Determining required processing time of a data network

Abstract

End-to-end latency in a data network containing a succession of network devices through which a data packet passes via data connections is determined by first providing the data packet with a trigger packet. Then each device generates and adds to the trigger packet a respective reception timestamp indicating when the packet is received by the respective device. This added data indicates time needed for travel from the immediately upstream network device such that, when reaching the furthest downstream device of the succession of network devices, the trigger packet holds a plurality of timestamp representing when the trigger packet was received by the network devices. Finally the end-to-end latency is calculated at the furthest downstream network device from all of the time stamps in the trigger packet.

Claims

1. A method of determining end-to-end latency in a data network containing a succession of network devices through which a data packet passes via data connections, the method comprising: providing the data packet with a trigger packet; at each device generating and adding to the trigger packet a respective reception timestamp indicating when the packet is received by the respective device and therefore indicating time needed for travel from the immediately upstream network device such that, when reaching the furthest downstream device of the succession of network devices, the trigger packet holds a plurality of timestamp representing when the trigger packet was received by the network devices; and calculating the end-to-end latency at the furthest downstream network device from all of the time stamps in the trigger packet.

2. The method according to claim 1, further comprising the step, in addition to generating the timestamp on reception of the trigger packet, of: generating a timestamp at the time of transmission of a trigger packet and adding it to the data packet.

3. The method according to claim 1, further comprising the steps of: inserting the timestamp generated in at least one further network device into the trigger packet as a partial data packet and forwarding the partial data packet into which the time stamp is inserted.

4. The method according to claim 3 further comprising the step of: storing the timestamp established in the at least one further network device on this network device and providing the timestamp for further network devices and/or a network management system.

5. The method according to claim 1, further comprising the step of: assigning each of the timestamp further data of the network device that generates the timestamp.

6. The method according to claim 1, further comprising the step of: determining the temporal profile of the data relaying of the trigger packet over the data connections that are involved from the timestamp of a respective network device.

7. The method according to claim 1, further comprising the step, upon arrival of a data packet that functions as a trigger packet on a network device or upon transmission of a data packet that functions as a trigger packet, of: recording and storing the timestamp on the network device on which the timestamp was generated.

8. The method according to claim 1, further comprising the step, upon arrival of a data packet that functions as a trigger packet on a network device, or upon transmission of a data packet that functions as a trigger packet, of: recording and inserting a timestamp into the data packet.

9. The method according to claim 1, further comprising the step of at each device: adding to the trigger packet when sending the data packet to the next downstream device a transmission time stamp indicating when the data packet is being sent on, the calculation of end-to-end latency taking these reception and transmission time stamps.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The method according to the invention is described below and explained with reference to the figures.

(2) In the figures:

(3) FIG. 1: shows a network in a line topology,

(4) FIG. 2: shows a network in a line topology with trigger packets and a database for access via a network management system,

(5) FIG. 3: shows the insertion of a timestamp “inline” and in a database of the network management system,

(6) FIG. 4: shows an exemplary structure of a trigger packet, and

(7) FIG. 5: shows a trigger packet in the event of an error.

SPECIFIC DESCRIPTION OF THE INVENTION

(8) FIG. 1 shows, by way of example, where illustrated in detail, a network in a line topology. An actual start of the network is determined by the network device ED1 and an actual end of the network is determined by the network device ED2. Between this actual end and the actual start of the network are any desired number of network devices, such as for example two switches SW1 and SW2 that are connected to one another by suitable transmission media (such as for example in a wired manner via cable or wirelessly, for example via radio, infrared or the like) and exchange data packets, not illustrated in more detail. In addition to these data packets, trigger packets TP are transmitted. The illustration of a respective trigger packet to the left of the switch or to the left of the network device in FIG. 1 indicates that, whenever such a trigger packet arrives at the input of the network device in question, the time of the arrival (the reception) is established, that is to say a timestamp is generated. As an alternative or in addition thereto, the time at which a trigger packet leaves the respective network device may also be determined. In order to achieve a resolution or determination of the transmission time that is as precise as possible, both the reception and the transmission time are determined.

(9) FIG. 2 illustrates a network in a line topology with trigger packets and a database for access via a network management system. The network according to FIG. 2 is based on the operation of the network as is illustrated in FIG. 1, but with the difference that a network management system (NMS) is permanently connected to or temporarily able to be used with at least one network device (in this exemplary case the switch SW1). The network management system may obviously also be permanently connected or able to be connected to more than one network device or all network devices that are situated in the network (independently of its topology). The arrival timestamp and/or the departure timestamp of the trigger packet, following acquisition thereof, is then stored in a storage unit of the respective network device (for example in a database, Mgmnt DB). The network management system may access this database and read the timestamp for each trigger packet that has reached or left the respective network device, and, in connection with the time stamps of the other network devices, determine the end-to-end latency for the entire network (that is to say from ED1 to ED2) or else for particular freely selectable segments of the network (such as for example from ED1 to SW2 or from SW2 to ED2) therefrom.

(10) FIG. 3 shows the case of insertion of a timestamp “inline” and in a database of the network management system. The time of arrival of the trigger packet is in this case referenced by TS.sub.in and the time of transmission of the trigger packet is referenced by TS.sub.out. These two times and/or the time interval arising therefrom may be inserted into the trigger packet, which by this network device (here referenced as SWx, x=1, 2, 3, etc.) and forwarded and/or stored in the management database Mgmnt DB. The times or time intervals may be read from this database and used for the latency determination. In the structure of the trigger packet in FIG. 3, the term “trigger frame” is used in the FIG. itself, the terms “trigger frame” and “trigger packet” being able to be understood in principle as being synonymous with one another. If the method according to the invention is carried out on the layer 2 plane, the term “trigger frame” may be used, whereas the term “trigger packet” may be used if the method according to the invention is performed on the layer 3 plane or above.

(11) FIG. 4 shows an exemplary structure of a trigger packet, it being able to be seen that not just the arrival and departure time stamps of the respective network device are contained in the trigger packet, but rather that further data (for example metadata) may also optionally be contained in the trigger packet and be transmitted. The number of time stamps in this trigger packet thus indicates the number of network devices, in particular the number of terminals or interposed devices, such as for example switches. Such a trigger packet may but does not have to contain the data of the actual first network device (here ED1) or of the actual last network device (here ED2), but rather may also contain just the data of the network devices switched between these terminals, for example.

(12) FIG. 5 shows, based on the trigger packet as illustrated in FIG. 4, a trigger packet in the event of an error, with exemplary indications of time for the respective arrival and transmission time in the respective network device.

(13) A line topology with two terminals may serve as an example for determining the end-to-end latency between two devices (see FIG. 1, illustrating a line topology with a trigger packet). In this case, a trigger packet TP is transmitted from a network device ED1 and received by another network device ED2. Following reception of the trigger packet by the network device ED2, the end-to-end latency is able to be determined in that the transmission time of the trigger packet from the network device ED1 is derived from the reception time of the trigger packet in the network device ED2 (in this respect see FIG. 4, illustrating the structure of the trigger packet). This gives the precise end-to-end packet propagation time between the network devices ED1 and ED2. In contrast to the method of determining the end-to-end latency as is performed for example in path delay measurements in the case of IEEE 1588 E2E 2C, in the method described here, the transmission and reception times of the trigger packet on the respective network device on the relay path (transmission medium) are present in individual form. As a result of this, it is possible to draw more accurate conclusions as to the temporal path behavior in the latency determination. Furthermore, the trigger packets may be transmitted independently of the network priority, predefined by the time synchronization protocol, on a freely selected network priority. As a result, it is possible to assess the relaying of the trigger packet during the forwarding in various priority classes.

(14) If the trigger packet cited in the above example now has an unexpectedly high delay from th1 network device ED1 to the network device ED2, on the basis of the invention, it becomes possible to consider the individual delays on each step of the transmission path and thereby to achieve a precise definition of the error source. In FIG. 5, an error is present, as an exemplary case, in the network device SW2. The determined end-to-end latency between the network devices ED1 and ED2, at 670 ns, is well beyond the expected latency. The cause of the error may now be localized to the network device SW2, since the residence time in the network device SW2, at 430 ns, is able to be determined precisely by the network management system, for example, and greatly exceeds the normal residence time—assumed to be exemplary—in a switch of 100 ns. The above numerical values are purely exemplary and not restrictive.

(15) In the figures, the metadata that are illustrated are an exemplary packet structure.

(16) With respect to the network devices mentioned in the embodiment and also in general, these are for example what are known as terminals (such as for example personal computers, sensors, actuators, industrial controllers and the like) that form an actual start or an actual end of a network (for example in a line or else in a ring topology). Those network devices that are arranged between these terminals generally serve for the actual distribution or relaying of data packets (containing payload signal content) and do not send, with the exception of the trigger packets provided according to the invention, any new data packets to the network or change the payload signal content of a forwarded data packet.

(17) The invention is reproduced once again below in other words:

(18) 1. Inline: A “trigger packet” is transmitted that has the effect that individual devices, preferably each device on the transmission path that supports the method described in this case, records time stamps (for example the respective reception and/or transmission time) and inserts the measured values and optional metainformation (for example a device ID and/or the like) into the trigger packet. This results in complete recording of the temporal profile of the data relaying on individual relay paths, preferably on each relay path (including terminals supporting the method) within the network. This recording may be processed by the at least one receiver (device) or provided for further processing (for example by forwarding to a management system or by retransmission of the packet to the initiator of the measurement).

(19) 2. Out-of-band: As in 1., with the difference that the measured values and metainformation are not inserted directly into the packet on the respective device, but rather buffer-stored and made available on the network participant on which they were generated. The stored values may be queried for example via a management protocol from a management system. In this second variant of the method, mechanisms from existing time synchronization protocols (such as for example IEEE 1588) may also be used as “trigger packet” and used to generate the time stamps.

(20) Both of the methods described above may each be applied on their own or in combination.

(21) Further general information: To measure the time stamps, a common time base that is as accurate as possible should be present in the network (for example on the basis of IEEE 1588). In order to achieve a time measurement that is as precise as possible, the time stamping method should have extremely high accuracy (for example ideally hardware-assisted). The measurement method is suitable for use with unicasts, multicasts and broadcasts.

(22) The novelty of the invention comes to the fore in that, in contrast to existing methods such as for example IEEE 1588, there is no aggregation of the overall processing times in the trigger packet, but rather the measured values are recorded separately for a packet during the relaying and provided individually. This makes it possible for example to determine the latency contributions that are caused inter alia by individual network participants in the relaying. In addition, due to this, in time-slot methods, it is possible to monitor the compliance with temporal specifications for the transmission of individual packets and diagnose error cases.

(23) The described measurement may be performed for example on the basis of a reserved time slot in the context of the time-slot method.