand, it does not allow transmission of synchronous data, and in particular speech transmission on the same network. Moreover, when the length of the latter increases, the propagation times become large, risks of collision are multiplied and transmission efficiency decreases. Thus, in a - . . . : . , ~ : ,, .:
; - : ... ~ .. .
2(~0716 network that is theoretically capable of a flow rate of 10 Mbits/s, the maximum flow rate in practice is only 5 Mbits/s.
Accordingly, the length of the network is ùsually limited to a few kilometers. Likewise, in cases where the number of messages to 05 be sent begins to increase, the collision probability rises, so reducing the systems efficiency.
A second known procedure consists in having a token circulating in a network configured as a loop. The *oken authorizes transmission to the transmission terminal that intercepts it.
This allows the coexistence, on a same network, of data transmissions in the form of both asynchronous packets and synchronous speech data, possibly with a dynamic allocation of time channels of each frame in a packet mode (data) or a circuit mode (speech). -Performance is little affected by the propagation times -thus making it possible to manage very extensive networks.
However, in the case of very long networks, it is necessary to provide costly connection interfaces between the network and the data transmission terminals.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and apparatus for accessing a distributed communications network linking several synchronous or asynchronous data transmission terminals and avoiding the above-mentioned drawbacks of networks employing a CSMA/CD type or a token type protocol.
In particular, the invention has for object a process and apparatus for accessing a network, offering the possibility of simultaneously transmitting asynchronous data, packets or signalling information, and synchronous data over a large distance without calling for costly connection interfaces at the level of each terminal.
This object is attained by means of a method for accessing a distributed communications network of the type comprising stations having data transmission terminals connected 201~ 6 thPreto and which are joined by links according to an arbitrary topology, said links conveying at least one token, or access token, which, when intercepted by a station, authorizes said station to grant its terminals access for transmission on a link 05 corresponding to said token and to which said station is connected, wherein said links define at least one virtual loop forming at least one communications channel passing through all said stations and conveying frames that carry at least one token, signalling information, and data; wherein said terminals connected to a station having taken a said token for access to a said communications channel can gain access to said channel by a common local bus that is specific to said station and into which right of access by said terminals is controlled by a contention system;
wherein said station having intercepted a token for transmission access to a communications channel in response to a request for access from one or several terminals connected to said station, retransmits said access token on said communications channel after the said one or several said requesting terminal(s) has/have successively transmitted its/their respective message(s) via said local bus.
Here, the term contention system to control right access onto the local bus is taken to mean a protocol of the CSMA/CA (Access/Collision/Avoidance), CSMA/CR (Carrier Sense Multiple Access/Collision Resolution) or CSMA/CD (Carrier Sense Multiple Access/Collision Detection) type, or a similar protocol.
Therefore, the invention combines a token system for granting a communications channel to a station wishing to transmit, and a ~CSMA type or similar procedure to solve local contention problems at the level of each station.
By virtue of this combination, the proposed solution combines the advantages of both proceduras while avoiding each of their drawbacks. The network can be very extensive and the connection cost per data transmision terminal can be relatively low. Furthermore, the possibility of conveying synchronous data in sddition to asynchronous data frames makes it possible to h3ve - 20~07~6 non-speech data transmission terminals coexisting with speech processing terminals.
In each station, except the one having intercepted a communications channel access token, the signalling information 05 and/or data circulating in that channel are fed into the local bus for resd access by the terminals connected to the station.
But, in the station having intercepted the communications channel access token, the loop forming the latter is open for retransmission of data on the channel. Loop closure in that channel is carried out in response to reception of a second token, or looping token, which is transmitted on the communications channel when the station has finished transmitting on that channel.
The looping token can be transmitted by the station having just finished transmitting, immediately after retransmitting the access token. Accordingly, if the access token is intercepted by a new station informed of a request for transmission access on the communications channel, the looping token will be ahead when it reaches the station that has just finished transmission, after having gone round the loop forming the communications channel.
Alternatively, the looping token can be transmitted by station located downstream of the one tha~ has just finished transmitting, e.g. by the new station having intercepted the access token. The links joining the stations together can be made to define several virtual loops forming several communication channels passing through all stations and each having a transmission access token. The virtual loops forming the different channels may have different topologies while passing through all stations.
The transmission mode may be asynchronous, e.y. ATM
(Asynchroncus Transfer Mode) or any other type, or synchronous, e.g. conveying PCM (Pulse Code Modulation) type frames, or of the FDDI type (Fiber Distributed Digital Interface). As an example, each link can csrry four bi-directional PCM synchronous channels, each at 2,048 kb/s, conveying synchronization information and data The access token for a channel need not necessarily be conveyed on that channel. For instance, the access tokens for ~...
-` 2010~6 :
different channels could be transmitted on a single channel or distriSuted over a limited number of channels.
Likewise, the signalling data relative to the different channels can be transmitted over a single chsnnel or over a limited 05 number of channels.
When the signalling information and data are transmittsd on respective channels, the signalling channel conveys a third token which, when intercepted by a station, grants the latter transmission access to the signalling channel, the third token being distinct from the access token conveyed by the data channel.
Finally, still in the case where the links between stations support a plurality of communication channels, a mixing can be carried out at each station between the communications channels and a number of channel~ carried by a local bus.
The flow rates on the, or each, communications channel and on the local buses can be different. In that case, a change in modulation speed is performed between the, or each, communications channel passing via a station and the local bus of the latter.
Likewise, a change of modulation speed can be performed in a station between the data transmission terminals and the local bus, in the form of time multiplexing or demultiplexing going from the terminals' transmission outputs to the local bus and 8 time demultiplexing or multiplexing going from the local bus to the terminals' receiving inputs.
The invention also relates to an apparatus for implementing the above process. `
BRIEF DESCRIPTIûN OF THE DRAWINGS
Other features and advantages of the invention shall be more clearly understood from reading the following description of the preferred embodiments, given as a non-limiting example, with reference to the appended drawings in which:
- Figure 1 is a general diagram of 3 communications network access according to the present invention;
- Figure 2 is a general disgram of a station inserted .~,, , - .. : ... ~ , ... . : . .. . .. .. .
20~0716 into the network of figure 1;
- Figure 3 depicts an embodiment of a PCM interface circuit forming part of the station shown in figure 2; and - Figure 4 illustrates an embodiment of a terminal 05 interface circuit forming part of the station shown in figure 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The network, as shown in figure 1, comprises a transmission medium consisting of links in the form of bi-directional PCM channels that interconnect stations S1, S2, ~.., S(n-1), Sn, S(n+1), ..., Sp. References PCM(n-1)-n and pcmn(n+1) designate the PCM channels respectively connecting station S(n-1) to station Sn, and station Sn to station S(n+1).
On each link, there can be e.g. four PCM channels having a data rate of 2,048 kb/s" They each support a time multiplex capable of transmitting, within frames, asynchronous data (packets), synchronous data (digitized speech) and signalling information.
A communications channel for the data and signalling information passing through all stations is set up by successively employing the PCM channels in one propagation direction, with tha return to the initial station for looping obtained by using the opposite propagation direction along the same PCM channels or another path. In the present example, since a link between two stations consists of four bidirectional PCM channels, it is possible to define four looped communication channels that pass through all stations without necessarily having the same topology.
~ Each of the stationsicomprises a local bus BL1, BL2, ....
BLn, ..., BLp to which several data transmission terminals or speech processing terminals are connected. Thus, terminals T1~
T1-2, .... , T1-n1 are connected to bus BL1, terminals T2-1, T2-2, ..., T2-n2 are connected to bus BL2, terminals Tn-1, Tn-2, ....
Tn-nn are connected to bus BLn and terminals Tp-1, Tp-2, ... , Tp-np `
are connected to bus BLp.
To each communications channels configured as a loop going ~hrough all the stations there is associated a first token, ' ~:
' ~
20~07~6 or access token, that circulates concomitantly with the conveyed data and/or signalling information. The access token is conveyed by the communications channel to which it is associated. It is also possible to convey four tokens on a same communications 05 channel and, if needs be, on at least one other for redundancy, or to distribute these tokens over two channels.
Only the station that intercepts the access token associated to a given communications channel is authorized to transmit on the latter. The station retains the access token all lû the while it transmits data or signa~ling information on the corresponding communications channel. At the end of transmission, it frees the access token which then propagates along the communications channel in the same direction and at the same speed as the data or the signalling information travelling along that communications channel.
The data transmission terminals connected to a same local bus can trans~it on that bus according to a contention system of the CSMA/CA, GSMA/CR, CSMA/CD type or similar, in order to prevent collisions thereon, or to accommodate for them. Each message transmitted from a terminal on the local bus is thus available at the input of all terminals connected to this same local bus. It may be noted that the use of a protocol allowing collisions, such as CSMA/CD is not too troublesome since the number of potential transmitters on the bus is limited to the number of terminals attached to the station having intercepted the access token, and the probability of virtually simultaneous transmission is low, owing to the short propagation time of the bus. It may also be noted that the ChSA/CR protocol can here be used at high modulation speed since the contention only occurs on the local bus having a limited length, and since moreover the length of the links between stations does not come into play, which is not the case in a simple bus network structure where it is necessary to wait till a bit has propagated from one end of the bus to the other before transmitting the following bit.
Each local bus comprises a time multiplex of four 8 ~0~
bi-directional PCM channels, as for the link between the stations.
Advantageously, the local bus is enabled for writing on one or several PCM channel(s) only during the time when the station possesses the access token(s) associated to the communications 05 channel~s) corresponding to the PCM channel(s) of the local bus.
In this way, for a given communications channel, when the associated access token has not been intercepted by a station, the corresponding PCM channel of the local bus is disabled for writing onto the bus by the station.
As soon as a terminal wishes to transmit data or signalling information, it sends a transmission request signal to the station to which it belongs. The station intercepts the first passing access token and write enables the local bus for the PCM
channel of the bus corresponding to the communications channel associated to the intercepted access token. The requesting terminal can then transmit its message e.g. data in the form of frames, over that PCM channel of the local bus according to a chosen contention system: CSMA/CA, CSMA/CR, CSMA/CD, or similar.
The data sent by the terminal are transmitted over the communications channel corresponding to the intercepted access token. In each of the other stations, these data are fed into the the local bus for read access by the various terminals attached thereto. Thus, the same data are supplied to all the connected terminals of the network without requiring intermediate storage.
The communications channel is opened by interrupting the retransmission of the PCM channel data entering the transmitting station in the opposite direction to the data in order to prevent that data from being transmitted a second time by that station.
ûnce the transmitting terminal has finiæhed its transmission, the PCM channel of the corresponding local bus becomes available to any other terminal attached to the same station and having addressed a transmit request signal. When all the local transmit requests addressed to the station have been satisfied, or when the maximum allocated time for keeping an access token is exceeded, the token is freed, making the 201~
corresponding communications channel available. At the same time, a second token is transmitted by the station immediately behind the data just transmitted. This second token, or looping token, follows these data up to the transmitting station. The latter is 05 thus informed that all the data it has transmitted have arrived at their destination and that it can close the communication channel at its level.
Alternatively, the looping token is transmitted by a station located downstream of the transmitting station, e.g. by the new station intercepting the access token that has been freed, just before this new station transmits on the corresponding communications channel. Any other solution resulting in the looping token being received at the initial transmitting station before the arrival of data originating from a downstream station is of course possible.
The looping token can be transmitted on the corresponding communications channel or on any other channel, e.g. a channel conveying the signalling information in so fsr as that channel does not have a path exceeding that of the data.
By providing several bidirectional PCM channels in each link between the stations - four channels in the present example -it is possible, as already shown, to exploit four relatively independent communications channels in the form of loops.
Thus, should there occur a collision between seYeral terminals on a local bus, one of the terminals having lost the contention will be able to retransmit if an access token on another communications channel appears. The same applies for terminals attached to differènt stations: the fact that a station has intercepted a communications channel access token does not block transmissions for the other stations, along the other communications channels. This therefore provides a decrease in the average wait time. It is also possible to customize the communications channels, e.g. by having some that will only allow a token to be kept for a limited time, so as to minimize the maximum wait time.
- : .:: :: ~ ~ :: :: : . : : . . : : -; .
~0~0716 By configuring the four communications channels so that they have different topologies, it is also possible, in the case of point-to-point transmissions, to select the communications channel access token for which the path to the target is the shortest, so 05 minimizing token utilization time.
Also, the availability of several access tokens reduces the risk of a total failure of the network in ca~e of the loss of a token. Finally, it is possible to specialize the communications channels~ so that each deals with a limited number of types of transmission: packets or circuits, and to authorize connection to a communications channel only to those terminals corresponding to a type of transmission for which the channel is destined. In the same general concept, the signalling information relative to the four communications channels can be conveyed on a single channel as well as possibly on at least one other channel for redundancy, rather than passing the signalling information for a respective channel on each channel.
As already explained, the data and or signalling information conveyed by the four communications channels are fed into the local bus of each station ~o be made accessible to their data transmission terminals. The local bus is, in this case, a high-speed bus supporting four time multiplexed bidirectional PCM channels and, in the present case, operating at a speed of 4 x 2,048 kbit/s. The bits of the four communications channels are interlaced on the local bus, and a mixing may be carried out by the station between the four communications channels and the four PCM channels of the local bus.
iHowaver, should ~the components providing the interface between the terminals and the local bus not be capable of operating at 4 x 2,048 kb/s and working on 1 out of every 4 bits, the following alternatives will be required:
- while keeping the high-speed local bus, providing 3 multiplexer between the transmission outputs of the terminals and the local bus, and a demultiplexer between the local bus and the retransmission inputs of the terminals; or 2010~6 - physically separating the local bus into several elementary bidirectional buses e.g. four 2,048 kb/s bidirectional buses, and placing a multiplexer between the elementary buses forminy the local bus and the link supporting the communications 05 channels and passing through the station, and a demultiplexer between the link passing through the station and the elementary buses forming the local bus.
There shall now be given a more detailed description of a station Sn in the context of the invention when applied to an Integrated Service Private Branch eXchange (ISPBX) having a decentralized architecture.
A PCM interface circuit 10 (figure 2) is connected to the PCM(n-1)-n and PCMn-(n+1) channels and is joined to a local PCM
bus to form an interface between the external PCM channels and the PCM channels of the local bus. The data transmission terminals and optionally the speech processors served by the station Sn are locally connected to the latter through interface links S (as defined by note I430 of the CCITT). The terminals at interface S
are connected to circuits 30 of that interface S, which control the latter and are themselves connected to the local bus BLn. Also9 the PCM interface circuit 10 receives transmit request signals TR~
coming from the terminals via the circuits 30 of the interfaces, when the terminals wish to transmit, and produces by ready-to-transmit signals RTT applied to the circuits 30 of the interface S to authorize transmission from the requesting terminals according to a CSMA/CA, CSMA/CR or CSMA/CD procecdure.
Exchanges between the circuits 30 of interface S and the PCM
interface circuit 10 are through the local bus BLn.
Each link to the interface S joining the terminals to the station Sn is capable of conveying speech, data and signalling information between the corresponding terminal and the station in both directions.
As an example, there shall be considered the transmission of signalling data. The latter are transmitted in the form of normalized High-level Data Link Control (HDLC).
20~716 In the overall frame, or superframe, conveyed by a communications channel, time interval N 16 or TI16, is reserved for conveying signalling frames between stations. Likewise, TI16 of one of the PCM channels of the local bus is reserved for 05 exchanging signalling information between the circuits 30 of interface S and circuit 10 of interface PCM.
The signalling channel conveys signalling information used to manage the channels in a circuit mode in the communications channels and to provids the signalling associated to each packet.
lû The latter can also be conveyed in the data channels at predetermined positions or according to specific codes.
When a terminal wishes to transmit a signalling frame, the associated interface circuit S sends a TRQ signal to the PCM
interface circuit 10. The latter intercepts the first access token coming from the PCM communications channel as soon as it arrives and sends an RTT signsl intended for all the circuits 30 of interface S. Correspondingly, the TI16 connection, which is normally established between the PCM(n-1)-n and PCMn-(n~
channels, is temporarily interrupted in the propagation direction of the intercepted token, and replaced by TI16 of the concerned PCM channel of the local bus. The interface circuit S
corresponding to the requesting terminal can then transmit its signalling frame which shall be transmitted throughout the communication~ channel to be made present on all the local buses of all stations connected to that communications channel.
If several circuits 30 of the interface S belonging to a same station request to transmit, a CSMA/CA, CSMA/CR or CSMA/CD
procedure is established on T116 of the PCM channel on ~he local bus to avoid collison, or accommodate for them without undue 3û waste of time, and to transmit the signalling frames in succession.
When there are no more requests to be satisfied, the PCM
interface circuit 10 frees the access token, sending it to the external PCM communications channel and at the same time sends a looping token which re-establishes the TI16 connection between the PCM(n-1)-n and PCMn-(n+1) sections in the propogation directiùn when it returns to the transmitting circuit 10.
An embodiment of the PCM interface circuit is shown on figure 3.
A processing unit 11 e.g. based on the 80188 û5 microprocessor from Intel Corp.of the USA controls the different successive phases of the procedure carried out by the active components of circuit 10 which are connected to the bus 12 of the microprocessor unit 11.
The PCM interface circuit is adapted to the external PCM
channels PCM(n-1)-n and PCMn-(n+1) by means of two respective circuits 13, 14. The latter are connected to a switching matrix 15 via respective circuits 16, 17 that serve to manage the PCM frames and adapt them to the switching matrix. The latter can be controlled by the processing unit 11 to carry out all possible connections between the different TI's of the external PCM
communications channel and the PCM channel of the local bus to which the switching matrix is also connected. A circuit 18 is provided for the exchange of signalling frames between TI1~ of the PCM channel of the local bus and the processing unit 11.
Circuits 13 to 18 can e.g. be produced using components from Siemens of West Germany. Accordingly, the adaptor circuits 13 and 14 are of the "IPAT-PEB 2235" type, the PCM frame management circuits are of the "ACFA PEB 2035" type, the switching matrix of "PEB 2045" type and circuit 18 of the "3SAB 82520 HSCC" type.
When circuit 18 intends to transmit signalling data, it produces a TRQ signal to a gate 19 providing a logical OR
function. The gate also receives TRa signals from the interface circuits S upon reqùest of the terminals connected to the station.
The output of the OR gate is acknowledged by the processing unit 11 to control the interception of the access token at its following passage, in response to the appearance of a TRQ
signal. The token can e.g. be in the form of a bit transmitted in the time interval N O (TIO) on the external PCM channel.
Once the access token is intercepted, the processing unit 11 sets high the contents of a register 20 whose output is Z0~07~6 connected to the input of a gate 21 providing an AND funcion. The passage through ~he gate 21 is authorized when TI16 of the PCM
channel of the local bus is enabled. This authorization to transmit at the output of register 20, after passage through gate 21, 05 constitutes the ready-to-transmit signal RTT applied to circuits 18. The RTT signal is also applied in parallel to the circuits 3û of interface S. At the same time, the processing unit 11 sends a command to the switching matrix 15 to cut off locally the transmission of TI16 of the external communications channel, in the propa~ation direction, so as to prevent looping of the signalling information that would otherwise have gone round the loop formed by that external channel a first time.
Once all the TRQ requests have been satisfied, the drop in logic state of output of gate 19 commands, via the processing unit 11 the retransmission of the access token for the external PCM communications channel and the transmission of the looping token the return of which serves to signal to the processing unit 11 that it must instruct the switching matrix 15 to locally close the previously interrupted TI16. The looping token can also be in the form of a bit transmitted in TIO.
An embodiment of a circuit 30 of the interface S is shown in figure 4.
The illustrated circuit 3û allows connection of several terminals (three in the example shown) onto interfaces S connected to interface lines 31, 32, 33. Each of the latter serves to adapt the logic signals of a respective circuit 34, 35, 36 used for the local processing of that interface and connected to a bus of a local processing unit controlled by a microprocessor 38.
The interface processing circuits 34, 35, 36 are also connected to a circuit serving to provide connection of the B
channels to the PCM channel of the local bus BLn to which it is connected. It is known that the interface according to the S
protocol is characterized by two channels termed B channels at 64 kb/s occupying 2 x 8 bits in the frame, a signalling channel, or D
channel, at 16 kb/s occupying two bits in the frame, the , .
;
~"~ , " ",~ - "~
Z0107~6 re-reading of the signalling bus tCSMA/CR procedure) at 16 kb/s occupying two bits and the parity control occupying four bits. In the present example, the focus is on the signalling. The two signalling bits are read cyclically in successive frames to be 05 configured as a HDLC format message. The signalling frames, exchanged on the D channels of the different terminals, are transmitted over a bus 37 of the control unit 38 and by a circuit connected to the PCM channel of the local bus flow in TI16 of that local PCM channel according to the above described procedure.
To that end, the circuit 4û sends a TRQ signal to gate 19 of the PCM interface circuit in response to a transmission request coming from a channel and interpreted by the control unit 38 and the circuit 41 receiving the RTT signal.
The circuits 34, 35, 36 can e.g. comprise ~ISAC-S PE~
~085" type components from Siemens men~ioned above, while circuits 39 and 40 can e.g. respectively consist of "PBC-PEB 2050~ and ~SAB-82520 HSCC" components from the same company.
Naturally, the above described procedures for conveying signalling information can be used to transmit data within a frame.
In the case of data transmission, time intervals different to TI16 can be used. It is also possible to increase the flow rate by making the data link support several B channsls having an access circuit 30.
The above example of channels carried by syncronous PCM
frames is not limiting. In particular it is possible to use synchronous frames such as FDDI or others as well as asynchronous frames.
The physical nature of the transmission medium can alternatively include a twisted wire pair, coaxial cable, optical fibers, etc. ... The coupling between the external communications channel and the local bus can be achieved by means of e.g. coaxial couplers, controllable optical couplers, etc. ...
In each station, the local bus, having a limited size, can be made using a different technology and can operate at speeds higher than the link between stations. This will in particular 201;0716 allow local exchanges between terminals connected to a station in addition to the exchange of traffic with the external PCM channels.
lQ
~ : , .
~ ;
Claims (23)
1. A method for accessing a distributed communications network comprising stations having data transmission terminals conected thereto and which are joined by links according to an arbitrary topology, said links conveying at least a token, or access token, which, when intercepted by a station authorizes said station to grant its terminals access for transmission on a link corresponding to said token and to which said station is connected, wherein:
- said links define at least one virtual loop forming at least one communications channel passing through all said stations and conveying frames that carry at least one token, signalling information, and data;
- said terminals connected to a station having taken a said token for access to a said communications channel can gain access to said channel by a common local bus that is specific to said station and into which access by the said terminals is controlled by a contention system;
- said station having intercepted a token for transmission access to a said communications channel in response to a request for access from one, or several, said terminal(s) connected to said station, re-transmits said access token on said communications channel after the said one or several requesting terminals has/have successively transmitted its/their respective messages via said local bus.
- said links define at least one virtual loop forming at least one communications channel passing through all said stations and conveying frames that carry at least one token, signalling information, and data;
- said terminals connected to a station having taken a said token for access to a said communications channel can gain access to said channel by a common local bus that is specific to said station and into which access by the said terminals is controlled by a contention system;
- said station having intercepted a token for transmission access to a said communications channel in response to a request for access from one, or several, said terminal(s) connected to said station, re-transmits said access token on said communications channel after the said one or several requesting terminals has/have successively transmitted its/their respective messages via said local bus.
2. A method as claimed in claim 1, wherein for each station other than the said station having taken a said communication channel access token, the said signalling information and/or data circulating in said channel are fed into the said local bus to be made accessible for reading by terminals connected to the said each station.
3. A method as claimed in claim 1, wherein said loop forming said communications channel is open at the said station having taken said token for access thereto, at the start of transmission on the said channel.
4. A method as claimed in claim 1, wherein a second token, or looping token is transmitted on said communications channel at the end of transmission thereon by a station, to order a closure of the said loop at that station upon said station receiving said looping token.
5. A method as claimed in claim 1, wherein, in each station, write access into a said local bus is controlled by a CSMA type contention system.
6. A method as claimed in claim 1, wherein said links define several virtual loops carrying several communications channels each passing through each said station and each having a transmission access token.
7. A method as claimed in claim 6, wherein the said tokens relative to said different channels are transmitted along a single channel, or a limited number of channels.
8. A method as claimed in claim 7, wherein the said signalling relative to the said different channels is transmitted along a single channel, or a limited number of channels.
9. A method as claimed in claim 8, wherein said local bus of each said station carries several channels, and a mixing is performed in a station between all said channels comprised by said links and all said channels of said local bus.
10. A method as claimed in claim 9, wherein said virtual loops forming the said different channels have different topologies.
11. A method as claimed in claim 1, wherein, at each said station, there is carried out a change in modulation speed between said data transmission terminals and said local bus in the form of time multiplexing or demultiplexing, in going from a transmission output of said terminal to said local bus, as well as a time demultiplexing or multiplexing in going from said local bus to said transmission of said terminals.
12. A method as claimed in claim 1, wherein, at each station, there is carried out a change in modulation speed between the or each said communications channel passing via the said station and the said local bus.
13. A method as claimed in claim 1, wherein said signalling information and said data are transmitted along respective communication channels, said signalling information channel conveying a third token which, when taken by a said station, grants the latter access to transmit on said signalling information channel, and which is distinct from said access token conveyed by said data channel.
14. A method as claimed in claim 1, wherein the or each said communication channel conveys PCM type synchronous frames.
15. A method as claimed in claim 1, wherein the or each said communication channel conveys FDDI type synchronous frames.
16. A method as claimed in claim 1, wherein the or each said communication channel conveys signals in accordance with the ATM
mode.
mode.
17. An apparatus for accessing a distributed communications network comprising stations having transmission terminals connected thereto and which are joined by links according to an arbitrary topology, said links conveying at least one token, or access token, which, when intercepted by a station, authorizes said station to grant its terminals access for transmission on a link corresponding to said token and to which said token is connected, wherein:
- said links define at least one virtual loop forming at least one communication channel passing through all said stations and conveying frames that carry at least one token, signalling information, and data;
- each said station comprises its own local bus into which write access by said data transmission terminals is controlled by a contention system, the access to said communication channel by a transmitting terminal being achieved via said local bus; and - each station comprises means for intercepting said access token transmitted on said communication channel in response to an access request originating from one or several terminals depending on the said station, and means for re-transmitting said access token on said communication channel after the said requesting terminals have successively transmitted their respective messages via said local bus.
- said links define at least one virtual loop forming at least one communication channel passing through all said stations and conveying frames that carry at least one token, signalling information, and data;
- each said station comprises its own local bus into which write access by said data transmission terminals is controlled by a contention system, the access to said communication channel by a transmitting terminal being achieved via said local bus; and - each station comprises means for intercepting said access token transmitted on said communication channel in response to an access request originating from one or several terminals depending on the said station, and means for re-transmitting said access token on said communication channel after the said requesting terminals have successively transmitted their respective messages via said local bus.
18. An apparatus as claimed in claim 17, wherein each station comprises a link interface circuit connected between said links to which said station is connected and said local bus of said station, said interface allowing said signalling information and/or data conveyed by said communication channel to be fed into said local bus when said station is not transmitting along said bus, and said link interface controls, at the level of said station, the opening of said loop forming said communication channel when said station transmits thereon.
19. An apparatus as claimed in claim 18, wherein said link interface circuit further comprises means for controlling the closure, at the level of said station, of the loop forming said communication channel in response to detecting a looping token relative to said communication channel.
20. An apparatus as claimed in claim 19, wherein said links define several virtual loops forming several communication channels.
21. An apparatus as claimed in claim 20, wherein said virtual loops forming said different communication channels have different topologies.
22. An apparatus as claimed in claim 17, wherein each station comprises terminal interface circuits inserted between said data transmission channels connected to said station and said local bus.
23. An apparatus as claimed in claim 22, wherein time multiplexing/demultiplexing means are inserted between said local bus and said terminal interface circuits in order to obtain a change in modulation speed between the or each said communication channel passing through said station and said local bus.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8902364 | 1989-02-23 | ||
| FR8902364A FR2643525A1 (en) | 1989-02-23 | 1989-02-23 | METHOD AND DEVICE FOR ACCESSING AN EXTENDED COMMUNICATION NETWORK |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2010716A1 true CA2010716A1 (en) | 1990-08-23 |
Family
ID=9379057
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002010716A Abandoned CA2010716A1 (en) | 1989-02-23 | 1990-02-22 | Method and apparatus for accessing a distributed communications network |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0384847A1 (en) |
| JP (1) | JPH0316346A (en) |
| CN (1) | CN1017295B (en) |
| CA (1) | CA2010716A1 (en) |
| FI (1) | FI900884A0 (en) |
| FR (1) | FR2643525A1 (en) |
| OA (1) | OA09164A (en) |
| TN (1) | TNSN90023A1 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3638287B2 (en) * | 1995-06-15 | 2005-04-13 | コーニンクレッカ フィリップス エレクトロニクス エヌ ヴィ | Data bus system with supply control means |
| CN1214352C (en) * | 1996-09-04 | 2005-08-10 | 英特托拉斯技术公司 | Trusted infrastructure support system, method and techniques for secure electronic commerce, electronic transactions, commerce process control and automation distributted computing and rights manageme |
| DE19702107C2 (en) * | 1997-01-22 | 1999-05-12 | Siemens Ag | Method for realizing emulated ring network structures in a communication network designed according to the asynchronous transfer mode ATM |
| JP4776904B2 (en) * | 2004-09-15 | 2011-09-21 | グローリー株式会社 | Change replenishment management system, change replenishment management method, bar storage, apparatus and management system provided with determination means |
| CN111682913B (en) * | 2019-03-11 | 2022-03-29 | 华为技术有限公司 | Method and device for discovering AP and method and device for sending beacon frame by AP in WLAN |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4602365A (en) * | 1984-02-10 | 1986-07-22 | Prime Computer, Inc. | Multi-token, multi-channel single bus network |
| US4536873A (en) * | 1984-03-19 | 1985-08-20 | Honeywell Inc. | Data transmission system |
-
1989
- 1989-02-23 FR FR8902364A patent/FR2643525A1/en not_active Withdrawn
-
1990
- 1990-02-22 TN TNTNSN90023A patent/TNSN90023A1/en unknown
- 1990-02-22 FI FI900884A patent/FI900884A0/en not_active IP Right Cessation
- 1990-02-22 CA CA002010716A patent/CA2010716A1/en not_active Abandoned
- 1990-02-23 JP JP2044250A patent/JPH0316346A/en active Pending
- 1990-02-23 EP EP90400504A patent/EP0384847A1/en not_active Withdrawn
- 1990-02-23 CN CN90100910A patent/CN1017295B/en not_active Expired
- 1990-02-23 OA OA59741A patent/OA09164A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| EP0384847A1 (en) | 1990-08-29 |
| CN1017295B (en) | 1992-07-01 |
| FI900884A0 (en) | 1990-02-22 |
| CN1045206A (en) | 1990-09-05 |
| JPH0316346A (en) | 1991-01-24 |
| TNSN90023A1 (en) | 1991-03-05 |
| FR2643525A1 (en) | 1990-08-24 |
| OA09164A (en) | 1992-03-31 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |