GB2273023A

GB2273023A - Token bus protocol

Info

Publication number: GB2273023A
Application number: GB9224746A
Authority: GB
Inventors: Kim Philip Lyon
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-11-26
Filing date: 1992-11-26
Publication date: 1994-06-01
Anticipated expiration: 2012-11-26
Also published as: GB9224746D0; GB2273023B

Abstract

The Token Bus protocol is a protocol that uses a numerical token that is passed by the network hardware from one unit to another thus providing high speed data transfer through the resulting low data link overhead. The protocol operates on a bussed topology and as such has the inherent high reliability of this topology. In addition the protocol has an arbitrary unit number assignment system providing greatly increased ease of connectability of units. The protocol also has provision for the connection of intra and inter network gateways. <IMAGE>

Description

Token Bus Protocol Number 1 The Token Bus Protocol Number 1 The Token Bus Protocol Number 1 , henceforth also refered to in this patent application as The Token Bus Protocol has been designed to provide a simple but sophisticated solution to many of the problems found within current local area networking systems The Token Bus Protocol uses a numerical token that is passed by the network hardware from one unit to another thus providing high speed data transfer through the resulting low data link overhead . The data link overhead is approximately the same as the data link overhead with a token loop \ ring network - around 3 % . This is as opposed to the data link overhead for Carrier Sense Multiple Access \ Collision Detection protocols of 25 % to 50 & % . CSMA \ CD protocols are commonly used on bussed topologies .The data link overhead of CSMA \ CD protocols is high due to both the communication response time and the collisions and their associated random retry times The data link overhead increases exponentially in proportion to the number of units trying to gain access to the network at any one time due to the effect of the collisions The Token Bus Protocol operates on a bussed topology and as such has the inherrent high reliability of this topology If one unit breaks down the operation of the network as a whole is not effected . This is as opposed to the inherrent unreliability of the loop \ ring network where the reliability of the network is dependent on the reliability of each of the individual units on the network . If one unit breaks down the whole network breaks down .As such the Mean Time Before Failure of the loop \ ring network is equal to the MTBF of the individual units divided by the number of units on the network The Bussed Topology

I Unit uni 1 Unit 2 Unit 3 | Unit 4 i , I i Figure 1 Token Bus Protocol Number 1 The Loop \ Ring Topology

CE Unit 1 Unit 2 ; 9 Untt 4 Figure 2 In addition the Token Bus Protocol has an arbitrary unit number assignment system providing greatly increased ease of connectability of units . Units can be plugged into the network without setting up their addresses The Token Bus Protocol also has provision for the connection of intra and inter network gateways .This allows traffic to be easily managed on the network and allows for porting into other networks Conventions The Following conventions are used :1) The most significant bit ( the left most bit ) shown is shifted out first 2) All bit patterns are shown in binary except those shown with an H suffix which are shown in hexadecimal The Token Bus Protocol on a Basic Level The Token Bus protocol uses the following basic format :1) All characters \ data have a basic length of 8 bits 2) There are 3 unique characters :: the Flag character with a bit pattern of 01111110 the Poll character with a bit pattern of 01111111 and the Terminate character with a bit pattern of 11111111 3) All non unique characters ( ie. data ) are checked on a bit by bit basis for the occurence of consecutive l's Token Bus Protocol Number 1 At the transmitter if 5 consecutive l's occur then a 0 is inserted IE. the bit pattern 11111111 becomes 111110111 Similarly at the receiver if 5 consecutive l's followed by a 0 occur then the 0 will be removed IE. the bit pattern 11111000 becomes 1111100 As such the uniqueness of the unique characters is preserved 4) Addresses are encoded as non unique characters and consist of gateway numbers and unit numbers . The bit pattern or number group of the gateway numbers is uniquely different than the unit numbers .The gateway address path within a destination address preceedes the unit number . As such the unit number delimits the destination address IE. if the gateway addresses are defined by the upper nibble being set to 1111 then the following example shows the use of gateway addresses within a destination address 1111 0001 first gateway address 1111 0010 second gateway address 1111 0001 third gateway address 0001 0101 final destination unit address Source addresses are encoded in the same way and show the path taken to take from the destination to the source 5) The error check syndrome is encoded as a non unique set of characters and may use any technique such as Hamming codes or Cyclic Redundantcy Check codes .

The Token Bus Protocol on a Message Level The Token Bus protocol consists of two types of messages encoded in the following basic format : The first consists of :- FLAG SOURCE ADDRESS SOURCE ADDRESS POLL and is used to indicate that no data is to be transfered Token Bus Protocol Number 1 The second consists of :- FLAG DESTINATION ADDRESS SOURCE ADDRESS DATA ERROR CHECK SYNDROME POLL and is used to transfer data Access to the network is passed onto a subsequent unit at the transmission of the poll The token position is tracked by the use of the source address If a consecutive numbered unit is not on the network an inactive byte is inserted in between the poll and the subsequent flag .This becomes a free slot for a subsequent unit to occupy in the token passing sequence If a unit is switched on it will monitor the network for a specified time ( eg. 65536 bytes time ) for any activity . If there is no activity it will assign itself the lowest number ( eg. 01H ) and transmit a " no data to be transfered " message and then monitor again for any activity .If the network is active it will monitor for an inactive byte and will assign the number corresponding to that inactive byte to itself If a unit is removed from an active network it will he replaced by a number of inactive bytes corresponding to the number of units between the previous unit and the subsequent unit for one cycle and then the subsequent unit will place just one inactive byte between the previous unit and itself IE. if units 1 , 2 and 4 are present on the network and the subsequent cycle mode is being used there will be an inactive byte between units 2 and 4 .If unit 2 is taken off the network there will be an initial 2 inactive bytes between units 1 and 4 ( corresponding to units 2 and 3 and then on the subsequent cycle a single inactive byte between units 1 and 4 The inactive byte is used for the subsequent entering of other units into the token passing sequence The Terminate character is used to indicate the end of a transmission when an error condition occurs Token Bus Protocol Number 1 Addresses The following address types are used :1) A unique number is reserved as a local network general broadcast number . This allows all units within a network to be simultaneously addressed 2) A range of unique numbers are reserved for the unit numbers 3) A range of unique numbers are reserved for global broadcast numbers . These allow party conversations to occur 4) A range of unique numbers are reserved for gateway unit numbers .These allow communication with the gateways to occur 5) A unique gateway general broadcast number . This allows all gateways to be simultaneously addressed 6) A range of unique numbers are reserved for the gateway numbers . These allow the data to be transfered through the gateway 7) A unique number is used as a wide area network general broadcast number . This allows broadcasts to all units on the network to occur Please Note :- implementations of the protocol may assign a zero range of numbers to any of the above addresses . IE. there may be no numbers assigned to a specific address type The destination address for units transfering data through gateways consists of path information specifying the path to be taken from the source unit to the destination unit The source address for units transfering data through gateways consists of path information specifying the path that was taken from the source unit to the destination unit Each gateway strips off the destination address corresponding to itself and adds the source address to itself as it passes the message from its' network receiver on one network to its' network transmitter on the other network Token Bus Protocol Number 1 Examples of the Operation of the Token Bus Protocol The convention used is that the arrow points to what occurs next in time A Single Unit is Present On the Network

I FLAG 01H 01H POLL LF ' 65,536 bytes inactive time Figure 3 A Second Unit is Plugged into the Network The second unit hears the first unit during its' inactive time . It then assigns itself the next free number - > 2 and places itself into the cycle

FLAG 01H 01H POLL FLAG 02H 02H POLL L 1 byte inactive time Figure 4 Token Bus Protocol Number 1 A Third Unit is Plugged into the Network

FLAG 01H 01H POLL FLAG 02H 02H POLL FLAG 03H 03H POLL Ly~ 1 byte inactive time Figure 5 The First Unit is Unplugged from the Network Initial Cycle

1 FLAG 02H 02H POLL FLAG 03H 03H POLL Ly~ 254 bytes inactive time Figure 6 Token Bus Protocol Number 1 Subsequent Cycles

FLAG 02H 02H POLL FLAG 03H 03H POLL Lo 1 byte inactive time Figure 7 Communication

Unit 1 Unit 2 Unit 3 Unit 4 Figure 8 If unit no. 1 wishes to transfer data to unit no. 3 it transmitts the sequence : FLAG start of packet 03H destination address 01H source address DATA data ERROR CHECK SYNDROME error check syndrome POLL end of packet Token Bus Protocol Number 1 Usage of Gateways

OFOH , . OFEH Gateway E [im Figure 9 If unit no. 1 in the left hand network wishes to transfer data to unit no. 2 in the right hand network it transmitts the sequence : FLAG start of packet OFOH gateway address 02H destination unit 01H source address DATA data ERROR CHECK SYNDROME error check syndrome POLL end of packet After passing through the gateway the packet becomes : FLAG start of packet 02H destination address OFEH gateway address O1H source unit DATA data ERROR CHECK SYNDROME error check syndrome POLL end of packet OFEH,O1H being the complete source address OFEH being the address of the unit ( in this example a gateway ) that last transmitted the message . This address also being the one that is used to signify the current token position and hence to provide a link to the next unit in the numerical order

Claims

Token Bus Protocol Number 1 Claims l The Token Bus Protocol Number 1 has the following advantages :1) Low data link overhead providing high speed data transfer due to the token passing 2) High network medium reliability due to the bussed topology 3) Greatly increased ease of connectability of units due to the arbitrary unit number assignment . IE. No unit address setup is required . Units are just plugged into the network 4) Greatly increased ease of interconnectability of local area networks through the use of gateways to connect local area networks of the same type or of different types into a wide area network . This allows traffic management to be easily carried out within the Token Bus Network . It also allows connections to other networks to be easily carried out Token Bus Protocol Number 1 Claims 1) A token bus protocol that uses

i) a bussed network topology .The bussed network topology being by definition a single communication medium onto which all the network units are connected and

ii) a retrospective token passing method where each unit monitors the prior transmission sequence using this to identify the transmission of the previous unit and the number ( address ) of the previous unit and hence determining the starting position of it's transmission The retrospectivity being where the current unit does not know the number ( address ) of the subsequent unit but where the current unit does know the number ( address ) of the previous unit Thus knowledge is not maintained as to where the token is going to but is retained as to where the token has come from The unit that holds the numerical token by definition has sole access to the network bus The unit releases it's sole access to the network bus thus allowing the next unit to access the network by completing it's transmission and indicating this fact . The next unit not having a specific number or consecutive number but being the next numerically numbered unit currently connected to the network bus . The current unit indicates that it has the token by transmitting it's source address and releases it's sole access to the network bus by transmitting the poll ( message end ) character The unit's transmission occurs immediately after it's previous unit has finished transmission and with or without inactive bytes inserted between the previous unit's transmission and the unit's transmission as required Token Bus Protocol Number 1 2) A token bus protocol as defined in claim 1 that provides for arbitrary unit number ( address ) assignment The arbitrary unit number ( address ) assignment by definition being that the unit does not have a predefined number ( address ) but assigns itself an available number ( address ) on connection to the network bus The arbitrary unit number ( address ) assignment being accomplished by the use of the retrospective token passing in conjunction with the inactive bytes such that the unit comming onto the network assigns the number ( address ) corresponding to the source address plus 1 of the first received message that is immediately followed by an inactive byte .This being the first available address 3) A token bus protocol as defined in claim 1 that provides for the connection to and communication via intra and inter network gateways The gateways being by definition a method of connecting the network to other networks of the same or differing types This being accomplished by the token bus protocol via destination and source address paths that have defined characteristics and defined positions and hence both the paths and their component addresses have identifyable positions Token Bus Protocol Number 1 Claims 1) A Token Bus protocol that uses

i) a single communication medium such a 2 wires , a star connected electrically ored fibre optic network or a Super High Frequency radio network medium and

ii) unique characters to define the start and the end of the messages and

iii) unique address number ranges for unit addresses and gateway addresses and

iv) a retrospective token passing system where each unit monitors the prior transmission sequence using this to identify the transmission of the previous unit and the address of the previous unit and hence determining the starting position of it's transmission .The unit's transmission occuring immediately after it's previous unit has finished transmission and with or without inactive bytes inserted between the previous unit's transmission and the unit's transmission as required If no data is to be transfered the unique message start character is followed by the address of the unit ( the source address ) which is followed directly by the source address ( duplicated for error detection which is followed by the unique message end character If data is to be transfered the unique message start character is followed by the destination address path which is followed directly by the source address path which is followed directly by the data which is directly followed by the error check syndrome which is followed by the unique message end character Token Bus Protocol Number 1 The address of the unit transmitting the message is situated directly after the first occurence of the source address in a no data sequence and after the destination address in a data sequence . This is used by the subsequent unit to determine the previous unit's address and hence to be able to retrospectively pass the token The retrospective token passing is non hierachical in nature and as such each unit on the network communicates on a peer to peer basis 2) A token bus protocol as defined in claim 1 that provides for arbitrary unit number ( address ) assignment .The retrospective token passing in conjunction with the inactive bytes allows a unit to come onto the network by the unit assigning the address corresponding to the first received source address , with an inactive byte following the message , plus 1 to itself 3) A token bus protocol as defined in claim 1 that provides for units to be connected to and to be disconected from the network at will without disrupting the communication being carried out on the network or requiring any other unit on the network to take any action on the network with regards the unit that was connected to or disconnected from the network . This is accomplished by the retrospective token passing which does not require any unit to have any knowledge of any susequent unit . The retrospective token passing provides a simple mechanism for subsequent units via the inactive bytes to provide for the connection of units to the network and the disconnection of units from the network without the subsequent unit being required to transmit any message on the network in order to be able to handle the connection of the unit to the network or the disconnection of the unit from the network 4) A token bus protocol as defined in claim 1 that provides for the connection to and communication via intra and inter network gateways .This is accomplished via the use of the unique character that is used to define the start of the message and the use of unique address ranges for the unit addresses and the gateway addresses and the placement of the final destination and initial source unit addresses at the end of their respective address paths Token Bus Protocol Number 1 Amendments to the claims have been filed as follows 1) A data communications protocol that allows token passing to occur on a bussed network topology 2) A data communications protocol that allows arbitrary unit number ( address ) assignment 3) A data communications protocol that allows units to be connected to and to be disconected from the network at will without disrupting the communication being carried out between the other units on the network 4) A data communications protocol that allows the connection to and communication via intra and inter network gateways