CA1250969A - Network signalling protocol for communications system - Google Patents
Network signalling protocol for communications systemInfo
- Publication number
- CA1250969A CA1250969A CA000485881A CA485881A CA1250969A CA 1250969 A CA1250969 A CA 1250969A CA 000485881 A CA000485881 A CA 000485881A CA 485881 A CA485881 A CA 485881A CA 1250969 A CA1250969 A CA 1250969A
- Authority
- CA
- Canada
- Prior art keywords
- station
- network
- signal
- transmitted
- stations
- 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.)
- Expired
Links
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]
Abstract
NETWORK SIGNALLING PROTOCOL FOR COMMUNICATIONS SYSTEM
Abstract of the Disclosure A network signalling protocol for transmitting signalling and control information from each station to one or more other stations over a common transmission line. At each station the protocol comprises transmitting in a commonly recognized sequence at least a header signal in a uniquely allocated time slot, thence marking each time slot in which no signal was transmitted and thereafter transmitting at least the header signals sequentially so as to eliminate the marked time slots in which no signal was transmitted.
Abstract of the Disclosure A network signalling protocol for transmitting signalling and control information from each station to one or more other stations over a common transmission line. At each station the protocol comprises transmitting in a commonly recognized sequence at least a header signal in a uniquely allocated time slot, thence marking each time slot in which no signal was transmitted and thereafter transmitting at least the header signals sequentially so as to eliminate the marked time slots in which no signal was transmitted.
Description
NETWORK SIGNALLING PROTOCOL FOR COMMUNICATIONS SYSTEM
This invention relates to a network signalling protocol and more particularly to one for establishing and main-taining communication between a plurality of s-tations ~"hen connected to a common transmission lineO
Background of the Invention In communication systems it is often necessary to transmit signalling and control information from each node or station to one or more of the other stations over a common transmission line.
In one arrangement, each station is allocated a unique time slot in which to transmit its pertinent signalling information. In general, such systems must be capable of adding stations to or removing them from the common transmission line without disrupting the operation of the balance of the network.
The capacity of such a system is determined by the maxilnuln number of time slots which have been allocated by the network protocol. However if much o-f the time this maximum capacity is not being utilized then it is more efficient to eliminate the time slots of the unused nodes or stations. This can also help to alleviate many of the problems in coupling two independently operating portions of the network together, which can occur when a fault or break in the transmission line has separated major portions of the network from each other. After this break occurs, communications must continue between the functioning portions of the network. However, when the fault is rectified, the two portions of the network must be rejoined with minimal disruption to each other.
~s~
If the operating sequence has been compacted so as to eliminate unused time slots, it is necessary to in-form all oF the stations when one or more stations wants to join the network so that the required time slots can be allocated. When a single station joins the network it can first monitor the operation of the other stations on the transmission line. However, operating sub-sec-tions which join each other cannot initially monitor each other without interference occurring on the common transmission line. The key therefore is to provide a protocol in which all of the stations on the network can be made aware that one or more stations will be joining the network or portions of the network will be joined to each other.
Statement of the Invention The present invention provides an improved network signalling protocol for communicating between a plurality of sta-tions when connected to a common transmission line. The protocol at each station comprises ini-tializing the network by transmitting in a commonly recogni7ed sequence, at least a header signal from each station in a uniquely allocated time slot which commences a corresponding number of time slots following the previously transmitted signal. The protocol includes marking each time slot in which no signal has been transmitted and thereafter transmitting at least the header signal for the station in the next time slot following that of the immediately preceding transmitted signal so as to eliminate the marked time slots in which no signal has been transmitted.
In order to inform each of the stations that the ~5 ~
network is to be reinitialized, the protocol provides for allocating one additional time slot, commonly referred to as a null slot, in which any one station can insert an initializing request signal (i.e. a break signal for a preselected time in-terval) in response to selected conditions at that station. This occurs whenever one or more stations are to join the network. When opera-ting portions of the network are initially joined together, interference or clashing o-f the signals occurs on the line. This is recognized by each of the stations on the network and the result is that all stations then cease transmission. Thereafter, the network is reinitialized by following the same sequence as the first initialization.
Brief Description of the Drawings An example embodiment of the invention will now be described with re-ference to the accompanying drawings in which:
Figure 1 is a block and schematic diagram of a network encompassing the signalling protocol of the present invention in which one of the s-tations is illustra-ted in further detail, and Figures 2A and 2B illustrate the typical time slots of the network illus-trated in Figure 1 both during and after initialization.
Description of the Pre-Ferred_Embodiment Referring to Figure 1, the network comprises 15 nodes or stations of which stations 9 to 12 are shown in block form while 10 is illustrated in further detail. It will be evident tha-t the principles could be readily extended to large networks with hundreds of nodes.
~5 ~
The network uses a common transmission line 20 having two unidirectional channels 21 and 22 transmitting in easterly and westerly directions respectively.
Referring more particularly to station IO which is typical of each of the stations in the network~ there is i11ustrated a microprocessor control uni-t 30 in which signalling information such as the status of the station is coupled to and -from the control unit 30 on data signalling lines 31 and 32. Each station can function as an end terminal for portions of the network so that information can be IO received and transmitted in one direction only. Alternately, the station IO can be effectively bypassed so that all information on the common transmission line 20 passes directly there-through.
Information then received from station 9 passes through an OR gate 23, the output of which is coupled to station 11. Similarly, signalling information from station 11 is passed through an OR gate 24 to station 9.
All received information on the transmission line 20 is coupled from the output of OR gates 23 and 24 through OR gate 25 to the control unit 30. This arrangement insures that all signalling information on the line 20 is received by the station and that the information transmitted to the line 20 from the local station IO is the same as that appearing on the line. Any discrepancy can indicate interference from another station which will result in the ne-twork being reinitialized.
Figure 2A illustrates the sequential transmission from each station in its allotted time slot during initialization. Each 6~
closed segment indicates signal transmission -From that station during its alloted time slot, while an open segmen-t indicates no transmission by the station. The latter time slots are marked by each of the o-ther stations so that the system can be compacted during subsequent cycles.
The null slot 0 is used for requesting initialization of -the network.
To achieve this a break signal from any one or more oF the stations is transmitted for at least a preselected time interval during this null slot so as to cause the network to immediately expand to its maximum capacity as shown in Figure 2A. This minimum time interval is chosen so that spurious bits or spikes on the line 20 will not cause reinitialization of the network. Each station on the network then transmits at least its header signal after a minimum time-out interval. However this can be followed by additional signalling information and ends with a trailer signal, which extends the length of the time slot up to a preselected maximum time-out interval.
Although each station transmits in a unique commonly recognized seguence, it is common practice For the header signal to include the address of the transmitting station as well as that of the receiving station or stations. This ensures that no errors have developed in the transmitting sequence. When a station fails to transmit during its allotted time slot, a time interval of twice the transmission time for the system occurs before the next sta-tion commences transmission of its header signal. This ensures that each station notes the absence of transmission and marks the blank time slot. After three repeated failures of a station to transmit its header signal, the network will further compact to remove that station from the ~2 ~ 3 transmission sequence as shown in ~igure 2B. The addresses of each of the stations are arranged so that the odd-numbered stations transmi-t in ascending order followed by the even-numbered stations in descending order. Assuming the sta-tions have been numbered in increasing order this minimizes the variations in propaga-tion delay between consecutive stations.
In the illustrated embodiment, stations 4, 5, 13, and 15, are currently disconnected from or are not transmitting on the network. When initialization takes place, the lowest numbered station on the network, (in this case station 1) will immediately after the null slot commence transmission of its header signal followed if necessary by additional status or other signalling information and a trailer signal. This is recognized by station 3 which then commences transmission immediately thereaFter. Since station S is disconnected from the network, no transmission takes place immediately following the end of transmission from station 3. However after a further minilnum time-out interval has elapsed, station 7 commences transmission of its header signal and other signalling information.
This is followed by stations 9 and 11. Since both stations 13 and 15 are disconnected from the network two time slots will elapse before station 14 commences transmission oF its header signal. This is followed by sta-tions 12, 10, 8, and 6, and after another time slot interval for station 4, which is also disconnected from the network, station 2 transmits its header signal. The one additional null slot 0 is then automatically inserted by all stations prior to the repe-tition of the sequence.
~ 5 ~ 3 During the initial sequence each sta-tion marks the -time slots 4, 5, 13, and 15 in which no address has been transmitted.
Thereafter, with the exception of null slot 0, each sta-tion as shown in Figure 2B, transmits its header signal right after the reception oF
the signal from the station which transmitted immediately preceding it so as to eliminate the marked -time slots in which no header signal was transmitted. Thus continued transmission takes place from each of the stations on the network with the exception of null slot 0 in which no transmission normally takes place.
However, should one of the stations 4, 5, 13, or 15, attempt to join the network, an initialization request (or break) signal is stuffed into the null slot 0 by this station alerting all other stations they must go through a reinitialization sequence.
Reinitialization can also take place if any station detects the signalling information being transmitted to the transmission line 20 is not the same as that appearing on the line. This can occur whenever a -Fault develops on the line 20. That station will then insert a break signal in time slot 0 which also results in a reinitialization of the network. Thus any station connected to the network, whether currently transmitting or not, can trigger reinitialization of the network. The transmission sequence then expands to its maximum number of nodes or stations and af-ter marking each of the time slots in which no header signal has been transmitted, contracts to only the active stations with the exception of the additional null slot 0. Each station recognizes a minimum time slot as equal to twice the maximum propagation time between alternate ~ 5 numbered nodes on the system.
One advantage of compacting the network to only ac-tive stations is that interference will occur immediately upon opera-ting portions o-f the network being joined to each other. If the -two portions remain in an expanded state they could conceivably be superimposed without interference occurring for some time. While they would eventually clash with each other, there is a prolonged period in which there is no controlled flow of information through the network.
It is therefore desirable that the network reinitialize immediately upon the sections of the network being joined to each other.
When two operating portions of the network are initially coupled together signal clashing will be immediately evident to the two stations transmitting at that instant. Each station will then attempt to retransmit its entire signal up to its maximum time-out interval at which time they will cease transmission. At this point all of the other stations on the network will be aware of the garbled nature of the transmission and once transmission of both stations has ceased, each station will recognize it as the beginning of a null slot prior to reinitialization o-f the network. Each station in turn will then commence to transmit at least its header address in the assigned order.
This invention relates to a network signalling protocol and more particularly to one for establishing and main-taining communication between a plurality of s-tations ~"hen connected to a common transmission lineO
Background of the Invention In communication systems it is often necessary to transmit signalling and control information from each node or station to one or more of the other stations over a common transmission line.
In one arrangement, each station is allocated a unique time slot in which to transmit its pertinent signalling information. In general, such systems must be capable of adding stations to or removing them from the common transmission line without disrupting the operation of the balance of the network.
The capacity of such a system is determined by the maxilnuln number of time slots which have been allocated by the network protocol. However if much o-f the time this maximum capacity is not being utilized then it is more efficient to eliminate the time slots of the unused nodes or stations. This can also help to alleviate many of the problems in coupling two independently operating portions of the network together, which can occur when a fault or break in the transmission line has separated major portions of the network from each other. After this break occurs, communications must continue between the functioning portions of the network. However, when the fault is rectified, the two portions of the network must be rejoined with minimal disruption to each other.
~s~
If the operating sequence has been compacted so as to eliminate unused time slots, it is necessary to in-form all oF the stations when one or more stations wants to join the network so that the required time slots can be allocated. When a single station joins the network it can first monitor the operation of the other stations on the transmission line. However, operating sub-sec-tions which join each other cannot initially monitor each other without interference occurring on the common transmission line. The key therefore is to provide a protocol in which all of the stations on the network can be made aware that one or more stations will be joining the network or portions of the network will be joined to each other.
Statement of the Invention The present invention provides an improved network signalling protocol for communicating between a plurality of sta-tions when connected to a common transmission line. The protocol at each station comprises ini-tializing the network by transmitting in a commonly recogni7ed sequence, at least a header signal from each station in a uniquely allocated time slot which commences a corresponding number of time slots following the previously transmitted signal. The protocol includes marking each time slot in which no signal has been transmitted and thereafter transmitting at least the header signal for the station in the next time slot following that of the immediately preceding transmitted signal so as to eliminate the marked time slots in which no signal has been transmitted.
In order to inform each of the stations that the ~5 ~
network is to be reinitialized, the protocol provides for allocating one additional time slot, commonly referred to as a null slot, in which any one station can insert an initializing request signal (i.e. a break signal for a preselected time in-terval) in response to selected conditions at that station. This occurs whenever one or more stations are to join the network. When opera-ting portions of the network are initially joined together, interference or clashing o-f the signals occurs on the line. This is recognized by each of the stations on the network and the result is that all stations then cease transmission. Thereafter, the network is reinitialized by following the same sequence as the first initialization.
Brief Description of the Drawings An example embodiment of the invention will now be described with re-ference to the accompanying drawings in which:
Figure 1 is a block and schematic diagram of a network encompassing the signalling protocol of the present invention in which one of the s-tations is illustra-ted in further detail, and Figures 2A and 2B illustrate the typical time slots of the network illus-trated in Figure 1 both during and after initialization.
Description of the Pre-Ferred_Embodiment Referring to Figure 1, the network comprises 15 nodes or stations of which stations 9 to 12 are shown in block form while 10 is illustrated in further detail. It will be evident tha-t the principles could be readily extended to large networks with hundreds of nodes.
~5 ~
The network uses a common transmission line 20 having two unidirectional channels 21 and 22 transmitting in easterly and westerly directions respectively.
Referring more particularly to station IO which is typical of each of the stations in the network~ there is i11ustrated a microprocessor control uni-t 30 in which signalling information such as the status of the station is coupled to and -from the control unit 30 on data signalling lines 31 and 32. Each station can function as an end terminal for portions of the network so that information can be IO received and transmitted in one direction only. Alternately, the station IO can be effectively bypassed so that all information on the common transmission line 20 passes directly there-through.
Information then received from station 9 passes through an OR gate 23, the output of which is coupled to station 11. Similarly, signalling information from station 11 is passed through an OR gate 24 to station 9.
All received information on the transmission line 20 is coupled from the output of OR gates 23 and 24 through OR gate 25 to the control unit 30. This arrangement insures that all signalling information on the line 20 is received by the station and that the information transmitted to the line 20 from the local station IO is the same as that appearing on the line. Any discrepancy can indicate interference from another station which will result in the ne-twork being reinitialized.
Figure 2A illustrates the sequential transmission from each station in its allotted time slot during initialization. Each 6~
closed segment indicates signal transmission -From that station during its alloted time slot, while an open segmen-t indicates no transmission by the station. The latter time slots are marked by each of the o-ther stations so that the system can be compacted during subsequent cycles.
The null slot 0 is used for requesting initialization of -the network.
To achieve this a break signal from any one or more oF the stations is transmitted for at least a preselected time interval during this null slot so as to cause the network to immediately expand to its maximum capacity as shown in Figure 2A. This minimum time interval is chosen so that spurious bits or spikes on the line 20 will not cause reinitialization of the network. Each station on the network then transmits at least its header signal after a minimum time-out interval. However this can be followed by additional signalling information and ends with a trailer signal, which extends the length of the time slot up to a preselected maximum time-out interval.
Although each station transmits in a unique commonly recognized seguence, it is common practice For the header signal to include the address of the transmitting station as well as that of the receiving station or stations. This ensures that no errors have developed in the transmitting sequence. When a station fails to transmit during its allotted time slot, a time interval of twice the transmission time for the system occurs before the next sta-tion commences transmission of its header signal. This ensures that each station notes the absence of transmission and marks the blank time slot. After three repeated failures of a station to transmit its header signal, the network will further compact to remove that station from the ~2 ~ 3 transmission sequence as shown in ~igure 2B. The addresses of each of the stations are arranged so that the odd-numbered stations transmi-t in ascending order followed by the even-numbered stations in descending order. Assuming the sta-tions have been numbered in increasing order this minimizes the variations in propaga-tion delay between consecutive stations.
In the illustrated embodiment, stations 4, 5, 13, and 15, are currently disconnected from or are not transmitting on the network. When initialization takes place, the lowest numbered station on the network, (in this case station 1) will immediately after the null slot commence transmission of its header signal followed if necessary by additional status or other signalling information and a trailer signal. This is recognized by station 3 which then commences transmission immediately thereaFter. Since station S is disconnected from the network, no transmission takes place immediately following the end of transmission from station 3. However after a further minilnum time-out interval has elapsed, station 7 commences transmission of its header signal and other signalling information.
This is followed by stations 9 and 11. Since both stations 13 and 15 are disconnected from the network two time slots will elapse before station 14 commences transmission oF its header signal. This is followed by sta-tions 12, 10, 8, and 6, and after another time slot interval for station 4, which is also disconnected from the network, station 2 transmits its header signal. The one additional null slot 0 is then automatically inserted by all stations prior to the repe-tition of the sequence.
~ 5 ~ 3 During the initial sequence each sta-tion marks the -time slots 4, 5, 13, and 15 in which no address has been transmitted.
Thereafter, with the exception of null slot 0, each sta-tion as shown in Figure 2B, transmits its header signal right after the reception oF
the signal from the station which transmitted immediately preceding it so as to eliminate the marked -time slots in which no header signal was transmitted. Thus continued transmission takes place from each of the stations on the network with the exception of null slot 0 in which no transmission normally takes place.
However, should one of the stations 4, 5, 13, or 15, attempt to join the network, an initialization request (or break) signal is stuffed into the null slot 0 by this station alerting all other stations they must go through a reinitialization sequence.
Reinitialization can also take place if any station detects the signalling information being transmitted to the transmission line 20 is not the same as that appearing on the line. This can occur whenever a -Fault develops on the line 20. That station will then insert a break signal in time slot 0 which also results in a reinitialization of the network. Thus any station connected to the network, whether currently transmitting or not, can trigger reinitialization of the network. The transmission sequence then expands to its maximum number of nodes or stations and af-ter marking each of the time slots in which no header signal has been transmitted, contracts to only the active stations with the exception of the additional null slot 0. Each station recognizes a minimum time slot as equal to twice the maximum propagation time between alternate ~ 5 numbered nodes on the system.
One advantage of compacting the network to only ac-tive stations is that interference will occur immediately upon opera-ting portions o-f the network being joined to each other. If the -two portions remain in an expanded state they could conceivably be superimposed without interference occurring for some time. While they would eventually clash with each other, there is a prolonged period in which there is no controlled flow of information through the network.
It is therefore desirable that the network reinitialize immediately upon the sections of the network being joined to each other.
When two operating portions of the network are initially coupled together signal clashing will be immediately evident to the two stations transmitting at that instant. Each station will then attempt to retransmit its entire signal up to its maximum time-out interval at which time they will cease transmission. At this point all of the other stations on the network will be aware of the garbled nature of the transmission and once transmission of both stations has ceased, each station will recognize it as the beginning of a null slot prior to reinitialization o-f the network. Each station in turn will then commence to transmit at least its header address in the assigned order.
Claims (3)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A network signalling protocol for communicating between a plurality of stations when connected to a common transmission line, the protocol at each station comprising:
initializing the network by transmitting in a commonly recognized sequence at least a header signal from each station, in a uniquely allocated time slot, which commences a corresponding number of time slots following the previously transmitted header signal;
marking each time slot in which no header signal has been transmitted; and thereafter transmitting at least said header signal in the time slot immediately following that of the immediately preceding transmitted header signal so as to eliminate the marked time slots in which no header signal has been transmitted.
initializing the network by transmitting in a commonly recognized sequence at least a header signal from each station, in a uniquely allocated time slot, which commences a corresponding number of time slots following the previously transmitted header signal;
marking each time slot in which no header signal has been transmitted; and thereafter transmitting at least said header signal in the time slot immediately following that of the immediately preceding transmitted header signal so as to eliminate the marked time slots in which no header signal has been transmitted.
2. A network signalling protocol as defined in claim 1 which additionally comprises allocating a null slot between the end of one sequence of signals and the beginning of the next, and inserting an initialization request signal in said null slot in response to selected conditions at the station; and reinitializing the network in response to the detection of said initialization request signal.
3. A network signalling protocol as defined in claim 2 which additionally comprises:
comparing the signalling information transmitted to the line from that station, with that appearing on the line; and inserting said initializing request signal in said null slot in response to a discrepancy between the compared signalling information.
comparing the signalling information transmitted to the line from that station, with that appearing on the line; and inserting said initializing request signal in said null slot in response to a discrepancy between the compared signalling information.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000485881A CA1250969A (en) | 1985-06-28 | 1985-06-28 | Network signalling protocol for communications system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000485881A CA1250969A (en) | 1985-06-28 | 1985-06-28 | Network signalling protocol for communications system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1250969A true CA1250969A (en) | 1989-03-07 |
Family
ID=4130877
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000485881A Expired CA1250969A (en) | 1985-06-28 | 1985-06-28 | Network signalling protocol for communications system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1250969A (en) |
-
1985
- 1985-06-28 CA CA000485881A patent/CA1250969A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |