Patent Application: US-201314395289-A

Abstract:
the invention relates to a method for establishing deterministic communication routes in a large computer network , wherein all affected end systems and switches of the computer network have a global time and a deterministic communication route is generated on the basis of an existing communication route between two or more end systems of the computer network in that a time - triggered connection manager of an end system reserves the deterministic communication route in a reservation phase by sending a reservation message to each network switch of the existing communication route up to the reservation commitment time , and then confirms this deterministic communication route in an accept phase by sending an accept message to the network switches of the existing communication route before the kzpt .

Description:
fig1 shows the progress of real time in cycles . in this illustration , the progress of real time is illustrated in the form of periods and phases , in fig1 time proceeds in the clockwise direction 1110 . the start of a period is synchronised at the time 100 with the global time . an event that occurs within a period ( for example the event 101 ) is characterised by the specification of the angle , that is to say the phase , between the start of the period 100 and the event 101 . when the time has passed through a full period — that is to say an angle of 360 degrees — the subsequent period thus starts . in the subsequent period , the time - controlled actions have the same phase as in the previous period . the cyclical image of the progress of real time is particularly well suited for illustrating periodic processes as occur in time - controlled real - time systems . fig2 shows a small part of a large computer network . in fig2 the five end systems 210 , 211 , 212 , 213 , 214 and the four switches 220 , 221 , 222 , 223 are illustrated . in addition , the route 230 from the end system 210 via the switches 220 , 221 , 222 , 223 to the end system 213 is shown in in fig2 . the progress of a message transmission over time along the route 130 is illustrated in fig1 . at the time 101 , the end system 210 ( the transmitting computer node ) starts with the transmission of a message . at the time 102 , following the start latency , the first bit of this message arrives at the switch 220 . the message resides in the switch up to the time 103 , at which the first bit of the message leaves the switch 220 in the direction of the switch 221 . at the time 104 , the first bit of the message arrives at the switch 221 . the period between the event 102 and the event 104 is referred to in a simplified manner as the residence time of the message in the switch 102 . this term ( residence time ) not only comprises the actual residence time in the switch , but also the time for the transport of the first bit of the message via the communication channel to the following message receiver . the described procedure , repeated up to the time 108 , at which the message arrives at the switch 223 immediately before the receiving end system 213 . following the residence time in the switch 223 , the first bit of the message arrives at the end system 213 at the time 110 . the transmission of the message is concluded at the time 111 , that is to say the time at which the last bit of the message has arrived at the end system 213 . the interval ( 110 , 111 ) is referred to as end latency . further terms that are used in this document will be explained hereinafter . a time - controlled route between two end systems is characterised by the exact specification of the phase and period [ sec ] at the start of the route , the phase and period at the end of the route , and the length [ bit ] of a time - controlled message . these parameters determine the real - time properties of a route . the bandwidth [ bit / second ] of the time - controlled route is given from a desired bandwidth can be achieved either by short messages with short period ( or high frequency ) or longer messages with longer periods . a time - controlled route is structured in physical segments , which are connected via switches . the physical bandwidths along a time - controlled route may be different in the individual segments . the minimum period required by the first bit of a time - controlled message in order to pass from arrival in one switch to arrival in the subsequent switch ( or the end system ) is referred to as the necessary residence time of the message ( nvd ) in the switch . the actual residence time required by a time - controlled message in order to pass from arrival in one switch to arrival in the subsequent switch ( or the end system ) is referred to as the actual residence time ( tvd ) of the message in the switch . the difference between the necessary residence time and the actual residence time is referred to as the slack of the message . in an optimal time - controlled route , the sum of the slacks in all switches is equal to zero . when there is a direct physical connection between the end systems , the latency of a message transmission is given by the latency of a time - controlled message along a time - controlled route with n switches is given over channels with identical physical bandwidth by the quality of a time - controlled route is expressed by the ratio when the end system 210 intends to establish a time - controlled route for a data stream along the route 230 , the following three - stage method is preferably performed . in the first phase ( start phase ), the time - triggered connection manager ( ttcm ) of the end system 210 sends a non - binding request with following content to all switches arranged in the route desired time - controlled bandwidth of the route start time of the provision of the route azpt end time of the provision of the route ezpt the switches arranged in the route , that is to say in fig2 the four switches 220 , 221 , 222 , 223 check which twd the switch can guarantee in the provision time ( that is to say the interval between the start time ( azpt ) of the provision of the route and the end time of the provision of the route ( ezpt )) and which nvd would be possible in the best case . the ttcm decides on the basis of this information whether an establishment of a time - controlled route along the existing route appears to be expedient or whether a new route has to be sought . when the ttcm decides to establish a time - controlled route along the existing route , the second phase ( reservation phase ) thus starts . the ttcm sends a reservation message with the following content desired time - controlled bandwidth of the route start time of the provision of the route azpt end time of the provision of the route ezpt commitment time of the reservation kzpt formation time bzpt of the reservation message start phase and start message length to all switches arranged in the route . the formation time of the reservation message bzpt is the time at which the reservation message was formed . the switches arranged in the route , that is to say in fig2 the four switches 220 , 221 , 222 , 223 , process this reservation message sequentially in the order in which they occur in the route 230 and reserve the time - controlled connection for the provision time . the last switch in the route from the view of the ttcm , that is to say switch 223 in fig2 , communicates the successful reservation to the ttcm by means of a confirmation message , in which the guaranteed tvd and nvd in each switch of the route is contained . furthermore , any switch may present proposals for reducing the tvd in this switch by changing the phase and period ( or the message length ). after receipt of this information by the ttcm , the ttcm can change the phase and message length in order to reduce the tvds in the switches in a next iteration of the reservation . when the quality of the connection has reached a previously determined level of quality or when a maximum number of iterations has been executed , the ttcm transmits the result to the end user for the decision . when the end user accepts the result , the third phase ( accept phase ) then starts . in the accept phase , an accept message is transmitted by the ttcm to all involved switches before the kzpt in order to confirm the reservation of the time - controlled route . the switch responds with an accept reply message . when no accept message arrives at a switch before the kzpt , the ( preliminary ) reservation is deleted . when a time - controlled route for the specified provision period has been reserved , the route from the switch to the ezpt is deleted autonomously ( that is to say at the end of the provision period ). when a route does not have a point - to - point , but a multi - point topology , the ttcm thus receives the information of all switches arranged in the multi - point route . the ttcm then decides whether a further iteration is necessary on the basis of this information . in a large network , in which many end users and switches are provided , a number of ttcms may be active simultaneously . a deadlock may be reached as a result of uncoordinated parallel reservations . the deadlock is prevented by placing all reservations in a temporal order on the basis of the formation time bzpt of the reservation message contained in the reservation message . when a reservation in a switch , due to a reservation message having a later bzpt , is in conflict with a reservation having an earlier bzpt , the reservation having the later bzpt is thus to be cancelled by the switch . due to the global time provided , all decisions in the network can thus be placed in a temporal order consistently , such that conflicts can be resolved consistently . simultaneity can be eliminated by placing the ttcms in a sequence . in order to prevent an intruder from falsely making reservations , the reservation traffic between the ttcm and the switches can be secured by cryptographic methods . the proposed innovative method functions in accordance with the fate - sharing model of clark [ 7 ], which mandates that all key state data of a connection are managed in the endpoints of the connection and there is no central authority in the network managing all time - controlled connections . the method builds on the published standards of ethernet , tt ethernet [ 1 , 8 ] and ieee 1588 clock synchronisation [ 9 ] and can therefore be incorporated into existing networks without substantial modifications . the method disclosed here for self - organising establishment of time - controlled routes in a large computer network brings large economical advantages , since the quality and therefore the applicability of modern network technology is considerably extended . 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